title: A cryospectroscopic infrared and Raman study of the CX⋯π halogen bonding motif: complexes of the CF3Cl, CF3Br, and CF3I with ethyne, propyne and 2-butyne.
abstract: Experimental information on the C-X⋯π halogen bonding motif was obtained by studying the formation of molecular complexes of CF3Cl, CF3Br and CF3I with ethyne, propyne and 2-butyne in liquid krypton, using FTIR and Raman spectroscopy. For CF3Br, experimental evidence was found for the formation of 1:1 complexes with propyne and 2-butyne only, while for CF3I spectroscopic features confirming the existence of the halogen bonded complexes were observed for ethyne, propyne and 2-butyne. In addition, at higher concentrations of CF3I and 2-butyne, weak absorptions due to a 2:1 complex were also observed. The experimental complexation enthalpies, obtained by using spectra recorded at temperatures between 120 K and 140 K, are -5.9(3) kJ mol(-1) for CF3I.ethyne, -5.6(3) kJ mol(-1) for CF3Br.propyne, -8.1(2) kJ mol(-1) for CF3I.propyne, -7.3(2) kJ mol(-1) for CF3Br.2-butyne, -10.9(2) kJ mol(-1) for CF3I.2-butyne and -20.9(7) kJ mol(-1) for (CF3I)2.2-butyne. The experimental study is supported by theoretical data obtained from ab initio calculations at the MP2/aug-cc-pVDZ(-PP) and MP2/aug-cc-pVTZ(-PP) levels, and Monte Carlo Free Energy Perturbation (MC-FEP) simulations. The experimental and theoretical values on the C-X⋯π halogen-bonding motifs studied are compared with previously reported data for the complexes with ethene and propene and with preliminary results obtained for benzene and toluene.
authors.affiliation: Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Nick
authors.initials: N
authors.lastname: Nagels
authors.affiliation: Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium. Electronic address: wouter.herrebout@ua.ac.be.
authors.forename: Wouter A
authors.initials: WA
authors.lastname: Herrebout
mesh_terms: D000114:Acetylene / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry*; D001554:Benzene / Q000737:chemistry; D064228:Bromochlorofluorocarbons / Q000737:chemistry*; D017402:Chlorofluorocarbons / Q000737:chemistry; D006219:Halogens / Q000737:chemistry; D006846:Hydrocarbons, Halogenated / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D009010:Monte Carlo Method; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature; D013816:Thermodynamics; D014050:Toluene
chemical_list: D000480:Alkynes; D064228:Bromochlorofluorocarbons; D017402:Chlorofluorocarbons; D006219:Halogens; D006846:Hydrocarbons, Halogenated; C022030:methylacetylene; D014050:Toluene; C105057:trifluoroiodomethane; C034013:bromotrifluoromethane; D001554:Benzene; D000114:Acetylene
keywords: CX⋯π halogen bonding; Cryosolutions; Halogen bonding motifs; Infrared; Raman