The characteristics and structures of single-electron halogen bond complexes [H 3 C⋅⋅⋅Br-Y (Y = H, CCH, CN, NC, C 2 H 3 )] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H 3 C⋅⋅⋅Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH 3 (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a "three-electron bond". Due to the formation of the single-electron Br bond, the C-H bonds of the CH 3 radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.single-electron halogen bond, single-electron hydrogen bond, single-electron lithium bond, MP2, DFT, NBO, AIM

The optimized geometries of the three complexes between MeH n (Me=Na, Mg, Be; n=1 or 2) and SiH 4 have been calculated at the B3LYP/6-311++g**, MP2/6-311++g(3df,3pd) and MP2/aug-cc-pvtz levels, respectively. The red-shift inverse hydrogen bonds (IHBs) based on Si-H, an electron donor, were reported. The calculated binding energies with basis set super-position error (BSSE) correction of the three complexes are 5.98, 8.65 and 3.96 kJ mol 1 (MP2/6-311++g(3df, 3pd)), respectively, which agree with the results obtained via MP2/aug-cc-pvtz (6.18, 9.12 and 4.28 kJ mol 1 , respectively). The relative stabilities of the three complexes are in the order of SiH 4 ···MgH 2 > SiH 4 ···NaH > SiH 4 ···BeH 2 . Natural bond orbital theory (NBO) analysis and the chemical shift calculation of the related atoms revealed that the charges flow from SiH 4 to MeH n and the chemical shifts of the interacting H shift to downfield. Here, the Si1-H3 of SiH 4 acts as both a bond hydrogen donor and an electron donor. Therefore, compared with conventional hydrogen bonds, they formed IHB complexes. Atoms in molecules (AIM) theory have been used to investigate the topological properties of the critical points in the three IHB structures.SiH 4 , metal hydride, inverse hydrogen bond, electron density topological property