On the properties of Se⋯N interaction: the analysis of substituent effects by energy decomposition and orbital interaction.

The nature and strength of intermolecular Se⋯N interaction between selenium-containing compounds HSeX (X = CH3, NH2, CF3, OCH3, CN, OH, NO2, Cl, F), and NH3 have been investigated at the MP2/aug-cc-pVDZ level. The Se⋯N interaction is found to be dependent on the substituent groups, which greatly affect the positive electrostatic potential of Se atoms and the accepting electron ability of X-Se σ(∗) antibonding orbital. Energy decomposition of the Se ⋯N interaction reveals that electrostatic and induction forces are comparable in the weak-bonded complexes and induction becomes more significant in the complexes with strong electron-withdrawing substituents. Natural bond orbital (NBO) analysis indicates that the primary source of the induction is the electron transfer from the N lone pair to the X-Se σ(∗) antibonding orbital. The geometry of the complex and the interaction directionality of NH3 to X-Se bond can be regarded as a consequence of the exchange-repulsion. The topological analysis on the electron density reveals the nature of closed-shell interaction in these X-Se⋯N contacts. The Se⋯N interaction in the complexes with the strong electron-withdrawing substituent has a partly covalent character.