Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 35–45
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1-Pentamethylbenzyl-3-nbuthylbenzimidazolesilver(I)bromide complex: Synthesis, characterization and DFT calculations _ Kani c, Yusuf Atalay b, Bekir Çetinkaya d Ahmet Kunduracıog˘lu a, Ömer Tamer b, Davut Avcı b,⇑, Ibrahim a
Pamukkale University, Tavas Vocational College, 20225 Tavas, Denizli, Turkey Sakarya University, Art and Science Faculty, Department of Physics, 54140 Sakarya, Turkey c Anadolu University, Faculty of Science, Department of Chemistry, 26470 Eskisßehir, Turkey d Ege University, Faculty of Science, Department of Chemistry, 35100 Bornova, Izmir, Turkey b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The novel silver(I) complex of
The electrostatic potential, contour plots of HOMO, LUMO and ESP for silver(I) NHC complex.
1-pentamethylbenzyl-3n buthylbenzimidazolesilver(I) bromide was synthesized. The title complex was solved by X-ray diffraction, FT-IR, UV–vis and NMR spectroscopies. To obtain further information, DFT calculations were performed on silver(I) complex. The NLO, NBO and HOMO–LUMO analysis were carried out on silver(I) complex. DFT levels successfully predict the different properties of silver(I) complex.
a r t i c l e
i n f o
Article history: Received 26 September 2013 Received in revised form 9 October 2013 Accepted 17 October 2013 Available online 26 October 2013 Keywords: X-ray structure determination FT-IR DFT and PBE1PBE calculations NLO properties HOMO–LUMO analysis Silver(I) NHC complex
a b s t r a c t A novel NHC complex of silver(I) ion, 1-pentamethylbenzyl-3-nbuthylbenzimidazolesilver(I)bromide, was prepared and fully characterized by single crystal X-ray structure determination. FT-IR, NMR and UV–vis spectroscopies were employed to investigate the electronic transition behaviors of the complex. Additionally, the molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) 1H and 13C chemical shift and electronic transition values of silver(I) complex were calculated by using density functional theory levels (B3LYP and PBE1PBE) with LANL2DZ basis set. Also, the vibrational frequencies were supported on the basis of the potential energy distribution (PED) analysis calculated for PBE1PBE level. We were also investigated total static dipole moment (l), the mean polarizability (hai), the anisotropy of the polarizability (Da), the mean first-order hyperpolarizability (hbi) of the title complex. Natural bond orbital (NBO) analysis was performed to determine the presence of hyperconjugative interactions, and charge distributions. Ó 2013 Elsevier B.V. All rights reserved.
Introduction The legendary journey of NHC salts and their transition metal complexes started in 1968. Öfele [1] and Wanzlick and ⇑ Corresponding author. Tel.: +90 264 295 6097; fax: +90 264 295 5950. E-mail address:
[email protected] (D. Avcı). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.10.075
Schönherr [2] reported the synthesis of the first chromium and mercury NHC complexes uninformed from each other. In 1991, Arduengo et al. [3] isolated the first silver(I) NHC complex. Due to their better sigma donor ability, NHCs have attracted a rising interest from the pioneers of organometallic chemistry world. During the past decades N-heterocyclic carbenes (NHCs) have emerged as a versatile class of dative ligands in metal
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coordination chemistry, particularly in the field of homogeneous catalysis [4,5]. The metalANHC complexes exhibit excellent catalytic activity for many practically useful organic transformations, notably the CAC and CAN cross coupling reactions [6–9], CAH bond activation [10–11] as well as the extremely useful metathesis reaction [12,13]. Among the NHCAmetal complexes, AgANHC complexes have been utilized for several purposes. Because of their facilitation of ‘‘fine tuning’’, transition metalANHC complexes have been widely studied for their catalytic activity [14]. The NHC complexes of coinage metals are concessive compounds with their antitumor activity besides being good catalysis. But their costs shadowed the charm. As an affordable alternative to other coinage metals such as platinum and gold, silver has seemed to be a suitable metal to form complexes of NHCs for industrial demands. SilverANHCs were studied for their antimicrobial activity by Youngs and his co-workers in 2004 [15]. For a long term of study, most researchers synthesized these complexes for mainly two purposes; for transmetallation and for antimicrobial activity. But recently silverANHCs have given rise to an untouched field of study with their antitumor activity [16] and catalytic activity [17]. Quantum chemical calculation is one of the recent emerging tools in unraveling physical and chemical properties of molecules. The availability of software packages makes the quantum chemical computation is a simple task. The molecular structure, harmonic force fields, vibrational wavenumbers, electronic transitions as well as IR intensities and Raman activities of organic molecules have been investigated by using density functional theory (DFT) computations. In our ongoing research, we have recently synthesized Ag(I) NHC complex, and a combined investigation of the geometrical parameters, fundamental frequencies, GIAO 1H and 13C NMR chemical shifts and electronic transitions of the silver(I) complex were experimentally investigated. In order to help to make further investigation on the properties of the complex, DFT calculations were performed. Since it meets with the requirements of being accurate, easy to use and fast enough to allow the study of relatively large molecules of transition metal complexes, density functional theory is frequently used to examine the electronic structure. It is well known that the comparison of the experimental and theoretical results is very important in modeling technology. And so, these calculations are valuable for providing insight into molecular analysis.
Table 1 Crystal data and structure refinement parameters for complex. Formula Formula weight (g) Temperature (K) Wavelength (Mo Å) Crystal system Space group
C23H28CuN2BrAg 520.25 296(2) 0.71073 Monoclinic P21/c
Unit cell dimensions a (Å) b (Å) c (Å) b (°) Volume (Å3) Z Calculated density (g cm3) Absorption coefficient (mm1) F(0, 0, 0) Crystal size (mm) h ranges (°)
10.519(2) 15.069(3) 13.819(3) 97.427(10) 2172.0(8) 4.00 1.591 2.777 1048.0 0.54 0.29 0.16 1.95–28.49
Index ranges
14 < h < 13 20 < k < 17 15 < l < 18
Reflections collected/unique Completeness to theta Absorption correction Refinement method Data/restrains/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Largest diff. peak and hole (e Å3)
24976/5358 [R(int) = 0.0545] 28.41 99.4% Integration Full-matrix least-squares on F2 5358/0/232 1.108 R1 = 0.0505, wR2 = 0.1392 R1 = 0.0671, wR2 = 0.1468 3.486 and 2.112
Routine UV–vis spectra were obtained in a quartz cuvette on an Agilent 8453 UV–vis spectrophotometer. Synthesis NHC salt and corresponding silver complex have been synthesized in high yields via the conventional methods in our laboratory. The chemicals such as benzimidazole, 1-bromobutane and pentamethylbenzene were acquired from suppliers and used without further purification. Pentamethylbenzylbromide and other intermediate products were synthesized according to the methods in literatures [22,23]. Silver complex was synthesized via Ag2CO3 as silver base in a 50 mL schlenk tube and reaction was monitored by disappearing of the insoluble solid particles in reaction mixture. The stages of synthesis are given in Fig. 1.
Materials and methods Computational details General remarks Diffraction data for the complex were collected with Bruker AXS APEX CCD diffractometer equipped with a rotation anode at 296(2) K using graphite monocromated Mo Ka radiation (k = 0.71073 Å). Diffraction data were collected over the full sphere and were corrected for absorption. The data reduction was performed with the Bruker SMART [18] program package. For further crystal and data collection details see Table 1. Structure solution was found with the SHELXS-97 [19] package using the directmethods and was refined SHELXL-97 [20] against F2 using first isotropic and later anisotropic thermal parameters for all nonhydrogen atoms. Hydrogen atoms were added to the structure model on calculated positions. Geometric calculations were performed with Platon [21]. FT-IR was recorded on SHIMADZU IR-PRESTIGE-2 spectrophotometer. 1H and 13C NMR spectra were measured in dimethyl sulfoxide-d6 (DMSO-d6) on spectrometer at VARIAN Infinity Plus 300 and at 75 MHz, respectively. 1H and 13C chemical shifts are referenced to the internal deuterated solvent.
All calculations were performed by using GAUSSIAN 09 package program [24], and the obtained results were visualized with the aid of Gauss View-5 software [25]. The structural properties and vibration spectra of the silver(I) NHC complex were determined through the application of DFT/B3LYP [26,27] and DFT/PBE1PBE [28] with LANL2DZ basis set [29–31]. B3LYP is the Becke’s three-parameter hybrid model using the Lee–Yang Parr correlation functional. PBE1PBE is the generalized-gradient-approximation exchange– correlation functional of Perdew, Burke, and Ernzerhof. The LANL2DZ effective core potential basis set was used for all of the calculations. The LANL2DZ basis replaces the 1s through 2p electrons of the heavy atoms with a potential field for a considerable computational savings. Moreover, the assignments of vibrational modes of the silver(I) complex were performed on the basis of potential energy distribution (PED) by using VEDA 4 program [32,33]. 1 H NMR and 13C NMR chemical shifts are calculated within GIAO approach [34,35] which is one of the most common approaches for calculating nuclear magnetic shielding tensor. The electronic
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Fig. 1. Synthesis of 1-pentamethylbenzyl-3-nbuthylbenzimidazole silver(I)bromide complex.
Fig. 2. (a) The experimental structure of the silver(I) NHC crystal and the atoms numbering scheme. (b) The calculated geometric structure of the silver(I) NHC complex (PBE1PBE/LANL2DZ).
properties, such as HOMO–LUMO energies, absorption wavelengths, and oscillator strengths were calculated using the TD-DFT [36,37] based on the optimized structures. Additionally, various non-linear optical properties, the electric dipole moment (l), the mean polarizability (hai), the anisotropy of the polarizability (Da), and the total first static hyperpolarizability (hbi) were computed. Natural bonding orbital (NBO) analysis was carried out to investigation of intra- and intermolecular bonding and interaction among bonds and conjugative interactions or charge transfer in silver(I)ANHC. Molecular electrostatic potential (MEP)
surface as well as the Mulliken, APT (atomic polar tensor) and NBO charges were predicated by using the same levels.
Results and discussion Structural characterization and geometry optimization The atomic numbering scheme of title complex and the optimized structure calculated with PBE1PBE level were given in
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Table 2 Selected structural parameters by X-ray and theoretical calculations for silver(I) NHC complex. Parameters
X-ray
Theoretical B3LYP/LANL2DZ
PBE1PBE/LANL2DZ
Bond lengths (Å) C1AC2 C2AC3 C3AC4 C3AC5 C5AC6 C5AC7 C7AC8 C7AC9 C9AC10 C9AC11 C11AC2 C1AN1 N1AC13 C13AN2 N2AC19 N1AC14 C14AC19 C14AC15 C15AC16 C16AC17 C17AC18 C18AC19 C13AAg1 Ag1ABr2 N2AC20 C20AC21 C21AC22 C22AC23
1.524(6) 1.396(6) 1.508(7) 1.397(6) 1.513(7) 1.409(8) 1.498 (7) 1.389(7) 1.505(7) 1.409 (7) 1.512(7) 1.463(6) 1.357(6) 1.356(6) 1.387(6) 1.383(6) 1.402(6) 1.383(7) 1.383(7) 1.399(8) 1.382(7) 1.387(7) 2.078(5) 2.431(8) 1.468(7) 1.492(8) 1.338(8) 1.544(8)
1.526 1.419 1.524 1.420 1.525 1.421 1.525 1.421 1.525 1.419 1.421 1.491 1.378 1.375 1.409 1.413 1.416 1.406 1.404 1.418 1.404 1.404 2.130 2.525 1.475 1.543 1.544 1.542
1.517 1.413 1.515 1.414 1.516 1.416 1.515 1.415 1.516 1.413 1.415 1.477 1.371 1.369 1.401 1.405 1.410 1.401 1.399 1.413 1.398 1.399 2.108 2.502 1.464 1.533 1.534 1.533
Bond angles (°) N1AC1AC2 C1AN1AC13 N1AC13AAg1 C13AAg1ABr2 Ag1AC13AN2 C13AN2AC20 N1AC14AC5 N2AC19AC18
112.6(4) 125.4(4) 126.5(3) 178.2(12) 127.4(3) 123.3(4) 106.3(4) 132.8(4)
115.26 122.67 127.89 178.88 125.93 124.32 133.11 131.80
114.78 122.70 127.76 178.16 126.12 124.15 133.03 131.23
Fig. 2a and b, respectively. The crystal structure of the silver(I) NHC is monoclinic and space group is C21/n. The crystal structure parameters of the silver(I) NHC are a = 10.519(2) Å, b = 15.069(3) Å, c = 13.819(3) Å, b = 97.427(10) and V = 2172.02(8) Å3 (see in Table 1). The optimized parameters of the silver(I) NHC were calculated through the application of B3LYP and PBE1PBE methods with LANL2DZ basis sets. These parameters were summarized in Table 2, and compared with the X-ray data of silver(I) NHC. Additionally, the crystal packing of the title complex has been shown in Fig. 3. The bond lengths between the N and C atoms on the benzimidazole ligand were defined by the bond lengths of 1.357(6) Å (N1AC13), 1.356(6) Å (C13AN2), 1.387(5) Å (N2AC19) and 1.383(5) Å (N1AC14). These bond lengths were calculated as 1.378–1.371 Å, 1.375–1.369 Å, 1.409–1.401 Å and 1.413–1.405 Å for B3LYP–PBE1PBE levels, respectively. In the case of free benzene, i.e. without substituent, the carbonAcarbon bond lengths in benzene ring are almost equal to each other. The bond lengths between the C atoms of the benzene ring fall in the range of 1.388(6) and 1.409(6) Å experimentally. The same bond lengths fall in the range of 1.419–1.421 Å for B3LYP and 1.413–1.416 Å for PBE1PBE level. Accordingly, it was demonstrated that there are different CAC bond lengths due to the substitution of benzene ring. The N1AC1 and N2AC20 bonds lengths were defined as 1.463(6) Å and 1.468(7) Å. In DFT calculations, the N1AC1 and N2AC20 bonds lengths were calculated as 1.491–1.475 Å for B3LYP level and 1.477–1.464 Å for PBE1PBE level. The experimental Ag1ABr2 and C13AAg1 bonds
Fig. 3. A view of packing diagram of the silver(I) NHC complex.
were observed by the bond lengths of 2.431(8) Å and 2.078(5) Å. These data were consistent with those of the known silverANHC complexes having CAAgAX motif [38,39]. In theoretical calculations, these bond lengths calculated as 2.525–2.130 Å for B3LYP level and 2.502–2.108 Å for PBE1PBE. From Table 2, Br2AAg1AC13 bond angle is observed 178.16(12)° which is almost linear. This bond angle is calculated 178.88° and 178.16° by using the B3LYP and PBE1PBE levels, respectively. The bond angles between benzimidazole and the substituents were defined as 112.7 (4)° (N1AC1AC2), 125.4(4)° (C1AN1AC13), 123.3(4)(5)° (C13AN2 AC20), 106.3(4)° (N1AC14AC19), and 132.8(4)° (N2AC19AC18). These bond angles were found 115.26–114.78°, 122.67–122.70°, 124.32–124.15°, 133.11–133.03° and 131.80–131.23 for B3LYP– PBE1PBE, respectively. Therefore, there is a good agreement between the X-ray and theoretical bond angles. As for the bond lengths, most of the optimized bond lengths are slightly longer than experimental values. It should be noted that theoretical calculations refer to the equilibrium structure of isolated molecule in gas phase and the experimental results belong to another similar molecule in condensed phase. Additionally, the CAH bond lengths are not discussed here since these bond lengths are in general difficult to determine experimentally, which is reflected by large uncertainty of XRD values. To determine the most stable energy conformation of the silver(I) NHC complex, complex conformational analysis was performed by using DFT methods. In this PES scan process, the potential energy surface was built by varying the N1AC1AC2AC3 and C19AN2AC20AC21 dihedral angles from 0° to 360° in every 10°, while all of the other geometrical parameters have been simultaneously relaxed. The potential energy surface (PES) scans along with the minimum energy conformers for these dihedral angles are presented in Fig. S1 (Supplementary information). As can be seen from Fig. S1 (Supplementary material), both conformers are of local minima near the 180° with energy values of 0.0456242 Hartree for conformer 1 and 0.0193934 Hartree for conformer 2.
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The maximum energies are obtained 0.0651824 and 0.0542477 Hartree for conformers 1 and 2, respectively.
Assignments of the vibration modes The aim of the vibrational analysis is to find vibrational modes connected with molecular structure of silver(I) NHC complex. The numerical harmonic vibrational analysis was performed based on the optimized geometry, and the absence of the imaginary frequencies, as well as of negative eigenvalues of the second-derivative matrix, confirmed that the stationary points correspond to minima of the potential energy surfaces. It is well known that the frequency values computed at quantum chemical methods such as DFT and Hartree–Fock method contain well-known systematic errors. So, the scaling factor values of 0.96 for B3LYP/ LANL2DZ and PBE1PBE/LANL2DZ methods were used in order to correct anharmonicity and neglected part of electron correlation, respectively [40]. The FT-IR and theoretical infrared spectra of the silver(I) NHC are shown in Fig. 4, where calculated intensity was plotted against the wavenumbers. The observed and calculated wavenumbers along with their relative intensities and probability assignments with PED of the silver(I) NHC were presented in Table 3. Calculated IR and Raman intensities help us to distinguish and more precisely assign fundamental vibration modes which are close in frequency. Due to the decrease of dipole moment caused by the reduction of negative charge on the carbon atoms, the CAH stretching frequencies exist as a multiplicity of weak to moderate bands compared with the aliphatic CAH stretch. In aromatic compounds, the CAH stretching, CAH in-plane and CAH out-of-plane bending modes are appearing in the range of 3000–3100 cm1, 1000– 1300 cm1 and 750–1000 cm1, respectively [41,42]. In this study, aromatic CAH stretching vibrations were observed at the range of 3097–3045 cm1 for PBE1PBE level. According to PED, these modes were quite pure modes with 88–99% contribution of PED. The vibration peak observed at 3024 cm1 was designated as methyl group which bound to benzene ring stretching vibration. This mode was theoretically calculated at the wavenumber region of 3067 and 3083 cm1 as pure modes. The asymmetric CAH stretching vibration of CH3 group (on tail side) observed at 2960 cm1 was calculated at 3024 cm1 with 96% contribution of PED. As for the symmetric one, this mode was observed at 2870 cm1, and calculated at 2936 cm1. The asymmetric CH3 vibrations of ring methyl were observed 2906 cm1, and this mode
Fig. 4. Experimental and theoretical IR spectra of silver(I) NHC complex.
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was calculated at the range of 2941–2947 cm1. The scissoring vibrations of methyl groups bounded to the ring observed at 1494 cm1 was calculated at the range of 1505 and 143 cm1. The CAH scissoring vibrations of aliphatic group were calculated at 1479 and 1474 cm1. The CAC stretching vibrations were observed at 1602, 1570, 1411, 1285, 1199 and 1062 cm1, as would be expected [43]. The corresponding peaks were calculated at 1629, 1590, 1447, 1324, 1256 and 1062 cm1 by using PBE1PBE level. The vibration peaks at 1199 and 950 cm1 were originated from the in-plane CAC bending vibrations b(CCC). These peaks were calculated at 1256 and 1005 cm1 with 34% and 52% contribution of PED, respectively. The NAC stretching vibrations were observed at 1330, 1328 and 1147 cm1. This vibration peak was calculated at the range of 1421 and 1213 cm1 as modes coupled with the b HCC vibrations. It is observed that the peak at 783 cm1 was originated from AgAC stretching vibration, and this peak was theoretically assigned at 789 cm1. The calculated wavenumbers are generally higher than corresponding experimental values thanks to the electron correlation effect. Additionally, it should be noted that experimental results belong to solid phase while theoretical calculations belong to a gas phase. Assignments of chemical shifts Experimental measurements and theoretical calculations on NMR chemical shift become one of the key factors in the determination and design of molecular structures. DFT calculations of NMR chemical shift are quite useful both for understanding the relationship between the molecular structure and electronic properties of molecules. It also provides a guideline to experimentalists for the design and synthesis of organic materials [44]. Table 4 presents the experimental and theoretical 1H and 13C chemical shift values of the silver(I) NHC complex. The chemical shifts of aromatic protons of organic molecules are usually observed in the range of 7.00–8.00 ppm, while aliphatic protons resonance in the high field [45]. From our experimental data, H15, H16, H17 and H18 protons resonance in the range of 7.45–7.91 ppm, while these signals were theoretically calculated in the range of 7.261–7.699 ppm for PBE1PBE and 7.349–7.715 ppm for B3LYP level. The methyl protons substituted to benzene ring resonance at 2.06 ppm, as consistent with the literature [46]. In the calculations, these protons were assigned at the range of 1.546–2.764 ppm for PBE1PBE and 1.695– 2.707 ppm for B3LYP level. The chemical shift values of the H1A, H1B, H20A and H20B which are the closest to nitrogen atoms were observed in more downfield than other proton signals because of the electronegativity of nitrogen atom. Other aliphatic CH2 group signals appear in the range of 1.12–1.74 ppm, while CH3 group signals appear at 0.78 ppm. It is well known that the aromatic carbon signals fall at the range from 100 to 150 ppm in organic molecules [47,48]. In this paper, the chemical shift values of C atoms belong to rings [C2, C3, C5, C7, C9, C11, C14, C15, C16, C17, C18 and C19] resonance in the range of 118.655–124.925 ppm. Similarly, theoretical data concerning these carbons were calculated at the range of 112.725–139.490 ppm for PBE1PBE level and 113.734– 141.716 ppm for B3LYP level. The signal of C13 atom which bound to both N and Ag atoms was not observed, but this signal was calculated at 200.527 and 204.237 ppm for PBE1PBE and B3LYP levels, respectively. This shift to low field is originated from electronegative nature of N atoms. As for the aliphatic carbons, these carbons gave peaks at the range of 14.164–47.243 ppm. As can be seen from Table 4, C1 signal was larger than other aliphatic carbon signals due to the N atom. This difference was also proved by DFT calculations.
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Table 3 Comparison of the FT-IR and calculated vibration frequencies of silver(I) NHC complex. Assignments with PBE1PBE/LANL2DZ (PED%)a
FT-IR
Theoretical PBE1PBE/LANL2DZ
tas CH (93) (ring) tas CH (96) (ring) ts CH (88) (ring) ts CH (99) (ring) tas CH3 (79) (ring) tas CH3 (84) (ring) tasCH3 (78) (ring) tas CH3 (80) (ring) tas CH3 (88) (ring) tas CH2 (97) tas CH2 (87) tas CH3 (96) tas CH3 (93) tas CH3 (96) tas CH (89) tas CH (96) tas CH (88) tas CH (78) tas CH (93) tas CH (93) tas CH (88) tas CH (91) ts CH3 (76) (ring) ts CH3 (73) (ring) ts CH3 (80) (ring) ts CH3 (77) (ring) ts CH3 (84) (ring) ts CH2 (93) ts CH3 (91) t CC (66) b CNC (24) + b CCN (26) t CC (44) t CC (44) d HCH (48) (ring) d HCH (27) (ring) d HCH (29) (ring) d HCH (40) (ring) d HCH (45) (tail) d HCH (79) (tail) b HCH (52) b HCH (75) b HCH (56) b HCH (70) + s HCCC (14) b HCH (15) b HCH (64) b HCH (80) b HCH (53) b HCH (39) t CC (20) + b HCC (46) b HCH (53) t NC (10) + b HCC (32) b HCH (40) b HCH (53) b HCH (24) b HCH (17) b HCH (34) b HCH (65) b HCH (94) t NC (11) t CC (10) + s HCNC (12) t NC (22) + b HCC (12) + s HCNC (10) t NC (12) + s HCCC (15) t NC (15) + s HCCC (14) t NC (25) + b HCC (22) t CC (14) t CC (34) b HCC (48) + s HCCC (10) b HCC (27) b HCC (31) s HCCC (40) t CC (30) + b CCC (34)
3097
3045
3024
2960
2906
2870 1602 1570 1494
1477
1467
1450 1411 1396
1381 1350
1330
1328 1285
1260 1199
B3LYP/LANL2DZ
Scaled freq.b
IIRc
IRd
Scaled freq.b
IIRc
IRd
3153 3136 3122 3109 3083 3081 3078 3075 3067 3050 3042 3041 3035 3024 3017 3014 3012 3008 3005 2982 2981 2972 2947 2944 2943 2942 2941 2940 2936 1629 1612 1590 1507 1505 1494 1491 1483 1479 1474 1470 1469 1467 1464 1462 1461 1457 1456 1452 1447 1427 1421 1401 1399 1396 1393 1390 1389 1388 1387 1371 1364 1351 1343 1340 1325 1324 1298 1283 1278 1263 1256
6.270 13.565 10.736 1.296 0.759 15.391 40.014 19.867 17.159 10.096 56.256 41.803 30.267 14.839 16.659 13.866 19.554 21.335 13.281 7.787 4.202 35.974 28.705 35.323 21.024 23.608 31.402 24.852 37.710 30.179 7.208 0.209 4.751 5.593 5.163 27.497 33.371 27.023 8.026 18.538 7.442 25.571 2.338 4.292 1.854 11.154 38.937 11.238 1.080 13.268 3.162 0.712 20.498 28.975 19.207 24.531 15.522 36.074 1.906 26.171 84.265 22.736 67.451 14.455 9.010 0.317 20.708 17.346 0.015 6.518 0.935
160.127 150.650 87.988 39.556 34.343 62.749 46.240 37.336 87.971 49.088 62.115 39.971 37.743 58.582 60.209 61.554 71.184 61.065 2.262 215.299 84.497 102.366 76.460 311.838 186.265 187.494 111.002 188.439 121.356 50.313 12.873 34.032 48.013 4.773 2.248 1.125 4.365 0.799 8.382 8.734 1.255 9.605 12.780 24.492 22.358 15.459 17.032 8.485 7.387 5.674 1.184 1.031 24.944 20.561 0.983 15.635 23.651 11.713 6.588 9.561 123.014 52.562 10.674 7.191 10.075 37.536 7.522 14.874 30.207 14.447 0.900
3132 3106 3091 3077 3058 3055 3053 3050 3048 3033 3015 3005 3000 2991 2979 2978 2976 2975 2972 2950 2946 2921 2920 2918 2917 2916 2915 2914 2906 1593 1581 1560 1558 1504 1501 1490 1488 1480 1477 1474 1467 1464 1463 1460 1459 1458 1457 1452 1451 1448 1444 1400 1397 1393 1391 1388 1386 1383 1377 1362 1345 1338 1333 1313 1293 1286 1276 1273 1269 1260 1232
5.16 18.45 14.300 1.769 1.704 2.550 33.538 56.416 17.233 13.366 37.336 56.826 58.300 20.077 6.750 32.092 26.568 14.792 14.252 33.890 8.073 30.401 40.885 23.685 15.496 54.670 18.814 27.212 30.510 6.923 0.699 0.202 4.447 1.921 6.606 9.658 36.857 7.486 24.722 11.282 1.087 1.619 11.766 13.546 7.486 0.473 45.619 0.721 0.837 13.685 23.706 10.101 4.545 15.630 3.599 9.651 1.609 10.258 11.539 14.347 57.410 85.318 74.089 2.509 25.411 27.321 2.417 20.728 22.032 0.417 0.505
138.035 176.898 97.336 43.964 29.099 95.083 47.298 30.946 89.002 51.678 20.454 90.240 37.586 64.173 37.932 97.272 82.406 2.931 191.600 79.645 101.846 107.990 459.809 157.627 63.744 119.778 36.108 134.424 68.834 14.256 33.095 37.497 48.047 6.436 1.116 1.397 4.176 3.448 0.695 7.982 9.981 20.711 14.281 17.442 2.557 41.556 6.772 6.339 2.260 6.270 4.226 6.708 16.287 6.274 10.889 13.213 5.799 1.005 22.265 4.217 15.441 94.971 33.264 48.149 1.975 43.940 30.659 3.093 33.435 1.081 0.758
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Table 3 (continued) Assignments with PBE1PBE/LANL2DZ (PED%)a
FT-IR
Theoretical PBE1PBE/LANL2DZ
b HCC (26) t NC (14) + b HCC (17) b HCC (44) b HCC (13) b HCC (12) + b NCN (21) t CC (23) t CC (13) + s HCCC (15) t CC (32) t CC (36) + s HCCC (24) t CC (10) s HCCC (15) t CC (90) s HCCC (28) t CC (15) + s HCCC (15) t CC (15) s HCCC (36) t CC (30) + b CCC (12) s HCCC (58) + s CCCN (26) b CCC (52) b HCC (14) + s HCCC (16) s HCCC (93) b HCC (33) + s HCCC (12) t CC (42) + s HCCC (31) s HCCC (77) b CCN (11) b CNC (20) s HCCC (10) t AgC (42) s HCCC (39) + r CNCC (16) s HCCC (18) + s CNCN (10) + r CNCC (30) b HCC (28) + s HCCC (42) b NCN (10) + b CCN (11) s CNCN (15) s CNCN (13) r CCCC (35) s CCCN (34) b CCC (10) b CNC (10)
1147 1134
1062
1016
950 854
844 806 783 746
638 603 567
532
B3LYP/LANL2DZ
Scaled freq.b
IIRc
1251 1213 1198 1174 1148 1132 1118 1110 1093 1083 1074 1071 1065 1053 1047 1043 1036 1013 1005 983 974 956 948 929 900 864 863 789 779 772 762 760 756 732 712 639 587 563
2.613 0.39 6.623 14.194 1.453 0.872 7.370 4.304 14.079 1.910 2.716 6.631 0.234 14.312 0.848 0.354 15.030 1.227 12.278 0.210 0.094 0.298 0.446 1.515 1.533 24.887 5.295 11.838 11.564 6.658 6.502 7.864 60.853 28.710 9.593 0.520 0.448 6.128
IRd 17.592 1.971 64.651 11.768 3.298 20.860 4.971 9.502 6.015 1.314 3.783 1.751 11.160 1.976 0.096 0.795 1.195 5.281 28.426 0.415 0.863 3.769 2.599 0.593 4.393 5.373 14.779 7.484 2.619 6.089 5.792 1.050 2.139 2.847 1.090 3.249 0.502 2.160
Scaled freq.b
IIRc
1202 1180 1162 1133 1115 1102 1093 1064 1058 1055 1051 1043 1042 1032 1029 1015 1005 986 979 947 942 923 886 855 819 805 802 761 754 752 728 703 640 627 591 583 555 521
9.187 16.328 2.700 5.292 4.108 3.693 16.548 2.161 9.225 14.488 1.934 0.185 0.588 7.898 10.423 0.957 16.414 0.135 3.804 0.406 1.358 1.504 3.875 0.037 7.090 27.912 9.515 9.379 19.089 58.390 9.787 0.452 0.440 1.811 3.529 2.716 0.543 1.536
IRd 66.133 27.895 0.411 35.570 4.180 8.362 5.817 5.781 2.350 2.217 0.286 1.046 12.512 2.168 0.630 4.553 0.563 0.819 1.540 2.325 0.624 4.639 16.147 0.548 3.374 12.023 6.604 10.664 2.530 0.943 0.228 1.039 10.022 2.874 2.545 0.334 3.175 14.358
t: stretching; b: bending (in-plane); s: bending (out-of-plane); d: scissoring; r: deformation; PED analysis. a b c d
Vibrational modes are based on potential energy distribution (PED) and only contributions over 10% 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.
Frontier molecular orbitals and UV–vis spectra The frontier molecular orbital energies of the silver(I) complex was calculated with DFT/B3LYP and DFT/PBE1PBE methods with the LANL2DZ basis set. The patterns of the principle highest occupied (HOMO) and the lowest unoccupied molecular orbitals (LUMO) have been given in Fig. 5, while the HOMO and LUMO energies, electronegativity, chemical hardness and total energy for silver(I) complex have been tabulated in Table 5. LUMO as an electron acceptor represents the ability to obtain an electron, HOMO represents the ability to donate an electron. That is, while the energy of the HOMO is directly related to the ionization potential, LUMO energy is directly related to the electron affinity. Therefore these orbitals play an important role in the electric and optical properties as well as UV–vis spectra. The positive phase is symbolized with red1 while the negative phase is symbolized is green. The energy gap between the HOMO and LUMO orbitals is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. Additionally, this energy gap characterizes the molecular chemical stability and 1 For interpretation of color in Figs. 5 and 7, the reader is referred to the web version of this article.
chemical and spectroscopic properties of the molecules [49]. As can be seen Table 5, the energy gap of the silver(I) complex was calculated 2.327 eV for B3LYP and 2.325 eV for PBE1PBE method. In the title complex, HOMO orbitals were localized on mainly Br atom (89%) with contributions of Ag atom (7%), phenyl group (2%) and benzimidazole ring (%2). As for the LUMO orbitals, these orbitals were localized on benzimidazole ring (90%) with the contributions of phenyl group (4%), Ag (3%), CH2CH2CH2CH3 group (2%) and Br (1%). It was demonstrated that dAg orbitals play a significant role in the HOMO 2 (30%), HOMO 7 (38%), LUMO + 5 (39%) and LUMO + 6 (46%), while HOMO (89%), HOMO 1 (88%) and HOMO 2 (36%) were mainly formed by Br molecular orbitals. The p-bonding molecular orbitals of benzimidazole ligand play an important role in the HOMO 5 (90%), HOMO 6 (91%), LUMO (90%) and LUMO + 1 (84%). And finally, phenyl group has a significant role in the HOMO 3 (82%), HOMO 4 (87%), LUMO + 2 (63%) and LUMO + 4 (49%). CH2CH2CH2CH3 substituent does not play an important role in the formations of molecular orbitals. The electronegativity (v) and chemical hardness (g) can be calculated from the frontier molecular orbital energies [50]. For any two molecules, electron will be partially transferred from the one of low v to that of high v (electrons flow from high chemical potential to low chemical potential). Additionally, the more
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Table 4 Experimental and theoretical 13C and 1H isotropic chemical shifts (with respect to TMS, all values in ppm) for silver(I) NHC complex. Atom
Experimental (with DMSOd6)
PBE1PBE/ LANL2DZ
B3LYP/ LANL2DZ
H17 H16 H18 H15 H1A H2A H20A H20B H12A H12B H12C H10A H10B H10C H6A H6B H6C H8A H8B H8C H4A H4B H4C H21A H21B H22A H22B H23A H23B H23C
7.82–7.91 dt
7.699 7.489 7.489 7.261 5.907 5.584 4.533 3.866 2.764 2.555 2.495 2.672 2.364 2.364 2.632 2.230 2.205 2.271 2.269 2.096 2.495 2.205 1.546 2.077 1.913 1.786 1.423 1.297 1.183 0.963
7.715 7.531 7.468 7.349 5.902 5.563 4.570 3.887 2.707 2.565 2.507 2.616 2.359 2.332 2.372 2.279 2.260 2.506 2.883 2.270 2.678 2.257 1.695 2.186 2.018 1.864 1.501 1.309 1.239 1.025
200.527 139.490 138.871 136.778 136.569 136.569 135.817 132.008 128.045 128.105 116.451 112.725 58.04 55.760 36.126 23.726 23.667 22.779 21.589 21.589 20.392 17.192
204.237 141.716 141.15 139.525 139.755 138.922 138.979 134.421 128.99 129.083 117.309 113.734 61.332 59.084 38.895 26.412 24.929 23.971 22.962 22.910 21.918 18.372
C13 C3 C5 C11 C14 C9 C19 C2 C17 C16 C15 C18 C1 C20 C21 C22 C4 C8 C6 C10 C12 C23
7.45–7.48, m 5.49, s 4.22, t 2.06 s
2.06 s
2.06 s
2.06 s
2.06 s
1.65–1.74, m 1.12–1.21, m 0.78, t
– 124.925 133.641 124.638 133.511 133.641 133.511 136.123 112.764 112.764 118.655 118.655 47.243 – 32.647 20.029 17.665 17.528 17.467 17.467 17.665 14.164
HOMO–LUMO energy gap is low, the more charge transportation is prospective. The obtained v and g values were listed in Table 5. The theoretical electronic excitation energies, oscillator strengths and nature of the first 6 spin-allowed electronic transitions were calculated time-dependent DFT (TD-DFT) calculations on electronic absorption spectrum in vacuum were performed by using B3LYP and PBE1PBE methods with LANL2DZ basis set. Fig. 6 presents the experimental and theoretical UV–vis spectra of the title complex. The major contributions of the transitions were designated with the aid of SWizard program [51]. The experimental and calculated results of UV–vis spectral data were compared in Table 6. Each calculated transition is represented by a Gaussian function; 2
y ¼ c½expðbx Þ
with the height c equal to the oscillator strength and b equal to 0.04 nm2 [52–54]. The experimental bands observed at 270 nm and 260 nm are assigned predominantly p–p⁄ transitions. As can be seen from Table 6, these bands theoretically were calculated at 347–293 nm and 319–278 nm for B3LYP and PBE1PBE level, respectively. NLO properties Non-linear optical (NLO) effects are based on the interactions of electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristics from the incident fields [55]. A large number of publications reporting new NLO response formalisms have appeared in the recent literature because of its importance in providing the key functions of frequency shifting, optical modulation, optical switching, optical logic, and optical memory in areas such as telecommunications, signal processing, and optical interconnections [56]. In present study, the electronic dipole moment, molecular polarizability, anisotropy of polarizability and molecular first hyperpolarizability of present compound were investigated [57–59]. As can be seen Table 7, molecular polarizability (hai), anisotropy of polarizability (Da) and molecular first hyperpolarizabiliy (hbi) were calculated as 76.854 1024 esu, 8.085 1024 esu and 15.745 1030 esu for PBE1PBE method, while calculated as 78.312 1024 esu, 8.518 1024 esu and 17.886 1030 esu for B3LYP method, respectively. The typical NLO material, PNA [60,61] was chosen as a reference molecule because there were no experimental values about the title compound in the literature. When silver(I) complex is compared with the PNA molecule in terms of NLO properties, it can be seen that NLO properties that of silver(I) complex are quite remarkable. Molecular electrostatic potential (MESP) surfaces In the present study, 3D plot of molecular electrostatic potential (MEP) of silver(I) complex is illustrated in Fig. 7. It is well known that the molecular electrostatic potential surface which is a method of mapping electrostatic potential on the iso-electron density surface simultaneously displays electrostatic potential (electron + nuclei) distribution, molecular shape, size and dipole moments of the molecule and it provides a visual method to understand the relative polarity. The MEP is a useful tool to study reactivity given that an approaching electrophile will be attracted to negative regions (where the electron distribution effect is dominant). In the majority of the MESP, the maximum negative region which preferred site for electrophilic attack indications as red color, while the maximum positive region which preferred site for nucleophilic attack symptoms as blue color. The resulting surface simultaneously displays molecular size and shape and electrostatic potential value. The different values of the electrostatic potential at the surface are represented by different colors. Potential increases in the order red < orange < yellow < green < blue. The color code of these maps is in the range between 0.07288 a.u. (deepest red) and 0.07288 a.u. (deepest blue) in compound, where blue indicates the strongest attraction and red indicates the strongest repulsion. Regions of negative V(r) are usually associated with the lone pair of electronegative atoms. As can be seen from the MEP map of the title molecule, while regions having the negative potential are over the electronegative bromine atom, the regions having the positive potential are over the hydrogen atoms. According to Fig. 7, the MESP shows that the negative potential sites are on bromine atom as well as the positive potential sites are around the hydrogen atoms.
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Fig. 5. The frontier molecular orbital with energies of silver(I) NHC complex.
Table 5 The calculated total molecular energies, frontier molecular orbital energies, electronegativity (v) and hardness (g) of silver(I) NHC complex.
EHOMO (eV) ELUMO (eV) DE = ELUMO EHOMO (eV) I (eV) (EHOMO) A (eV) (ELUMO) v (eV) g (eV) ETOTAL (a.u.)
B3LYP/6-311++G(d,p)
PBE1PBE/6-311++G(d,p)
7.170 4.843 2.327 7.170 4.843 6.007 2.327 1162.903
7.176 4.851 2.325 7.176 4.851 6.014 2.325 1161.678
Fig. 6. The experimental and theoretical UV–vis spectra of silver(I) NHC complex.
NBO analysis and charge distributions The NBO analysis can be used to estimate delocalization of electron density between occupied Lewis-type orbitals and formally
unoccupied non-Lewis NBOs, which corresponds to a stabilizing donor–acceptor interaction [62]. The electronic configuration of Ag(I) ion in the title complex is [core]5s0.604d9.855p0.20, 35.99520 core electrons (mainly on 4s and 4p), 10.64878 valance electrons (on 5s, 5p and 4d) and 0.00593 Rydberg electrons (on 6s, 6p and 5d). This gives the total of 46.64991, which is consistent with the calculated natural charge [+0.35] on the Cu atom. The largest negative charges are located on the carbon atoms C4 (0.67 e), C6 (0.68 e), C8 (0.68 e), C10 (0.68 e) and C12 (0.69 e) which substituted to phenyl ring for silver(I) complex. The strong intramolecular hyperconjugative interaction of the r and p electrons of CAC to anti CAC bond of the ring leads to stabilization of some part of the ring as can be seen from Table 8. The intramolecular hyperconjugative interaction of r (C14AC19) distribute to r⁄ (C14AC15, C19AC18, C14AN1, C19AN2) leading to stabilization of the energies in the range of 0.32–3.48 kcal/mol. This reinforced additional conjugation with anti-bonding orbital of p⁄ (C18AC17) which leads to strong delocazation of 20.73 kcal/mol. The same kind of interaction has been calculated in the C11AC9 and C2AC3 bonds shown in Table 8. The magnitude of charges from lone pair nitrogen LP (N1) and LP (N2) show that stabilization energy of about 35 kcal/mol. This is an evidence that elongation as well as the weaking the bonds N1AC1 and N2AC20. Additionally, the delocalization of electron p⁄ (C14AC19) to p⁄ (C18AC17) and p⁄ (C16AC15) are of stabilization energies about 344 and 248 kcal/mol, respectively. The Mulliken, APT and NBO charges were calculated by using PBE1PBE level with the LANL2DZ basis set. The calculation of effective atomic charge plays an important role in the application of quantum mechanical calculations for the molecular system. The total charge distribution is very important parameters to investigate the electron-donating/withdrawing ability of group. Our interest here is in the comparison of Mulliken, APT and NBO charges to describe the electron distribution in silver(I) NHC complex as broadly as possible, and assess the sensitivity of the calculated charges. Comparative of Mulliken, NBO and APT plots using LANL2DZ basis set of title molecule are shown in Fig. S2
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Table 6 Theoretical and experimental electronic transitions and oscillator strength for silver(I) NHC complex. Exp. (nm)
k (nm)
Osc. strength
Major contributions
PBE1PBE/LANL2DZ 270 260
319.9 278.1
0.0615 0.0089
HOMO ? LUMO (92%) HOMO 2 ? LUMO (69%)
B3LYP/LANL2DZ 270 260
347.5 293.7
0.0501 0.0059
HOMO ? LUMO (93%) HOMO 2 ? LUMO (94%)
Table 7 Total static dipol moment (l, 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) for silver(I) NHC complex. Property
PBE1PBE/LANL2DZ
B3LYP/LANL2DZ
lx ly lz l l
7.146 8.349 0.5001 11.0015 2.44a
7.055 8.235 0.5549 10.8587
axx ayy azz hai Da hai
52.151 40.717 39.110 76.854 8.085 22b
52.288 41.241 39.905 78.312 8.518
bx by bz hbi hbi
7.739 10.411 8.923 15.745 15.5c
8.586 11.175 11.015 17.886
a,b,c
Table 8 Second-order perturbation theory analysis of Fock matrix on NBO basis for silver(I) NHC complex (obtained from B3LYP level). Donor
Type
Acceptor
Type
E(2) (kcal/ mol)
E(j) E(i) (a.u.)
F(ij) (a.u.)
C14AC19
r
C14AN1
p r
C19AC18
r
C19AN2
r
C18AC17
r
C14AC15 C14AN1 C19AC18 C19AN2 C18AC17 C14AC19 C19AC18 C7AN2 C14AC19 C14AN1 C18AC17 C7AN2 C14AC19 C14AC15 C7AN2 C19AC18 C19AN2 C17AC16 C14AC19 C16AC15 C14AC15 C14AN1 C17AC16 C14AC19 C18AC17 C14AC15 C19AC18 C14AC15 C19AC18 C1AC2 C2AC11 C3AC34 C11AC9 C5AC7 C2AC11 C9AC7 C2AC3 C5AC7 C14AC19 C14AC19 C18AC17 C16AC15
r⁄ r⁄ r⁄ r⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ p⁄ r r⁄ r⁄ p⁄ p⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ r⁄ p⁄ p⁄ r⁄ r⁄ p⁄ p⁄ p⁄ p⁄ p⁄ p⁄
3.40 0.72 3.48 0.74 20.73 0.83 4.22 1.54 3.68 2.26 1.91 3.49 0.82 4.10 1.59 2.38 7.87 1.50 23.48 21.29 2.35 8.03 1.51 23.069 22.55 0.85 4.85 4.91 0.86 1.62 3.86 3.35 24.15 21.18 3.47 3.30 22.55 23.43 35.88 35.24 344.59 248.81
1.26 1.11 1.26 1.12 0.31 1.36 1.37 1.26 1.27 1.14 1.30 1.17 1.36 1.38 1.26 1.27 1.12 1.27 0.29 0.31 1.27 1.12 1.26 0.29 0.30 1.40 1.40 1.40 1.40 1.09 1.27 1.28 0.31 0.31 1.27 1.27 0.30 0.31 0.31 0.30 0.01 0.01
0.059 0.025 0.060 0.026 0.073 0.030 0.068 0.039 0.061 0.046 0.045 0.057 0.030 0.067 0.040 0.049 0.084 0.039 0.077 0.072 0.049 0.085 0.039 0.076 0.074 0.031 0.074 0.074 0.031 0.038 0.063 0.058 0.078 0.073 0.059 0.058 0.074 0.076 0.094 0.093 0.087 0.087
Taken from Refs. [60,61].
p C16AC15
r
p C13AN1
r
C13AN2
r
C2AC3
r
p
Fig. 7. The total electron density isosurface mapped with molecular electrostatic potential for silver(I) NHC complex (obtained from PBE1PBE/LANL2DZ level).
(Supplementary information). As can be seen in Fig. S2 (Supplementary information), the Mulliken charges show a behavior similar to those of the APT and NBO charges most of the hydrogen atoms have a net positive charge while nearly all the carbon atoms have negative charge. From the calculation, the carbon atoms with the attached nitrogen atoms C9, C13, C14, and C20 have exhibited more positive charges in comparison with the other carbon in the molecule. The nitrogen atoms are more electronegative than the carbon atoms, so it is sensible to expect that the nitrogen atoms act as electron acceptors and the carbon atoms as electron donors.
HOMO 3 ? LUMO (25%)
C11AC9
r
N1 N2 C14AC19
LP(I) LP(I)
p⁄ p⁄
According to Fig. S2 (Supplementary information), Ag atom has a positive charge density while bromine has a negative charge density. Conclusion A complete structural, vibrational and electronic investigation along with FT-IR, NMR, UV–vis, NBO and NLO analysis have been performed on the title complex by using PBE1PBE and B3LYP levels with the LANL2DZ basis set. In addition to giving spectroscopic and electronic information concerning the title complex for the first time, this study also prepares the ground for the future investigations. Considering that experimental and theoretical studies are
A. Kunduracıog˘lu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 35–45
performed in different phase, it can be said that there is a good agreement between the experimental and theoretical data. Nonlinear optical behavior of the silver(I) complex was investigated by means of determination of the electric dipole moment, the polarizability and the hyperpolarizability. Obtained data indicate that the title complex is a material which has substantial non-linear optical properties. NBO analysis was carried out to display interaction between the ‘filled’ donor-type NBO and ‘empty’ acceptor-type NBO in the molecule and their stabilization energies are estimated by second order Fock matrix. NBO analysis indicates that the strong intramolecular hyperconjugative interaction of the r and p electrons of CAC to anti CAC bond of the ring leads to stabilization of some part of the ring. Acknowledgements The authors are grateful to Anadolu University and the Medicinal Plants and Medicine research Centre of Anadolu University, Eskisßehir, Turkey, for the use of X-ray Diffractometer. Crystallographic data (excluding structure factors) for the structure in this paper have been deposited with the Cambridge Crystallographic Data Centre as the supplementary publication no CCDC 871763 for complex. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. Fax: +44 1223 336 408; e-mail:
[email protected] or on the web: http://www.ccdc.cam.ac.uk. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2013.10.075. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
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