A three-dimensional pyrazine-2,5-dicarboxylate CdII coordination framework with new (4,4,4)-connected three-nodal topology

Poly[(mu(4)-pyrazine-2,5-dicarboxylato) cadmium(II)], [Cd(C6H2-N2O4)](n) or [Cd(pzdc)](n) (pzdc is the pyrazine-2,5-dicarboxylate dianion), has been synthesized hydrothermally. The asymmetric unit consists of a Cd-II atom and two independent halves of pzdc ligands that can be expanded via inversion through the centres of the ligands so that each ligand binds to four Cd-II atoms with the same binding mode using six donor atoms. The Cd-II centre is in a distorted octahedral coordination geometry with four O- and two N-atom donors from four pzdc ligands. The infinite linkage of the metal atoms and ligands forms a three-dimensional framework with a rectangular channel which is so narrow that there is no measurable void space in the overall structure. This coordination polymer represents the first example of (4,4,4)-connected three-nodal framework.