Preparative, potentiometric and NMR studies of the interaction of beryllium(II) with oxalate and malonate. X-ray structure of K-3 [Be-3(OH)(3)(O2C-CH2-CO2)(3)]center dot 6H(2)O

The complexes formed by beryllium(II) with the bidentate ligands oxalate, L=(O2C-CO2)(2-) and malonate, L=(O2C-CH2-CO2)(2-), have been investigated in aqueous solution using both potentiometric and Be-9 NMR measurements. The species [BeL(H2O)(2)], [BeL2](2-), (Be-3(OH)(3)L-3](3-) and [Be-3(OH)(3)(H2O)(3)L](+) have been identified and their formation constants have been determined at 25 degrees C in 0.5 mol dm(-3) NaClO4. The malonate complexes are much more stable than the oxalate ones. New crystalline salts of formula K-3 [Be-3(OH)(3)L-3] . nH(2)O have been isolated using conditions established with the aid of speciation calculations. The structure of K-3 [Be-3(OH)(3)(malonate)(3)] . 6H(2)O has been determined by an X-ray structure analysis: orthorhombic, space group Pc2(1)n, a = 9.011(3), b = 14.041(4), c = 18.761(9) Angstrom, Z = 4. Each beryllium atom is tetrahedrally coordinated by two hydroxo groups and two oxygen atoms from the chelating malonate. The (Be(OH))(3) core is a puckered six-membered ring with each hydroxo group bridging two beryllium centres.