Synthesis, spectroscopic characterization, second and third-order nonlinear optical properties, and DFT calculations of a novel Mn(II) complex

Journal of Organometallic Chemistry 797 (2015) 110e119

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Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem

Synthesis, spectroscopic characterization, second and third-order nonlinear optical properties, and DFT calculations of a novel Mn(II) complex € Sümeyye Altürk, Omer Tamer, Davut Avcı*, Yusuf Atalay Sakarya University, Faculty of Arts and Sciences, Department of Physics, 54187, Sakarya, Turkey

a r t i c l e i n f o

a b s t r a c t

Article history: Received 27 April 2015 Received in revised form 27 July 2015 Accepted 18 August 2015 Available online 20 August 2015

A novel Mn(II) complex with 1,3-Thiazolidine-2,4-dicarboxylic acid and 1,10 phenanthroline has been synthesized, and its FT-IR, FT-Raman and UVevis spectra have been recorded. Density functional theory calculations with the HSEH1PBE/6e311þþG(d,p) level have been used to determine optimized molecular geometry, harmonic vibrational frequencies, electronic transitions, infrared and Raman intensities and bonding features of [Mn(tda)(phen)] complex (tda ¼ 1,3-Thiazolidine-2,4-dicarboxylic acid; Mn ¼ Manganese (II); phen ¼ 1,10 phenanthroline). The assignments of vibrational modes have been performed on the basis of the weightiness of internal coordinates contributing to the vibrational frequencies calculated by HSEH1PBE method. The calculated small energy gap between HOMO and LUMO energies shows that the charge transfer occurs within Mn(II) complex. Molecular stability, hyperconjugative interactions, intramolecular charge transfer (ICT) and bond strength have been investigated by the applying of natural bond orbital (NBO) analysis. DFT calculations have been also performed to investigate total static dipole moment (m), the mean polarizability (), the anisotropy of the polarizability (Da), the mean first-order hyperpolarizability (), and the mean second-order hyperpolarizability () for Mn(II) complex. The obtained values show that Mn(II) complex is an excellent candidate to NLO materials. © 2015 Elsevier B.V. All rights reserved.

Keywords: Synthesis IR and Raman 1,3-Thiazolidin-2,4-dicarboxylic acid 1,10-Phenanthroline DFT calculations Nonlinear optics

1. Introduction The heterocyclic rings containing nitrogen or/and sulfur have common properties within the structure of numerous natural products used as pharmaceuticals and agrochemicals [1]. The synthesis of these heterocyclic systems has been particularly attractive because of its application in above mentioned fields. Thiazole-containing compounds are familiar group of heterocycles possessing a wide variety of drugs, most vitamins, many natural products, biomolecules and biologically active compounds including, antitumor, anti-inflammatory, anti-HIV, antimicrobial, antifungal, antiviral and antibacterial agents [2]. It is also reported that the biological and pharmaceutical properties of thiazoles and their derivates can be modified or even improved with the coordination of metal ions or atoms. Hence, the transition metal complexes derived from thiazole ligands have gathered great attention

* Corresponding author. E-mail address: [email protected] (D. Avcı). http://dx.doi.org/10.1016/j.jorganchem.2015.08.014 0022-328X/© 2015 Elsevier B.V. All rights reserved.

in coordination compounds [3,4]. Carboxylates are known as attractive metal binding units in coordination chemistry because of the negative charge that significantly enhances their ability to bind strongly to metals centers. In this regard, carboxylic ligands containing heterocyclic aromatic rings have been commonly used as building blocks in the construction of metaleorganic framework (MOF), since carboxylic groups can be completely or partially deprotonated, and can coordinate to metal centers with a variety of coordination modes [5]. 1,10-Phenanthroline (phen) used in the present paper is known as a bidentate chelating ligand for transition metal ions that has an important role in the development of coordination chemistry [6,7]. Phen ligand containing two aromatic nitrogen whose unshared electron pairs are magnificently placed to act cooperatively in binding cations is known as excellent p-acceptor [8,9]. As a class of significant fluorescent molecules, 1,10-phenanthroline, exhibiting definite photochemical, electrochemical and biological activities, can be used in many fields [10]. Furthermore, remarkable effort has been devoted on the use of 1,10-phenanthroline complexes as intercalating agents of DNA [11] and as artificial nucleases [12e14].

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119

Moreover, 1,10-phenanthroline is well-known benchmark ligand and has been used in the coordination chemistry for the complex formation of transition metal ions [15]. For instance 1,10phenanthroline can be successfully used as an accelerator for silver-catalyzed electroless copper deposition processes [16] and with copper (II) complexes show cytotoxic activity against a plane of human tumor cell lines [17e19]. Additionally, the synthesis and structural characterization of manganese (II) carboxylate complexes have been used as catalysts in particular with added 1,10phenanthrolines [20]. In this paper, [Mn(tda)(phen)] was synthesized and its FT-IR, FTRaman and UVevis spectra were measured in order to investigate the vibration frequencies of functional groups, and electronic transitions within the title complex. In order to both support the experimental results and convert the study to more advanced level, density functional theory calculations were performed by HSEH1PBE/6e311þþG(d,p). Nonlinear optical (NLO) properties of synthesized Mn (II) complex were evaluated by using the same level. Natural bond orbital (NBO) analysis has been applied to study the stability of Mn (II) complex from charge delocalization.

111

polarizability (Da), total first-order hyperpolrizability (), and the mean second-order hyperpolarizability () were computed in order to evaluate the nonlinear optical properties. Natural bond orbital (NBO) calculation was performed to understand various second order interaction between the filled orbital of one subsystem and vacant orbital of another subsystem which is measure of the molecular delocalization or hyperconjugation.

4. Results and discussion 4.1. Geometry optimization The optimized molecular structure in the ground state has been calculated by HSEH1PBE/6e311þþG(d,p) level. Selected bond lengths and angles for Mn (II) complex are given in Table 1 and compared with previously reported XRD results of similar structures. Fig. 1 shows the molecular structure of Mn (II) complex obtained from HSEH1PBE method with the 6e311þþG(d,p) basis set. As can be seen in Fig. 1, tda is coordinated to manganese (II) ion as a tridentate ligand. In [Mn(tda)(phen)] complex, Mn (II) center lies

2. Materials and methods 2.1. Synthesis All chemical reagents were analytical grade commercial products. Solvents were purified by conventional methods. An aqueous solution of H2tda (1 mmol) and NaOH (2 mmol) in ethanol/water (40 mL, ca 1:1 v/v) was added to an aqueous solution of MnCl2 (1 mmol) in water and phen (1 mmol) in water with continuous stirring. The resulting solution was refluxed for 4 h and then filtered. The blue filtrates were dehydrated for about 2 weeks at room temperature, and then adequate [Mn(tda)(phen)] complex for spectroscopic studies were obtained. 2.2. General methods FT-IR was recorded on SHIMADZU IR-PRESTIGE-2 spectrophotometer in the region of 4000e600 cm1. FT-Raman was measured in Kaiser RAMANRXN1 spectrophotometer in the range of 3200e200 cm1. Routine UVevis spectrum was obtained in a quartz cuvette on an Agilent 8453 UVevis spectrophotometer using ethanol solvent. 3. Computational details The calculations of geometrical parameters in the ground state were performed by using the Gaussian 09W program [21]. The output files were visualized via GaussView 5 software [22]. The structural properties and vibration spectra of Mn (II) complex were determined through the applying of HSEH1PBE (The recommended version of the full Heyd-Scuseria-Ernzerhof functional, referred to as HSE06 in the literature) [23e27] with 6e311þþG(d,p) basis set [28]. Moreover, the vibrational frequencies and percentage weightings of the contributions of the internal coordinates to the frequencies for the optimized molecular structure have been calculated at the same level [29]. The theoretical IR spectrum was plotted using pure Lorentzian band shape with a bandwidth of full width and half maximum (FWHM) of 10 cm1. The electronic spectrum, absorption wavelengths, and oscillator strengths of Mn (II) complex were calculated using the TD-HSEH1PBE [30] based on the optimized structure. The HOMOeLUMO energies and related parameters such as electronegativity, chemical hardness and softness were calculated at the same level. Additionally, the electric dipole moment (m), mean polarizability (), anisotropy of the

Table 1 Selected theoretical and experimental bond lengths and bond angles for [Mn(tda)(phen)] complex. Parameters Bond lengths (Å) Mn14eN6 Mn14eN35 Mn14eN36 Mn14eO12 Mn14eO11 C8eO11 C8eO9 C2eN6 C2eH38 C1eS4 C3eN6 C3eS4 C7eO10 C7eO12 C27eN35 C17eN35 C15eN36 C16eN36 Bond angles ( ) N36eC16eH20 H33eC27eN35 N35eC17eC15 C17eC15eN36 C15eN36eC16 N36eC16eC19 C18eC15eN36 C17eN35eC27 N35eC27eC30 C21eC17eN35 N36eMn14eN35 O12eMn14eO11 O12eMn14eN6 O11eMN14eN6 O11eC8eO9 O9eC8eC2 O11eC8eC2 C8eC2eN6 H38eC2eN6 C2eN6eC3 N6eC3eH37 C3eC7eO12 C3eC7eO10 O10eC7eO12 C7eC3eS4 C3eS4eC1

Experimental 2.117 2.268 2.297 2.038

[31] [32] [32] [31]

1.386 [33] 1.786 [33] 1.755 [33]

72.5 [32] 81.13 [31]

115.1 [33]

125.0 [31] 93.1 [33]

HSEH1PBE/6e311þþG(d,p) 1.775 2.060 2.043 1.892 1.938 1.311 1.209 1.452 1.107 1.843 1.433 1.847 1.199 1.330 1.323 1.351 1.349 1.322 115.73 116.54 115.78 115.71 118.40 121.97 123.91 118.37 122.25 123.68 78.40 132.17 81.98 83.28 126.18 125.34 108.39 105.72 107.66 110.59 111.03 109.81 125.12 124.94 118.10 91.35

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Fig. 1. The optimized molecular structure of Mn (II) complex.

on a general position and is penta-coordinated by two nitrogen atoms from phen and two oxygen atoms together with one nitrogen atom from tda. The MneN and MneO bond lengths in metaletda complex were reported as 2.117 and 2.038 Å, respectively [31]. In our calculations, these bond lengths are predicted as 1.7747 and 1.892 Å, respectively. The MneN bond lengths in Mn-phen complex were observed as 2.268e2.297 Å [32], and the corresponding bond lengths in our calculations are predicted as 2.0603e2.043 Å. The O12eMneN6 and N36eMn14eN35 bond angle were observed as 81.13 and 72.5 , respectively [31,32]. These bond angles are calculated as 81.98 and 78.40 by using HSEH1PBE level. In the tda, bond angles were observed as (C2eN6eC3) 115.1 [33], (O10eC7eO12) 125.0 [31] and (C3eS4eC1) 93.1 [33], and these bond angles are calculated as 110.59 , 124.94 and 91.35 . From Table 1, it can be said that there is a good agreement between the experimental and theoretical geometric parameters for Mn (II) complex. 4.2. Vibrational assignments The [Mn(tda)(phen)] complex consist of 38 atoms, which have 108 normal modes of fundamental vibrations. The FT-IR and FTRaman spectra for Mn (II) complex were recorded in frequency region of 4000e600 cm1 and 3200e200 cm1, respectively. A detailed assignment of vibrational modes is performed by the percentage weightings of the contributions of the internal coordinates to the calculated frequencies. The observed vibration frequencies in FT-IR, FT-Raman along with the calculated IR and Raman intensities are given in Table 2. The comparison of FT-IR and calculated IR spectra for Mn (II) complex are presented in Fig. 2, and the comparison of FT-Raman and calculated Raman spectra for Mn (II) complex are given in Fig. 3. 4.2.1. CH vibrations In the aromatic molecules, the CH stretching vibrations appear in the range of 3100e3000 cm1 [34]. The nature of substituent cannot affect the bands much in this region. The observed peaks at 3110.37, 3077.37 and 3059.39 cm1 in FT-Raman spectrum is

designated as CH stretching vibration for phen ligand. The corresponding peak at FT-IR is observed at 3051.25 cm1 as a single band. In theoretical calculations, the n(CH) stretching vibrations are computed at the range of 3108.40e3072.73 cm1. When it comes to tda part, the n(CH) stretching vibrations are observed at 2959.45 and 2935.57 cm1 in FT-Raman. These vibration peaks are calculated at the frequency region of 3045.43e2824.21 cm1. The b(HCC) vibrations are mainly determined by the number of adjacent hydrogen atoms on the ring. The CH in-plane bending frequencies appear in the range of 1300e1000 cm1, while CH out-of-plane bending vibration is in the range of 1000e750 cm1 [35]. The peaks appeared at the range of 1418.14e1031.97 cm1 in FT-Raman and 1382.43e1046.09 cm1 in FT-IR spectrum is assigned as the CH in plane bending vibrations. The corresponding peaks at the theoretical spectrum are calculated at 1416.14e1019.18 cm1 with the contribution range of 60e2%. When it comes to CH out of plane bending vibrations, these peaks are calculated at the range of 999.86e708.36 cm1. The corresponding peaks are observed at the range of 950.16e711.22 cm1 in FT-IR and 1003.47e727.41 cm1 in FT-Raman spectrum.

4.2.2. CC vibrations The existence of one or more aromatic rings in the molecular systems is readily determined from the CeH and C]CeC ring related vibrations. The ring stretching vibrations are very much important in the spectrum of the aromatic rings. In general, the bands are of variable intensity and observed at 1625e1590, 1590e1575, 1540e1470, 1460e1430, and 1380e1280 cm1 from the frequency ranges given by Varsanyi [36]. The band observed at 1619.17 cm1 in FT-IR and 1622.89 cm1 in FT-Raman is assigned as the CC stretching vibration for phen. The corresponding peak in calculated spectrum is found as 1623.52 cm1 with the contribution of 27%. The calculated peak at 1324.33 cm1 is assigned as the CC stretching vibration for tda with the contribution of 6.8%. In Mn (II) complex, the CC stretching vibrations calculated at the range 1623.52e1019.18 cm1 are observed at the range of 1619.17e1046.09 cm1 in FT-IR and 1622.89e1031.97 cm1 in FTRaman. The CC in plane bending vibrations are observed at the

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119

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Table 2 Comparison of the FT-IR and calculated (with HSEH1PBE/6e311þþG(d,p)) vibration frequencies for [Mn(tda)(phen)] complex. Mod Assignments (% weightage of internal coordinates contribution to the frequencies, >2%)a

108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42

y(CH) 79.8 phen y(CH) 78.5 phen y as(CH) 78.6 phen y(CH) 75.2 phen y as(CH) 74.6 phen y as(CH) 76.9 phen y as(CH) 70.7 phen y as(CH) 78.2 phen y as(CH) 62.5 tda y(CH) 72.9 tda y(CH) 52.3 tda y(CH) 45.8 tda y (CO) 31.8 tda þ b(CCO) 11.5 tda y (CO) 26.5 tda þ b(CCO) 10.8 tda y(CC) 27 phen þ b(CCH) 15 phen þ b(CCC) 5.4 phen þ b(CCN) 4.6 phen y(CC) 20.7 phen þ y(CN) 6.1 phen þ b(CCH)16.6 phen þ b(CCC) 9.9 phen þ b(CCN) 4 phen y(CC) 14.3 phen þ b(CCH) 18.9 phen þ b(CCC)2.3 phen þ b(CCN) 2.1 phen þ b(HCN) 5.5 phen y(CC) 17.1 phen þ y(CN) 7 phen þ b(CCH) 21.8 phen þ b(CCC) 2.2 phen þ b(HCN) 2.9 phen y(CC) 14.3 phen þ y(CN) 9.9 phen þ b(CCH) 13.8 phen þ b(HCN) 9.4 phen y(CC) 18.2 phen þ y(CN) 4 phen þ b(CCH) 37.2 phen y(CC) 28.4 phen þ y(CN) 4.7 phen þ b(CCH) 25.7 phen þ b(CCN) 4.8 phen b(CCH) 10.3 tda þ b(SCH) 5.9 tda þ b(HCH) 15.1 tda þ g(HCCN) 12.12 tda þ g(HCSC) 15.1 tda y(CC) 14.5 phen þ b(CCH) 42.2 phen þ b(HCN) 2.5 phen y(CC) 6.8 phen þ y(CN) 5.8 phen þ b(CCH) 24.6 phen þ b(HCN) 11.1 phen b(HCC) 54.6 phen y(CC) 26.7 phen þ y(CN) 15.8 phen þ b(CCH) 15.2 phen þ b(CCC) 4.1 phen y(CC) 4.6 phen þ y(CN) 5.4 phen þ b(CCH) 13.9 phen þ b(HCN) 10.9 phen y(CC) 6.8 tda þ b(CCH) 15.3 tda þ g(HCNC) 7.4 tda þ g(HCNMn) 7.5 tda þ g(HCCO) 7 tda y(CC)15.3 phen þ y(CN) 11.9 phen þ b(CCH) 22 phen y(CC) 2.6 tda þ y(CO) 2.3 tda þ b(CCH) 4.1 tda þ b(NCH) 7 tda þ g(SCCH) 6.3 tda þ g(HCCO) 13.6 tda y(CN) 4.8 phen þ b(CCH) 21.2 phen þ b(CCC) 6.5 phen þ b(HCN) 10.7 phen y(CN) 2.9 tda þ b(CCH) 5 tda þ b(SCH) 2 tda þ b(NCH) 8.6 tda þ g(HCSC) 8.4 tda þ g(HCCO) 13.4 tda y(CC) 8.2 phen þ y(CN) 3.1 phen þ b(CCH) 35.5 phen þ b(CCC) 2 phen þ b(HCN) 2 phen y(CC) 7 phen þ y(CN) 2.8 phen þ b(CCH) 20.6 phen y(CO) 4.1 tda þ b(CCH) 2.8 tda þ b(NHC) 3.4 tda þ b(CCO) 2.2 tda þ g(HCCN) 2.3 tda þ g(HCCO) 5.2 tda þ g(HCNMn) 2.2 tda þ g(SCCH) 3.9 tda y(CC) 4.7 phen þ b(CCH) 34.1 phen þ b(HCN) 6.8 phen b(CCH) 8.5 tda þ b(SCH) 8 tda þ g(HCSC) 3.2 tda þ g(HCNC) 6.9 tda þ g(HCNMn) 7 tda þ g(HCCO) 3.9 tda y(CC) 2.8 tda þ y(CN) 4.1 tda þ b(CCH) 11.5 tda þ b(SCH) 7.6 tda þ g(HCSC) 4.5 tda þ g(HCNC) 8.8 tda þ g(HCNMn) 3.6

FT-IR

Raman

3110.37

3051.25

3077.37 3059.388 2959.446 2935.568

1676.57 1619.17 1622.89 1606.63 1592.769 1560.83 1518.65 1483.29 1454.661 1426.30 1418.135 1382.43 1349.83 1349.08

1306.155

1228.99 1212.529 1204.71

tda y(CN) 7.4 tda þ b(SCH) 4.1 tda þ b(NCH) 2.4 tda þ g(SCCH) 2 tda þ g(HCCN) 5.3 þ g(HCCO) 7.8 tda þ g(HCNMn) 3.4 tda 1143.154 y(CC) 8.4 tda þ y(CO) 8 tda þ b(CCH) 2.1 tda þ b(CCO) 4.2 tda þ b(OCO) 3.8 tda þ b(COMn) 2.1 tda 1132.50 b(HCC) 58.6 phen b(HCC) 40.2 phen b(CCH) 4.7 tda þ b(SCH) 3.3 tda þ b(NCH) 2.6 tda þ g(HCCN) 5.4 tda þ g(HCSC) 3.3 tda þ g(HCCO) 2.3 tda b(HCC) 29.5 phen 1104.61 b(CCH) 6.8 tda þ b(SCH) 7 tda þ b(NCH) 2.5 tda þ g(HCCN) 2.8 tda þ g(HCSC) 2.4 tda þ g(CCCO) 2.4 tda þ g(HCCO) 5.9 1083.17 tda y(CC) 5.7 phen þ b(CCN) 4.7 phen þ b(HCN) 4.9 phen þ b(CCC) 4.1 phen þ b(CCH) 17.6 phen y(CC) 15.5 phen þ b(CCH) 24.7 phen þ b(HCN) 4.4 phen 1046.09 1048.552 y(CC) 8.9 phen þ b(CCH) 10.1 þ b(CCN) 15.2 phen þ b(CCC) 4.4 1031.967 y(NMn) 2.7 tda þ b(SCH) 4.6 tda þ g(HCCN) 5.8 tda þ g(HCCC) 7 tda þ g(HCCH) 3.3 tda 1003.470 t (HCCH) 20.1 phen þ g(NCCH) 8.4 phen þ g(HCNMn) 4.1 phen þ g(HCCC) 12.9 phen t (HCCH) 23.2 phen þ g(NCCH) 4.8 phen þ g(HCNMn) 3.1 phen þ g(HCCC) 14.9 phen t(HCCH) 19.2 phen þ g(HCCC) 32.2 phen 950.16 g(HCCC) 5 tda þ g(CCCO) 2.9 tda þ g(CCOMn) 2 tda t(HCCH) 14.7 phen þ g(HCCC) 23.3 phen þ g(HCNC) 5 phen þ g(HCNMn) 6.1 phen t(HCCH) 12.4 phen þ g(HCCC) 22.7 phen þ g(HCNC) 6 phen þ g(HCNMn) 7.1 phen b(SCH) 8 tda þ g(HCCH) 9.9 tda þ g(HCCC) 12.4 tda þ g(HCCN)8 tda þ g(HCSC) 6 tda y(NMn) 4.3 phen þ b(CCC) 4.6 phen y(CS) 2.2 tda þ y(CO) 2.1 tda 888.68 y(NMn) 6.2 phen þ b(CCC) 6.8 phen þ b(CCN) 11.2 phen þ b(MnNC) 4 phen 865.503 w(CCCH) 36.1 phen þ g(HCCN) 5.7 phen þ g(HCNMn) 4.1 phen 830.19 g(SCCO) 5 tda þ g(NCCO) 4 tda þ g(HCCO) 5.8 tda þ g(CCNC) 2.1 tda þ g(CCNMn) 3.1 tda þ g(CCOMn) 3.8 808.85 810.718 tda þ g(OCOMn) 2 tda g(HCCC) 9.2 phen þ g(CCCC) 17.2 phen þ g(NCCC) 10.6 tda þ g(CCNMn) 4 phen þ g(NCCH) 4 phen y(SC) 2 tda þ y(OMn) 2.4 tda þ b(OCO) 2.3 tda þ g(CCCO) 2.8 tda þ g(NCCO) 2 tda þ g(HCCO) 2.1 tda 794.35 g(HCCC) 27 phen þ g(HCCN) 9.2 phen y(SC) 2.6 tda þ y(OMn) 3.8 tda þ b(OCO) 3.4 tda þ b(COMn) 2.2 tda 766.790 g(HCCC) 55.7 phen þ g(HCCN) 10.3 phen g(HCCS) 5.6 tda þ g(HCCO) 4.5 tda þ g(OCCC) 4 tda þ g(NCCO) 2.9 tda

HSEH1PBE/6 e311þþG(d,p) Scaled freq.b

IIRc

IRd

3108.40 3107.82 3097.15 3088.59 3086.38 3078.69 3078.11 3072.73 3045.43 2976.88 2947.08 2824.21 1759.84 1730.62 1623.52 1605.35 1584.10 1583.33 1512.09 1483.82 1450.08 1421.14 1416.14 1409.60 1391.05 1338.46 1330.48 1324.33 1310.48 1280.68 1239.05 1227.71 1207.61 1205.69 1201.17

3.6 1.8 1.3 10.1 0.4 1.3 2.2 0.06 3.07 14.6 10.4 8.9 621.7 731.1 2.8 0.6 4.4 9.5 5.1 8.9 2.9 2.33 11.0 50.1 0.2 7.3 3.4 18.2 3.8 109.6 1.1 25.8 5.6 13.2 121.7

211.1 251.7 76.7 324.6 53.2 77.7 96.4 54.2 102.0 139.5 119.7 75.4 45.1 37.9 44.6 154.7 79.6 124.9 349.2 2.3 683.7 6.8 44.7 1.0 5.3 17.4 91.5 5.0 156.2 4.2 0.9 37.4 12.2 44.2 28.5

1192.62 1189.25 1169.23

1.3 31.1 1.7

112.1 16.8 40.1

1147.33 30.5 1137.43 218.1 1124.74 2.6 1124.07 9.7 1120.22 7.0 1088.98 3.3 1083.11 14.1

53.4 61.4 18.1 5.5 1.6 65.9 21.1

1073.60 1040.81 1019.18 999.86 970.53 966.21 950.15 944.67 937.85 931.60 913.33 895.06 888.81 856.90 824.59 810.46

2.5 3.1 1.1 43.5 0.3 0.5 0.2 19.0 1.3 0.3 17.8 7.1 54.5 1.2 73.5 5.8

0.1 97.6 4.9 22.8 0.6 0.3 0.6 2.3 1.0 0.7 6.2 27.04 27.8 95.0 0.4 13.5

801.81 789.69 779.89 767.68 752.01 729.70

0.1 15.5 0.1 33.3 7.6 18.3

3.4 2.5 0.2 13.0 0.8 66.4

(continued on next page)

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Table 2 (continued ) Mod Assignments (% weightage of internal coordinates contribution to the frequencies, >2%)a

FT-IR

Raman

HSEH1PBE/6 e311þþG(d,p) Scaled freq.b

41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

y(NMn) 4.7 phen þ b(CCC) 4.5 phen b(CCC) 15.4 phen þ b(NCC) 6 phen g(NCCC) 21.9 phen þ g(HCCC) 6.6 phen þ g(HCCN) 4.5 phen þ g(CCCC) 4.1 phen y(SC) 9.4 tda þ b(CCC) 2.3 tda þ b(CCS) 2.8 tda y(SC) 3.3 tda þ y(OMn) 2.7 tda y(MnN) 6.9 phen þ b(HCC) 4.1 phen þ b(CCC) 11.8 phen þ b(CCN) 9.8 phen g(NCCC) 8.9 phen þ g(CCCC) 9.8 phen g(NCCO) 5.1 tda þ g(CNMnN) 2.7 tda b(CCC) 16.7 phen þ b(CCN) 6.1 phen g(CNMnO) 4.1 tda þ g(NCCO) 2.9 tda þ g(COMnO) 2.6 tda g(CCCC) 10.8 phen þ g(NCCC) 5.3 phen þ g(CCNMn) 4.2 phen þ g(NCCN) 2.8 phen g(OMnNC) 3 þ g(NMnNC) 5.1 þ g(HCSC) 2.1 tda b(CCC) 13.1 phen g(NMnNC) 2.1 g(COMnN) 2.4 g(COMnO) 2.1 tda g(NCCC) 6.4 phen þ g(CCCC) 5.4 phen g(CCCC) 5 phen þ g(CCNC) 2.8 phen þ g(NMnNC) 2.6 g(CCCC) 6.3 phen g(CCCC) 4.1 phen y(OMn) 3.1 tda þ g(CNMnN) 10.4 y(CS) 2.1 tda þ y(NMn)as 2.3 tda y(OMn) 2.6 tda g(HCSC) 4.3 tda þ g(CCCO) 2.8 tda b(MnNC) 9.6 phen g(CCCC) 10.4 phen þ g(CCNMn) 4.5 phen y(OMn) 2 tda þ g(HCCN) 3.4 tda g(CCCC) 8.4 phen þ g(NCCC) 6.1 phen y(MnN) 2.1 phen þ g(CNMnO) 2.3 tda þ g(COMnO) 2.2 tda g(NMnNC) 2.1 g(OMnNC) 2.1 y(MnN) 2.7 tda þ g(CCNMn) 3.1 tda þ g(CNMnO) 5.7 þ g(OCOMn) 3.6 tda y(NMn) 2.1 phen þ g(CCNMn) 2.4 phen y(NMn) 2.5 phen g(HCSC) 7.1 tda þ g(CCSC) 7.1 tda þ g(HCCO) 5.2 tda þ g(NCCO) 5.5 tda þ g(OCOMn) 2.2 tda þ g(CNMnO) 2.1 tda þ g(CCNMn) 2.1 tda g(SCCO) 4.5 tda þ g(NCCO) 4.5 tda þ g(HCCO) 4.9 tda þ g(OCOMn) 8.3 tda þ g(CCOMn) 3 tda þ g(CCOMn) 2 tda þ g(COMnN) 5.3 g(OMnNC) 9 þ g(NMnNC) 5.5 þ g(CCCC) 9.8 phen þ g(NCCC) 4.9 phen g(HCCO) 5.9 tda þ g (NCCO) 5.9 tda þ g(SCCO) 5.7 tda þ g(CCOMn) 3.3 tda þ g(COMnN) 2.2 tda þ g(OCOMn) 5.8 tda þ g(NCSC) 4.1 tda þ g(SCCC) 2.3 tda þ g(NCCC) 2.3 tda þ g(HCSC) 2.1 tda þ g(HCNC) 2.2 tda þ g(COMnN) 6.4 g(CNMnN) 4.5 þ g(OMnNC) 2.2 þ g(OCOMn) 2.1 tda g(CCNMn) 16.3 phen þ g(HCNMn) 5.2 phen þ g(NMnNC) 6 phen þ g(NMnNC) 15.6 þ g(OMnNC) 14.7 b(OMnO) 2.1 tda þ b(OMnN) 3 tda þ b(NMnN) 4.6 þ g(SCCC) 2 tda þ g(NCCC) 2 tda þ g(HCNC) 2.1 tda þ g(COMnN) 15.6

727.406 711.22 679.16 660.02 624.98

641.822 610.769 556.041

510.819

475.376 427.302 407.951

268.508 249.043

IIRc

IRd

725.57 710.19 708.36 683.65 646.54 634.33 596.84 577.99 548.09 541.65 537.13 513.68 496.66 494.83 485.41 473.97 449.65 427.82 417.15 411.29 384.75 373.89 352.26 329.76 289.38 264.67 239.20 226.60 212.18 188.05 179.20 170.17 155.84 145.46 134.31

1.2 5.8 42.8 2.5 44.8 2.0 0.2 17.7 1.5 10.2 0.1 9.3 1.2 0.3 3.7 3.1 7.4 24.3 2.8 20.9 15.1 3.2 9.5 1.3 1.0 1.5 7.5 2.4 0.1 1.2 2.6 4.5 4.1 1.3 6.9

217.0 12.2 4.7 13.1 2.0 33.9 2.1 8.6 4.5 2.2 0.7 4.6 1.5 0.9 34.2 13.0 0.4 19.5 20.2 7.9 22.1 54.3 4.1 8.7 24.9 1.4 5.9 0.7 1.5 2.9 2.3 3.4 2.7 0.7 0.9

124.89

1.5

0.6

84.41 62.01

3.8 3.1

0.5 2.5

44.13 29.32 25.57

1.5 0.7 1.3

8.6 5.4 5.6

y: Stretching; b: in plane bending; g: outeof plane bending; t: twisting; w: torsion. a b c d

Vibrational modes are based on % weightage of internal coordinates contribution to the frequencies and only contributions over 2% are given. Scaled frequencies are in unit of cm1. IIR infrared inten. are in unit of km mol1. IR Raman activ. are in unit of Å4 amu1.

range of 865.50e556.04 cm1 in FT-Raman and 830.50e624.98 cm1 in FT-IR spectrum. The theoretical CC in plane bending vibrations is found at the range of 895.06e496.66 cm1 as mostly coupled modes by the contribution of 16.7e2.3%.

Fig. 2. The comparison of FT-IR and calculated IR spectra for Mn (II) complex.

4.2.3. CN and CS vibrations Silverstein and Webster [37] assigned the CeN stretching vibration in the region 1328e1266 cm1. In our calculation, the CeN stretching vibration is calculated at 1338.46 cm1 for HSEH1PBE, and observed at 1349.83 cm1 in the FT-IR, and the corresponding peak in FT-Raman spectrum was observed at 1349.08 cm1. This peak is a coupled mode with the contribution of 15.8%. In theoretical calculations, the n(CN) stretching vibrations are computed at the range of 1338.46e1147.33 cm1. These stretching vibrations are observed at the range of 1349.08e1143.15 cm1 in FT-Raman and 1349.83e1204.71 cm1 in FT-IR spectrum. CeS stretching vibration are calculated at the range of 888.81e646.54 cm1 for HSEH1PBE,

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119

Fig. 3. The comparison of FT-Raman and calculated Raman spectra for Mn (II) complex.

and observed at the range of 888.68e660.02 cm1 in the FT-IR spectrum. 4.2.4. COO group and MnO vibrations The carboxylate group in metal complexes can take different configurations such as ionic, monodentate, chelating or bridging. A general tendency in the bonding between Dn [(the variation between the asymmetric and the symmetric stretches of carboxylate group] and the types of coordination of the COO group is well known: (1) monodentate complexes exhibit Dn values that are much greater than Dn calculated for the ionic complexes, (2) chelating complexes show Dn values that are significantly less than the ionic values, (3) the Dn values for bridging complexes are greater than those of chelating complexes, and close to the ionic value. The most important characteristic feature of carboxylic group is a single sharp band observed usually in the range of 1690e1655 cm1 [38] due to the COO stretching vibration. The COO stretching vibrations are observed at 1320e1210 cm1 owing to n(CO) stretching vibration [39]. In our calculations, the strong bands at 1759.84 and 1730.62 cm1 in HSEH1PBE spectrum of Mn (II) complex are assigned to n(CO), and the another absorption band at 1280.68 and 1201.17 cm1 is also attributed to n(CO) vibration (Table 2). These are very strong band sensitive to the type of metal coordination bonds. The n(CO) vibration modes appear at the lower wave number in our calculations. This case indicates that the carboxyl group is coordinated the Mn (II) ion as a two-dentate molecule. The new band observed at 794.35 cm1 in FT-IR is assigned n(MnO) stretching vibration. n(MnO) vibration is calculated at 789.69 cm1 for HSEH1PBE method. 4.3. UVevis spectra analysis and HOMO-LUMO energies The UVevis electronic spectrum of Mn (II) complex in ethanol solvent was recorded within 900e200 nm range. The theoretical electronic excitation energies and oscillator strengths were calculated by the TD-HSEH1PBE level using gas phase and ethanol solvent. The major contributions of the transitions were designated with the aid of SWizard program [40]. Obtained theoretical results are summarized along with the experimental ones in Table 3, and the measured UVevis spectra of Mn (II) complex is given in Fig. 4. Each calculated transition is represented by a Gaussian function y ¼ 2 cebx with the height c equal to the oscillator strength and b equal to 0.04 nm2 [41]. The TD-DFT calculation demonstrates that the electronic absorption at the highest wavelength is found at 711.55 nm, and

115

mainly formed by three electronic transition modes H1 / L þ 3(þ51%), H-2 / Lþ3(22%) and H-1 / L þ 2(þ11%). This absorption peak is observed at 732.74 nm in ethanol solvent. The other high wavelength transitions observed at 641.80 and 608.49 nm are calculated at 515.70 and 440.76 in ethanol solvent, and 589.92 and 537.73 in gas phase. From Fig. 5, these high wavelength absorption peaks is formed by the contribution of dMn / dMn and tda/phen / dMn transitions. The experimental bands observed at the range of 292.76e217.02 nm originate predominantly in the intraligand (IL) transitions between the pbonding and p*-antibonding orbital of tdaephen ligand. The corresponding peaks in DFT calculations are found at range of 351.59e295.42 nm in ethanol, 415.09e346.90 nm in gas phase. The frontier molecular orbital (FMO) energies of Mn (II) complex are calculated by using the TD-HSEH1PBE with 6e311þþG(d,p) basis set. The occupied and unoccupied MOs which are active in electronic transitions for Mn (II) complex are given Fig. 5. HOMO energy characterizes the electron giving ability, while LUMO energy characterizes the electron withdrawing ability. Energy gap between HOMO and LUMO characterizes the molecular chemical stability and it is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. From Fig. 5, HOMO energy is calculated as 5.5713 eV, and LUMO energy is calculated as 3.4003 eV by using HSEH1PBE level. The small energy gap between HOMO and LUMO indicates that charge transfer occurs within the Mn (II) complex, and Mn (II) complex can be easily polarized. Using HOMO and LUMO energies ionization potential and electron affinity can be explicated as IP ~ eEHOMO, EA ~ eELUMO. The variation of c values is supported by the electrostatic potential. For any two molecules, electron will be partially transferred from the one of low c to that of high c (electrons flow from high chemical potential to low chemical potential). The chemical hardness (h) ¼ (IPeEA)/2, electronegativity (c) ¼ (IP þ EA)/2, chemical potential (m) ¼ (IP þ EA)/2 and chemical softness (S) ¼ 1/2h values were calculated as 1.0855, 4.4858, 4.4858 and 0.4606 eV for HSEH1PBE level, respectively [42]. Obtained small h value means that the charge transfer occurs in the complex. Considering the h values, large HOMO-LUMO gap means a hard molecule and small HOMO-LUMO gap means a soft molecule. Additionally, it can be said that the small HOMO-LUMO energy gap represents more reactive molecule.

4.4. NBO analysis The natural bond orbital (NBO) analysis provides an efficient method for investigating intra- and intermolecular bonding and interaction among bonds. Furthermore, it provides a reliable basis for investigating charge transfer or conjugative interaction in molecular system [43]. The larger the E(2) value, the more intensive is the interaction between electron donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system. The hyperconjugative interaction energy was deduced from the second-order perturbation approach [44,45]. For each donor (i) and acceptor (j), the stabilization energy Eð2Þ associates with the delocalization i / j is estimated as

Eð2Þ ¼ DEij ¼ qi

Fði; jÞ2 εi  εj

(1)

Where qi is the donor orbital occupancy, εj and εi the diagonal elements and Fði; jÞ is the off diagonal NBO Fock matrix element. The NBO analysis demonstrates appreciable donoreacceptor type delocalization from lone-pair (n) of oxygen and nitrogen orbitals

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Table 3 Experimental and theoretical electronic transitions, oscillator strength for [Mn(tda)(phen)] complex. Experimental l (nm) (ethanol)

HSEH1PBE 6e311 þ þG(d,p) l Osc. (nm) (gas) Strength

HSEH1PBE 6e311 þ þG(d,p) l (nm) (ethanol)

Osc. Strength

Major contributions

732.74

729.17

0.0001

711.55

0.0001

641.80

589.92

0.0143

515.70

0.0010

608.49 292.76

537.73 415.09

0.0013 0.0245

440.76 351.59

0.0441 0.0562

261.64

399.02

0.0211

312.85

0.0408

H1 / L þ 3(þ51%) H2 / L þ 5(þ28%) H / L( þ 56%) H2 / L þ 2(þ49%) H-5 / L( þ 64%)

226.50

352.60

0.0232

304.81

0.0322

217.02

346.90

0.0022

295.42

0.0025

H2 / L þ 3(22%) H1 / L þ 5(26%) H / L þ 2(13%) H / L þ 2(þ14%)

H1 / L þ 2(þ11%) H / L þ 5(14%) H-2 / L( þ 12%) H-2 / L(12%)

HH / L þ 3(þ6%) 3 / L þ 3(þ7%) H-6 / L(83%) H4 / L þ 1(þ11%) HH3 / L þ 1(þ77%) 4 / L þ 1(þ8%)

H: HOMO; L: LUMO.

4.5. NLO properties

Fig. 4. The measured UVevis spectrum for Mn (II) complex.

with anti-lone-pair (n*) of metal orbital. The delocalization effects due to nen* interactions in [Mn(tda)(phen)] complex play a highly important role on the coordination environments of the Mn (II) ion. The possible intensive interactions for Mn(II) complex are given in Table 4. As concluded from the calculated NBO results, the strongest stabilization energies within Mn (II) complex are calculated at the lone pair of nitrogen, oxygen and sulfur and anti-lone pair of manganese (II) atom. For example, the most important interaction energy, related to the resonance in the Mn (II) complex is calculated between the LP(1) N35 and LP*(4) Mn14, which leads to a strong stabilization energies of 1658.50 kcal/mol. The interactions p(C15eC18) / p*(C16eN36) and p(C19eC23) / p*(C16eN36) designate the conjugation of respective p-bonds in phen ring due to high electron density at the conjugated p bonds (1.57282 and 1.68339) and low electron density at p* bonds (0.35570e0.35570) and stabilized the complex with 14.39 and 79.16 kcal/mol, respectively. The strong hyperconjugative interactions between the bonding orbitals (C1eC2, C2eN6 C3eN6, C3eC7 and C2eC8) in tda and anti-lone pair orbitals of manganese (II) ion leads the stabilization of Mn (II) complex with the range of 129.64 and 724.97 kcal/ mol stabilization energy. The charge transfer interactions are formed by the orbital overlap between bonding (p) and antibonding (p*) orbitals, which results in intramolecular charge transfer (ICT) causing stabilization of the system. The large hyperconjugative interaction energies display the presence of ICT and may be responsible for the excellent NLO properties of Mn (II) complex.

NLO is at the forefront of current research due to its importance in providing key functions of frequency shifting, optical modulation, switching, laser, fiber optical materials logic and optical memory for the emerging technologies in areas such as telecommunications, signal processing, and optical inter connections [46e48]. Importance of polarizability and first- and second-order hyperpolarizabilities of molecular systems depend on the efficiency of electronic communication between acceptor and donor groups playing a key role in determining the intramolecular charge. It is well known that the second hyperpolarizability (g) for the investigation of third-order nonlinear optical properties is one of the important parameters, g has three contributions, such as electronic (ge), vibrational (gv) and orientational (gorient) or dipolar rotational contributions. Lately, it was determined that the orientational contribution gorient of a molecule, which is one of major contributions of Y obtained by degenerate four-wave mixing (DFWM) measurement [49,50], can be related to the anisotropy of the polarizability (Da) according to the Prasad's equation [51]. In present work, we have performed the calculations of average secondorder hyperpolarizabilities using the following equations with respect to the Kleinman symmetry [52].

¼


 1 þ gyyyy þ gzzzz þ 2 gxxyy þ gxxzz þ gyyzz g 5 xxxx

The higher values of dipole moment, molecular polarizability, and hyperpolarizabilities are important for more active NLO properties. The first-order hyperpolarizability (b), the mean second-order hyperpolarizability (g) and related properties (m, a and Da) for Mn (II) complex is calculated with HSEH1PBE level. Obtained results are tabulated in Table 5. The values of polarizability and first-order hyperpolarizability are reported in atomic units (a.u), the calculated values have been converted into electrostatic units (esu) (for a; 1 a.u ¼ 0.1482  1024 esu, for b; 1 a.u ¼ 8.6393  1033 esu) [53,54]. The C]O, C]N and C]C stretching vibrations were found to be strong and simultaneously active in IR and Raman spectra. Therefore, the stretching vibration modes of Mn (II) complex clearly demonstrate the charge transfer interactions providing more active NLO properties for the complex. The results for second- and thirdorder nonlinearities of Mn(II) complex can be used to provide a deep understanding in the origin of the nonlinearities and lead to prediction of hyperpolarizabilities for new materials, such as inorganic, organic and organometallic, etc. In Mn (II) complex, dipole

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119

117

Fig. 5. The occupied and unoccupied molecular orbitals and energies for Mn (II) complex.

Table 4 Second eorder perturbation theory analysis of Fock matrix on NBO basis for [Mn(tda)(phen)] complex (obtained from HSEH1PBE level). Donor

Type

ED(i) (e)

Acceptor

C1eC2 C2eN6 C3eN6 C2eC8 C3eC7 C3eC7 N6eMn14 N6eMn14 C7eO10 C7eO10 C7eO12 C8eO9 C15eC18 C17eN35 C19eC23 C22eC26 LP(1) S4 LP(1) O9 LP(1) O9 LP(1) O10 LP(1) O11 LP(3) O12 LP(2) O12 LP(5) Mn14 LP(1) N6 LP(1) N35 LP(1) N36

s s s s s s s s p p s p p s p s

1.97198 1.96764 1.98056 1.97270 1.97036 1.97036 1.93553 1.93553 1.98831 1.98831 1.98609 1.98755 1.57282 1.92290 1.68339 1.97877 1.98646 1.97932 1.97932 1.97852 1.93743 1.63547 1.70950 0.25658 1.63166 1.69986 1.67870

LP*(5) Mn14 LP*(5) Mn14 LP*(5) Mn14 LP*(5) Mn14 LP*(4) Mn14 LP*(5) Mn14 C8eO9 C7eO10 C17eC21 LP*(4) Mn14 LP*(4) Mn14 C8eO9 C16eN36 LP*(5) Mn14 C16eeN36 C27eN35 LP*(5) Mn14 C27eC30 LP*(5) Mn14 LP*(5) Mn14 LP*(5) Mn14 LP*(5) Mn14 C7eO10 N6eMn14 LP*(3) Mn14 LP*(4) Mn14 LP*(3) Mn14

Type

p* s* p* p* p* p* s* s*

p* s*

ED (i) (e)

E(2)a (kcal/mol)

E(j)-E(i)b (a.u)

F(i,j)c (a.u)

0.25658 0.25658 0.25658 0.25658 0.42532 0.25658 0.25880 0.21640 0.39853 0.42532 0.42532 0.25880 0.35570 0.25658 0.35570 0.02233 0.25658 0.01971 0.25658 0.25658 0.25658 0.25658 0.21640 0.21424 0.60885 0.42532 0.60885

710.51 351.81 129.64 300.82 437.30 724.97 29.45 3.64 381.60 179.52 245.53 38.69 14.39 301.19 79.16 74.27 325.58 418.89 6.06 21.68 315.33 108.61 23.42 46.22 79.79 1658.50 71.94

0.27 0.29 0.31 0.14 0.31 0.37 0.52 1.17 0.03 0.12 2.73 0.78 0.25 1.14 0.08 3.87 0.78 0.02 0.27 0.26 0.10 0.06 0.43 0.39 0.24 0.08 0.29

0.414 0.300 0.129 0.192 0.367 0.489 0.117 0.059 0.180 0.145 0.821 0.166 0.055 0.548 0.070 0.479 0.480 0.071 0.038 0.074 0.168 0.072 0.091 0.246 0.132 0.331 0.139

ED ¼ electron density; a E(2) means energy of hyperconjugative interaction (stabilization energy); b Energy difference between donor and acceptor i and j NBO orbitals; c F(i,j) is the Fock matrix element between i and j NBO orbitals.

moment, polarizability and hyperpolarizabilities are calculated as 12.376 D, 43.913  1024 esu, 41.689  1030 esu and 121.06  1036 esu by using HSEH1PBE/6e311þþG(d,p) level. When the obtained results for Mn (II) complex are compared with

those of pNA which is a typical NLO material [55,56], the hyperpolarizability values for Mn (II) complex are 2.69 and 8.07 times higher than pNA molecule. These remarkable NLO properties of Mn (II) complex may be originated from the position of carboxylic

118

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119 Table 5 Total static dipol moment (m, in Debye), the mean polarizability (hai, in 1024 esu), the anisotropy of the polarizability (Da, in 1024 esu), the mean first-order hyperpolarizability (hbi, in 1030 esu), the mean second-order hyperpolarizability (hgi, in 1036 esu) for [Mn(tda)(phen)] complex. Property

HSEH1PBE-6-311 þ þG(d,p)

mx my mz m m axx ayy azz hai Da hai bx by bz hbi hbi gxxxx gyyyy gzzzz gxxyy gxxzz gyyzz hgi g

12.058 1.337 2.448 12.376 2.44a 58.356 44.724 28.659 43.913 25.747 22b 41.446 2.3915 3.8109 41.689 15.5c 357.157 42.6501 22.5022 58.8687 22.2628 10.3729 121.06 15d

a,b,c,d

pNA results taken from Refs. [55,56].

groups located at opposite sides of tda, nature of manganese (II) ion and the small HOMO-LUMO energy gap. Consequently, Mn (II) complex displays significant polarizability and hyperpolarizabilities parameters, and is an excellent candidate for NLO material. 4.6. Molecular surfaces The molecular electrostatic potential (MEP) surface is a method of mapping electrostatic potential onto the iso-electron density surface. MEP simultaneously displays molecular size, shape and electrostatic potential regions in terms of color grading and is very useful tool in the research of correlation between molecular

structure and the physiochemical property relationship of molecules including bio molecules and drugs [57e62]. The color scheme for the MEP surface is as follows: red for electron rich, partially negative charge; blue for electron deficient, partially positive charge; light blue for slightly electron deficient region; yellow for slightly electron rich region; green for neutral (zero potential); respectively [63]. As can be seen from MEP of Mn (II) complex (see in Fig. 6), which regions having the negative potential are over the electronegative atoms, and regions of negative electrostatic potential (ESP) are usually associated with the lone pair of electronegative atoms. The most negative potential is over the carboxylic groups, while the most positive regions are over the hydrogen atoms. Sulfur atom surrounded by yellow color has the negative potential, and the other carbon atom seem to have zero potential. From MEP and ESP surfaces given in Fig. 6, the most reactive sides are carboxylic groups which located the opposite sides of thiazole ring.

5. Conclusions The novel [Mn(tda)(phen)] complex was synthesized, and its structure was investigated via FT-IR, FT-Raman and UVevis spectroscopies. The optimized molecular structure of Mn (II) complex was also obtained at HSEH1PBE/6e311þþG(d,p) basis set. Additionally, the calculations of vibrational frequencies and electronic absorption wavelengths were also calculated at the same level. The frequency intervals between the symmetric and asymmetric C]O stretching vibrations demonstrate that carboxylic groups coordinate to manganese (II) ion as a mono-dentate ligand, hence tda coordinates to manganese (II) ion as an tri-dentate ligand. Additionally, the C]O, C]C and C]N stretching vibrations found as strong and very active in IR and Raman spectra induce the intramolecular charge transfer (ICT) and provide more active NLO properties for Mn (II) complex. Obtained small HOMO-LUMO energy gap also displays that Mn (II) complex can be easily polarized and exhibit considerable NLO properties. The coordination environment of manganese (II) ion was investigated by NBO analysis, and the penta-coordination through the nitrogen and oxygen atoms were proved at HSEH1PBE level. The polarizability and hyperpolarizabilities parameters of Mn (II) indicate that the complex under investigation is an excellent candidate for NLO material.

Fig. 6. a) Molecular electrostatic potential (MEP) and b) Electrostatic potential (ESP) surfaces for Mn (II) complex.

S. Altürk et al. / Journal of Organometallic Chemistry 797 (2015) 110e119

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