The dehydration process in the DL-phenylglycinium trifluoromethanesulfonate monohydrate crystal revealed by XRD, vibrational and DSC studies.

Thermal analysis, X-ray diffraction and temperature-dependent IR spectroscopy were used to study the dehydration process of crystalline DL-phenylglycinium trifluoromethanesulfonate monohydrate (PGTFH), C8H10NO2+·CF3SO3-·H2O. PGTFH dehydrates in one step centred at 353 K and crystallizes in the monoclinic space group C2/c, whereas the anhydrous compound (PGTF) crystallizes in the triclinic space group P-1. The dehydration process in PGTFH is preceded by a weakening of both the noncovalent aromatic-aromatic interactions and the packing contacts. This process is accompanied by the breakage of medium-strength O-H...O hydrogen bonds between ions inside layers and a reorganization of the ions within the layers. This reorganization results in the formation of two different ion pairs (DL-phenylglycinium trifluoromethanesulfonate) and the formation of a new hydrogen-bond network. The dehydration process does not destroy the nature of the crystal structure. Both crystals, i.e. hydrated and anhydrous, have a layered structure, although the layers of each crystal are arranged somewhat differently.

Sliding Polymeric Layers and Anion Displacement Coupled with Spin Crossover in Two-Dimensional Networks of [Fe(hbtz)2 (CH3 CN)2 ](BF4 )2.

The abrupt high spin (HS)→low spin (LS) transition (T↓ 1/2 =136 K) in [Fe(hbtz)2 (CH3 CN)2 ](BF4 )2 (hbtz=1,6-di(tetrazol-2-yl)hexane) is finished at 100 K and further thermal treatment influences the spin crossover. Subsequent heating involves a change of the spin state in the same way (T↑ 1/2 =136 K) on cooling. In contrast, cooling below 100 K triggers different behavior and T↑ 1/2 is shifted to 170 K. The extraordinary structural changes that occurred below 100 K are responsible for the observed diversity of properties. A unique feature of the low-temperature phase is the rebuilding of the anion network expressed by a shift of anions inside the polymeric layer at a distance of 1.2 Šas well as the relative shift of neighboring layers at over 4 Å. These structural alterations, connected with a phase transition, become the origin of the strain, which in most cases causes crystal cleaving. In a sample composed from crystals crushed as a result of the phase transition or as a result of mechanical crumbling, the hysteresis loop vanishes; however, annealing the sample allows to its partial restoration. A replacement of acetonitrile by other nitriles leads to preservation of the polymeric structure and spin crossover, but no phase transition follows.

Different ß-alanine dimeric forms in trifluoromethanesulfonic acid salts. XRD and vibrational studies.

Two new crystalline salts: ß-alaninium trifluoromethanesulfonate (ß-AlaOTf) and bis(ß-alanine) trifluoromethanesulfonate (ß-2AlaOTf) were obtained. The former one contains diprotonated ß-alanine dimer, the latter one monoprotonated ß-alanine dimer. Both compounds were studied by single crystal XRD, vibrational (IR and Raman) spectroscopy and calorimetric method. The quantum-mechanical calculations (DFT/B3LYP/6-311++G(2d,2p)) for the diprotonated dimer were carried out. The ß-AlaOTf salt crystallizes in the P1¯ space group of triclinic system (Z=2), the ß-2AlaOTf in the P21/m space group of monoclinic system (Z=2). The vibrational data for the studied compounds are discussed in relation to their crystal structure, and provide insight into the character of hydrogen bonds and ß-alanine protonation. The studied crystals do not exhibit phase transitions in the solid state.

Vibrational, XRD and (13)C NMR studies of DL-phenylglycinium methanesulfonate crystal.

A new crystal formed by DL-phenylglycine and methanesulfonic acid (PGLYMS) was obtained and studied by X-ray diffraction, IR and Raman spectroscopy, solid state NMR and DSC methods. Additionally, theoretical computations for the phenylglycine cation were carried out (DFT/B3LYP/aug-cc-pVDZ). Our results show that PGLYMS does not exhibit any phase transitions and crystallizes in the P21/c space group of monoclinic system (Z=4). Detailed analysis of its structure and its IR, Raman and NMR spectra is presented.

Phase transitions in non-centrosymmetric pyridinium trifluoromethanesulfonate crystal: Vibrational studies.

Infrared spectroscopy (4000-400 cm(-1)) in the wide temperature range, from 11 to 473 K, has been used to investigate the non-centrosymmetric pyridinium trifluoromethanesulfonate crystal, exhibiting several phase transitions. The assignments of the bands observed in the studied spectra have been proposed. The temperature dependence of the wavenumbers and the full width at half maximum (FWHM) of the bands arising from some internal vibrations of the pyridinium cation and the triflate anion have been analyzed in order to achieve a knowledge of whether these both ions are involved in the phase transitions and what is the role of these both ions in these phase transitions. The infrared measurements showed that the both ions, pyridinium cation and triflate anion are involved in the high temperature phase transitions of the order-disorder type, previously reported at 305.1 and 396.7 K. They also revealed that these transitions are governed by a rotational mobility (changes in dynamical states) of both the pyridinium and triflate ions. Our results show that the multiple structures of the νNH and νND bands observed in the studied infrared spectra is due to the Fermi resonance interaction between the stretching vibration of the N-H⋯O hydrogen bond and the overtones and combinations of the internal vibrations of the pyridinium cation.

Experimental evidence on interaction between xenon and bovine serum albumin.

Xenon gas interacts with bovine serum albumin (BSA) dissolved in a physiological buffer solution. The fluorescence quenching related to the Trp emission is reversible and depends linearly on the time of saturation by Xe. The most probable site of this interaction is Trp212. The common emission of all BSA fluorophores is also influenced by Xe but this quenching is more complex and suggests: (i) at least two sites occupied by Xe and related to the Tyr and Trp residues; (ii) structural variations of BSA induced by the Xe guest atoms.

Participation of xenon guest in hydrogen bond network of ß-hydroquinone crystal.

In the ß-hydroquinone (ß-HQ)-Xe crystal, the Xe guest is placed between two hexagonal rings of coupled [···O-H···O-](6) H-bonds. This clathrate is treated as the model for monitoring the H-bonding system with the Xe participation. Three kinds of isotope effects due to the H/D substitution in the [···O-H···O-](6) bonds are considered: (i) structural changes in the clathrate (X-ray diffraction), (ii) variations of (129)Xe NMR signal of the guest (CP MAS), and (iii) variations of selected vibrations of the host (IR). This study predicts subtle inclination of every other hydroxyl group of the [···O-H···O-](6) rings into the Xe atom and formation of six Xe···H-O pairs in every cage, the frequency shift of the γOH mode due to these contacts, -ΔγOH(Xe···H) > 74 cm(-1), as well as the enthalpy formation, -ΔH(Xe···H) > 6-8 kJ mol(-1). Our IR results reveal a tendency of the Xe atom to form the H-bond-like network inside its cage and much weaker Xe···D-O interactions in the H/D substituted crystal. The (129)Xe NMR results do not reflect this kind of interactions due to averaging of the (129)Xe shielding phenomena, probably. We also predict elongation of the O···O distances due to the ß-HQ-Xe crystal heating and the Xe escape.

Polarised vibrational spectra of betaine ortho-phosphoric acid complex. Part II. Phase transitions studies.

Polarised infrared transmission and Raman spectra of betaine ortho-phosphoric acid crystal in temperature ranges 13-393 and 13-300 K, respectively are reported and discussed in relation to phase transitions: antiferrodistortive at T(c1) = 365 K and antiferroelectric at T(c3) = 81 K. The spectra are consistent with unit cell doubling below T(c3). The participation of all hydrogen bonds apparent in the crystal in the antiferroelectric phase transition was shown. Quite large freedom of -N(CH(3))(3) groups reorientation in the antiferroelectric phase was detected. No changes were found in the transmission spectra taken in the vicinity of the antiferrodistortive phase transition temperature.