An unprecedented coordination mode of the orotate ligand in novel polynuclear cadmium(II)-orotate complexes

Two novel carboxylate-bridged Cd(II)-orotate polynuclear complexes with 2-(2-ethylamino)pyridine (2-etapy), [Cd(mu-HOr)(2-etapy)](n) (1), and N,N-diethylethylenediamine (N,N-eten) ligands, {[Cd(mu-HOr)-(H2O)(N,N-eten)]center dot H2O}(n) (2) (H(3)Or = orotic acid), have been synthesized and characterized by TGA-evolved gas analysis (TGA-EGA), IR spectroscopy and single crystal X-ray diffraction techniques. The orotate ligand acts as a bridging ligand with two different coordination modes, showing an unprecedented tetradentate coordination mode. The HOr ligand simultaneously chelates Cd(II) ions through the carboxylate oxygen, deprotonated pyrimidine nitrogen atoms and carboxyl oxygen atoms as a tetradentate ligand in 1. In complex 2, the HOr ligand bridges two Cd(II) ions through the carboxylate oxygen and deprotonated pyrimidine nitrogen atoms and oxygen atom of a carboxylate group of a neighbouring complex unit. Three-dimensional (3D) supramolecular structures are generated by hydrogen-bonding, and pi center dot center dot center dot pi and C-H center dot center dot center dot pi interactions between the closest chains in both complexes. (C) 2010 Elsevier Ltd. All rights reserved.