An unusual function of the anion of 1-hydroxyethane-1,1-diphosphonic acid (H4L): Crystal structure of [Ni(Phen)(3)](H7L2)(0.5)(H5L2)(0.5)center dot 2H(2)O

Crystals of [Ni(Phen)(3)](H3L)(2) . 2H(2)O (H4L is 1-hydroxyethane-1,1-diph osphonic acid) have been synthesized, and their structure has been determin ed by X-ray diffraction analysis. The cationic complexes [Ni(Phen)(3)](2+), the centrosymmetric dimeric anions H7L2- and H5L23-, and the molecules of crystallization water are the structural units of the crystal. The outer-sp here function of the H4L anions in transition metal compounds and also the presence of differently charged dimeric anions are revealed for the first t ime. The structural units are joined together by an extended system of hydr ogen bonds, including symmetric (or pseudosymmetric) hydrogen bonds in dime ric anions (O...O, 2.436 and 2.466 Angstrom). The Ni-N(Phen) bond lengths f all in the range 2.074-2.107 Angstrom. The compound has the structural form ula [Ni(Phen)(3)](H7L2)(0.5)(H5L2)(0.5) . 2H(2)O (C) 2000 MAIK "Nauka/Inter periodica".