An Isolated Complex of Ethyne and Gold Iodide Characterized by Broadband Rotational Spectroscopy and Ab initio Calculations

A molecular
complex of C2H2 and AuI has been
generated and isolated in the gas phase through laser ablation of
a gold surface in the presence of an expanding sample containing small
percentages of C2H2 and CF3I in a
buffer gas of argon. Rotational, B0, centrifugal
distortion, ΔJ and ΔJK, and nuclear quadrupole coupling constants, χaa(Au), χbb(Au) – χcc(Au), χaa(I), and χbb(I) – χcc(I), are
measured for three isotopologues of C2H2···AuI
through broadband rotational spectroscopy. The complex is C2v and T-shaped with C2H2 coordinating to the gold atom via donation of
electrons from the π-orbitals of ethyne. On formation of the
complex, the CC bond of ethyne extends by 0.032(4) Å
relative to r(CC) in isolated ethyne when
the respective r0 geometries are compared.
The geometry of ethyne distorts such that ∠(*CH)
(where * indicates the midpoint of the CC bond) is 194.7(12)°
in the r0 geometry of C2H2···AuI. Ab initio calculations
at the CCSD­(T)­(F12*)/AVTZ level are consistent with the experimentally
determined geometry and further allow calculation of the dissociation
energy (De) as 136 kJ mol–1. The χaa(Au) and χaa(I) nuclear quadrupole coupling constants of AuI
and also the AuI bond length change significantly on formation
of the complex consistent with the strong interaction calculated to
occur between C2H2 and AuI.