title: [Ni(H2O)6]2[Na(H2O)3]2[V10O28].4H2O, bis(nickel hexahydrate) bis(sodium trihydrate) decavanadate tetrahydrate.
abstract: Polyoxometallates are capable of including transition metals in their crystal structures as either discrete cations or heteroatoms. The title compound crystallizes with triclinic symmetry and consists of a centrosymmetric [V(10)O(28)](6-) anion, a trimeric [Na(H(2)O)(3)][Ni(H(2)O)(6)][Na(H(2)O)(3)](4+) cation, an [Ni(H(2)O)(6)](2+) cation and four water molecules of crystallization. The compound possesses two Ni atoms (each on independent inversion centres), one as a discrete cation and one in a disodium-nickel trimeric cation involved in the one-dimensional polycation-polyanion hybrid polymer. The polymers are bound together via hydrogen bonds to the water molecules and the nickel(II) hexahydrate cation. Several structures of decavanadate compounds having transition metal atoms, monovalent cations and [V(10)O(28)](6-) anions in the ratio 2:2:1 have been reported previously. However, the present compound differs from these in its arrangement of monovalent cations and transition metal atoms.