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Inorganic Chemistry

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Rare earth metals -- Magnetic properties, Luminescent probes, Macrocyclic compounds, Contrast media (Diagnostic imaging), Magnetic resonance imaging


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 Gd3+ studied by X-ray crystallography, luminescence, and relaxometry. In the crystal these complexes are dimeric and possess 8-coordinate Ln3+ 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 5D07F0 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 (KSVτ = 1101 M−1, KSVΦ = 40780 M−1) support the presence of a complicated monomer/dimer equilibrium. Relaxivity studies of GdPCTMB in H2O/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.


This is the authors' version of a paper that subsequently appeared in Inorganic Chemistry, vol. 48, no. 24: 11767-11778. The version of record may be found at



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