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(O 2C–CH 2–CO 2) 3]·6H 2O

Abstract

The complexes formed by beryllium(II) with the bidentate ligands oxalate, L=(O 2C–CO 2) 2−, and malonate, L=(O 2C–CH 2–CO 2) 2−, have been investigated in aqueous solution using both potentiometric and 9Be NMR measurements. The species [BeL(H 2O) 2], [BeL 2] 2−, [Be 3(OH) 3L 3] 3− and [Be 3(OH) 3(H 2O) 3L] + have been identified and their formation constants have been determined at 25°C in 0.5 mol dm −3 NaClO 4. The malonate complexes are much more stable than the oxalate ones. New crystalline salts of formula K 3[Be 3(OH) 3L 3]· nH 2O have been isolated using conditions established with the aid of speciation calculations. The structure of K 3[Be 3(OH) 3(malonate) 3]·6H 2O 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) Å, 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.