Metal complexes formed by metal-assisted solvolysis of di-pyridylketone azine: structures and magnetic properties

Abstract

A series of metal complexes were achieved from the metal-assisted solvolysis reaction of di-pyridylketone azine (dpka). The tetranuclear nickel cluster 1, {Ni₂[dpk(O)(OH)][dpk(O)(OCH₃)](N₃)₂}₂, is centrosymmetric with a central core described as an edge-shared triangle core. Neighboring Ni(II) ions are alternately bridged by (µ₂-N₃, µ₃-O) and (µ₂-O, µ₃-O) double bridges. Complex 2, {Cu₄[dpk(O)(OCH₃)]₄(N₃)₂}(CuCl₂)₂ contains a tetranuclear cluster and two identical [CuCl₂]M⁻ anions. The tetranuclear structure has two crystallographically imposed twofold axes, in which the four copper ions are arranged to be rhombic shape. The neighboring copper(II) ions along the lateral are bridged by single µ₂-O from the ligand dpk(O)(OCH₃) and the short diagonal copper ions are bridged by two symmetric end-on azides. In dinuclear Cu(II) complex {Cu₂[dpka(OCH₂CH₃)]Cl₂}(ClO₄) (3), the metal centers are coordinated in a planar configuration and bridged by a –N–N– bridge. It is also observed that the Cl atom coordinated to one Cu^II center is also weakly coordinated to another inversion related Cu^II to generate a centrosymmetric dimer. The metal centers in one-dimensional polymeric Cu(II) complex {Cu₂[dpka(OCH₃)](N₃)₂(ClO₄)}_n (4), however, are bridged by a –N–N– bridge and an end-to-end azide bridge, alternately. Magnetic susceptibility measurements indicate that 1 shows ferromagnetic interaction within the tetranuclear cluster, and that 2 displays moderately strong antiferromagnetic interaction (J = −56.7 cm⁻¹) for the bis(µ-N₃) bridge. For compound 4, it shows strong antiferromagnetic coupling (J = −286 cm⁻¹) between the intradinuclear Cu^II ions mediated by the single N–N bridge and negligible magnetic interactions between the adjacent dinuclear Cu^II ions mediated by the single end-to-end azide bridge. The mechanism of the metal-assisted solvolysis reaction was also discussed.