Polymeric coordination compounds of nickel(II), cobalt(II), and zinc(II) with oxalate ions as symmetric tetradentate bridging ligands

Abstract

Coordination compounds having the general formula ML₂Ox are described, with Ox = oxalato dianion; M = Ni, Co and Zn; 1 = water and imidazoles. The compounds are characterised by chemical analyses, i.r., far-i.r., Raman, ligand field and e.s.r. spectra. Magnetic susceptibility measurements at low temperatures indicate a polymeric structure of ant i-ferromagnetically coupled M²⁺ ions. All physical measurements agree with a polymeric structure built up by oxalate ions as tetradentate bridging ligands forming one-dimensional linear chains. Flach metal ion is coordinated by four oxalate oxygens and two donor atoms (N or O) in distorted octahedron. For M = Ni, the magnetic susceptibility measurements can be best described with the Heisenberg model including a zero-field splitting; for M = Co, the Ising model gives the best results. The exchange coupling constants, IJ1, vary from 9-13 cm⁻¹.