Observation of a double C-H[small pi] interaction in the CH2ClFHCCH weakly bound complex

• Published in: Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (31), p.14043-14049
• Main Authors: Elmuti, Lena F, Peebles, Rebecca A, Peebles, Sean A, Steber, Amanda L, Neill, Justin L, Pate, Brooks H
• Format: Article
• Language: English
• Subjects: Acetylene; Chlorine; Constants; Holes; Hydrogen atoms; Mathematical analysis; Microwave spectroscopy; Quadrupole interaction
• ISSN: 1463-9076
• DOI: 10.1039/C1CP20684B

The structure of the CH2ClFHCCH dimer has been determined using both chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy. The complex has Cs symmetry and contains both a double C-H[small pi] interaction, in which one [small pi]-bond acts as acceptor to two hydrogen atoms from the CH2ClF donor, and a weak C-HCl interaction, with acetylene as the donor. Analysis of the rotational spectra of four isotopologues (CH235ClFH12C12CH, CH237ClFH12C12CH, CH235ClFH13C13CH, and CH237ClF-H13C13CH) has led to a structure with C-H[small pi] distances of 3.236(6) A and a C-HCl distance of 3.207(22) A, in good agreement with ab initio calculations at the MP2/6-311++G(2d,2p) level. Both weak contacts are longer than those observed in similar complexes containing a single C-H[small pi] interaction that lies in the Cs plane; however, this appears to be the first double C-H[small pi] contact to be studied by microwave spectroscopy, so there is little data for direct comparison. The rotational and chlorine nuclear quadrupole coupling constants for the most abundant isotopologue are: A = 5262.899(14) MHz, B = 1546.8074(10) MHz, C = 1205.4349(7) MHz, [small chi]aa = 28.497(5) MHz, [small chi]bb = -65.618(13) MHz, and [small chi]cc = 37.121(8) MHz.