Conformational Equilibria of 2-Methoxypyridine⋅⋅⋅CO2 : Cooperative and Competitive Tetrel and Weak Hydrogen Bonds.

The rotational spectrum of 2-methoxypyridine⋅⋅⋅CO2 was recorded and analysed employing a cavity-based Fourier transform microwave spectrometer, complemented with quantum chemical calculations which predicted three possible isomers within energies less than 1000 cm-1 . The two most stable isomers were observed in the pulsed jet, which are stabilized by a network of C⋅⋅⋅N/O tetrel and C-H⋅⋅⋅O weak hydrogen bonds. The relative population ratio of the two detected isomers was estimated to be NI /NII ≈2.5. The competition and cooperation of the present non-covalent interactions in both isomers are discussed within the framework of Bader's quantum theory of atoms in molecules and Johnson's non-covalent interaction analyses. The study shows, that when looking for CO2 adsorbents, one might prefer candidates with multiple interactions in one site over candidates with few but strong interactions.