Computational evidence that hyperconjugative orbital interactions are responsible for the stability of intramolecular Te⋯O/Te⋯S non-covalent interactions and comparable to hydrogen bonds in quasi-cyclic systems
Non-covalent interactions involving chalcogens play a significant role in chemistry and biology. However, tellurium has received scant attention compared to other chalcogens. The importance of tellurium compounds in inorganic and organic chemistry prompted us to examine the non-covalent interactions involving this maverick element. The 1,5-intramolecular interaction (Y → X, Y = O, S & X = Te–H/Te–F) with tellurium showed remarkable stability throughout the non-covalent interactions. The DFT M06-2X/aug-cc-pVQZ level of calculations reveals that the strength of such interactions are comparable to and/or stronger than the hydrogen bonding interactions arising from analogous systems. The hydrogen bonding interaction energies with sulphur and oxygen atoms in 1,5-intramolecular interactions (N–H⋯O & N–H⋯S) are 30 and 29 kJ mol−1, respectively, however the non-covalent interactions involving tellurium (Y → X, Y = O, S & X = Te–H) in such systems are ∼28 and 32 kJ mol−1, respectively. The strength of Te⋯O and Te⋯S interactions can be modulated through substituent effects. An electron withdrawing substituent can enhance the interaction dramatically compared to an electron donating group. Importantly, the AIM and NBO analyses reveal that the hyperconjugative interaction involving Y → X (Y = O, S & X = Te–H/F) contributes to enhance such an interaction compared to the electrostatic effect. Further, the Te⋯S interaction energy has been found to be 31.9 kJ mol−1 calculated at the M06-2X/aug-cc-pVQZ level of theory, and stronger than the Te⋯O interaction (27.7 kJ mol−1). The lighter chalcogens, such as oxygen and sulphur show an opposite trend with larger a contribution from electrostatic interactions. The calculations performed for σ-hole bonds of these quasi-cyclic chalcogen systems suggest that such an interaction also contributes to stabilize the Te⋯O and Te⋯S interactions. The impact of such stronger non-covalent interactions involving tellurium in supramolecular assembly/aggregation would be important to augment the rigidity in such systems and can compete with the typically-known hydrogen bonds.