A novel triple aqua-, phenoxo- and carboxylato-bridged dinickel(ii) complex, its magnetic properties, and comparative biomimetic catalytic studies with analogous dinickel(ii) complexes

Abstract

This paper describes the synthesis and structures of three dinickel(II) complexes, namely [Ni₂(μ-L)(μ-OH)](ClO₄)₂ (1), [Ni₂(μ-H₂L)(μ-OH)(NCS)₃](NCS) (2), and [Ni₂(μ-HL)(μ-OBz)(μ-H₂O)(OBz)](ClO₄)₂·2.5H₂O (3) (where HOBz = benzoic acid), with an end-off compartmental ligand (HL) obtained via the Schiff base condensation of 2,6-diformyl-4-methylphenol and N,N-dimethyldipropylenetriamine in methanol. Structural characterization reveals that both 1 and 2 are phenoxo- and hydroxo-bridged compounds, while complex 3 is a unique triple aqua-, phenoxo- and carboxylato-bridged dinickel(II) complex. Although similar bridging patterns to that found in 3 are known, the combination of aqua-, carboxylato- and phenoxo-bridging in a dinickel(II) complex has not been reported in the literature. Variable temperature magnetic susceptibility analysis reveals that the two nickel centres are antiferromagnetically coupled, with J values ranging from −12 to −143 K, in these complexes. The phenoxazinone-synthase-like activities of these complexes have been investigated using o-aminophenol as a model substrate in a methanol medium, as this area is yet to be explored for nickel(II) systems. Mass spectrometry and EPR spectroscopic studies were further carried out to gain insight into the course of the reaction, and the reactivity trend has been further explored. The present work highlights the novel triply bridged dinickel(II) complex and its magnetic properties and demonstrates a comparative biomimetic catalytic study relating to phenoxazinone synthase.