Complexes of CO₂ with the Azoles: Tetrel Bonds, Hydrogen Bonds and Other Secondary Interactions

• Published in: Molecules (Basel, Switzerland) Switzerland), 2018-04, Vol.23 (4), p.906
• Main Authors: Del Bene, Janet E, Elguero, José, Alkorta, Ibon
• Format: Article
• Language: English
• Subjects: Atomic properties; Azoles; Azoles - chemistry; Carbon dioxide; Carbon Dioxide - chemistry; Charge transfer; Complex formation; Heterocyclic compounds; hydrogen bond; Hydrogen Bonding; Hydrogen bonds; Hydrogen storage; Imidazole; IR spectra; Molecular chains; Molecular Conformation; Pyrazole; spin-spin coupling constants; Symmetry; Tetrazoles; tetrel bond; Thermodynamics; Vibration
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules23040906

Ab initio MP2/aug'-cc-pVTZ calculations have been performed to investigate the complexes of CO₂ with the azoles pyrrole, pyrazole, imidazole, 1,2,3- and 1,2,4-triazole, tetrazole and pentazole. Three types of complexes have been found on the CO₂:azole potential surfaces. These include ten complexes stabilized by tetrel bonds that have the azole molecule in the symmetry plane of the complex; seven tetrel-bonded complexes in which the CO₂ molecule is perpendicular to the symmetry plane; and four hydrogen-bonded complexes. Eight of the planar complexes are stabilized by Nx···C tetrel bonds and by a secondary interaction involving an adjacent Ny-H bond and an O atom of CO₂. The seven perpendicular CO₂:azole complexes form between CO₂ and two adjacent N atoms of the ring, both of which are electron-pair donors. In three of the four hydrogen-bonded complexes, the proton-donor Nz-H bond of the ring is bonded to two C-H bonds, thereby precluding the planar and perpendicular complexes. The fourth hydrogen-bonded complex forms with the strongest acid pentazole. Binding energies, charge-transfer energies and changes in CO₂ stretching and bending frequencies upon complex formation provide consistent descriptions of these complexes. Coupling constants across tetrel bonds are negligibly small, but J(Ny-C) across Nz-H···C hydrogen bonds are larger and increase as the number of N atoms in the ring increases.