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High-pressure polymorphism in pyridine

DOI: 10.1107/S2052252519015616 DOI Help

Authors: Nico Giordano (University of Edinburgh; Advanced Light Source) , Christine M. Beavers (Advanced Light Source; University of California, Santa Cruz; Diamond Light Source) , Branton J. Campbell (Brigham Young University) , Václav Eigner (University of Edinburgh; Institute of Physics of the AS CR, v.v.i.) , Eugene Gregoryanz (University of Edinburgh) , William G. Marshall (ISIS Neutron and Muon Source) , Miriam Peña-Álvarez (University of Edinburgh) , Simon J. Teat (Advanced Light Source) , Cara E. Vennari (Advanced Light Source; University of California, Santa Cruz) , Simon Parsons (University of Edinburgh)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 7 , PAGES 58 - 70

State: Published (Approved)
Published: January 2020

Open Access Open Access

Abstract: Single crystals of the high-pressure phases II and III of pyridine have been obtained by in situ crystallization at 1.09 and 1.69 GPa, revealing the crystal structure of phase III for the first time using X-ray diffraction. Phase II crystallizes in P212121 with Z′ = 1 and phase III in P41212 with Z′ = ½. Neutron powder diffraction experiments using pyridine-d5 establish approximate equations of state of both phases. The space group and unit-cell dimensions of phase III are similar to the structures of other simple compounds with C2v molecular symmetry, and the phase becomes stable at high pressure because it is topologically close-packed, resulting in a lower molar volume than the topologically body-centred cubic phase II. Phases II and III have been observed previously by Raman spectroscopy, but have been mis-identified or inconsistently named. Raman spectra collected on the same samples as used in the X-ray experiments establish the vibrational characteristics of both phases unambiguously. The pyridine molecules interact in both phases through CH⋯π and CH⋯N interactions. The nature of individual contacts is preserved through the phase transition between phases III and II, which occurs on decompression. A combination of rigid-body symmetry mode analysis and density functional theory calculations enables the soft vibrational lattice mode which governs the transformation to be identified.

Journal Keywords: polymorphism; pressure; in situ crystallization; phase transitions.

Subject Areas: Chemistry

Facility: Advanced Light Source

Added On: 22/01/2020 15:49

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Organic Chemistry Chemistry

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