Hydrogen-bonded Crystals Research Articles

Observation of Quantum Paraelectricity in an Intermolecular Ionic Hydrogen-Bonded Crystal of a Squaric Acid Derivative

Proton transfer in a hydrated crystal of a squaric acid derivative, p-phenylenebis(squaric acid) (PBSQ), was investigated by means of ac dielectric measurements. The crystal consisted of PBSQ monoanions and protonated water dimer (H5O2+) counter cations, and a highly symmetric, one-dimensional hydrogen-bonded chain was formed through strong OH· · ·O- ionic hydrogen bonding between deprotonated PBSQ moieties. The permittivity of the hydrated crystal was nearly temperature independent (ε‘ ∼ 9), but the deuterated crystal exhibited a Curie−Weiss type temperature dependence and underwent depression of the permittivity at 28 K, which is the characteristic of an (anti)ferroelectric phase transition. Thus, we conclude that the dielectric response of the hydrated PBSQ crystal originates from proton transfer along the intermolecular hydrogen bond and that the temperature-independent dielectric behavior can be interpreted in terms of quantum paraelectricity.

Crystal engineering of urea alpha-network via I...O2N synthon and design of SHG active crystal N-4-iodophenyl-N'-4'-nitrophenylurea.

Crystalline nitrodiphenyl ureas adopt the N-H...O tape alpha-network only when stabilization accrues from the I...O(2)N or C[triple bond]C-H...O(2)N synthon, otherwise the ureanitro motif is preferred; soft, weak interactions can direct polar self-assembly in strong N-HO hydrogen-bonded crystals.

Phases Coexistence of Hydrogen-Bonded Mixed Ferroelectric and Antiferroelectric Crystals

The problem proton-glass and ferroelectric phases coexistence in Rb1−x (NH4) x H2AsO4 (RADA) and K1−x (NH4) x H2PO4 (KADP) crystals based on dielectric studies up to temperature 0.3 K is presented. The measurements were performed in the helium-3 cryostat in the temperature range from 300 K to 0.3 K. Glass behavior for the RADA is present even for a small concentration x = 0.01, whereas for the KADP the proton glass occurs for a concentration x > 0.05. The partial phase diagrams of RADP and KADP as a function of fractional ammonium concentration x and temperature T are presented.

Hydrostatic Pressure Effect on Phase Transition in Novel Crystalline 2-Aminopirydyne Phosphate Ferroelectrics

Aminopyridine phosphate NC4H4NH2*H3PO4 (APP) is a new hydrogen-bonded ferroelectric crystal. One expects that the phase transition at 103.5 K is connected with proton ordering in hydrogen bonds. We have studied the hydrostatic pressure effect on dielectric properties to confirm the role of proton ordering in the molecular mechanism of phase transition in APP crystals. The negative nonlinear shift of phase transition was observed with dTc/dp\\p=0 = 1.84 K/Gpa. The phase diagram in the pressure–temperature plane is proposed.

Crystals with disordered hydrogen-bond networks and superprotonic conductivity. Review

The class of hydrogen-containing salts in which the phases with dynamically disordered hydrogen-bond nets are formed has been considered. Unlike other hydrogen-bonded crystals, the crystals of this class are characterized by delocalized hydrogen bonds producing considerable influence on their physical and physical-chemical properties. The structural transitions between the phases with ordered and disordered hydrogen-bond networks are described with the emphasis being made on the structural mechanisms of anomalously high (superprotonic) conductivity associated with delocalization of hydrogen bonds. The perspectives of the use of crystals with delocalized hydrogen bonds in fuel cells and other electrochemical devices are discussed.

Phase transitions in hydrogen-bonded phenol–amine adducts: analysis by ferroelastic theory

Phase transitions in a recently discovered class of hydrogen-bonded organic crystals are analyzed by Landau theory. It is shown that the transitions are ferroelastic. Two types of transition, orthorhombic-to-monoclinic and monoclinic-to-triclinic, are analysed using an expansion of the free energy in symmetry-allowed powers of the strain components. For three examples, new data are presented for the crystallographic parameters in a range of temperature including the phase transition point T c. These data show that the transitions are second order and the temperature dependences are consistent with the mean-field analysis. We propose that the making and breaking of the hydrogen bond interactions with variation of temperature accounts for these reversible ferroelastic phase transitions. Expressions are derived for the entropy and the specific-heat discontinuity at T c. It is pointed out that the transitions should be accompanied by ‘soft-mode’ behavior in a phonon of appropriate symmetry.

1H and39K Nuclear Magnetic Resonance Relaxation Study in a KHSO4Single Crystal

¹H and³⁹K Nuclear Magnetic Resonance Relaxation Study in a KHSO₄Single Crystal

Modeling Hydrogen‐Bonded Crystals

AbstractFor Abstract see ChemInform Abstract in Full Text.

Dynamical Susceptibility in KDP-type Crysals above and belowTcII

The path probability method (PPM) in the tetrahedron-cactus approximation is applied to the Slater-Takagi model with dipole-dipole interaction for KH2PO4-type hydrogen-bonded ferroelectric crystals in order to derive a small dip structure in the real part of dynamical susceptibility observed at the transition temperature Tc. The dip structure can be ascribed to finite relaxation times of electric dipole moments responsible for the first order transition with contrast to the critical slowing down in the second order transition. The light scattering intensity which is related to the imaginary part of dynamical susceptibility is also calculated above and below the transition temperature and the obtained central peak structure is consistent with polarization fluctuation modes in Raman scattering experiments.

Ferroelectric order of parallel bistable hydrogen bonds.

A new NH.N hydrogen-bonded ferroelectric crystal of [C6H12N2H]+ReO - 4 (dabcoHReO4) exhibits exceptional dielectric properties that result from the unique structure where all the bistable NH...N hydrogen bonds are parallel and directed exactly in the same sense. Consequently, the main structural origin of the spontaneous polarization of the crystal is the identical orientation of the asymmetric NH+...N hydrogen bonds along [001]. This first observation of a ferroelectric with parallel arrangement of the NH+...N bonded aggregates, gives temperature-independent and the highest spontaneous polarization ever reported for an organic or water-soluble substance.

Ferroelectricity and isotope effects in hydrogen-bonded KDP crystals.

Based on an accurate first principles description of the energetics in H-bonded potassium-dihydrogen-phosphate crystals, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Tunneling is allowed only for clusters involving correlated protons and heavy ion displacements, the main effect of deuteration being a depletion of the proton probability density at the O-H-O bridge center, which in turn weakens its proton-mediated covalent bonding. The ensuing lattice expansion couples self-consistently with the proton off-centering, thus explaining both the giant isotope effect and its close connection with geometrical effects.

Reassigning hydrogen-bond centering in dense ice.

Hydrogen bonds in H2O ice change dramatically upon compression. Thereby a hydrogen-bonded molecular crystal, ice VII, is transformed to an atomic crystal, ice X. Car-Parrinello simulations reproduce the features of the x-ray diffraction spectra up to about 170 GPa but allow for analysis in real space. Starting from molecular ice VII with static orientational disorder, dynamical translational disordering occurs first via creation of ionic defects, which results in a systematic violation of the ice rules. As a second step, the transformation to an atomic solid and thus hydrogen-bond centering occurs around 110 GPa at 300 K and no novel phase is found up to at least 170 GPa.

Modeling hydrogen bonded crystals

After a perspective on simulation methods for intermolecular interactions in general, some aspects peculiar to the hydrogen bond are examined. Quantum chemical versus empirical force field methods, with their functional forms, are discussed. Electrostatic energies from accurate calculations are compared with electrostatic ‘prejudices’. Static, temperature-less calculations are compared with dynamic simulations. The relationships of hydrogen bonding (HB) in crystals to close-packing and lattice energies are examined, and possible use of HB in crystal structure prediction from molecular structure is discussed. Uses of full dynamic simulations in molecular recognition, particularly in the case of hydrogen-bonding dimers versus chains in carboxylic acids, are reviewed; dynamic simulations of molecular motions and eventual crystal melting in hydrogen-bonding crystals are also described.

NMR chemical shifts in periodic systems from first principles

A recently developed ab-initio method for the calculation of NMR chemical shifts and magnetic susceptibilities in systems under periodic boundary conditions is presented and applied to a hydrogen-bonded molecular crystal. The calculations can unambiguously assign the chemical shifts to individual atoms in experimental spectra, and can further serve for the validation of simulated atomic trajectories and geometries. Apart from the example presented, the method can be applied to crystalline and amorphous insulators, as well as to isolated molecules using a supercell technique. The results are in good agreement with experiment.

Vanishing of Transition Temperature in Hydrogen-Bond Crystals Under High Pressure

Some of hydrogen-bond crystals are well known to undergo order-disorder type phase transitions at ambient pressure. After recent experimental studies, however, transition temperatures T c of these crystals vanish at respective critical pressures p c contrary to the third law of thermodynamics. The Curie constants in KDP (KH 2 PO 4 ) and DKDP(KD 2 PO 4 ) were shown to hold finite values in contrast to the vanishing of T c for p > p c . This fact has been explained as the crossover of phase transition mechanism from the order-disorder type to the displacive one under high pressure. The saturation of the divergence in the dielectric constant k c near T = 0 in both crystals has been fitted with the Barrett formula given in terms of three parameters used to discuss the quantum paraelectricity. The pressure dependences of the three parameters have been evaluated for p > p c . The mechanism of phase transition in hydrogen-bond crystals under high pressure has been discussed on the basis of these experimental results.

Vanishing of Transition Temperature in Hydrogen-Bond Crystals Under High Pressure

Some of hydrogen-bond crystals are well known to undergo order-disorder type phase transitions at ambient pressure. After recent experimental studies, however, transition temperatures T c of these crystals vanish at respective critical pressures p c contrary to the third law of thermodynamics. The Curie constants in KDP (KH 2 PO 4 ) and DKDP(KD 2 PO 4 ) were shown to hold finite values in contrast to the vanishing of T c for p > p c . This fact has been explained as the crossover of phase transition mechanism from the order-disorder type to the displacive one under high pressure. The saturation of the divergence in the dielectric constant k c near T = 0 in both crystals has been fitted with the Barrett formula given in terms of three parameters used to discuss the quantum paraelectricity. The pressure dependences of the three parameters have been evaluated for p > p c . The mechanism of phase transition in hydrogen-bond crystals under high pressure has been discussed on the basis of these experimental res...

Surface Transformation of Hydrogen-Bonded Crystals at High-Temperatures and Topochemical Nature

Many hydrogen-bonded crystals undergo ambiguous transformations at high temperatures in addition to the well-established ferroelectric and/or ferroelastic transitions at low temperatures. The electric conductivity shows superprotonic phase at high temperatures. However, high-temperature properties strongly depend on the sample history. Therefore, it is as yet obscure whether the high temperature transformations are structural phase transitions in the bulk, or surface melting or chemical reaction at the surface. The crystal surfaces in KH 2 PO 4 , RbH 2 PO 4 , CsH 2 PO 4 , TIH 2 PO 4 , (NH 4 ) 2 SO 4 , and LiH 3 (SeO 3 ) 2 reveal drastic change near onset temperature ( T p ) and various kinds of patterns appear in the form of cracks, pores, sheaves, spherulites and so on. All of these are sensitive to changes in the conditions at the surface and seem to be due to an onset of thermal decomposition at the surface. These results are discussed in terms of 'topochemical' nature.

Ferroelastic-Superionic Phase Transition in (NH 4 ) 3 H(SO 4 ) 2 Single Crystals: FT NIR Raman, DSC and Ferroelastic Domain Studies

(NH 4 ) 3 H(SO 4 ) 2 , a member of M 3 H(XO 4 ) 2 hydrogen-bonded crystal family. The transition from the superionic phase (R3m) to the low-temperature phase (A2/a) at T S =413 K is accompanied by an anisotropic spontaneous deformation, which leads to the appearance of ferroelastic properties. The paper presents results of temperature variation of heat capacity, ferroelastic domain pattern and NIR Raman spectra in the close vicinity of T S .

The Mechanism of Proton Conductivity in Quasi-One Dimensional Hydrogen-Bonded Crystals

The mechanisms of proton transport in partially deuterated ammonium hydrogen selenate, NH 4 HSeO 4 (AHSe), and partially deuterated mixed crystals of betaine phosphate (DBP) and betaine phosphite (DBPI), DBP 1 m x DBPI x are studied by means of two-dimensional (2D) 2 H NMR and dielectric measurements. In both systems the ionic conductivity is very likely to be realised via jumps of the protons or deuterons between different hydrogen bonds (inter-bond jumps). The importance of certain defects for the conductivity process is revealed. In AHSe jumps occur through non-occupied hydrogen positions. In the mixed crystals DBP 1 m x DBPI x the creation of defects is in fact favoured by the substitution of DBP for DBPI molecules or vice versa.

Surface Transformation of Hydrogen-Bonded Crystals at High-Temperatures and Topochemical Nature

Surface Transformation of Hydrogen-Bonded Crystals at High-Temperatures and Topochemical Nature