Structure and magnetism of analogous O-bridged (phenolato) and S-bridged (thiophenolato) binuclear copper(II) complexes. Crystal structure of the binuclear S-bridged complex µ-[2,6-bis(4′-cyclohexyl-4′-hydroxy-2′,3′-diazabuta-1′,3′-dien-1′-yl)-4-methylthiophenolato(3–)-S,N2,O(Cu1,2)]-methanol-µ-(pyrazolyl-N,N′)-dicopper(II)

Abstract

Magnetostructural correlations have been made on a matched pair of O-bridged (phenolato) and S-bridged (thiophenolato) binuclear copper(II) complexes of type [Cu₂(L-X)(pz)], where L-O and L-S are 2,6-bis(4′-cyclohexyl-4′-hydroxy-2′,3′-diazabuta-1′,3′-dien-1′-yl)-4-methyl-phenolat(3–) and -thiophenolate(3–) respectively and pz is an exogenous bridging pyrazolyl ligand. The crystal structure of [Cu₂(L-S)(pz)(CH₃OH)] is the first structure reported for a binuclear copper(II) complex containing a thiophenolato bridging group within a binucleating ligand framework. Crystals are monoclinic, space group P2₁/c, with a= 15.887(5), b= 12.714(4), c= 29.178(6)Å, β= 91.81(2)°, T= 23 ± 1 °C, and Z= 8. Crystals were generally of poor quality and it was only with difficulty that a suitable crystal for intensity data collection was obtained. Automatic diffractometry provided Bragg intensities for 4 594 independent reflections and the structure has been refined by least-squares methods to R 0.163 (all data) and 0.086 [I > 2σ(I)]. The structure consists of two crystallographically unique but chemically similar binuclear molecules in the asymmetric unit, each with one four-co-ordinate and one five-co-ordinate copper atom bridged by a thiophenolate-sulphur atom of the binucleating ligand and by a pyrazolyl group. The Cu ⋯ Cu separations are 3.474(3) and 3.424(3)Å in the two molecules, with Cu–S–Cu angles of 101.5(2) and 99.5(2)° respectively. The angles around the S atom are compatible with a pyramidal (sp³) disposition of bonds which contrasts with the (presumed) trigonal-planar (sp²) bonding of the phenolato O atom in [Cu₂(L-O)(pz)]. Variable-temperature magnetic susceptibility measurements have shown that the antiferromagnetic coupling in [Cu₂(L-S)(pz)] is much weaker (2J=–5.2 cm^–1) than in [Cu₂(L-O)(pz)](2J=–382 cm^–1). In a related S-bridged complex possessing different side groups attached to the thiophenolate ring, the coupling is weakly ferromagnetic. These differences in exchange coupling can be related to geometric differences in the Cu₂(L-X) bridging moiety.