Inverse halogen bonds interactions involving Br in the electronic deficiency systems of CH3＋...Br-Y （Y=H, CCH, CN, NC） have been investigated by B3LYP/6- 311＋＋G（d, p） and MP2/6-311＋＋G（d, p） methods. The calculated interaction energies with basis set super-position error correction of the four IXBs complexes are 218.87, 219.48, 159.18, and 143.05kJ/mol （MP2/6-311＋＋G（d, p））, respectively. The relative stabilities of the four complexes increased in the order： CH3＋ … BrCN〈CH3＋…- BrNC〈CH3＋… BrH≈CH3＋ …BrCCH. Natural bond orbital theory analysis and the chemical shifts calculation of the related atoms revealed that the charges flow from Br-Y to CH3e. Here, the Br of Br-Y acts as both a halogen bond donor and an electron donor. Therefore, compared with conventional halogen bonds, the IXBs complexes formed between Br-Y and CH3＋. Atoms-in-molecules theory has been used to investigate the topological properties of the critical points of the four IXBs structures which have more covalent content.
The optimized geometries of the three complexes between MeH,~ （Me=Na, Mg, Be; n=1 or 2） and Sill4 have been calculated at the B3LYP/6-31 1＋＋g＊＊, MP2/6-31 1＋＋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 SiH4...MgH2 〉 SiH4...NaH 〉 SiH4...BeH2. Natural bond orbital theory （NBO） analysis and the chemical shift calculation of the related atoms revealed that the charges flow from Sill4 to MeHn and the chemical shifts of the interacting H shift to downfield. Here, the Sil-H3 of Sill4 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.
