Trioxides structural chemistry

Quantum chemical methods are valuable tools for studying atmospheric nucle-ation phenomena. Molecular geometries and binding energies computed using electronic structure methods can be used to determine potential parameters for classical molecular dynamic simulations, which in turn provide information on the dynamics and qualitative energetics of nucleation processes. Quantum chemistry calculations can also be used to obtain accurate and reliable information on the fundamental chemical and physical properties of molecular systems relevant to nucleation. Successful atmospheric applications include investigations on the hydration of sulfuric acid and the role of ammonia, sulfur trioxide and/or ions... 

Figure 6.12 Structure of MoO3. (Reprinted with permission from Materials Chemistry and Physics, Preparation and characterization of layered molybdenum trioxide pillared with chro-mia byX. Wang, W. Hou, X. Guo and Q. Van, 73, 1. Copyright (2002) Elsevier Ltd)...

The chemistry of sulphur trioxide, to any large extent has not been studied in non-aqueous media. Compounds of sulphur trioxide with a few electron donors such as pyridine, dimethylamine, dimethylaniline, dioxane, acetic acid and butyric acid have been utilised for synthetic purposes without much attention having been paid to their structure and their solution chemistry. Based upon conductivity work the formation of compounds of sulphur trioxide with ethers (2) and fatty acids (3) has been briefly reported. These and other physicochemical studies such as potentiometric titrations, viscosity, density, dipole moment and molecular weight determinations have revealed in our work the formation of definite compounds of sulphur trioxide with alcohols, ethers, esters and fatty acids. 

Having considered the incorporation of alcohols into polyoxoanion frameworks as alkoxide groups, we now turn to their transformation into aldehydes or ketones (oxidation) and alkenes (dehydration). As above, the selection of the polyoxoanion system to be studied was dictated in part by analogies with molybdenum trioxide chemistry. Molybdenum trioxide has a layer structure [21], and the structure of a single M0O3 layer is shown in 16. 

The sulfur-oxygen bond is an important feature of sulfur chemistry, just as the silicon-oxygen bond is of silicon chemistry. The best-known simple oxides are the dioxide, SO2, and the trioxide, SO3 (although highly reactive lower oxides SO and S2O have been described). The bonding in SO2 and SO3 is usually described in terms of S=0 double bonds, VSEPR theory predicting the shapes shown in Structures 12.14-12.17. 

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