Synthesis and Relaxometric Properties of Gadolinium(III) Complexes of New Triazine-Based Polydentate Ligands

Two new derivatives based on an s-triazine structural motif were synthesized by attaching two 2,2-hydrazinylidenebis[acetic acid] moieties to the triazine ring to reach an overall heptadenticity for the complexation of lanthanide(III) cations. The remaining reactive site was exploited for the substitution with a functionizable amino group (see H4L1) and a lipophilic moiety (see H4L2). Luminescence-lifetime determinations revealed the presence of a single H2O molecule coordinated for [Eu(L1)]. A complete 1H-NMR relaxometric study was carried out for the octacoordinated [Gd(L1)] and [Gd(L2)] complexes. A remarkably long H2O residence lifetime (298M=5.2 s) was found by 17O-NMR in the case of [Gd(L1)]. Micelle formation of the lipophilic complex [Gd(L2)] was evidenced, the critical micellization concentration (cmc) determined, and relaxometric properties of the system investigated.