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Title: 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

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(μ 2-3,5-diiso­propyl-1,2,4-triazolato-κ 2 N 1: N 2)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 P2 1/n phase above 1 GPa, followed by a P2 1/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P2 1/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P2 1/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 displaysmore » 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.« less
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [3] ;  [1] ;  [1] ;  [4] ;  [4] ;  [5] ;  [5] ;  [6]
  1. Univ. of Bath, Bath (United Kingdom)
  2. Harwell Oxford, Oxfordshire (United Kingdom)
  3. Univ. of Bath, Bath (United Kingdom); Harwell Oxford, Oxfordshire (United Kingdom)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Univ. de Montreal, Montreal, QC (Canada)
  6. Diamond Light Source, Oxfordshire (United Kingdom)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
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Additional Journal Information:
Journal Volume: 3; Journal Issue: 5; Journal ID: ISSN 2052-2525
International Union of Crystallography
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; re-entrant phase transitions; high-pressure crystallography; gold(I); luminescence spectroscopy; DFT calculations
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