Interpretation of Electronic and EPR Spectra of Copper(II) Amine Complexes - a Test of the MM-AOM Method

The strain energy minimized structures (MM) of a series of copper(II) tetraamines ([Cu((R)-ahaz)((S)-ahaz)]2+, (R)-ahaz (1) = (R)-3-aminohexahydroazepine, (S)-ahaz (2) = (S)-3-aminohexahydroazepine; [Cu((S)-ahaz)2-(OH2)]2+; [Cu(mn[13]aneN4)(OH2)2]2+, mn[13]aneN4 (3) = 12-methyl-12-nitro-1,4,7,10-tetraazacyclotridecane; [Cu(mn[13]aneN4)(OH2)]2+; [Cu(mn[14]aneN4)(OH2)]2+, mn[14]aneN4 (4) = 6-methyl-6-nitro-1,4,8,11-tetraazacyclotetradecane; [Cu(mn[15]aneN4)(OH2)]2+, mn[15]aneN4 (5) = 10-methyl-10-nitro-1,4,8,12-tetraazacyclopentadecane; [Cu(mn[15]aneN4)(OH2)2]2+; [Cu(mn[16]aneN4)(OH2)]+, mn[16]ane N4 (6) = 3-methyl-3-nitro-1,5,9,13-tetraazacyclohexadecane; [Cu(en)2(OH2)2]2+, en (7) = ethane-1,2-diamine), with square planar, square pyramidal, and distorted octahedral chromophores exhibiting various degrees of tetrahedral distortion of the central coordination plane, are in good agreement with published X-ray structures (where available) and the two crystal structures reported in this paper. [Cu(2)2(ClO)4](ClO4) crystallizes in the orthorhombic space group P212121, with a = 7.815(5) Å, b = 14.350(2) Å, c = 18.194(4) Å, Z = 4, and Rw = 0.061. [Cu(5)(Cl)2]·2H2O crystallizes in the triclinic space group P1, with a = 6.884(2) Å, b = 9.090(3) Å, c = 9.214(2) Å, α = 105.13(2)°, β = 107.40(2)°, γ = 107.85(2)°, Z = 1, and Rw = 0.022. The spin Hamiltonian parameters and electronic transitions, estimated with the angular overlap model (AOM) based on the strain energy minimized structures of the chromophores, where generally water is used as axial ligand (MM-AOM), are in reasonable agreement with the calculated spectroscopic parameters based on experimental structures (AOM) and with the experimental spectroscopic data (UV-vis-near-IR and EPR spectra of single crystals, powders, glasses, and solutions). The calculated spectroscopic data are based on a constant set of electronic parameters which depend on the degree of substitution of the amine, on the Cu-N bond length, and on the degree of misdirected valences. © 1995 American Chemical Society.