A SYNCHROTRON X-RAY STUDY OF THE ELECTRON-DENSITY IN Y2BACUO5

The deformation density (Delta rho) for Y2BaCuO5, barium diyttrium cup rate, determined by single-crystal X-ray diffraction with synchrotron radiation, is affected to only a limited degree by the bonding interac tions involving the O anions. Electron density is strongly depleted al ong the cation-cation contacts within the mirror plane in the structur e and is transferred to regions between mirror planes that do not lie along short cation-cation vectors. The structural geometry for the CuO 5 moiety, with the Cu atom in the +2 state, closely resembles that of the Cu2O5 group in YBa2Cu3O7-delta, for which the +3 state involvement for Cu has been suggested. Space group Pnma, orthorhombic, M(r) = 458 .68, a = 12.1793(7), b = 5.6591 (5), c = 7.1323 (4) Angstrom, V = 491. 6 Angstrom(3), Z = 4, D-x = 6.197 Mg m(-3), lambda = 0.9 Angstrom, mu( 0.9) = 28.893 mm(-1), F(000) = 812, T = 293 K, R = 0.020, wR = 0.020, S = 3.09(5) for 2225 unique reflections.