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]-μ4-oxido-hexa-μ3-oxido-octa-μ2-oxido-tetra­oxido­tetra­nickel(II)hexa­tantalum(V) nona­deca­hydrate

Reaction of K8{Ta6O19}·16H2O with [Ni(tren)(H2O)Cl]Cl·H2O in different solvents led to the formation of single crystals of the title compound, [Ni4Ta6O19(C6H18N4)4]·19H2O or {[Ni2(κ4-tren)(μ-κ3-tren)]2Ta6O19}·19H2O (tren is N,N-bis­(2-amino­eth­yl)-1,2-ethanediamine, C6H18N4). In its crystal structure, one Lindqvist-type anion {Ta6O19}8– (point group symmetry \overline{1}) is connected to two NiII cations, with both of them coordinated by one tren ligand into discrete units. Both NiII cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON5] octa­hedra for one and [NiO3N3] 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.