Spinning crystals leads to significant enhancement in 13C spectral resolution in MAS experiments on organic compounds: a new aid in studying phase transitions
✍ Scribed by Alexander Klymachyov; Naresh Dalal
- Book ID
- 104357882
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 154 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0926-2040
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✦ Synopsis
While Andrew [E.R. Andrew, Arch. Sci. (Geneva), 12 (1959) 103; E.R. Andrew, A. Bradbury and R.G. Eades, Nature, 183 (1959) 1802] utilized single crystals in his pioneering magic angle spinning (MAS) experiments, current studies use powders. Our recent MAS measurements on some organic compounds show that single crystals yield significantly narrower peaks than powders, especially for the 13 C atoms that are not protonated. In our 13 C CP (cross polarization)/MAS measurements on squaric acid (H 2 C 4 O 4 ), for example, single crystals yielded a four-fold reduction in line widths as compared to its powder. This additional gain in resolution enabled us to differentiate between the order-disorder versus displacive contributions to the mechanism of the paraelectric-antiferroelectric phase transition of squaric acid at 373 K, which had not been possible with other techniques. Moreover, this gain in resolution appears to increase in proportion to the applied Zeeman field, while retaining the benefit of higher dispersion.