Crystal data for isotypic Cs₂[M(CN)₄].H₂O compounds, M=Pt, Pd and Ni

Cs₂[Pd(CN)₄].H₂O and Cs₂[Ni(CN)₄].H₂O were found to be isotypic with the known hexagonal Pt compound which shows an unusual helical chain of six [Pt(CN)₄]^2- groups in the unit cell, space group P6₁ or P6₅. The crystal data are a = 9.559 (2) and c = 19.308 (4) Å, D_m = 2.87 (4), D_x = 2.912 Mg m^-3 for the Ni compound, and a = 9.704 (2), c = 19.388 (4) Å, D_m = 3.12 (4), D_x = 3.115 Mg m^-3 for the Pd compound. X-ray powder data are given.