An ab initio study on cationic chalcogen bond interactions between F3−H S+ (n= 0–2) and nitrogen bases

Participation of S and Se in hydrogen and chalcogen bonds

The heavier chalcogen atoms S, Se, and Te can each participate in a range of different noncovalent interactions. They can serve as both proton donor and acceptor in H-bonds. Each atom can also act as electron acceptor in a chalcogen bond.

Synergistic and Diminutive Effects between Regium and Aerogen Bonds

The aerogen bond is formed in complexes of HCN-XeF₂ O and C₂ H₄ -XeF₂ O. The lone pair on the N atom of HCN is a better electron donor in the aerogen bond than the π electron on the C=C bond of C₂ H₄ . The coinage substitution strengthens the aerogen bond in MCN-XeF₂ O (M=Cu, Ag, and Au) and its enhancing effect becomes larger in the Au<Cu<Ag pattern. The aerogen bond is further enhanced by the regium bond in C₂ H₂ -MCN-XeF₂ O and C₂ H₄ -MCN-XeF₂ O, but is weakened by the regium bond in MCN-C₂ H₄ -XeF₂ O and C₂ (CN)₄ -MCN-XeF₂ O. Simultaneously, the regium bond is also strengthened or weakened in these triads. The synergistic and diminutive effects between regium and aerogen bonds have been explained by means of charge transfer and electrostatic potentials.

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.

The Many Facets of Chalcogen Bonding: Described by Vibrational Spectroscopy

A diverse set of 100 chalcogen-bonded complexes comprising neutral, cationic, anionic, divalent, and double bonded chalcogens has been investigated using ωB97X-D/aug-cc-pVTZ to determine geometries, binding energies, electron and energy density distributions, difference density distributions, vibrational frequencies, local stretching force constants, and associated bond strength orders. The accuracy of ωB97X-D was accessed by CCSD(T)/aug-cc-pVTZ calculations of a subset of 12 complexes and by the CCSD(T)/aug-cc-pVTZ //ωB97X-D binding energies of 95 complexes. Most of the weak chalcogen bonds can be rationalized on the basis of electrostatic contributions, but as the bond becomes stronger, covalent contributions can assume a primary role in the strength and geometry of the complexes. Covalency in chalcogen bonds involves the charge transfer from a lone pair orbital of a Lewis base into the σ* orbital of a divalent chalcogen or a π* orbital of a double bonded chalcogen. We describe for the first time a symmetric chalcogen-bonded homodimer stabilized by a charge transfer from a lone pair orbital into a π* orbital. New polymeric materials based on chalcogen bonds should take advantage of the extra stabilization granted by multiple chalcogen bonds, as is shown for 1,2,5-telluradiazole dimers.

Modulating of the pnicogen-bonding by a H⋯π interaction: An ab initio study

An ab initio study of the cooperativity in XH₂P⋯NCH⋯Z and XH₂P⋯CNH⋯Z complexes (X=F, Cl, Br, CN, NC; Z=C₂H₂,C₆H₆) connected by pnicogen-bonding and H⋯π interactions is carried out by means of MP2 computational method. A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes considered, a favorable cooperativity is observed, especially in X=F and CN complexes. However, for a given X or Z, the amount of cooperativity effects in XH₂P⋯CNH⋯Z complexes are more important than XH₂P⋯NCH⋯Z counterparts. Besides, the influence of a H⋯π interaction on a P⋯N (C) bond is more pronounced than that of a P⋯N (C) bond on a H⋯π bond. The quantum theory of atoms in molecules shows that ternary complexes have increased electron densities at their bond critical points relative to the corresponding binary systems. The results also indicate that the strength of the P⋯N(C) and H⋯π interactions increases in the presence of the solvent.