The macrocyclic ligand 3,6,9-tris(methylenebutyl phosphonic acid)-3,6,9-15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene (PCTMB) was synthesized and complexes of Eu3+, Tb3+, and Gd 3+ studied by X-ray crystallography, luminescence, and relaxometry. In the crystal these complexes are dimeric and possess 8-coordinate Ln 3+ centers that are linked by bridging phosphonates. The rigidity introduced by the pyridyl nucleus forces the EuPCTMB and TbPCTMB to adopt a twisted snub disphenoid (TSD) coordination geometry. Examination of the 5D0 → 7F0 luminescent transition of EuPCTMB in the solid state confirmed the existence of a single distinct Eu3+ coordination environment, whereas two Eu3+ coordination environments were observed in aqueous solution. Lifetime analysis of aqueous TbPCTMB solutions determined that q = 0.1 and q = 1.0 for the two coordination environments and Stern-Volmer quenching constants (K SVTau;= 1101 M-1, KSV Φ= 40780 M-1) support the presence of a complicated monomer/dimer equilibrium. Relaxivity studies of GdPCTMB in H 2O/CH3OH exhibited a concentration dependency (0.02 mM-10.00 mM) ranging from r1 = 7.0 mM-1 s-1 to 4.0 mM-1 s-1 consistent with the trend observed by luminescence.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry