Tripodal aminophenolate ligand complexes of aluminum(III), gallium(III), and indium(III) in water

Four water-soluble amine phenols have been prepared: tris(((2-hydroxy-5-sulfobenzyl)amino)ethyl)amine (H(6)TRNS), 1,1,1-tris(((2-hydroxy-5-sulfobenzyl)amino)methyl)ethane (H(6)TAMS), 1,2,3-tris((2-hydroxy-5-sulfobenzyl)amino)propane (H(6)TAPS), and cis,cis-1,3,5-tris((2-hydroxy-5-sulfobenzyl)amino)cyclohexane (H(6)TACS). Complex formation constants have been measured at 25 degrees C (mu = 0.16 M NaCl): log K [M(TRNS)](3-) ([M(HTRNS)](2-)) M = Ga 28.55 (36.90), In 29.3 (34.9); log K [M(TAMS)](3-) ([M(HTAMS)](2-)) M = Al 22.5 (29.3), Ga 31.53, In 28.49; log K [M(TAPS)](3-) ([M(HTAPS)](2-)) M = Al 22.8 (29.0), Ga 31.54 (35.15), In 27.56 (31.93). The order of stability is Ga(III) > In(III) > Al(III) for H(6)TAMS and H(6)TAPS, while far H(6)TRNS it is Ga(III) approximate to In(lII) > Al(III). The solution structures of the complexes have been probed by multinuclear NMR (H-1, C-13, Al-27, Ga-71, In-115) and UV spectroscopic studies, and these solution structures are compared with solid state structures for analogous complexes. The H-1 NMR spectrum in D2O establishes TAPS to be preorganized for metal ion binding. H(6)TACS exists in the wrong conformation for metal ion binding, and this results in slow complexation kinetics and relatively weaker binding.