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Cross‐polarization for quadrupolar nuclei—proton to molybdenum‐95
Author(s) -
Edwards John C.,
Ellis Paul D.
Publication year - 1990
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260281312
Subject(s) - chemistry , molybdenum , polarization (electrochemistry) , dipole , spin–lattice relaxation , spectral line , analytical chemistry (journal) , nuclear magnetic resonance , atomic physics , molecular physics , physics , inorganic chemistry , nuclear quadrupole resonance , organic chemistry , chromatography , astronomy
High‐field, 95 Mo, solid‐state nuclear magnetic resonance spectra of (NH 4 ) 6 Mo 7 O 24 · 4H 2 O and (Bu 4 N) 2 Mo 2 O 7 were obtained using solid‐echo techniques together with 1 H cross‐polarization and dipolar decoupling. The results show that reliable second‐order powder line shapes can be obtained with excellent cross‐polarization enhancements of 66–86% of maximum theoretical enhancement. The lower than maximum enhancements are due to the relatively long T IS values, which are similar in magnitude to the T H 1ρ values. Experiments were performed which reveal the dynamics involved in the cross‐polarization process, including measurement of the cross‐relaxation time constant and the 1 H and 95 Mo rotating‐frame spin‐lattice relaxation times. It was found that the principal relaxation process causing low gain in the observed signal was the 1 H T 1ρ , which was found to be on the order of 23–24 ms. The experimental results obtained indicate that selective cross‐polarization dynamics occur in molybdenum cluster species with inequivalent molybdenum sites. The 95 Mo rotating‐frame spin‐lattice relaxation rate is long in comparison with the other relaxation processes, making molybdenum a good cross‐polarization candidate but precluding the use of multiple contact cross‐polarization.