Structural evolution within a series of hydrated bis(dithiooxalato)nickelate(II) of rare earths (RE) 2(H 2O) 2nNi 3(S 2C 2O 2) 6, xH 2O

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Single crystals of a series of hydrated bis(dithioxalato) nickelate(II) of rare-earths have been synhesized, namely RE III, Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er and Yb. The crystal structures were determined by X-ray techniques. The former part of the series (up to Dy) crystallizes in the monoclinic system, space group P2 1|c, while the latter part crystallizes in the triclinic system, space group P 1 . Full-matrix least-squares refinement led to a final reliability factor R = 0.0350 for the europium complex and R = 0.0266 for ytterbium. The characteristic feature of both structures consists of neutral centrosymmeric heteropentanuclear entities (RE) 2(H 2O) 2nNi 3(S 2C 2O 2) 6, which only differ by the number n of water-molecules coordinated to the rare earth: n = 5 for Eu, while n =4 for Yb. The rare earth atom is also bound to four oxygen atoms of two dithiooxalate groups, so the environment of the europium atom can be represented as a tricapped trigonal prism, while only a bicapped trigonal prism is observed for Yb. The conversion between the two structures involves the loss of one water molecule, in the rare earth sphere of coordination, and a concomitant rearrangement of the ligans dithiooxalate on the summits of the coordination polyhedra. In both structures the nickel atoms are coordinated to two dithiooxalate groups via their sulfur atoms. The monoclinic network exhibits channels, running parallel to the direction [1 0 0], in which some water molecules are inserted. The triclinic structure can be described as a pseudo lamellar structure, water molecules being inserted between layers.