ISOLATION AND STRUCTURAL CHARACTERIZATION OF THE COPPER BARIUM ALKOXIDE CLUSTER BA2CU2(OCH2CH2OCH3)4(ACAC)4.2HOCH2CH2OCH3 FROM PRECURSOR SOLUTIONS TO YBA2CU3O7 THIN-FILMS

Attempts to identify intermediates in a solution route to thin films of the high-temperature superconductor YBa2Cu3O7 have led to the isolation of the mixed-metal cluster Ba2Cu2(OR)4(acac)4-2HOR (R = CH2CH2OCH3) (1). This compound, which is the first example of a molecular barium-copper cluster, was isolated from the reaction of the copper dimer [(acac)Cu(OCH2CH2OCH3)]2 with barium 2-methoxyethoxide, the first stage in the preparation of the thin-film precursor solution. Crystallographic data for 1 are as follows: formula = Ba2Cu2O20C3gH72, FW = 1250.5 g/mol, Dx = 1.57 g/cm3, space group = P1, a = 10.797 (3) Å, b = 11.269 (1)Å, c = 12.109 (1) Å, α = 106.18 (1)°, β = 100.93 (2)° γ = 102.98 (2)°, Z = 1, R = 0.031 for 4059 reflections with I ≥ 2σ(I) and 2θ≤50°, μ = 23.5 cm-1, λ(MoKα1) = 0.70930, F(000) = 630. Data were collected at 23°C. The metals are arranged in a rhomboid with triply bridging alkoxide oxygens above and below the two triangular planes defined by two barium atoms and one copper atom. Each metal atom is also bound to an acac ligand, and the barium is further coordinated by the methoxy oxygen of the triply bridging alkoxides and a 2-methoxyethanol. Thin films prepared from this route showed superconducting transition temperatures of 85 K, only small amounts of impurity phases by X-ray powder diffraction, and ≤0.1 atom % carbon as determined by nuclear reaction analysis. © 1990, American Chemical Society. All rights reserved.