Five-coordinate anion-bound copper(II) complexes with non-planar tridentate ligands. X-ray structures of [Cu(L³)(N₃)₂] and [Cu(L³)(ONO)(OClO₃)] (L³=2,6-bis(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine)

Abstract

Synthesis and characterisation of two new nitrite-bound copper(II) compounds [Cu(L¹/L³)(ONO)(OClO₃)] have been achieved [L¹=2,6-bis(pyrazol-1-ylpyridine); L³=2,6-bis(3,5-dimethylpyrazol-1-ylpyridine)]. The complex [Cu(L³)(ONO)(OClO₃)] and a previously reported complex [Cu(L³)(N₃)₂] have been characterised structurally. They belong to only a handful of anion-bound mononuclear five-coordinate copper(II) complexes having a tridentate capping ligand providing a pyridine and two pyrazole donor sites, separated by methylene spacers. The stereochemistry of copper(II) in both the compounds can be described as square-based pyramid with trigonal bipyramidal distortion and the distortion is more pronounced in [Cu(L³)(N₃)₂]. Conductivity data revealed that one of the coordinated anions in [Cu(L¹/L³)(ONO)(OClO₃)] is dissociated in solution, suggesting solvent coordination in solution. Absorption and EPR spectral features of the nitrito complexes represent that the copper(II) centres adopt essentially a square pyramidal geometry. Cyclic voltammetric data clearly revealed predominance of steric over electronic effect (L¹ vs. L³).