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Vibrational spectral characterization, NLO studies and charge transfer analysis of the organometallic material l -Alanine cadmium chloride
Accepted Manuscript Vibrational spectral characterization, NLO studies and Charge transfer analysis of the organometallic material, L-Alanine Cadmium Chloride B.S. Arunsasi, K.C. Bright, C. James PII:
S0022-2860(15)30240-4
DOI:
10.1016/j.molstruc.2015.08.052
Reference:
MOLSTR 21784
To appear in:
Journal of Molecular Structure
Received Date: 28 March 2015 Revised Date:
19 August 2015
Accepted Date: 25 August 2015
Please cite this article as: B.S. Arunsasi, K.C. Bright, C. James, Vibrational spectral characterization, NLO studies and Charge transfer analysis of the organometallic material, L-Alanine Cadmium Chloride, Journal of Molecular Structure (2015), doi: 10.1016/j.molstruc.2015.08.052. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Vibrational spectral characterization, NLO studies and Charge transfer analysis of the organometallic material, L-Alanine Cadmium Chloride B. S. Arunsasia, K.C.Brightb and C.Jamesa* b
Department of Physics, Scott Christian College, (Autonomous), Nagercoil – 629 003, Tamil Nadu, India
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a
Department of Physics, St.Johns College Anchal, Kollam-690110, Kerala, India *
E-mail: [email protected]
* Corresponding Author: C. JAMES, Department of Physics & Research Centre, Scott Christian
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College (Autonomous), Nagercoil – 629 003, Tamil Nadu, India.
Email: [email protected]
Abstract
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Tel: +91 9443746555; Fax: +91 4652229800
An organometallic nonlinear crystal, L-Alanine Cadmium Chloride (LACC) was synthesized by slow evaporation technique. The effects of hydrogen bonding on the structure,
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binding of ligand to metal ion, natural orbital occupancies, and vibrational frequencies were investigated using density functional theory (DFT) with the combined B3LYP and LANL2DZ basis set. Vibrational assignments were made on the basis of calculated potential energy distribution values from MOLVIB program. The topological analysis of electron localization
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(ELF) provides basin population N (integrated density over the attractor basin), standard deviation (σ), and their relative fluctuation, defined as λ= σ2/N, which are sensitive criteria of
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delocalization. The molecular stability, electronic exchange interaction, and bond strength of the molecule were studied by natural bond orbital (NBO) analysis. The second harmonic generation (SHG) efficiency was determined using Kurtz and Perry method. Natural bond orbital analysis was carried out to study various intramolecular interactions that are responsible for the stabilization of the molecule.
Keywords: DFT, FT-IR, FT-Raman, NBO, ELF, Vibrational analysis.
1. Introduction 1
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Research on organometallic crystals play a major role in the domain of optoelectronics including integrated optics, optical switching, telecommunication bistability and modulation [1, 2]. They have the combined properties of both inorganic and organic crystals and have large damage threshold, less deliquescence, low angular sensitivity, wide transparency range and
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excellent nonlinear optical coefficient [3, 4]. Combination of amino acid with a metal compound has been proposed as a new candidate for NLO application which crystallizes in non centrosymmmetric space group. The proton donor carboxyl group (-COO) and the proton acceptor amino (-NH2) group present in the amino acid contribute some physiochemical
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properties. The metal–organic coordination compounds have increased NLO efficiency, via metal-ligand binding interactions. In LACC the organic part is an amino acid, more dominant in nonlinearity and the metallic part cadmium usually have high transparency in the UV region,
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because of their closed d10 configuration. L-Alanine mixed organometallic material will be of special interest as a fundamental building block to NLO properties [5].The crystal structure of LACC was first reported by Kathleen et.al [6]. Recently growth and properties of LACC have been reported [7-9]. The Density functional theory (DFT) calculation has now become the preferred method for understanding and predicting structure and reactivity in complex chemical
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system. DFT calculation along with vibrational spectral analysis is used as a promising tool to display a significant number of molecular properties of NLO materials [10]. In the present work, L-alanine Cadmium Chloride (LACC) has been grown from aqueous solution using slow evaporation technique. The grown crystal was characterized by various spectral analyses.
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Structure of the newly synthesized metal ion complex, its ground state properties and bonding characteristics of the ligand have been elucidated using experimental and theoretical methods.
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2. Experimental Techniques
2.1 Samples and instrumentation A mixture of L-alanine and cadmium chloride monohydrate taken in the equimolar ratio
was thoroughly dissolved in double distilled water and stirred well for about 2 hours using a magnetic stirrer to obtain a homogenous mixture. The reaction mixture was filtered and allowed to crystallize by slow evaporation at room temperature. Single crystals of size up to 12×7×2 mm3 were obtained in few weeks.
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FT-Raman spectrum of LACC was recorded in the range 3500-50cm-1 using Bruker RFS27 spectrometer with an Nd:YAG laser source at 1064nm. Thermo Nicolet, Avatar 370 spectrophotometer was used to measure the FT-IR spectrum with KBr pellet in the range from
visible double beam spectrophotometer in the range 200-800 nm.
3. Computational details
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4000-400 cm-1. The UV-visible absorption spectrum was recorded using Systronics 2200 UV-
In computational procedure, electronic structure of LACC was obtained using the hybrid
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density functional B3LYP (Becke-Lee-Yang-Parr) method with LANL2DZ basis set as implemented in Gaussian 09 [11]. The B3LYP method and the effective core potential basis set
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LANL2DZ have been widely used in studying the structure and properties of the organometallic compound. The optimized geometry corresponding to the minimum on the potential energy surface has been obtained by solving self–consistent field equations iteratively. The normal coordinate analysis including assignment of the force field in the internal coordinate representation suggested by Pulay et.al was performed using MOLVIB program [12, 13]. To offset the systematic errors caused by basis set incompleteness, over estimation of force constant,
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neglect of electron correlation and vibrational anharmonicity [14] uniform scaling (0.9612) of the force field were performed by the SQM (scaled quantum mechanics) procedure [15]. In order to study the possibility of charge transfer interaction, we have performed natural bond orbital (NBO) calculation at the B3LYP/LANL2DZ level of theory using NBO 3.1 program [16]. The
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Electron localization function (ELF) analysis was done using the Topmod program developed by Silvi et.al [17] and visualized with the Molekel program [18].
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4. Result and discussion 4.1. Optimized geometry
The molecular structure of LACC belongs to Cs point symmetry. The unit cell is
monoclinic containing 4 molecules (z=4) with lattice parameters a=16.33, b=7.31 and c=8.00 Å. The molecular structure of the compound with atom numbering scheme adopted in the computation is shown in Fig.1. The optimized geometrical bond lengths, bond angles and
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dihedral angles by DFT/B3LYP method with LANL2DZ as basis is compared with the X ray [6] experimental counterparts (Table 1). Position for Figure1
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Position for Table 1
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•
The crystal structure is stabilized by ionic interactions and hydrogen bonds. From XRD analysis it is clear that the H atom attached to the carboxylic group is protonated to form NH3+ ion. The geometrical parameters show that most of the bonds were altered upon the complexation
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of L-alanine with metal [19]. The Cd7 atom is bonded to two chlorine atoms with one having bond length 2.40 Å (Cd7-Cl6) and the other one (Cd7-Cl8) having longer bond length (2.55 Å).
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The intrinsic difference in the bond lengths of two Cd-Cl is due to the formation of N1-H16…Cl8 hydrogen bonding in the crystal with inter atomic distance 2.14 Å. The C2-C3-O9 and C2-C3-O5 angles are 114.35° and 117.20° respectively. The variation in the C-C-O angles arises due to the intramolecular participation of the carbonyl oxygen atoms of the ligand with the metal ions due to chelation. 4.2. Natural bond orbital analysis
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Analysis of orbital picture in the form of localized molecular orbitals applying the natural bond orbital (NBO) approach is widely used to interpret electronic structures. NBO analysis is carried out by examining all possible interactions between filled (donor) Lewis type and empty (acceptor) non Lewis NBOs and estimating their energetic importance by second order
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perturbation theory [20-22]. These interactions allow the assignment of the hybridization of atomic lone pairs and of the atoms involved in bond orbitals. Some selected interactions which
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result in stabilization energies exceeding an arbitrary chosen threshold are tabulated in Table 2. The bonding-antibonding interaction can be effectively described in terms of NBO
approach which is expressed by means of second order perturbation interaction energy E ( 2) = − n σ
Fij2 σFσ = −nσ ∆E ε σ* − ε σ 2
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……. (1)
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where
σ Fσ
2
2
or Fij is the Fock matrix element i and j NBO orbitals,
ε σ and ε σ* are the
energies of σ and σ* NBOs and n σ is the population of the donor σ orbital. This perturbation energy allows to examine all possible interactions between filled Lewis-type NBOs (donor
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orbitals) and weakly occupied non-Lewis-type NBOs (acceptor orbitals), and evaluate their relevance.
Fig. 1 shows two intramolecular interactions (N1-H15…O9 and N1-H16…Cll8) which stabilize the molecule and is responsible for hydrogen bonding. The interaction between lone
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pair n(Cl8) and the antibonding orbital σ*(N1 – H16) shows the existence of N–H...Cl intrarmolecular hydrogen bonding that have stabilization energies 1.02, 19.69 and 1.14 kcal/mol for n1 (Cl8) → σ* (N1 – H16), n3 (Cl8) → σ* (N1 – H16) and n4 (Cl8) →σ* (N1 – H16), respectively.
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Considering the N1-H15…O9 (1.458 Å) interaction, the n1 (O9) → σ* (N1 – H15), n2 (O9) → σ* (N1 – H15), have stabilization energies 0.64, 2.40 kcal/mol respectively. The stabilization energy E(2) associated with hyperconjugative interaction n2(O9)→ σ*(C2–C3), n2(O9)→ σ*(C3–O5) are obtained as 16.86 and 23.10 kcal/mol respectively. As a result of this intramolecular interactions, the electron density in the antibonding orbital increases which leads to slight elongation
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(Table 1) of the respective bond.
An important aspect of utilizing organometallic structures for nonlinear optics is in their unique charge transfer capability associated with charge transfer transitions either from metal to ligand or ligand to metal [23]. In title molecule the contributions of stabilization energies for the
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n4 (Cd7) →σ*(C3–O5), n5 (Cd7) → σ*(C3–O5) are 0.10 and 0.08 kcal/mol respectively, which is further stabilized by the hyper conjugative interaction n2 (O5) → π* (C3 – O9) with stabilization energy 77.68 kcal/mol. These charge transfer interactions from metal to ligand enhances NLO
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activity of the molecule. 4.3. ELF analysis
The topological analysis of ELF provides a nice picture of the electronic structure in
molecules, offering an atom based partition of the molecular space where electrons get localized maximum. The ELF was analyzed with the TopMod [24] program using density matrices obtained from Gaussian orbital computations. The ELF function proposed by Becke and Edgecombe as a ‘simple measure of electron localization in atomic and molecular systems’ [25, 26] is defined as: 5
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……. (2)
In which Dσ andD0σ represent the curvature of the electron pair density for electrons of identical spins (the Fermi hole) for the actual system and a homogenous electron gas with the same
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density, respectively. Dσ were the Laplacian of the conditional probability calculated from a single determinental Hartree-Fock wave function. Hence, η(r) =0 in those regions where the relative probability of finding electrons with parallel spin close together was high (i.e., where the
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local Pauli repulsion is strong), whereas η(r) =1 in those regions with a high probability of finding a single electron or a pair of opposite spin electrons.
The graphical representation of the ELF function at η(r) =0.80 for LACC is shown in Fig. 2. Such representation depicts different types of electronic basins, the average number of electrons (N), the standard deviation (σ2) and the relative fluctuations (λ) of the molecule and is summarized in Table S1.
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ELF provides a convenient characterization of hydrogen bond, by the presence of a protonated valence basin sharing a separatrix with at least another valence basin which does not participate to same atomic valence shell [27]. The protonated valence basin is generally a
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disynaptic whereas the valence basin is monosynaptic (involving lone pair), disynaptic (H-bond involving a bond) or protonated disynaptic. In title molecule, due to the intramolecular charge transfer from n1(O9)→ σ*(N1–H15), n2(O9)→ σ*(N1–H15), n1(Cl8)→ σ*(N1–H16), n3(Cl8)→
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σ*(N1–H16), n4(Cl8)→ σ*(N1–H16), the population of disynaptic basin V(N1,H15) and V(N1,H16) increased considerably than that of V(N1,H14). According to Bader [28] the relative fluctuation is a good measure of the delocalization. It is of the order of 0.1 for Core basins, 0.3 for basins of the protonated disynaptic attractor of the C-H bonds, 0.4 for basins related to single and double C-C bonds, and 0.5 for delocalized bonds. ELF analysis shows that the relative fluctuation in the core basin is very low while these values get maxima for the disynaptic basins. For basins of the disynaptic attractor of the C-O bonds the relative fluctuation is high (0.64 and 0.61), which shows COO- ion is strongly delocalized. The electron delocalization in Cd2+ is enhanced due to 6
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the unfilled d10 electron shell that allows the possibility of low energy charge transfer interaction. In LACC, as a result of charge transfer interaction from metal (Cd2+) to organic ligand (C-O), the population of V(C, O) increased about 0.16 e- than that of other V(C, O). In addition to this the combination of orbitals of Cd2+ and Cl overlap to form highly delocalized system. The
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topological analysis shows the absence of disynaptic basin between cadmium and oxygen atom, and the interaction can be treated as ionic. These topological parameters and high value of delocalization enhances the NLO property of the molecule.
4.4. Vibrational modes description
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Vibrational analysis based on both theoretical and experimental approach is a useful tool for the assessment of structural changes and for predicting spectral features. The non-redundant
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set of internal coordinates was constructed according to Pulay’s recommendations (Table 3). The computed vibrational wavenumbers and their IR and Raman intensities corresponding to the different normal modes are used to identify the vibrational modes clearly. The observed and calculated wavenumbers together with the infrared and Raman intensities and normal modes description (characterized by PED) of LACC are reported in Tables 4. The observed and simulated FT-IR and FT-Raman spectra are presented in Figs. 3 and 4 respectively. • • •
Position for Figure 4 Position for Table 3 Position for Table 4
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4.4.1. NH3+ vibrations
Position for Figure 3
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The asymmetric and symmetric stretching band of NH3+ generally appears in the region
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3330 and 3080 cm-1 respectively [30]. In LACC the medium broad band observed in FT-IR at 3232 cm-1 and its counterpart in Raman observed as a weak band at 3240 cm-1 is assigned to the asymmetric vibration of NH3+. The NH3+ symmetric stretching mode appears as weak bands in IR and Raman at 3146 cm-1 and 3154 cm-1, respectively. The asymmetric NH3+stretching wavenumber is theoretically calculated at 3396 cm-1 and the symmetric stretching at 3218 cm-1. The deviation of computed amino stretching wave number from the free ion values is considered as the possible redshift due to N-H…Cl and N-H…O hydrogen bonding. The NH3+ symmetric and asymmetric bending mode generally appear in the range 1550-1485 cm-1 and 1660-1610 cm7
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respectively [31]. The asymmetric NH3+ bending mode is observed as a strong band in IR at
1616 cm-1. The strong band at 1495 cm-1 in IR and weak band at 1502 cm-1 in Raman corresponds to the NH3+symmetric bending mode. According to the calculated PED, these vibrational modes are coupled with some contribution from the COO- vibrations. NH3+ rocking
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mode appears as a medium band in IR at 1109 cm-1 and Raman at 1108 cm-1. One of the finger print identification of NH3+ group in LACC crystal is observed in IR at 1995 cm-1, which can be assigned as the combination of torsional oscillation and the degenerate deformation of the NH3+ group.
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4.4.2. Methyl and methine group vibrations
The asymmetric and symmetric stretching vibrations of CH3 group are normally observed in the range 2980-2875 cm-1 [32, 33]. For the title compound, the strong band observed at 3044
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cm-1 in IR and the weak band at 3046 cm-1 in Raman is assigned to asymmetric stretching vibration of methyl group. The symmetric stretching mode is observed as a strong band in both IR and Raman at 2948 cm-1 and 2937cm-1 respectively. The blue shifting of the methyl stretching wave number due to C-H…Cl interaction, is mainly manifested by the shortening of C4–H10 bond (0.0037Å), and low value of electron density (0.0102e) in the σ* (C4 – H10 ) orbital [n2 (Cl8)
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→ σ* (C4 – H10) ˜ 0.45 kcal/mol]. The CH group stretching vibrations are noticeably observed as weak bands in IR at 2998 cm-1 and as a medium band in Raman at 3005 cm-1. The deformation frequencies observed in the region 1470-1420 cm-1 and 1390-1370 cm-1 corresponds to asymmetric and symmetric bending vibrations of methyl group [34]. The asymmetric bending
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vibration appears as a medium band in both IR and Raman at 1453cm-1 while its symmetric part is observed in IR at 1372 cm-1 (medium) and Raman at 1371cm-1 (weak). The theoretically
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computed wavenumbers at 1466 and 1396 cm-1 show well agreement with the experimental values. The methyl rocking, twisting vibrations generally observed to be weak in the region 1120-1050 and 900-800 cm-1 [35] are observed in IR at 970 cm-1 (weak) and Raman at 971 cm-1 (medium). Out of plane bending vibrations of the methyl group are listed in Table 4. 4.4.3. COO- group vibration In LACC, the metal is bonded to carboxylate through ionic interaction, and the resulting arrangement becoming unusual can stretch asymmetrically and symmetrically. This can produce two bands and is important to predict the binding mode of the ligand. The stretching vibration of 8
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carboxylate ion is expected in the region 1650-1550 cm-1 (asymmetric) and near 1400 cm-1 (symmetric) [31, 36]. The strong band in IR spectrum at 1566 cm-1 is assigned to asymmetric stretching mode of COO- group. The symmetric COO- stretching vibration is identified as a medium band in IR at 1210 cm-1 and weak Raman band at 1214 cm-1. The lowering of this mode
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is due to the interaction of the lone pair oxygen atom of COO- group with the Cd atom, also owing to the consequence of metal coordination. According to PED analysis, the symmetric stretching COO- vibration (1262 cm-1) has only 47% contribution. The frequency difference [ν = νas(COO-)- νs(COO-)] is greater than 200 cm-1 which shows an indication of the binding mode of
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carboxylate in a monodenate manner [37]. The inplane and out of plane bending modes of carboxylate vibrations appearing in the region 780-650 cm-1, coupled with some other mode are identified and assigned in Table 4. The medium band in IR at 623 cm-1and the weak band in the
4.4.4. Skeletal mode vibrations
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Raman at 621 cm-1 are assigned to in plane bending mode of carboxylate ion. The C-N and C-C skeletal mode vibrations appear in the range 1150-850 cm-1 [36,38,39] .The strong bands observed in both IR at 838 cm-1 and Raman at 841cm-1 is assigned to C-C stretching vibrations. Similarly the C-N stretching mode appears in IR at 1131 cm-1 (medium)
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and at 1130 cm-1 (weak) in Raman spectrum. 4.4.5. Cd–Cl, Cd…O vibrations
The Cd–Cl stretching mode is observed at 248 cm-1 as a strong band which agrees well with the computed value 299 cm-1 from B3LYP/LANL2DZ. The Cd–O stretching vibrations are
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coupled with Cd-Cl stretching region as evident from the PED analysis. The bending vibration band is observed in Raman at 177 cm-1 (medium) and 97 cm-1 (strong) which is in agreement
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with the computed results.
4.5. First-order hyperpolarizability calculations Molecular nonlinear optics is the description of the change of the molecular optical
properties by the presence of an intense electric field. NLO effects of organic molecules arise from electronic motion and photonic influence on it, in contrast to inorganic material whose NLO effects are mainly due to the contribution from polar optical lattice vibration. The first order hyper polarizability β is an important parameter for designing better electro optic NLO material in high speed communication. The main outcome of organic NLO materials is low cost 9
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and ease of processing which make them very attractive to the industry for emerging technologies in the areas of telecommunications, signal processing, and optical interconnections The second order polarizability or first hyperpolarizability β was calculated using HF
hyperpolarizability can be calculated using the following equation
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/LANL2DZ basis set on the basis of the finite-field approach. The components of the first
βi = βiii + 1/3 Σ (βijj + βjij + βjji) , (i≠j) ……(3)
calculated by β = (β2x + β2y + β2z) ½ …… (4) where
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βx = βxxx + βxyy + βxzz
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Using the x, y and z components, the magnitude of the first hyperpolarizability tensor can be
βy = βyyy + βyzz + βyxx βz = βzzz + βzxx + βzyy
The magnitude of first hyperpolarizability [40] calculated from Gaussian 09W output is given as follows
β = [(βxxx + βxyy + βxzz) 2 + (βyyy + βyzz + βyxx) 2 + (βzzz + βzxx + βzyy) 2] ½ ……(5)
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Hyperpolarizability is a third rank tensor that can be described by taking in to account the Kleiman symmetry relation [41].The first order hyperpolarizability (β) of LACC is calculated to be 1.076 x10-30 esu which is about 0.68 times that of KDP. The large value of hyperpolarizability, associated with the intramolecular charge transfer interaction shows that
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LACC is the best material for NLO applications. The components of the hyperpolarizability tensor of LACC are shown in Table S2.
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4.6. SHG measurement:
Second harmonic generation (SHG) is a nonlinear optical process that results when light
propagated through a crystalline solid, which have noncentrosymmetry generates light at second and higher harmonics of the applied frequency. The NLO property of the title compound LACC was measured by Kurtz Perry powder reflection technique [42]. The finely powdered sample was densely packed between two transparent glass slides. Laser beam from Nd:YAG pulsed laser (1064 nm,8 ns) was used. The power of the incident beam was measured using a power meter. Potassium dihydrogen Orthophosphate (KDP) was used as the reference material in the SHG 10
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measurement. The SHG efficiency of the grown LACC crystal was found to be 0.57 times that of KDP but 1.66 times greater than that of ligand L-alanine (0.34 times). This clearly shows that Lalanine ionically bonded to cadmium chloride, has increased nonlinearity.
4.7. Electronic properties
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4.7.1. UV-Vis-NIR spectral studies
The UV-Visible spectrum of LACC was measured in water as solvent. The observed and simulated UV-visible absorption spectrum of the title compound is shown in Fig. 5. The lower cut off wavelength for LACC is found to be 208 nm. The theoretical calculation (water medium)
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shows that a strong transition is expected at 217 nm with oscillator strength 0.0337. The wide optical transparency range in the visible and UV spectral region enhances the usefulness of
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LACC for optoelectronics which make it a potential material for NLO application. The electronic vertical singlet transmission energies, oscillator strength (f), absorption wavelength (λ) and transition levels for solvate phase calculated at PCM-TD-DFT method are listed in Table S3. The longest absorption wavelength λonset is used to calculate the optical gap [5.72eV] energy, Eg, according to the equation
Eg = 1242/λonset ……(6)
Position for Figure 5
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4.7.2. HOMO-LUMO analysis
Frontier orbital theory tells us that the HOMO and the LUMO play a leading role in chemical reactions. Homo-Lumo analysis reveals the theoretical basis for a close correlation
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between the HOMO-LUMO energy separation and energy barriers to chemical reactions [22, 43]. A molecule with a small HOMO-LUMO gap is chemically reactive, optically polarizable
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and it implies low kinetic stability, because it is energetically favorable to add electrons to a highlying LUMO, or to extract electrons from a low-lying HOMO, and so to form the activated complex of any potential reaction. HOMO – LUMO gap (5.43eV) represents the optical gap which nicely fits with the energy gap obtained from UV analysis and is also closely related to the first order hyperpolarizability. Electron distribution of HOMO and LUMO energy levels are shown in
Fig. 6. •
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Conclusion The single crystals of L-alanine cadmium chloride were grown by slow evaporation technique. Density functional calculations have been carried out for vibrational spectral analysis
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using B3LYP/LANL2DZ basis set. The redshift in NH3+ stretching wavenumber is due to the formation of inter and intramolecular hydrogen bonding which is further substantiated by NBO analysis. The binding of cadmium ion to carboxylate group in a monodentate fashion is evident from the spectral analysis. The cadmium ligand binding increases hyperpolarizability value
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(1.076 x10-30 esu) which is 0.68 times that of KDP. The second harmonic generation study confirms the increased NLO efficiency, due to the ionic nature of the bond between of L-alanine
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with cadmium chloride. The low value of energy gap (EHOMO- ELUMO =5.43ev, Eguv=5.72ev) indicate the possibility of intra molecular charge transfer which enhances the NLO activity of the molecule.
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[27] M.E. Alikhani, F. Fuster and B. Silvi, Struct. Chem. 16 (2005) 203-210.
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[28] A. Savin, B.Silvi and, F. Colonna, Can.J.chem.74 (1996) 1088-1096.
[30] L.J. Bellamy, The Infra-red Spectra of Complex Molecules, John Wiley and Sons, Inc., New York, 1975.
[31] R.M. Silverstein and F.X. Webster, Spectrometric identification of Organic compounds, John Wiley and sons, New York, 2003.
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[32] B. Smith, Infrared spectral interpretation, CRC Press, Washington, DC, 1999. [33] M. Amalanathan, I. Hubert Joe and V.K. Rastogi, J. Mol. Stru. 985 (2011) 48-56.
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[34] D.L. Vien, N.B. Colthup, W.G. Fateley and J.G. Grasselli, The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academic Press, Boston, 1991.
AC C
[35] N.P.G. Roeges, a Guide to the Complete Interpretation of Infrared Spectra of Organic Structures, Wiley, New York, 1994. [36] G.Socrates, Infrared Characteristic Group Frequencies, Wiley-Interscience Publication, Newyork, 1980.
[37] K.Nakamoto, Infrared and Raman spectra of inorganic and Raman spectra of Inorganic and coordination compounds, Wiley, Newyork, 1986.
14
ACCEPTED MANUSCRIPT
[38] T.Vijayakumar, I. Hubert Joe, C.P. Regunadhan nair, V.S. Jayakumar, J. Raman spectrosc. 40 (2009) 18-30. [39] V. Alabugin, M. Manoharan, S. Peabody, F.Weinhold, J. Am. Chem.Soc. 125 (2003) 5973-
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5987. [40] K.S. Thanthiriwatte and K.M. Nalin de Silva, J. Mol. Struct. (Theochem). 617 (2002) 169175.
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[41] D.A. Kleinman, Phys. Rev. 126 (1962) 1977-1979.
[42] S.K. Kurtz and T.T. Perry, J. Appl. Phys. 39 (1968) 3798-3813.
AC C
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[43] C. Ravikumar, I. Hubert Joe and V.S. Jayakumar.Chem.Phys.Lett.460 (2008) 552-558.
15
ACCEPTED MANUSCRIPT
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Figures Captions Fig.1. Molecular structure of LACC calculated at B3LYP/LANL2DZ
Fig.2. Electron Localization Function value defining the bonding isosurface η(r) = 0.80 for LACC
B3LYP/LANL2DZ level of theory IR spectra .
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Fig.3. (b) Experimental FT-IR spectra of LACC in the range 4000–400 cm-1 and (a) Simulated
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Fig.4. (b) Experimental FT-Raman spectra of LACC in the range 3500–50 cm-1 and (a) Simulated B3LYP/LANL2DZ level of theory Raman spectra. Fig.5. (b) UV Visible spectra of LACC in the range 800–200 cm-1 and (a) Simulated B3LYP/LANL2DZ level of theory
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Fig.6. (b) LUMO and (a) HOMO plot of LACC by B3LYP/LANL2DZ level of theory
16
ACCEPTED MANUSCRIPT Table 1. Optimized geometrical parameters (Å,˚) of LACC atom. Bond Length
Calc
Exp.
Bond Angle
Calc
Exp.
C2-N1
1.54
1.46
C3-C2-N1
101.23
108.20
O5-C3-C2-N1
C3-C2
1.56
1.55
C4-C3-N1
111.60
111.03
Cl6-Cd7-O5-C3
156.42
77.20
C4-C2
1.52
1.54
O5-C3-C2
117.20
114.30
Cd7-O5-C3-C2
100.64
131.84
O5-C3
1.30
1.27
Cl6-Cd7- O5
87.38
86.68
Cl8-Cd7-O5-C3
-31.72
-8.88
Cl6-Cd7
2.40
2.60
Cd7-O5-C3
122.06
125.56
O9-C3-C2-N1
49.99
3.06
Cd7- O5
2.16
2.35
Cl8-Cd7- O5
93.36
90.28
H10-C4-C2-N1
55.57
0.00
Cl8- Cd7
2.55
2.62
O9-C3- C2
114.35
118.15
H11-C4-C2-N1
-66.69
-120.00
O9- C3
1.26
1.25
H10-C4- C2
111.47
109.47
H12- C4-C2-N1
174.08
120.00
H10-C4
1.09
1.07
H11- C4-C2
111.58
109.47
H13- C2-C3-O5
123.33
63.93
H11- C4
1.09
1.07
H12-C4- C2
108.55
109.47
H14-N1-C2-C3
-171.23
-180.00
H12- C4
1.09
1.07
H13-C2- N1
106.14
109.72
H15- N1-C2-C3
-48.27
-60.00
H13- C2
1.09
1.07
H14-N1- C2
113.26
109.47
H16-N1-C2-C3
66.07
60.00
H14-N1
1.02
1.00
H15-N1-C2
105.44
109.47
H15-N1
1.03
1.00
H16-N1-C2
107.33
109.47
H16-N1
1.05
1.00
Calc
-125.40
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Calc- calculated, exp- experimental
Dihedral angle
Exp.
-176.21
ACCEPTED MANUSCRIPT Table 2. Second order perturbation theory analysis of Fock matrix in NBO basis of LACC
E(j)-E(i) b
F(i,j) c
ED(j)
(kcal mol-1)
(a.u.)
(a.u.)
0.10761
2.30
0.65
0.035
0.43
0.033
0.34
0.040
77.68
0.27
0.132
0.64
1.30
0.023
2.40
0.61
0.035
Acceptor (j) ED(i) 1.92639
σ *Cl6-Cd7
n(2)O5
1.89628
σ *Cl6-Cd7
3.20
n(3)O5
1.64404
σ *Cl6-Cd7
5.11 0.31173 0.02409
1.97167
σ *N1-H15
n(2)O9
1.8724
σ *N1-H15
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n(1)O9
σ *C3-O5
0.08663
23.10
0.66
0.111
σ *C2-C3
0.10335
16.86
0.55
0.086
0.08663
0.10
1.03
0.009
0.08
1.03
0.008
1.02
0.87
0.027
σ* N1-H16
19.69
0.67
0.103
1.14
0.66
0.025
0.45
0.73
0.016
0.12
0.81
0.009
1.99961
σ *C3-O5
n(5)Cd7
1.99784
σ *C3-O5
n(1)Cl8
1.99083
n(3)Cl8
1.90807
n(4)Cl8
1.81301
σ * N1-H16
n(2)Cl8
1.97117
σ *C4-H10
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n(4)Cd7
σ *N1-H16
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a
π *C3-O9
0.07851
0.01022
n(3)Cl8
1.90807
σ *C4-H10
σC2-C3
1.96922
σ*N1-H14
0.01248
3.25
0.88
0.053
σ C2-C4
1.98631
σ*N1-H15
0.02409
1.91
1.00
0.051
σC2-H13
1.96779
σ*N1-H16
0.07851
2.57
1.00
0.039
E(2) means energy of hyperconjugative interactions (stabilization energy). Energy difference between donor i and acceptor j NBO orbitals. c Fock matrix element between i and j NBO orbitals. b
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n(1)O5
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Donor (i)
E(2) a
ACCEPTED MANUSCRIPT Table 3: Definition of internal valence coordinates of LACC Symbol
Type
Definition Stretching C2-C3, C2-C4.
ri
C-C
3-4
ri
C-O
C3-O9, C14-O5.
5-6
ri
Cd-Cl
Cd7-Cl8, Cd7-Cl6.
7
ri
C-N
C2-N1.
8
ri
C-H
C2-H13.
9
ri
Cd-O
Cd7-O5.
10-12
Ri
N-H(amino)
N1-H15, N1-H14, N1-H16.
13-15
Ri
C-H (methyl)
16-18
αi
H-N-H (amino)
19-21
βi
C-N-H (amino)
22-24
αi
H-C-H (methyl)
25-27
βi
C-C-H (methyl)
28-29
βi
C-C-O
C2-C3-O9, C2-C3-O5.
30
βi
O-C-O
O9-C3-O5.
31
βi
C-O-Cd
C3-O5-Cd7.
32-33
βi
O-Cd-Cl
O5-Cd7- Cl8, O5-Cd7- Cl6.
34
βi
Cl-Cd-Cl
Cl8-Cd7-Cl6.
35
αi
C-C-H(1)
C3-C2-H13
36
γi
N-C-C(1)
N1-C2-C4
37
βi
C-C-C
C3-C2-C4.
38
βi
C-C-H(2)
C4-C2-H13.
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1-2
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No
C4-H11, C4-H10, C4-H12.
Bending H14-N1-H16, H15-N1-H16, H15-N1-H14. C2-N1-H15, C2-N1-H14, C2-N1-H16.
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H10-C4- H12, H11-C4-H12,H11-C4- H10.
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C2-C4- H11, C2-C4- H10, C2-C4- H12.
ACCEPTED MANUSCRIPT 39
βi
N-C-C(2)
N1-C2-C3.
40
βi
N-C-H
N1-C2-H13.
41
ωi
C-O
O10-C3-O5-C2
42
ωi
O-Cd
O5-Cd7-Cl8-Cl6. Torsion
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Out-of-Plane bending (wagging)
C3-C2-N1-H15, C3-C2-N1-H15, H13-C2-N1-H16,
τi
tN-H (amino)
H13-C2-N1-H15, H13-C2-N1-H14,H13-C2-N1-H16,
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43-51
C4-C2-N1-H15, C4-C2-N1-H14, C4-C2-N1-H16.
tC-H (methyl1)
61-62
τi
tCd-O
63-64
τi
tC-O
65-70
τi
tC-C
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τi
C3-O5-Cd7-Cl6,C3-O5-Cd7-Cl8.
C2-C3-O5-Cd7, O9-C3-O5-Cd7.
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52-60
C3-C2-C4-H11, C3-C2-C4-H10, C3-C2-C4-H12, H13-C2-C4-H11, H13-C2-C4-H10, H13-C2-C4H12, N1-C2-C4-H11, N1-C2-C4-H10, N1-C2C4-H12
N1-C2-C3-O9, N1-C2-C3-O5, H13-C2-C3-O9, H13C2-C3-O5, C4-C2-C3-O9, C4-C2-C3-O.
ACCEPTED MANUSCRIPT Table 4.Detailed assignment of fundamental vibrations LACC by NCA based on SQM force field calculations. Calculated wavenumbers
Observed wavenumbers
(cm-1)
(cm-1) FTIR
Characterization of normal modes with PED ( ≥10%)
Raman
3396
3232m
3240w
61.68
3217
3146w
3154w
84.19
3052
3044s
3046w
5.23
6.71 CH3ops(98)
3026
-
-
18.99
8.52 CH3ips(90)
2993
2998w
3004m
3.35
2937
2948s
2937vs
26.72
2872w
845.75
NH3ops(52),NH3ip(34),NH3ss(14)
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12.24 NH3ss(64),NH3ips(31)
22.46 CHstr(95)
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2867
13.65
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Scaled
IR Raman Intensity Intensity
1616s
-
81.75
1600
1584vs
1590m
28.6
1550
1566vs
1485
67.60 NH3ops(43),NH3ss(41),NH3ips(16) 3.01 NH3opb(60),NH3ipb(35)
14.18 NH3opb(50), NH3ipb(24), COO-astr (16)
-
277.24
16.28 COO-astr (65), NH3sd(15)
1495vs
1502w
424.92
2.92 NH3sd(70), COO-astr (14)
1466
1453s
1453m
10.43
7.03 CH3ipb(72 ), CH3opb(14)
1453
1412s
1396
1372m
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1652
36.55 CH3ss(93)
1308 1262
6.99
1371w
46.39
1340s
1341m
7.26
1300m
1300w
20.84
4.84 CHCsci(25),CHCrck (22), CCstr(21)
130.80
12.52 COO-str ( 47), CHCsci(17), OCOb(12) 12.38 NH3ipr (24), CH3opr (19),CHCtw(12)
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1338
1411m
1210m 1214vw
1196
-
-
45.32
1101
1109m
1108m
73.26
1072
1001m
1003w
38.80
19.1 CH3opb(74), CH3ipb (27) 1.89 CH3sd(90) 2.51 CHCwag(48),CHCtwt (30)
4.81 NH3opr (36), CHCsci(31) 10.12 CH3ipr (37), CCstr (18), CNstr (14)
ACCEPTED MANUSCRIPT 970w
971m
1.65
961
925w
922w
11.99
16.11 NH3ipr (41), CCstr (33),CH3ipr (10)
834
838m
843s
14.69
11.34 CCstr (59), CNstr (26)
767
761m
763w
18.24
34.05 gC=O (19),CCstr (16), CNstr (14)
-
19.56
7.27 gC=O (50),COCb (12), CHCrck(10)
540m
538w
18.27
9.74
502
-
-
4.37
26.99 COOrck (40),CCstr(19),CHCtw(11)
393
-
416w
8.68
20.02 τNH3(40),CCHsci(23)
-
9.44
17.87 COCb(25), gC=O (17), τNH3(15)
-
60.01
297w
79.97
80.54 CdCl str(29), COCb(21), CCHsci(15)
248s
16.38
81.39 Cd..O str(22), CCHsci(18), CdCl str(15)
351 346
-
315 299
-
11.25 -
214
-
185 106
-
79 62 53 25
-
0.63
177m
39.68
-
6.85 Cd..O str(39), CdCl str(20), COCb(10)
40.9 CdCl str(56), tCH3(10)
47.49 tCdC (20), COO-rck(16),CHCtw(10) 5.06 τCH3 (60) 4.38 τCO (29), CdClb(11)
96s
3.02
58.66 COCb (60), CdOb(30)
-
6.61
22.63 τCO (53), COCb(29)
72m
18.61
AC C
92
29.39
EP
228
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247
OCOb(29), COCb (13), gC=O (13), CCstr (12)
SC
558
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722
3.84 CH3opr (27), NH3opr (20),CHCtw(12)
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978
63.26 τCO (50), COCb(21),gOCd(19)
8.23
43.30 tCdC(56),COCb (26)
-
-
4.19
50.58 CdClb(40), CdOb(44)
-
-
2.94
100 tCdC(76), COCb(18)
vs- very strong, m- medium, s- strong, w- weak, vw- very weak, str-stretching, ss-symmetric stretching, ips-in plane stretching, ops-outplane starching,sd-symmetric deformation,ipb-inpane bending, opb-out of plane bending, b- bending, rck-rocking, sci-scissoring, tw-twisting, wag-wagging, t- torsion, g- gauche
ACCEPTED MANUSCRIPT ► Synthesis and characterization of organometalic compound LACC. ► Kurtz-Perry powder techniques confirms the nonlinear property of the crystal. ► Topological approach opens new ways for better undrestanding of the structure and bonding properties of the compound.
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► Spectral data showed the binding mode of carboxylate ion in a monodentate fashion.
ACCEPTED MANUSCRIPT Table S1: Different types of electronic basins, ELF value at attractor (ELF), basins population (N), standard deviation (σ2) and relative fluctuation (λ) of LACC ELF
N
σ2
λ
total
C( N )
1.00
2.10
0.30
0.14
1
C( Ci )
1.00
2.08
0.26
0.12
3
C( Oi )
1.00
2.12
0.33
0.15
V(Hi,Cj)
1.00
2.01
0.69
0.34
V(H13,C2)
1.00
2.10
0.69
0.32
V(H14,N1)
1.00
2.01
0.78
0.38
V(H15,N1)
1.00
2.06
0.83
0.40
V(H16,N1)
1.00
2.12
0.89
V(C2,N1)
0.908
1.56
0.93
V(C2,C3)
0.939
2.29
1.15
0.50
1
V(C2,C4)
0.948
1.94
1.03
0.53
1
V(C3,O9)
0.855
1.45
0.94
0.64
1
V(C3,O5)
0.914
2.06
1.26
0.61
1
V(C16,C17)
0.971
2.37
1.09
0.45
1
V(O9´)
0.904
3.03
1.32
0.43
2
V(Cl8) V(Cl6)
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V(Cd7)
2
3
1
1
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1
0.41
1
0.59
1
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V(O5)
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BASINS
0.917
2.86
1.24
0.43
2
0.903
3.95
1.37
0.34
2
0.900
3.93
1.38
0.35
2
0.412
2.55
1.80
0.70
4
ACCEPTED MANUSCRIPT Table S2. The first hyperpolarizability (esu) components of LACC
HF/LANL2DZ
βxxx
167.885
βxyy
-20.128
βxzz
-29.952
βyyy
-11.292
βyzz
11.024
βyxx
38.482
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Parameter
βzzz
9.223
βzxx
-1.337
βzyy
7.422
βxyz
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-14.979
ACCEPTED MANUSCRIPT Table S3. Calculated electronic absorption spectrum of LACC molecule.
CI expansion coefficient
Wavelength(nm)
Calc.
0.30691
35 → 39
-0.16817
36 → 38
-0.35331
36 → 39
0.17956
37→ 38
0.40425
37 → 39
-0.20543
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35 → 38
0.008
228.63
0.0034
-0.32907 0.18266
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32 → 39
240.93
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excited state 2
32 → 38
Expt.
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excited state 1
Oscillator Strength(f)
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Excitation
0.47997
34 → 39
-0.16075
AC C
34→ 38
36→ 38
0.16181
37 → 38
0.23018
excited state 3
34 → 38
-0.16115
35 → 38
-0.40077
36 → 38
0.21546
37 → 38
0.46416
37 → 39
0.14841
217.10
208
0.0337
S0022-2860(15)30240-4
DOI:
10.1016/j.molstruc.2015.08.052
Reference:
MOLSTR 21784
To appear in:
Journal of Molecular Structure
Received Date: 28 March 2015 Revised Date:
19 August 2015
Accepted Date: 25 August 2015
Please cite this article as: B.S. Arunsasi, K.C. Bright, C. James, Vibrational spectral characterization, NLO studies and Charge transfer analysis of the organometallic material, L-Alanine Cadmium Chloride, Journal of Molecular Structure (2015), doi: 10.1016/j.molstruc.2015.08.052. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
AC C
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ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
Vibrational spectral characterization, NLO studies and Charge transfer analysis of the organometallic material, L-Alanine Cadmium Chloride B. S. Arunsasia, K.C.Brightb and C.Jamesa* b
Department of Physics, Scott Christian College, (Autonomous), Nagercoil – 629 003, Tamil Nadu, India
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a
Department of Physics, St.Johns College Anchal, Kollam-690110, Kerala, India *
E-mail: [email protected]
* Corresponding Author: C. JAMES, Department of Physics & Research Centre, Scott Christian
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College (Autonomous), Nagercoil – 629 003, Tamil Nadu, India.
Email: [email protected]
Abstract
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Tel: +91 9443746555; Fax: +91 4652229800
An organometallic nonlinear crystal, L-Alanine Cadmium Chloride (LACC) was synthesized by slow evaporation technique. The effects of hydrogen bonding on the structure,
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binding of ligand to metal ion, natural orbital occupancies, and vibrational frequencies were investigated using density functional theory (DFT) with the combined B3LYP and LANL2DZ basis set. Vibrational assignments were made on the basis of calculated potential energy distribution values from MOLVIB program. The topological analysis of electron localization
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(ELF) provides basin population N (integrated density over the attractor basin), standard deviation (σ), and their relative fluctuation, defined as λ= σ2/N, which are sensitive criteria of
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delocalization. The molecular stability, electronic exchange interaction, and bond strength of the molecule were studied by natural bond orbital (NBO) analysis. The second harmonic generation (SHG) efficiency was determined using Kurtz and Perry method. Natural bond orbital analysis was carried out to study various intramolecular interactions that are responsible for the stabilization of the molecule.
Keywords: DFT, FT-IR, FT-Raman, NBO, ELF, Vibrational analysis.
1. Introduction 1
ACCEPTED MANUSCRIPT
Research on organometallic crystals play a major role in the domain of optoelectronics including integrated optics, optical switching, telecommunication bistability and modulation [1, 2]. They have the combined properties of both inorganic and organic crystals and have large damage threshold, less deliquescence, low angular sensitivity, wide transparency range and
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excellent nonlinear optical coefficient [3, 4]. Combination of amino acid with a metal compound has been proposed as a new candidate for NLO application which crystallizes in non centrosymmmetric space group. The proton donor carboxyl group (-COO) and the proton acceptor amino (-NH2) group present in the amino acid contribute some physiochemical
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properties. The metal–organic coordination compounds have increased NLO efficiency, via metal-ligand binding interactions. In LACC the organic part is an amino acid, more dominant in nonlinearity and the metallic part cadmium usually have high transparency in the UV region,
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because of their closed d10 configuration. L-Alanine mixed organometallic material will be of special interest as a fundamental building block to NLO properties [5].The crystal structure of LACC was first reported by Kathleen et.al [6]. Recently growth and properties of LACC have been reported [7-9]. The Density functional theory (DFT) calculation has now become the preferred method for understanding and predicting structure and reactivity in complex chemical
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system. DFT calculation along with vibrational spectral analysis is used as a promising tool to display a significant number of molecular properties of NLO materials [10]. In the present work, L-alanine Cadmium Chloride (LACC) has been grown from aqueous solution using slow evaporation technique. The grown crystal was characterized by various spectral analyses.
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Structure of the newly synthesized metal ion complex, its ground state properties and bonding characteristics of the ligand have been elucidated using experimental and theoretical methods.
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2. Experimental Techniques
2.1 Samples and instrumentation A mixture of L-alanine and cadmium chloride monohydrate taken in the equimolar ratio
was thoroughly dissolved in double distilled water and stirred well for about 2 hours using a magnetic stirrer to obtain a homogenous mixture. The reaction mixture was filtered and allowed to crystallize by slow evaporation at room temperature. Single crystals of size up to 12×7×2 mm3 were obtained in few weeks.
2
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FT-Raman spectrum of LACC was recorded in the range 3500-50cm-1 using Bruker RFS27 spectrometer with an Nd:YAG laser source at 1064nm. Thermo Nicolet, Avatar 370 spectrophotometer was used to measure the FT-IR spectrum with KBr pellet in the range from
visible double beam spectrophotometer in the range 200-800 nm.
3. Computational details
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4000-400 cm-1. The UV-visible absorption spectrum was recorded using Systronics 2200 UV-
In computational procedure, electronic structure of LACC was obtained using the hybrid
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density functional B3LYP (Becke-Lee-Yang-Parr) method with LANL2DZ basis set as implemented in Gaussian 09 [11]. The B3LYP method and the effective core potential basis set
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LANL2DZ have been widely used in studying the structure and properties of the organometallic compound. The optimized geometry corresponding to the minimum on the potential energy surface has been obtained by solving self–consistent field equations iteratively. The normal coordinate analysis including assignment of the force field in the internal coordinate representation suggested by Pulay et.al was performed using MOLVIB program [12, 13]. To offset the systematic errors caused by basis set incompleteness, over estimation of force constant,
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neglect of electron correlation and vibrational anharmonicity [14] uniform scaling (0.9612) of the force field were performed by the SQM (scaled quantum mechanics) procedure [15]. In order to study the possibility of charge transfer interaction, we have performed natural bond orbital (NBO) calculation at the B3LYP/LANL2DZ level of theory using NBO 3.1 program [16]. The
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Electron localization function (ELF) analysis was done using the Topmod program developed by Silvi et.al [17] and visualized with the Molekel program [18].
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4. Result and discussion 4.1. Optimized geometry
The molecular structure of LACC belongs to Cs point symmetry. The unit cell is
monoclinic containing 4 molecules (z=4) with lattice parameters a=16.33, b=7.31 and c=8.00 Å. The molecular structure of the compound with atom numbering scheme adopted in the computation is shown in Fig.1. The optimized geometrical bond lengths, bond angles and
3
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dihedral angles by DFT/B3LYP method with LANL2DZ as basis is compared with the X ray [6] experimental counterparts (Table 1). Position for Figure1
•
Position for Table 1
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•
The crystal structure is stabilized by ionic interactions and hydrogen bonds. From XRD analysis it is clear that the H atom attached to the carboxylic group is protonated to form NH3+ ion. The geometrical parameters show that most of the bonds were altered upon the complexation
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of L-alanine with metal [19]. The Cd7 atom is bonded to two chlorine atoms with one having bond length 2.40 Å (Cd7-Cl6) and the other one (Cd7-Cl8) having longer bond length (2.55 Å).
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The intrinsic difference in the bond lengths of two Cd-Cl is due to the formation of N1-H16…Cl8 hydrogen bonding in the crystal with inter atomic distance 2.14 Å. The C2-C3-O9 and C2-C3-O5 angles are 114.35° and 117.20° respectively. The variation in the C-C-O angles arises due to the intramolecular participation of the carbonyl oxygen atoms of the ligand with the metal ions due to chelation. 4.2. Natural bond orbital analysis
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Analysis of orbital picture in the form of localized molecular orbitals applying the natural bond orbital (NBO) approach is widely used to interpret electronic structures. NBO analysis is carried out by examining all possible interactions between filled (donor) Lewis type and empty (acceptor) non Lewis NBOs and estimating their energetic importance by second order
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perturbation theory [20-22]. These interactions allow the assignment of the hybridization of atomic lone pairs and of the atoms involved in bond orbitals. Some selected interactions which
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result in stabilization energies exceeding an arbitrary chosen threshold are tabulated in Table 2. The bonding-antibonding interaction can be effectively described in terms of NBO
approach which is expressed by means of second order perturbation interaction energy E ( 2) = − n σ
Fij2 σFσ = −nσ ∆E ε σ* − ε σ 2
4
……. (1)
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where
σ Fσ
2
2
or Fij is the Fock matrix element i and j NBO orbitals,
ε σ and ε σ* are the
energies of σ and σ* NBOs and n σ is the population of the donor σ orbital. This perturbation energy allows to examine all possible interactions between filled Lewis-type NBOs (donor
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orbitals) and weakly occupied non-Lewis-type NBOs (acceptor orbitals), and evaluate their relevance.
Fig. 1 shows two intramolecular interactions (N1-H15…O9 and N1-H16…Cll8) which stabilize the molecule and is responsible for hydrogen bonding. The interaction between lone
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pair n(Cl8) and the antibonding orbital σ*(N1 – H16) shows the existence of N–H...Cl intrarmolecular hydrogen bonding that have stabilization energies 1.02, 19.69 and 1.14 kcal/mol for n1 (Cl8) → σ* (N1 – H16), n3 (Cl8) → σ* (N1 – H16) and n4 (Cl8) →σ* (N1 – H16), respectively.
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Considering the N1-H15…O9 (1.458 Å) interaction, the n1 (O9) → σ* (N1 – H15), n2 (O9) → σ* (N1 – H15), have stabilization energies 0.64, 2.40 kcal/mol respectively. The stabilization energy E(2) associated with hyperconjugative interaction n2(O9)→ σ*(C2–C3), n2(O9)→ σ*(C3–O5) are obtained as 16.86 and 23.10 kcal/mol respectively. As a result of this intramolecular interactions, the electron density in the antibonding orbital increases which leads to slight elongation
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(Table 1) of the respective bond.
An important aspect of utilizing organometallic structures for nonlinear optics is in their unique charge transfer capability associated with charge transfer transitions either from metal to ligand or ligand to metal [23]. In title molecule the contributions of stabilization energies for the
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n4 (Cd7) →σ*(C3–O5), n5 (Cd7) → σ*(C3–O5) are 0.10 and 0.08 kcal/mol respectively, which is further stabilized by the hyper conjugative interaction n2 (O5) → π* (C3 – O9) with stabilization energy 77.68 kcal/mol. These charge transfer interactions from metal to ligand enhances NLO
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activity of the molecule. 4.3. ELF analysis
The topological analysis of ELF provides a nice picture of the electronic structure in
molecules, offering an atom based partition of the molecular space where electrons get localized maximum. The ELF was analyzed with the TopMod [24] program using density matrices obtained from Gaussian orbital computations. The ELF function proposed by Becke and Edgecombe as a ‘simple measure of electron localization in atomic and molecular systems’ [25, 26] is defined as: 5
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……. (2)
In which Dσ andD0σ represent the curvature of the electron pair density for electrons of identical spins (the Fermi hole) for the actual system and a homogenous electron gas with the same
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density, respectively. Dσ were the Laplacian of the conditional probability calculated from a single determinental Hartree-Fock wave function. Hence, η(r) =0 in those regions where the relative probability of finding electrons with parallel spin close together was high (i.e., where the
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local Pauli repulsion is strong), whereas η(r) =1 in those regions with a high probability of finding a single electron or a pair of opposite spin electrons.
The graphical representation of the ELF function at η(r) =0.80 for LACC is shown in Fig. 2. Such representation depicts different types of electronic basins, the average number of electrons (N), the standard deviation (σ2) and the relative fluctuations (λ) of the molecule and is summarized in Table S1.
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ELF provides a convenient characterization of hydrogen bond, by the presence of a protonated valence basin sharing a separatrix with at least another valence basin which does not participate to same atomic valence shell [27]. The protonated valence basin is generally a
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disynaptic whereas the valence basin is monosynaptic (involving lone pair), disynaptic (H-bond involving a bond) or protonated disynaptic. In title molecule, due to the intramolecular charge transfer from n1(O9)→ σ*(N1–H15), n2(O9)→ σ*(N1–H15), n1(Cl8)→ σ*(N1–H16), n3(Cl8)→
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σ*(N1–H16), n4(Cl8)→ σ*(N1–H16), the population of disynaptic basin V(N1,H15) and V(N1,H16) increased considerably than that of V(N1,H14). According to Bader [28] the relative fluctuation is a good measure of the delocalization. It is of the order of 0.1 for Core basins, 0.3 for basins of the protonated disynaptic attractor of the C-H bonds, 0.4 for basins related to single and double C-C bonds, and 0.5 for delocalized bonds. ELF analysis shows that the relative fluctuation in the core basin is very low while these values get maxima for the disynaptic basins. For basins of the disynaptic attractor of the C-O bonds the relative fluctuation is high (0.64 and 0.61), which shows COO- ion is strongly delocalized. The electron delocalization in Cd2+ is enhanced due to 6
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the unfilled d10 electron shell that allows the possibility of low energy charge transfer interaction. In LACC, as a result of charge transfer interaction from metal (Cd2+) to organic ligand (C-O), the population of V(C, O) increased about 0.16 e- than that of other V(C, O). In addition to this the combination of orbitals of Cd2+ and Cl overlap to form highly delocalized system. The
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topological analysis shows the absence of disynaptic basin between cadmium and oxygen atom, and the interaction can be treated as ionic. These topological parameters and high value of delocalization enhances the NLO property of the molecule.
4.4. Vibrational modes description
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Vibrational analysis based on both theoretical and experimental approach is a useful tool for the assessment of structural changes and for predicting spectral features. The non-redundant
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set of internal coordinates was constructed according to Pulay’s recommendations (Table 3). The computed vibrational wavenumbers and their IR and Raman intensities corresponding to the different normal modes are used to identify the vibrational modes clearly. The observed and calculated wavenumbers together with the infrared and Raman intensities and normal modes description (characterized by PED) of LACC are reported in Tables 4. The observed and simulated FT-IR and FT-Raman spectra are presented in Figs. 3 and 4 respectively. • • •
Position for Figure 4 Position for Table 3 Position for Table 4
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4.4.1. NH3+ vibrations
Position for Figure 3
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•
The asymmetric and symmetric stretching band of NH3+ generally appears in the region
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3330 and 3080 cm-1 respectively [30]. In LACC the medium broad band observed in FT-IR at 3232 cm-1 and its counterpart in Raman observed as a weak band at 3240 cm-1 is assigned to the asymmetric vibration of NH3+. The NH3+ symmetric stretching mode appears as weak bands in IR and Raman at 3146 cm-1 and 3154 cm-1, respectively. The asymmetric NH3+stretching wavenumber is theoretically calculated at 3396 cm-1 and the symmetric stretching at 3218 cm-1. The deviation of computed amino stretching wave number from the free ion values is considered as the possible redshift due to N-H…Cl and N-H…O hydrogen bonding. The NH3+ symmetric and asymmetric bending mode generally appear in the range 1550-1485 cm-1 and 1660-1610 cm7
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1
respectively [31]. The asymmetric NH3+ bending mode is observed as a strong band in IR at
1616 cm-1. The strong band at 1495 cm-1 in IR and weak band at 1502 cm-1 in Raman corresponds to the NH3+symmetric bending mode. According to the calculated PED, these vibrational modes are coupled with some contribution from the COO- vibrations. NH3+ rocking
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mode appears as a medium band in IR at 1109 cm-1 and Raman at 1108 cm-1. One of the finger print identification of NH3+ group in LACC crystal is observed in IR at 1995 cm-1, which can be assigned as the combination of torsional oscillation and the degenerate deformation of the NH3+ group.
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4.4.2. Methyl and methine group vibrations
The asymmetric and symmetric stretching vibrations of CH3 group are normally observed in the range 2980-2875 cm-1 [32, 33]. For the title compound, the strong band observed at 3044
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cm-1 in IR and the weak band at 3046 cm-1 in Raman is assigned to asymmetric stretching vibration of methyl group. The symmetric stretching mode is observed as a strong band in both IR and Raman at 2948 cm-1 and 2937cm-1 respectively. The blue shifting of the methyl stretching wave number due to C-H…Cl interaction, is mainly manifested by the shortening of C4–H10 bond (0.0037Å), and low value of electron density (0.0102e) in the σ* (C4 – H10 ) orbital [n2 (Cl8)
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→ σ* (C4 – H10) ˜ 0.45 kcal/mol]. The CH group stretching vibrations are noticeably observed as weak bands in IR at 2998 cm-1 and as a medium band in Raman at 3005 cm-1. The deformation frequencies observed in the region 1470-1420 cm-1 and 1390-1370 cm-1 corresponds to asymmetric and symmetric bending vibrations of methyl group [34]. The asymmetric bending
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vibration appears as a medium band in both IR and Raman at 1453cm-1 while its symmetric part is observed in IR at 1372 cm-1 (medium) and Raman at 1371cm-1 (weak). The theoretically
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computed wavenumbers at 1466 and 1396 cm-1 show well agreement with the experimental values. The methyl rocking, twisting vibrations generally observed to be weak in the region 1120-1050 and 900-800 cm-1 [35] are observed in IR at 970 cm-1 (weak) and Raman at 971 cm-1 (medium). Out of plane bending vibrations of the methyl group are listed in Table 4. 4.4.3. COO- group vibration In LACC, the metal is bonded to carboxylate through ionic interaction, and the resulting arrangement becoming unusual can stretch asymmetrically and symmetrically. This can produce two bands and is important to predict the binding mode of the ligand. The stretching vibration of 8
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carboxylate ion is expected in the region 1650-1550 cm-1 (asymmetric) and near 1400 cm-1 (symmetric) [31, 36]. The strong band in IR spectrum at 1566 cm-1 is assigned to asymmetric stretching mode of COO- group. The symmetric COO- stretching vibration is identified as a medium band in IR at 1210 cm-1 and weak Raman band at 1214 cm-1. The lowering of this mode
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is due to the interaction of the lone pair oxygen atom of COO- group with the Cd atom, also owing to the consequence of metal coordination. According to PED analysis, the symmetric stretching COO- vibration (1262 cm-1) has only 47% contribution. The frequency difference [ν = νas(COO-)- νs(COO-)] is greater than 200 cm-1 which shows an indication of the binding mode of
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carboxylate in a monodenate manner [37]. The inplane and out of plane bending modes of carboxylate vibrations appearing in the region 780-650 cm-1, coupled with some other mode are identified and assigned in Table 4. The medium band in IR at 623 cm-1and the weak band in the
4.4.4. Skeletal mode vibrations
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Raman at 621 cm-1 are assigned to in plane bending mode of carboxylate ion. The C-N and C-C skeletal mode vibrations appear in the range 1150-850 cm-1 [36,38,39] .The strong bands observed in both IR at 838 cm-1 and Raman at 841cm-1 is assigned to C-C stretching vibrations. Similarly the C-N stretching mode appears in IR at 1131 cm-1 (medium)
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and at 1130 cm-1 (weak) in Raman spectrum. 4.4.5. Cd–Cl, Cd…O vibrations
The Cd–Cl stretching mode is observed at 248 cm-1 as a strong band which agrees well with the computed value 299 cm-1 from B3LYP/LANL2DZ. The Cd–O stretching vibrations are
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coupled with Cd-Cl stretching region as evident from the PED analysis. The bending vibration band is observed in Raman at 177 cm-1 (medium) and 97 cm-1 (strong) which is in agreement
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with the computed results.
4.5. First-order hyperpolarizability calculations Molecular nonlinear optics is the description of the change of the molecular optical
properties by the presence of an intense electric field. NLO effects of organic molecules arise from electronic motion and photonic influence on it, in contrast to inorganic material whose NLO effects are mainly due to the contribution from polar optical lattice vibration. The first order hyper polarizability β is an important parameter for designing better electro optic NLO material in high speed communication. The main outcome of organic NLO materials is low cost 9
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and ease of processing which make them very attractive to the industry for emerging technologies in the areas of telecommunications, signal processing, and optical interconnections The second order polarizability or first hyperpolarizability β was calculated using HF
hyperpolarizability can be calculated using the following equation
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/LANL2DZ basis set on the basis of the finite-field approach. The components of the first
βi = βiii + 1/3 Σ (βijj + βjij + βjji) , (i≠j) ……(3)
calculated by β = (β2x + β2y + β2z) ½ …… (4) where
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βx = βxxx + βxyy + βxzz
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Using the x, y and z components, the magnitude of the first hyperpolarizability tensor can be
βy = βyyy + βyzz + βyxx βz = βzzz + βzxx + βzyy
The magnitude of first hyperpolarizability [40] calculated from Gaussian 09W output is given as follows
β = [(βxxx + βxyy + βxzz) 2 + (βyyy + βyzz + βyxx) 2 + (βzzz + βzxx + βzyy) 2] ½ ……(5)
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Hyperpolarizability is a third rank tensor that can be described by taking in to account the Kleiman symmetry relation [41].The first order hyperpolarizability (β) of LACC is calculated to be 1.076 x10-30 esu which is about 0.68 times that of KDP. The large value of hyperpolarizability, associated with the intramolecular charge transfer interaction shows that
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LACC is the best material for NLO applications. The components of the hyperpolarizability tensor of LACC are shown in Table S2.
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4.6. SHG measurement:
Second harmonic generation (SHG) is a nonlinear optical process that results when light
propagated through a crystalline solid, which have noncentrosymmetry generates light at second and higher harmonics of the applied frequency. The NLO property of the title compound LACC was measured by Kurtz Perry powder reflection technique [42]. The finely powdered sample was densely packed between two transparent glass slides. Laser beam from Nd:YAG pulsed laser (1064 nm,8 ns) was used. The power of the incident beam was measured using a power meter. Potassium dihydrogen Orthophosphate (KDP) was used as the reference material in the SHG 10
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measurement. The SHG efficiency of the grown LACC crystal was found to be 0.57 times that of KDP but 1.66 times greater than that of ligand L-alanine (0.34 times). This clearly shows that Lalanine ionically bonded to cadmium chloride, has increased nonlinearity.
4.7. Electronic properties
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4.7.1. UV-Vis-NIR spectral studies
The UV-Visible spectrum of LACC was measured in water as solvent. The observed and simulated UV-visible absorption spectrum of the title compound is shown in Fig. 5. The lower cut off wavelength for LACC is found to be 208 nm. The theoretical calculation (water medium)
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shows that a strong transition is expected at 217 nm with oscillator strength 0.0337. The wide optical transparency range in the visible and UV spectral region enhances the usefulness of
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LACC for optoelectronics which make it a potential material for NLO application. The electronic vertical singlet transmission energies, oscillator strength (f), absorption wavelength (λ) and transition levels for solvate phase calculated at PCM-TD-DFT method are listed in Table S3. The longest absorption wavelength λonset is used to calculate the optical gap [5.72eV] energy, Eg, according to the equation
Eg = 1242/λonset ……(6)
Position for Figure 5
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•
4.7.2. HOMO-LUMO analysis
Frontier orbital theory tells us that the HOMO and the LUMO play a leading role in chemical reactions. Homo-Lumo analysis reveals the theoretical basis for a close correlation
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between the HOMO-LUMO energy separation and energy barriers to chemical reactions [22, 43]. A molecule with a small HOMO-LUMO gap is chemically reactive, optically polarizable
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and it implies low kinetic stability, because it is energetically favorable to add electrons to a highlying LUMO, or to extract electrons from a low-lying HOMO, and so to form the activated complex of any potential reaction. HOMO – LUMO gap (5.43eV) represents the optical gap which nicely fits with the energy gap obtained from UV analysis and is also closely related to the first order hyperpolarizability. Electron distribution of HOMO and LUMO energy levels are shown in
Fig. 6. •
Position for Figure 6
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Conclusion The single crystals of L-alanine cadmium chloride were grown by slow evaporation technique. Density functional calculations have been carried out for vibrational spectral analysis
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using B3LYP/LANL2DZ basis set. The redshift in NH3+ stretching wavenumber is due to the formation of inter and intramolecular hydrogen bonding which is further substantiated by NBO analysis. The binding of cadmium ion to carboxylate group in a monodentate fashion is evident from the spectral analysis. The cadmium ligand binding increases hyperpolarizability value
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(1.076 x10-30 esu) which is 0.68 times that of KDP. The second harmonic generation study confirms the increased NLO efficiency, due to the ionic nature of the bond between of L-alanine
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with cadmium chloride. The low value of energy gap (EHOMO- ELUMO =5.43ev, Eguv=5.72ev) indicate the possibility of intra molecular charge transfer which enhances the NLO activity of the molecule.
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[32] B. Smith, Infrared spectral interpretation, CRC Press, Washington, DC, 1999. [33] M. Amalanathan, I. Hubert Joe and V.K. Rastogi, J. Mol. Stru. 985 (2011) 48-56.
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[34] D.L. Vien, N.B. Colthup, W.G. Fateley and J.G. Grasselli, The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academic Press, Boston, 1991.
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[35] N.P.G. Roeges, a Guide to the Complete Interpretation of Infrared Spectra of Organic Structures, Wiley, New York, 1994. [36] G.Socrates, Infrared Characteristic Group Frequencies, Wiley-Interscience Publication, Newyork, 1980.
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[38] T.Vijayakumar, I. Hubert Joe, C.P. Regunadhan nair, V.S. Jayakumar, J. Raman spectrosc. 40 (2009) 18-30. [39] V. Alabugin, M. Manoharan, S. Peabody, F.Weinhold, J. Am. Chem.Soc. 125 (2003) 5973-
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5987. [40] K.S. Thanthiriwatte and K.M. Nalin de Silva, J. Mol. Struct. (Theochem). 617 (2002) 169175.
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[43] C. Ravikumar, I. Hubert Joe and V.S. Jayakumar.Chem.Phys.Lett.460 (2008) 552-558.
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Figures Captions Fig.1. Molecular structure of LACC calculated at B3LYP/LANL2DZ
Fig.2. Electron Localization Function value defining the bonding isosurface η(r) = 0.80 for LACC
B3LYP/LANL2DZ level of theory IR spectra .
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Fig.3. (b) Experimental FT-IR spectra of LACC in the range 4000–400 cm-1 and (a) Simulated
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Fig.4. (b) Experimental FT-Raman spectra of LACC in the range 3500–50 cm-1 and (a) Simulated B3LYP/LANL2DZ level of theory Raman spectra. Fig.5. (b) UV Visible spectra of LACC in the range 800–200 cm-1 and (a) Simulated B3LYP/LANL2DZ level of theory
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Fig.6. (b) LUMO and (a) HOMO plot of LACC by B3LYP/LANL2DZ level of theory
16
ACCEPTED MANUSCRIPT Table 1. Optimized geometrical parameters (Å,˚) of LACC atom. Bond Length
Calc
Exp.
Bond Angle
Calc
Exp.
C2-N1
1.54
1.46
C3-C2-N1
101.23
108.20
O5-C3-C2-N1
C3-C2
1.56
1.55
C4-C3-N1
111.60
111.03
Cl6-Cd7-O5-C3
156.42
77.20
C4-C2
1.52
1.54
O5-C3-C2
117.20
114.30
Cd7-O5-C3-C2
100.64
131.84
O5-C3
1.30
1.27
Cl6-Cd7- O5
87.38
86.68
Cl8-Cd7-O5-C3
-31.72
-8.88
Cl6-Cd7
2.40
2.60
Cd7-O5-C3
122.06
125.56
O9-C3-C2-N1
49.99
3.06
Cd7- O5
2.16
2.35
Cl8-Cd7- O5
93.36
90.28
H10-C4-C2-N1
55.57
0.00
Cl8- Cd7
2.55
2.62
O9-C3- C2
114.35
118.15
H11-C4-C2-N1
-66.69
-120.00
O9- C3
1.26
1.25
H10-C4- C2
111.47
109.47
H12- C4-C2-N1
174.08
120.00
H10-C4
1.09
1.07
H11- C4-C2
111.58
109.47
H13- C2-C3-O5
123.33
63.93
H11- C4
1.09
1.07
H12-C4- C2
108.55
109.47
H14-N1-C2-C3
-171.23
-180.00
H12- C4
1.09
1.07
H13-C2- N1
106.14
109.72
H15- N1-C2-C3
-48.27
-60.00
H13- C2
1.09
1.07
H14-N1- C2
113.26
109.47
H16-N1-C2-C3
66.07
60.00
H14-N1
1.02
1.00
H15-N1-C2
105.44
109.47
H15-N1
1.03
1.00
H16-N1-C2
107.33
109.47
H16-N1
1.05
1.00
Calc
-125.40
RI PT
SC
M AN U
TE D
EP
AC C
Calc- calculated, exp- experimental
Dihedral angle
Exp.
-176.21
ACCEPTED MANUSCRIPT Table 2. Second order perturbation theory analysis of Fock matrix in NBO basis of LACC
E(j)-E(i) b
F(i,j) c
ED(j)
(kcal mol-1)
(a.u.)
(a.u.)
0.10761
2.30
0.65
0.035
0.43
0.033
0.34
0.040
77.68
0.27
0.132
0.64
1.30
0.023
2.40
0.61
0.035
Acceptor (j) ED(i) 1.92639
σ *Cl6-Cd7
n(2)O5
1.89628
σ *Cl6-Cd7
3.20
n(3)O5
1.64404
σ *Cl6-Cd7
5.11 0.31173 0.02409
1.97167
σ *N1-H15
n(2)O9
1.8724
σ *N1-H15
M AN U
n(1)O9
σ *C3-O5
0.08663
23.10
0.66
0.111
σ *C2-C3
0.10335
16.86
0.55
0.086
0.08663
0.10
1.03
0.009
0.08
1.03
0.008
1.02
0.87
0.027
σ* N1-H16
19.69
0.67
0.103
1.14
0.66
0.025
0.45
0.73
0.016
0.12
0.81
0.009
1.99961
σ *C3-O5
n(5)Cd7
1.99784
σ *C3-O5
n(1)Cl8
1.99083
n(3)Cl8
1.90807
n(4)Cl8
1.81301
σ * N1-H16
n(2)Cl8
1.97117
σ *C4-H10
TE D
n(4)Cd7
σ *N1-H16
EP
AC C
a
π *C3-O9
0.07851
0.01022
n(3)Cl8
1.90807
σ *C4-H10
σC2-C3
1.96922
σ*N1-H14
0.01248
3.25
0.88
0.053
σ C2-C4
1.98631
σ*N1-H15
0.02409
1.91
1.00
0.051
σC2-H13
1.96779
σ*N1-H16
0.07851
2.57
1.00
0.039
E(2) means energy of hyperconjugative interactions (stabilization energy). Energy difference between donor i and acceptor j NBO orbitals. c Fock matrix element between i and j NBO orbitals. b
SC
n(1)O5
RI PT
Donor (i)
E(2) a
ACCEPTED MANUSCRIPT Table 3: Definition of internal valence coordinates of LACC Symbol
Type
Definition Stretching C2-C3, C2-C4.
ri
C-C
3-4
ri
C-O
C3-O9, C14-O5.
5-6
ri
Cd-Cl
Cd7-Cl8, Cd7-Cl6.
7
ri
C-N
C2-N1.
8
ri
C-H
C2-H13.
9
ri
Cd-O
Cd7-O5.
10-12
Ri
N-H(amino)
N1-H15, N1-H14, N1-H16.
13-15
Ri
C-H (methyl)
16-18
αi
H-N-H (amino)
19-21
βi
C-N-H (amino)
22-24
αi
H-C-H (methyl)
25-27
βi
C-C-H (methyl)
28-29
βi
C-C-O
C2-C3-O9, C2-C3-O5.
30
βi
O-C-O
O9-C3-O5.
31
βi
C-O-Cd
C3-O5-Cd7.
32-33
βi
O-Cd-Cl
O5-Cd7- Cl8, O5-Cd7- Cl6.
34
βi
Cl-Cd-Cl
Cl8-Cd7-Cl6.
35
αi
C-C-H(1)
C3-C2-H13
36
γi
N-C-C(1)
N1-C2-C4
37
βi
C-C-C
C3-C2-C4.
38
βi
C-C-H(2)
C4-C2-H13.
M AN U
SC
RI PT
1-2
EP
No
C4-H11, C4-H10, C4-H12.
Bending H14-N1-H16, H15-N1-H16, H15-N1-H14. C2-N1-H15, C2-N1-H14, C2-N1-H16.
TE D
H10-C4- H12, H11-C4-H12,H11-C4- H10.
AC C
C2-C4- H11, C2-C4- H10, C2-C4- H12.
ACCEPTED MANUSCRIPT 39
βi
N-C-C(2)
N1-C2-C3.
40
βi
N-C-H
N1-C2-H13.
41
ωi
C-O
O10-C3-O5-C2
42
ωi
O-Cd
O5-Cd7-Cl8-Cl6. Torsion
RI PT
Out-of-Plane bending (wagging)
C3-C2-N1-H15, C3-C2-N1-H15, H13-C2-N1-H16,
τi
tN-H (amino)
H13-C2-N1-H15, H13-C2-N1-H14,H13-C2-N1-H16,
SC
43-51
C4-C2-N1-H15, C4-C2-N1-H14, C4-C2-N1-H16.
tC-H (methyl1)
61-62
τi
tCd-O
63-64
τi
tC-O
65-70
τi
tC-C
M AN U
τi
C3-O5-Cd7-Cl6,C3-O5-Cd7-Cl8.
C2-C3-O5-Cd7, O9-C3-O5-Cd7.
AC C
EP
TE D
52-60
C3-C2-C4-H11, C3-C2-C4-H10, C3-C2-C4-H12, H13-C2-C4-H11, H13-C2-C4-H10, H13-C2-C4H12, N1-C2-C4-H11, N1-C2-C4-H10, N1-C2C4-H12
N1-C2-C3-O9, N1-C2-C3-O5, H13-C2-C3-O9, H13C2-C3-O5, C4-C2-C3-O9, C4-C2-C3-O.
ACCEPTED MANUSCRIPT Table 4.Detailed assignment of fundamental vibrations LACC by NCA based on SQM force field calculations. Calculated wavenumbers
Observed wavenumbers
(cm-1)
(cm-1) FTIR
Characterization of normal modes with PED ( ≥10%)
Raman
3396
3232m
3240w
61.68
3217
3146w
3154w
84.19
3052
3044s
3046w
5.23
6.71 CH3ops(98)
3026
-
-
18.99
8.52 CH3ips(90)
2993
2998w
3004m
3.35
2937
2948s
2937vs
26.72
2872w
845.75
NH3ops(52),NH3ip(34),NH3ss(14)
SC
12.24 NH3ss(64),NH3ips(31)
22.46 CHstr(95)
M AN U
2867
13.65
RI PT
Scaled
IR Raman Intensity Intensity
1616s
-
81.75
1600
1584vs
1590m
28.6
1550
1566vs
1485
67.60 NH3ops(43),NH3ss(41),NH3ips(16) 3.01 NH3opb(60),NH3ipb(35)
14.18 NH3opb(50), NH3ipb(24), COO-astr (16)
-
277.24
16.28 COO-astr (65), NH3sd(15)
1495vs
1502w
424.92
2.92 NH3sd(70), COO-astr (14)
1466
1453s
1453m
10.43
7.03 CH3ipb(72 ), CH3opb(14)
1453
1412s
1396
1372m
EP
TE D
1652
36.55 CH3ss(93)
1308 1262
6.99
1371w
46.39
1340s
1341m
7.26
1300m
1300w
20.84
4.84 CHCsci(25),CHCrck (22), CCstr(21)
130.80
12.52 COO-str ( 47), CHCsci(17), OCOb(12) 12.38 NH3ipr (24), CH3opr (19),CHCtw(12)
AC C
1338
1411m
1210m 1214vw
1196
-
-
45.32
1101
1109m
1108m
73.26
1072
1001m
1003w
38.80
19.1 CH3opb(74), CH3ipb (27) 1.89 CH3sd(90) 2.51 CHCwag(48),CHCtwt (30)
4.81 NH3opr (36), CHCsci(31) 10.12 CH3ipr (37), CCstr (18), CNstr (14)
ACCEPTED MANUSCRIPT 970w
971m
1.65
961
925w
922w
11.99
16.11 NH3ipr (41), CCstr (33),CH3ipr (10)
834
838m
843s
14.69
11.34 CCstr (59), CNstr (26)
767
761m
763w
18.24
34.05 gC=O (19),CCstr (16), CNstr (14)
-
19.56
7.27 gC=O (50),COCb (12), CHCrck(10)
540m
538w
18.27
9.74
502
-
-
4.37
26.99 COOrck (40),CCstr(19),CHCtw(11)
393
-
416w
8.68
20.02 τNH3(40),CCHsci(23)
-
9.44
17.87 COCb(25), gC=O (17), τNH3(15)
-
60.01
297w
79.97
80.54 CdCl str(29), COCb(21), CCHsci(15)
248s
16.38
81.39 Cd..O str(22), CCHsci(18), CdCl str(15)
351 346
-
315 299
-
11.25 -
214
-
185 106
-
79 62 53 25
-
0.63
177m
39.68
-
6.85 Cd..O str(39), CdCl str(20), COCb(10)
40.9 CdCl str(56), tCH3(10)
47.49 tCdC (20), COO-rck(16),CHCtw(10) 5.06 τCH3 (60) 4.38 τCO (29), CdClb(11)
96s
3.02
58.66 COCb (60), CdOb(30)
-
6.61
22.63 τCO (53), COCb(29)
72m
18.61
AC C
92
29.39
EP
228
TE D
247
OCOb(29), COCb (13), gC=O (13), CCstr (12)
SC
558
M AN U
722
3.84 CH3opr (27), NH3opr (20),CHCtw(12)
RI PT
978
63.26 τCO (50), COCb(21),gOCd(19)
8.23
43.30 tCdC(56),COCb (26)
-
-
4.19
50.58 CdClb(40), CdOb(44)
-
-
2.94
100 tCdC(76), COCb(18)
vs- very strong, m- medium, s- strong, w- weak, vw- very weak, str-stretching, ss-symmetric stretching, ips-in plane stretching, ops-outplane starching,sd-symmetric deformation,ipb-inpane bending, opb-out of plane bending, b- bending, rck-rocking, sci-scissoring, tw-twisting, wag-wagging, t- torsion, g- gauche
ACCEPTED MANUSCRIPT ► Synthesis and characterization of organometalic compound LACC. ► Kurtz-Perry powder techniques confirms the nonlinear property of the crystal. ► Topological approach opens new ways for better undrestanding of the structure and bonding properties of the compound.
AC C
EP
TE D
M AN U
SC
RI PT
► Spectral data showed the binding mode of carboxylate ion in a monodentate fashion.
ACCEPTED MANUSCRIPT Table S1: Different types of electronic basins, ELF value at attractor (ELF), basins population (N), standard deviation (σ2) and relative fluctuation (λ) of LACC ELF
N
σ2
λ
total
C( N )
1.00
2.10
0.30
0.14
1
C( Ci )
1.00
2.08
0.26
0.12
3
C( Oi )
1.00
2.12
0.33
0.15
V(Hi,Cj)
1.00
2.01
0.69
0.34
V(H13,C2)
1.00
2.10
0.69
0.32
V(H14,N1)
1.00
2.01
0.78
0.38
V(H15,N1)
1.00
2.06
0.83
0.40
V(H16,N1)
1.00
2.12
0.89
V(C2,N1)
0.908
1.56
0.93
V(C2,C3)
0.939
2.29
1.15
0.50
1
V(C2,C4)
0.948
1.94
1.03
0.53
1
V(C3,O9)
0.855
1.45
0.94
0.64
1
V(C3,O5)
0.914
2.06
1.26
0.61
1
V(C16,C17)
0.971
2.37
1.09
0.45
1
V(O9´)
0.904
3.03
1.32
0.43
2
V(Cl8) V(Cl6)
AC C
EP
V(Cd7)
2
3
1
1
SC
1
0.41
1
0.59
1
M AN U
TE D
V(O5)
RI PT
BASINS
0.917
2.86
1.24
0.43
2
0.903
3.95
1.37
0.34
2
0.900
3.93
1.38
0.35
2
0.412
2.55
1.80
0.70
4
ACCEPTED MANUSCRIPT Table S2. The first hyperpolarizability (esu) components of LACC
HF/LANL2DZ
βxxx
167.885
βxyy
-20.128
βxzz
-29.952
βyyy
-11.292
βyzz
11.024
βyxx
38.482
M AN U
SC
RI PT
Parameter
βzzz
9.223
βzxx
-1.337
βzyy
7.422
βxyz
AC C
EP
TE D
-14.979
ACCEPTED MANUSCRIPT Table S3. Calculated electronic absorption spectrum of LACC molecule.
CI expansion coefficient
Wavelength(nm)
Calc.
0.30691
35 → 39
-0.16817
36 → 38
-0.35331
36 → 39
0.17956
37→ 38
0.40425
37 → 39
-0.20543
M AN U
35 → 38
0.008
228.63
0.0034
-0.32907 0.18266
EP
32 → 39
240.93
TE D
excited state 2
32 → 38
Expt.
SC
excited state 1
Oscillator Strength(f)
RI PT
Excitation
0.47997
34 → 39
-0.16075
AC C
34→ 38
36→ 38
0.16181
37 → 38
0.23018
excited state 3
34 → 38
-0.16115
35 → 38
-0.40077
36 → 38
0.21546
37 → 38
0.46416
37 → 39
0.14841
217.10
208
0.0337