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 oxala te, L=(O2C-CO2)(2-) and malonate, L=(O2C-CH2-CO2)(2-), have been inves tigated in aqueous solution using both potentiometric and Be-9 NMR mea surements. 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 formatio n constants have been determined at 25 degrees C in 0.5 mol dm(-3) NaC lO4. 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, spa ce 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 hydrox o groups and two oxygen atoms from the chelating malonate. The (Be(OH) )(3) core is a puckered six-membered ring with each hydroxo group brid ging two beryllium centres.