Self-assembly of a mixed-ligand metal-coordination polymeric network of cadmium(II) croconate with 4,4'-bipyridine

A new cadmium croconate (C5O5(2-)) complex, [Cd2(C5O5)2(4,4'-bpy)(H2O)]infinity (4,4-bpy=4,4'-bipyridine) with an extended network has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction studies. The title compound crystallizes in the monoclinic system, space group P2(1)/n, with empirical formula C20H12Cd2N2O12, a=15.9623(3) A, b=7.5837(1) A, c=18.1181(3) A, beta=99.95(2) degrees, and Z=4. Structural determination reveals that the title compound has a bilayered network, containing two crystallographically independent Cd(II) ions in different coordination environments. Cd(1) lies in a distorted pentagonal bipyramidal environment, consisting of three croconate ions and one 4,4'-bpy nitrogen donor, while Cd(2) lies in a distorted octahedral environment, consisting of two croconate anions, one 4,4'-bpy nitrogen donor, and one water molecule. Of the two crystallographic independent croconate ligands, one presents a bis-bidentate adjacent mu3-coordination mode and the other a new bidentate/three-adjacent mu5-coordination mode. A two-dimensional hybrid layer is formed by two rectangular boxes as the building units through the connectivity between Cd(II) and croconate and 4,4'-bpy ligands.