Synthesis and Properties of Bis[N-R-(5-chloro-α-phenyl-2-hydroxybenzylidene)aminato]copper(II) Complexes and Crystal and Molecular Structures of the Derivatives with R = N-butyl and R = Isobutyl (two Structural Isomers)

A series of bis[N-R-(5-chloro-α-phenyl-2-hydroxybenzylidene)aminato]copper(II) complexes, with R = alkyl (or benzyl), has been prepared and studied using magnetic, spectroscopic, and crystallographic techniques. Unlike the N-methyl derivative, the compounds are magnetically normal and are presumed to consist of monomeric distorted planar (R = H, ethyl, n-propyl, isobutyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, benzyl) or distorted tetrahedral (R = isopropyl, sec-butyl, cyclohexyl) species, usually having the alkyl groups pointing to opposite sides of the approximate O2N2 ligand plane (“trans”). The n-butyl and isobutyl complexes are exceptional and their crystal structures were determined by single-crystal x-ray diffraction using counter techniques. The isobutyl complex exists in two distinct crystalline forms, green and red. The green isomer has the isobutyl groups pointing to the same side of the approximate CuO2N2 plane (“cis”). The n-butyl complex, which is dark green, has the same arrangement of the n-butyl groups. The red isomer of the isobutyl complex contains two crystallographically independent molecules, each having the isobutyl groups trans. The metal environment of the n-butyl complex (cis) is much closer to tetrahedral (dihedral angle 31°) than the green isobutyl (also cis) complex (14.5°). Crystal data for the n-butyl complex: space group P21/c, Z = 4, a = 9.026 (4) Å, b = 19.52 (3) Å, c = 17.88 (2) Å, β = 94.46 (7)°, V = 3142 Å3, R = 3.6%, 2624 reflections. Crystal data for the green isomer of the isobutyl complex: space group P1, Z = 2, a = 10.964 (5) Å, b = 11.490 (5) Å, c = 12.861 (7) Å, α = 99.52 (5)°, β = 97.07 (5)°, γ = 97.59 (6)°, V = 1566 Å3, R = 3.8%, 2309 reflections. Crystal data for red isomer of isobutyl complex: space group P1, Z = 2, a = 8.900 (2) Å, b = 9.991 (2) Å, c = 17.998 (3) Å, α = 102.54 (4)°, β = 94.61 (4)°, γ = 92.49 (2)°, V = 1554 Å3, R = 4.8%, 5194 reflections