Crystallography in Russia
Kirensky Institute of Physics
Searching for new crystals demands systematic analysis of known structures to provide a foundation for a reliable prognosis. Such analysis has been performed for oxide- and halogen-based perovskites, antiperovskites, elpasolites, anion- and cation-deficient and layered perovskite-like structures, including high temperature superconductors. Group-theory and crystallographic analyses of phase transitions in these structural families have been made as well.
Structures of synthesized crystals are investigated using powder and single crystal X-ray analysis. Neutron scattering data are used in collaboration with the Joint Institute of Nuclear Research (Dubna, Russia), the Hahn-Meitner Institute in Germany and the Laboratoire Leon Brillouin at the Saclay Neutron Center in France.
A theory of structural phase transitions is being developed in parallel with experimental investigations. Phase transition sequences with interacting order parameters are developed based on group theory and thermodynamics and applied to families of crystals. Attention is focused on model descriptions of these phase transition sequences. Ab initio approaches are being developed that describe the stability, lattice dynamics and physical properties for complex crystal structures like layered perovskites and elpasolites.
In 1976 the Krasnoyarsk School of Crystal Physics began a series of Soviet (now - Russian) - Japanese symposia on the physics of ferroelectrics that continues to the present day.
Contact: K.S. Aleksandrov email@example.com
Material studies in Petrozavodsk
At the X-ray laboratory of the Petrozavodsk State University, amorphous oxide films, amorphous and crystalline powders and bulk materials are studied. X-ray diffraction patterns from symmetric and asymmetric reflection and transmission geometry are obtained on a DRON-4 diffractometer using monochromatized radiation of various wavelengths.
The short-range order characteristics of amorphous, amorphous-crystalline and small dispersion materials are defined using the Finbak-Warren approach: the D(r) curves are presented as a sum of pair functions. We have identified the short-range order characteristics of amorphous oxide films of aluminum, silicon, tantalum, niobium, tungsten, yttrium, and vanadium, produced under different conditions of anode oxidation; WO3 films, thermally evaporated in vacuum; silicon films, produced by monosilane pyrolysis at various temperatures; thermal silicon dioxide films; and manganese dioxide produced by pyrolysis of manganese dihydrate. Computer simulations of the structures of amorphous materials are calculated using the methods of continuous static relaxation, molecular dynamics, and non-ordering networks.
Octahedrally and tetrahedrally coordinated cations with distorted fcc packing of oxygen atoms in the system 'aluminum-vacant cationic positions' were considered in terms of short-range order coefficients. The cationic subsystem of amorphous aluminum oxides is characterized by a short-range order qualitatively analogous to the arrangement of aluminum atoms in the boehmite and pseudoboehmite modifications of the γ-Al2O3 phase. The correlation length in the system 'aluminum-vacant cationic positions' is not less than 5 Å. It was shown that the short-range order in amorphous oxide films of Ta2O5 and Nb2O5 can be regarded as similar to the atom positions in the crystal modifications β-Ta2O5 and γ-Nb2O5. The X-ray study and molecular dynamic computer simulation of amorphous anodic tungsten oxide showed that the arrangement of W and O atoms in the coordination spheres corresponds to the characteristics of the crystalline WO3·(1/3)2 modification. WO3 films, thermally vaporized-on in vacuum, have a quasi-amorphous structure characterized by the presence of crystallites shaped like orthorhombic phase parallelepipeds with dimensions 15 x 8 x 20 Å.
The short-range order in amorphous oxide films and powder of Y2O3 depends on anode oxidation conditions. Moreover, the first coordination number changes from 5 in colored oxides to 7 in black and powdered oxides. The short-range order is described in terms of models of disordered networks of octahedra, pyramids, and structural units, consisting of seven oxygen atoms. In amorphous fulleride C60 short-range order corresponds to the lonsdeillite crystalline phase. The main publications describing this work are in Crystallography Reports and Acta Crystallographica.
Crystallography in Novosibirsk
Almost 1.5 million people live in Novosibirsk, more than 30 000 are involved in the work of the Novosibirsk Scientific Center. Novosibirsk State University is surrounded by about 40 research institutes of the Russian Academy of Science. Integration of the Novosibirsk State University with the Russian Academy of Sciences was always exceptionally high for Russia. Crystallography is widely applied in many institutes, ranging from traditional applications in chemistry, physics, biology, and ending with archeology. Novosibirsk is a huge high technology industrial center with vast potential for studies with broad applications.
Solid state chemistry and mechanochemistry
The group of Elena Boldyreva divides its activities between the Institute of Solid State Chemistry and Mechanochemistry (Siberian RAS, Novosibirsk) and the Novosibirsk State University.
ResearchBoldyreva is a physical chemist who specializes in studies involving solid-state kinetics, inorganic solids, coordination compounds, and organic molecular solids with a special emphasis on pharmaceutical and biomimetic systems. Fields of research include solid-state reactivity, crystal engineering, polymorphism, crystallographic computing, database analysis, high-pressure and low-temperature crystallography using single-crystal and powder X-ray structure analysis, systems studied include Co(III)-ammine complexes and polymorphs of paracetamol, glycine, serine, hexafluorosilicates, benzoquinone, and sodium oxalate. The effect of high pressure on a solid has been systematically compared with that of cooling. Diffraction studies are complemented by IR- and Raman spectroscopy, thermal analysis and calorimetry, and optical microscopy. The group collaborates with other research teams studying mechanochemical synthesis and mechanochemical modification of pharmaceuticals. They also work with colleagues from the Institute of Mineralogy, the Institute of Catalysis, the Institute of Semiconductor Physics, the Institute of Genetics, and the Institute of Archeology in Novosibirsk. With the latter, they have characterized samples of ancient Siberian ceramics. The group is actively involved in research in a multidisciplinary Research and Education Center REC-008 'Molecular Design and Ecologically Safe Technologies', and in the Center of Joint Exploitation of Equipment 'Integration'.
The group is active in teaching solid state chemistry, crystallography, structural analysis and supramolecular chemistry at Novosibirsk State University. All chemistry students at the university attend the courses. Former students work at various research institutes of the Russian Academy of Sciences, in industry and abroad. In recent years the group has included PhD students and post-docs from Barnaul, Tomsk, Kemerovo, and Petrozavodsk. The teaching activities of the group were described in articles in the Journal of Chemical Education [J. Chem. Educ, 1993, 70(7), 551-556 and 2000, 77(2), 222-226]. E. Boldyreva, a lecturer at international schools, has translated E. Wood's 'Crystals' and 'Supramolecular chemistry' by J.-M. Lehn into Russian. In 2000 the group initiated a series of Novosibirsk summer and winter schools on 'Hot Topics of Chemistry, Biology, and Physics', which are attended by schoolchildren and teachers from all over Siberia. The group is an active member of the SigmaXi International Research Society and participates in the 'Distinguished Lecturers' program.
Boldyreva has been a visiting research scientist in Germany, France, Italy, and Great Britain. Many of her former hosts and 'western colleagues' have visited Novosibirsk, to lecture, exchange ideas, and test equipment. The group has traditional collaborations in Europe, good contacts in the USA, and has recently signed an Agreement for Cooperation with Wits-University (Johannesburg, South Africa).
in vivo X-ray diffraction analysis of cystic calculusThe potential to use synchrotron radiation for medical diagnosis via in vitro X-ray diffraction is being explored at the Synchrotron Center of the Institute of Nuclear Physics in Novosibirsk.
We have attempted to model in vivo X-ray diffraction analysis of a cystic calculus. A surgically obtained calculus (5 x 3 x 3 mm) was placed into pig tissue with a high fat content. The investigation was carried out with quanta in the range 30-34 keV at an X-ray diffraction station installed at the 4th synchrotron radiation beamline of the VEPP-3 storage ring in the Synchrotron Center.
First, a diffraction pattern of the cystic calculus was obtained. Then, the calculus was placed into the model fatty tissue and a new diffraction pattern was recorded. An example of a diffraction pattern from a cystic calculus in fatty tissue is shown in Fig. 1. Fig. 2 illustrates a comparison between the calculus embedding in fatty tissue (top) and the pattern for a sample of monohydrate calcium oxalate (bottom).
Such an investigation does not require a detailed analysis of the diffraction pattern, because most of the calculi are of three main types (oxalates, phosphates and urates). The diffractograms of these types differ sharply and identification of a calculus can be made with the signal/noise ratio as low as ~10. This method of recording the diffractograms does not require precise positioning of the sample.
As shown in Fig. 2, the type of the calculus can be determined from such data. These experiments demonstrate the feasibility of collecting the diffraction pattern of a cystic calculus embedded in fatty tissue. Although current radiation doses required for in vivo analysis exceed permissible levels, the development of more sensitive detectors could make the technique feasible.
 Ancharov A.I. et al., 'New station at the 4th beamline of the VEPP-3 storage ring' Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 470 (2001), 1-2, P.80-83
Contact: B. P. Tolochko (firstname.lastname@example.org)
Superconducting wigglers and shifters
Contacts: B.P. Tolochko B.P.Tolochko@inp.nsk.su
High-quality powder patterns of bulk materials and films prepared in the institute (S. Gromilov) have been provided for the ICDD Grant-in-Aid Program (V. Lisoivan). Software that includes searches for cation sublattices and cavities, comparison and visualization of structures has been written (D. Naumov).
The laboratory produces about 100 crystal structures and 50 publications per year. Interesting recent results include:
- The structure-forming role of cations in some classes of inorganic compounds that results in regular close-packed cationic arrays;
- The structure-forming role of Hg-O, Hg-S, and Hg-Hg covalent bonds that results in the formation of rigid mixed mercury-anion clusters, ribbons, layers and 3D frameworks in inorganic mercury-containing compounds;
- Algorithms for generating 3D tetrahedral clathrate frameworks using the duality of polyhedral clathrate hydrates and intermetallic structures.
Contact: Sergey Gromilov, email@example.com
Helically polarized radiation sources development in Budker INP, NovosibirskIn recent years Budker INP has designed and manufactured several insertion devices for the generation of helically polarized radiation.
General view of one of two halves of elliptical electromagnetic undulator for advanced SR source SLS (Switzerland).
Contact: B. P. Tolochko (firstname.lastname@example.org)
Advanced X-ray detectors, INP
|Main parameters of the OD-3 detector|
|inlet beryllium window||200 mm x 10mm x 0.2mm|
|conventional operational gas mixture||Ar/10% CO2|
|excessive pressure in gas chamber||0.2 atm|
|photon energy range||5-15 keV|
|detection efficiency (for 8 keV photons)||30 %|
|maximum detection angle||± 15 degrees at the focal distance 350 mm, ± 3.5 degrees at the focal distance 1.5 meter|
|channel width||60 μm (0.01 degree at f = 350 mm)|
|maximum number of frames||1024 frames|
|frame time range||1 μs / 1024 seconds|
|space resolution (Eγ = 8 keV, STP), FWHM||150 μu;m (0.025 degree at f = 350 mm)|
|differential nonuniformity, R.M.S.||< 2.5 %|
|counting rate (at 50 % non-efficiency)||10 MHz/detector|
Contact: B.P. Tolochko, B.P.Tolochko@inp.nsk.su
The structure of quantum dots by XAFS
 Erenburg, S.B., Bausk, N.V., Stepina, N.P., Nikiforov, A.I., Nenashev, A.V., and Mazalov, L.N., Nucl. Instr. & Meth. Phys. Res. A. (2001) 470/1-2, 283-289.  Erenburg, S., Bausk, N., Mazalov, L., Nikiforov, A, and Yakimov, A., J. Synchrotron Rad. (2003), 10, 380-383.
Contact: B. P. Tolochko, B.P.Tolochko@inp.nsk.su
Nanoparticles nucleation under extreme conditions
 B.P. Tolochko, N.Z. Lyakhov et al. NIMA, v. 467-468, Part 2, 2001, p. 990.
Contact: B.P. Tolochko, B.P.Tolochko@inp.nsk.su
An X-ray detector for imaging explosions
 A.N. Aleshaev et al., Nucl. Instr.and Meth. A470 (2001), 240.
 B.P. Tolochko et al., Nucl. Instr.and Meth. A467-468 (2001), 990.
Contact: L. Shekhtman (email@example.com)
International Tomography Center
Contacts: Dr. Galina Romanenko firstname.lastname@example.org
Neutron diffraction in Russia
In the Kurchatov Institute, a IR-8 steady state reactor of 8 MW nominal power and average neutron flux of about 1 x 1014 n/cm2/s is used. The single crystal MOND and powder DISC diffractometers are the main instruments used for crystal studies. The PG double-monochromators are used at both diffractometers, which helps in varying wavelengths over a wide range (0.7 Å - 5.5 Å for MOND) with a 1 x 106 n/cm2/s flux at a sample position if λ=2.4 Å. With the MOND instrument dynamical effects were discovered in neutron magnetic scattering. ('Magnetic Pendellosung effect in neutron scattering by perfect magnetic crystals' Acta Cryst. A, 1992, v.48, 100). Resonance magneto-acoustic and acousto-magnetic effects were experimentally found in perfect crystals of weak ferromagnets. It was found that measured neutron magneto-acoustic resonances are essentially non-linear in nature, which can be seen in the conditions of their stimulation, shape of resonance peaks, and evolution of oscillations over time. It was also established that magneto-acoustic non-linearity is connected with anharmonicity of a magnetic sub-system (Physica B, 1998, v.241-243, 736).
The multi-counter diffractometer DISC is intended for structural studies of microsamples. The low background levels and large solid angle of the detector system allow measurement of diffraction patterns from samples about 1 mm3 in volume in reasonable time. It permits crystal structure studies at very high external pressure in sapphire or diamond anvil cells. The main advantages of these cells are their small dimensions and the possibility of putting them into a refrigerator and cooling them down to helium temperatures. At DISC atomic structures and phase transitions in hydrides, oxides, fullerenes and amorphous substances are studied (see, for instance, 'Pressure induced spin-orientation transition in FeBO3' High Pressure Research, 2000, v.17, 179).
The steady state reactor IVV-2M of 15 MW power (Fig. 1), which operates up to 6000 hours annually, supports the 'Neutron investigations of condensed matter' Centre, which belongs to the Institute of Metal Physics (Yekaterinburg). In this Centre there are several neutron diffractometers and special devices for investigations of physical properties of both conventional and radioactive samples. Among them: a multi-counter high-resolution powder diffractometer (λ=1.515 Å, Δd/d=0.002), two medium-resolution diffractometers, and a multi-counter four-circle single-crystal diffractometer. They are all equipped with special cells for radioactive samples studies in 4.2/1000 range after their irradiation in the reactor core. For high-pressure experiments, cylinder-piston cells up to 1.2 GPa are used. In the Centre, study of the influence of various defects (doping, non-stoichiometry, disorder caused by irradiation with fast neutrons, light or heavy ions, electrons) on crystal structure is the main topic. The main goal of these studies is to study the relation between real (defect) crystal structure and physical properties. In the Centre, studies of structural and magnetic phase transitions, charge ordering in oxides and inter-metallic rare earths or 3d-transition element compounds are also carried out (J. of Alloys and Compounds, 2001, v. 315, 82).
At the Joint Institute for Nuclear Research (JINR) in Dubna, neutron scattering experiments are performed at the IBR-2 pulsed reactor with record average power (2 MW) and pulsed neutron flux (1 x 1016 n/cm2/s). The IBR-2 set-up includes three diffractometers for structural studies of single crystals and powders and three diffractometers for texture and internal stress measurements.
The Fourier high-resolution diffractometer (HRFD) is analogous to the mini-SFINKS facility in Gatchina, but with higher d-spacing resolution (Δd/d=0.001 - 0.0005). A study of mercury-based high-Tc superconductors with various percentages of oxygen or fluorine in the basal plane is an example of an experiment using the HRFD (Figs. 2 and 3). In these studies several results of significance for understanding high-Tc superconductivity in copper oxides have been obtained. Recently, a series of diffraction experiments with doped CMR manganites has been performed. Precision structural analysis of several compounds, including compositions enriched with 18O isotope, provides unique data (Eur. Physical J. B, 2001, v.19, p.215, Fig. 4). HRFD can be used for single crystals if its very high resolution is needed. A typical example of such a problem is the mesoscopic phase separation in La2CuO4+δ, which appears to be due to low-temperature diffusion of extra oxygen. Despite extremely small difference in lattice parameters arising from a homogeneous state, the HRFD helped in measuring split diffraction peaks and in determination of sizes of the coherent regions with antiferromagnetic and superconducting phases (Fig. 5).
DN-12 is a time-of-flight complementary version of the DISC diffractometer for micro-samples. Its parameters allow one to study powders of about 1 mm3 volume inside sapphire or diamond anvils cells. The crystal and magnetic structures of manganites Pr0.7Ca0.3Mn1-yFeyO3 and Pr0.8Na0.2MnO3 with the CMR effect were investigated at pressures up to 4.5 GPa and in a temperature range of 16-300o. In these compounds which have significantly different magnetic structures at normal pressure, stabilization of the AFM state of A-type takes place at high pressures and low temperatures (High Pressure Research, 2003, v.23, p.149 and J. Magn. Mat., 2003, v.267, p.120). With this instrument it is possible to simultaneously measure elastic (diffraction) and inelastic neutron scattering. This mode was used for investigation of structure, phase transitions and atomic dynamics in ammonium halides at pressures up to 10 GPa (High Pressure Research, 2000, v.17, p.251).
The DN-2 diffractometer is used for single crystals. Very high neutron flux (~107 n/cm2/s) at the sample position and an extremely large d-spacing interval available at DN-2 are used in real time experiments with powders. Simultaneously with diffraction patterns, small angle scattering data can also be collected (Fig. 6).
The FSD diffractometer (Δd/d≈0.004) continues the development of neutron Fourier techniques at long-pulse neutron sources, which is carried out in collaboration with PNPI. FSD is optimized for internal stress measurements in bulk materials (Applied Physics A, 2002, v.74, S86). Auxiliary equipment (loading device, mirror furnace, Huber goniometer etc.) allows one to broadly vary experimental conditions. EPSILON (Δd/d≈0.003) is used for stress measurements with rocks. SCAT is a diffractometer with a ring detector intended for texture analysis on rock samples. It is equipped with a high pressure chamber (Pmax≈1.5 x 104 N, Tmax≈700oC) in which the diffraction study of textures of amphibolites and gneisses from the super deep borehole SG-3 in the Kola Peninsula and their analogues from the surface were performed (XXVIII General Assembly of the European Seismological Commission, Italy, Genova, 2002).
Broad perspectives for neutron diffraction studies in Russia will be opened when a new steady state high-flux reactor PIK (W=100 MW), which is under construction in PNPI (Gatchina) opens. Very high neutron flux from PIK, modern equipment, and wide experience in diffraction studies will all help in solving both fundamental and applied problems.
Contact: Anatoly M. Balagurov email@example.com
L.Ya. Karpov Institute of Physical ChemistryThe X-ray Laboratory in Karpov Institute established in 1938 by G. Zhdanov has become one of the largest centers of X-ray analysis in the former Soviet Union and Russia. The laboratory staff is engaged in projects with chemists from the Russian Federation, Georgia, Latvia, Moldova, the Ukraine, Sweden, Denmark, Spain, Portugal, and South Africa. Several thousand structures have been determined and deposited in the the Cambridge and Karlsruhe databases.
Special procedures have been developed to speed the process of data collection using programs PROFIT (profile fitting) and PAN32 (profile analysis) to treat data collected on Syntex, Nicolet and Enraf Nonius diffractometers. A method has been developed for evaluating the contribution of thermal diffuse scattering (TDS) to structure factors based on scanning peak profiles (program DISCONT). The Rietveld method is also widely used in powder crystal experiments.
High-precision X-ray diffractometry has allowed us to perform electron density studies and a new method for determination of the electron localization function from electron density has been developed. Recently, new computer software for charge density studies (WinXPRO2003) was released as part of a joint project with the Mendeleev University, Moscow.
St Petersburg State University, Department of CrystallographyThe Department of Crystallography at St Petersburg State University was established in 1924 by students of E.S. Fedorov. During the last ten years investigations have focused on structural chemistry, structural mineralogy, and crystal growth. Almost every year a national or international conference is organized by the Dept. The XV International Conference on X-ray Diffraction and Crystal Chemistry of Minerals in September, 2003 was organized by the Commissions of X-ray Analysis of Minerals and Crystal Chemistry of the Russian Mineralogical Society RAS. The Department has collaborations with institutes and universities in Germany, USA, Switzerland, Netherlands, and Austria, etc. Below we provide a brief description of the main scientific groups.
The Borate and borosilicate group (Rimma S. Bubnova, firstname.lastname@example.org and Stanislav K. Filatov, filatov@crystal. pu.ru) investigates borate and borosilicate crystals and glasses in collaboration with Peter Paufler (Paufler@physik.tu-dresden.de) at Dresden Technical University, Germany. The first crystal structure determinations of borates at elevated temperatures demonstrated the rigidity of boron-oxygen groups that maintain their configuration and size on heating. Highly anisotropic thermal expansion of 40 borates has been described for the first time and has been interpreted as a result of hinge deformations. (S.K. Filatov, R.S. Bubnova, Phys. Chem. Glasses, 2000, 41, N 5, 216-224).
The Crystal chemistry of paraffins group (Elena N. Kotelnikova, email@example.com, and S.K. Filatov) has studied normal alkanes CnH2n+2 as representatives of the rotatory state of crystalline matter. Experimental data on structural deformations, phase transitions, solid solutions, and phase equilibria of synthetic (n=17-24) and natural (n=17-37) n-paraffins have been obtained and generalized as functions of homological composition and temperature. In additions, phase diagrams of binary paraffin systems have been developed ('Neva', 2002, 352 p. (in Russian)). The First Russian Meeting on Organic Mineralogy was held in 2002 (chairmen: E.N. Kotelnikova and S.K. Filatov).
The Pathology of crystals group of Yurii Punin (Head of the Dept., firstname.lastname@example.org) investigates crystal growth instability that leads to the drastic distortion of the outer form and inner structure of crystals during their growth. As a result of this research, a theory of autodeformation defects has been elaborated. The group also developed a complex approach to the problem of growth dissymmetrization and the nature of optical anomalies in crystals on the basis of extensive kinetic and morphological studies of crystal growth in a surface-active environment.
The Tubular silicate group of Ira V. Rozhdestvenskaya (email@example.com) works on alkali calcium silicates with tubular radicals, including studies of such exotic silicate minerals as frankamenite, canasite, miserite, tokkoite, tinaksite and agrellite found in charoitite rocks of the Murun massif, western Aldan Shield, southeastern Siberia. They are layer structures that consist of alternating structural modules: walls of Ca-, and Ca, Na-polyhedra with silicate anions located between the walls. The silicate anions form tubes or bent ribbons in wide channels.
X-ray Laboratory, Dept. of Inorganic Chemistry, Faculty of Chemistry. The laboratory is involved in studies of inhomogenous crystals (solid solutions decomposition, nucleation) and nonstoichiometric compounds (R.A. Zvinchuk, Head of the lab); structures of modified steroid estrogens exhibiting selective biological activity and analysis of structure-property relationships for creation of new drugs (CCDC 164249-164261) (G.L. Starova, starova@VK4829.spb.edu); short-range order in complex stoichiometric 'disordered' oxides with heterovalent isomorphism and Rietveld refinement (Yu.E. Smirnov); and construction of derivative structures on the basis of non-characterictic crystallographic orbits and cyclotomical Patterson's sets.
Contacts have been included in the text.
Laboratory of Diffraction Methods in Kazan
Contact: Igor Litvinov firstname.lastname@example.org
Kurnakov Institute of General and Inorganic Chemistry, Moscow
New projects at the laboratory include:
(1) Investigation of a wide spectrum of secondary interactions (traditional hydrogen bonds, C-H…π contacts, proton-hydride, attractive, agostic, and stacking interactions, etc.) that play an important role in the formation of crown-ether styryl dyes, charge-transfer complexes based on π-donating bis(18-crown-6)stilbenes, diaryl esters exhibiting liquid-crystalline properties, and dipyridyls and their coordination polymers with Ag(I).
(2) The trans effect of multiply bound peroxo ligands in pseudo octahedral VO(η-O2)L4 complexes (where L is a donor atom of a monodentate and/or polydentate ligand) was characterized and the structures of the Group IV-VI metal (Ti, Ta, V, Nb, Mo, W) oxoperoxo complexes of this type were analyzed;
(3) Specific features of regioselective acid-catalyzed substitution of exo-polyhedral hydrogen atoms in the decaborate anion B10H102- were studied. The main product of these reactions is the equatorially monosubstituted derivative.
(4) Structures of LaL3(Phen)n mixed-ligand complexes (where L is dipivaloylmethanate or hexafluoroacetylacetonate) were determined to establish correlations between the structure and luminescence properties.
Important results have been obtained for nontransition p elements at low oxidation states. Mixed-ligand polymeric compounds of tin(II) with nitrogen-containing organic cation supramolecular compounds having large hollows and channels. Some uranyl complexes with fluoride ligands and tetradentate bridging oxalate ions contain infinite channels approximately 7-10 Å in cross-section. Channels that are formed by cyclic dioxygen anions were found in the structures of some boratobismuthates, the high-temperature modification of Na2B4O7, and double potassium-bismuth citrate.
A large series of mixed-cation RE compounds with condensed anions (phosphates, phosphatoborates, phosphatogermanates, germanates, oxophosphatovanadates) have been studied to reveal the effect of cations on the structure of the anionic group. It was found that in the noncentrosymmetric ultraphosphates, the (P8O23)6- anion contains isolated oligomers consisting of three connected six-membered rings. These compounds are candidates for quantum electronics. In the last three years, efforts have involved structural studies of polymeric coordination compounds of tin, bismuth, and uranyl with bridging oxo anions, polymeric complexes of silver with nitrogen- containing organic compounds, supramolecular compounds of doubly and triply charged metals with hexamethylenetetramine and different aminopolycarboxylic acids. Crystal structures of these compounds contain large hollows and channels that can be used for preparation of molecular sieves and ion exchangers. Over 150 crystal structures a year are determined by two groups using two Enraf-Nonius CAD-4 diffractometers.
Contacts: V. S. Sergienko (email@example.com), Yu. N. Mikhailov (firstname.lastname@example.org)
Electron density at Mendeleev UniversityResearch in the Mendeleev University group, headed by Vladimir Tsirelson, deals with describing bonding in solids in terms of electron density and electrostatic potential, as well as related functions describing local energies and potentials. Early studies were based on the Bader's quantum mechanical topological theory, which was applied to experimental electron density for the first time by Tsirelson and Streltsov in 1985. This approach is now widely accepted. The extensive range of compounds studied spans simple and binary crystals, perovskites, spinels, garnets, silicates, and molecular crystals. The materials were studied using topological theory to quantify atomic and molecular interactions and to elucidate the physical nature of the spatial architecture of crystalline systems.
Other studies are devoted to topological analysis of the electrostatic potential in molecules and crystals. It has been demonstrated that the nuclei of neighboring atoms are separated in the inner-crystal electric field by surfaces of the zero-flux potential gradient, inside of which the nuclear charge is completely screened by an electronic cloud. These electrically neutral bonded pseudoatoms define the regions in a crystal dominated by a charge of one or another nucleus, no gradient lines connecting the anions were found. The results led to a physically reasonable description of the Coulomb field features in a system, which is a key point in the development of corresponding models for force field.
Contacts: Vladimir G. Tsirelson email@example.com
Inorganic structure in Samara
Molecular Voronoi-Dirichlet polyhedra (a) of a cavity and (b) of a substrate molecule inside a cucrbituril molecule.
At present SSU researchers are working on a unique program package (TOPOS) for multi-purpose crystallochemical analysis (a user manual and demo and beta versions are available at www.topos.ssu.samara.ru/). TOPOS is an integrated interactive shell that supports a relational crystal structure database. To analyze crystal structure information TOPOS uses methods based on the quantitative characteristics of Voronoi-Dirichlet polyhedra that avoid using crystallochemical radii or a priori assumptions concerning the nature of interatomic bonds. The methods provide for unified analysis of crystalline substances at the atomic, molecular and supramolecular levels. Commercial and non-commercial versions of TOPOS are installed in a number of institutes of the RAS and in universities in France, Japan, Italy, Spain, and the UK.
TOPOS provides the user with tools to (i) calculate coordination numbers of atoms or molecules, (ii) assess a number of geometrical characteristics of atomic and molecular domains; (iii) estimate stereo effects caused by lone pairs or by the Jahn-Teller effect; (iv) analyze the far coordination spheres of atoms or molecules, and study the topology of atomic and molecular packing; (v) search for topological relationships between chemically and stoichiometrically different crystal structures, perform crystallochemical classification; (vi) estimate sizes of voids, cavities and channels in crystals, reveal agostic contacts and non-valence interactions; and (vii) predict stability of coordination compounds and supramolecular aggregates.
Various aspects of TOPOS have been demonstrated by analyzing different inorganic and coordination compounds including σ- and π-complexes, minerals, superionic conductors, zeolites, etc. Using uranium(VI) compounds as an example it was shown that the solid angles by which the faces of a Voronoi-Dirichlet polyhedron are 'seen' from the nucleus of a complexing atom can be used to evaluate the electron-donor capabilities of oxygen-containing ligands with the 18 electron rule. It has been proven that using the ligand electron-donor characteristics obtained with crystal structure data, one can predict the directions of stepwise complexation in water solutions as well as the composition and structure of resulting uranium(VI) complexes.