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)3XeO3 (1) and (4-(CH3)2NC5H5N)3 XeO3·H2O (3), respectively, whereas their reactions in HF-acidified CH3CN yielded [C5H5NH]4[HF2]2[F]2(XeO3)2 (2) and [4-(CH3)2NC5H4NH][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⋯F secondary bonds and N(H)⋯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⋯N, Xe⋯O, and Xe⋯F secondary bonding interactions are electrostatic in nature and may be described as σ-hole bonds.