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Effect of pressure on the crystal structure of salicylaldoxime-I, and the structure of salicylaldoxime-II at 5.93 GPa

DOI: 10.1107/S0108768106031752 DOI Help
PMID: 17108665 PMID Help

Authors: Peter Wood (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , Ross S. Forgan (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , David Henderson (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , Simon Parsons (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , Elna Pidcock (Cambridge Crystallographic Data Centre) , Peter A. Tasker (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , John Warren (Daresbury Laboratory, U.K.)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Crystallographica Section B Structural Science , VOL 62 , PAGES 1099-1111

State: Published (Approved)
Published: December 2006

Abstract: The effect of pressure on the crystal structure of salicylaldoxime has been investigated. The ambient- pressure phase (salicylaldoxime-I) consists of pairs of molecules interacting through oximic OH(...)O hydrogen bonds; taken with phenolic OH(...)N intramolecular hydrogen bonds, these dimers form a pseudo-macrocycle bounded by an R(4)(4)(10) motif. The dimers interact principally via pi(...)pi stacking contacts. Salicylaldoxime derivatives are used industrially as selective solvent extractants for copper; the selectivity reflects the compatibility of the metal ion with the pseudo-macrocycle cavity size. On increasing the pressure to 5.28 GPa the size of the cavity was found to decrease by an amount comparable to the difference in hole sizes in the structures of the Cu(2+) salicylaldoximato complex and its Ni(2+) equivalent. On increasing the pressure to 5.93 GPa a new polymorph, salicylaldoxime-II, was obtained in a single-crystal to single-crystal phase transition. PIXEL calculations show that the phase transition is driven in part by relief of intermolecular repulsions in the dimer-forming OH(...)O-bonded ring motif, and the ten-centre hydrogenbonding ring motif of the phase I structure is replaced in phase II by a six-centre ring formed by oximic OH(...)N hydrogen bonds. The transition also relieves repulsions in the pi(...)pi stacking contacts. The intramolecular OH(...)N hydrogen bond of phase I is replaced in phase II by a intermolecular phenolic OH(...)O hydrogen bond, but the total interaction energy of the pairs of molecules connected by this new contact is very slightly repulsive because the electrostatic hydrogen-bond energy is cancelled by the repulsion term. The intra- to intermolecular hydrogen-bond conversion simply promotes efficient packing rather than contributing to the overall lattice energy.

Journal Keywords: Salicylaldoxime; Pressure Dependence; Phase Transitions; Hydrogen Bonding.

Subject Areas: Chemistry

Facility: Daresbury

Added On: 01/04/2012 13:26

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