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

Synthesis and characterisation of two new nitrite-bound copper(II) compound s [Cu(L-1/L-3)(ONO)(OClO3)] have been achieved [L-1 = 2,6-bis(pyrazol-1-ylp yridine); L-3 = 2,6-bis(3,5-dimethylpyrazol-1-ylpyridine)]. The complex [Cu (L-3)(ONO)(OClO3)] and a previously reported complex [Cu(L-3)(N-3)(2)] have been characterised structurally. They belong to only a handful of anion-bo und mononuclear five-coordinate copper(II) complexes having a tridentate ca pping ligand providing a pyridine and two pyrazole donor sites, separated b y methylene spacers. The stereochemistry of copper(II) in both the compound s can be described as square-based pyramid with trigonal bipyramidal distor tion and the distortion is more pronounced in [Cu(L-3)(N-3)(2)]. Conductivi ty data revealed that one of the coordinated anions in [Cu(L-1/L-3)(ONO)(OC lO3)] is dissociated in solution, suggesting solvent coordination in soluti on. 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 elec tronic effect (L-1 vs. L-3). (C) 2001 Elsevier Science Ltd. All rights rese rved.