|
Research Focus
|
|
Our interests are very broad and range from very basic studies to applied research of academic, Government or industrial interest. We are particularly interested in high energy density materials (HEDM), inorganic main group chemistry, polynitrogen and nitramine chemistry, high-oxygen carriers, energetic ionic liquids, chemistry at the limits of oxidation and coordination, the synthesis and characterization of novel carbocation and fluorocarbon compounds, and the development of quantitative scales for fundamental properties, such as Lewis acidity, oxidizer strength and the “nakedness” of fluoride ion sources. Our work exploits the synergism of theory and synthesis and greatly benefits from close collaborations with several groups of theoreticians. The main goal of our research is to advance the state of the art and strive for spectacular breakthroughs, rather than settling for small incremental improvements.
The work of our group has been financially supported over the years by the National Science Foundation, the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office, DARPA, and the Department of Energy.
In the following section, some typical examples of our work in different areas are highlighted. Because of space limitations, we have omitted a vast body of work in the areas of halogen fluorides, inorganic halogen oxidizers and singlet delta oxygen gas generators. The pertinent references to these data can be found in the publications list in the bio of Karl Christe by clicking on his picture.
|
|
Novel oxygen-balanced, energetic ionic liquids of interest for liquid monopropellants:
(C. Bigler Jones, Ralf Haiges, Thorsten Schroer, and Karl O. Christe, Angew. Chem. Int. Ed. 2006, 45, 4981)
|
|
|
|
Polynitrogen Chemistry:
One of the most recent discoveries, which has received coverage even in the New York Times (Feb 2, 1999) and London Times (Feb 10, 1999) and was selected by Chem. & Eng. News as one of chemistry’s top five achievements of 1999, is the single-step synthesis of the N5+ cation in essentially quantitative yield and determination of its structure. The N5+ cation is only the second homonuclear polynitrogen species that has been isolated in bulk and may provide the basis for new high-energy-density materials. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Polyazide Chemistry:
During the past three years, Ralf Haiges from our group has prepared and characterized a very large number of polyazido compounds. Typical examples are shown below.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
“Naked Fluoride” and High Coordination Number Chemistry: • Complex fluoro anions are ideally suited for studies at the limits of oxidation and coordination. However, there were two problems with the alkali metal fluorides, generally used for their syntheses. Ø
- poor solubilities Ø - cations were not large enough to stabilize some of the salts Because the high oxidation state compounds usually are strong oxidizers, the large cations had to be oxidizer resistant. Tetraalkylammonium fluorides had the desired cation sizes and solubilities but, except for the methyl compound, lacked the chemical inertness. The problem with tetramethylammonium fluoride (TMAF) was the difficulty of obtaining it in anhydrous form.
• We developed a convenient synthesis for anhydrous TMAF and demonstrated its potential for the preparation of many new high coordination number (CN) compounds (K. O. Christe, W. W. Wilson, R. D. Wilson, R. Bau, J. Feng, J. Am. Chem. Soc. 1990, 112, 7619).
• This discovery spurred a renaissance in high CN chemistry.
|
|
|
 |
 |
|
Chemical Synthesis of Elemental Fluorine: • The chemical synthesis of elemental fluorine had been pursued unsuccessfully since at least 1813 (Davy), and essentially every textbook stated that F2 cannot be prepared by chemical means because it is the most electronegative element. In 1986, KOC was invited to review the chemical synthesis of F2 in Paris at the Centanniary of the discovery of fluorine by Moissan. One week before the Congress, while preparing his slides, he realized that there was no reason why F2 should not be preparable by chemical means. The combination of two rudimentary chemical principles should afford F2.
|
|
He also knew that MnF62- can be prepared in an aqueous medium
2 KMnO4 + 2 KF + 10 HF + 3 H2O2 ® K2MnF6¯ + 8 H2O + 3 O2
and that MnF4 is thermodynamically unstable and decomposes to a lower fluoride and F2
MnF4 ® MnF3 + ½ F2
So he raced to the lab, prepared K2MnF6 from aqueous HF, ran displacement reaction with SbF5
K2MnF6 + SbF5 ® KSbF6 + MnF3 + ½ F2
and in 3 days he had successfully prepared elemental fluorine by chemical means in high yield and at atmospheric pressure. The rest is history. The only irony that both K2MnF6 and SbF5 had been known for more than 100 years and even Moissan could have come up with this scheme, had he thought of it. |
|
|
|
Onium Salts:
|
|
|
|
|
|
NF4+ Chemistry:
|
|
|
|
|
|
Quantitative Scales for Oxidizing Power, Lewis Acidity and “Nakedness of Fluoride Ion Sources:
|
|
|
|
|
|
|
