High-resolution solid-state 11B and 13C MAS NMR of icosahedral carboranes

• Published in: Spectrochimica acta. Part A: Molecular spectroscopy 1988, Vol.44 (3), p.273-276
• Main Authors: Harris, Robin K., Bowles, Jenny, Stephenson, Ian R., Wong, Edward H.
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Molecular properties and interactions with photons; Nuclear resonance and relaxation; Physics
• ISSN: 0584-8539
• DOI: 10.1016/0584-8539(88)80016-3

The globular-shaped icosahedral carboranes, o-, m-, and p-C 2B 10H 12, yield high-resolution 11B and 13C MAS solid-state NMR spectra. Chemical shifts and linewidths are comparable to those of solution spectra. Spin—lattice relaxation times indicate the quadrupolar mechanism to be dominant for the B-11 relaxation. Linewidths of spectra recorded at 96 MHz and 64 MHz were similar. At 298 K, the 13C T 1 of p-carborane was found to be an order of magnitude smaller than those of the other two isomers. This can be attributed to the higher phase transition temperature of p-carborane indicative of the stronger intermolecular dipolar CH interactions made possible by the para-carbon vertices. Substitution on o-carborane by a methyl group yields spectra of comparable linewidths to those of the parent compound. Substitution by a bulkier phenyl group, however, results in extensive broadening of both 11B and 13C signals of the derivative 1-Ph- o-C 2B 10H 11.