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Copper(II) complexes [CuL2(i-PrNH2)2·H2O] (1a), [CuL2(i-PrNH2)2] (1b), [CuL2(EtNH2)2·H2O] (2a), [CuL2(EtNH2)2]·CHCl3 (2b), [CuL2(EtNH2)2·H2O]·2CHCl3 (2c), and [CuL2(EtNH2)2·MeOH] (2d) (L = 5,5-diphenylhydantoinate) have been prepared. The crystal structures of 1a, 2c, and 2d were determined by X-ray analysis. Each CuN4O chromophore is a five-coordinated square-based pyramidal geometry. The axial Cu–O distances are Cu(1)–O(1)(water) = 2.362(10) Å, Cu(1)–O(1)(water) = 2.436(9) Å and Cu(1)–O(1)(MeOH) = 2.33(1) Å, for complexes 1a, 2c, and 2d, respectively. Intramolecular hydrogen bonds are formed between the carbonyl oxygens and amino hydrogens (C=O···H–N) as well as the axial ligand (C=O···H–O). The latter hydrogen bonds stabilize the axial ligand for coordination. Moreover, double intermolecular hydrogen bonds link the 5,5-diphenylhydantoinate ligands (C=O···H–N) belonging to be adjacent complex molecules in all three complexes. The electronic spectra of the complexes in the solid state and in chloroform solutions were determined at room temperature, and a considerable change in ligand field bands was observed. The five-coordinated complexes in the chloroform solutions release their axial water ligand and the CuN4O chromophore converts into a distorted tetrahedral CuN4 chromophore.

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Square planar [CuN4] copper(II) complexes, Rb2[Cu(succim)4]•2H2O (1), trans-[CuL2(R-chea)(S-chea)] (2), trans-[CuL2(R-chea)2] (3), (succim = succinimidate, L = 5,5-diphenylhydantoinate, and chea = 1-cyclohexylethylamine) were prepared and crystal structures were determined. Crystal data for 1 are monoclinic with space group C2/m; a = 16.279(4), b = 8.382(3), c = 8.297(3) Å; β = 93.13(3) °; V = 1130.4(6) Å3; Z = 2. Crystal data for 2 are monoclinic with space group P21/c; a = 8.485(2), b = 9.7854(8), c = 26.334(4) Å; β = 92.83(1) °; V = 2183.8(5) Å3; Z = 2. Crystal data for 3 are monoclinic with space group P21; a = 8.472(2), b = 9.803(2), c = 26.331(6) Å; β = 92.67(2) °; V = 2184.6(8) Å3; Z = 2. The polarized crystal electronic spectra were determined for square planar [CuN4] 1, 2, and 3 and distorted square planar [CuN4] trans-[CuL2(R-phenea)(S-phenea)] (4) and trans-[CuL2(R-phenea)2][CuL2(S-phenea)2] (5) (phenea = 1-phenylethylamine). These spectra were deconvoluted by Gaussian curve fitting by considering selection rules for electric dipole transitions. The 3d orbital orders were determined to be dx2−y2 > dxy > dz2 > dyz,dzx for 1, dx2−y2 > dxy > dz2 > dyz > dzx for 2 and 3, and dx2−y2 > dxy > dz2 > dyz > dzx for 4 and 5 by means of polarized crystal spectra and angular overlap model (AOM) calculations. Since the dz2 → dx2−y2 transition could be observed separately for 4 for the first time, the present assignment could be established certainly. Distortion of [CuN4] chromophores decreases the peak wave numbers for a series of trans-[Cu(imidate)2(amine)2] complexes. The results of 1, 2, and 3 suggest that lone pairs of imidate ligands destabilize the dxy orbital by distributing in the [CuN4] plane.

A copper(II) complex [Cu(succim)2(N-Eten)(H2O)2] (succim = succinimidate and N-Eten = N-ethylethylenediamine) was prepared and characterized by X-ray crystallography and polarized crystal electronic spectra. The complex has a distorted octahedral [CuN4O2] chromophore. The π-donor succim ligands on cis-positions raise the potential of axial coordination up to six-coordination to maintain electroneutrality of the complex.

Copper(II) complexes [Cu(succim)2(phen)H2O]·H2O (1) (succim = succinimidate, phen = 1,10-phenanthroline) and [Cu(succim)2(bpy)H2O] (2) (bpy = 2,2′-bipyridine) were prepared and the crystal structures were determined by X-ray crystallography. The coordination geometries are found to be five-coordinated square-based pyramidal [CuN4O] for each complex. Crystal data for complex 1 are monoclinic with space group P21/n; a = 9.602(4), b = 12.003(4), c = 17.618(4) Å; β = 100.38(3)°; V = 1997(1) Å3; Z = 4. Crystal data for complex 2 are monoclinic with space group P21/n; a = 9.616(2), b = 11.616(3), c = 15.871(2) Å; β = 90.61(2)°; V = 1772.8(6) Å3; Z = 4. The axial Cu–O(water) bond distances of the present complexes (2.548(5) Å for 1 and 2.673(4) Å for 2) are appreciable longer than those of other square pyramidal trans-[CuN4O] complexes. The diffuse reflectance spectra showing a broad peak at about 17000 cm−1 were analyzed by means of Gaussian curve fitting and angular overlap model (AOM) calculations with respect to dxy, dyz, and dzx orbitals distributing in the [CuN4] basal plane. According to the analyses, transferability of AOM parameters is valid for succim. The ligand field of bpy can be described by the same parameters as py (py = pyridine). However, it is necessary to set a larger π-bonding AOM parameter for phen than that of py to reproduce the experimental results. The reason for this is out-of-plane lone pairs and π-conjugation of phen. The assignment of the one-electron orbital sequences is presumed to be dx2−y2 > dz2 > dxy > dyz > dzx based on the AOM calculations for each complex.

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