Lanthanide complexation with 1,3,5-triamino 2,4,6-trihydroxycyclohexane

The protonation constants of 1,3,5-triamino-2,4,6-trihydroxycyclohexane (taci), at 25 °C in I = 1.00 M (NaClO4) were determined to be: pK a1, 5.57 (0.08); pK a2, 7.45 (0.02); pK a3, 9.05 (0.04). The log of the stability constants, log β 302, at 25°C in I = 1.00 M (NaClO4) for formation of View the MathML source[Ln(H-3taci)23+] were measured by potentiometry to be: Nd(III), 25.33 (0.09); Eu(III), 26.42 (0.06); Tm(III), 30.07 (0.10); Lu(III), 33.68 (0.07) ; Y(III), 28.59 (0.07). 1H NMR spectra were consistent with formation of a single complex from pcH 6 to 10. Laser fluorescence measurements of the 7Fo–5Do transition of Eu(III) complexed by taci indicated a single complexed species. The shift in this peak relative to that of Eu3+(aq) was significantly greater than the values reported for the complexes of other organic ligands with Eu(III). Luminescence lifetime measurements indicated two water molecules bound to each of the Eu(III) cations in the taci complex.