Oximato complexes. Part 1. Solution study, synthesis, structure, spectroscopic and magnetic properties of polynuclear copper(II) complexes containing dimethylglyoxime

Abstract

Copper(II) complexes of composition [Cu₂(Hdmg)₂(H₂dmg)(H₂O)₂][ClO₄]₂·H₂O 1, [Cu₂(dmg)(Hdmg)(H₂dmg)]ClO₄·1.5H₂O 2 and [Cu₃(dmg)₂(H₂dmg)₂][ClO₄]₂·2H₂O 3(H₂dmg = dimethylglyoxime) were obtained. The crystal structure of complex 1 was solved by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P2₁/n, with a= 15.991(3), b= 11.682(1), c= 14.363(4)Å, β= 90.82(5)° and Z= 4. The structure consists of cationic dinuclear [Cu₂(Hdmg)₂(H₂dmg)(H₂O)₂]²⁺ units, unco-ordinated perchlorate anions and lattice water. The Cu(H₂dmg)²⁺ fragment co-ordinates to the second copper(II) ion through the depronated oximate oxygens of Cu(Hdmg)₂ to afford a dinuclear structure doubly bridged by the oximate groups in a cis arrangement. The intramolecular Cu(1)⋯ Cu(2) separation is 3.526(4)Å. The configuration about the copper atoms is a distorted square pyramid: the basal plane for Cu(1) comprises two nitrogens of H₂dmg and two oximate oxygens whereas that of Cu(2) is formed by four nitrogens of two Hdmg^– groups; a water molecule occupies the apical position in both cases. Variable-temperature magnetic susceptibility measurements (50–300 K) on complexes 1–3 revealed the occurrence of a very strong intramolecular antiferromagnetic interaction through the oximate bridges. The formation of mononuclear, dinuclear and trinuclear copper(II) dimethylglyoxime complexes have been observed by spectrophotometry in ethanolic solutions of copper(II) perchlorate and [Cu(Hdmg)₂]. A rational scheme accounting for the nature of the existing species has been proposed in the light of the coupled solution–solid state studies.