Microwave spectrum and structure of the 3,5-difluoropyridine...CO2 van der Waals complex

The rotational spectrum of the weakly bound complex 3,5-difluoropyridine...CO2 has been observed using pulsed-nozzle Fourier transform microwave spectroscopy. Spectroscopic constants are reported for the parent and (CO2)-C-13 isotopologues. The data indicate a planar structure in which the nitrogen approaches the carbon of the CO2 with either a C-2v or effectively C-2v geometry in the ground vibrational state. The N...C van der Waals bond distance is 2.8245(16) angstrom and the oxygen...ortho-hydrogen distance is 3.091(2) angstrom. The N...C van der Waals bond length is 0.027(8) angstrom longer than that previously determined for pyridine-CO2, but is still considerably shorter than the 2.998 angstrom distance in HCN...CO2. M06-2X/6-311 ++G(3df,3pd) calculations place the binding energy of the complex at 4.3 kcal/mol (4.1 kcal/mol with counterpoise correction). The calculations further indicate that a secondary interaction between the ortho-hydrogens of the ring and the CO2 oxygens account for similar to 50% of the total binding energy. (C) 2016 Elsevier Inc. All rights reserved.