Two new barium-copper-ethylene glycol complexes: synthesis and structure of BaCu(C2H6O2)n(C2H4O2)2 (n = 3, 6)

Abstract

Two crystalline barium-copper-ethylene glycol complexes have been isolated and structurally characterized by single-crystal x-ray diffraction. The solution-phase complex has also been investigated as a molecular precursor for use in sol-gel synthesis of high-temperature superconductors. The first crystalline form has the formula BaCu(C[sub 2]H[sub 6]O[sub 2])[sub 6](C[sub 2]H[sub 4]O[sub 2])[sub 2] (1) and has been isolated directly from ethylene glycol solutions of the barium-copper salt. In this molecule, copper is coordinated to the four xygens of two ethylene glycolate ligands in a nearly square planar geometry. Barium is coordinated by three bidentate ethylene glycol molecules and three monodentate ethylene glycol molecules; the 9-fold coordination resembles a trigonal prism with each rectangular face capped. Copper and barium moieties do not share any ethylene glycol or glycolate oxygens; they are found by hydrogen bonding to form linear chains. The second crystal type has formula BaCu(C[sub 2]H[sub 6]O[sub 2])[sub 3](C[sub 2]H[sub 4]O[sub 2])[sub 2] (2). It was prepared via crystallization of the mixed-metal alkoxide from an ethylene glycol/methyl ethyl ketone solution. As for 1, the copper is coordinated to four oxygen atoms of two ethylene glycolate ligands in a nearly square planar arrangement. Barium is 8-coordinate in a distorted cubic geometry. It is coordinatedmore » to three bidentate ethylene glycol molecules and shares two of the oxygen atoms bound to the copper (one from each coordinated ethylene glycol) to form a discrete molecular barium-copper complex.« less