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 time-and pH-dependent ⁹Be NMR spectroscopy. In the neutral region (pH 6.5-6.9) the maleinato complexes are in an equilibrium with trinuclear compounds M₃{[Be(C₄H₂O₄)OH]₃} as the predominating species, while in acid solution (at pH 1.3) only the aquo complex [Be(H₂O)₄]²⁺ remains. In the intermediate pH region various complexes of the above types coexist, with only very slow ligand exchange (on the NMR time scale).