Oxygen coordination to
the Xe(VI) atom of XeO<sub>3</sub> was observed in its adducts with
triphenylphosphine oxide, dimethylsulfoxide, pyridine-N-oxide, and acetone. The
crystalline adducts were characterized by low-temperature, single-crystal X-ray
diffraction and Raman spectroscopy. Unlike solid XeO<sub>3</sub>, which
detonates when mechanically or thermally shocked, the solid [(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>PO]<sub>2</sub>XeO<sub>3</sub>,
[(CH<sub>3</sub>)<sub>2</sub>SO]<sub>3</sub>(XeO<sub>3</sub>)<sub>2</sub>,<sub>
</sub>and (C<sub>5</sub>H<sub>5</sub>NO)<sub>3</sub>(XeO<sub>3</sub>)<sub>2</sub>
adducts are insensitive to mechanical shock, but undergo rapid deflagration
when ignited by a flame. Both [(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>PO]<sub>2</sub>XeO<sub>3
</sub>and (C<sub>5</sub>H<sub>5</sub>NO)<sub>3</sub>(XeO<sub>3</sub>)<sub>2</sub>
are air-stable whereas [(CH<sub>3</sub>)<sub>2</sub>SO]<sub>3</sub>(XeO<sub>3</sub>)<sub>2</sub>
slowly decomposes over several days and [(CH<sub>3</sub>)<sub>2</sub>CO]<sub>3</sub>XeO<sub>3</sub>
undergoes adduct dissociation at room temperature. The xenon coordination
sphere of [(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>PO]<sub>2</sub>XeO<sub>3</sub>
is a distorted square pyramid which provides the first example of a
five-coordinate XeO<sub>3</sub> adduct. The xenon coordination spheres of the
remaining adducts are distorted octahedra comprised of three Xe---O secondary
contacts that are approximately trans to the primary Xe–O bonds of XeO<sub>3</sub>. Quantum-chemical
calculations were used to assess the Xe---O adduct bonds, which are
predominantly electrostatic σ-hole
bonds between
the nucleophilic oxygen atoms of the bases and the σ-holes
of the xenon atoms.
alpha-Hydroxylation of fatty acids in brain. Substrate specificity and deuterium isotope effect.
