Research Interests
The Ruhlandt-Senge group's research focus is the chemistry of the heavy alkali and alkaline earth metals. Particular research interests lie in two distinct areas: the preparation of novel organometallic species with applications in polymerization and synthetic chemistry, and the development of novel source materials for MOCVD applications.
Despite exciting applications in synthetic and polymer chemistry, the organometallic chemistry of the heavy alkaline earth metals remains poorly understood within the scientific community. The small number of well-characterized target compounds prevents a detailed structure-function analysis. Further progress critically depends on the development of reliable and facile synthetic regimen and the introduction of novel ligand systems to achieve improved understanding and utility of the many applications. In the last few years our group has prepared several families of alkaline earth organometallics, including acetylides, di- and triphenylmethanides, many of them the first of their kind; a barium diphenylmethanide derivative is shown above right. Current work is extending this group of compounds and testing the novel materials in the above-mentioned applications.
 Our second major research focus is the preparation of novel precursor materials for MOCVD leading to alkaline earth metal containing solid-state materials. Solid-state materials containing group 2 elements range from insulators to high temperature superconductors. Widely recognized are capacitance-based devices such as dynamic random access memory (DRAM) circuits. These require materials with a high dielectric performance, as displayed by alkaline earth metal titanates MTiO3 (M= Sr, Ba or mixtures thereof). Other applications include high temperature superconductors such as YBa2Cu3O7-δ′ Bi2Sr2CaCu2O8-δ and Tl2Ba2Ca2Cu3O8 with a Tc as high as 134 K. Alkaline earth metals are also essential in flat panel displays based on electroluminesce technology. These contain a doped dielectric layer, typically a binary metal sulfide where the metal is either Ca, Sr, or Zn. Electroluminescent displays are not shock sensitive like liquid crystal displays, and do not require backlighting, cross polarizers or filters. Moreover, the displays are brighter than the more common LCD counterparts and display higher contrast.
The preparation of the MOCVD precursors requires thermally stable, highly volatile precursor materials to enable the deposition of thin films. With a continuing need for optimal precursors our work is geared towards the development of facile synthetic routes and the introduction of novel ligand systems. Due to the large diameter of the metals, multidentate ligands, preferably with additional intramolecular coordination are tested to increase thermal stability while preventing aggregation. Research methods in the laboratory include inert gas chemistry both on a Schlenk line and in the glove box, low temperature crystallography, 1H and heteronuclear as well as temperature dependent NMR spectroscopy, IR spectroscopy, thermogravimetrical analysis, and more.
Selected Publications
Gillette-Kunath, M.; Teng. W.; Ruhlandt-Senge, K. Synthesis and Structures of Monomeric Magnesium, Calcium, Strontium and Barium Amides involving the 2,4,6-trimethylphenyl-N-trimethylsilyamide ligand. Inorg. Chem. 2005, 44, 4862.
Hitzbleck, J.; Deacon, G.B.; Ruhlandt-Senge, K. Amazing Linear Finite "Mers" - Polynuclear Heavy Alkaline Earth Metal Pyrazolates. Angew. Chem. Int. Ed. Engl. 2004, 43, 5218-5220.
Teng, W.; Ruhlandt-Senge, K. Syntheses and Structures of the First Heavy Alkaline Earth Metal Bis(tris(trimethylsilyl))silanides. Organometallics 2004, 23(11), 2694-2700.
Teng, W.; Ruhlandt-Senge, K. Syntheses and Structures of the First Heavy Alkaline Earth Metal Germanides M(THF)n(Ge(SiMe3)3)2 (M= Ca, n= 3; M= Sr, n= 3; and M= Ba, n= 4). Organometallics 2004, 23(5), 952-956.
Alexander, J. S.; Allis, D. G.; Hudson, B. S.; Ruhlandt-Senge, K. An Examination of Metal-Ligand Binding Modes in Rubidium Diphenylmethanide. J. Am. Chem. Soc. 2003, 125(49), 15002-15003.
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