11B NMR spectroscopy

This paper covers developments in 11B NMR spectroscopy subsequent to a previous review in this series. In addition, it serves to complement the preceding chapter. As in previous years, a major use of 11B has been archival - that is, use for routine characterization of new compounds - although considerable efforts to elucidate correlations between structure and NMR parameters continue. However, some significant trends may be noted. First, availability of high-field spectrometers with multinuclear capability as well as software for sophisticated data manipulation is increasingly common, and, with these instruments, lack of chemical-shift dispersion in the face of relatively large linewidths presents much less of a problem than previously when complex polyboron compounds are to be characterized. Coupled with this, potent separation techniques, exemplified by thin-layer, high-pressure and ion-exchange chromatography, are able to unravel complex mixtures and make pure compounds available for study. Use of X-ray crystallographic facilities with which to structurally characterize compounds whose spectra are reported is today almost routine. Less routine is an appreciation of the fact that one crystal teased from a reaction mixture is not necessarily representative of the system from which it was extracted; use of X-ray powder-diffraction analysis to test this hypothesis is to be encouraged. Thus inability to separate mixtures, to secure high-resolution spectra and structural data are of decreasing importance in boron chemistry, leaving, perhaps, as the rate-limiting factors, creativity and the propensity to select for detailed study systems that offer new, significant and fundamental insights into the chemistry of boron and of the elements to which it bonds