Homonuclear SQ-DQ correlations in solids: applications of the broadband BaBa scheme to reveal 31P-31P spatial correlations in two-, three-, four-, and five-spin systems

• Published in: Magnetic resonance in chemistry Vol. 49; no. 12; pp. 801 - 811
• Main Authors: Szalontai, Gábor, Besenyei, Gábor, Párkányi, László
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.12.2011
• Subjects: 31P SQ-DQ spectroscopy; and five-spin systems; BaBa excitation-reconversion scheme; fast MAS; four; Pd-phosphine complexes; three; two; two‐, three, four, and five‐spin systems; weak dipolar couplings
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.2842

In this paper, we report on the use and limitations of the popular double‐quantum recoupling sequence back‐to‐back in studies of 31P‐31P spatial proximities in Pd‐phosphine complexes at medium field (9.38 T) under the conditions of fast MAS. The effects of internuclear distances in different spin systems and the impact of isotropic chemical shift and chemical shift anisotropy (CSA) offsets on the detectibility of SQ‐DQ correlations were of particular interest to us. Selected model compounds with these requirements in mind were synthesized. By optimization of the excitation times of SQ‐DQ correlations up to 4.6 Å could be obtained even in four‐spin systems; however, certain long‐range correlations may be weak or missing. Although under fast MAS, CSA values up to 270 ppm are well tolerated, in multi‐spin systems in cases of isotropic chemical shift offsets larger than 50 ppm, the DQ coherences cannot be properly excited. Copyright © 2011 John Wiley & Sons, Ltd. Limitations of the homonuclear DQ recoupling sequence BaBa in studies of 31P‐31P spatial proximities in Pd‐phosphine complexes were explored under the conditions of fast MAS. Effects of internuclear distances, isotropic chemical shift and chemical shift anisotropy (CSA) offsets on the detectibility of SQ‐DQ correlations were examined. Correlations up to 4.6 Å could be obtained even in four‐spin systems. CSA values up to 270 ppm are well tolerated; however, for isotropic chemical shift offsets larger than 50 ppm, the intensity of DQ coherences is too small.