Synthesis, crystal structure and magnetic properties of new molybdenum(V) phosphates containing Mn2+ or Co2+ with three-dimensional structures directed by the nature of the transition metal

Abstract

A new manganese molybdenum(V) hydroxyphosphate, Na15Mn10[(HPO4)(PO4)3Mo6O12(OH)3]4(PO4)·48H2O (1), based on the {MnII[P4Mo6O28(OH)3]2}16− building block has been synthesized hydrothermally and its structure solved by single-crystal X-ray diffraction. Its structure consists of linear manganese phosphate tetramers with edge sharing manganese octahedra. Four tetramers are connected via a phosphato group lying on a axis, leading to infinite chains of manganese to which {MnII[P4Mo6O28(OH)3]2}16− anions are anchored. The variable temperature magnetic susceptibility data for 1 were fitted with a model taking into account only magnetic interactions arising betweeen manganese sharing oxygen atoms. Thus, the spin Hamiltonian ĤS = −J1(Ŝ1Ŝ2 + Ŝ3Ŝ4) − J2Ŝ2Ŝ3 was used, and the best fit was found for g = 2.018, J1 = −1.09 cm−1 and J2 = −3.65 cm−1, showing the antiferromagnetic character of the exchange interactions in 1. Attempts to obtain the analogous cobalto compound led to the cobalt molybdenum(V) phosphate Na12Co3[(PO4)4Mo6O12(OH)3]2·44H2O (2). 1 and 2 present two radically different three-dimensional structures. In 2, the {Co[P4Mo6O28(OH)3]2}16− units are connected via monomeric Co2+ in an octahedral environment to give a three-dimensional framework, with long Co2+–Co2+ distances. The sodium counter-ions are located in tunnels running along the [001] and [010] axes. This clearly shows that the three-dimensional structure is determined by the nature of the transition metal.