Crystal and Molecular Structures of Six Five-coordinated Binuclear Copper(II) Complexes of Gradually Varying Geometry

A series of binuclear copper(II) complexes have been synthesized from bidentate salicylaldimines with nitrogen (R) and ring (R′) substituents and another bidentate ligand (X). The complexes were studied by single-crystal x-ray diffraction using counter methods and their structures were determined. Crystal data are as follows: (a) bis[nitrato(N-n-propyl-2-hydroxybenzylideniminato-μ-O)copper(II)], Cu2O8N4C28H28, X = NO3, R = n-propyl, R′ = 5,6-benzo, space group P1, Z = 1, a = 10.420 (3) Å, b = 8.489 (8) Å, c = 11.687 (2) Å, α = 107.38 (6)°, β = 90.96 (2)°, γ = 131.19 (8)°, V = 709 Å3, R = 5.6%, 2142 reflections; (b) bis[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato(N-(2-methylethyl)-2- hydroxybenzylideniminato-μ-O)copper(II)], Cu2S2F6O6N2C 36H32, X = thenoyltrifluoroacetylacetone (thac), R = isopropyl, R′ = H, space group P1, Z = 1, a = 7.978 (2) Å, b = 11.031 (1) Å, c = 12.399 (3) Å, α = 117.89 (2)°, β = 100.46 (2)°, γ = 92.65 (2)°, V = 938 Å3, R = 3.6%, 2676 reflections; (c) bis[1,1,1,5,5,5-hexafluoro-2,4-pentanedionato(N-phenyl-2- hydroxybenzylideniminato-μ-O)copper(II)], Cu2F12O6N2C36H 22, X = hexafluoroacetylacetone (hfa), R = phenyl, R′ = H, space group P1, Z = 1, a = 9.066 (1) Å, b = 10.583 (3) Å, c = 10.710 (6) Å, α = 99.64 (3)°, β = 114.33 (3)°, γ = 94.58 (2)°, V = 910 Å3, R = 5.1%, 2642 reflections; (d) bis[1,1,1,5,5,5-hexafluoro-2,4-pentanedionato(N-ethyl-5-chloro-2- hydroxybenzylideniminato-μ-O)copper(II)], Cu2Cl2F12O6N2C 28H20, X = hfa, R = ethyl, R′ = 5-Cl, space group P1, Z = 1, a = 9.044 (3) Å, b = 9.300 (3) Å, c = 12.432 (4) Å, α = 95.46°, β = 117.51°, γ = 108.14 (2)°, V = 845 Å3, R = 3.5%, 2392 reflections; (e) bis[ 1,1,1,5,5,5-hexafluoro-2,4-dionato(N-(2-methylethyl)-2-hydroxybenzylideniminato- μ-O)copper(II)], Cu2F12O6N2C30H 26, X = hfa, R = isopropyl, R′ = H, space group P21/c, Z = 2, a = 12.142 (3) Å, b = 16.104 (6) Å, c = 8.835 (1) Å, β = 94.88 (1)°, V = 1721 Å3, R = 4.9%, 2389 reflections; (f) bis[1,1,1,5,5,5-hexafluoro-2,4-pentanedionato(N-(2,2-dimethylethyl)-2- hydroxybenzylideniminato-μ-O)copper(II)], Cu2F12O6N2C32H 28, X = hfa, R = tert-butyl, R′ = H, space group P21/c, Z = 2, a = 8.918 (3) Å, b = 12.776 (3) Å, c = 16.674 (4) Å, β = 103.57 (2)°, V = 1847 Å3, R = 6.4%, 1723 reflections. The metal atoms are five-coordinated, with four stronger and one weaker bond in each case, but the binucleation ranges from A pairs of (distorted) square pyramids joined at the edges of their coplanar bases to B pairs of square pyramids joined at the apices. Between the two extremes (A and B), the distortion toward trigonal-bipyramidal geometry is strongest. The strengths of the bridging bonds and the coplanarity of the pyramid bases (and hence the strength of antiferromagnetic exchange interactions) increase with increasing electronegativity of ligand X. This trend is observed independently of steric constraints, but an additional trend from A to B is observed with decreasing bulkiness of X for a limited sample and with other factors kept constant