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

Solid compounds containing the complexes Al(taci)2(3+), Ga(taci)2(3+), and Tl(taci)2(3+) (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 AlO6, GaN3O3, and TlN6 coordination sphere for Al(taci)2Br3.7H2O: monoclinic, space group C2/c, Z = 4, a = 9.413(1) angstrom, b = 14.560(2) angstrom, c = 20.264(4) angstrom, = 93.36(1)-degrees; Ga(taci)2(NO3)3.3H2O: triclinic, space group P1BAR, Z = 2, a = 9.270(1) angstrom, b = 9.795(1) angstrom, c 13.524(1) angstrom, a = 92.83(1)-degrees, beta = 88.46(1)-degrees, gamma = 94.15(1)-degrees; Tl(taci)2(NO3)3.2H2O: monoclinic, space group C2/c, Z = 4, a = 23.497(12) angstrom, b = 8.811(4) angstrom, c = 14.942(8) angstrom, beta = 128.82(3)-degrees. 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)2(3+) and Ga(taci)2(3+) as the major components at pH 7. Hydrolytic polymerization of Ga(taci)2(3+) and Tl(taci)2(3+) 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 less-than-or-equal-to 4). Significant hydrolysis of the Al(III) complex was only observed at temperatures greater-than-or-equal-to 80-degrees-C after several hours. The hydrolysis of the Al(III) and Ga(III) complexes at 25-degrees-C was sufficiently slow to investigate a preequilibrium of exclusively mononuclear species. The formation constants beta2 = [M(taci)2][M]-1 [taci]-2 (M = Al3+, Ga3+) were determined by acidimetric titrations (M(taci)2(3+) + 6H+ --> M3+ + 2H-3(taci)3+) as well as by alkalimetric titrations (M(taci)2(3+) + 4OH- --> M(OH)4- + 2taci). The two independent methods gave identical values for 62 Within significance. The formation constants beta1 = [M(taci)][M]-1[taci]-1, and a set of pK values, pK(i) = [H(-i)M(taci)2][H][H(1-i)M(taci)2]-1, where 1 less-than-or-equal-to i less-than-or-equal-to 4 and M = Al3+, Ga3+, were also evaluated. Al3+ (25-degrees-C, 0.1 M KCl): log beta1 = 11.8(1), log beta2 = 18.8(1), pK1 = 8.1(1), pK2 = 8.9(1). Ga3+ (25-degrees-C, 0.1 M KNO3): log beta1 = 16.5(1), log beta2 = 25.7(1), pK1 = 7.4(1), pK2 = 8.7(1). The hydrolysis of Tl(taci)2(3+) had already occurred at 25-degrees-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)+.