New polynuclear manganese(II) complexes with orotic acid and some of its derivatives: crystal structures, spectroscopic and magnetic studies

Abstract

Three polynuclear manganese(II) complexes containing orotic acid (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, H3L1) or one of its substituted derivatives [3-methyl-(H2L2) or 5-nitro-2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid (H3L1)] have been synthesized and characterized by X-ray crystallography, UV/VIS and magnetic susceptibility measurements. Complex 1 consists of neutral [Mn2(HL1)2(H2O)6] units, which form polymer chains along the z axis with a Mn(1)⋯ Mn(2) distance in the unit cell of 5.628(1)A while the Mn(2)⋯ Mn(2) distance in the chain is 4.715(1)A. Each unit cell of complex 2 contains one neutral centrosymmetric dimer [Mn2(L2)2(H2O)6] containing a short Mn ⋯ Mn distance [3.472(2)A] and an antiferromagnetic exchange interaction is present. The experimental data were fitted to the susceptibility equations resulting from the Hamiltonian H=–2JS1S2 to give exchange parameter J=–1.3 cm–1 and g= 1.95. From EPR spectra of 2, the hyperfine interaction parameter A=–0.27 GHz and the zero-field splitting parameter D=±2.93 GHz have been calculated. Each unit cell of complex 3 consists of one dinuclear anion [Mn2(HL3)2(H2O)4Cl2]2– and of one cation [K2(H2O)]2+. The Mn(1) and Mn(2) atoms and the water molecule of the cation [K2(H2O)]2+ are situated at inversion sites. The dinuclear anions are associated to form chains but the shortest Mn ⋯ Mn distance of 5.642(3)A is observed within the [Mn2(HL3)2(H2O)4Cl2]2– unit between Mn(1) and Mn(2).