Hydrated and anhydrous cobalt (II) barbiturates: Crystal structures, spectroscopic and thermal properties

Three new complexes of barbituric acid (H₂BA), a discrete molecular complex [Co(H₂O)₄(HBA)₂] (1), a barbiturate-bridged 1D Co(II) coordination polymer [Co(H₂O)₂(μ₂-HBA)₂] (2) and a 3D Co(II) coordination polymer [Co(μ₃-HBA)₂] (3) were synthesized and structurally characterized by X-ray powder diffraction. In 1–3, the HBA⁻ ions are coordinated to Co(II) only through O atoms with cobalt ions in an octahedral environment. In 1, Co(II) is coordinated to four terminal water molecules and two HBA⁻ ions. In compound 2, Co(II) is bonded to two terminal water molecules and two μ₂-HBA⁻ ions forming polymer chains. In the 3D-polymeric form 3, a bridging μ₃-HBA ligand is connected through three oxygen atoms of the carbonyl groups with three Co(II) ions. All three structures are stabilized by intermolecular hydrogen bonds and π–π stacking interactions between HBA⁻ ions. The IR spectroscopic data supports the results of the X-ray diffraction analysis. The thermal decomposition of the compounds comprises the dehydration steps and the organic ligand oxidation to form cobalt oxides.