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 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-Hπ interaction, with a secondary C-ClH-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) Å, the distance between the chlorine atom and the acetylenic hydrogen is 3.061(38) Å, and the C-Hπ 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.

Reduced bandwidth chirped-pulse microwave spectroscopy for analysis of weakly bound dimers: Rotational spectrum and structural analysis of CH2ClF⋯FHCCH2

“…Weakly bound dimers serve as prototype systems for weak CAHÁ Á ÁX interactions, where the polarity of the CAH bond can be tuned by varying the number and type of electronegative substituents to the carbon atom. While many studies have focused on complexes of CH 3 F [1][2][3], CH 2 F 2 [4][5][6][7][8][9][10][11], and CHF 3 (for example: [2,[12][13][14][15][16][17][18][19]) as the proton donor, more recent investigations have examined a variety of hydrochlorofluorocarbons as CAH donors [20][21][22][23][24][25]. In most of the halogenated methane complexes, cyclic structures have been observed in which a halogen atom also acts as a weak hydrogen bond acceptor.…”

“…At Eastern Illinois University (EIU), we have recently investigated a series of dimers of CH 2 F 2 [4,6,7], CHF 3 [12][13][14], CH 2 ClF [21,24], CHClF 2 [20,22] (and CHBrF 2 [26]) with acetylene and ethylene. All species in this series that have been studied so far have displayed weak CAHÁ Á Áp interactions.…”

A chirped pulse Fourier transform microwave study of the refrigerant alternative 2,3,3,3-tetrafluoropropene

“…1. 1 For averaging a large number of FID signals in the time domain to improve spectrometer sensitivity, the phase stability of all of the microwave signals and the temporal stability of associated timing and triggering pulses is critical. The microwave phase stability is tied to the 100 MHz time base of the LeCroy oscilloscope, which provides an external reference for both the Tektronix 7101 AWG and the PDRO, as shown by the dashed (blue) lines in Fig.…”

“…The co-planarity of the C, H and F1 atoms is consistent with that commonly observed in an ethylenic moiety, while a favorable intramolecular electrostatic interaction is responsible for placing F2 in the same plane. Indeed, a relaxed scan in which the F2-C3-C2-C1 dihedral angle is varied from 0°to 110°in 10°steps [24] while the remain- 1 For interpretation of color in Figs. 1 and 2, the reader is referred to the web version of this article.…”

“…The chirped pulse, Fourier transform microwave, CP-FTMW, spectroscopy technique recently developed by Brooks Pate and coworkers is a productive tool for studying structure, properties and dynamics of polar molecules that can be entrained in a supersonic expansion [1][2][3][4][5][6][7]. This paper presents initial results from a newly constructed CP-FTMW instrument at Amherst College.…”