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

The protonation and stability constants of 1,3,5-triamino-2,4,6-trihydroxycyclohexane (taci), in I = 1.00 M (NaClO4) were measured. The stability constants, log β′ for formation of [Ln(H-3taci)23+] ranged from 25.33 Nd(III) to 33.69 Lu(III). 1H NMR spectra and laser fluorescence measurements were consistent with formation of a single complex from pcH 6 to pcH 10. The shift in the peak relative to that of Eu3+(aq) was significantly greater than the values reported for most other complexes with organic ligands and Eu(III). Luminescence lifetime measurements of the flourescence spectra indicated two water molecules bound to each of the Eu(III) cations in the taci complex.