Geometries of H2S⋯MI (M = Cu, Ag, Au) complexes studied by rotational spectroscopy: The effect of the metal atom.

Complexes formed between H2S and each of CuI, AgI, and AuI have been isolated and structurally characterised in the gas phase. The H2S⋯MI complexes (where M is the metal atom) are generated through laser vaporisation of a metal rod in the presence of a low concentration of H2S and CF3I in a buffer gas of argon undergoing supersonic expansion. The microwave spectra of six isotopologues of each of H2S⋯CuI, H2S⋯AgI and three isotopologues of H2S⋯AuI have been measured by chirped-pulse Fourier transform microwave spectroscopy. The spectra are interpreted to determine geometries for the complexes and to establish the values of structural parameters. The complexes have Cs symmetry at equilibrium and have a pyramidal configuration about the sulfur atom. The local C2 axis of the hydrogen sulfide molecule intersects the linear axis defined by the three heavy atoms at an angle, ϕ = 75.00(47)° for M = Cu, ϕ = 78.43(76)° for M = Ag, and ϕ = 71.587(13)° for M = Au. The trend in the molecular geometries is consistent with significant relativistic effects in the gold-containing complex. The force constant describing the interaction between the H2S and MI sub-units is determined from the measured centrifugal distortion constant, ΔJ, of each complex. Nuclear quadrupole coupling constants, χaa(M) and χaa(I) (where M denotes the metal atom), are determined for H2S⋯CuI and H2S⋯AuI for the first time.