Trinuclear mixed-valent MnII/MnIV/MnII complexes -: Structure and magnetic behavior

Examples of mixed-valent manganese compounds with 2e(-) difference between the oxidation states of the metal ions are rare. Herein we report the synthesis, crystal structure, spectroscopic and magnetic studies of a series of Mn-II-Mn-IV-Mn-II trinuclear compounds of the general composition (MnMnMnII)-Mn-II-Mn-IV(pko)(4)(CH3O)(2)(X)(2) [X = Cl- (1), NCO- (2), NCS- (3)]. These molecules can be prepared by adding the ketonoxime ligand in the presence of sodium hydroxide and the analogous pseudohalide salt to MnCl(2)(.)4H(2)O in methanol and with exposure to air. The crystal structures for the three compounds are quite similar with one six coordinate Mn-IV ion in an MnO6 coordination environment and two six coordinate Mn-II ions having an N5O or N4OCl coordination environment. Four nitrogen atoms come from two ketonoximato ligands, an oxygen atom from a methoxide bridge and a chloro or nitrogen atom from the halide or pseudohalide terminal ligand. Each pko(-) ligand acts as a tridentate chelating agent by using a pyridine, and an oximato-nitrogen, bound to the Mn-II ion and the oximato oxygen, coordinated to the Mn-IV central ion. The other nitrogen atom of the pko- ligand remains uncoordinated. The magnetic parameters obtained from the fitting procedure are J(12) = +7.8 cm(-1) and g(Mn)(IV) = 2.07 for 1, J(12) + 8.1 cm(-1) and g(Mn)(IV) = 2.08 for 2, and J(12) +6.1 cm(-1) and g(Mn)(IV) = 2.09 for 3 which indicate a ferromagnetic behavior. The ground states for all the compounds are S = 13/2.