11B NMR studies of the paramagnetic effects of samarium(II) in tetrahydrofuran solutions on neutral and anionic borane and carborane clusters

Sophie M. Cendrowski-Guillaumet, James T Spencer

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Abstract

The dependence of 11B NMR spectral parameters of several neutral and anionic borane ([B 3H 8] -, [B 5H 8] -, and B 5H 9) and carborane (Et 2C 2B 4H 6, [Et 2C 2B 4H 5] - and C 2B 10H 12) clusters on the concentration of the paramagnetic samarium(II) cation in THF solutions was investigated. The magnitude of the paramagnetic isotropic chemical shifts in the 11B NMR spectra was found to depend solely on the samarium(II) solution concentration for all the borane clusters studied. In general, the isotropic shifts observed were significantly larger for the anionic borane and carborane clusters. The anionic cages displayed upfield isotropic shifts while the neutral cages showed only relatively small downfield isotropic shifts. In addition, the paramagnetic isotropic shifts for the nido-cage species ([B 5H 8] - and [Et 2C 2B 4H 5] -) were found to be much larger for the basal boron atoms than for the apical atom. The 11B- 1H tJ BH NMR coupling constants (where H t is a terminal BH cage proton) for the anionic clusters were observed to decrease and the spectral line widths (Δυ 1/2) increase with increasing samarium(II) concentration in solution. Finally, a linear temperature dependence of the isotropic chemical shift of the arachno-octahydrotriborate(1-) anion, [B 3H 8] -, was observed at constant samarium(II) concentration. A mechanism is proposed to account for these observations.

Original languageEnglish (US)
Pages (from-to)791-805
Number of pages15
JournalMain Group Metal Chemistry
Volume19
Issue number12
StatePublished - 1996

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ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

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