A new strontium-copper ethylene glycol complex: synthesis and structure of [Sr(C2H6O2)5][Cu(C2H4O2)2]·C2H6O2

Abstract

A new crystalline strontium-copper ethylene glycol complex has been isolated and structurally characterized by single-crystal X-ray diffraction. The solution-phase complex has also been investigated as a possible molecular precursor for use in sol-gel synthesis of SrCuO2. [Sr(C2H6O2)5][Cu(C2H4O2)2]·C2H6O2 has been isolated by crystallization from an ethylene glycol/methylethylketone solution of the strontium-copper salt. Crystallographic data are as follows: orthorhombic, space group Pna21, a = 18.494(3), b = 9.3076(8), c = 16.615(3)Å, V = 2860(2) Å3, Z = 4, R = 0.044. In this molecule, copper is coordinated by two bidentate ethylene glycolate ligands in roughly a square planar geometry. Strontium is coordinated by three bidentate ethylene glycol molecules and two monodentate ethylene glycol molecules; the eight-fold coordination resembles a highly-distorted square antiprism. An additional ethylene glycol of crystallization is present which does not directly coordinate the strontium ion. Copper and strontium ion complexes are held together by hydrogen bonding. The solution-phase bimetallic complex is hydrolytically unstable, giving rise to a ‘muddy’ brown precipitate upon exposure to water. The apparent decomposition is in direct contrast with hydrolysis of similar barium-copper complexes which gives rise to stable blue gels. This decomposition made the strontium-copper diol complex unsuitable for use in alkoxide sol-gel synthesis of strontium-copper oxides.