Magnetic properties and structure of some copper(II) complexes of pyridine and quinoline N-oxides

Abstract

The magnetism of various copper(II) complexes of pyridine and quinoline N-oxides¹ has been further investigated. The compounds Cu(C₅H₅NO)_nX₂ (where n = 4 or 6, X = ClO₄; n = 2, X = Cl, Br, NCS; n = 1, X = Cl, Br, CH₃COO) and Cu(C₉H₇NO)_nX₂ where n = 4, X = ClO₄; n = 2, X = Cl, Br, NO₃; n = 1, X = Cl, Br, CH₃COO) have been studied. The variation of the magnetic susceptibilities of most of these compounds is reported over a temperature range. The variation of the magnetic susceptibility with temperature for the weakly paramagnetic complex Cu(C₅H₅NO)Cl₂ is discussed in terms of the binuclear oxygen-bridged structure previously postulated.¹ The compound exhibits anti-ferromagnetic interaction between pairs of copper(II) atoms with a singlet-triplet separation of 2.1 kcal/mole. The compounds Cu(C₅H₅NO)₂Cl₂, Cu(C₅H₅NO)Br₂, and Cu(C₉H₇NO)X₂ (X = Cl, Br) are more weakly paramagnetic due to a larger singlet-triplet separation. The compound Cu(C₅H₅NO)₂Br₂ possesses a higher paramagnetic susceptibility than those of the previous compounds, and its magnetic properties are consistent with a dimeric structure involving a singlet- triplet separation of 0.7 kcal/mole. The copper(II) acetate adducts, Cu(CH₃COO)₂,L (L = C₅H₅NO or C₉H₇NO), possess very similar magnetic properties to binuclear copper(II) acetate monohydrate and presumably possess a similar structure, with the N-oxides replacing the water molecules. These compounds exhibit singlet-triplet energies of c. 1 kcal/mole similar to values reported for a large number of copper(II) alkanoates. The compounds Cu(C₅H₅NO)₂(NCS)₂, Cu(C₅H₅NO)4₍ClO₄)₂, Cu(C₅H₅NO)₆- (ClO₄)₂, Cu(C₉H₇NO)₂X₂ (X = Cl, Br, NO₃), all obey the Curie-Weiss law and possess mean magnetic moments of 1.89, 1.80, 1.93, 1.88, 1.96, and 1.88 B.M. (corrected for θ values of -12, -7, -8, + -4, and -16°) respectively.