| Summary: | In the title compound, Na2CaNi2(P2O7)2(H2O)10, there are two distinct P-atom sites, each tetrahedrally coordinated by four O atoms. The resulting phosphate tetrahedra link through a common O atom, forming a [P2O7]4− diphosphate unit. The Ni—O coordination is square pyramidal with four O atoms from two diphosphate groups in equatorial positions and the vertex occupied by a water O atom. The (P2O7)(H2O) units link the Ni atoms, forming a chain of pyramids and tetrahedra. As a result of the d-glide and twofold-axis symmetry of space group Fdd2, the chains propagate along [101] and [10overline{1}], and chains in adjacent layers are mutually orthogonal. The Ca cation, located on a rotation axis, and the Na cation are each octahedrally coordinated by four O atoms and two waters. The Ni-chain arrangement is stabilized by Ca and Na coordination and a network of O—H...O hydrogen bonds.
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