1,3,5-Triamino-1,3,5-trideoxy-cis-inositol, a New Ligand with a Remarkable Versatility for Metal Ions. 3. Preparation and Characterization of the Aluminum(III), Gallium(III), and Thallium(III) Complexes

Kaspar Hegetschweiler, Michele Ghisletta, Thomas F. Fässler, Reinhard Nesper, Helmut W. Schmalle, Greti Rihs

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Solid compounds containing the complexes Al(taci)23+, Ga(taci)23+, and Tl(taci)23+ (taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol = C6H15N3O3) have been prepared by combining methanolic solutions of taci and of appropriate metal salts. Single-crystal X-ray analysis revealed an A106, GaN3O3, and T1N6 coordination sphere for Al(taci)2Br3·7H2O: monoclinic, space group C2/c, Z = 4, a = 9.413(1) Å, b = 14.560(2) Å, c = 20.264(4) Å, β = 93.36(1)° Ga(taci)2(NO3)3·3H2O: triclinic, space group P1̄, Z = 2, a = 9.270(1) Å, b = 9.795(1) Å, c = 13.524(1) Å, α = 92.83(1)°, β = 88.46(1)°, γ = 94.15(1)°; Tl(taci)2(NO3)3·2H2O: monoclinic, space group C2/c, Z = 4, a = 23.497(12) Å, b = 8.811(4) Å, c = 14.942(8) Å, β = 128.82(3)°. The binding of Al(III) and Ga(III) to the hydroxyl groups of taci resulted in an internal proton transfer: (H2N−)3(C6H6)(−OH)3 + M → (H3N−)3-(C6H6)(−O−)3M. The same structures have also been observed in aqueous solution. NMR measurements in D2O revealed Al(taci)23+ and Ga(taci)23+ as the major components at pH 7. Hydrolytic polymerization of Ga(taci)23+ and Tl(taci)23+ was indicated by an increase of the signals of the free ligand in the NMR spectra and the appearance of solid hydrolysis products in slightly acidic solutions (pH ≤ 4). Significant hydrolysis of the Al(III) complex was only observed at temperatures ≥80 °C after several hours. The hydrolysis of the Al(III) and Ga(III) complexes at 25 °C was sufficiently slow to investigate a preequilibrium of exclusively mononuclear species. The formation constants β2 = [M(taci)2][M]−1[taci]−2 (M = Al3+, Ga3+) were determined by acidimétric titrations (M(taci)23+ + 6H+ → M3+ + 2H3(taci)3+) as well as by alkalimetric titrations (M(taci)23+ + 40H → M(OH)4 + 2taci). The two independent methods gave identical values for β2 within significance. The formation constants β1 = [M(taci)][M]−1[taci]−1, and a set of pK values, pKi, = [H−iM(taci)2][H][H1−i,M(taci)2]−1, where 1 ≤ i ≤ 4 and M = Al3+, Ga3+, were also evaluated. Al3+ (25 °C, 0.1 M KCl): log β1 = 11.8(1), log β2 = 18.8(1), pK1, = 8.1(1), pK2 = 8.9(1). Ga3+ (25 °C, 0.1 M KNO3): log β1 = 16.5(1), log β2 = 25.7(1), pK1, = 7.4(1), pK2 = 8.7(1). The hydrolysis of Tl(taci)23+ had already occurred at 25 °C to a significant extent in freshly prepared solutions. In addition a slow aging was observed over a period of several weeks. H−2M(taci)2+ was the dominant species in the FAB MS of the Al and Ga complex. The Tl complex was partially reduced in the glycerol matrix, as indicated by the observation of Tl+, Tl(glycerol)+, and Tl(taci)+.

Original languageEnglish
Pages (from-to)2032-2041
Number of pages10
JournalInorganic Chemistry
Issue number10
StatePublished - 1993
Externally publishedYes


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