Chemical Crystallography and Electron Microscopy

The scope of the service is the characterization of materials and the structure determination of chemical substances with crystallographic and microscopic methods. This includes single crystal structure determination, powder diffractometry, transmission and scanning electron microscopy in connection with different methods for sample preparation. Our research areas are electron density determination, polymorphism and crystal-engineering studies.

Christian W. Lehmann

Prof. Dr. Christian W. Lehmann

Vita Publications

since 2009: Honorarprofessor for Inorganic Chemistry at the Bergische Universität Wuppertal
since 2008: Head of department Electron Microscopy at the Max-Planck-Institut für Kohlenforschung
since 1998: Head of department Chemical Crystallography at the Max-Planck-Institut für Kohlenforschung
1997: Visiting Professor at the University of LaPlata (Argentina)
1993-1997: Senior Research Officer, Durham University (Great Britain)
1991-1992: Post-Doc Queen-Mary-College London and University of Cardiff (M. B. Hursthouse)
1990: Doctorate in Crystallography (P. Luger, FU-Berlin)
1988: Sabbatical at the University of Pittsburgh (G. A. Jeffrey)
1984-1988: Studies for a degree in Chemistry at the FU-Berlin
1964: Born in Berlin

2010

WERNER, G., LEHMANN, C. W., BUTENSCHOEN, H. (2010); Advanced Synthesis & Catalysis, 352, 1345-1355. The First Anionic Thia-Fries Rearrangements at Ferrocene: Ready Access to Trifluoromethylsulfonyl-Substituted Hydroxyferrocenes and an Extremely High Interannular Stereoinduction between Cyclopentadienyl Ligands.

PISIEWICZ, S., RUST, J., LEHMANN, C. W., MOHR, F. (2010); Polyhedron, 29, 1968-1972. Cationic palladium(II), platinum(II) and ruthenium(II) complexes containing a chelating difluoro-substituted thiourea ligand.

LU, A.-H., NITZ, J.-J., COMOTTI, M., WEIDENTHALER, C., SCHLICHTE, K., LEHMANN, C.W., TERASAKI, O., SCHÜTH, F. (2010); J. Am. Chem. Soc. 132, 14152–14162. Spatially and Size Selective Synthesis of Fe-Based Nanoparticles on Ordered Mesoporous Supports as Highly Active and Stable Catalysts for Ammonia Decomposition.

ITANI, H., KEIL, P., LÜTZENKIRCHEN-HECHT, D., HAAKE, U., BONGARD, H., DREIER, A., LEHMANN, C.W., GRUNDMEIER, G. (2010); Surface and Coatings Technology 205, 2113-2119. XANES studies of the formation of Ag-nanoparticles in LbL deposited polyelectrolyte thin films.

ZENG, X., H., WILLNER, H., LEHMANN, C.W. (2010); Z. Anorg. Allg. Chem. 636, 2447–2453. Bis(methanesulfonyl) Peroxide, CH₃S(O)₂OOS(O)₂CH₃: Spectroscopic, Structural, and Thermal Properties.

RAMOS, L.A., ULIC, S.E., ROMANO, R.M., ERBEN, M.F., LEHMANN, C.W., BERNHARDT, E., BECKERS, H., WILLNER, H., DELLA VÉDOVA C.O. (2010); Inorg. Chem. 49, 11142-11157. Vibrational Spectra, Crystal Structures, Constitutional and Rotational Isomerism of FC(O)SCN and FC(O)NCS.

BOCK, D.A., LEHMANN, C.W., LIST, B. (2010); Proc. Nat. Acad. Science 107, 20636-20641. Organocatalysis Special Feature: Crystal structures of proline-derived enamines.

SEIDEL G, LEHMANN, C.W., FÜRSTNER, A. (2010); Angew. Chem. Int. Ed. 49, 8466-8470. Elementary Steps in Gold Catalysis. The significance of gem-Diauration.

2009

Peri-Diaurated Naphthalene: Synthesis and Reactions of a New Class of Organogold(I) Complexes Containing Bridging, Dianionic Naphthalenediyl Ligands. Meyer, N., Lehmann, C. W., Lee T. K.-M., Rust, J., Yam, V. W.-W., Mohr, F. (2009); Organometallics, 28, 2931-2934.

Coordination chemistry at carbon. Alcarazo , M., Lehmann. C. W., Anoop, A., Thiel, W., Fürstner, A. (2009); Nature Chemistry., 1, 295-301.

Bridge cleavage reactions of cyclopalladated nitrosamines with thioamides and related compounds. Fuge, F., Lehmann, C. W., Rust, J., Mohr, F. (2009); J. Organomet. Chem., 694, 2395-2401.

Weak interactions in chain polymers [M(μ-X)2L2]¥ (M = Zn, Cd; X = Cl, Br; L = substituted pyridine) – an electron density study. Wang, R., Lehmann, C. W., Englert, U. (2009); Acta Cryst., B65, 600-611.

2008

Carbenes Stabilized by Ylides: Pushing the Limits. Fürstner, A., Alcarazo , M., Radkowski, K., Lehmann. C. W. (2008); Angew. Chem. Int. Ed., 47, 8302-8306.

Synthesis and Characterization of Bis[bis(pentafluoroethyl)phosphinyl]imides, M⁺N[(C₂F₅)₂P(O)]₂-, M = H, Na, K, Cs, Ag, Me₄N⁺.; Bejan, D., Willner, H., Ignatiev, N., Lehmann, C. W. (2008); Inorg. Chem., 47 , 9085–9089.

Coordination Chemistry of the Ene-1,1-diamines and a Prototype “Carbodicarbene”. Fürstner, A., Alcarazo , M., Goddard, R., Lehmann. C. W. (2008); Angew. Chem. Int. Ed., 47, 3210-3214.

Direct Imaging of Surface Topology and Pore System of Ordered Mesoporous Silica (MCM-41, SBA-15, and KIT-6) and Nanocast Metal Oxides by High Resolution Scanning Electron Microscopy. Tüysüz, H., Lehmann, C. W., Bongard, H., Tesche, B., Schmidt, R., Schüth, F. (2008); J. Am. Chem. Soc., 130, 11510-11517.

A Cheap Metal for a "Noble" Task: Preparative and Mechanistic Aspects of Cycloisomerization and Cycloaddition Reactions Catalyzed by Low-Valent Iron Complexes. Fürstner, A., Majima, K., Martin, R., Krause, H., Kattnig, E., Goddard, R., Lehmann, C. W. (2008); J. Am. Chem. Soc., 130, 1992-2004.

Preparation, Structure, and Reactivity of Nonstabilized Organoiron Compounds. Implications for Iron-Catalyzed Cross Coupling Reactions. Fürstner, a., Martin, R., Krause, H., Seidel, G., Goddard, R., Lehmann, C. W. (2008); J. Am. Chem. Soc., 130, 8773-8787.

Download Complete List of Publications (PDF)

Research Topics

Experimental electron density determination: Experimental electron density determination

The electron density of a molecule is the key for the understanding of chemical interactions. On one hand, the electron density can be calculated directly from the wave function. On the other hand, the electron density - in contrast to the wave function - can be observed experimentally. Of special interest for us are transition metal catalysts, co-ordination polymers and organic molecules with special photonic properties. The optical properties of these so-called push-pull chromophores change sometimes drastically between being in solution or forming a crystalline solid. Since the crystalline state usually forms the basis for applications, crystallographic methods are especially useful for these investigation.
Polymorphism and Crystal-Engineering: Polymorphism and Crystal-Engineering

Polymorphism describes the ability of a chemical substance to form more than one crystalline state. These different crystalline states have different properties with respect to solubility, colour, or melting point. This phenomenon is known for inorganic and organic molecules. Polymorphism is especially interesting in cases of pigments and pharmaceuticals. X-ray powder diffraction is exceptionally suited to distinguish between different polymorphs. The high transmission of the X-rays allows investigation even of formulated and packaged tablets and can be used to detect counterfeits.

Instrumentation

Single crystal structure determination

Single crystal structure determination

Currently, there are three single crystal diffracometers in use: (Bruker AXS Mach3) with area detectors (Apex II, KappaCCD, Proteum). The X-rays are generated by rotating anodes (Bruker AXS FR591) with Molybdenum and Copper anodes, respectively.

Determination of the exact three –dimensional arrangement of all atoms contained in a crystalline chemical substance
Information about constitution, conformation, exact bond lengths and angles as well as the three-dimensional packing in the solid state
Measurements of organic and metal organic substances, Screening of protein crystals
Especially substances sensitive to air, temperature and moisture at temperatures down to -173 °C
Measurements of extremely small crystals using focussing X-ray mirrors
Determination of the absolute configuration of chiral substances

Powder diffractometry

$Powder diffractometry$

Powder diffractometry

Presently there are three Stoe STADI P diffractometers comprising primary monochromators (Mo-K"alpha"1 and Cu-Kα1), Debye-Scherrer geometry and position sensitive detectors. A further PANalytical X’Pert diffractometer is equipped with a copper X-ray tube and can be used either in Bragg-Brentano geometry with different primary and secondary optics or in capillary mode.

Qualitative and quantitative phase determination for identifying polycrystalline materials
In-situ powder diffractometry between -173 and 900 °C for investigating phase transitions
Rietveld refinement and ab-initio structure solution
Monitoring of solid state chemistry reaction under variable pressure, temperature conditions and reactive gas mixtures

Transmission electron microscopy (TEM)

Transmission electron microscopy (TEM)

Transmission electron microscopy of nano particles and nano structured materials (zeolites and mesoporous silicates and their replica) reveals structural details in the sub nanometer range.

High resolution imaging and chemical analysis using a 200 kV electron microscope with cold field emitter, CCD-camera and EDS (Hitachi HF-2000)
Cryo microscopy (100 K) and thermo microscopy (Gatan sample holder)
Determination of particle size distributions and optimization of reaction conditions (100 kV, Hitachi H-7100 and H-7500)

Scanning electron microscopy (SEM)

Scanning electron microscopy (SEM)

Scanning electron microscopy is employed to visualize details of the sample surface on the nano meter scale.

Ultra high resolution scanning electron microscopy with a point resolution of up to 4 Å at 30 kV (Hitachi S-5500)
Combination with bright field and dark field scanning transmission electron microscopy (STEM)
Elemental analysis using EDS achieving nano meter resolution
SEM of bulk samples in combination with EDS and under variable pressure (Hitachi S-3500N)

Sample preparation for Electron microscopy

Sample preparation for Electron microscopy

The sample preparation for electron microscopy is of utmost importance. Delicate structures must not be destroyed or changed; the sample should be representative for the whole material.

Preparation of carbon support films with a thickness of a few nano meters; tungsten coating using our in-house designed coating apparatus
Preparation of ultra thin sections using an ultra microtome (Reichert Ultracut)
Gold coating of SEM samples for the deposition of a conducting layer using a sputtering process (Balzers MED010)
Preparation of cross-section of extremely fragile micro- and mesoporous nano structures (Hitachi E-3500)