Assignment of d-d transitions of square planar [(CuN4)-N-II] complexes containing imidate and amine ligands by means of polarized crystal spectra.

Square planar [CuN4] copper(II) complexes, Rb-2[Cu(succim)(4)]. 2H(2)O (1), trans-[CuL2(R-chea)(S-chea)] (2), trans-[CuL2(R-chea)(2)] (3), (succim = s uccinimidate, L = 5,5-diphenylhydantoinate, and chea = 1-cyclohexylethylami ne) 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) Angstrom; beta = 93.13(3) degrees; V = 1130.4(6) Angstrom (3); Z = 2 . Crystal data for 2 are monoclinic with space group P2(1)/c; a = 8.485(2), b = 9.7854(8), c = 26.334(4) Angstrom; beta = 92.83(1) degrees; V = 2183.8 (5) Angstrom (3); Z = 2. Crystal data for 3 are monoclinic with space group P2(1); a = 8.472(2), b = 9.803(2), c = 26.331(6) Angstrom; beta = 92.67(2) degrees; V = 2184.6(8) Angstrom (3); Z = 2. The polarized crystal electron ic spectra were determined for square planar [CuN4] 1, 2, and 3 and distort ed square planar [CuN4] trans-[CuL2(R-phenea)(S-phenea)] (4) and trans-[CuL 2(R-phenea)(2)] [CuL2(S-phenea)(2)] (5) (phenea = 1-phenylethylamine). Thes e spectra were deconvoluted by Gaussian curve fitting by considering select ion rules for electric dipole transitions. The 3d orbital orders were deter mined to be d(x2-y2) > d(xy) > d(z2) > d(yz,zx) for 1, d(x2-y2) > d(xy) > d (z2) > d(yz) > d(zx) for 2 and 3, and d(x2-y2) > d(xy) > d(z2) > d(yz) > d( zx) for 4 and 5 by means of polarized crystal spectra and angular overlap m odel (AOM) calculations. Since the d(z2) --> d(x2-y2) transition could be o bserved separately for 4 for the first time, the present assignment could b e established certainly. Distortion of [CuN4] chromophores decreases the pe ak 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 dest abilize the d(xy) orbital by distributing in the [CuN4] plane.