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Thallium(III) coord...
Abstract
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- Tl-205 longitudinal relaxation rate measurements were performed on several thallium(III) complexes with the composition Tl(OH)(n)(H2O)(6-n)((3-n)+) (n = 1,2), Tl(Cl)(n)(H2O)(m-n)((3-n)+), Tl(Br)(n)(H2O)(m-n)((3-n)+) (m = 6 for n = 1-2, m = 5 for n = 3, m = 4 for n = 4), Tl(CN)n(H2O)(m-n)((3-n)+) (m = 6 for n = 1-2, m = 4 for n = 3-4) in aqueous solution, at different magnetic fields and temperatures. C-13 and D-2 isotopic labelling and 114 decoupling experiments showed that the contribution of the dipolar relaxation path is negligible. The less symmetric lower complexes (n < 4) had faster relaxation rate dominantly via chemical shift anisotropy contribution which depended on the applied magnetic field: T, values are between 20 and 100 ms at 9.4 T and the shift anisotropy is &UDelta;σ = 1000-2000 ppm. The tetrahedral complexes, n = 4, relax slower; their T-1 is longer than 1 s and the spin-rotation mechanism is probably the dominant relaxation path as showed by a temperature dependence study. In the case of the TICl4- complex, presumably a trace amount of TICl52- causes a large CSA contribution, 300 ppm. Since the geometry and the bond length for the complexes in solution are known from EXAFS data, it was possible to establish a correlation between the CSA parameter and the symmetry of the complexes. The relaxation behaviour of the Tl-bromo complexes is not in accordance with any known relaxation mechanism.
Keyword
- NMR
- Tl-205 longitudinal relaxation
- aqueous solution
- thallium halide complexes
- thallium cyanide complexes
- spin-lattice relaxation
- acidic aqueous-solution
- equilibrium dynamics
- magnetic-resonance
- cyanide complexes
- exchange
- system
- c-13
- spectroscopy
- bromide
Publication and Content Type
- ref (subject category)
- art (subject category)
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