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Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations
Author’s Accepted Manuscript Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations H. Kchaou, K. Karoui, A. Bulou, A. Ben Rhaiem www.elsevier.com/locate/physe
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S1386-9477(16)30586-0 http://dx.doi.org/10.1016/j.physe.2016.11.019 PHYSE12658
To appear in: Physica E: Low-dimensional Systems and Nanostructures Received date: 8 June 2016 Revised date: 7 November 2016 Accepted date: 11 November 2016 Cite this article as: H. Kchaou, K. Karoui, A. Bulou and A. Ben Rhaiem, Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations, Physica E: Low-dimensional Systems and Nanostructures, http://dx.doi.org/10.1016/j.physe.2016.11.019 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 galley proof before it is published in its final citable 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.
Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations. H. Kchaou1, K. Karoui1, A. Bulou2, A. Ben Rhaiem1,* 1
University of Sfax, Faculty of Sciences, Laboratory of Condensed Matter, BP1171, 3018 Sfax, Tunisia
2
LUNAM Université, Université du Maine, CNRS UMR 6283, Institut des Molécules et Matériaux du Mans(IMMM), Avenue Olivier Messiaen, F-72085, Le Mans Cedex 09, France
*
Author to whom correspondence should be addressed. Tel: +21698667650 [email protected]
Abstract [N(CH3)3H]CdCl3 between 295 and 433 K possesses four phases. Three phase transition at T1 = 416 K, T2 = 373 K and T3 = 330 K (on heating) and T1 = 410 K, T2 = 386 K and T3 = 322 K (on cooling) was determined by differential scanning calorimetry. Thermal hysteresis of these transitions ∆T1 = 6 K, ∆T2= 13 K and ∆T3 = 8 K, indicating a first order character. The X-ray diffraction study at room temperature revealed an orthorhombic system with Pbnm space group. The vibrational characteristics have been measured at room temperature by infrared spectroscopy (400–3800 cm-1) and by polarized Raman spectroscopy (10–3800 cm-1) on microcrystals orientated with respect to the organic and inorganic sublattice. The structure of this compound was optimized by density functional theory (DFT) using B3LYP with LanL2DZ and LanL2MB basis sets. The temperature dependence of the Raman line shifts ν and the half-width ∆ν detect the phase transitions (T1, T2 and T3). Keywords: differential scanning calorimetry, Raman spectroscopy, Density functional theory 1. Introduction Crystals with general formula AMeCl3.H2O and AMeCl3 (A = N(CH3)3H, N(CH3)4, N(CH3)H2; Me: metal = Co, Cu, Zn, Cd…) have a large set of different structures, properties and applications [1-5]. Most of these materials undergo multiple structural phase transitions often related to the reorientational dynamics of the substituted ammonium group; several interesting properties characterize these compounds such as the ferroelectricity, ferroelasticity and low dimensional magnetism. These properties are related to the structural phase transition which characterizes this family, such as the possibilities of application of these crystals
as a temperature and humidity sensors [6-7]. The vibrational spectroscopy applied to organic-inorganic materials is one of the most broadly applied techniques for the identification and characterization of molecules and the control of 1
the reaction, as well as for the determination of molecular structures [8-10]. Infrared and Raman spectroscopy frequently offer additional information about molecular vibrations. The calculation of vibrational frequencies by density functional theory (DFT) is developing rapidly as a cost-effective general procedure [11]. Its advantage is to determine reasonable vibrational frequencies and geometries much superior to the conventional methods [12]. However, it is agreed that the frequency of vibration, obtained by DFT, are usually smaller or larger than their experimental equivalents for organic and inorganic components. Thus, empirical scaling factors are always used to improve and describe the experimental and vibrational frequencies [13-14]. The scale factors depend not only on the method but also on the basic sets selected from the DFT. They are deducted from the average difference between the experimental and calculated frequencies [15]. In this context, we have successfully synthesized the [N(CH3)3H]CdCl3 hybrid compound. The structure of this hybrid compound at room temperature was previously determined by Walther [16]. It crystallizes in the orthorhombic system with Pbnm space group and unit cell parameters: a= 8.957 (2) Å, b= 14.34 (4) Å and c = 6.6873 (9) Å. The phase formed above 342 K is hexagonal (HHT1) with space group P63/m. In the range of [342K; 374K], the lattice parameters: ah1= 26.049 (5) Å and Ch1= 6.756 (1) Å become stable in the temperature range from 374 to 415 K with (HHT2): ah2=15.06 (2) Å and ch2= 6.74 (2) Å; Z = 6 [17]. [N(CH3)3H]CdCl3 consists of two entities: trimethylammonium [N(CH3)3H]+ and [CdCl6]tetrahedron. The atomic arrangement can be described by an alternation of the organic and inorganic entities. This compound is characterized by two simple hydrogen bonds N–H---Cl linking the organic [N(CH3)3H]+ cation to the [CdCl6]-. The purpose of this document is to report on the temperature behavior of [N(CH3)3H]CdCl3 justified by differential scanning calorimetry and Raman scattering. The experimental data are analyzed from the vibrational characteristics that are compared with the calculated results by using DFT (B3LYP) with LanL2DZ and LanL2MB basis sets that are explained by the geometric and normal vibration modes of the organic and inorganic compound. 2. Experimental 2.1. Synthesis Colorless single crystals of [N(CH3)3H]CdCl3 with prismatic shape were grown at room temperature by slow evaporation of aqueous solution of hydrochloric acid (1M) containing an [N(CH3)3H]Cl and (CdCl2) in a molar ratio 2:1. The reaction scheme is the following:
2
[N(CH3)3H]Cl + CdCl2
[N(CH3)3H]CdCl3
2.2. Characterization The structure of obtained powder was determined by X-ray powder diffraction on an Empyrean Cu LFF HR diffractometer with Cu Kα radiation (45 kV, 30 mA), at room temperature. Data of the Rietveld refinement were collected in the 2θ range 8– 65°. The refinement was performed with the FullProf computer program [18] which adopts the Rietveld calculation method. The differential scanning calorimetry measurements were performed on a DSC (Q-100) calorimeter. The powder sample (about 7.3 mg) was placed within capsules in thermal recording conditions, whose heating and cooling speed was 10°C/min and in the temperature range from 300 to 455 K. The infrared spectrum of the [N(CH3)3H]CdCl3 sample was measured at room temperature with a Perkin-Elmer FT-IR 1000 spectrometer using KBr pellet technique in the wavenumber range between 400 and 3800cm-1. Temperature dependent Raman spectra were measured by a T64000 Horiba-Jobin-Yvon spectrometer equipped with nitrogen cooled CCD detector. The wavelength radiation for excitation was 514.5 nm using an Ar/Kr laser. The laser power in the samples was limited to 60 mW. All measurements were conducted under microscope using X50 LF objective in backscattering geometry on transparent single crystal employing the parallel polarization. The spectra were collected with 600 tr/mm grating, from 10 to 3800 cm-1 for different temperatures (under Linkam stages for the high and low temperatures). The wavenumbers and widths of the Raman lines were determined by fitting, using the LabSpec5 software with a combined Lorentzian–Gaussian band shape. 3. Results and discussion 3.1. X-ray diffraction study The X-ray diffraction studies at room temperature showed that synthesized powder is single phase [N(CH3)3H]CdCl3.The graphic result of Rietveld structural refinement as the best fit between calculated and observed X-ray diffraction pattern is shown in Fig. 1. The Rietveld method was applied for refining structural parameters (atomic displacement parameters, occupation factors and lattice parameters) using the software Full-PROF [18] directly from complete powder diffraction patterns. XRD refinement was continuous until convergence was reached with a goodness factor close to 1. We found that the sample crystallizes in the orthorhombic structure with Pbnm space group. The refined lattice 3
parameters are a = 8.980 Å, b = 14.486 Å, c = 6.704 Å and V = 872.289 Å3; Z= 4, which are in good agreement with the published results [16]. The value of the discrepancy factor (Rwp= 8.35%) and expected value (Rexp= 6.53%) with the goodness of fit index (2 = 1.68). The asymmetric unit of the synthesized compound is made up of an [N(CH3)3H]CdCl3 compound as shown in Fig. 2. A projection along the b-axis of the structure presents an arrangement of layers, [CdC16] - anions and layers [N(CH3)3H]+ cations Fig. 3. Indeed, the organic layers, observed at z/a= ¼ and at z/a=3/4, are formed by the organic cations [N(CH3)3H]+ direct their groups (NH2) outside of the organic layer to establish weak hydrogen bonds of N-H...Cl. The inorganic layer, observed at z/a=0 and at z/a=1/2, is formed by infinite chains of face sharing [CdC16] octahedral. The trimethylammonium ion has a parallel chain structure. The organic group is formed by three carbon atoms and only one nitrogen atom, the C–N bond length values are 1.464 (2) Ǻ and 1.475 (8) Ǻ. The C-N-C angles are in the range between 111.9 (7)° and 112.71(8)°. The Bond length and angles values are in good agreement with the bond lengths of other similar compounds [19, 20]. The [CdC16] consists of two face-sharing CdCl3 octahedra. The Cd−Cl distances vary from 2.350 (1) to 2.671(7) Å. The Cl-Cd-Cl angles are in the range 77.8 (2)179.9 (1)°. Accordingly, bond lengths and angles within the organic cations are normally compared to similar compounds [19-21]. 3.2. Thermal properties DSC is a reliable thermodynamic technique to detect the reversible phase transition nature of a compound with respect to temperature change. In this respect, the sample of [N(CH3)3H]CdC13 was subjected to DSC measurements in an aluminum container under nitrogen conditions. Fig. 4 reveals the presence of three reversible phase transitions at 410/ 416K, 386/373 K and 322/330 K, respectively, on cooling and heating, respectively. The large thermal hysteresis of ∆T1 = 6 K, ∆T2= 13 K and ∆T3 = 8 K, respectively, show that these transitions can be classified as a first order type [22]. Moreover, an entropy change ∆S1= 0.12J.mol-1.K-1, ∆S2= 1.46 J.mol-1.K-1 and ∆S3 = 0.52 J.mol-1.K-1 [23]. The entropies ∆S1 and ∆S3 are too low which indicates the mechanism displacive are involved in the phase transitions T1 and T3, by against, the entropy corresponding to T2 does not indicate the pure “order disorder” mechanism of this transition; such results suggest that both order–disorder and displacive mechanism are involved in the phase transition [23]. 3.3. Raman and Infrared spectra at room temperature
4
The Infrared and Raman spectra of [N(CH3)3H] CdCl3 recorded at room temperature between 400 and 3800 cm-1 and 10 to 3800 cm-1 , respectively, are shown in Figs. 5 and 6. The tentative assignment is done on the basis of the characteristic vibrations of the cation [N(CH3)3H]+ and the anionic part [CdCl3]- as deduced from literature [24, 25] and ab initio calculations. All the bands assignments are summarized in Table 1. 3.4. Ab initio calculation results and assignments of the Infrared and Raman spectra The optimized geometry and vibrational frequencies calculations of [N(CH3)3H]CdC13 compound were determined at the density functional theory (DFT) [26] level using the Lee– Yang–Parr correlation functional B3LYP [27] with LanL2DZ [28] and LanL2MB [29] basis sets implemented within Gaussian 09 program [30]. 3.4.1. Geometry optimization The calculated geometrical parameters such as bond lengths and bond angles were compared with available experimental data. These parameters, calculated for our compound in B3LYP method with LanL2DZ and LanL2MB basis sets, are listed in Table 2. Whatever the basis, the calculated bond lengths are slightly bigger than the experimental values due to fact that the theoretical calculations belong to the molecule in the gaseous phase and the experimental results belong to the molecule in solid state. In the inorganic part [CdCl3]-, it appears that the LanL2MB basis set gives the best agreements with the experimental angles and bond lengths compared to LanL2DZ.
By
contrast, for the organic [N(CH3)3H]+ entity, the best agreement between the optimized geometries and experimental values is observed with B3LYP/ LanL2DZ. 3.4.2. Vibrational spectra The experimental IR spectra of [N(CH3)3H]CdC13 is given in Fig. 5 , and the experimental Raman spectrum with the calculated are represented in Fig. 6. The calculated frequencies of this molecule are performed by using ab initio DFT (B3LYP) with the LanL2DZ and LanL2MB basis set. Furthermore, their calculated and experimental IR and Raman data together with their tentative assignments are quoted in Table 1. a. Vibrations of [CdCl3]- anion The [CdCl3] - (D3h symmetry) [31] has 6 normal modes of vibration because, in general, the number of vibrational modes must be equal to 3N-6. Based on the group theory calculation, these vibrational modes have the same symmetry properties as the A1+2E+ A2 irreducible representation of the D3h point group (Γvib =A1+2E+ A2). The 2E representation indicates 5
that the Raman and infrared active. By contrast, The A1 is Raman active and the A2 representation is only infrared active [10]. The correlation of the internal vibrational modes of MX3 in the D3h point symmetry groups is recalled in Table 3 [10]. Hence, it appears that the ν1 and ν2 are expected to give one Ag and three Bg modes (B1g, B2g, B3g) in the crystal, and for ν3 and ν4 with D3h symmetry each giving tow Ag and six Bg modes (2B1g, 2B2g, 2B3g). It is worthwhile to note that for all modes, the Bg are expected with much weaker intensity than the Ag ones. All the bands in the range of 10-350 cm-1 observed in the Raman spectrum of [N(CH3)3H]CdC13 single crystal Fig. 6 (a), show that they are related to the internal [CdCl3]and modes for both externals (organic and inorganic). It is reported that the distinction between these modes is not easy [32]. The Raman activities (Si) calculated with the GAUSSIAN 09program were subsequently converted into relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [33-35].
I i f ( 0 - i ) 4
1 hc i 1 exp( kT )
Si
1
i
(1)
where ν0 is the existing frequency in cm−1, νi the vibrational wave number of the ith normal mode, h, c and k are the fundamental constants and f is a suitably chosen common normalization factor for all the peak intensities. The calculated intensities (Ii) and the ab initio calculation (Si) using (B3LYP) with the LanL2DZ and LanL2MB basis set are reported in Table 4. The strong band observed in Raman spectrum Fig. 6 (a), at 249 cm-1 is assigned to the Cd-Cl symmetric stretching (ν1(Cd-Cl)) which is predicted theoretically at 265.5 cm-1 (LanL2DZ) and 268.6 cm-1 LanL2MB). The asymmetric stretching (ν3 (Cd-Cl)) vibration appears as bands 170.5/265 cm-1. The weak bands located in Raman spectrum at 78.1/122 cm-1 are attributed to scissoring vibration out of the plan ν4. The activation of this mode in Raman spectrum confirms the symmetry of the sciss (CdCl2). b. Vibrations of [N(CH3)3H]+ cations The different modes that appear in the experimental spectrum of [N(CH3)3H]+ entity are awarded on the basis of the calculated frequencies and intensities (Ii) and (Si), using (B3LYP/ LanL2DZ) and (B3LYP/ LanL2MB)
Table 4. The infrared and Raman spectra of the 6
compound are shown in Figs. 5 and 6 (b), respectively, and their bands assignments are summarized in Table 4. This attribution is performed from the whole calculations ab initio, using the molecular viewer Jmol.34 [36]. The bands observed in the IR and Raman spectra 458- 1256.4 cm-1 are associated with r (CH3) methyl rocking modes. All of the bands observed at 979.3 cm-1 and 814.8-1060 cm-1 are related to the vas (N-C) and vs (N-C), respectively. The symmetric and antisymmetric bending of methyl groups (CH3) are observed at 1240.6-1413.6- 1447 and 1473 cm-1, respectively. Besides, the band at 2784.4 cm-1 is assigned to the vs (N–H) stretching mode. Finally, stretching (symmetric and asymmetric) modes of the CH3vibrations are seen in the region of 2800–3100 cm-1. The observed bands at 2816, 2939, 3025 and 3076.1 cm-1 are related to vs (CH3). In the IR spectrum, only the modes at 2814.9, 2927.3, 3020.2 and 3068.6 cm-1 are clearly seen. The bands that appear at 2888, 2958, 2972 and 3036.1 cm-1 are assigned to the vas (CH3). By contrast, the infrared observes only 2962.7 and 3031 cm-1. c. Overview of the results Figs.7 and 8 show plots of the calculated versus experimental vibrational frequencies of [CdCl3]- and [N(CH3)3H]+. In both bases, the calculated values are slightly different from the experimental ones (dashed lines), but they are well described by a linear-fitting. For the inorganic anions [CdCl3]- Fig. 7, the calculated scaling factors are 0.92 for (B3LYP/ LanL2DZ) and 0.84 for (B3LYP/ LanL2MB) basis. Concerning [N(CH3)3H]+ Fig. 8, we note that R (LanL2DZ) is better than R (LanL2MB). The scaling factors of all bases Table 5 are used to minimize the root-mean-square deviation δrms calculated from the Eq.2. They also determine the variation between the calculated and the observed vibrational frequencies: n
rms
( i 1
iexp
ical ) 2
(2)
n
Where n is the number of the experimental and calculated data. The calculated rms deviation (δrms) for [CdCl3]- and [N(CH3)3H]+ in the [N(CH3)3H]CdC13 crystal and different bases are summarized in Table 5. It is observed that the frequencies calculated by (B3LYP/ LanL2MB) are closer to the experimental frequencies than those calculated using (B3LYP/ LanL2DZ), and that this basis leads to the weaker value of (δ rms), which is therefore used for the attribution modes of 7
[CdCl3]- entity in the [N(CH3)3H]CdC13 crystal. For the cation [N(CH3)3H]+, The lowest value of this deviation is obtained by the B3LYP method with LanL2DZ basis. 3.5. Temperature evolution of the Raman spectra Figs. 9(a) - 9(d) show the temperature dependent Raman spectra of the [N(CH3)3H]CdC13 in the 295-433K temperature range. However, several bands exhibit a significant change in the position of the band, half-width and intensity in the vicinity of the phase transition detected by DSC. That conduct may be related to changes in the interactions between the organic and inorganic parts increasing with temperature, which can be attributed to the increase of the dynamic movement of the alkyl chains and / or the degree of anions distortion [37]. The position, intensity and the half-width of the Raman lines were refined using a combination of Gaussian and Lorentzian functions. Figs. 10(a) - 10(d) show an example of deconvolution of the Raman spectrum at 295 K. The positions and width at half maximum for selected lines, obtained between 10 and 3100 cm-1, are shown in Figs. 11 and 12 (a-c). In phase 1, most of the modes have normal temperature dependence except for the modes ν4= 78.1 cm-1, ν1= 249 cm-1 for the inorganic part [CdCl3]-, stretching mode at 814.8 cm-1 (vs (N–C)), 2958 cm-1 (vas (CH3)), 2972 cm-1 (vas (CH3)) and 3036.1 cm-1 (vas (CH3)), asymmetric bending mode at 1447 cm-1 and r (CH3) methyl rocking modes at 1256 cm-1 for the cation [N(CH3)3H]+. The change of positions of the peaks at 249 cm-1 and 814.8 cm-1 is assigned to ν1 and (vs (N–C)), respectively. In this transition, the half-width variations Fig. 12 of all the analyzed bands are noted. Figs. 11 and 12 (a-c) show a continuous spectral evolution at temperature superior T1. This transition is of the reconstructive type and it is associated with a change of the stoichiometry of the material [17]. Many of the new modes have normal temperature dependence in the hexagonal (HHT2) phase like 122, 170.5 and 979.3 cm-1assigned to ν4 [sciss(CdCl2) and external mode], ν3 [vas (Cd–Cl)] and vas (N–C), respectively. Figs. 11 and 12 show the positions and half-widths variation of all peaks at the level of T1. In the hexagonal (HHT1) phase, new modes have temperature dependence at 1060, 2784.4, 2816 and 2888 cm-1 assigned to vs (N–C), vs (N–H), vs (CH3) and vas (CH3), respectively. The slight variations of the positions of the peaks at 78.1, 122, 170.5, 249, 1473 and 2972 cm-1 related to ν4, ν4, ν3, ν1, δas (CH3) and vas (CH3), respectively.
The peak at 1256.4 cm-1assigned to r (CH3) is broken up into two peaks: r (CH3) and δs (CH3). 8
The mode δs (CH3) is split up into two peaks at 1413.6 and 1447 cm-1.
The peak at 2958 cm-1assigned to vas (CH3) is split up into two peaks: vs (CH3) and vas (CH3).
The peak at 3036.1 cm-1assigned to vas (CH3) is broken up into two peaks: vs (CH3) and vas (CH3).
Eventually, two new modes which appear only in the orthorhombic phase like 458 and 3076.1 cm-1 assigned to r (CH3) and vs (CH3). The Slight variations in the position of all modes, the variations of the half-widths of almost all of the peaks increase with temperature. Most of the modes of (HHT1) and (HHT2) phases are also present in the orthorhombic phase after transition. This could be due to the fact that hexagonal to orthorhombic transition involves some minor changes in the local structure. The mechanisms of the phase transitions found in this hybrid compound can be accounted for in two different ways [38-40]. The first mechanism related to order-disorder processes attributed to the reorientation of organic cations. The other one, the displacive mechanism, is associated with the continuous variation of orientation of the inorganic part [CdCl3] and / or N(CH3), and / or H. Based on the above mentioned discussion, the Raman spectra, upon heating of the [N(CH3)3H]CdCl3 single crystals, can be attributed to the phase transitions T1, T2 and T3, since the Raman spectroscopy is very sensitive to the local lattice dynamics and the structural transitions. Therefore, the anomalies of wavenumber and half-widths are effective tools to reveal the phase transitions. From these results, the mechanisms of phase transition at T2 can be specified in two possible ways. The first one would be related to a ‘‘displacive’’ type process due to the continuous displacement of the organic part. The other mechanism order–disorder type is related to the reorientation of the organic cations. This outcome is backed by the results of DSC in view of the weak entropy associated with this phase transition. To support the fact that the phase transition is correlated with changes of the [N(CH3)3H]+ groups, we monitored the analysis of the full width at half maximum (FWHM) , which is based on the theory used for the damping combined with an order–disorder mechanism. the width of a band is usually de fined as [41]:
FWHM (T ) (a bT ) c exp (-
Ea ) KT
9
(3)
Where Ea is the activation energy for the mode connected to the order-disorder transition, K is the Boltzmann constant and T is the temperature. The constant a accounts for the broadening arising from factors other than the phonon decay, such as structural and compositional defects. The second and third term of Eq (3) represents the influence of anharmonicity and thermally activated reorientational processes, respectively. Eq (3)
enables us to determine the activation energy of reorientational processes for
[N(CH3)3H]+ cation in the studied compound using temperature dependence of the FWHM for the bands s (CH3) and as (CH3) situated at 3025 cm−1 3036.1 cm−1, respectively. These contribute to the phase transition at 372 K Fig. 13. The obtained activations energy values for s (CH3) and as (C-H) are Ea(I) = 0.962 eV, Ea(I) = 1.034 eV for T T2 , respectively. While the activations energies for these bands for T T2 are Ea(II) = 0.915 eV, Ea(II) = 0.982 eV, respectively. The decrease of the activation energy values for this band can be explained by the increase of the disorder in the crystal due to increased of the dynamics of cations. These behaviors suggest that the transition T2 is related to the reorientation motion of the cationic part. 4. Conclusions In this work, the [N(CH3)3H]CdCl3, using a solution-based chemical method at room temperature, has been synthesized and found to belong to the orthorhombic system (space group Pbnm). The atomic arrangement of the hybrid compound can be described by the alternation of organic-inorganic layers. Moreover, the material cohesion of the compound is assured by hydrogen bonds (N-H---Cl) established between anions and cations. According to DSC investigations, the title compound exhibits three solid-solid reversible phase transitions, first order, at T1 = 416/410 K, T2 = 373/386 K and T3 = 373/386 K on heating and cooling, respectively. The Infrared, Raman spectroscopy and theoretical calculation using Density Functional Theory methods with LanL2DZ and LanL2MB basis sets are used to study the [N(CH3)3H]CdCl3 synthesized compound. They are also used to calculate the geometric parameters and the vibrational frequencies of the [CdCl3]- anion and [N(CH3)3H]+cation in the ground state. In this respect, the inorganic and organic entities and the calculation of the root mean square difference δrms between the observed and calculated frequencies allow to give the scaling factors and to deduce that the best agreements are obtained by B3LYP/ LanL2DZ for [N(CH3)3H]+ and B3LYP/ LanL2MB for [CdCl3]-. The detailed analysis of frequencies is 10
consistent with a dynamics reorientation of the trimethylammonium cations at the phase transition at T2.
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[15] P. Sinha, S. E. Boesch, C. Gu, R. A. Wheeler, A. K. Wilson, J. PhysChem A. 108 (2004), pp: 9213-9217. [16] U. Walther, D. Brinkmann, G. Chapuis,H. Arend, Solid State Communi, 27 (1978), pp: 901-905. [17] By. Gervais. Chapuis, F. Javier .Zuniga, ActaCryst. B, 36 (1980), pp: 807-812. [18] C. Opagistea, M.J. Jacksona, R.-M. Galéraa, E. Lhotela, C. Paulsena, B. Ouladdiaf, Journal of Magnetism and Magnetic Materials, 340 (2013), pp: 46-49. [19] N. Weslati, I.Chaabane, A.Bulou, F.Hlel, PhysicaB, 441 (2014), pp: 42–46. [20] A. Jarboui, A. Ousleti, K. Adil, K. Guidara and F.Hlel, Ionics, 17 (2011), pp: 145–155. [21] Josefina Pons, Jordi García-Antón, Mercè Font-Bardia, Teresa Calvet, Josep Ros, Inorganica Chimica Acta, 362 (2009), pp: 2698–2703. [22] Chen-Yu Mao, Wei-Qiang Liao, Zhong-Xia Wang, Peng-Fei Li, Xing-Hui Lv, HengYun Ye and Yi Zhang, Royal Society of chemistry, 45 (2016), pp: 5229-5233. [23] L. E. House Jr and C. David Dunbar, Thermochimica. Acta, 204 (1992), pp: 213-219. [24] Y. Mlik , A. Daoud, and M. Couzi, phys. stat. sol. (a), 52 (1979), pp: 175-188. [25] Y. Mlik, and M. Couzi, Solid State Phys, 15 (1982), pp: 6891-6906. . [26] A. Tamulis, V.I. Tsifrinovich, S. Tretiak, G.P. Berman, D.L. Allara, Chemical Physics Letters, 436 (2007), pp: 144-149. [27] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B, 37 (1988), pp: 785–789. [28] P.J. Hay, W.R. Wadt, J. Chem. Phys, 82 (1985), pp: 270–283. [29] H.B. Schlegel, M. Frisch, Int. J. Quantum. Chem, 54 (1995), pp: 83–87. [30] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
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G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian Inc., Wallingford, CT, 2009. [31] J. E. D. Davies and D. A. Long, J. Chem. SOC. (A), (1968), pp: 2054-2058. [32] B. Bednarska-Bolek, J. Zaleski, G. Bator and R. Jakubas, J. Phys.Chem.Solids, 61 (2000), pp: 1249-1261. [33] P. L. Polavarapu, J. Phys. Chem, 94(1990), pp: 8106-8112. [34] S. D. Williams, T. J. Johnson, T. P. Gibbons, C. L. Kitchens, TheorChem Accounts, 117 (2007), pp: 283-290. [35] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta A, 49 (1993), pp: 2007–2026. [36] Jmol program. http://www.jmol.org/ [37] J. Tarasiewicz, R. Jakubas, J. Baran, J. Mol. Struc. 614 (2002), pp: 333-338. [38] P. Szklarza, R. Jakubas, G. Bator, T. Lis, V. Kinzhybalo, J. Baran, J. Phys. and Chem. of Solid. 68(2007), pp: 2303-2316. [39] R. Jakubas, G. Bator, Z. Ciunik, Phys. Rev. B. 64 (2003), pp:1-6. [40] W. Mzdycki, K. Uolderna-Natkaniec, J. Swiergiel, R. Jakubas, Solid Stat NMR. 24 (2003), pp: 209-217. [41] C. Carabatos-Nedelec, P. Becker, J. Raman Spectrosc. 28 (1997), pp: 663-671.
13
Fig. 1. X-Ray diffraction patterns at room temperature of [N(CH3)3H]CdCl3 sample. The circles are the observed profile; the solid line is the calculated one. Tick marks below the profile indicate the position of allowed Bragg reflections.
Fig. 2. Asymmetric unit for the title compound
14
Fig. 3. Projection of part of the unit cell content of [N(CH3)3H]CdCl3 along the b-axis.
H bonds linking the [CdCl6] octahedra and (CH3)3NH+ ions are represented by dotted lines.
Fig. 4. Differential scanning calorimetric of [N(CH3)3H]CdCl3 compound. 15
Fig. 5. Infrared spectrum of [N(CH3)3H] CdCl3 at room temperature.
16
Fig. 6. Blue- experimental Raman spectrum, red- Calculated Raman spectrum of [N(CH3)3H] CdCl3 compound by DFT/B3LYP with LanL2DZ basis set and green- Calculated Raman spectrum of [N(CH3)3H] CdCl3 compound by DFT/B3LYP with LanL2MB basis set.
Fig. 7. Correlation graphics between the calculated and experimental vibrational frequencies of [CdCl3] - entity.
17
Fig. 8. Correlation graphics between the calculated and experimental vibrational frequencies of [N(CH3)3H]+ entity.
18
Fig. 9. Temperature evolution of the Raman spectra in the 10-3100cm-1 frequency range.
19
Fig. 10. Deconvolution of the Raman spectrum at T = 295 K.
20
Fig. 11. Temperature dependence of the positions of the modes in the 10-3100cm-1 spectral range. 21
*
22
Fig. 12. Temperature dependence of the half-width of the modes in the 10-3100cm-1 spectral range.
Fig. 13. Variation of half-width of the s (CH3) and as (CH3) mode in function of temperature. The red lines represent the theoretical fit.
Table 1 Observed Raman and Infrared scattering wavenumber (cm-1) of [N(CH3)3H]CdCl3 using DFT method with tow basis sets.
Experimental
Calculated B3LYP
[N(CH3)3H] CdCl3
[N(CH3)3H]CdCl3
23
Raman
Infrared
LanL2DZ
LanL2MB
Assignment
78.1
---
85.4
87.5
ν4
122
---
112.2
134.1
ν4
170.5
---
163.3
184.3
ν3
265
---
327.2
328.1
ν3
249
---
265.5
268.7
ν1
458
---
457.6
410
r (CH3)
814.8
806.6
852.3
932.3
vs (N–C)
979.3
980.2
1045.6
1150.1
vas (N–C)
1060
1055.5
1057.2
1162
vs (N–C)
1240.6
---
1223.4
1266.4
δs (CH3)
1256.4
1255.8
1230.9
1276.4
r (CH3)
1413.6
1414.4
1417.3
1467.5
δs (CH3)
1447
1454.1
1611.6
1697.7
δs (CH3)
1473
1476.2
1664.4
1776.2
δas (CH3)
2784.4
2779.1
2962.1
3234.5
vs (N–H)
2816
2814.9
3117.9
3450.3
vs (CH3)
2888
---
3121.1
3452.2
vas (CH3)
2939
2927.3
3131.9
3455.6
vs (CH3)
2958
2962.7
3220.3
3629.5
vas (CH3)
2972
---
3222.5
3633.4
vas (CH3)
3025
3020.2
3231.1
3642.8
vs (CH3)
3036.1
3031
3238.1
3644.6
vas (CH3)
3076.1
3068.6
3238.2
3646
vs (CH3)
vs: Symmetric Stretching; vas: Asymmetric Stretching; δs: Symmetric Bending; δas: Asymmetric Bending; r: Rocking
Table 2 Calculated (B3LYP/LANL2DZ) and (B3LYP/LanL2MB) and experimental geometrical parameters (bond lengths and bond angles) of [N(CH3)3H]CdCl3 hybrid compound
Parameters
LanL2DZ
LanL2MB
24
X-ray
Cd-Cl
bond
lengths Cl-Cd-Cl bond angles N-H
bond
lengths N-C
bond
lengths C-H
bond
lengths N-C-H bond angles H-C-H
bond
angles C-N-C
bond
angles
2.417-2.561
2.486-2.610
2.627-2.671
100.944
100.374
84.332
1.060
1.097
0.909
1.514
1.538
1.421-1.468
1.092-1.094
1.103-1.106
0.958-0.960
108.896
107.967
109.394
108.896
110.172
109.210
112.050
111.807
112.718
Table 3 Correlation between the symmetries of the normal modes of free MX3 (D3h), those of free [CdCl3] - and those expected in [N(CH3)3H] CdCl3 (Pbnm) in view of the C1 symmetry of the site (C1) where the molecular ion sets.
CdCl3
Site (CdCl3)
Crystal
D3h
C1
D2h (Pbnm)
(ν1) A1
(ν2) A2
A
Ag B1g, B2g, B3g Au B1u, B2u, B3u
A
Ag B1g, B2g, B3g B1u, B2u, B3u Au
25
Ag B1g, B2g, B3g Au B1u, B2u, B3u Ag B1g, B2g, B3g Au B1u, B2u, B3u
A
(ν3, ν4) E
A
Table 4 Experimental frequencies (i) and intensities (Ii) of the IR/Raman lines associated with both organic/inorganic entities. Theoretical frequencies (vi) and intensities (Si) calculated using DFT method with tow basis sets for [N(CH3)3H]CdCl3 compound.
Calculated values
Experimental values
Calculated values
(LanL2DZ)
(LanL2MB ) i(cm-1) Ii IR/Raman ---/78.1
(%) 4.9 1
i(cm-
Si
1
)
IR/Raman
85.4
0/1.43
Ii
i(cm-1)
7
Assignment
IR/Raman
(%) 5.4
Si
87.5
0/1.67
ν4 [sciss(CdCl2 ) + external mode]
---/122
1.2 3
112.2
0/0.58
0.4 5
134.1
0/0.30
ν4 [sciss(CdCl2 ) + external mode]
---/170.5
---/265
---/249
0.4 7
1.2 3
2.7 0
163.3
0/0.43
327.2
0/3.43
265.5
0/5.46
0.2 8
1.2 1
5.2 2 26
184.3
0/0.32
328.1
0/3.37
268.7
0/10.76
ν3 [vas (CdCl)] ν3 [vas (Cd– Cl)]
ν1 [ vs (Cd–
Cl)] ---/458
806.6/814.8
0.6 7 1.4 9
457.6
0/3.02
852.3
4.83/14.97
0 1.2 3
0.8
1045.
5
6
1.0
1057.
3
2
0.3
1223.
0
4
1255.8/1256.
0.2
1230.
4
1
9
1414.4/1413.
0.5
1417.
6
0
3
0.1
1611.
9
6
1.4
1664.
5
4
2779.1/2784.
7.0
2962.
1268.36/404.2
5.0
4
4
1
1
1
2814.9/2816
0
28.86/4.94
0
980.2/979.3
1055.5/1060
---/1240.6
1454.1/1447
1476.2/1473
---/2888
2927.3/2939
2962.7/2958
---/2972
3020.2/3025
3031/3036.1 3068.6/3076.
3117. 9
1.2
3121.
8
1
4.0
3131.
5
9
0.2
3220.
1
3
0.3
3222.
4
5
1.2
3231.
8
1
0.8
3238.
9
1
1.2
3238.
54.91/11.09
51.97/13.53
0/4.76
0/3.46
2.63/9.61
0.27/4.32
8.65/34.60
0/80.64
14.43/256.47
5.60/14.54
0/22.64
23.20/85.86
13.94/60.21 6.16/83.69
0.6 8 0.8 6 0.1 1 0 0.5 4 0.2 0 0.2 3
0.8 0 0.8 2 0 0.6 4 0.1 8 0.6 6 0.6
27
410
0/0.21
932.3
0.22/13.81
1150.1
27.20/9.96
vas (N–C)
1162
24.53/12.78
vs (N–C)
1266.4
0/1.85
δs (CH3)
1276.4
1.23/0.38
r (CH3)
1467.5
6.53/11.3
δs (CH3)
1697.7
5.14/4.94
δs (CH3)
1776.2
0.10/38.38
δas (CH3)
3234.5
1727.48/335.9 6
r (CH3) vs (N–C)
vs (N–H)
3450.3
0.39/3.79
vs (CH3)
3452.2
0/61.04
vas (CH3)
3455.6
0.70/ 62.70
vs (CH3)
3629.5
1.80/1.61
vas (CH3)
3633.4
0/53.90
vas (CH3)
3642.8
5.47/15.34
vs (CH3)
3644.6
1.03/5.39
vas (CH3)
3646
11.72/55.65
vs (CH3)
1
4
2
6
sciss: scissoring
Table 5 Root-mean-square deviation ??rms (cm-1) and scaling factor (Sf) for [N(CH3)3H]+ and [CdCl3]- entities.
LanL2DZ
LanL2MB
Sf [CdCl3]-
0.92
0.89
Sf [N(CH3)3H]+
0.93
0.84
δrms [CdCl3]-
15.98
10.15
δrms [N(CH3)3H]+
59.10
89.95
Highlights
The Infrared, Raman spectroscopy and theoretical calculation using Density Functional Theory methods with LanL2DZ and LanL2MB basis sets are used to study the [N(CH3)3H]CdCl3 synthesized compound. The inorganic and organic entities and the calculation of the root mean square difference δrms between the observed and calculated frequencies allow to give the scaling factors and to deduce that the best agreements are obtained by B3LYP/ LanL2DZ for [N(CH3)3H]+ and B3LYP/ LanL2MB for [CdCl3]-. The detailed analysis of frequencies is consistent with a dynamics reorientation of the trimethylammonium cations at the phase transition at T2.
28
PII: DOI: Reference:
S1386-9477(16)30586-0 http://dx.doi.org/10.1016/j.physe.2016.11.019 PHYSE12658
To appear in: Physica E: Low-dimensional Systems and Nanostructures Received date: 8 June 2016 Revised date: 7 November 2016 Accepted date: 11 November 2016 Cite this article as: H. Kchaou, K. Karoui, A. Bulou and A. Ben Rhaiem, Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations, Physica E: Low-dimensional Systems and Nanostructures, http://dx.doi.org/10.1016/j.physe.2016.11.019 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 galley proof before it is published in its final citable 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.
Raman spectroscopy studies of temperature induced phase transitions in [N(CH3)3H]CdCl3 and DFT (B3LYP) calculations. H. Kchaou1, K. Karoui1, A. Bulou2, A. Ben Rhaiem1,* 1
University of Sfax, Faculty of Sciences, Laboratory of Condensed Matter, BP1171, 3018 Sfax, Tunisia
2
LUNAM Université, Université du Maine, CNRS UMR 6283, Institut des Molécules et Matériaux du Mans(IMMM), Avenue Olivier Messiaen, F-72085, Le Mans Cedex 09, France
*
Author to whom correspondence should be addressed. Tel: +21698667650 [email protected]
Abstract [N(CH3)3H]CdCl3 between 295 and 433 K possesses four phases. Three phase transition at T1 = 416 K, T2 = 373 K and T3 = 330 K (on heating) and T1 = 410 K, T2 = 386 K and T3 = 322 K (on cooling) was determined by differential scanning calorimetry. Thermal hysteresis of these transitions ∆T1 = 6 K, ∆T2= 13 K and ∆T3 = 8 K, indicating a first order character. The X-ray diffraction study at room temperature revealed an orthorhombic system with Pbnm space group. The vibrational characteristics have been measured at room temperature by infrared spectroscopy (400–3800 cm-1) and by polarized Raman spectroscopy (10–3800 cm-1) on microcrystals orientated with respect to the organic and inorganic sublattice. The structure of this compound was optimized by density functional theory (DFT) using B3LYP with LanL2DZ and LanL2MB basis sets. The temperature dependence of the Raman line shifts ν and the half-width ∆ν detect the phase transitions (T1, T2 and T3). Keywords: differential scanning calorimetry, Raman spectroscopy, Density functional theory 1. Introduction Crystals with general formula AMeCl3.H2O and AMeCl3 (A = N(CH3)3H, N(CH3)4, N(CH3)H2; Me: metal = Co, Cu, Zn, Cd…) have a large set of different structures, properties and applications [1-5]. Most of these materials undergo multiple structural phase transitions often related to the reorientational dynamics of the substituted ammonium group; several interesting properties characterize these compounds such as the ferroelectricity, ferroelasticity and low dimensional magnetism. These properties are related to the structural phase transition which characterizes this family, such as the possibilities of application of these crystals
as a temperature and humidity sensors [6-7]. The vibrational spectroscopy applied to organic-inorganic materials is one of the most broadly applied techniques for the identification and characterization of molecules and the control of 1
the reaction, as well as for the determination of molecular structures [8-10]. Infrared and Raman spectroscopy frequently offer additional information about molecular vibrations. The calculation of vibrational frequencies by density functional theory (DFT) is developing rapidly as a cost-effective general procedure [11]. Its advantage is to determine reasonable vibrational frequencies and geometries much superior to the conventional methods [12]. However, it is agreed that the frequency of vibration, obtained by DFT, are usually smaller or larger than their experimental equivalents for organic and inorganic components. Thus, empirical scaling factors are always used to improve and describe the experimental and vibrational frequencies [13-14]. The scale factors depend not only on the method but also on the basic sets selected from the DFT. They are deducted from the average difference between the experimental and calculated frequencies [15]. In this context, we have successfully synthesized the [N(CH3)3H]CdCl3 hybrid compound. The structure of this hybrid compound at room temperature was previously determined by Walther [16]. It crystallizes in the orthorhombic system with Pbnm space group and unit cell parameters: a= 8.957 (2) Å, b= 14.34 (4) Å and c = 6.6873 (9) Å. The phase formed above 342 K is hexagonal (HHT1) with space group P63/m. In the range of [342K; 374K], the lattice parameters: ah1= 26.049 (5) Å and Ch1= 6.756 (1) Å become stable in the temperature range from 374 to 415 K with (HHT2): ah2=15.06 (2) Å and ch2= 6.74 (2) Å; Z = 6 [17]. [N(CH3)3H]CdCl3 consists of two entities: trimethylammonium [N(CH3)3H]+ and [CdCl6]tetrahedron. The atomic arrangement can be described by an alternation of the organic and inorganic entities. This compound is characterized by two simple hydrogen bonds N–H---Cl linking the organic [N(CH3)3H]+ cation to the [CdCl6]-. The purpose of this document is to report on the temperature behavior of [N(CH3)3H]CdCl3 justified by differential scanning calorimetry and Raman scattering. The experimental data are analyzed from the vibrational characteristics that are compared with the calculated results by using DFT (B3LYP) with LanL2DZ and LanL2MB basis sets that are explained by the geometric and normal vibration modes of the organic and inorganic compound. 2. Experimental 2.1. Synthesis Colorless single crystals of [N(CH3)3H]CdCl3 with prismatic shape were grown at room temperature by slow evaporation of aqueous solution of hydrochloric acid (1M) containing an [N(CH3)3H]Cl and (CdCl2) in a molar ratio 2:1. The reaction scheme is the following:
2
[N(CH3)3H]Cl + CdCl2
[N(CH3)3H]CdCl3
2.2. Characterization The structure of obtained powder was determined by X-ray powder diffraction on an Empyrean Cu LFF HR diffractometer with Cu Kα radiation (45 kV, 30 mA), at room temperature. Data of the Rietveld refinement were collected in the 2θ range 8– 65°. The refinement was performed with the FullProf computer program [18] which adopts the Rietveld calculation method. The differential scanning calorimetry measurements were performed on a DSC (Q-100) calorimeter. The powder sample (about 7.3 mg) was placed within capsules in thermal recording conditions, whose heating and cooling speed was 10°C/min and in the temperature range from 300 to 455 K. The infrared spectrum of the [N(CH3)3H]CdCl3 sample was measured at room temperature with a Perkin-Elmer FT-IR 1000 spectrometer using KBr pellet technique in the wavenumber range between 400 and 3800cm-1. Temperature dependent Raman spectra were measured by a T64000 Horiba-Jobin-Yvon spectrometer equipped with nitrogen cooled CCD detector. The wavelength radiation for excitation was 514.5 nm using an Ar/Kr laser. The laser power in the samples was limited to 60 mW. All measurements were conducted under microscope using X50 LF objective in backscattering geometry on transparent single crystal employing the parallel polarization. The spectra were collected with 600 tr/mm grating, from 10 to 3800 cm-1 for different temperatures (under Linkam stages for the high and low temperatures). The wavenumbers and widths of the Raman lines were determined by fitting, using the LabSpec5 software with a combined Lorentzian–Gaussian band shape. 3. Results and discussion 3.1. X-ray diffraction study The X-ray diffraction studies at room temperature showed that synthesized powder is single phase [N(CH3)3H]CdCl3.The graphic result of Rietveld structural refinement as the best fit between calculated and observed X-ray diffraction pattern is shown in Fig. 1. The Rietveld method was applied for refining structural parameters (atomic displacement parameters, occupation factors and lattice parameters) using the software Full-PROF [18] directly from complete powder diffraction patterns. XRD refinement was continuous until convergence was reached with a goodness factor close to 1. We found that the sample crystallizes in the orthorhombic structure with Pbnm space group. The refined lattice 3
parameters are a = 8.980 Å, b = 14.486 Å, c = 6.704 Å and V = 872.289 Å3; Z= 4, which are in good agreement with the published results [16]. The value of the discrepancy factor (Rwp= 8.35%) and expected value (Rexp= 6.53%) with the goodness of fit index (2 = 1.68). The asymmetric unit of the synthesized compound is made up of an [N(CH3)3H]CdCl3 compound as shown in Fig. 2. A projection along the b-axis of the structure presents an arrangement of layers, [CdC16] - anions and layers [N(CH3)3H]+ cations Fig. 3. Indeed, the organic layers, observed at z/a= ¼ and at z/a=3/4, are formed by the organic cations [N(CH3)3H]+ direct their groups (NH2) outside of the organic layer to establish weak hydrogen bonds of N-H...Cl. The inorganic layer, observed at z/a=0 and at z/a=1/2, is formed by infinite chains of face sharing [CdC16] octahedral. The trimethylammonium ion has a parallel chain structure. The organic group is formed by three carbon atoms and only one nitrogen atom, the C–N bond length values are 1.464 (2) Ǻ and 1.475 (8) Ǻ. The C-N-C angles are in the range between 111.9 (7)° and 112.71(8)°. The Bond length and angles values are in good agreement with the bond lengths of other similar compounds [19, 20]. The [CdC16] consists of two face-sharing CdCl3 octahedra. The Cd−Cl distances vary from 2.350 (1) to 2.671(7) Å. The Cl-Cd-Cl angles are in the range 77.8 (2)179.9 (1)°. Accordingly, bond lengths and angles within the organic cations are normally compared to similar compounds [19-21]. 3.2. Thermal properties DSC is a reliable thermodynamic technique to detect the reversible phase transition nature of a compound with respect to temperature change. In this respect, the sample of [N(CH3)3H]CdC13 was subjected to DSC measurements in an aluminum container under nitrogen conditions. Fig. 4 reveals the presence of three reversible phase transitions at 410/ 416K, 386/373 K and 322/330 K, respectively, on cooling and heating, respectively. The large thermal hysteresis of ∆T1 = 6 K, ∆T2= 13 K and ∆T3 = 8 K, respectively, show that these transitions can be classified as a first order type [22]. Moreover, an entropy change ∆S1= 0.12J.mol-1.K-1, ∆S2= 1.46 J.mol-1.K-1 and ∆S3 = 0.52 J.mol-1.K-1 [23]. The entropies ∆S1 and ∆S3 are too low which indicates the mechanism displacive are involved in the phase transitions T1 and T3, by against, the entropy corresponding to T2 does not indicate the pure “order disorder” mechanism of this transition; such results suggest that both order–disorder and displacive mechanism are involved in the phase transition [23]. 3.3. Raman and Infrared spectra at room temperature
4
The Infrared and Raman spectra of [N(CH3)3H] CdCl3 recorded at room temperature between 400 and 3800 cm-1 and 10 to 3800 cm-1 , respectively, are shown in Figs. 5 and 6. The tentative assignment is done on the basis of the characteristic vibrations of the cation [N(CH3)3H]+ and the anionic part [CdCl3]- as deduced from literature [24, 25] and ab initio calculations. All the bands assignments are summarized in Table 1. 3.4. Ab initio calculation results and assignments of the Infrared and Raman spectra The optimized geometry and vibrational frequencies calculations of [N(CH3)3H]CdC13 compound were determined at the density functional theory (DFT) [26] level using the Lee– Yang–Parr correlation functional B3LYP [27] with LanL2DZ [28] and LanL2MB [29] basis sets implemented within Gaussian 09 program [30]. 3.4.1. Geometry optimization The calculated geometrical parameters such as bond lengths and bond angles were compared with available experimental data. These parameters, calculated for our compound in B3LYP method with LanL2DZ and LanL2MB basis sets, are listed in Table 2. Whatever the basis, the calculated bond lengths are slightly bigger than the experimental values due to fact that the theoretical calculations belong to the molecule in the gaseous phase and the experimental results belong to the molecule in solid state. In the inorganic part [CdCl3]-, it appears that the LanL2MB basis set gives the best agreements with the experimental angles and bond lengths compared to LanL2DZ.
By
contrast, for the organic [N(CH3)3H]+ entity, the best agreement between the optimized geometries and experimental values is observed with B3LYP/ LanL2DZ. 3.4.2. Vibrational spectra The experimental IR spectra of [N(CH3)3H]CdC13 is given in Fig. 5 , and the experimental Raman spectrum with the calculated are represented in Fig. 6. The calculated frequencies of this molecule are performed by using ab initio DFT (B3LYP) with the LanL2DZ and LanL2MB basis set. Furthermore, their calculated and experimental IR and Raman data together with their tentative assignments are quoted in Table 1. a. Vibrations of [CdCl3]- anion The [CdCl3] - (D3h symmetry) [31] has 6 normal modes of vibration because, in general, the number of vibrational modes must be equal to 3N-6. Based on the group theory calculation, these vibrational modes have the same symmetry properties as the A1+2E+ A2 irreducible representation of the D3h point group (Γvib =A1+2E+ A2). The 2E representation indicates 5
that the Raman and infrared active. By contrast, The A1 is Raman active and the A2 representation is only infrared active [10]. The correlation of the internal vibrational modes of MX3 in the D3h point symmetry groups is recalled in Table 3 [10]. Hence, it appears that the ν1 and ν2 are expected to give one Ag and three Bg modes (B1g, B2g, B3g) in the crystal, and for ν3 and ν4 with D3h symmetry each giving tow Ag and six Bg modes (2B1g, 2B2g, 2B3g). It is worthwhile to note that for all modes, the Bg are expected with much weaker intensity than the Ag ones. All the bands in the range of 10-350 cm-1 observed in the Raman spectrum of [N(CH3)3H]CdC13 single crystal Fig. 6 (a), show that they are related to the internal [CdCl3]and modes for both externals (organic and inorganic). It is reported that the distinction between these modes is not easy [32]. The Raman activities (Si) calculated with the GAUSSIAN 09program were subsequently converted into relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [33-35].
I i f ( 0 - i ) 4
1 hc i 1 exp( kT )
Si
1
i
(1)
where ν0 is the existing frequency in cm−1, νi the vibrational wave number of the ith normal mode, h, c and k are the fundamental constants and f is a suitably chosen common normalization factor for all the peak intensities. The calculated intensities (Ii) and the ab initio calculation (Si) using (B3LYP) with the LanL2DZ and LanL2MB basis set are reported in Table 4. The strong band observed in Raman spectrum Fig. 6 (a), at 249 cm-1 is assigned to the Cd-Cl symmetric stretching (ν1(Cd-Cl)) which is predicted theoretically at 265.5 cm-1 (LanL2DZ) and 268.6 cm-1 LanL2MB). The asymmetric stretching (ν3 (Cd-Cl)) vibration appears as bands 170.5/265 cm-1. The weak bands located in Raman spectrum at 78.1/122 cm-1 are attributed to scissoring vibration out of the plan ν4. The activation of this mode in Raman spectrum confirms the symmetry of the sciss (CdCl2). b. Vibrations of [N(CH3)3H]+ cations The different modes that appear in the experimental spectrum of [N(CH3)3H]+ entity are awarded on the basis of the calculated frequencies and intensities (Ii) and (Si), using (B3LYP/ LanL2DZ) and (B3LYP/ LanL2MB)
Table 4. The infrared and Raman spectra of the 6
compound are shown in Figs. 5 and 6 (b), respectively, and their bands assignments are summarized in Table 4. This attribution is performed from the whole calculations ab initio, using the molecular viewer Jmol.34 [36]. The bands observed in the IR and Raman spectra 458- 1256.4 cm-1 are associated with r (CH3) methyl rocking modes. All of the bands observed at 979.3 cm-1 and 814.8-1060 cm-1 are related to the vas (N-C) and vs (N-C), respectively. The symmetric and antisymmetric bending of methyl groups (CH3) are observed at 1240.6-1413.6- 1447 and 1473 cm-1, respectively. Besides, the band at 2784.4 cm-1 is assigned to the vs (N–H) stretching mode. Finally, stretching (symmetric and asymmetric) modes of the CH3vibrations are seen in the region of 2800–3100 cm-1. The observed bands at 2816, 2939, 3025 and 3076.1 cm-1 are related to vs (CH3). In the IR spectrum, only the modes at 2814.9, 2927.3, 3020.2 and 3068.6 cm-1 are clearly seen. The bands that appear at 2888, 2958, 2972 and 3036.1 cm-1 are assigned to the vas (CH3). By contrast, the infrared observes only 2962.7 and 3031 cm-1. c. Overview of the results Figs.7 and 8 show plots of the calculated versus experimental vibrational frequencies of [CdCl3]- and [N(CH3)3H]+. In both bases, the calculated values are slightly different from the experimental ones (dashed lines), but they are well described by a linear-fitting. For the inorganic anions [CdCl3]- Fig. 7, the calculated scaling factors are 0.92 for (B3LYP/ LanL2DZ) and 0.84 for (B3LYP/ LanL2MB) basis. Concerning [N(CH3)3H]+ Fig. 8, we note that R (LanL2DZ) is better than R (LanL2MB). The scaling factors of all bases Table 5 are used to minimize the root-mean-square deviation δrms calculated from the Eq.2. They also determine the variation between the calculated and the observed vibrational frequencies: n
rms
( i 1
iexp
ical ) 2
(2)
n
Where n is the number of the experimental and calculated data. The calculated rms deviation (δrms) for [CdCl3]- and [N(CH3)3H]+ in the [N(CH3)3H]CdC13 crystal and different bases are summarized in Table 5. It is observed that the frequencies calculated by (B3LYP/ LanL2MB) are closer to the experimental frequencies than those calculated using (B3LYP/ LanL2DZ), and that this basis leads to the weaker value of (δ rms), which is therefore used for the attribution modes of 7
[CdCl3]- entity in the [N(CH3)3H]CdC13 crystal. For the cation [N(CH3)3H]+, The lowest value of this deviation is obtained by the B3LYP method with LanL2DZ basis. 3.5. Temperature evolution of the Raman spectra Figs. 9(a) - 9(d) show the temperature dependent Raman spectra of the [N(CH3)3H]CdC13 in the 295-433K temperature range. However, several bands exhibit a significant change in the position of the band, half-width and intensity in the vicinity of the phase transition detected by DSC. That conduct may be related to changes in the interactions between the organic and inorganic parts increasing with temperature, which can be attributed to the increase of the dynamic movement of the alkyl chains and / or the degree of anions distortion [37]. The position, intensity and the half-width of the Raman lines were refined using a combination of Gaussian and Lorentzian functions. Figs. 10(a) - 10(d) show an example of deconvolution of the Raman spectrum at 295 K. The positions and width at half maximum for selected lines, obtained between 10 and 3100 cm-1, are shown in Figs. 11 and 12 (a-c). In phase 1, most of the modes have normal temperature dependence except for the modes ν4= 78.1 cm-1, ν1= 249 cm-1 for the inorganic part [CdCl3]-, stretching mode at 814.8 cm-1 (vs (N–C)), 2958 cm-1 (vas (CH3)), 2972 cm-1 (vas (CH3)) and 3036.1 cm-1 (vas (CH3)), asymmetric bending mode at 1447 cm-1 and r (CH3) methyl rocking modes at 1256 cm-1 for the cation [N(CH3)3H]+. The change of positions of the peaks at 249 cm-1 and 814.8 cm-1 is assigned to ν1 and (vs (N–C)), respectively. In this transition, the half-width variations Fig. 12 of all the analyzed bands are noted. Figs. 11 and 12 (a-c) show a continuous spectral evolution at temperature superior T1. This transition is of the reconstructive type and it is associated with a change of the stoichiometry of the material [17]. Many of the new modes have normal temperature dependence in the hexagonal (HHT2) phase like 122, 170.5 and 979.3 cm-1assigned to ν4 [sciss(CdCl2) and external mode], ν3 [vas (Cd–Cl)] and vas (N–C), respectively. Figs. 11 and 12 show the positions and half-widths variation of all peaks at the level of T1. In the hexagonal (HHT1) phase, new modes have temperature dependence at 1060, 2784.4, 2816 and 2888 cm-1 assigned to vs (N–C), vs (N–H), vs (CH3) and vas (CH3), respectively. The slight variations of the positions of the peaks at 78.1, 122, 170.5, 249, 1473 and 2972 cm-1 related to ν4, ν4, ν3, ν1, δas (CH3) and vas (CH3), respectively.
The peak at 1256.4 cm-1assigned to r (CH3) is broken up into two peaks: r (CH3) and δs (CH3). 8
The mode δs (CH3) is split up into two peaks at 1413.6 and 1447 cm-1.
The peak at 2958 cm-1assigned to vas (CH3) is split up into two peaks: vs (CH3) and vas (CH3).
The peak at 3036.1 cm-1assigned to vas (CH3) is broken up into two peaks: vs (CH3) and vas (CH3).
Eventually, two new modes which appear only in the orthorhombic phase like 458 and 3076.1 cm-1 assigned to r (CH3) and vs (CH3). The Slight variations in the position of all modes, the variations of the half-widths of almost all of the peaks increase with temperature. Most of the modes of (HHT1) and (HHT2) phases are also present in the orthorhombic phase after transition. This could be due to the fact that hexagonal to orthorhombic transition involves some minor changes in the local structure. The mechanisms of the phase transitions found in this hybrid compound can be accounted for in two different ways [38-40]. The first mechanism related to order-disorder processes attributed to the reorientation of organic cations. The other one, the displacive mechanism, is associated with the continuous variation of orientation of the inorganic part [CdCl3] and / or N(CH3), and / or H. Based on the above mentioned discussion, the Raman spectra, upon heating of the [N(CH3)3H]CdCl3 single crystals, can be attributed to the phase transitions T1, T2 and T3, since the Raman spectroscopy is very sensitive to the local lattice dynamics and the structural transitions. Therefore, the anomalies of wavenumber and half-widths are effective tools to reveal the phase transitions. From these results, the mechanisms of phase transition at T2 can be specified in two possible ways. The first one would be related to a ‘‘displacive’’ type process due to the continuous displacement of the organic part. The other mechanism order–disorder type is related to the reorientation of the organic cations. This outcome is backed by the results of DSC in view of the weak entropy associated with this phase transition. To support the fact that the phase transition is correlated with changes of the [N(CH3)3H]+ groups, we monitored the analysis of the full width at half maximum (FWHM) , which is based on the theory used for the damping combined with an order–disorder mechanism. the width of a band is usually de fined as [41]:
FWHM (T ) (a bT ) c exp (-
Ea ) KT
9
(3)
Where Ea is the activation energy for the mode connected to the order-disorder transition, K is the Boltzmann constant and T is the temperature. The constant a accounts for the broadening arising from factors other than the phonon decay, such as structural and compositional defects. The second and third term of Eq (3) represents the influence of anharmonicity and thermally activated reorientational processes, respectively. Eq (3)
enables us to determine the activation energy of reorientational processes for
[N(CH3)3H]+ cation in the studied compound using temperature dependence of the FWHM for the bands s (CH3) and as (CH3) situated at 3025 cm−1 3036.1 cm−1, respectively. These contribute to the phase transition at 372 K Fig. 13. The obtained activations energy values for s (CH3) and as (C-H) are Ea(I) = 0.962 eV, Ea(I) = 1.034 eV for T T2 , respectively. While the activations energies for these bands for T T2 are Ea(II) = 0.915 eV, Ea(II) = 0.982 eV, respectively. The decrease of the activation energy values for this band can be explained by the increase of the disorder in the crystal due to increased of the dynamics of cations. These behaviors suggest that the transition T2 is related to the reorientation motion of the cationic part. 4. Conclusions In this work, the [N(CH3)3H]CdCl3, using a solution-based chemical method at room temperature, has been synthesized and found to belong to the orthorhombic system (space group Pbnm). The atomic arrangement of the hybrid compound can be described by the alternation of organic-inorganic layers. Moreover, the material cohesion of the compound is assured by hydrogen bonds (N-H---Cl) established between anions and cations. According to DSC investigations, the title compound exhibits three solid-solid reversible phase transitions, first order, at T1 = 416/410 K, T2 = 373/386 K and T3 = 373/386 K on heating and cooling, respectively. The Infrared, Raman spectroscopy and theoretical calculation using Density Functional Theory methods with LanL2DZ and LanL2MB basis sets are used to study the [N(CH3)3H]CdCl3 synthesized compound. They are also used to calculate the geometric parameters and the vibrational frequencies of the [CdCl3]- anion and [N(CH3)3H]+cation in the ground state. In this respect, the inorganic and organic entities and the calculation of the root mean square difference δrms between the observed and calculated frequencies allow to give the scaling factors and to deduce that the best agreements are obtained by B3LYP/ LanL2DZ for [N(CH3)3H]+ and B3LYP/ LanL2MB for [CdCl3]-. The detailed analysis of frequencies is 10
consistent with a dynamics reorientation of the trimethylammonium cations at the phase transition at T2.
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[15] P. Sinha, S. E. Boesch, C. Gu, R. A. Wheeler, A. K. Wilson, J. PhysChem A. 108 (2004), pp: 9213-9217. [16] U. Walther, D. Brinkmann, G. Chapuis,H. Arend, Solid State Communi, 27 (1978), pp: 901-905. [17] By. Gervais. Chapuis, F. Javier .Zuniga, ActaCryst. B, 36 (1980), pp: 807-812. [18] C. Opagistea, M.J. Jacksona, R.-M. Galéraa, E. Lhotela, C. Paulsena, B. Ouladdiaf, Journal of Magnetism and Magnetic Materials, 340 (2013), pp: 46-49. [19] N. Weslati, I.Chaabane, A.Bulou, F.Hlel, PhysicaB, 441 (2014), pp: 42–46. [20] A. Jarboui, A. Ousleti, K. Adil, K. Guidara and F.Hlel, Ionics, 17 (2011), pp: 145–155. [21] Josefina Pons, Jordi García-Antón, Mercè Font-Bardia, Teresa Calvet, Josep Ros, Inorganica Chimica Acta, 362 (2009), pp: 2698–2703. [22] Chen-Yu Mao, Wei-Qiang Liao, Zhong-Xia Wang, Peng-Fei Li, Xing-Hui Lv, HengYun Ye and Yi Zhang, Royal Society of chemistry, 45 (2016), pp: 5229-5233. [23] L. E. House Jr and C. David Dunbar, Thermochimica. Acta, 204 (1992), pp: 213-219. [24] Y. Mlik , A. Daoud, and M. Couzi, phys. stat. sol. (a), 52 (1979), pp: 175-188. [25] Y. Mlik, and M. Couzi, Solid State Phys, 15 (1982), pp: 6891-6906. . [26] A. Tamulis, V.I. Tsifrinovich, S. Tretiak, G.P. Berman, D.L. Allara, Chemical Physics Letters, 436 (2007), pp: 144-149. [27] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B, 37 (1988), pp: 785–789. [28] P.J. Hay, W.R. Wadt, J. Chem. Phys, 82 (1985), pp: 270–283. [29] H.B. Schlegel, M. Frisch, Int. J. Quantum. Chem, 54 (1995), pp: 83–87. [30] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
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G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian Inc., Wallingford, CT, 2009. [31] J. E. D. Davies and D. A. Long, J. Chem. SOC. (A), (1968), pp: 2054-2058. [32] B. Bednarska-Bolek, J. Zaleski, G. Bator and R. Jakubas, J. Phys.Chem.Solids, 61 (2000), pp: 1249-1261. [33] P. L. Polavarapu, J. Phys. Chem, 94(1990), pp: 8106-8112. [34] S. D. Williams, T. J. Johnson, T. P. Gibbons, C. L. Kitchens, TheorChem Accounts, 117 (2007), pp: 283-290. [35] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta A, 49 (1993), pp: 2007–2026. [36] Jmol program. http://www.jmol.org/ [37] J. Tarasiewicz, R. Jakubas, J. Baran, J. Mol. Struc. 614 (2002), pp: 333-338. [38] P. Szklarza, R. Jakubas, G. Bator, T. Lis, V. Kinzhybalo, J. Baran, J. Phys. and Chem. of Solid. 68(2007), pp: 2303-2316. [39] R. Jakubas, G. Bator, Z. Ciunik, Phys. Rev. B. 64 (2003), pp:1-6. [40] W. Mzdycki, K. Uolderna-Natkaniec, J. Swiergiel, R. Jakubas, Solid Stat NMR. 24 (2003), pp: 209-217. [41] C. Carabatos-Nedelec, P. Becker, J. Raman Spectrosc. 28 (1997), pp: 663-671.
13
Fig. 1. X-Ray diffraction patterns at room temperature of [N(CH3)3H]CdCl3 sample. The circles are the observed profile; the solid line is the calculated one. Tick marks below the profile indicate the position of allowed Bragg reflections.
Fig. 2. Asymmetric unit for the title compound
14
Fig. 3. Projection of part of the unit cell content of [N(CH3)3H]CdCl3 along the b-axis.
H bonds linking the [CdCl6] octahedra and (CH3)3NH+ ions are represented by dotted lines.
Fig. 4. Differential scanning calorimetric of [N(CH3)3H]CdCl3 compound. 15
Fig. 5. Infrared spectrum of [N(CH3)3H] CdCl3 at room temperature.
16
Fig. 6. Blue- experimental Raman spectrum, red- Calculated Raman spectrum of [N(CH3)3H] CdCl3 compound by DFT/B3LYP with LanL2DZ basis set and green- Calculated Raman spectrum of [N(CH3)3H] CdCl3 compound by DFT/B3LYP with LanL2MB basis set.
Fig. 7. Correlation graphics between the calculated and experimental vibrational frequencies of [CdCl3] - entity.
17
Fig. 8. Correlation graphics between the calculated and experimental vibrational frequencies of [N(CH3)3H]+ entity.
18
Fig. 9. Temperature evolution of the Raman spectra in the 10-3100cm-1 frequency range.
19
Fig. 10. Deconvolution of the Raman spectrum at T = 295 K.
20
Fig. 11. Temperature dependence of the positions of the modes in the 10-3100cm-1 spectral range. 21
*
22
Fig. 12. Temperature dependence of the half-width of the modes in the 10-3100cm-1 spectral range.
Fig. 13. Variation of half-width of the s (CH3) and as (CH3) mode in function of temperature. The red lines represent the theoretical fit.
Table 1 Observed Raman and Infrared scattering wavenumber (cm-1) of [N(CH3)3H]CdCl3 using DFT method with tow basis sets.
Experimental
Calculated B3LYP
[N(CH3)3H] CdCl3
[N(CH3)3H]CdCl3
23
Raman
Infrared
LanL2DZ
LanL2MB
Assignment
78.1
---
85.4
87.5
ν4
122
---
112.2
134.1
ν4
170.5
---
163.3
184.3
ν3
265
---
327.2
328.1
ν3
249
---
265.5
268.7
ν1
458
---
457.6
410
r (CH3)
814.8
806.6
852.3
932.3
vs (N–C)
979.3
980.2
1045.6
1150.1
vas (N–C)
1060
1055.5
1057.2
1162
vs (N–C)
1240.6
---
1223.4
1266.4
δs (CH3)
1256.4
1255.8
1230.9
1276.4
r (CH3)
1413.6
1414.4
1417.3
1467.5
δs (CH3)
1447
1454.1
1611.6
1697.7
δs (CH3)
1473
1476.2
1664.4
1776.2
δas (CH3)
2784.4
2779.1
2962.1
3234.5
vs (N–H)
2816
2814.9
3117.9
3450.3
vs (CH3)
2888
---
3121.1
3452.2
vas (CH3)
2939
2927.3
3131.9
3455.6
vs (CH3)
2958
2962.7
3220.3
3629.5
vas (CH3)
2972
---
3222.5
3633.4
vas (CH3)
3025
3020.2
3231.1
3642.8
vs (CH3)
3036.1
3031
3238.1
3644.6
vas (CH3)
3076.1
3068.6
3238.2
3646
vs (CH3)
vs: Symmetric Stretching; vas: Asymmetric Stretching; δs: Symmetric Bending; δas: Asymmetric Bending; r: Rocking
Table 2 Calculated (B3LYP/LANL2DZ) and (B3LYP/LanL2MB) and experimental geometrical parameters (bond lengths and bond angles) of [N(CH3)3H]CdCl3 hybrid compound
Parameters
LanL2DZ
LanL2MB
24
X-ray
Cd-Cl
bond
lengths Cl-Cd-Cl bond angles N-H
bond
lengths N-C
bond
lengths C-H
bond
lengths N-C-H bond angles H-C-H
bond
angles C-N-C
bond
angles
2.417-2.561
2.486-2.610
2.627-2.671
100.944
100.374
84.332
1.060
1.097
0.909
1.514
1.538
1.421-1.468
1.092-1.094
1.103-1.106
0.958-0.960
108.896
107.967
109.394
108.896
110.172
109.210
112.050
111.807
112.718
Table 3 Correlation between the symmetries of the normal modes of free MX3 (D3h), those of free [CdCl3] - and those expected in [N(CH3)3H] CdCl3 (Pbnm) in view of the C1 symmetry of the site (C1) where the molecular ion sets.
CdCl3
Site (CdCl3)
Crystal
D3h
C1
D2h (Pbnm)
(ν1) A1
(ν2) A2
A
Ag B1g, B2g, B3g Au B1u, B2u, B3u
A
Ag B1g, B2g, B3g B1u, B2u, B3u Au
25
Ag B1g, B2g, B3g Au B1u, B2u, B3u Ag B1g, B2g, B3g Au B1u, B2u, B3u
A
(ν3, ν4) E
A
Table 4 Experimental frequencies (i) and intensities (Ii) of the IR/Raman lines associated with both organic/inorganic entities. Theoretical frequencies (vi) and intensities (Si) calculated using DFT method with tow basis sets for [N(CH3)3H]CdCl3 compound.
Calculated values
Experimental values
Calculated values
(LanL2DZ)
(LanL2MB ) i(cm-1) Ii IR/Raman ---/78.1
(%) 4.9 1
i(cm-
Si
1
)
IR/Raman
85.4
0/1.43
Ii
i(cm-1)
7
Assignment
IR/Raman
(%) 5.4
Si
87.5
0/1.67
ν4 [sciss(CdCl2 ) + external mode]
---/122
1.2 3
112.2
0/0.58
0.4 5
134.1
0/0.30
ν4 [sciss(CdCl2 ) + external mode]
---/170.5
---/265
---/249
0.4 7
1.2 3
2.7 0
163.3
0/0.43
327.2
0/3.43
265.5
0/5.46
0.2 8
1.2 1
5.2 2 26
184.3
0/0.32
328.1
0/3.37
268.7
0/10.76
ν3 [vas (CdCl)] ν3 [vas (Cd– Cl)]
ν1 [ vs (Cd–
Cl)] ---/458
806.6/814.8
0.6 7 1.4 9
457.6
0/3.02
852.3
4.83/14.97
0 1.2 3
0.8
1045.
5
6
1.0
1057.
3
2
0.3
1223.
0
4
1255.8/1256.
0.2
1230.
4
1
9
1414.4/1413.
0.5
1417.
6
0
3
0.1
1611.
9
6
1.4
1664.
5
4
2779.1/2784.
7.0
2962.
1268.36/404.2
5.0
4
4
1
1
1
2814.9/2816
0
28.86/4.94
0
980.2/979.3
1055.5/1060
---/1240.6
1454.1/1447
1476.2/1473
---/2888
2927.3/2939
2962.7/2958
---/2972
3020.2/3025
3031/3036.1 3068.6/3076.
3117. 9
1.2
3121.
8
1
4.0
3131.
5
9
0.2
3220.
1
3
0.3
3222.
4
5
1.2
3231.
8
1
0.8
3238.
9
1
1.2
3238.
54.91/11.09
51.97/13.53
0/4.76
0/3.46
2.63/9.61
0.27/4.32
8.65/34.60
0/80.64
14.43/256.47
5.60/14.54
0/22.64
23.20/85.86
13.94/60.21 6.16/83.69
0.6 8 0.8 6 0.1 1 0 0.5 4 0.2 0 0.2 3
0.8 0 0.8 2 0 0.6 4 0.1 8 0.6 6 0.6
27
410
0/0.21
932.3
0.22/13.81
1150.1
27.20/9.96
vas (N–C)
1162
24.53/12.78
vs (N–C)
1266.4
0/1.85
δs (CH3)
1276.4
1.23/0.38
r (CH3)
1467.5
6.53/11.3
δs (CH3)
1697.7
5.14/4.94
δs (CH3)
1776.2
0.10/38.38
δas (CH3)
3234.5
1727.48/335.9 6
r (CH3) vs (N–C)
vs (N–H)
3450.3
0.39/3.79
vs (CH3)
3452.2
0/61.04
vas (CH3)
3455.6
0.70/ 62.70
vs (CH3)
3629.5
1.80/1.61
vas (CH3)
3633.4
0/53.90
vas (CH3)
3642.8
5.47/15.34
vs (CH3)
3644.6
1.03/5.39
vas (CH3)
3646
11.72/55.65
vs (CH3)
1
4
2
6
sciss: scissoring
Table 5 Root-mean-square deviation ??rms (cm-1) and scaling factor (Sf) for [N(CH3)3H]+ and [CdCl3]- entities.
LanL2DZ
LanL2MB
Sf [CdCl3]-
0.92
0.89
Sf [N(CH3)3H]+
0.93
0.84
δrms [CdCl3]-
15.98
10.15
δrms [N(CH3)3H]+
59.10
89.95
Highlights
The Infrared, Raman spectroscopy and theoretical calculation using Density Functional Theory methods with LanL2DZ and LanL2MB basis sets are used to study the [N(CH3)3H]CdCl3 synthesized compound. The inorganic and organic entities and the calculation of the root mean square difference δrms between the observed and calculated frequencies allow to give the scaling factors and to deduce that the best agreements are obtained by B3LYP/ LanL2DZ for [N(CH3)3H]+ and B3LYP/ LanL2MB for [CdCl3]-. The detailed analysis of frequencies is consistent with a dynamics reorientation of the trimethylammonium cations at the phase transition at T2.
28