Coupling of displacive and order-disorder transformations in hydrogen-bonded ferroelectrics

An investigation into structural changes due to deuteration

“…The structures for KH 2 PO 4 and the deuterated KD 2 PO 4 can be found in the ICSD (Karlsruhe, 2008). Comparison of the deuterated (ICSD code 201372) and hydrogenated (ICSD code 201370) structures (Nelmes et al, 1982) reveal a change of 0.73 relating to a 10.3 change as previously described by Katrusiak (1995). A survey of isotope effects predominantly on Table 2 Space group, Z number and unit-cell parameters for all isomorphous compounds studied.…”

“…Changes in molecular function upon deuteration are known. The effect of deuteration on thermal properties through structural change has been documented before and is known as the Ubbelohde effect (Robertson & Ubbelohde, 1939;Katrusiak, 1995). McMahon et al (1998) report the change in phase-transition temperature due to deuteration for the compound KH 2 PO 4 and state how a change in hydrogen-bond geometry is responsible.…”

Molecular structure of hydrated complex of 1,4-dimethylpiperazine di-betaine with l-tartaric acid

“…Different protonation of identical functional groups is occasionally observed in the crystals built of small ions or molecules like KH 2 PO 4 -type ferroelectrics, with the OAHÁ Á ÁO hydrogen bonds, enolized diketones, NAHÁ Á ÁN bonded ferroelectrics and relaxors, and in analogues of nucleic acid bases. The correlation between the proton sites and their crystal environment can provide information on the coupling between the molecular structure and external forces, allowing one to better understand the mechanisms of the frequent processes regulated by the proton transfer [28][29][30][31][32][33][34][35][36][37][38][39].…”

Variable-temperature and variable-pressure studies of small-molecule organic crystals

“…The same does the β-form. If, temperature and pressure being the same, NH 3 and H 2 O are present simultaneously in contact with a solid sample, a reverse transformation, that is from the α-form into the γ-form is observed. β-Glycine also transforms into the γ-form under this conditions.…”

“…hydrogen bonds into "head-to-tail" chains along the crystallographic axis a, similar to those in the polymorphs of glycine. Every NH 3 The directions of the principal axes of strain ellipsoids on cooling and with increasing pressure coincide with the a, b, and c crystallographic directions in the structure of L-serine and can be correlated with the structure of the NH…O and OH…O hydrogen bond network ( Figure 20, 21). The most rigid (both on cooling and with increasing pressure) direction in the structure of L-serine is the direction along axis a, corresponding to the shortest cell parameter.…”