Structures and electronic spectra of aquadiiminebis(succinimidato)copper(II) complexes with square pyramidal [CuN₄O] chromophores (diimine = 1,10-phenanthroline and 2,2'-bipyridine)

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) ų; 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) ų; 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 d(xy), d(yz), and d(zx) 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 d(x2- y2) > d(z2) > d(xy) > d(yz) > d(zx) based on the AOM calculations for each complex.