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)Å while the Mn(2)⋯ Mn(2) distance in the chain is 4.715(1)Å. 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)Å] 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)Å is observed within the [Mn₂(HL³)₂(H₂O)₄Cl₂]^2– unit between Mn(1) and Mn(2).