Ge(IV)-citrate complex formation: synthesis and structural characterisation of GeCl4(bipy) and GeCl(bipy)(Hcit) (bipy=2,2 '-bipyridine, H(4)cit = citric acid)

The adduct [GeCl4(bipy)] (I), obtained by direct treatment of the parent ha lide with 2,2'-bipyridine (bipy), reacts with citric acid (H(4)cit) in acet onitrile solution to provide the chelate derivative [GeCl(bipy)(Hcit)] (II) . The structures of compounds I and II have been determined by single cryst al X-ray diffraction. For I the central germanium shows octahedral geometry with two mutually cis-chlorine atoms, Ge-Cl (mean) 2.244(1) Angstrom, and the bidentate ligand, Ge-N (mean) 2.065(4) Angstrom occupying equatorial po sitions and two mutually tuans-chlorine atoms, Ge-Cl (mean) 2.267(1) Angstr om in axial locations. For II the citrate ligand is terdentate and bound to the central germanium via its hydroxyl, alpha -carboxylate and one of the beta -carboxylate groups in a fac-octahedral arrangement. Ge-O-hydroxyl 1.8 00(3) Angstrom, Ge-O-carboxylate (mean) 1.904(3) Angstrom, Ge-Cl 2.209(1) A ngstrom, Ge-N (mean) 2.012(3) Angstrom. The uncoordinated P-carboxylate gro up remains intact as a 'dangling arm'. The structure also contains poorly d efined and disordered acetonitrile (solvent) molecules trapped in the latti ce. (C) 2001 Elsevier Science B.V. All rights reserved.