Structural chemistry by diffraction methods [ LCHM2251 ]

Passing the course "Eléments de cristallographie et spectroscopie moléculaire", first part: "Cristallographie" [CHM1251B] or knowledge of basic crystallography obtained in daily experimental research.

1. Crystallisation. 2. X-ray diffraction, theory and experimental methods. 3. Crystalline and molecular structures determination methods. 4. Interpretation of results.

- theoretical and experimental methods of X-ray and neutron diffraction

- determination of crystal structure from single-crystal and powder data

- ability to interpret structural information in terms of bonding & structural chemistry knowledge

Lectures will be given using PowerPoint slides with an extensive use of web-based applications, crystallographic software, databases etc. A number of problems will be solved on a computer during the classes and as a part of exercises.

1.      Introduction. Refreshing the basic knowledge of crystallography: symmetry & principles of diffraction. Phase problem

2.      Single crystal diffraction experiment: geometries, diffractometers and detectors, resolution

3.      Powder diffraction experiment. Experimental geometries, instruments. Angular resolution. Complementarity of techniques. Powder vs single-crystal diffraction. Possibilities and limits of different diffraction techniques.

4.      Indexing - a challenge for powder diffraction. Reconstruction of reciprocal space sections from single crystal data. Systematic absences, space group determination

5.      Structure solution: Patterson and direct methods, molecular replacement, isomorphous replacement, use of the anomalous dispersion, MAD (multi-wavelength anomalous dispersion) and SAD (single-wavelength anomalous dispersion) methods

6.      Modern structure solution methods: charge flipping & direct space methods

7.      Structure refinement, constraints and restraints, absolute structure, validation of the results

8.      Problems: defects, twinning, disorder. Diffuse scattering

9.      Quality of the data, interpretation of results. Publishing the results in a thesis or a publication

10.  Description of a structure, structural chemistry. Databases, Pearson symbol, Wyckoff sequence, structure type. Identifying bonding schemes

11.  Going beyond a structure. Structural evolution and reactivity under non-ambient conditions: with time, temperature, hydrostatic or gas pressure. Sequential refinement. Large facilities, writing a proposal

Exercises:

1.      structure determination on a single-crystal (CrysAlis, Shelx, Platon)

2.      indexing, structure solution & Rietveld refinement on powder data (Dicvol, FOX, Fullprof)

3.      analysis and presentation of crystallographic results, explanation/evaluation of a crystal structure report