Penta­ammonium hepta­sodium bis­[penta­kis(μ(2)-oxido)deca­oxido­bis­(μ(5)-phosphato)penta­molybdenum(VI)] henicosa­hydrate

The title compound, (NH(4))(5)Na(7)[Mo(5)P(2)O(23)](2)·21H(2)O, was prepared under atmospheric conditions in aqueous solution at room temperature. The structure contains the [Mo(5)P(2)O(23)](6−) heteropolyoxometallate anion, which has been previously reported a number of times with a variety of differing counter-cations. Each anion is built up of five MoO(6) octa­hedra sharing an edge and forming a ring which is closed by common corners of the terminal octa­hedra. The rings are closed on both sides by two asymmetric PO(4) tetra­hedra, sharing three corners with three MoO(6) octa­hedra. The anions are chiral and the two independent anions in the asymmetric unit were arbitarily chosen with the same chirality, but the centrosymmetric crystal contains both enanti­omers. The structure can alternatively be described as a succession of layers parallel to (101), formed by the [Mo(5)P(2)O(23)](6−) anions and linked by sodium chains. Water mol­ecules and ammonium ions fill the remaining space and ensure the cohesion through extensive N—H⋯O and O—H⋯O hydrogen bonding.