Complexation of Beryllium(II) by Maleic and Succinic Acid

Beryllium succinate dihydrate [Be(C4H4O4)](H2O)2 is formed in the reaction of equimolar quantities of beryllium sulfate, succinic acid and barium hydroxide in aqueous solution at pH 3.2. Sodium, potassium, and ammonium bis(succinato)beryllates M2[Be(C4H4O4)2] are obtained using the same reagents in the molar ratio 1:2:1 and adjusting the pH to 6.3-6.5 with NaOH, KOH or concentrated aqueous ammonia, respectively. The corresponding potassium bis(maleato)beryllate is prepared similarly and obtained as a crystalline monohydrate, the structure of which has been determined by X-ray methods. The lattice contains spiro-bicyclic dianions with the Be atom chelated by two dicarboxylate ligands. The compounds undergo slow hydrolysis in water as shown by timeand pH-dependent Be NMR spectroscopy. In the neutral region (pH 6.5-6.9) the maleinato complexes are in an equilibrium with trinuclear compounds M3f[Be(C4H2O4)OH]3g as the predominating species, while in acid solution (at pH 1.3) only the aquo complex [Be(H2O)4] remains. In the intermediate pH region various complexes of the above types coexist, with only very slow ligand exchange (on the NMR time scale).