Synthesis, structure, spectroscopic properties, DFT and TDDFT investigations of copper(II) complex with 2-(2-hydroxyphenyl)benzimidazole

Journal of Molecular Structure 841 (2007) 34–40 www.elsevier.com/locate/molstruc

Synthesis, structure, spectroscopic properties, DFT and TDDFT investigations of copper(II) complex with 2-(2-hydroxyphenyl)benzimidazole Yi-Ping Tong b

a,*

, Shao-Liang Zheng

b,*

a Department of Chemistry, Hanshan Normal University, Chaozhou 521041, China MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, Sun Yat-Sen University, Guangzhou 510275, China

Received 16 September 2006; received in revised form 19 November 2006; accepted 20 November 2006 Available online 13 March 2007

Abstract A Cu(II) complex with 2-(2-hydroxyphenyl)benzimidazole [Cu(pbm)2] (1), (Hpbm = 2-(2-hydroxyphenyl)benzimidazole) has been prepared and isolated under hydrothermal condition, and its structural and spectroscopic properties thoroughly investigated. The square-planar geometry was verified by both the density functional theory level (DFT) calculation and X-ray crystallography. A further theoretical analysis of electronic structure of this complex has also been undertaken to gain a deeper insight into the properties of relevant molecular orbitals. The time-dependent density functional theory level (TDDFT) calculation, together with DFT-based molecular orbital analyses, demonstrates that the low-lying absorption bands in UV–vis spectrum are all mainly p ! dx2 –y 2 and/or ðP;rÞ ! dx2 –y 2 ligand-to-metal charge transfer transition (LMCT) in nature.  2007 Published by Elsevier B.V. Keywords: Cu(II) complex; 2-(2-Hydroxyphenyl)benzimidazole; Density functional theory calculation; Time-dependent density functional theory calculation; Spectroscopic properties

1. Introduction The d9- and/or d10-copper(I, II) complexes have been widely interesting in recent years owing to their physical, chemical and biological properties, such as light-emitting, magnetic, metalloproteinic and supramolecular-isomerized properties [1–5]. Among them, the d10-copper(I) complexes have been excellent in photoluminescence and/or electroluminescence [6–8]; while d9-copper(II) complexes have been important for their potential ability in magnetic materials [9,10]; more recently some newly found d10-copper(I) complexes have also been proven to be much important in stereochemistry for the preparation of supramolecular architectures for various types of molecular polygons, and helix or zigzag chain polymers [5]. *

Corresponding authors. E-mail address: [email protected] (Y.-P. Tong).

0022-2860/$ - see front matter  2007 Published by Elsevier B.V. doi:10.1016/j.molstruc.2006.11.055

Imidazole and its derivatives are an important class of heterocycle with N-donor atoms, therefore they can be excellent organic ligands to generate various complexes upon ligation to both d9- and d10-copper centers [5,11– 13]. For example, the imidazole d10-copper(I) systems have demonstrated capacities for construction of inorganic-organic hybrid supramolecular isomers [5], while the imidazole groups of histidyl residuals of some cupric metalloproteins are usually quite important binding sites when coordinated to other metal ions [14,15], so that have profound effects on functions in biological systems. 2-(2-Hydroxyphenyl)benzimidazole (Hpbm = 2-(2-hydroxyphenyl)benzimidazole) has been considered to be another interesting imidazole-derivated ligand with N, O-donor atoms in photoluminescence [16,17]. This compound has been found for decades [18], and some d10-metal derivative, e.g. [Zn(pbm)2], together with photoluminescent properties and theoretical calculations has been investigated previously

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[17], but its copper derivatives have not been available so far. As a part of program of systematically investigating copper complexes with Hpbm, in this paper we report the synthesis, structure and characterization of copper(II) complex with Hpbm, namely [Cu(pbm)2] (1), together with the DFT and TDDFT calculations and analyses for its geometric structure, electronic structure and spectroscopic property. 2. Experimental All the reagents and solvents employed were commercially available and used as received without further purification. The C, H and N micro-analyses were carried out on an Elementar Vario El elemental analyzer. The FTIR spectra were recorded using a Bruker Vector22 spectrometer in the KBr pellets in the range 4000– 400 cm1. The UV–vis spectra were recorded on a Varian Cary-100 spectrometer. The ESI-MS was carried out on a high-resolution Finnigan MAT LCQ mass spectrometer. 2.1. Preparation of [Cu(pbm)2] (1) Hpbm was prepared using similar method with slight modification based on literature [18]. To a solution of copper sulfate tetrahydrate (0.1 mmol, 0.025 g) in 5 mL water were added Hpbm (0.2 mmol, 0.042 g) and potassium hydroxide (0.2 mmol, 0.011 g); after stirred vigorously for half an hour, the mixed solution was transferred into a 23 ml Teflon-lined stainless steel autoclave, sealed and heated inside a furnace to 165 C for 72 h, then slowly cooled to room temperature at a rate of 5 C per 1 h. Finally, brown block crystals of 1 were recovered by filtration in approximate 75% yield based on Hpbm. ESI-MS (CH2Cl2): m/z = 483 [CuL2 + H]+. Calcd. for C26H18CuN4O2: C, 64.79; H, 3.76; N, 11.62. Found: C, 64.85; H, 3.81; N, 11.54%. FT-IR (cm1): 3433m, 1812w, 1605m, 1564s, 1473m, 1448m, 1401m, 1316w, 1253w, 1146w, 1092w, 1015w, 877w, 825w, 736w, 653w, 565m, 480m, 422w. 2.2. X-ray crystallography Diffraction intensities for 1 were collected at 293 K on a Bruker Smart Apex CCD diffractometer (MoKa, k = ˚ ). Absorption corrections were applied by using 0.71073 A SADABS [19]. The structures were solved with direct methods and refined with full-matrix least-squares technique using SHELXTL program package [20]. The organic hydrogen atoms were generated in ideal positions. Anisotropic thermal parameters were applied to all non-hydrogen atoms. Experimental details of the X-ray analyses are provided in Table 1. Selected bond lengths and angles are listed in Table 2.

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Table 1 Crystal data and structure refinement for 1 Compound

1

Empirical formula Formula weight Crystal system Crystal size/mm Space group ˚ a/A ˚ b/A ˚ c/A

C26H18CuN4O2 481.98 Orthorhombic 0.16 · 0.14 · 0.03 Pbcn (No. 60) 11.0225(12) 8.0157(10) 22.208(3) 90 90 90 1962.1(4) 4 1.632 1.148 988 1.83–27.00 13 6 h 6 10,  10 6 k 6 6, 24 6 l 6 28 7340/2113 (0.0354) 0.986 2113/0/151 0.0418 and 0.1018 0.0655 and 0.1148 1.031 0.422 and 0.298

a/ b/ c/ ˚3 V/A Z Dc/g cm3 l/mm1 F(0 0 0) h range for data collection/ Index ranges

Total reflections/unique reflections (Rint) Completeness to hmax Observed data/restraints/parameters R1 and wR2 [I > 2r(I)] R1 and wR2 (all data) S on F2 ˚ 3 Largest difference peak and hole/e A

2.3. Calculation details The geometric optimization was performed on a Dell precision 490 computer using experimental geometry as input, employing the Gaussian98 suite of programs [21]. The complex was treated as an open-shell system using spin unrestricted DFT wavefunctions (UB3LYP) [22,23], i.e. the Becke three-parameter exchange functional in combination with the LYP correlation functional of Lee, Yang and Parr with 6-31G* basis set for C, H, N and O atoms, and effective core potentials basis set LanL2DZ for Cu atoms. No symmetry constrains were applied and only the default convergence criteria were undertaken during optimization. Based on the optimized geometries, time-dependent density functional level (TDDFT) calculations and molecular orbital calculations were performed at the same B3LYP level and basis set to calculate the vertical electron transition energies. The electron density diagrams of molecular orbitals were obtained with the Molden 3.5 graphics program [24]. 3. Results and discussion 3.1. Synthesis Though the powder crystalline sample of 1 can be readily prepared in solution by simple mixture of solution of copper sulfate with Hpbm in ethanol with a ratio of the former to

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Y.-P. Tong, S.-L. Zheng / Journal of Molecular Structure 841 (2007) 34–40

Table 2 ˚ ) and angles () for 1 Selected experimental/calculated bond length (A Cu(1)–O(1) Cu(1)–N(1) O(1)–C(1) N(1)–C(7) O(1)–Cu(1)–O(1a) O(1)–Cu(1)–N(1a) O(1a)–Cu(1)–N(1a)

1.9390(17)/1.9305 1.980(2)/2.0385 1.327(3)/1.3065 1.334(3)/1.3385 180/180.0 91.06(8)/91.3 88.94(8)/88.7

N(1)–C(8) N(2)–C(7) N(2)–C(13) C(6)–C(7) O(1)–Cu(1)–N(1) O(1a)–Cu(1)–N(1) N(1a)–Cu(1)–N(1)

1.398(3)/1.3995 1.354(3)/1.3735 1.381(3)/1.3845 1.454(3)/1.4475 88.94(8)/88.7 91.06(8)/91.3 180.0(1)/180.0

Symmetry code: a: 1  x, y, 1  z.

the latter of 1 to 2 under heating, the single crystal for 1 has been experimentally proven to be very hard to grow employing conventional solution and diffusion methods, as 1 is almost insoluble to common organic solvents. It is well known that hydrothermal synthesis technique is effective to the growth of single crystal, especially to those of difficult single crystals. Thus after all efforts, hydrothermal method was employed to grow the single crystal of 1, avoiding the difficulty of insolubility in common organic solution, and finally, as expected, the brownish red block single crystal of 1 was successfully isolated under hydrothermal condition; thus the systematic investigations of its electronic structure and spectroscopic properties could be carried out based on experimental geometry. 3.2. Crystal structure 1 is a monomer and has a square-planar geometry with CuN2O2 core. The central Cu(II) is coordinated by two deprotonated Hpbm, i.e. monoanionic pbm in a trans configuration, furnishing a centrosymmetrical structure (Fig. 1). The CuN2O2 core is perfectly coplanar due to the centrosymmetry, and this plane further forms dihedral angles of 37.1 and 31.1 with the conjoint phenolate ring

Fig. 1. Perspective view of 1 with the thermal ellipsoids at 50% probability level. Symmetry code: (A) 1  x, y, 1  z.

and benzimidazole ring, respectively. As presented in Table 2, the bond angles around central Cu(II) are O(1)–Cu(1)– N(1a) 91.06(8), O(1)–Cu(1)–N(1) 88.94(8), O(1)–Cu(1)– O(1a) 180 and N(1a)–Cu(1)–N(1) 180, which are all very close or identical to 90/180, strongly indicating the slightly distorted square-planar configuration. The Cu–N and ˚ , respectively, Cu–O lengths are 1.980(2) and 1.9390(17) A which are typical to those documented previously [25,26]. On the other hand, the central copper(II) atom and the ligands form two stable six-membered rings which increase the stability of the complex, but these six-membered rings formed by Cu1, O1, C1, C6, C7 and N1 are not coplanar (Fig. 1), as indicated by the large mean deviation of these ˚ ). In the ligand system, the dihedral angle atoms (0.178 A between benzimidazole ring and phenolate ring is 18.2, indicating the basic non-coplanarity of ligand system and obviously further twist along the C(6)–C(7) bond axis with respect to neutral ligand (the corresponding dihedral of only 2.2) [17]. Strong intermolecular hydrogen bonding between imidazole NH group and phenolate O atom of ˚ ) is adjacent complex molecule (N(2A)  O1 2.857(3) A present (Fig. 2); moreover the intermolecular p–p stacking interactions between ligand rings of adjacent molecules are also observed in an offset unparallel way in the lattice with ˚ (Fig. 3). Both the an inter-plane distance of ca. 3.21–4.06 A hydrogen bonding and p–p stacking interactions connect adjacent complex molecules and extend them into three-dimensional network, therefore, both of them play critical role to the stability of the crystal lattice.

Fig. 2. Perspective view of hydrogen-bonding interactions in 1. Symmetry code: (A) 0.5 + x, 0.5  y, 1  z.

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are dz2–dyz (25%), dxz (23%) and dz2 + dyz (82%), respectively (Fig. 4). 3.21-4.06 Å

Fig. 3. Perspective view of p–p stacking interactions in 1.

3.3. Ground state electronic structure DFT calculations were carried out for 1 to elucidate the electronic properties and thus understand the nature of the transitions observed in the UV–vis spectra (mentioned below). The DFT-optimized structure converged successfully to a structure, which is in well agreement with the experimental X-ray structure (Table 2), thus implying the adequacy of the theoretical method employed for the geometry optimizations of this particular system. The calculated ground state b-spin molecular orbital energy level diagram is presented in Fig. 4. All the Cu b-spin d orbitals are occupied, except for the Cu dx2 –y 2 , which can be regarded to be the only unoccupied d orbital (b-spin LUMO), though it is a combination of Cu d orbitals (59% dx2 –y 2 ) and ligand orbitals, while b-spin HOMO is predominantly ligand p bonding orbital with little contribution from Cu d orbitals (3%). The b-spin LUMO + 1 and LUMO + 2 are mainly ligand p* antibonding orbitals being very close in energy, thus would be degenerate. The occupied orbitals just below b-spin HOMO in energy (from HOMO-1 to HOMO-8) are all typically ligand p bonding orbitals with negligible contribution from Cu d orbitals except that HOMO-6 is a combination of P orbitals of ligand O atoms and r bonding orbitals of other ligand atoms (Fig. 4). The b-spin HOMO-9 is Cu–O r bonding orbital, but has obvious Cu d orbital character (19% dx2 –y 2 + dxy); HOMO-10, HOMO-11 and HOMO-13 are another three occupied orbitals with larger Cu d orbital character, they are all combinations of Cu d orbitals and ligand p bonding orbitals, in which the corresponding Cu d orbital compositions

3.4. Electronic spectrum and spectroscopic properties The UV–vis spectra of 1 in chloroform (ca. 106 M) is depicted in Fig. 5 and presented in Table 3. 1 displays two clearly bands centering at 370 and 403 nm, and the latter is a broader band. Moreover, a weaker band with redshift in energy centering at 444 nm is also observed (Fig. 5). TDDFT calculations show that the calculated low-lying absorption maxima (393, 421 and 451 nm, Table 3) all involve the b-spin LUMO frontier orbital (as shown in Fig. 6) as the main arrival orbital of transitions and the ligand p bonding orbitals as the main starting ones of transitions. Because of the main Cu dx2 –y 2 orbital character of the b-spin LUMO (mentioned above), thus these low-lying absorption maxima should be mainly ascribed to similar p ! dx2 –y 2 ligand-to-metal charge transfer (LMCT) transitions. As shown in Table 3 and Fig. 5, the TDDFT calculated results are consistent well with experimental ones. In general, the absorption bands in experimental UV–vis spectra originate from the transitions from ground state to higher energy excited states. According to our TDDFT calculations, the low-lying absorption maximum at 451 nm, and an oscillator strength as low as 0.016 can be well cor-

0.14 0.0265

Absorbance

3.21-4.06 Å

0.0260

0.10

0.0255 0.0250 0.0245 438

0.06

0.02 325

375

442

425

446

450

475

Wavelength / nm Fig. 5. UV–vis spectrum of 1 in chloroform (ca. 106 M). The inset shows an enlargement of the 435–455 nm zone.

0.0

+2 π) +1 π

E / Har tree

-1.5 -3.0

LUMO

-4.5

HOMO

-6.0 -7.5 -9.0

x2-y2

-1 π -3 π -4 π -6 P, σ -9 (x2-y2)+xy -10 z2-yz -11 xz -13 z2+yz

(59%)

Table 3 Experimental and calculated UV–vis absorption bands, oscillator strengths and transition properties of 1 Experimental (nm)

(19%) (25%) (23%) (82%)

Fig. 4. The b-spin frontier molecular orbital energy level diagram of 1.

Calculated (nm)

Oscillator strength

Transition property

403

687 451 441 421

0.009 0.016 0.003 0.077

370

393

0.048

p ! dx2 –y 2 (LMCT) p ! dx2 –y 2 (LMCT) p fi p* (LCCT) p ! dx2 –y 2 (LMCT); ðP;rÞ ! dx2 –y 2 (LMCT) ðP ; rÞ ! dx2 –y 2 (LMCT); p ! dx2 –y 2 (LMCT)

444

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Fig. 6. Contour surfaces of b-spin frontier molecular orbitals most involved in the calculated excitations of UV–vis spectra of 1: LUMO + 2 (a), LUMO + 1 (b), LUMO (c), HOMO (d), HOMO  1 (e), HOMO  3 (f), HOMO  4 (g) and HOMO  6 (h).

related with the 444 nm weak band in experimental electronic spectrum. This transition is mainly associated with transition from b-spin HOMO-3 to b-spin LUMO with configuration interaction coefficient up to 0.87 and transition from b-spin HOMO-4 to b-spin LUMO with configuration interaction coefficient up to 0.36; both b-spin HOMO-3 and HOMO-4 are predominantly ligand p bonding orbitals character and contribution from central Cu d orbitals is negligible, while b-spin LUMO is mainly Cu d orbitals (dx2 –y 2 ) character with minor contribution from ligand orbitals (Fig. 6), thus this transition can be reasonably ascribed to p ! dx2 –y 2 ligand-to-metal charge transfer

transition (LMCT). As for the low-lying absorption maximum of 421 nm with an oscillator strength 0.077, it can readily be correlated with the relatively intense absorption band of 403 nm in experimental UV–vis spectrum. In going from 451 nm absorption maximum to 421 nm one, the oscillator strength variation is consistent with the change of experimental absorption band intensity in UV–vis spectra (Fig. 5). This absorption maximum (421 nm) is mainly associated with similar transition from b-spin HOMO-4 to b-spin LUMO with configuration interaction coefficient up to 0.63 and transition from b-spin HOMO-3 to b-spin LUMO with configuration interaction coefficient up to 0.46, as well as an additional transition from b-spin HOMO-6 to b-spin LUMO with configuration interaction coefficient up to 0.56. Because of the P orbital character of ligand O atoms and r bonding orbital character of other ligand atoms for b-spin HOMO-6, the transition (421 nm) can be ascribed to similar p ! dx2 –y 2 ligand-tometal charge transfer transition (LMCT), admixed with ðP;rÞ ! dx2 –y 2 ligand-to-metal charge-transfer transition (LMCT). Similarly, the calculated low-lying absorption maximum of 393 nm with oscillator strength 0.048 can be correlated with the 370 nm absorption band in UV–vis spectra. In terms of TDDFT results, this absorption maximum mainly arises from two transitions that start from b-spin HOMO-6 orbital and b-spin HOMO-4 orbital (Fig. 6) and both finish at the b-spin LUMO orbital with corresponding configuration interaction coefficients 0.71 and 0.66, respectively. Thus the 393 nm absorption maximum can be mainly ascribed to ðP;rÞ ! dx2 –y 2 ligand-tometal charge transfer transition (LMCT), admixed with p ! dx2 –y 2 ligand-to-metal charge-transfer transition (LMCT). The TDDFT calculation predicts another two relatively much weak charge-transfer absorption maxima (687 nm, oscillator strength 0.009; and 441 nm, oscillator strength 0.003, Table 3), the former absorption maximum (687 nm) predominantly arises from transition from b-spin HOMO  1 to b-spin LUMO with configuration interaction coefficient up to 0.99, and this transition is predominantly p ! dx2 –y 2 ligand-to-metal charge-transfer transition (LMCT) in nature. While the latter one (441 nm) is much more complicated in transition compositions, as it mainly has up to four transitions, which start from a-spin HOMO, a-spin HOMO  1, b-spin HOMO and b-spin HOMO  1, and finish at a-spin LUMO, a-spin LUMO + 1, b-spin LUMO + 1 and b-spin LUMO + 2, respectively. The corresponding configuration interaction coefficients for the four transition compositions are 0.57, 0.46, 0.53 and 0.44, respectively. According to our molecular orbital analyses, all these molecular orbitals involved in this transition are ligand p bonding (a-spin HOMO, a-spin HOMO  1, b-spin HOMO and b-spin HOMO  1) and ligand p* antibonding orbitals (a-spin LUMO, a-spin LUMO + 1, b-spin LUMO + 1 and b-spin LUMO + 2), thus this transition can be ascribed to p fi p* ligand-centered charge transfer transition (LCCT). As expected, both

Y.-P. Tong, S.-L. Zheng / Journal of Molecular Structure 841 (2007) 34–40

predicted absorption maxima have not been observable in experimental UV–vis spectrum, consistent with the fact that they have relatively quite much low oscillator strengths. It is worth mentioning that according to the current TDDFT calculation, no d–d transition bands may occur in the low-lying energy region, which is different from other N, O-donor square-planar Cu(II) complexes where the dz2 ! dx2 –y 2 absorption bands occur at low-lying energy region (approximately 565–651 nm) [27]. In terms of molecular orbital analyses for 1 (mentioned above), though the b-spin LUMO is mainly Cu dx2 –y 2 orbital in character, the occupied Cu d orbitals, or orbitals with significant to considerable Cu d orbital character lie far away below b-spin HOMO, which are b-spin HOMO-9, b-spin HOMO-10, b-spin HOMO-11 and b-spin HOMO-13, thus, the d-d transition bands should occur in much higher energy region, not the low-lying energy region, which is consistent with our TDDFT results. On the other hand, although our TDDFT calculations predict a quite much weak absorption maximum (687 nm), which is very close to the dz2 ! dx2 –y 2 ligand field absorption band in energy [27], this transition is just p ! dx2 –y 2 ligand-to-metal chargetransfer transition (LMCT) in nature, and in contradiction to the dz2 ! dx2 –y 2 ligand field transition. The reason for this is probably due to the fact that the ligands, pbm, provide high-lying occupied p bonding orbitals, and as a result the high-lying occupied orbitals, e.g. HOMO and HOMO  1, are mainly ligand p bonding orbitals in nature, and the resulting lowest energy transition is changed from dz2 ! dx2 –y 2 ligand field transition to the p ! dx2 –y 2 ligand-to-metal charge-transfer transition (LMCT) in nature. In summary, our TDDFT calculations correctly predict the low-lying absorption bands in experimental UV–vis spectrum for 1. These low-lying absorption bands are mainly p ! dx2 –y 2 and/or ðP;rÞ ! dx2 –y 2 ligand-to-metal charge transfer transition (LMCT) in nature. 1 is not photoluminescent both in solid state and in common organic solvents, which is usual for Cu(II) complexes owing to the d-electron quenching mechanism. 4. Conclusion A square-planar Cu(II) complex with Hpbm has been described and its geometric structure, electronic structure and spectroscopic properties thoroughly investigated by X-ray crystallography, spectroscopic investigation, DFT and TDDFT theoretical level calculations. This has allowed us to look into the correlated relationship of geometric and electronic structure with spectroscopic properties for this complex, which in turn permitted us to rationalize its spectroscopic properties. The TDDFT calculations demonstrate that the low-lying absorption bands in UV–vis spectrum are all mainly p ! dx2 –y 2 and/ or ðP;rÞ ! dx2 –y 2 ligand-to-metal charge transfer transition (LMCT) in nature.

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Acknowledgements This work was supported by the Natural Science Foundation of Guangdong Province (Grant No. 06301028) and the Natural Science Foundation of Department of Education of Guangdong Province, China. Thanks to Prof. X.M. Chen at MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, Sun Yat-Sen University for the Xray data collection. Appendix A. Supplementary data Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre (Deposition No. CCDC-603129 for 1). Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2006.11.055. References [1] (a) D.V. Scaltrito, D.W. Thompson, J.A. O’Callaghan, G.J. Meyer, Coord. Chem. Rev. 208 (2000) 243; (b) D.R. McMillin, K.M. McNett, Chem. Rev. 98 (1998) 1201. [2] Y.-M. Lee, H.-W. Lee, Y.-I. Kim, Polyhedron 24 (2005) 377. [3] X.-H. Bu, M. Du, L. Zhang, Z.-L. Shang, R.-H. Zhang, J. Chem. Soc. Dalton Trans. (2001) 729. [4] M.A. Halcrow, L.M.L. Chia, X. Liu, E.J.L. McInnes, L.J. Yellowlees, F.E. Mabbs, I.J. Scowen, M. McPartlin, J.E. Davies, J. Chem. Soc. Dalton Trans. (1999) 1753. [5] (a) X.-C. Huang, J.-P. Zhang, X.-M. Chen, J. Am. Chem. Soc. 126 (2004) 13218; (b) X.-C. Huang, J.-P. Zhang, Y.-Y. Lin, X.-M. Chen, Chem. Commun. (2005) 2232. [6] Y. Ma, C.-M. Che, H.-Y. Chao, X. Zhou, W.-H. Chen, J. Shen, Adv. Mater. 11 (1999) 852. [7] X.-M. Ouyang, D.-J. Liu, T.-A. Okamura, H.-W. Bu, W.-Y. Sun, W.X. Tang, N. Ueyama, J. Chem. Soc. Dalton Trans. (2003) 1836. [8] D. Felder, J.-F. Nierengarten, F. Barigelletti, B. Ventura, N. Armaroli, J. Am. Chem. Soc. (2001) 6291. [9] T. Kajiwara, N. Kon, S. Yokozawa, T. Ito, N. Iki, S. Miyano, J. Am. Chem. Soc. 124 (2002) 11274. [10] Y. Liang, R. Cao, W. Su, M. Hong, W. Zhang, Angew. Chem. Int. Ed. 39 (2000) 3304. [11] S.S. Tandon, L.K. Thompson, J.N. Bridson, J.C. Dewan, Inorg. Chem. 33 (1994) 54. [12] (a) X.-H. Bu, M. Du, L. Zhang, Z.-L. Shang, R.-H. Zhang, M. Shionoya, J. Chem. Soc. Dalton Trans. (2001) 729; (b) D. Cheng, M.A. khan, R.P. Houser, J. Chem. Soc. Dalton Trans. (2002) 4555; (c) S.-A. Li, D.-F. Li, D.-X. Yang, Y.-Z. Li, J. Huang, K.-B. Yu, W.X. Tang, Chem. Commun. (2003) 880. [13] (a) S. Abuskhuna, M. McCann, J. Briody, M. Devereux, V. McKee, Polyhedron 23 (2004) 1731; (b) A.L. Abuhijleh, C. Woods, Inorg. Chem. Commun. 4 (2001) 119; (c) S.M. Morehouse, H. Suliman, J. Haff, D. Nguyen, Inorg. Chim. Acta 297 (2000) 411. [14] (a) J.S. Valentine, M.W. Pantoliano, in: T.G. Spiro (Ed.), Copper Proteins, Springer, London, 1981, p. 292; (b) A.W. Eddison, in: K.D. Karlin, J. Zubieta (Eds.), Copper Coordination Chemistry: Biochemistry and Inorganic Perspectives, Adenine Press, Guilderland, New York, 1983, pp. 109–128. [15] W.J. Eilbeck, F. Holmes, A.E. Underhill, J. Chem. Soc. (1967) 757. [16] Y.-P. Tong, S.-L. Zheng, X.-M. Chen, Inorg. Chem. 44 (2005) 4270.

40

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[17] [18] [19] [20]

Y.-P. Tong, S.-L. Zheng, X.-M. Chen, Eur. J. Inorg. Chem. (2005) 3734. A.W. Addison, P.J. Burke, J. Heterocyclic Chem. 18 (1981) 803. R. Blessing, Acta Crystallogr. A 51 (1995) 33. G.M. Sheldrick, SHELXTL 6.10, Bruker Analytical Instrumentation, Madison, Wisconsin, USA, 2000. [21] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennuci, C. Pomelli, C. Adamo, S. CliVord, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Oritz, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,

[22] [23] [24] [25] [26] [27]

C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, J.L. Andres, M. HeadGordon, E.S. Replogle, J.A. Pople, GAUSSIAN 98, Revision A9, Gaussian, Inc., Pittsburgh, PA, 1998. A.D. Becke, J. Chem. Phys. 98 (1993) 5648. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. G. Schaftenaar, Molden, Version 3.5, CAOS/CAMM Center Nijmegen, Toernooiveld, Nijmegen, The Netherlands, 1999. L.-Z. Li, C. Zhao, T. Xu, H.-W. Ji, Y.-H. Yu, G.-Q. Guo, H. Chao, J. Inorg. Biochem. 99 (2005) 1076. R. Kannappan, S. Tanase, I. Mutikainen, U. Turpeinen, J. Reedijk, Inorg. Chim. Acta 358 (2005) 383. Z.D. Matovic´, V.D. Miletic´, G. Samardzˇic´, G. Pelosi, S. Ianelli, S. Trifunovic´, Inorg. Chim. Acta 358 (2005) 3135.