NEW POLYNUCLEAR MANGANESE(II) COMPLEXES WITH OROTIC-ACID AND SOME OF ITS DERIVATIVES - CRYSTAL-STRUCTURES, SPECTROSCOPIC AND MAGNETIC STUDIES

Three polynuclear manganese(ii) complexes containing erotic acid ,6-di oxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, H(3)L(1)) or one o f its substituted derivatives [3-methyl-(H(2)L(2)) or ,6-dioxo-1,2,3,6 -tetrahydropyrimidine-4-carboxylic acid (H(3)L(1))] have been synthesi zed and characterized by X-ray crystallography, UV/VIS and magnetic su sceptibility measurements. Complex 1 consists of neutral [Mn-2(HL(1))( 2)(H2O)(6)] units, which form polymer chains along the z axis with:a M n(1)... Mn(2) distance in the unit cell of 5.628(1) Angstrom while the Mn(2)... Mn(2) distance in the chain is 4.715(1) Angstrom. Each unit cell of complex 2 contains one neutral centrosymmetric dimer [Mn-2(L(2 ))(2)(H2O)(6)] containing a short Mn ... Mn distance [3.472(2) Angstro m] and an antiferromagnetic exchange interaction is present. The exper imental data were fitted to the susceptibility equations resulting fro m the Hamiltonian H = -2JS(1)S(2) 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 o f one dinuclear anion [Mn-2(HL(3))(2)(H2O)(4)Cl-2](2-) and of one cati on [K-2(H2O)](2+). The Mn(1) and Mn(2) atoms and the water molecule of the cation [K-2(H2O)](2+) are situated at inversion sites. The dinucl ear anions are associated to form chains but the shortest Mn ... Mn di stance of 5.642(3) Angstrom is observed within the [Mn-2(HL(3))(2)(H2O )(4)Cl-2](2-) unit between Mn(1) and Mn(2).