Small molecule and non-metal chemistry

Small molecules

The primary objective of our work is to make very simple isolatable classes of compounds that chemists would consider not preparable based on generally accepted views and past experience.

These small compounds should

• be novel in terms of their stereochemistry and bonding
• be first examples of a new class of compounds
• open up new areas of chemistry of the elements.

These aims are often the result of discoveries rather than well thought out planned syntheses. Such is the case for many (often binary) group 15-halogen and group 15-chalcogen species, especially when the group 15 element was nitrogen and the halogen was fluorine.

We are particularly interested in the elucidation of the molecular structures both in the solid state (X-ray) and in the gas phase (electron diffraction). Furthermore, the interplay of experiment with both qualitative (thermodynamic estimations) and quantitative theory (MO ab initio computations) is one of the major interests.

Since many compounds are thermodynamically and kinetically unstable the research group is used in handling shock-sensitive and highly explosive materials. Moreover, powerful oxidizers (ClF₃, F₂, UF₆, AsF₅ etc.) are often applied to realize high oxidation states. The chemistry of elemental fluorine and anhydrous HF is an important branch of research.

The applied side of our work again lies in the preparation and computation (semiempirical, ab initio and density functional) of high-energy-density materials (HEDMs) in collaboration with the WIWEB (a division of the German MoD). We are particularly interested in the research of primary detonators (initiators), bulk explosives and propellant charges for military application.

Non-metal molecules

Academic preparative research

• fluorine chemistry
• the chemistry of covalent azides,
• Se-N compounds and
• nitro compounds

Covalent binary nonmetal azides have been known for over 100 years, while the isolation on a preparative scale and the determination of the structures of these highly explosive species has only been feasible in the last few years. With the aid of correlated, high-level ab initio computations it was possible for the first time to obtain theoretical insight into unusual, experimentally observable structural characteristics of covalent azides. The excellent agreement between experiment and theory gives credence to those calculated structures for which there are no experimental data due to the extreme lability of the compounds in question, for instance the novel N-oxides ON-N₃, O₂N-N₃ and O(N₃)₂ the isocyanate derivative OCN-NCO and the elusive gas-phase species (FSO₂)₂ N-N₃.

The structure of the hydracid CS₂N₃H and the pseudoaromatic interpseudohalogen compound CS₂N₃-CN were both predicted on the basis of high-level ab initio computations and finally confirmed by single crystal X-ray diffraction techniques.

Why are we so strongly interested in the preparation of a class of compounds such as the covalent azides that need to be handled with such extreme care and precautions?

We wish to demonstrate that even, and particularly, in the area of main group and fluorine chemistry of very simple binary compounds there are still many unanswered questions with regard to structure and bonding. There are also many new compounds in this area that are waiting to be synthesized on a preparative scale.

Now that questions about structure and bonding in binary halogen azides XN₃ azides appear to be answered to a certain extent, we wish to pay particular attention in the future to comparative discussions of gas-phase and solid-state structures and to the underlying questions of bonding.

Until now the pair IN₃ (g) / [IN₃]_x (s) remains a singular result. Therefore the experimental determination of further structures of covalent azides and related molecules, especially in the solid state, is necessary. We will face up to these challenges in the future.