Synthesis and structure of a three-dimensional lanthanum(III) coordination polymer with mellitate, {La-2[C-6(COO)(6)](H2O)(9)}.2H(2)O

The crystal and molecular structure of a lanthanum(III) mellitate, La2C12H22O23, has been determined by X-ray structural analysis using a combination of direct and heavy atom methods. The complex crystallizes in the monoclinic space group P2(1)/n with unit-cell dimensions of a = 6.723(4), b = 11.368(5), c = 29.813(4) Angstrom and beta = 95.851(3)degrees. Block-diagonal least-squares refinement using automated diffractometer-collected data resulted in R = 2.5 and R-w = 3.4. The crystal structure consists of layers perpendicular to the a axis. Each layer is formed by an extended network of lanthanum ions coordinated with mellitate anions and water molecules, and linked through a complex three-dimensional hydrogen-bonding network. Among the six carboxylate groups of the mellitate anion, five form coordination bonds to six lanthanum atoms. The two independent lanthanum ions are both nine-coordinate and the configuration around lanthanum is a tricapped trigonal prism with the La-O bond distances ranging from 2.457 Angstrom to 2.704 Angstrom.