Characterization of C-H π interactions in the structure of the CHClF2-HCCH weakly bound complexElectronic supplementary information (ESI) available: All fitted transition frequencies; principal axis coordinates for experimental and ab initio structures. See DOI: 10.1039/c0cp00924e

• Main Authors: Sexton, John M, Elliott, Ashley A, Steber, Amanda L, Peebles, Sean A, Peebles, Rebecca A, Neill, Justin L, Muckle, Matt T, Pate, Brooks H
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c0cp00924e

The microwave spectra of four isotopologues of the CHClF 2 -HCCH dimer have been measured and used to determine the structure of the complex. An initial scan over the 7-18 GHz region using the chirped-pulse microwave spectrometer at the University of Virginia provided initial assignments of the 35 Cl and 37 Cl isotopologues, with two additional H 13 C 13 CH species assigned using the resonant cavity Balle-Flygare microwave spectrometer at Eastern Illinois University. For the most abundant isotopologue, the rotational constants and quadrupole coupling constants are: A = 3301.21(4) MHz, B = 1353.4268(19) MHz, C = 1153.7351(18) MHz, χ aa = 34.681(12) MHz, χ bb = −69.70(3) MHz, χ cc = 35.02(2) MHz and χ ab = −8.8(3) MHz, in good agreement with ab initio calculations at the MP2/6-311++G(2d,2p) level. The alignment of CHClF 2 with respect to acetylene reveals a C-H π interaction, with a secondary C-Cl H-C interaction also present between the two monomers. The fitted distance between the CHClF 2 hydrogen atom and the center of the triple bond is 2.730(6) , the distance between the chlorine atom and the acetylenic hydrogen is 3.061(38) , and the C-H π angle is 148.2(6)°. In addition, the centrifugal distortion constants give an estimate of the binding energy for the weak interaction of about 4.9(5) kJ mol −1 , in reasonable agreement with several similar complexes. Chirped-pulse and cavity FT microwave spectroscopy reveal C-H π and C-H Cl-C interactions in the CHClF 2 -HCCH dimer.