High-pressure polymorphism in salicylamide

DOI: 10.1039/b921288d

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