Ge(IV)–citrate complex formation: synthesis and structural characterisation of GeCl4(bipy) and GeCl(bipy)(Hcit) (bipy=2,2′-bipyridine, H4cit=citric acid)

The adduct [GeCl4(bipy)] (I), obtained by direct treatment of the parent halide with 2,2′-bipyridine (bipy), reacts with citric acid (H4cit) in acetonitrile solution to provide the chelate derivative [GeCl(bipy)(Hcit)] (II). The structures of compounds I and II have been determined by single crystal X-ray diffraction. For I the central germanium shows octahedral geometry with two mutually cis-chlorine atoms, GeCl (mean) 2.244(1) Å, and the bidentate ligand, GeN (mean) 2.065(4) Å occupying equatorial positions and two mutually trans-chlorine atoms, GeCl (mean) 2.267(1) Å in axial locations. For II the citrate ligand is terdentate and bound to the central germanium via its hydroxyl, α-carboxylate and one of the β-carboxylate groups in a fac-octahedral arrangement. GeOhydroxyl 1.800(3) Å, GeOcarboxylate (mean) 1.904(3) Å, GeCl 2.209(1) Å, GeN (mean) 2.012(3) Å. The uncoordinated β-carboxylate group remains intact as a ‘dangling arm’. The structure also contains poorly defined and disordered acetonitrile (solvent) molecules trapped in the lattice.