HXeSH, the First Example of a Xenon−Sulfur Bond

Quite recently, we have reported a number of novel rare-gas compounds of type HXY (X ) Xe or Kr, and Y is a fragment with a large electron affinity). The compounds obtained so far include HXeH, HXeCl, HXeBr, HXeI, HXeCN, HXeNC, HKrCl, and HKrCN.1-4 They are prepared in rare-gas matrices at low temperatures (<50 K) by photolyzing a suitable precursor HY, which yields isolated hydrogen atoms and Y-fragments. After photolysis, thermal mobilization of hydrogen atoms leads to their reactions with the rare-gas atoms surrounding the Y-fragments. The resulting novel HXY rare-gas compounds are detected by IR spectroscopy mainly via extremely intense X-H stretching absorptions. In this report we introduce a new member of this family, HXeSH. This molecule expands the number of elements capable of making chemical bonds with xenon and represents the first compound with a xenon-sulfur bond. The electronic structure calculations for HXeSH were carried out with the Gaussian 94 package of computer codes.5 The relativistic effective core potential (ECP) by LaJohn et al. was used on Xe.6 This ECP includes the d-subshell in the valence space resulting in 18 valence electrons and was used in a decontracted form. The standard split-valence 6-311++G(2d,2p) basis set was used for hydrogen and sulfur. The calculated structural parameters of HXeSH at different computational levels are given in Table 1. Like H2S, HXeSH is also a bent molecule with an H-S-Xe angle near 90 degrees. The calculated S-H bond distance of 1.34 A in HXeSH is essentially the same as the experimental value in H2S. The Xe-H distance (1.84 A at the CCSD(T)-level) is somewhat larger than the value of free XeH+ (1.60 A)8 but much smaller than the van der Waals distance of neutral Xe-H (3.95 A).9 The calculated length of the Xe-H bond compares well with XeH2 and HXeI molecules, which both have experimental Xe-H stretching absorptions in the 1200 cm-1 region of the spectrum.1,2,10 The calculated Xe-S bond distance of 2.77 A can be compared with the recently calculated values for the excited states of Xe-S. For the 11Σ+ state (Xe+ S(1D)) and the lowest chargetransfer (Xe+S-) state 23Π, 2.62 and 3.32 A were obtained for the Re-values, respectively.11 Also, our Xe-S bond distance is near the I-S bond distance of 2.67 A for the linear S-I-S unit in [(S7I)2I)]. The calculated charge distribution indicates significant ion-pair character as in all the other HXY molecules observed thus far.1-4 Xenon carries a relatively large positive charge, and the SH group is negatively charged.