XeO3 adducts of pyridine, 4-dimethylaminopyridine, and their pyridinium salts

Xenon trioxide (XeO3), a highly shock-sensitive detonator, forms adducts with the N-bases, pyridine and 4-dimethylaminopyridine (4-DMAP). The reactions of pyridine and 4-DMAP with XeO3 in rigorously dried CH3CN and in CH3CN that had not been dried yielded (C5H5N)(3)XeO3 (1) and (4-(CH3)(2)NC5H5N)(3) XeO3 center dot H2O (3), respectively, whereas their reactions in HF-acidified CH3CN yielded [C5H5NH](4) [HF2](2)[F](2)(XeO3)(2) (2) and [4-(CH3)(2)NC5H4NH] [HF2]XeO3 (4). Crystalline (1), (2), and (4) failed to detonate when subjected to mechanical shock; however, (3) was significantly more sensitive to mechanical or thermal shock than XeO3. The adducts and their pyridinium salts were structurally characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. The crystal structures of (1) and (3) consist of XeO3 molecules that are N-coordinated to three pyridine and 4-DMAP ligands, respectively. A water molecule is also H-bonded to two oxygen atoms of two adjacent XeO3 molecules of (3). The pyridinium cations of (2) and (4) are H-bonded to [F](-) and/or [HF2](-) ions which are, in turn, F-coordinated to XeO3. Both [F](-) ions of (2) bridge two XeO3 molecules to form Xe2F2-rings. Each [HF2](-) anion of (4) bridges two cations and two XeO3 molecules by means of Xe center dot center dot center dot F secondary bonds and N(H)center dot center dot center dot F H-bonds. Quantum-chemical calculations for (1) and (2) provided energy-minimized geometries and calculated vibrational frequencies and intensities which were used to aid in the assignments of their Raman spectra. The NBO analyses showed the Xe center dot center dot center dot N, Xe center dot center dot center dot O, and Xe center dot center dot center dot F secondary bonding interactions are electrostatic in nature and may be described as a-hole bonds.