Synthesis and Structural Characterization of Two Aluminium Malate Complexes

• Published in: Zeitschrift für anorganische und allgemeine Chemie (1950) 2007-09, Vol.633 (11-12), p.1952-1958
• Main Authors: Happel, Oliver, Harms, Klaus, Seubert, Andreas
• Format: Article
• Language: English
• Subjects: Aluminium; Crystal structure; Malate ligands; Malic acid; Solid state; Speciation
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.200700241

The crystalline aluminium‐malate‐complex, (NH4)6[Al4(D‐C4H3O5)3(L‐C4H3O5)3]·6H2O (1), can be isolated from solutions containing a ratio of 1:2 aluminium to DL‐malic acid in a pH‐range of 5–6. Complex 1 crystallizes in space group $P{\bar 1}$, with a = 9.974(1) Å, b = 10.721(1) Å, c = 12.332(1) Å, α = 102.51(1)°, β = 112.16(1)°, γ = 104.44(1)°, V = 1109.5(2) Å3, and Z = 1. A second crystalline aluminium‐malate‐complex, (C3N2H5)2[Al4(L‐C4H3O5)4(OH)2 (H2O)4]·7H2O (2b), is available from solutions with pH 3 containing a ratio of 1:1 aluminium to L‐malic acid. Complex 2b crystallizes in space group P21, with a = 7.7596(5) Å, b = 25.290(1) Å, c = 10.5393(7) Å, β = 104.855(5)°, V = 1999.1(2) Å3, and Z = 2. A third structure with the same complex anion as it was found in complex 2a is available using aqueous ammonia for pH‐adjustment. The presence of pronounced disorder affecting the positions of the nitrate ion and solvent molecules prohibited a complete structure determination in this case. The two new crystallized complex anions can be used as a powerful tool for aluminium speciation with malic acid ligands. The solution chemistry of the dissolved malate complexes is investigated by NMR spectroscopy.