Ammonium cyanate: a DFT study of crystal structure, rotational barriers and vibrational spectrum

Abstract

The crystal structure, rotational barriers and vibrational spectrum of ammonium cyanate have been studied by DFT calculations. The results show that, in the most stable structure, the ammonium ion is oriented such that each N—H bond points towards the N atoms of a cyanate anion giving rise to N—H···N hydrogen bonding, rather than N—H···O hydrogen bonding. The N—C and C—O bond lengths suggest that the structure of the anion in the crystal is best described as ⁻N=C=O. These structural features are in agreement with recent results from neutron diffraction. At the transition state for rotation of the ammonium cation about an N—H bond, the cation is displaced and distorted from its equilibrium configuration. The barrier to the rotation of the ammonium cation about the 4 axis is found to be larger than the minimum barrier to rotation about an N—H bond, suggesting that the latter is the preferred rotational mode.

Acknowledgments

RJCB wishes to express his appreciation of more than a decade of productive collaboration with Professor Ruth Lynden-Bell during a sabbatical year and subsequent visits to Cambridge and Belfast, and thanks her for hospitality and many stimulating discussions. She has made valuable contributions during discussions of the present study.

This work was supported by the Natural Sciences and Engineering Research Council of Canada. RJCB gratefully acknowledges financial support from Trinity College, Cambridge.

KDMH, RLJ and SH gratefully acknowledge financial support from the University of Birmingham and EPSRC, and discussions with Professor J. D. Dunitz, FRS, and Professor Julian Gale are also gratefully acknowledged.

Notes

[email protected]; [email protected]

Additional information

Notes on contributors

Roy L. Johnston *

[email protected]; [email protected]