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High-pressure polymorphism in salicylamide
Authors:
Russell
Johnstone
(University of Edinburgh)
,
Alistair
Lennie
(Diamond Light Source)
,
Stewart
Parker
(stfc rutherford laboratory)
,
Simon
Parsons
(The University of Edinburgh)
,
Elna
Pidcock
(Cambridge Crystallographic Data Centre)
,
Patricia
Richardson
(University of Edinburgh)
,
John
Warren
(University of Liverpool)
,
Peter
Wood
(University of Edinburgh)
Co-authored by industrial partner:
No
Type:
Journal Paper
Journal:
Crystengcomm
, VOL 12 (4)
, PAGES 1065-1078
State:
Published (Approved)
Published:
April 2010
Abstract: We report the compression of a single crystal of salicylamide to 5.1 GPa. Between ambient pressure and 5.1 GPa the structure remains in a compressed form of the ambient-pressure phase, referred to as salicylamide-I. This phase has been investigated twice previously, but the coordinates appear to have been reported with respect to a non-standard space group origin, though no comment to this effect is made in either of the original reports. Short H center dot center dot center dot H contacts implied by the previously published coordinates are strongly destabilising according to PIXEL packing energy calculations, but are absent in the structure reported here. A new high-pressure polymorph, salicylamide-II, is formed if salicylamide is crystallised in situ from a saturated solution in a 4 : 1 mixture of methanol and ethanol at 0.2 GPa. Crystal growth yielded three crystallites within the pressure cell, and combination of single-crystal X-ray diffraction intensity data from all three yielded a dataset which was >90% complete. PIXEL calculations indicate that salicylamide-II exhibits weaker H-bonding but stronger dispersion interactions than phase-I. Harmonic frequencies calculated using periodic DFT (and validated by inelastic neutron scattering data) indicate that phase-II is favoured at high pressure by its lower volume, its lower zero-point energy and higher entropy, and we estimate that at 0.2 GPa the free energy of phase-II is lower than that of phase-I by about 3 kJ mol(-1).
Subject Areas:
Chemistry
Facility: SRS Daresbury Laboratory