Characterization of C–H⋯π interactions in the structure of the CHClF2–HCCH weakly bound complex

Abstract

The microwave spectra of four isotopologues of the CHClF₂–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 ³⁵Cl and ³⁷Cl isotopologues, with two additional H¹³C¹³CH 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 CHClF₂ 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 CHClF₂ hydrogen atom and the center of the triple bond is 2.730(6) Å, the distance between the chlorine atom and the acetylenic hydrogen is 3.061(38) Å, 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.