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Quantitative Structure–Property Relationships in Boron Nitrides: The 15N- and 11B Chemical Shifts

✍ Scribed by Christel M Marian; Marcus Gastreich

Publisher
Elsevier Science
Year
2001
Tongue
English
Weight
220 KB
Volume
19
Category
Article
ISSN
0926-2040

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✦ Synopsis

Nuclear Magnetic Resonance (NMR) chemical shifts(δ) for elements in solids may often be approached by ab initio cluster calculations. We employ this technique to investigate the influence of structural alterations on the 15 N and 11 B chemical shifts in boron nitrides-in both hexagonal and cubic modifications. Within a given class of connectivity, i.e., three-or fourfold coordinated nitrogen, for the first time, an almost linear correlation between the 15 N chemical shift and N-B bond lengths could be established. Also, the 11 B shifts in hexagonal boron nitride correlate with the B-N bond distance; however, the effect is less pronounced. For the value of the chemical shift (CS), the decisive property is the average bond length at the atom in focus. Variations of CS are predominantly caused by changes in the paramagnetic deshielding. Further, second-nearest neighbor effects on the shieldings at 15 N nuclei are quantified by subtraction schemes. The present work is closely related to the verification of models for amorphous high-demand Si/B/N ceramics.

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