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

Abstract

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 2hJ(Ny-C) across Nz-H···C hydrogen bonds are larger and increase as the number of N atoms in the ring increases.

Versatility of the Cyano Group in Intermolecular Interactions

“…Nor is there a limitation to planar geometries, as π-holes are also common in linear molecules, such as the area above the C atom of CO 2 [ 42 , 43 , 44 , 45 , 46 , 47 , 48 ], OCS [ 49 , 50 , 51 ], N 2 O, and CS 2 [ 52 , 53 , 54 ]. Just as their σ-hole analogs facilitate attractions toward a nucleophile, the same is true of these π-holes.…”

Sequestration of CO2by Phosphatrane Molecules

“…A few isolated systems (carbenes, guanidines and more recently phosphines) or combined in the form of frustrated Lewis pairs have been described to be able to react with CO 2 and form covalent aggregates . The mechanism and environment effect of the sequestration and activation of CO 2 has been studied theoretically by different groups …”

“…[11,12] The mechanism and environment effect of the sequestration and activation of CO 2 has been studied theoretically by different groups. [13][14][15][16][17][18][19][20] Phosphatrane molecules are a tricyclic cage-like heterocycles which present the possibility to have a transannular dative bond with a nitrogen or another heteroatom. The pioneer synthetic work in the groups of Alder and Verkade [21][22][23][24][25][26][27][28][29] showed that depending of the size, substituents and environment they can adopt out:out and/or in:out conformations.…”

Strong Tetrel Bonds: Theoretical Aspects and Experimental Evidence

“…The binding distances and interaction energies of these complexes are listed in Table 1 . According to the previous studies [ 37 , 62 , 65 , 67 , 84 , 85 ], the formation of such anionic tetrel-bonding interactions can be largely attributed to the localization of a positive electrostatic potential over the M atom, in the extension of the M-X bond. Indeed, the MEP analysis of XF 3 M monomers in Figure 1 reveals that the maximum positive electrostatic (V S,max ) of the Sn atom (96.5 kcal/mol) in SnF 4 is greater than that of Ge (70.2 kcal/mol) and Si (57.3 kcal/mol) in GeF 4 and SiF 4 , respectively.…”