Stereochemistry and structural phase transition of Cu(II) complexes containing orthophosphate ions and pyridine/picoline

Abstract

Copper complexes of the type Cu(L)4(H2PO4)2 designated as complex (I), and Cu(L)4 HPO4 designated as complex (II), (whereL = pyridine (py) or λ-picoline (pic)) have been synthesised, characterised by chemical analyses, IR, and electronic and magnetic susceptibility data. From ESR studies it is concluded that complexes (I) have elongatedtrans octahedral stereochemistry. The temperature dependence of the ESR spectrum of Cu(py)4(H2PO4)2 suggests a fluxional behaviour in the immediate coordination of Cu(II), whereas very little variation of the ESR spectrum of the Cu(pic)4(H2PO4)2 complex indicates that the stereochemistry of this complex is essentially static in nature. The differential scanning calorimetric studies in the case of Cu(py)4(H2PO4)2 complex have given clear evidence for the occurrence of a structural phase transition at 147 K. The absence of any abrupt changes in the ESR spectrum at that temperature excludes the possibility of any changes in the immediate environment of Cu(II).