The center of collective using
Department of X-ray diffraction study and quantum chemistry performs X-ray analysis of crystal and powder samples of organic, inorganic and coordination compounds. We are ready to collaborate with both academic and non-academic institutions. A confidentiality agreement can be made on your wish. Our service includes:
- Determination of molecular and crystal structure of relatively small molecules (we study as small organic molecules as calixarenes, crown-ethers, rotaxane, catenane, etc.)
- X-ray diffraction study of air-unstable compounds. Data collection can be selected from 100 to 300 K.
- Record a jpeg movie of the crystal for crystal face indexing.
- Analytical numeric absorption correction.
- Structure solution and refinement.
- Solution of disordered and twinned structures.
- Determination of configuration of stereogenic centers for enantiopure compounds.
- We are interested in studying of polymorphism by both monocrystal and powder diffraction methods.
- Solvates and co-crystals are included in area of our interests.
- Comprehensive analysis of molecular and crystal structures can be done. If necessary the quantum-chemistry calculations can be used for explanation of obtained features.
- Of particular interest we pay the study of intermolecular interactions and their influence on the formation of crystal packing. Our approach based on the estimation of pair intermolecular energies is applied for analysis of supramolecular architecture.
- Search of the known structures in the Cambridge Structural Database (CSD) and statistical analysis of some geometric characteristics.
(Siemens D500 diffractometer, filtered/monochromatic CuKa radiation, Bragg-Brentano geometry) may be applied for such purposes:
- Expess qualitative or semiquantitative phase analysis – revealing of phases including in powder sample, verification of phase purity of the sample or identification of impurities in the sample. Such analysis is carried out using PDF database and structure data taken from COD or CCDC databases. Results may be represented as figures/list of matched phases.
- Quantitative phase analysis – Rietveld refinement of the full-profile powder pattern using data taken from named databases or results of the single-crystal structure determination. Report may include figure obtained for completed Rietveld refinement and tables and detailed information on each refined phase. It should be noted the this analysis is reliable only for known crystalline substances, amorphous and unknown phases can not be detected and refined. Rietveld refinement also may be used for other purposes e.g. precise determination of unit cell dimensions, calculation of microstructure (nanocrystallinity, microstrains) etc.
- Characterization of new substances – phase purity, determination of the unit cell dimensions, space group symmetry, unit cell content, calculated density etc. Report may contain the primary crystal data.
- If new substance is pure, unit cell volume not exceeds ca. 2500-3000Å and number of atoms in the asymmetric unit of the cell is less then 25-30, then structure determination from the powder pattern may be provided. Initial information on required molecule(s) (molecular sketch) is needed for such determination. Results of powder determination need to be refined using the Rietveld method including geometrical constraints/restraints and may be presented as full structure report including tables and figures. It should be noted that results of the structure determination from powder pattern are less reliable as compared with single crystal ones. So sometimes it is better to obtain even low quality crystals for the single-crystal investigation and carry out the latter. In cases when studied substance may not form needed crystals or crystal growth process leads to the loss of useful properties (e.g. for high-temperature superconductors or catalysts, pharmaceutical drugs etc.) structure determination from the powder data remains the only applicable method.
- Powder method provides exhausting results for pharmaceutical drugs or substances containing different polymorph modifications.