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Observation of a re-entrant phase transition in the molecular complex tris(μ 2 -3,5-diisopropyl-1,2,4-triazolato-κ 2 N 1 : N 2 )trigold(I) under high pressure

DOI: 10.1107/S2052252516013129 DOI Help

Authors: Christopher H. Woodall (University of Bath) , Jeppe Christensen (Research Complex at Harwell, Rutherford Appleton Laboratory) , Jonathan M. Skelton (University of Bath) , Lauren E. Hatcher (University of Bath) , Andrew Parlett (University of Bath) , Paul R. Raithby (University of Bath) , Aron Walsh (University of Bath) , Stephen C. Parker (University of Bath) , Christine M. Beavers (Advanced Light Source, Lawrence Berkeley National Laboratory) , Simon J. Teat (Advanced Light Source, Lawrence Berkeley National Laboratory) , Mourad Intissar (Département de Chimie, Université de Montréal) , Christian Reber (Département de Chimie, Université de Montréal) , David R. Allan (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 3 , PAGES 367 - 376

State: Published (Approved)
Published: September 2016

Open Access Open Access

Abstract: We report a molecular crystal that exhibits four successive phase transitions under hydro­static pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(μ2-3,5-diiso­propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm−1 at 2.40 GPa, decreasing steeply to 13550 cm−1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.

Journal Keywords: re-entrant phase transitions; high-pressure crystallography; gold(I); luminescence spectroscopy; DFT calculations

Subject Areas: Chemistry, Physics

Instruments: I19-Small Molecule Single Crystal Diffraction

Other Facilities: Advanced Light Source

Added On: 18/11/2016 13:31


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