Solid State and Solution Dynamics of Pyridine Based Tetraaza-Macrocyclic Lanthanide Chelates Possessing Phosphonate Ligating Functionality (Ln-PCTMB): Effect on Relaxometry and Optical Properties

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• 作者：Garry E. Kiefer ; Mark Woods
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：December 21, 2009
• 年：2009
• 卷：48
• 期：24
• 页码：11767-11778
• 全文大小：1024K
• 年卷期：v.48,no.24(December 21, 2009)
• ISSN：1520-510X

文摘

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 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_SV^τ = 1101 M⁻¹, K_SV^Φ = 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.