A 3D experiment that provides isotropic homonuclear correlations of half-integer quadrupolar nuclei

摘要

Two 3D experiments, capable of producing enhanced resolution two-spin double-quantum (DQ) homonuclear correlations for half-integer quadrupolar nuclei, are described. The first uses a split-t(1) MQMAS sequence followed by a sandwiched oR(3) symmetry-based dipolar recoupling sequence to directly excite DQ coherences. In this case an isotropic single-quantum (SQ) coherence starts the homonuclear DQ excitation. In the second experiment a single strong pulse is used to create triple quantum (TQ) coherence followed by a further single pulse conversion to zero-order before a non-sandwiched oR(3) DQ sequence. The first experiment is demonstrated using Rb-87 in RbNO3, with three Rb sites in a similar to 5 ppm range, and the second to B-11 in caesium triborate, CsB3O5, with two three-coordinated sites separated by similar to 2 ppm and one four-coordinated boron site. In both cases, all sites are clearly resolved and their connections observed. The second experiment has higher sensitivity and a good signal to noise is obtained in a reasonable time despite the long T-1 relaxation time of B-11 in this material. (C) 2014 Elsevier Inc. All rights reserved.