Three-dimensional Mn/Fe molybdenum(V) phosphates

摘要

A new three-dimensional molybdenum(V) phosphate, Na_7Mn_4Fe_6[(Mo_2O_4)_3(HPO_4)_2(PO_4)_2(OH)_3]_4(PO_4)·50H_2O (2) has been synthesized under hydrothermal conditions and its structure solved by single-crystal X-ray diffraction. Its structure derives from that of Na_(15)Mn_(10)[(Mo_2O_4)_3(HPO_4)(PO_4)_3(OH)_3]_4(PO_4)·48H_2O (1), previously characterized, by the partial replacement of Mn ions by Fe ions. It is built up from a three-dimensional network of metal ions bridged by phosphate ions to which are anchored {MnII[P_4Mo_6O_(28)(OH)_3]_2}~(16-) sandwich units. The metallic grid is formed by the connection of four tetranuclear units by additional phosphato ligands. The attribution of the nature and the valence of the metal ions within the tetrameric units has been proposed on the basis of both elemental analysis and valence bond summations. Mossbauer and magnetic studies confirmed the oxidation states of the iron ions within the compound. A systematic study of the influence of the Mn/Fe ratio on the composition of the final product has been performed showing the degree of the substitution can be partly controlled.