Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 758–766

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Review Article

An experimental and theoretical approach of spectroscopic and structural properties of a new chelidamate copper (II) complex _ Hatice Vural a,⇑, Ibrahim Uçar b, M. Serkan Soylu c a

Department of Physics, Faculty of Arts and Sciences, Amasya University, Ipekköy, 05000 Amasya, Turkey Department of Physics, Faculty of Arts and Sciences, Ondokuzmayıs University, Kurupelit, 55139 Samsun, Turkey c Department of Physics, Faculty of Arts and Sciences, Giresun University, 28100 Giresun, 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 results of structural investigation

show that this complex has sixcoordinate geometry about the copper center.  The title complex displays an octahedrally elongated geometry and JT distortion, value of T parameter equals 0.81.  Theoretical calculations were done by DFT method.  The spin density distribution calculations reveal that 72% of spin density is located at the copper center atom.

a r t i c l e

i n f o

Article history: Received 19 August 2013 Received in revised form 13 November 2013 Accepted 5 December 2013 Available online 21 December 2013 Keywords: Quantum chemical calculation Chelidamic acid X-ray diffraction IR UV–Vis

a b s t r a c t The crystal structure of new chelidamate complex of copper (II) ion, [Cu(chel)H2O(pym)]H2O [chel: chelidamate or 4-hydroxypyridine-2,6-dicarboxylate; pym: 2-Pyridylmethanol] has been determined by single crystal X-ray crystallographic method. The complex was characterized by IR and UV–Vis spectroscopic techniques. The magnetic environment of copper (II) ion has been defined by electron paramagnetic technique (EPR). The central copper (II) ion is six-coordinate with a distorted octahedral geometry, which exhibits Jahn–Teller distortions along one of the OACuAO axes with tetragonality of 0.81. Chelidamate behaved as a tridentate ligand was bonded to Cu(II) ion through carboxyl oxygens with nitrogen. The crystal structure is stabilized by OAH  O hydrogen bond and p–p interactions. Theoretical calculations have been carried out by using the DFT method. The modeling of copper (II) complex was made by geometric optimization. The geometry optimization and EPR study were carried out using the following unrestricted hybrid density functionals: LSDA, BPV86, B3LYP, B3PW91, MPW1PW91 and HCTH. Frontier molecular orbital energies, absorption wavelengths and excitation energy were computed by time dependent DFT (TD-DFT) method with polarizable continuum model. IR spectra were discussed and compared to other relevant complexes together with theoretical results. The natural charges on the atoms and second-order interaction energies were derived from natural bond orbital analysis (NBO). Ó 2013 Elsevier B.V. All rights reserved.

Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759 Experimental and theoretical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759

⇑ Corresponding author. Tel.: +90 3582421613; fax: +90 3582421616. E-mail address: [email protected] (H. Vural). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.12.027

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General method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crystal structure determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DFT calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Molecular structure of [Cu(chel)H2O(pym)]H2O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optimized geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EPR study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electronic absorption spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vibrational frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Natural bond orbital analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A. Supplementary material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

759 759 759 760 760 760 760 762 763 764 764 765 765 765 765

Introduction Chelidamic acid (H2Chel), is commonly used inorganic chemistry, biochemistry, coordinate chemistry, medical chemistry and even in HIV investigation [1–7]. The multifunctional ligands containing N and O-donors such as chelidamates have attracted attention, since they may cause diversity in the coordination modes and interesting properties such as luminescent probe, radical adsorption and ferromagnetic interaction [8,9]. Thought the original report of chelidamic acid was published 1926, the crystal structure of the chelidamic acid was not determined until 2000 [10,11]. The studies concerning the transition metal complexes containing chelidamic acid are relatively rarely, to our best knowledge, the only known examples consisting of Cr, Fe, Sn, Gd, V and Zn up to now [2,12]. Recently some chelidamate copper (II) complexes have been synthesized and their crystal structures have been determined [13]. Chelidamic acids usually ligate to transition metals by either carboxylate bridges between metal centers, to form dimeric or polymeric complexes [14–16] or tridentate (O, N, O0 ) chelation to one metal ion [17–19].

Table 1 Crystal data and structure refinement for copper (II) complex. Formula Formula weight (g) Temperature (K) Wavelength (Mo Å) Crystal system Space group Unit cell dimensions a, b, c (Å) b (°) Volume (Å3) Z Calculated density (g cm3) l (mm1) F(0, 0, 0) Crystal size (mm) h Ranges (°) Index ranges

Reflections collected Independent reflections Reflection observed (>2r) 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)

C13H14CuN2O8 389.81 297 K 0.7107 Monoclinic C2/c 27.059(3), 6.0807(5), 18.4053(16) 99.143(9) 2989.9(5) 8 1.7320(3) 1.51 1592 0.25  0.20  0.18 3.4–28.7 25 6 h 6 36 6 6 k 6 7 24 6 l 6 17 5590 2934 [R(int) = 0.027] 2392 Integration Full-matrix least-squares on F2 2934/2/241 1.08 0.0421 0.0277 0.42 and 0.37

In this article, we have determined both the structural and energetic properties of chelidamate complex of copper (II) ion with the 2-Pyridylmethanol (pym) ligand. Vibrational frequencies, HOMO (Highest occupied molecular orbital) – LUMO (Lowest unoccupied molecular orbital) energies, frontier orbital energy gap and EPR parameters (g and A-tensor) were computed by Density Functional Theory (DFT) [20,21]. DFT has become the preferred method for electronic structure calculations of EPR parameters, such as g and A tensors due to the requirements of being accurate, easy to use and fast [22]. Experimental and theoretical methods General method The EPR measurement was carried out using a Varian E-109C model X-band spectrometer operating at 100 kHz the magnetic field modulation frequency, 10 mW microwave power. The Diphenylpicrylhydrazyl (DPPH) was used to calibrated magnetic field (g = 2.0036). Electronic absorption spectra were measured in the range of 900–200 nm using Perkin Elmer Lambda 35 UV–Vis spectrometer for three different solutions (water, methanol and ethanol) of compound. The FT-IR spectra were collected in range of 4000–400 cm1 using a Vertex 80v Bruker FTIR spectrometer, the specimen was prepared in KBr disc. Crystal structure determination The crystal data were recorded on an Agilent Technologies SuperNova [23], (Single source at offset and Eos CCD detector) diffractometer with SuperNova (Mo) X-Ray source with mirrormonochromated Mo Ka radiation wavelength of 0.71073 Å, at 293 K. The CrysAlisPro [23] software program was used for data collection, cell refinement and data reduction. Table 1 provides more information about the crystal structure. The structure was solved by direct-methods using SHELXS-97 [24]. Full-matrix least-squares refinement on F2 was carried out using SHELXL-97 [24]. All hydrogen atoms attached to carbon atoms were positioned geometrically and refined by a riding model with Uiso 1.2 times that of attached atoms and remaining hydrogen atoms were located from the Fourier difference map. Molecular drawings were obtained using DIAMOND 3.0 (demonstrated version) [25]. Synthesis An aqueous solution of H2Chel (1 mmol) in methanol/water (30 ml, ca 1:1 v/v) was added to an aqueous solution of CuCl22H2O (1 mmol) in water and pym (1 mmol) in methanol. The reaction

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mixture was stirred for 1 h at room temperature. The resulting suspension was filtered. The blue filtrates were allowed about 2 weeks at room temperature and then the blue crystals of suitable for Xray diffraction analysis were harvested. DFT calculations All calculations were optimized from initial molecular geometry. Theoretical calculations were performed at DFT method with 6-31 G (d, p) [26,27] basis set using GAUSSIAN 03 program packages [28]. Gaussian output files were visualized by means of GAUSSIAN VIEW 04 software [29]. In complex the copper (II) ion has one unpaired electron, so unrestricted hybrid functionals were used for an open-shell electronic structure. The geometry optimization and EPR parameters, such as g and A tensors were obtained using six different unrestricted DFT (UDFT) methods (B3LYP [30,31], B3PW91 [32,33], BPV86 [34,35], MPW1PW91 [36], LSDA [37], HCTH [38]). The unrestricted wavefunctions are not eigenfunctions of the spin-squared operator b S 2 , e.g. they are contaminated by states of higher spin multiplicity [39]. The expectation value of the total spin hb S 2 i (0.75 for doublet, 2.0 for triplet) is frequently used as a quantitative measure of spin contamination in an unrestricted wavefunction [39]. We have calculated the expectation value of the total spin. The final hb S 2 i is 0.7520, which is in good agreement with the expectation value of 0.7500 for the doublet ground state [40,41]. This confirms validity of the UDFT functionals for the title complex. The electronic absorption spectrum was calculated using TDDFT method starting from the ground-state geometry optimized in the gas phase. The solvent (water, methanol and ethanol) effect of molecule was examined by using the polarizable continuum model (PCM). The vibrational harmonic frequencies of the copper (II) complex were calculated using the only DFT/UB3LYP hybrid functional. For the structure, the stationary points found on the molecule potential energy hypersurfaces were characterized using standard analytical harmonic vibrational analysis. The absence of any imaginary frequency indicates that all the optimized structures are located as stationary points on the potential energy surfaces. VEDA4 [42] program has been used to calculate Potential Energy Distribution (PED) for the assignments of fundamental vibrational modes of the title complex. Results and discussion Molecular structure of [Cu(chel)H2O(pym)]H2O The molecular structure of the title complex is shown in Fig. 1. The corresponding interatomic bond distances and angles are listed in Table 2. X-ray structural analysis shows that the complex consists of a neutral ligand [Cu(chel)H2O(pym)] unit and one crystal water molecule. The chel acts as a tridentate ligand, while pym acts as two dentate ligand. Copper (II) ion lies on a general position and is hexa-coordinated by two oxygens together with one nitrogen atom from chel dianion and one nitrogen atom from pym composing the basal plane, and one oxygen atom from pym and one oxygen from the coordinated water occupying the axial sites, adopting a distorted octahedral sphere (Fig. 1). It is observed that the Cu1AOaqua: 2.557(3); Cu1AOpym: 2.333(2) bond lengths in the axial plane are longer than the Cu1AOchel: 2.054(2)–2.014(2) bond lengths in the equatorial plane. This difference can be attributed to the Jahn-Teller (JT) distortion. The JT is commonly encountered in the elongation of axial bond in octahedral geometry. The coordination sphere exhibits a tetragonality parameter T of 0.81 (T is ratio between the mean in-plane

Fig. 1. A view of copper (II) complex showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level and hydrogen atoms are shown as small spheres of arbitrary radii.

distances and the mean out-of-plane distances), which indicates an additional elongation of the octahedron along the OaquaACu1AOpym axis [symmetry code: x, +y, ½  z]. This distortion also indicates dx2 y2 ground state of the Cu (II) ion. The Cu1ANpym bond distance is significantly longer than Cu1ANchel length (see Table 2) due to the two carboxylate groups in ortho position. These carboxylate groups enhance the basicity of Nchel atom. The copper-chel bond lengths [Cu1ANchel and Cu1AOchel] are in good agreement with the corresponding distances reported for Cu(hypydc)(dmp)H2O[dmp = 2,9-Dimethyl1,10-phenanthroline, hypydc = 4-Hydroxypyridine-2,6-dicarboxylic 0 0 acid] [Cu1AO = 2.032(2)–2.026(2) Å A; Cu1AN1 = 1.904(2) Å A] [43], Cu(cda)(py)n[cda = 0chelidamic acid, py = pyridine] [Cu1AO = 0 2.029(3)-2.021(3) Å A; Cu1AN = 1.898(4) Å A] [44], {Cu3(C7H02NO5)20 2H2O}n[Cu1AO = 2.102(2)–2.091(2) Å A, Cu1AN = 1.905(2) Å A] [45], [Cu(hypydc)(phen)(H2O)]4.5H2O [phen = 1,10 phenanthroline, hypydcH2 = 4-Hydroxypyridine-2,6-dicarboxylic acid] [Cu1AO = 0 0 2.367(9)–2.3205(11) Å A, Cu1AN3 = 2.0036(9) Å A] [13], Cu(dpa)(dpc) 3H2O[dpa = 2,20 -dipyridylamine, dpc = dipicolinate or pyridine-2, 0 0 6-dicarboxylate] [CuAO = 2.051(6)–2.102(5) Å A, Cu1AN3 = 1.909(6) A Å] [46]. The Cu1ANpym = 1.967(2) and Cu1AOpym: 2.333(2) bond distances are similar to the corresponding distances reported for Cu(sac)2(mpy)2[sac = saccharinate anion, mpy = 2-pyridylmetha0 0 nol] [CuAOmpy = 2.1394(13) Å A, CuANmpy = 1.9667(13) Å A] [47], Cu(clof)2(2-pymeth)2[clof = 2-(4-chlorophenoxy)-2-methylpropionic, 0 2-pymeth0 = 2-pyridylmethanol] [CuAO4 = 2.388(2) Å A, CuAN1 = 1.981(2) Å A] [48], Cu(X-sal)2(2-pyme)2[X = 3-MeOsal = 3-methox0 ysalicylate, 2-pyme0 = 2-pyridylmethanol] [Cu1AO1 = 2.197(2) Å A, Cu1AN1 = 1.988(2) Å A] [49]. Analysis of the crystal packing indicates that there is only OAH  O type intermolecular hydrogen bond interactions in the complex (see Table 3 and Fig. 2). There is a strong intermolecular hydrogen bond between the uncoordinated water molecules with the O5 atom of the chel. Apart from these, there is also symmetry-related face to face p–p stacking interaction between the two pyridine rings of chel and pym [ring 4 (Cg4): C1/C2/C3/C4/C5/N1 and ring 5 (Cg5): C8/C9/C10/C11/C12/N2]. The centroid to centroid and centroid-to-plane distances between the pyridine rings are 0 4.3051(17) and 3.0420 Å A, respectively. The closest interatomic distance between these ring planes is [C4  C9(x, 1  y, 1/2 + z)] 0 3.5320 Å A. Optimized geometry Full geometry optimization of complex was carried out using the following unrestricted hybrid density functionals: LSDA, B3LYP, B3PW91, MPW1PW91, BPV86 and HCTH. Table 2 shows some optimized geometric parameters of the title complex. A superposition of the molecular structure of title complex as established by theoretical calculations and X-ray

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H. Vural et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 758–766 Table 2 Selected structural parameters by X-ray and theoretical calculations for copper (II) complex.

N1ACu1 N2ACu1 O1ACu1 O2ACu1 O6ACu1 O7ACu1 N1ACu1AN2 N1ACu1AO1 N2ACu1AO1 N1ACu1AO6 N2ACu1AO6 O1ACu1AO2 N2ACu1AO7 O1ACu1AO7 O1ACu1AO6 O2ACu1AO6 O2ACu1AN1 O2ACu1AN2

Exp.

BPV86

B3LYP

B3PW91

MPW1PW91

HCTH

LDSA

1.905(2) 1.969(2) 2.014(2) 2.054(2) 2.333(2) 2.570(3) 178.60(9) 80.85(8) 98.60(8) 101.72(9) 77.07(9) 160.40(7) 94.18(9) 91.53(9) 98.41(8) 88.10(8) 79.72(8) 100.88(9)

1.905 1.967 2.012 2.056 2.332 2.576 178.591 79.685 100.873 101.731 77.020 160.413 94.024 84.922 88.087 98.392 79.685 100.873

1.928 1.980 2.258 1.968 2.431 2.386 173.60 76.262 107.942 103.48 75.088 158.411 85.348 67.792 65.881 124.363 82.599 93.491

2.028 1.981 3.072 1.941 2.019 2.186 164.100 76.015 123.365 98.175 79.831 145.642 100.092 81.002 87.001 154.349 84.594 90.558

2.029 1.981 3.061 1.911 2.018 2.174 164.572 75.940 123.455 98.692 79.690 145.601 99.826 81.177 86.726 154.309 84.496 90.503

1.902 2.002 2.076 2.009 2.316 3.581 158.482 79.378 101.079 123.698 77.776 160.289 79.357 99.304 89.902 104.177 81.316 95.422

1.951 1.899 3.062 1.899 2.006 2.083 163.396 76.765 128.388 96.968 81.059 147.518 98.727 84.550 87.422 152.551 85.706 88.655

Table 3 Hydrogen bonding interactions for copper (II) complex. Hydrogen-bond geometry (Å, °) DAH  A

DAH

H  A

D  A

DAH  A

O5AH5  O8 O6AH6  O4i O6AH6  O1i O8AH8B  O2ii O8AH8A  O7iii O7AH7B  O5iv O7AH7B  O2

0.73(3) 0.81(2) 0.81(2) 0.75(4) 0.76(4) 0.98(4) 0.98(4)

1.87(3) 2.11(2) 2.53(3) 1.94(4) 2.42(5) 2.08(5) 2.61(4)

2.595(4) 2.892(3) 3.178(3) 2.691(4) 2.937(4) 2.955(3) 3.145(4)

175(3) 163(4) 138(4) 176(5) 127(4) 147(3) 114(3)

Symmetry codes: (i) x, y  1, z; (ii) x, y, z + 1/2; (iii) x, y + 1, z + 1/2; (iv) x + 1, y, z + 1.

Fig. 3. Atom-by-atom superimposition of the copper (II) complex calculated (red) over the X-ray structure (black). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. A partial view, along the a axis, of the packing of copper (II) complex, showing hydrogen bond interactions as dashed lines. Crystal water molecule was omitted for the clarity.

diffraction shows an excellent agreement (Fig. 3). When the X-ray study of the copper (II) complex is compared to the theoretical calculations, slight conformational disagreement is observed between them. The orientation of the pyridine ring in the chel is defined by the torsion angles C2AC1AC7AO1 [176.9(3)°] and C4AC5AC6AO2 [174.5(3)°] for the X-ray structure. These torsion angles have been calculated at 179.381° and 179.358° for the UB3LYP/6-31 G (d, p) level, respectively. The torsion angle of the pym ligand is C11AC12AC13AO6 [150.6(3)°] for X-ray, while the corresponding value is calculated at 175.460° for UB3LYP. According to X-ray study, the dihedral angle between the pyridine rings of the ligands is 66.41°, whereas this angle has been calculated at 55.87° for UB3LYP/6-31G (d, p) level.

Fig. 4. Epr spectra of [Cu(chel)H2O(pym)]H2O: (a) polycrystalline at 298 K and (b) in liquid nitrogen.

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Table 4 Calculated and experimental EPR parameters of [Cu(chel)H2O(pym)]H2O. Density func.

gx

gy

gz

Ax (G)

Ay (G)

Az (G)

Experimental B3LYP B3PW91 BPV86 HCTH LSDA MPW1PW91

2.129 2.143 2.135 2.071 2.058 2.084 2.139

2.001 2.074 2.106 2.060 2.083 2.066 2.115

2.277 2.302 2.259 2.186 2.197 2.163 2.291

88 122 106 88 83 88 122

62 59 83 62 60 64 59

80 181 189 150 143 152 181

modulation; g factors were determined relative to g = 2.0036 of DPPH (diphenylpicrylhydrazil). The ground state wave function of copper (II) with d9 electron configuration is often used EPR studies. In the powder spectrum of copper (II) complex, one broad signal with a g value of 2.105 is visible (Fig. 4a) but hyperfine splittings due to the coupling of the electron spin with the nuclear spin of the copper isotopes are not observed (63Cu and 65Cu). This can be explained by exchange interaction between the symmetry related 0 copper (II) centers [Cu1  Cu1 (+x, y1, +z) = 6.081(7) Å A]. In the frozen liquid nitrogen EPR spectrum of the copper (II) complex shows four obviously determined hyperfine lines originating from MI = 3/2, 1/2, 1/2, 3/2 transitions (DMs = ±1) for gz component (Fig. 4b). As can be seen from Table 4 the g values in the order of gz > gx > gy > 2.0 confirming the rhombic nature of the g-matrix. Theorical g-tensor can be separated into the different contributions as follows:

g ¼ g e þ g RMC þ g DC þ g OZ þ g SOC

Fig. 5. Computational [DFT/UB3LYP with 6-31G (d, p)]: (a) single occupied molecular orbital (SOMO) and (b) spin density distribution of [Cu(chel)H2O(pym)]H2O genereted with GaussView 4.1.2 (isovalue 0.0004).

The optimized bond lengths and bond angles are slightly different from the experimental ones due to the intermolecular interactions of the complex. The ULSDA, UB3LYP, UBPV86 and UHCTH functionals almost perform equally leading to results that are more accurate than those obtained with UB3PW91 and UMPW1PW91. EPR study Fig. 4 shows that the EPR spectra of Cu(II) complex at 298 K and liquid nitrogen were recorded in the X-band, using 100-kHz

where ge, the free electron values, with ge = 2.002319. The last four terms of this equation are the corrections [50,51] that represents contributions of three GIAO (gauge including atomic orbitals) nuclear magnetic shielding terms. The terms are relativistic mass correction, diamagnetic correction, orbital Zeeman and spin-orbit coupling [52] contribution, respectively. Comparison of experimental and calculated g and A values are listed in Table 4. The UB3LYP, UB3PW91 and UMPW1PW91 hybrid schemes show better performance to calculate the g-values than UHCTH, ULSDA and UBPV86. The HOMO–LUMO energy gap of the title complex was calculated at DFT methods, which display that energy gap can be related the anisotropy of the g-values. According to the results the UB3LYP, UB3PW91 and UMPW1PW91 functionals have also the same performance and they predict more stabilized HOMO–LUMO energy gap. Consequently, the UB3LYP, UB3PW91 and UMPW1PW91 functionals obtain the best estimation of the g-values for copper complex. The UHCTH, ULSDA and UBPV86

Table 5 Calculated electronic transitions for [Cu(chel)H2O(pym)]H2O with TD-DFT method. Solution

Water

Experimental k (nm)

DFT/UB3LYP with 6-31G (d, p) k (nm)

Osc. strenght

Major contributions

796

793 708 653 345 310 305 303 299 288

0.0002 0.0003 0.0012 0.0003 0.0071 0.0016 0.0033 0.0046 0.0132

HOMO3(b) ? LUMO(b)(+43%) HOMO1(b) ? LUMO(b)(+19%) HOMO19(b) ? LUMO(b)(+28%) HOMO(a) ? LUMO(a)(+68%) HOMO2(b) ? LUMO(b)(+49%) HOMO1(b) ? LUMO(b)(+55%) HOMO2(b) ? LUMO(b)(+22%) HOMO4(b) ? LUMO(b)(+79%) HOMO5(b) ? LUMO(b)(+51%)

HOMO15(b) ? LUMO(b)(12%) HOMO9(b) ? LUMO(b)(+19%) HOMO17(b) ? LUMO(b)(+28%) HOMO(a) ? LUMO+1(a)(+9%) HOMO3(b) ? LUMO(b)(+14%) HOMO9(b) ? LUMO(b)(11%) HOMO3(b) ? LUMO+1(b)(+14%) HOMO(b) ? LUMO+1(b)(+5%) HOMO(b) ? LUMO(b)(+9%)

HOMO2(b) ? LUMO(b)(+11%) HOMO15(b) ? LUMO(b)(+18%) HOMO6(b) ? LUMO(b)(+25%) HOMO2(a) ? LUMO+1(a)(+4%) HOMO2(a) ? LUMO+1(a)(+13%) HOMO3(b) ? LUMO(b)(+7%) HOMO2(b) ? LUMO+2(b)(+14%) HOMO7(b) ? LUMO(b)(+3%) HOMO4(b) ? LUMO+2(b)(+5%)

794 708 653 311 308 305 299 298 288

0.0002 0.0003 0.0012 0.0071 0.0006 0.0031 0.0041 0.0021 0.0131

HOMO3(b) ? LUMO(b)(+46%) HOMO1(b) ? LUMO(b)(+19%) HOMO17(b) ? LUMO(b)(+29%) HOMO2(b) ? LUMO(b)(+53%) HOMO7(b) ? LUMO+1(b)(+13%) HOMO2(b) ? LUMO(b)(+14%) HOMO4(b) ? LUMO(b)(+67%) HOMO(b) ? LUMO+1(b)(+47%) HOMO5(b) ? LUMO(b)(+55%)

HOMO15(b) ? LUMO(b)(+11%) HOMO15(b) ? LUMO(b)(+18%) HOMO19(b) ? LUMO(b)(+27%) HOMO2(b) ? LUMO+1(b)(+13%) HOMO7(a) ? LUMO(a)(+12%) HOMO2(b) ? LUMO+1(b)(+13%) HOMO(b) ? LUMO+1(b)(+14%) HOMO4(b) ? LUMO(b)(+17%) HOMO(b) ? LUMO(b)(+9%)

HOMO2(b) ? LUMO(b)(+9%) HOMO9(b) ? LUMO(b)(+18%) HOMO6(b) ? LUMO(b)(+26%) HOMO3(b) ? LUMO(b)(+12%) HOMO1(b) ? LUMO+2(b)(+11%) HOMO1(b) ? LUMO(b)(+12%) HOMO7(b) ? LUMO(b)(+4%) HOMO6(b) ? LUMO+1(b)(+4%) HOMO10(b) ? LUMO(b)(+4%)

794 708 653 312 308 305 299 298 289

0.0002 0.0003 0.0012 0.0072 0.0008 0.0025 0.0025 0.0041 0.0130

HOMO3(b) ? LUMO(b)(+47%) HOMO1(b) ? LUMO(b)(+19%) HOMO17(b) ? LUMO(b)(+29%) HOMO2(b) ? LUMO(b)(+54%) HOMO7(b) ? LUMO+1(b)(+13%) HOMO1(b) ? LUMO(b)(+49%) HOMO4(b) ? LUMO(b)(+38%) HOMO4(b) ? LUMO(b)(+44%) HOMO5(b) ? LUMO(b)(+56%)

HOMO15(b) ? LUMO(b)(+11%) HOMO15(b) ? LUMO(b)(+18%) HOMO19(b) ? LUMO(b)(+26%) HOMO2(b) ? LUMO+2(b)(+13%) HOMO7(a) ? LUMO(a)(+13%) HOMO9(b) ? LUMO(b)(+11%) HOMO(b) ? LUMO+1(b)(+35%) HOMO(b) ? LUMO+1(b)(+26%) HOMO(b) ? LUMO(b)(+9%)

HOMO13(b) ? LUMO(b)(+10%) HOMO10(b) ? LUMO(b)(+17%) HOMO6(b) ? LUMO(b)(+26%) HOMO3(b) ? LUMO(b)(+11%) HOMO1(b) ? LUMO+2(b)(+11%) HOMO3(b) ? LUMO(b)(+11%) HOMO2(a) ? LUMO(a)(3%)  HOMO10(b) ? LUMO(b)(+4%)

267

218 Methanol

789

268

213 Ethanol

792

267

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H. Vural et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 758–766

perform nearly equal leading to results which are faulty than those calculated from the UB3LYP, UB3PW91 and UMPW1PW91. Although the UBPV86 shows better performance to calculate the A-value than the other five hybrid density functionals, the hyperfine splitting components are not agreement with the corresponding experimental values. Some difficulties regarding the computation of hyperfine coupling in transition metal complexes have existed due to the core-shell spin polarization, which is mainly due to exchange interactions between SOMO (Fig. 5a) metal 3d orbitals and the outermost doubly occupied 3s and 2s-type core shells. In the title complex the spin density distribution calculations show that the donor atom directly attached to the metal carry positive spin density and from there on the spin density is propagated through the bonds of the ligand, but carbon atoms have slightly spin delocalization (Fig. 5b). A large part of the spins can be attributed to the metal d atomic orbitals (72%), because they present the major contributions to the SOMOs, although some spin density is delocalized to the ligands (25% for chel; 4% pym) and the spin population at the metal is often less than the number of electrons. The MO with the single electron is a combination of d (Cu) and p (mainly O, N) atomic orbitals. Electronic absorption spectra The UV–Vis spectrum of title complex in different solvents (water, methanol and ethanol) was recorded within 200–900 nm range. In order to understand electron transition between the

763

energy levels, the first 20 doublet ? doublet spin allowed excited states are considered and the theoretical electronic excitation energies, absorption wavelengths (k), oscillator strengths were calculated by the TD-DFT/PCM method for the same solvents. The contributions of the transitions were designated with the help of SWizard program [53]. In Table 5 the experimental and calculated results of UV–Vis spectral data for each solvent are summarized. Fig. 6 shows molecular orbital surfaces and energy levels. Since b-MOs play active role in the electronic transitions, only the b spin part is taken into account for frontier MOs. In the [Cu(chel)H2 O(pym)]H2O complex HOMO orbitals are localized on Cu (%53), chel (%20), pym (%17) and water (%10). d orbitals of Cu play an essential role in the HOMO3 (% 26), HOMO1 (%47), HOMO9 (%28) MOs, while HOMO1 (%40), HOMO2 (%90), HOMO5 (%76), HOMO6 (%78), HOMO8 (%87) are mainly formed by the chel p-bonding MOs. The pym ligand plays an important role only in the HOMO4 (%66) MO. The calculated absorption maxima values have been found to be 793, 310, 288 nm for water, 794, 311, 288 nm for methanol and 794, 312, 289 nm for ethanol at TD-DFT/PCM method. It is seen from the theoretical calculations that the longest wavelengths experimental data at 796 nm (water), 789 nm (methanol), and 792 nm (ethanol) originate in the transitions between some lowest HOMO orbitals and highest LUMO orbitals (Fig. 7). The LUMO orbital with b spin compose of mainly Cu dx2 y2 (%57) orbital with contributions chel (%31) and pym (%12) p-antibonding orbitals. The electronic transitions with longest wavelengths are happened from the mixed d ? d (LF) and chel/pym ? d (LMCT). Additionaly, the

LUMO

HOMO

HOMO-1

HOMO-2

-0.0734 a.u. Cu (%57) chel (%31) pym (%11)

-0,2318 a.u. Cu (%53) chel (%31) pym (%11)

-0,2394 a.u. Cu (%47) chel (%40) pym (%4)

-0,2413 a.u. Cu (%7) chel (%90) pym (%2)

HOMO-3

HOMO-4

HOMO-5

HOMO-6

-0.2481 a.u. Cu (%26) chel (%62) pym (%8)

-0.2527 a.u. Cu (%3) chel (%30) pym (%66)

-0.2574 a.u. Cu (%18) chel (%76) pym (%12)

-0.2635 a.u. Cu (%12) chel (%78) pym (%6)

HOMO-7

HOMO-8

HOMO-9

HOMO-10

-0.2753 a.u. Cu (%2) chel (%71) pym (%18)

-0.2834 a.u. Cu (%2) chel (%87) pym (%7)

-0.2885 a.u. Cu (%28) chel (%24) pym (%39)

-0.2935 a.u. Cu (%25) chel (%34) pym (%40)

Fig. 6. Molecular orbital surfaces and energy levels using the DFT/UB3LYP method for HOMO, HOMO1/10 and LUMO of title complex.

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coordinated carboxylate group [56], which is in agreement with the XRD results. These experimentally stretching vibrations for CO groups are slightly different with the calculated values. In the case of pyridine–metal complexes, the ring breathing mode, in pyridine and substituted pyridines is near 995 cm1, is shifted to higher wavenumber [57,58]. The strong bands at 1069 and 1048 cm1 are attributed to ring breathing mode of chel and pym ligands, respectively, indicating that these ligands are attached to Cu (II) ion. Natural bond orbital analysis

Fig. 7. The absorption spectrum in the region of 400–900 nm for the copper (II) complex.

experimental bands at 267, 218 nm (water); 268, 213 nm (methanol); 267, 214 nm (ethanol) arise from mainly in the intraligand (IL) transitions between the p-bonding and p-antibonding orbitals of ligands. Vibrational frequency Fig. 8 illustrates the FT-IR spectrum of the title complex in the frequency range from 4000 to 400 cm1. Vibrational assignments for 600–3700 cm1 frequency range have been made by comparison with the results from experimental and theoretical studies of IR spectrum of chel complexes (see Table 6). The calculated frequencies at unrestricted B3LYP levels were scaled with 0.96 [54]. It is observed that the wavenumbers are over 3100 cm1, the calculated vibrational frequencies have some blue shifts compared to the experimental IR data. Since the OAH groups of aqua and coordinated water molecules participate in the intermolecular hydrogen bonding, experimental data of these groups were obtained at a lower frequency. This discrepancy can be explained that the DFT calculations belong to isolated molecule in gase state while the experimental data belong to the same molecule in solid state. The experimental carboxyl vibrations in the free chelidamic acid were found at 1714 cm1and 1471 cm1 for which the first is assigned to m(C@O) and the second m(CO) stretching vibritations [55]. The appeared bands at 1638 and 1611 cm1 are assigned to symmetric and asymmetric m(C@O) stretching vibritations (Fig. 8). The value of Dm[m(C@O)Am(CAO)] of chel ligand is near 250 cm1 indicating the presence of monodentate-

Natural Bond Orbital (NBO) analyses of the title complex have provided very interesting and significant details on the electronic structure. According to the NBO results, the electron number of Cu 3d, 4s and 4p orbits are 9.15, 0.34 and 0.36, respectively (see Table 7). The electron numbers of 4d and 5p are smaller that can be neglected. Therefore we can conclude that the Cu atom coordination with N1, N2, O1, O2, O6 and O7 atoms are on 3d, 4s and 4p orbits. The electron number of N1 2s orbit is 1.31, 2p that of orbit is 4.23 and the electron number of N2 2s orbit is 1.31, 2p that of orbit is 4.19, indicating that the N atoms from coordination bonds with Cu atom by using 2s and 2p orbits. Likewise, coordinated O1, O2, O6 and O7 atoms provide electron of 2s (1.72, 1.73, 1.68, 1.74) and 2p (5.02, 5.10, 5.08, 5.23) to copper and form the coordination bonds. Charges on all atoms were calculated from natural population analysis (NPA). The calculated natural charge on the Cu atom in the title complex is equal to +1.14 deviating from the formal charge +2. This indicates a charge transfer from the ligands to the Cu (II) ion. The largest negative charges are located on the oxygen atoms O7 (0.97) and O8 (0.96) for copper (II) complex. The NBO analysis is a convenient tool for understanding delocalization of electron density from filled Lewis-type (donor) NBOs to properly empty non-Lewis type (acceptor) NBOs, which corresponds to a stabilizing donor–acceptor interaction [59]. The strength of this interaction can be predicted by the second order perturbation theory. The calculated second-order interaction energies (E2) using the NBO analysis display the lone pairs localized on the N and O atoms in complex. The second order interaction energies of N1 and N2 atoms are 24.34 kcal/mol and 22.56 kcal/mol. These values suggest similar strength metal-ligand bonds in complex for the corresponding ligands. Nevertheless chel oxygen atoms the second-order energy values [O1 (16.66 kcal/mol) and O2 (9.62 kcal/mol)] are smaller than corresponding values, indicating that Jahn Teller effect.

Fig. 8. Experimental and calculated FT-IR spectra of [Cu(chel)H2O(pym)]H2O.

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H. Vural et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 758–766 Table 6 Comparison of the observed and calculated vibrational spectra of [Cu(chel)H2O(pym)]H2O. PED(P10%)a assignments

[Cu(chel)H2O(pym)]H2O Experimental cm1

mas(OH2)aqua (49) mas(OH2)cw (96) ms(OH2)aqua (51) ms(CH2)cw (95) m(CH)(chel)(96) m(OH)(chel)(100) ms(CH)(pym)(96) mas(CH)(pym)(79) mas(CH2)(pym)(85) ms(CH2)(pym)((87) ms(C@O)(chel)(51) mas(C@O)(chel(51)) c(HOH)cw(86) [c(CHN(10)+CCC(16)+CCN(10))+m(ring)(39)](pym) [m(NC)(26)+m(CC)(16)+c(CCC)(12)](chel) [c(HCC)(39)+c(HCH)(26)](pym) [c(HCC)(13)+m(ring)(50)](chel) [c(HCC)(24)+m(CO)(38)](chel) [c(HCC)(76)+m(CC)(12)](chel) Ring breathing (chel) (31) Ring breathing (pym)(47) x(CH)(o.p)(chel)(84) x(CH)(o.p)(pym)(88) c(ring)(chel)(73) A

3544

3079 3310 2934 2876 2798 2735 1638 1611

1491 1449 1159 1176 1069 1048 923 746 768

b

Calculated scaled (cm1)

H2 Chel [55]

3678 3600 3532 3212 3076 3131 3153 3097 2972 2911 1631 1619 1556 1561 1551 1480 1440 1148 1173 1032 1011 902 757 761

3606

3208 3083 3121

[Zn(HCAM)]nH2O [60]

[Cu(hypydc)(dmp)]H2O [61]

3598

3464

3078 2943

1718 1616

1638 1622

1566 1471 1134

1469 919

1050 1044 900 762

753

853 735 639

cw: coordinated water; as: asymmetric, s: symmetric, m: stretching, c: bending, x: wagging, chel: chelidamate, pym: 2-pyridylmethanol. DFT/B3LYP method was applied.

b

Table 7 Selected natural atomic charges and electronic configurations for copper (II) complex. Atoms

Net Charge

Electronic configuration

Cu(1) N1 N2 O1 O2 O6 O7

1.13955 0.56106 0.53567 0.73939 0.82991 0.77272 0.97708

[core]4s (0.34)3d(9.15)4p(0.36)5p(0.01) [core]2s(1.31)2p(4.23)3p(0.02) [core]2s(1.31)2p(4.19)3p(0.02) [core]2s(1.72)2p(5.02)3p(0.01) [core]2s(1.73)2p(5.10) [core]2s(1.68)2p(5.08)3p(0.01) [core]2s(1.74)2p(5.23)

energies (second order perturbation energies) of the ligands are minimum level. Appendix A. Supplementary material 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 942687 for complex. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB12 1EZ, UK, fax: +44 1223 366 033, e-mail: [email protected] or on the web www: http://www.ccdc.cam.ac.uk.

Conclusions

Acknowledgement

In this study, [Cu(chel)H2O(pym)]H2O complex has been synthesized and characterized by structural (single crystal X-ray diffraction) and spectroscopic (FT-IR, UV–Vis and EPR) techniques. The results of structural investigation show that this complex has six-coordinate geometry about the copper center. The EPR spectra confirm an exchange interaction between the copper centers in solid state, while in frozen liquid nitrogen it shows four obviously determined hyperfine lines. Comparison of geometric parameters (bond lengths and bond angles) obtained by DFT methods with experimental data show that there are slight conformational discrepancy between them, which is related to some types of intermolecular interactions. The title complex displays an octahedrally elongated geometry and JT distortion, value of T parameter equals 0.81. While DFT is able to model the structure for electronic transition and g-anisotropy of the d9 complex, the agreement of the hyperfine splitting constant is poor. Different contributions to hyperfine coupling are not satisfactorily modeled at the present levels of theory. The spin density distribution calculations reveal that 72% of spin density is located at the copper center atom. The TDDFT/PCM calculations demonstrate that the longest wavelength experimental bands can be seen as mixed LMCT and LF transitions. NBO analysis of title complex indicates that the stabilization

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