1,3,5-TRIDEOXY-1,3,5-TRIS(DIMETHYLAMINO)-CIS-INOSITOL, AN EFFICIENT LIGAND FOR HARD TRIVALENT METAL-IONS - DETERMINATION OF THE STABILITY-CONSTANTS OF THE FE-III, AL-III, AND CU-II COMPLEXES IN AQUEOUS-SOLUTION

The complexes [Fe(tdci)2]Cl3 and [Al(tdci)2]Cl3 (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol) were prepared and characterized by mass spectrometry, NMR spectroscopy, and magnetic-susceptibility measurements. The formation constants were determined in aqueous solution (25-degrees, 0.1 M KCl) by potentiometric titration. pK values of H-3(tdci)3+ : 5.89, 7.62, 9.68; Fe(III) complexes: log beta(ML) = 18.8, log beta(ML2) = 32.6; Al(III) complexes: log beta(ML) = 14.3, log beta(ML2) = 26.4. The protonated complex [FeH(tdci)2]4+ has also been identified. In contrast to the high stability of the Fe(III) and Al(III) complexes, only weak interactions of tdci with Cu(II) have been observed in aqueous solution (25-degrees, 0.1 M KNO3).