Theoretical investigation on the effect of different nitrogen donors on intramolecular Se...N interactions

The effect of different donor nitrogen atoms on the strength and nature of intramolecular Se...N interactions is evaluated for organoselenium compounds having N,N-dimethylaminomethyl (dime), oxazoline (oxa) and pyridyl (py) substituents. Quantum chemical calculations on three series of compounds [2-(dime)C(6)H(4)SeX (1 a-g), 2-(oxa)C(6)H(4)SeX (2 a-g), 2-(py)C(6)H(4)SeX (3 a-g); X=Cl, Br, OH, CN, SPh, SePh, CH(3)] at the B3LYP/6-31G(d) level show that the stability of different conformers depends on the strength of intramolecular nonbonded Se...N interactions. Natural bond orbital (NBO), NBO deletion and atoms in molecules (AIM) analyses suggest that the nature of the Se...N interaction is predominantly covalent and involves nN-->sigma*(Se--X) orbital interaction. In the three series of compounds, the strength of the Se...N interaction decreases in the order 3>2>1 for a particular X, and it decreases in the order Cl>Br>OH>SPh approximately CN approximately SePh>CH(3) for all the three series 1-3. However, further analyses suggest that the differences in strength of Se...N interaction in 1-3 is predominantly determined by the distance between the Se and N atoms, which in turn is an outcome of specific structures of 1, 2 and 3, and the nature of the donor nitrogen atoms involved has very little effect on the strength of Se...N interaction. It is also observed that Se...N interaction becomes stronger in polar solvents such as CHCl(3), as indicated by the shorter r(Se...N) and higher E(Se...N) values in CHCl(3) compared to those observed in the gas phase.