Hexaaquanickel(II) disulfato(1,4,8,11-tetraazacyclotetradecane)nickelate(II) dihydrate

The title compound, [Ni(H2O)(6)][Ni(SO4)(2)(C10H24N4)]center dot 2H(2)O, is an unusual compound in that it is composed of a hexaaqua complex, formally a dication, and a mixed-donor complex (four N and two O atoms), formally a dianion, with substantial charge separation between the two nickel centres (6.536 A). The homoleptic dication complex consists of the weaker-field ligands, whilst the dianion retains the coordination of all the higher-field donors. Both nickel ions are located at centres of symmetry. This rare compound is placed in the context of previously reported structures which emphasizes its peculiarity.