High coordination chemically bound compounds of noble gases with hydrocarbons: Ng(CCH) ₄ and Ng(CCH) ₆, (Ng=Xe or Kr)

Ab initio calculations predict the existence of the compounds Ng (CCH)4 and Ng (CCH)6, where Ng=Xe or Kr. Presently known organic noble gas compounds have a coordination number of two at most. The Ng (CCH)4 molecules have D4h symmetry, and Ng (CCH)6 molecules have Oh symmetry. The bonding in all these compounds is partly ionic and partly covalent, with significant contributions from both types of bonding. The relatively high vibrational frequencies and the substantial Ng- (CCH) binding energy in these species indicate that these compounds should be fairly stable, at least in cryogenic conditions. These compounds could be a very interesting addition to the range of known organic noble gas compounds. Suggestions are made on possible approaches to their preparation.