NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning
2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 22, 224201Article in journal (Refereed) PublishedText
Orders of magnitude decrease of Pb-207 and Hg-199 NMR longitudinal relaxation times T-1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(II) halides, the most dramatic decrease of T-1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time. Published by AIP Publishing.
Place, publisher, year, edition, pages
American Institute of Physics Inc. , 2016. Vol. 144, no 22, 224201
Physical Sciences Chemical Sciences
IdentifiersURN: urn:nbn:se:kth:diva-189932DOI: 10.1063/1.4953540ISI: 000378926100014PubMedID: 27306000ScopusID: 2-s2.0-84974681701OAI: oai:DiVA.org:kth-189932DiVA: diva2:950224
QC 201607282016-07-282016-07-252016-07-28Bibliographically approved