J. Baran

Ferroelectricity in Gly · H3PO3 crystal

Abstract A new Gly · H 3 PO 3 crystal was grown and its physical properties were investigated. DSC measurements revealed a phase transition at about 224 K. Dielectric investigations showed a large anomaly of dielectric permittivity at 224.7 K along the b -axis. The appearance of spontaneous polarization (along the b -axis) observed by means of a Sawyer-Tower circuit gives evidence for a para-ferroelectric phase transition in this material.

Crystal structure, vibrational spectra and nonlinear optical properties of tetrakis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(selenate) trihydrate crystal

Abstract X-ray single crystal diffraction and the vibrational spectroscopic analysis of a new melaminium salt, tetrakis(2,4,6-triamino-1,3,5-triazin-1-ium) bis(selenate) trihydrate, (C3H7N6+)4·(SeO42−)2·3H2O, is reported. The compound crystallizes in the non centrosymmetric space group of triclinic system. Second harmonic generation efficiency deff=0.4deff(KDP). Intense hydrogen-bonded network is present in the crystal structure of the complex with notable vibrational effects.

New hydrogen-bonded molecular crystals with nonlinear second-order optical properties

Abstract Fifteen new hydrogen-bonded crystals exhibiting nonlinear optical properties were obtained. For the morpholinium dihydrogenphosphate crystal, the structure was determined by the X-ray diffraction methods. This crystal belongs to the P 2 1 space group of the monoclinic system. The lattice parameters are as follows: a =8.345(2), b =6.156(1), c=9.109(2) A ; β =116.64(3)°. The crystal is built up of the layers parallel to the (001) crystallographic planes. The layer consists of the dihydrogenphosphate chains running parallel to the [010] direction. The morpholinium cation participates in two hydrogen bonds with the O(4) oxygen atoms of dihydrogenphosphate anions belonging to two neighbour chains shifted by the a distance. In such a way, the chains of dihydrogenphosphates are joined by the morpholinium cations into the layer parallel to the (001) crystallographic plane. Additionally, the powder IR and Raman spectra are presented for this crystal.

Crystal structure, phase transitions and vibrational spectra of bis(betaine) nitrate

Abstract The crystal structure of bis(betaine) nitrate (BBN) has been determined by X-ray diffraction as monoclinic, space group P2 1 / c , with a = 5.668(1), b = 11.259(2) and c = 23.073(5) A, β = 93.65(3)°, Z = 4. The crystal comprises nitrate ions, NO 3 − , and betaine dimers: two betaine moieties are joined by a very strong asymmetric hydrogen bond with an O···O distance of 2.449(2) A. Fist order type phase transitions at 394 K, 439 K and 460 K (melting and decomposition) and very likely second order type at about 448 K were discovered for the BBN sample by the Differential Scanning Calorimetry method. In the deuterated analogue they appear at 394 K, 434 K, 448 K and 459 K. The FTIR and FT-Raman spectra for the powder samples were measured at room temperature. Additionally the FTIR spectra were taken at low temperatures (till 10 K). A strong band at about 900 cm −1 arises from the ν a OHO vibration of the very strong hydrogen bond. The site symmetry of the NO 3 − anions is C 1 according to X-ray data and the vibrational spectra.

Novel nonlinear optical crystals of noncentrosymmetric structure based on hydrogen bonds interactions between organic and inorganic molecules

Abstract For second harmonic generation (SHG), well-established inorganic crystals are now in direct competition with more efficient organic molecular crystals, made of highly polarizable conjugated molecules suitably packed to build up a noncentrosymmetrical structure. In recent years, a new strategy has been developed in material engineering, with intent to associate the strong quadratic nonlinear coefficients of some remarkable organic crystals to the mechanical and thermal stabilities of mineral structures, owing to the complexion of organic and inorganic molecules based on acid–base interactions. We present several hydrogen-bonded molecular crystals composed of various nonlinear organic molecules (cations) linked to the anions corresponding to phosphoric, selenic, orthoarsenic, and phenyloarsenic acids, respectively. SHG activity was measured using the Kurtz and Perry powder technique, crystal structure was determined from X-ray measurements, TF-IR and TF-Raman spectra were used to characterize the formation of hydrogen bonds.

Dielectric dispersion and vibrational studies of a new ferroelectric, glycinium phosphite crystal

The dielectric dispersion in glycine phosphite crystal over the frequency range 30 - 1000 MHz is presented. Ferroelectric dispersion of the Debye type along the b-axis occurs in the microwave-frequency region and is caused by a single relaxational soft mode. The powder IR (at low temperatures between 300 and 14 K) and FT Raman spectra in the region between 4000 and are measured. DSC measurements for the GPI and deuterated crystals are performed. The results confirm the order - disorder nature of a proper ferroelectric phase transition of second order.

Polarized infrared and Raman spectra of diglycine nitrate single crystal

Abstract Polarized infrared (4000-ca. 350 cm−1) and Raman (4000-10 cm−1) spectra of diglycine nitrate (DGN) single crystal were measured at room temperature; polarized infrared spectra were also measured at several low temperatures (230, 180, 15 K). In the paraelectric phase, the glycine ion pairs were found to be joined by a symmetrical (Ci) O···H···O hydrogen bond and the nitrate ions exhibited high symmetry (most likely D36) as a result of effectively free rotation. The ferroelectric phase transition occurs because of inhibition of the rotation of the nitrate ions, with consequent lowering of their symmetry to C1, as a result of increased N-H···O hydrogen bonding interaction with the +NH3 groups of the neighbouring glycine ions. The symmetry of the glycine ion pair also falls to C1 in the ferroelectric phase, but the proton motion in the O···H···O bond does not play a significant role in the phase transition.

Structure and IR spectra of the solid complex of bis (betaine)—telluric acid

Abstract Crystals of bis (betaine)-telluric acid of the formula [(CH 3 ) 3 NCH 2 CO 2 ] 2 · Te(OH) 6 are triclinic, space group P - 1, with a = 7.164(5), b = 8.325(5), c = 10.035(6) A, α = 108.58(5), β = 123.82(4), γ = 96.02(5)° and Z =1. The crystal structure, solved by the heavy atom method, has been refined to R = 0.0215 for 3887 non-zero reflections. The betaine molecules are linked to telluric acid molecules by three kinds of O⋯O hydrogen bonds of length 2.561(4) A, 2.760(3) A and 2.800 (3) A, respectively. Both species are joined into infinite chains along the a direction. Powder FT-IR spectra of the title crystal and its deuterated analogue at differential temperatures have been taken. The broad band at 3116 cm −1 is assigned to the stretching vibrations of the long hydrogen bonds. The two bands at 2671 and 2443 cm −1 are attributed to the stretching vibration of the short hydrogen bond. The internal vibrations of both the tellurate ions and betaine molecules are discussed. An assignment of the bands arising from these vibrations is proposed.

DFT studies of the structure and vibrational spectra of 8-hydroxyquinoline N-oxide

The geometry, frequency and intensity of the vibrational bands of 8-hydroxyquinoline N-oxide (8-HQNO) and its deuterated derivative (8-DQNO) were obtained by the density functional theory (DFT) with the BLYP and B3LYP functionals and 6-31G(d,p) basis set. The optimized bond lengths and bond angles are in good agreement with the X-ray data. The IR and INS spectra of 8-HQNO and 8-DQNO computed at the DFT level reproduce the vibrational wavenumbers and intensities with an accuracy, which allows reliable vibrational assignments.

Structure and vibrational spectra of the tetra(betaine) selenate crystal

Abstract The crystal structure of tetra(betaine) selenate has been determined by X-ray diffraction as orthorhombic, space group Fddd, with a = 13.243(8), b = 19.077(9) and c = 21.96(2) A , Z = 8. The crystal comprises selenate ions, SeO2−4, and the betaine dimers: two betaine moieties are joined by a very strong symmetric (C2) hydrogen bond with the O…O distance of 2.424(6) A. Powder FTIR and FT-Raman spectra were measured and assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the betaine molecules and selenate ions is proposed.