Veneta Videnova-Adrabinska

Infrared polarized spectra of KH(Cl3CCOO)2 single crystal with a very strong hydrogen bond

Abstract The polarized infrared spectra of KH(Cl 3 CCOO) 2 single crystal have been measured in the region 4000—350 cm −1 . On the basis of these experimental data a vibrational assignment is proposed and the vibrational properties of the very strong hydrogen bond are discussed. The ν a OHO stretching absorption is polarized parallelly to the Z axis and is observed in a much broader range than in the powder spectra. The strong interactions of the ν a OHO vibration with other vibrations are responsible for the structure of this absorption. However, the γOHO vibration is pure and fulfils the selection rules for the C 2 site symmetry of the protons in the hydrogen bonds.

Infrared polarized spectra of potassium hydrogen bis(dibromoacetate) single crystal with a very strong hydrogen bond

Abstract Polarized i.r. and Raman powder spectra of potassium hydrogen bis(dibromoacetate) have been measured in order to study the vibrational properties of the very strong centrosymmetric hydrogen bonding. The operation of the selection rules for the ν a OHO and νCO vibrations has been shown. The significance of correlation field coupling for the nature and the shape of the broad absorption, observed in the region 1400-300 cm −1 (of the powder i.r. spectrum), is emphasized. The most intriguing feature of the polarized spectra is the large (200 cm −1 ) Davydov splitting of the B 1 u and B 2 u components of ν a OHO.

Topochemical bias in the hydrogen-bonded networks of guanidinium carboxybenzenesulfonates

Herein we describe the changes in the packing patterns and discuss the structural modifications in guanidinium carboxybenzenesulfonates G·CBS [C(NH2)3]+[XC6H4SO3]− (where X is the carboxylic group) compared with those in guanidinium benzenesulfonate G·BS. Generally, the one-dimensional arrangements in all three crystals comprise the same ribbon formations. However, the further organization of the ribbons is significantly different in G·CBS. We analyse the donor and acceptor efficacy of the additional functional group to disrupt some of the basic hydrogen bonds between the guanidinium and the sulfonium portions in G·BS. Since the carboxylic group introduces a mismatching of the sites on the counter ions, the changes in the symmetry relations essentially depend upon the topology of the substituent X, which results in modified packing patterns. All engineering peculiarities are analysed with respect to the symmetry constraints and geometrical demands of the packing forces.

Polarized IR and Raman study of the Na3H(SO4)2 single crystal

Abstract The polarized absorption IR and the polarized Raman spectra of the Na 3 H(SO 4 ) 2 single crystal are presented. The polarization features of the internal vibrations of the SO 2− 4 ions and of the proton vibrations are discussed on the basis of the X-ray and neutron diffraction structural data by assuming that they contain some strong coupling effects. In addition, the model calculations of the directions cosines allow an unambiguous assignment of the observed bands in view of the symmetry species and the motion type to be made by taking into account the IR dichroism and the Raman polarization features.

Polarized infrared and raman spectra of monoclinic CsH2PO4 single crystal and its deuterated homologue CsD2PO4: Part 1. Hydrogen bond study

Abstract The object of clearly distinguishing the streching modes originating from the short (v2) and the long (v1) hydrogen bond in CsH2PO4 has been achieved by recording polarized IR spectra on the (010) plane using different orientations of the electric vector component. Band parameters of the v1 stretching mode are taken as a function of the temperature. Calculations of the orientation of the transition dipole moments for the six proton vibrations (v1, δ1, γ1 and v2, δ2, γ2) are performed and correlated with the experimental results.

Molecular organization and solution properties of N-substituted aminomethane-1,1-diphosphonic acids

The crystal structures of N-n-pentylaminomethane-1,1-diphosphonic (1), N-pyrrolidinomethane-1,1-diphosphonic (2), N-(3-carboxy-2-pyridyl)aminomethane-1,1-diphosphonic (3a) and N-(5-methyl-2-pyridyl)aminomethane-1,1-diphosphonic (3c) acids are determined and discussed with respect to their packing patterns and solid state organization. The molecular association and the possible aggregate forms in solution, resulting from the supramolecular features of these materials, are considered. The solution UV and NMR studies are focused on the N-2-pyridylaminomethane-1,1-diphosphonic acids 3a–e in order to establish the influence of the structural changes in passing from 3- to 5- or 6-pyridyl substituted aminomethane-1,1-diphosphonic acids on their general complexation properties.

Two-dimensional hydrogen-bonded networks in guanidinium hydrogen dicarboxylates

The crystal structures of three guanidinium hydrogen dicarboxylate systems are solved by X-ray diffraction methods and discussed with respect to similarities and dissimilarities of their hydrogen-bonded networks. The basic crystal chemical units in all of them are extended into ribbons, which are further organized in monolayers. However, the symmetry relations inside the layers vary from crystal to crystal and essentially depend upon the aliphatic spacer between the two carboxylic groups. Both the one- and the two-dimensional hydrogen-bonded networks in crystal 1 are polar and both are non-polar in crystal 2, whereas in crystal 3 the ribbons are polar but the monolayers are non-polar.

Polarized infrared and raman spectra of monoclinic CsH2PO4 single crystal and its deuterated homologue CsD2PO4: Part II. Internal vibrations of the PO4 ion

Abstract A correlation between the experimentally observed and the theoretically predicted bands of the internal orthophosphate ion vibrations was made. By measuring the infrared spectra in different orientations in the planes of the crystal axes, the problem of coupling effects was elucidated using the polarization properties and the isotopic effect for both internal PO 4 modes and the hydrogen bond modes. Intra-ion coupling for the PO 4 stretching modes, as well as interion couplings between the neighbouring PO 4 groups inside the primitive cell, are inferred from the infrared spectra. The observed anomalies of the paraectric phase with respect to the selection rules are explained by the disorder character of the short hydrogen bond. The band parameters for the PO 4 Raman stretching modes vs. temperature were measured and the problem of the abrupt changes observed in some of these characteristics in the vicinity of the ferroelectric temperature, T c , is discussed.

Vibrational study of (NH4)2HPO4 and (ND4)2DPO4 single crystals. The PO4 ion vibration couplings

The PO4 internal vibrations have been studied by measuring the polarized infrared (IR) spectra at room temperature (RT) and at low temperature (LT=20K) as well as the polarized Raman (R) spectra. The i.r. dichroism in the (010) plane is investigated in a great range of angles α (0°<α<135°) of the electric vector E with respect to the crystallographic axic c. Some intra ion couplings are inferred. No factor group splitting is observed in the RT IR spectra. However, simultaneously regarding the LT IR spectra and the R spectra promotes an interchain coupling inside the primitive cell. Strong resonance coupling effects are found for the PO4 stretching modes with the in-plane mode δOH(δOD).

The hydrogen bond in the monoclinic (NH42HPO4 single crystal

Abstract The problem of the origin of the ABC structure of the νOH stretching mode is elucidated by studying the infrared dichroism of this mode and correlating the νOH absorption region with the overtones and combinations of the PO 4 ion stretching modes, as well as with the overtones of the hydrogen bond deformations. The genesis of this structure appears to be very specific for (NH 4 ) 2 HPO 4 since the overtones of the deformations (2×δOH and 2×γOH) interacting in Fermi resonance with the νOH continuum do not create the minima between A, B and C (as is the case in KDP-type crystals), but do create maxima. However, the overtones and the combinations of the PO 4 ion internal vibrations overlap the νOH mode and/or interact with it generating the structure of B and C bands. Some intrachain couplings are inferred for the νOH and δOH modes on the base of the A-B splitting observed in the polarized spectra.