Cationic Noble Gas Hydrides: A Theoretical Investigation of Dinuclear HNgFNgH⁺(Ng = He−Xe)

Abstract

Theoretical calculations at the B3LYP, MP2, and CCSD(T) levels of theory disclose the conceivable existence of cationic noble gas hydrides containing two Ng atoms. These species have a general formula of HNgFNgH(+) (Ng = He-Xe), and are the cationic counterparts of the neutral HNgF. The optimized geometries, harmonic frequencies, and bonding properties point to ion-dipole complexes between a fluoride anion and two covalent H-Ng(+) cations, best formulated as (H-Ng(+))(2)F(-). The HXeFXeH(+) is also isoelectronic with the recently experimentally observed HXeOXeH (Khriachtchev et al. J. Am. Chem. Soc. 2008, 130, 6114-6118). The resulting HNgFNgH(+) are thermochemically stable with respect to dissociation into HNg(+) + HNgF and HNg(+) + H + Ng + F, but are largely unstable with respect to both the loss of HF (with formation of HNg(+) + Ng) and H(2)F(+) (with formation of two Ng atoms). These decompositions pass through bent transition structures, and only the heaviest HArFArH(+), HKrFKrH(+), and HXeFXeH(+) are protected by energy barriers large enough (ca. 10-15 kcal mol(-1)) to support their conceivable metastability. In line with other series of noble gas compounds, the neon cation HNeFNeH(+) is the least stable among the various HNgFNgH(+).

Cationic Complexes of Hydrogen with Helium

“…However, so far no stable compound containing helium has been synthesized, except for structures where helium atoms are physically trapped inside fullerene cages 4. One promising type of novel compounds are noble-gas hydrides of the form HNgY where Ng is a noble-gas atom and Y an electronegative fragment 5, 6. A recent review2 lists 23 of these hydrides, but none including helium.…”

Neon behind the signs

“…These calculations are in agreement with the fact that complexes of neon with neutral metal acceptors, including the compounds NeAuF and NeBeS recently detected in cold matrices 2,3 , are also in general less stable than their helium counterparts. There are also examples of helium and neon cations that feature this reversed order of stability 4 . Neon is bigger than helium, and possesses occupied p orbitals.…”

Noble gases

“…The diatomic cations, BaHe 2+ , BaAr 2+ , BaKr 2+ and BaXe 2+ were formed in a helium bath gas at room temperature in a selected ion flow tube (SIFT) tandem mass spectrometer. 22 The HXeFXeH + cation is isoelectronic with HXeOXeH, which was recently observed in a xenon matrix. Increasing polarisability of the noble gas atom increases the rate of BaNg 2+ formation and the strength of the interaction between Ng and Ba 2+ .…”