A prototype transition-metal olefin complex C_2H _4?AgCl synthesised by laser ablation and characterised by rotational spectroscopy and ab initio methods

摘要

C_2H_4?Ag-Cl has been synthesised in the gas phase in a pulsed-jet, Fourier-transform microwave spectrometer by the reaction of laser-ablated metallic silver with carbon tetrachloride to give AgCl, which subsequently reacts with ethene to give the complex. The ground-state rotational spectra of six isotopologues (C_2H_4? ~(107)Ag~(35)Cl, C_2H_4? ~(109)Ag~(35)Cl, C_2H_4? ~(107)Ag~(37)Cl, C_2H_4? ~(109)Ag~(37)Cl, ~(13)C_2H_4~(107)Ag~(35)Cl, and ~(13)C_2H _4~(109)Ag~(35)Cl) were recorded and analysed to give rotational constants A_0, B_0, and C_0, centrifugal distortion constants ΔJ and ΔJK, and Cl nuclear quadrupole coupling constants _(aa)(Cl) and _(bb)(Cl) - _(cc)(Cl). These spectroscopic constants were interpreted in terms of a geometry for C_2H_4Ag-Cl of C _(2V) symmetry in which the AgCl molecule lies along the C_2 axis of ethene that is perpendicular to the C_2H_4 plane. The Ag atom forms a bond to the midpoint of the ethene bond. A partial r _s-geometry and a r_0-geometry were determined, with the values r(*?Ag) = 2.1719(9)?, r(C-C) 1.3518(4) ?, and r(Ag-Cl) 2.2724(8) ? obtained in the latter case. The C-C bond lengthens on formation of the complex. Detailed ab initio calculations carried out at the CCSD(T)cc-pVQZ level of theory give results in good agreement with experiment and also reveal that the ethene molecule undergoes a small angular distortion. The distortion is such that the four H atoms move in a direction away from Ag but remain coplanar. The two C atoms are no longer contained in this plane, however. The electric charge redistribution when C_2H _4?Ag-Cl is formed and the strength of the π ? Ag bond are discussed.