Giant Deuteron Migration During the Isosymmetric Phase Transition in Deuterated 3,5‐Pyridinedicarboxylic Acid

Abstract

Deuterated 3,5-pyridinedicarboxylic acid exhibits reversible temperature-induced deuteron migration of a magnitude unprecedented in this class of compounds. We used a combination of variable-temperature powder and single-crystal neutron diffraction and density functional theory (DFT)-based computational methods to elucidate the origin of this remarkable behaviour. Single-crystal neutron diffraction shows that between 15 and 300 K, the deuteron moves by 0.32(1) Å and the structure changes from a low-temperature N-D···O form to a high-temperature N···D-O form. Variable-temperature powder neutron-diffraction data, which was fitted by using parametric Rietveld refinement, show that this deuteron migration is due to an isosymmetric, first-order phase transition that occurs by growth of the daughter phase in the parent-phase matrix. Similar phase transitions are observed in two selectively deuterated forms of the material. DFT calculations demonstrate the role of phonons and show that vibrational free-energy stabilisation, which plays a key role in the observed structural phase transitions, is more pronounced in the fully deuterated material and proportional to the mass of the molecule, that is, the level of deuteration. This is consistent with our experimental work, for which distinct crystallographic phase transitions were clearly observed for the three deuterated systems, but not for the fully protonated material.

Temperature dependent solid-state proton migration in dimethylurea–oxalic acid complexes

“…9 Urea-phosphoric acid is one of only two proton migration materials studied extensively using a combination of experimental techniques and theory, the other being pyridine-3,5dicarboxylic acid. 7,11,12 While the migration has not been attributed to increased thermal motion in either of these examples, this cannot be ruled out as a possible explanation in other materials exhibiting migration.…”

Structure and physicochemical characterization of a naproxen–picolinamide cocrystal

“…For example, two sulfathiazole-oxalic acid complexes have been shown to be salts by multinuclear SS-NMR (Koike et al, 2014) and recently a furosemide-isonicotinamide complex was confirmed to be a cocrystal by comparison of 15 N SS-NMR and DFT-calculated chemical shifts (Kerr et al, 2015). Another aspect of the study of proton position is the characterization of reversible proton migration over short strong hydrogen bonds, which is of fundamental interest but also potentially relevant to some types of functional materials (Ford et al, 2011;Frantsuzov et al, 2014).…”

Measurement of Proton Tunneling in Short Hydrogen Bonds in Single Crystals of 3,5 Pyridinedicarboxylic Acid Using Nuclear Magnetic Resonance Spectroscopy

“…At higher temperature the apparent dynamical rate saturates above 110 K whereas it could be expected to continue to increase given that diffraction [40], nuclear quadrupole resonance [50], and vibrational spectroscopy [51] report the crossover from donor to acceptor species at 200 K. Similarly, the temperature dependence of the spectral density amplitude [ Fig. 3(b)] shows a clear maximum at 105 K. In the usual model [21], in which …”

“…The intermolecular HB has a N-O distance of 2.54 Å and lies in the few percent of the shortest known N − H Á Á Á O HBs [37,38]. The proton is almost centered and is clearly observed in neutron diffraction [39,40] to migrate from the donor N at low temperature to the acceptor O at room temperature. The proton jump distance is 0.1 Å in the protonated crystal and at 200 K the proton is, on average, centered.…”