An ab initio study on properties of cationic chalcogen bonds in XF2Y+⋯NCZ (X═H, CN, F; Y═S, Se; Z═H, Cl, Br) complexes

Theoretical Investigation of Cyano-Chalcogen Dimers and Their Importance in Molecular Recognition

In this manuscript the different noncovalent interactions established between (HYCN)₂ dimers (Y=S, Se and Te) have been studied at the MP2 and CCSD(T) level of theory. Several homodimers have been taken into account, highlighting the capacity of these compounds to act both as electron donor and acceptor. The main properties studied were geometries, binding energy (E_b ), and molecular electrostatic potential (MEP). Given the wide application of chalcogen bonds, and more specifically of cyano-chalcogen moieties in molecular recognition, natural bond orbital (NBO), "atoms-in-molecules" (AIM), and electron density shift (EDS) analysis were also used to analyse the different noncovalent interactions upon complexation. The presence of hydrogen, chalcogen and dipole-dipole interactions was confirmed and their implications on molecular recognition were analysed.

Complexes of O=C=S with Nitrogen Bases: Chalcogen Bonds, Tetrel Bonds, and Other Secondary Interactions

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate chalcogen-bond formation through the σ-hole at S and tetrel-bond formation through the π-hole at C in complexes of OCS with a series of nitrogen bases. The binding energies of chalcogen- and tetrel-bonded complexes with the sp-hybridized bases correlate exponentially with the N-S and N-C distances, respectively. The presence of secondary interactions between an N-H or C-H group of an sp2 -hybridized base and OCS in chalcogen-bonded complexes decreases the correlation between binding energies and the N-S distance. These secondary interactions are stronger in the tetrel-bonded complexes with the sp2 bases, particularly in the isomers of OCS:imidazole and OCS : N2 H2 , where they may be described as distorted N-H⋅⋅⋅O or N-H⋅⋅⋅S hydrogen bonds. Charge-transfer interactions are consistent with the nature of the primary and secondary interactions in these complexes. The in-plane OCS bending frequencies are blue-shift in the chalcogen-bonded complexes, and red-shifted in the tetrel-bonded complexes. EOM-CCSD spin-spin coupling constants 1c J(N4-S) across chalcogen bonds have absolute values less than 9.0 Hz, while the two-bond coupling constants 2c J(N4-C) do not exceed 4.0 Hz. These are greater in absolute value that the one-bond coupling constants 1t J(N4-C) across tetrel bonds that are less than 0.5 Hz at much shorter N-C distances.