7Li, 6Li, 23Na and 133Cs multinuclear NMR studies of adducts formed with shift reagent, TmDOTP5

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Abstract

Interactions between Li+, Na+, Cs+, Ca2+ and Mg2+ and the shift reagent (SR), TmDOTP5-, were studied by 7Li, 6Li, 23Na and 133Cs multinulear NMR spectroscopy. The unusually large paramagnetic shifts (>>100 ppm) observed in the cation NMR resonances at low alkali metal ion to TmDOTP5- ratios indicated that the cations bind near the 4-fold symmetry axis of the complex. The geometric parameters for the adducts formed between 7Li, 6Li, 23Na and 133Cs cations and TmDOTP5- were obtained from shift and relaxation rate data and compared with those calculated using MMX energy minimization techniques. It is found that the larger Cs+ ion lies closest to the 4-fold axis of symmetry and displays the largest binding constant. The smaller Li+ ion deviates most from the 4-fold symmetry axis and has a less favorable binding interaction than Cs+. Na+ lies somewhere between these two extremes but has the largest limiting shifts due to its favorable distance from the paramagnetic metal center. A significant reversal of the 23Na shift upon addition of Ca2+ and Mg2+ indicate that these two divalent cations form very stable 1:1 adducts with TmDOTP5- (log K (Ca2+) = 5.69 and log K1 (Mg2+) = 3.85). An analysis of the Mg2+ titration data shows that the 2Mg2+:TmDOTP5- adduct becomes dominant at high Mg2+/TmDOTP5- ratio (log K2 (Mg2+) = 2.17). The significant influence of NH4+ on the TmDOTP5--induced 6Li shifts suggests that the NH4+ ion may form multiple H-bonds with the SR along the 4-fold axis of symmetry.

Original languageEnglish (US)
Pages (from-to)331-341
Number of pages11
JournalInorganica Chimica Acta
Volume246
Issue number1-2 SPEC. ISSUE
StatePublished - May 1 1996

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Keywords

  • Macrocyclic complexes
  • Metal ion complexes
  • Multinuclear NMR
  • Shift reagent complexes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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