Interaction of a pseudo-π C - C bond with cuprous and argentous chlorides: Cyclopropane"CuCl and cyclopropane"AgCl investigated by rotational spectroscopy and ab initio calculations

Daniel P. Zaleski, John C. Mullaney, Dror M. Bittner, David P. Tew, Nicholas R. Walker*, Anthony C. Legon

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

7 Citations (Scopus)

Abstract

Strongly bound complexes (CH2)3"MCl (M = Cu or Ag), formed by non-covalent interaction of cyclopropane and either cuprous chloride or argentous chloride, have been generated in the gas phase by means of the laser ablation of either copper or silver metal in the presence of supersonically expanded pulses of a gas mixture containing small amounts of cyclopropane and carbon tetrachloride in a large excess of argon. The rotational spectra of the complexes so formed were detected with a chirped-pulse, Fourier transform microwave spectrometer and analysed to give rotational constants and Cu and Cl nuclear quadrupole coupling constants for eight isotopologues of each of (CH2)3"CuCl and (CH2)3"AgCl. The geometry of each of these complexes was established unambiguously to have C2v symmetry, with the three C atoms coplanar, and with the MCl molecule lying along a median of the cyclopropane C3 triangle. This median coincides with the principal inertia axis a in each of the two complexes (CH2)3"MCl. The M atom interacts with the pseudo-π bond linking the pair of equivalent carbon atoms FC (F = front) nearest to it, so that M forms a non-covalent bond to one C - C edge of the cyclopropane molecule. The (CH2)3"MCl complexes have similar angular geometries to those of the hydrogen- and halogen-bonded analogues (CH2)3"HCl and (CH2)3"ClF, respectively. Quantitative details of the geometries were determined by interpretation of the observed rotational constants and gave results in good agreement with those from ab initio calculations carried out at the CCSD(T)(F12∗)/aug-cc-pVTZ-F12 level of theory. Interesting geometrical features are the lengthening of the FC - FC bond and the shrinkage of the two equivalent BC - FC (B = back) bonds relative to the C - C bond in cyclopropane itself. The expansions of the FC - FC bond are 0.1024(9) Å and 0.0727(17) Å in (CH2)3"CuCl and (CH2)3"AgCl, respectively, according to the determined r0 geometries. The C - C bond lengthening is in each case about four times that observed by similar methods in the corresponding complexes of MCl with ethyne and ethene, even though the cyclopropane complexes are more weakly bound than their ethyne and ethene analogues. Reasons for the larger increase in r(CC) in the pseudo-π complexes are discussed.

Original languageEnglish
Article number164314
JournalJournal of Chemical Physics
Volume143
Issue number16
DOIs
Publication statusPublished - 2015

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