Effect of chelate ring and rigidity on Se•••N interactions: a computational study

The intramolecular Se center dot center dot center dot N interactions between the selenium and the nitrogen atom in three series of o-substituted organoselenium compounds has been studied using density functional theory (DFT). The nature and the strength of these interactions and their dependence on substituents, the chelate ring size as well as the rigidity are predicted using a B3LYP/6-31G(d)/LanL2DZ method. The strength of the Se center dot center dot center dot N interactions is found to be dependent on the nature of Se-X (X = Cl, Br, I, SPh, CH2(P)h; Ph: Phenyl) acceptor orbitals and follow the order I. Br. Cl. SPh. CH2Ph. The natural bond orbital (NBO) analysis using DFT methods points to n(N)->sigma*(Se-X) electron delocalization as the key contributing factor towards Se center dot center dot center dot N nonbonding interactions. Both NBO and atoms in molecules (AIM) methods suggest that the intramolecular interaction in the organoselenium compounds is dominantly covalent in nature. Studies on the effect of solvent on the Se center dot center dot center dot N interaction show that a polar solvent stabilizes the Se center dot center dot center dot N interactions by shortening the Se center dot center dot center dot N distances.