Abstract

A new manganese molybdenum(V) hydroxyphosphate, Na₁₅Mn₁₀[(HPO₄)(PO₄)₃Mo₆O₁₂(OH)₃]₄(PO₄)·48H₂O (1), based on the {Mn^II[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 {Mn^II[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 Ĥ_S = −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.