Two new barium-copper-ethylene glycol complexes: Synthesis and structure of BaCu(C2H6O2)n(C2H 2O2)2 (n = 3, 6)

Article abstract of DOI:10.1021/ic00036a013

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(C₂H₆O₂)₆(C₂H ₄O₂)₂ (1) and has been isolated directly from ethylene glycol solutions of the barium-copper salt. Crystallographic data for 1 are as follows: monoclinic space group Cc (No. 9), a = 12.103 (6) ?, b = 13.527 (3) ?, c = 17.091 (8) ?, β = 93.17 (2)°, V = 2793.8 ?³, Z = 4, R = 0.030. In this molecule, copper is coordinated to the four oxygens 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 bound by hydrogen bonding to form linear chains. The second crystal type has formula BaCu(C₂H₆O₂)₃(C₂H ₄O₂)₂ (2). It was prepared via crystallization of the mixed-metal alkoxide from an ethylene glycol/methyl ethyl ketone solution. Crystallographic data for 2 are as follows: monoclinic space group P2₁/n (No. 14), a = 12.127 (4) ?, b = 11.913 (1) ?, c = 12.540 (4) ?, β = 102.47 (1)°, V = 1768.9 ?³, Z = 4, R = 0.025. 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 coordinated 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.