✍ Scribed by John C. Edwards; Paul D. Ellis
No coin nor oath required. For personal study only.
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.
📜 SIMILAR VOLUMES