REFINEMENT OF THE CRYSTAL-STRUCTURE OF METATORBERNITE

The crystal structure of metatorbernite with composition Cu0.9(UO2PO4)2 . 8 H2O from Vathi, Northern Greece, has been refined, using the intensities of 365 independent reflections, measured on an automated Philips PW 1100 single-crystal diffractometer. The cell constants, refined by least squares, are a = b = 6.972(1) angstrom, c = 17.277(8) angstrom, Z = 2; space group P4/n; rho(calc) = 3.706, rho(obs) = 3.52 g cm-3. The positional and thermal parameters were refined by full-matrix least-squares calculations. Absorption correction and correction for anomalous dispersion, for all atoms, were applied. The final R value is 0.056. The structure is essentially similar to that described by M. Ross, H. Evans and D. Appleman (1964) for metatorbernite, with a difference in the Cu atom position, which here is 1/4 1/4 0.31 instead of 1/4 1/4 0.80. The U atoms are six-coordinated by two O atoms (uranyl group) and four phosphate - oxygen atoms forming an asymmetrical tetragonal dipyramid. The Cu atoms are six-coordinated by two oxygen atoms of two different uranyl groups and four water molecules forming also an asymmetrical tetragonal dipyramid. The four water molecules form squares Cu(H2O)4, perpendicular to c, with the Cu atoms at their centers. There are two types of squares: with or without Cu atoms at their centers. The P atoms are four-coordinated by O atoms, forming the usual phosphate tetrahedra PO4. The structure consists of infinite (UO2PO4)n layers isostructural with those of meta-autunite and abernathyite. The connection between two successive layers is effected by the Cu - uranyl - oxygen bonds and by hydrogen bonds between the water molecules. Each water molecule of a Cu(H2O)4 square is hydrogen bonded to two water molecules of a (H2O)4 square devoid of Cu, and to two oxygen atoms of a phosphate group.