Formation of trimetallic compounds containing redox-active nitrosyl molybdenum tris(3,5-dimethylpyrazolyl)-borato groups. Schiff base complexes containing two molybdenum centres linked by <i>meta</i> hydroxy copper schiff base ligands

Abstract

The reaction of [Mo(NO)Tp*Cl2] [Tp* = tris(3,5-dimethyl-pyrazolyl)borate] with copper(II) Schiff base complexes derived by condensation of two mole equivalents of 2,4-dihydroxybenzaldehyde with a diamine [1,2-C6H4(NH2)2, NH2(CH2)nNH2, n = 2-5] affords trimetallic species containing three potential redox centres. The IR, UV-vis and EPR spectroscopic properties of these compounds are described and it is shown that, with increasing polymethylene bridges of the Schiff base ligands, the complexes distort from planarity probably towards tetrahedral structures. From cyclic and differential pulse voltammetry it is shown that the trimetallic species primarily undergo two sequential one electron reduction associated with the reduction of [Mo(NO)Tp*Cl]+ centres. By determination of conproportionation constants for the mono-reduced species, it is established that there is very weak interaction between the two [Mo(NO)Tp*Cl]+ centres in the trimetallic complexes. It is also demonstrated that the meta-substituted [Mo(NO)Tp*Cl]+ centres reduce at potentials more anodic than their para-substituted analogues. Reduction potentials of these complexes are also shown to be solvent dependent.