# Changes in the Geometries of C_{2}H_{2} and C_{2}H_{4} on Coordination to CuCl Revealed
by Broadband Rotational Spectroscopy and ab-Initio Calculations

journal contribution

posted on 06.10.2014, 00:00 by Susanna
L. Stephens, Dror M. Bittner, Victor A. Mikhailov, Wataru Mizukami, David P. Tew, Nicholas R. Walker, Anthony C. LegonThe molecular geometries
of isolated complexes in which a single
molecule of C

_{2}H_{4}or C_{2}H_{2}is bound to CuCl have been determined through pure rotational spectroscopy and ab-initio calculations. The C_{2}H_{2}···CuCl and C_{2}H_{4}···CuCl complexes are generated through laser vaporization of a copper rod in the presence of a gas sample undergoing supersonic expansion and containing C_{2}H_{2}(or C_{2}H_{4}), CCl_{4}, and Ar. Results are presented for five isotopologues of C_{2}H_{2}···CuCl and six isotopologues of C_{2}H_{4}···CuCl. Both of these complexes adopt*C*_{2v}, T-shaped geometries in which the hydrocarbon binds to the copper atom through its π electrons such that the metal is equidistant from all H atoms. The linear and planar geometries of free C_{2}H_{2}and C_{2}H_{4}, respectively, are observed to distort significantly on attachment to the CuCl unit, and the various changes are quantified. The ∠(*−C–H) parameter in C_{2}H_{2}(where * indicates the midpoint of the CC bond) is measured to be 192.4(7)° in the*r*_{0}geometry of the complex representing a significant change from the linear geometry of the free molecule. This distortion of the linear geometry of C_{2}H_{2}involves the hydrogen atoms moving away from the copper atom within the complex. Ab-initio calculations at the CCSD(T)(F12*)/AVTZ level predict a dihedral ∠(HCCCu) angle of 96.05° in C_{2}H_{4}···CuCl, and the experimental results are consistent with such a distortion from planarity. The bonds connecting the carbon atoms within each of C_{2}H_{2}and C_{2}H_{4}, respectively, extend by 0.027 and 0.029 Å relative to the bond lengths in the isolated molecules. Force constants,*k*_{σ}, and nuclear quadrupole coupling constants, χ_{aa}(Cu), [χ_{bb}(Cu) – χ_{cc}(Cu)], χ_{aa}(Cl), and [χ_{bb}(Cl) – χ_{cc}(Cl)], are independently determined for all isotopologues of C_{2}H_{2}···CuCl studied and for four isotopologues of C_{2}H_{4}···CuCl.