Synthesis, structural studies and vibrational spectroscopy of Fe2+ and Zn2+ complexes containing 4,4′-bipyridine and barbiturate anion

Two new coordination polymers of general formula FeB(2)bpy center dot 10H(2)O (1) and ZnB(2)bpy center dot 10H(2)O (2) (where B = barbiturate anion; bpy = 4,4'-bipyridine) were synthesized and characterized by X-ray diffraction, vibrational spectroscopy (Raman and infrared) and thermal analysis. The two complexes are isostructural and crystallize in a hexagonal crystal system with space group P6(4)22. The compound contains the 4,4'-bipyridine ligand coordinated to the metal sites in a bis-monodentate mode, and also four water molecules, in a slightly distorted octahedral geometry, giving rise to the cationic unit with two barbiturate anions. Each structure shows one covalent linear [M(bpY)(H2O)(4)](2+) one-dimensional chain, which interacts via hydrogen bond with barbiturate anions and crystallization water molecules, resulting in a three-dimensional arrangement. The vibrational spectra of both compounds are very similar; in all infrared spectra is observed an intense band at 1686 cm(-1) assigned to the vCO stretching mode of the barbiturate anion, as well as a medium band around 1610 cm-1, attributed to the vCC/vCN stretching modes of the 4,4'-bipyridine ligand. The Raman spectra show intense and conclusive bands for the nitrogen ligand at 1615, 1295 and 1020 cm(-1), assigned to the vCC/vCN, v(ring) + delta CH and v(ring) modes, respectively. The barbiturate anion is observed through the presence of a marker band at 680 cm(-1), assigned to the ring breathing mode. (C) 2010 Elsevier B.V. All rights reserved.