Phase transition in hydrogen-bonded ferroelectric compounds — Quantum fluctuations versus thermal fluctuations

The crystal structure of L-serine has been determined at room temperature at pressures between 0.3 and 4.8 GPa. The structure of this phase (hereafter termed L-serine-I), which consists of the molecules in their zwitterionic tautomer, is orthorhombic, space group P212121. The least compressible cell dimension (c), corresponds to chains of head-to-tail NH...carboxylate hydrogen bonds. The most compressible direction is along b, and the pressure-induced distortion in this direction takes the form of closing up voids in the middle of R-type hydrogen-bonded ring motifs. This occurs by a change in the geometry of hydrogen-bonded chains connecting the hydroxyl groups of the —CH2OH side chains. These hydrogen bonds are the longest conventional hydrogen bonds in the system at ambient pressure, having an O...O separation of 2.918 (4) Å and an O...O...O angle of 148.5 (2)°; at 4.8 GPa these parameters are 2.781 (11) and 158.5 (7)°. Elsewhere in the structure one NH...O interaction reaches an N...O separation of 2.691 (13) Å at 4.8 GPa. This is amongst the shortest of this type of interaction to have been observed in an amino acid crystal structure. Above 4.8 GPa the structure undergoes a single-crystal-to-single-crystal phase transition to a hitherto uncharacterized polymorph, which we designate L-serine-II. The OH...OH hydrogen-bonded chains of L-serine-I are replaced in L-serine-II by shorter OH...carboxyl interactions, which have an O...O separation of 2.62 (2) Å. This phase transition occurs via a change from a gauche to an anti conformation of the OH group, and a change in the NCαCO torsion angle from −178.1 (2)° at 4.8 GPa to −156.3 (10)° at 5.4 GPa. Thus, the same topology appears in both crystal forms, which explains why it occurs from one single-crystal form to another. The transition to L-serine-II is also characterized by the closing-up of voids which occur in the centres of other R-type motifs elsewhere in the structure. There is a marked increase in CH...O hydrogen bonding in both phases relative to L-serine-I at ambient pressure.

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Reversible phase transition of pyridinium-3-carboxylic acid perchlorate

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768110001576 ◽

2010 ◽

Vol 66 (3) ◽

pp. 387-395 ◽

Cited By ~ 33

Author(s):

Heng-Yun Ye ◽

Li-Zhuang Chen ◽

Ren-Gen Xiong

Keyword(s):

Phase Transition ◽

Carboxylic Acid ◽

Relative Displacement ◽

Temperature Phase ◽

Scanning Calorimetry ◽

Cell Parameters ◽

Dsc Measurements ◽

Reversible Phase Transition ◽

Reversible Phase ◽

Hydrogen Bonded

Pyridinium-3-carboxylic acid perchlorate was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurements show that this compound undergoes a reversible phase transition at ∼ 135 K with a wide hysteresis of 15 K. Dielectric measurements confirm the transition at ∼ 127 K. Measurement of the unit-cell parameters versus temperature shows that the values of the c axis and β angle change abruptly and remarkably at 129 (2) K, indicating that the system undergoes a first-order transition at T c = 129 K. The crystal structures determined at 103 and 298 K are all monoclinic in P21/c, showing that the phase transition is isosymmetric. The crystal contains one-dimensional hydrogen-bonded chains of the pyridinium-3-carboxylic acid cations, which are further linked to perchlorate anions by hydrogen bonds to form well separated infinite planar layers. The most distinct differences between the structures of the higher-temperature phase and the lower-temperature phase are the change of the distance between the adjacent pyridinium ring planes within the hydrogen-bonded chains and the relative displacement between the hydrogen-bonded layers. Structural analysis shows that the driving force of the transition is the reorientation of the pyridinium-3-carboxylic acid cations. The degree of order of the perchlorate anions may be a secondary order parameter.

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High‐pressure‐induced phase transition in 1,3‐diphenylurea: The approaching of N–H⋯O hydrogen‐bonded chains

Journal of Raman Spectroscopy ◽

10.1002/jrs.5706 ◽

2019 ◽

Vol 50 (11) ◽

pp. 1744-1752 ◽

Cited By ~ 1

Author(s):

Yuxiang Dai ◽

Yang Qi

Keyword(s):

Phase Transition ◽

High Pressure ◽

Hydrogen Bonded

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The influence of pressure on the infrared spectra of hydrogen bonded solids. II. Bihalide salts

Australian Journal of Chemistry ◽

10.1071/ch9760479 ◽

1976 ◽

Vol 29 (3) ◽

pp. 479 ◽

Cited By ~ 10

Author(s):

SD Hamann ◽

M Linton

Keyword(s):

Phase Transition ◽

High Pressure ◽

Hydrogen Bonds ◽

High Pressure Phase Transition ◽

Infrared Measurements ◽

Normal Hydrogen ◽

Combination Bands ◽

Pressure Phase ◽

Made In ◽

Hydrogen Bonded

Infrared measurements have been made of the influence of pressures between 0 and 40 kbar on the asymmetrical stretching frequencies v3 and bending frequencies v2 of the hydrogen-bonded ions FHF- and ClHCl- in the solid salts NaHF2, KHF2, NH4HF2, (CH3)4NHCl2 and (C2H5)4NHCl2 at 25�C. The behaviour of the symmetrical stretching frequency v1 for FHF- in KHF2 has been deduced indirectly from the shifts of combination bands. Contrary to the behaviour of compounds with weaker, 'normal', hydrogen bonds, the v3 bands shift to higher frequencies and the v2 bands shift to lower frequencies with increasing pressure. The vl band of KHF2 shifts to higher frequencies. These trends are all in agreement with predictions made in Part I for a simple model of hydrogen bonds. A new high-pressure phase transition has been found to occur in NaHF2 at about 40 kbar.

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