Galina Matveeva

The Use of Structure Analysis Methods in Combination with Semi-empirical Quantum-Chemical Calculations for the Estimation of Quadratic Nonlinear Optical Coefficients of Organic Crystals

An effective search for new organic crystals for prospective use in nonlinear optical (NLO) applications requires quantitative and fast experimental determination of their NLO properties at a molecular level. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time-consuming and sometimes impossible task. Single crystals of a considerably smaller size may be effectively used for complete structural analysis by electron diffraction combined with simulation methods. When the crystal structure of a given compound is known, its NLO properties may be estimated using quantum-chemical methods for calculation of the molecular nonlinearity tensor and the relationships between its components and the macroscopic coefficients of the crystalline nonlinearity tensor. In the present work, the semiempirical PM-3 method was employed for this aim.

Electron crystallography on polymorphic organics

Abstract Organic materials, such as non-linear optical active compounds (1-(2-furyl)-3-(4-aminophenyl)-2-propene-1-one (FBAPPO) and 1-(2-furyl)-3-(4-benzamidophenyl)-2-propene-1-one (FAPPO)), polymeric materials like the metal coordinated polyelectrolyte (Fe(II) [ditopic bis-terpyridin] (MEPE)) or polymorphic materials (e.g. Cu-phthalocyanine), which do not crystallize big enough for single crystal x-ray structure analysis have been investigated by electron diffraction (ED) at 100 and 300 kV acceleration voltage. Sample preparation (direct crystallization, ultra sonication, ultra microtomy), diffraction strategies (selected area diffraction, nano diffraction, use of double-tilt rotation holder), data collection and data processing as well as structure solution strategies have been chosen dependent on the different requirements of the compounds under investigation. Structure analysis was carried out by simulation using ab initio quantum-mechanical methods like density functional theory (DFT), semi-empirical approach (MNDO/AM1/PM3) and force field packing energy calculations (DREIDING). The structure models resulting from simulation were refined kinematically as rigid bodies. Subsequently, refinements by multi-slice least squares (MSLS) procedures taking dynamical scattering into account were performed. The described combination of different methods which was used successfully on crystallizable materials is also adaptable to insoluble organic materials (e.g. pigments) and polymorphic systems.

H-bonding schemes of di- and tri-p-benzamides assessed by a combination of electron diffraction, X-ray powder diffraction and solid-state NMR

The crystal structures of di- and tri-p-benzamides are solved by a combination of single crystal, electron and powder X-ray diffraction. Different hydrogen-bonding schemes observed in the two structures are described and classified. The hydrogen-bonding networks are correlated to complementary data obtained from multinuclear solid-state NMR.

Structural anisotropy and annealing-induced nanoscale atomic rearrangements in metamict titanite

Abstract The structural state of metamict titanite was studied by Raman spectroscopy, complementary high-resolution transmission electron microscopy, and single-crystal X-ray diffraction. The results show that Raman scattering collected from metamict titanite is highly anisotropic, which is typical of single crystals. But surprisingly, the observed Raman-scattering dependence on the sample orientation is much more pronounced for heavily metamict than for weakly metamict titanite samples. These radiation-induced anisotropic effects are related to the specific atomic arrangements in metamict titanite. The Raman spectra collected in backscattering geometry from a plane nearly perpendicular to the chains of corner-sharing TiO6 octahedra arise predominantly from phonon modes in crystalline nanoregions with radiation-induced defects, whereas the contribution of atomic vibrations in radiation-induced amorphous nanoregions is better pronounced in the Raman spectra collected from a plane containing TiO6 chains. This difference provides a unique opportunity to study separately, the structural transformations of the crystalline and amorphous fractions in metamict titanite. The results show that the radiation-induced periodic faults in the crystalline matrix are related to the disturbance of SiO4-TiO6-SiO4-TiO6 rings comprising TiO6 octahedra from different chains, whereas the radiationinduced amorphization is related to the partial change of Ti coordination from octahedral to pyramidal and/or tetrahedral, which in turn violates the Ti-O-Ti intrachain linkages. This indicates that the plane containing Si-O-Ti-O bond rings is less susceptible to a self-accumulation of radiation-induced defects resulting in the development of amorphous regions as compared to the perpendicular plane containing Ti-O bond chains. Sample-orientation-dependent Raman spectroscopy was further applied to annealed metamict titanite to give further insight into the temperature-driven recovery processes in the crystalline and amorphous nanoregions. Multistep annealing by 50 K for 2 h per step gradually suppresses the structural defects in the crystalline fraction as the improvement of the SiO4-TiO6 connectivity within planes nearly perpendicular to the TiO6 chains reaches saturation near 900 K. The annealing-induced recrystallization of the radiation-induced amorphous nanoregions takes place in the temperature range between approximately 650 and 950 K, with a maximum near 750 K. Raman scattering shows that multistep annealing up to 1173 K is insufficient to recover the crystalline structure of the studied metamict titanite sample, which has an accumulated radiation dose of 1.2 × 1018 α-event/g.

Automated electron diffraction tomography (ADT) and X-ray powder diffraction for structure characterization of layered materials

Layered materials attract increasing attention not only from the point of fundamental crystallography due to their structural diversity, but also due to their numerous industrial applications, for instance as gas storage systems or battery elements. Structural characterization is an essential key for understanding and controlling the desired properties. Layered materials have intrinsic features which turn their structure analysis into a challenging task. Large crystals suitable for singly-crystal X-ray analysis with exactly the same internal structure as fine powders can rarely be grown. Due to the internal construction of layered systems, the crystals predominantly have platelet on needle-like morphology causing problems with preferred orientation during the powder X-ray data collection. The systems are typically polyphasic, thus troubling the powder diffraction data analysis, and finally, they often show disorder in the stacking sequence. All above mentioned points make structural analysis of layered materials a complex mission demanding for a combination of advanced methods. One of the most beneficial approaches to the structure analysis of layered materials is the combination of electron diffraction tomography (Automated Diffraction Tomography – ADT [1-3]) and X-ray powder diffraction method [4-5]. The interaction of these complementary methods allowed gaining structural knowledge on a number of layered systems: sodium-titanates [6], carbonsilicates [7], CSH phases and hydrotalcites. Here, the successes and pitfalls of the methods will be demonstrated.

Advances in automated diffraction tomography

Crystal structure solution by means of electron diffraction or investigation of special structural features needs high quality data acquisition followed by data processing which delivers cell parameters, space group and in the end a 3D data set. The final step is the structure analysis itself including structure solution and subsequent refinement.

Structural investigation of four‐centre photopolymerisation of bis‐phthalamic bis‐chalcone derivative in the crystalline state

By combining the results obtained from an electron diffraction tilting series with solid state NMR and powder X-ray diffraction, it was possible to determine the unit cell parameters and space group of BPABC crystals grown from DMAA solution both before and after irradiation. Subsequently semi-empirical quantum mechanical and packing energy calculations led to a model structure which agreed well with all the electron diffraction data and thus provided insight into the cross-linking mechanism.