Complexation of Beryllium(II) Ion by Phosphinate Ligands in Aqueous Solution. Synthesis and XRPD Structure Determination of Be[(PhPO2)2CH2](H2O)2

Two bifunctional ligands, phenyl(carboxymethyl)phosphinate (ccp2-) and P,P'-diphenylmethylenediphosphinate (pcp2-) have been tested as chelating agents of beryllium(II). Both ligands have the same charge and similar chelating structure, but whereas the 1:1 adduct of pcp2-, Be(pcp)(H2O)2, cold be isolated as an insoluble white powder, no pure compound could be isolated from solutions containing beryllium(II) and ccp2-. Instead the solutions were investigated by means of potentiometry and 9Be NMR spectrometry. The complex species Be(ccp), [Be(Hccp)]+, [Be(ccp)2]2- and [BeH(ccp)2]- have been characterized. The formation constants found for the ccp2- complexes are lower than those repoted for related phosphonate ligands. However, the effective stability constant of the complex [Be(ccp)2]2- at low pH is greater than the effective constants of the corresponding phosphonoacetate and methylenediphosphonate complexes. The structure of Be(pcp)(H2O)2 was determined by X-ray powder diffraction methods and consists of discrete molecule interconnected by an extended 2D network of hydrogen bonds, resulting in a stacking of double layers with a polar core and a lipophilic surface.