Synthesis and crystal structure of bis­[μ-N,N-bis­(2-amino­eth­yl)ethane-1,2-di­amine]­bis­[N,N-bis­(2-amino­eth­yl)ethane-1,2-di­amine]-μ(4)-oxido-hexa-μ(3)-oxido-octa-μ(2)-oxido-tetra­oxido­tetra­nickel(II)hexa­tantalum(V) nona­deca­hydrate

Reaction of K(8){Ta(6)O(19)}·16H(2)O with [Ni(tren)(H(2)O)Cl]Cl·H(2)O in different solvents led to the formation of single crystals of the title compound, [Ni(4)Ta(6)O(19)(C(6)H(18)N(4))(4)]·19H(2)O or {[Ni(2)(κ(4)-tren)(μ-κ(3)-tren)](2)Ta(6)O(19)}·19H(2)O (tren is N,N-bis­(2-amino­eth­yl)-1,2-ethanediamine, C(6)H(18)N(4)). In its crystal structure, one Lindqvist-type anion {Ta(6)O(19)}(8–) (point group symmetry [Image: see text] ) is connected to two Ni(II) cations, with both of them coordinated by one tren ligand into discrete units. Both Ni(II) cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON(5)] octa­hedra for one and [NiO(3)N(3)] octa­hedra for the other cation. These clusters are linked by inter­molecular O—H⋯O and N—H⋯O hydrogen bonding involving water mol­ecules into layers parallel to the bc plane. Some of these water mol­ecules are positionally disordered and were refined using a split model. Powder X-ray diffraction revealed that a pure crystalline phase was obtained but that on storage at room-temperature this compound decomposed because of the loss of crystal water mol­ecules.