STRUCTURE OF DIPOTASSIUM TRANS-DIAQUABIS(OXALATO-O,O')NICKELATE(II)-WATER (1 4)/

The crystal structure of the title compound was studied by single-crys tal X-ray diffraction in order to determine the coordination geometry around the Ni(II) atom in the anionic complex. The crystal - structure comprises centrosymmetric [Ni(C2O4)2(H2O)2]2-complex anions, K+ catio ns and free water molecules linked together through electrostatic inte ractions, K-O coordination, and an extensive network of hydrogen bonds of types O(w)-H...O and O(w)-H...O(w). The complex anion exhibits act ahedral coordination around the Ni atom, with four O atoms belonging t o two bidentate oxalate ligands in the equatorial sites and two water molecules occupying the axial positions, in contrast to the Pd and Pt oxalato complexes which, although crystallizing in the same space grou p, show a square-planar coordination without coordinated water molecul es.