Hydrogen bonding in neutral and cation dimers of H2Se with H2O, H2S, and H2Se.

Structures, hydrogen bonding, and binding energies of H(4)SeA (A = O, S, Se) dimers and their cation radicals have been studied using DFT-B3LYP, MP2, and CCSD methods with 6-31++G(d,p), cc-pVTZ, and aug-cc-pVTZ basis sets. The binding energy (BE) order of the most stable neutral and cationic dimers have been found to be (H(2)Se···HOH) > (H(2)Se···HSH) > (H(2)Se···HSeH), and (H(2)Se···SeH(2))(+) > (H(2)Se···SH(2))(+) > (HSe···HOH(2))(+), respectively, by B3LYP/6-31++G(d,p) and MP2/aug-cc-pVTZ methods. Higher electronegativity of the heteroatom has been found to result in more stability of the neutral dimer but less of the cationic dimer. Among neutral dimers, structure with more electronegative heteroatom acting as proton donor has been found to be more stable. However, the hemibonded structure has been found to be more stable for the dimer cation radical unless the ionization potentials of the involved heteroatoms are very different, e.g., H(4)SeO(+). Vibrational frequency calculation suggests that an increase in electronegativity of A-atom results in a decrease in Se-H bond strength in H(4)SeA and H(4)SeA(+) dimers. The calculated values of Mulliken atomic charge/spin and hydrogen bond lengths of the dimers and their radical cations have also been discussed.