Self-Assembly of a Mixed-Ligand Metal-Coordination Polymeric Network of Cadmium(II) Croconate with 4,4‘-Bipyridine

A new cadmium croconate (C5O52-) complex, [Cd2(C5O5)2(4,4‘-bpy)(H2O)]∞ (4,4-bpy = 4,4‘-bipyridine) with an ex-tended 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 P21/n, with empirical
formula C20H12Cd2N2O12, a = 15.9623(3) Å, b = 7.5837(1) Å, c = 18.1181(3) Å, β = 99.95(2)°, 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 μ3-coordination
mode and the other a new bidentate/three-adjacent μ5-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.