Dipotassium nickel(II) bis­(di­hydrogendiphosphate) dihydrate, K2Ni(H2P2O7)2·2H2O

K2Ni(H2P2O7)2·2H2O is isostructural with its Zn analogue. Its structure is characterized by [Ni(H2O)2(H2P2O7)2]2−coordin­ation units. These are linked by hydrogen bonds and K+ ions. Ni2+ is situated on an inversion centre and has an almost regular octahedral coordination.