UMP2/aug-cc-pVTZ calculations are carried out to investigate the geometry, interaction energy and bonding properties of single-electron triel bond (SETB) interactions in binary X 3 ZCH 3 complexes, where Z = B, Al and X = H, F, Cl, Br, CN, NC, OH and CH 3 . The estimated binding distances are found to be in the range of 2.129–3.321 and 2.358–2.555 A ˚ for X 3 BCH 3 and X 3 AlCH 3 complexes, respectively, which are much smaller than the sum of the van der Waals radii of corresponding interacting atoms. The strength of SETBs strongly depends upon the nature of the Z and X substituents. For a given Z atom, the presence of electron-withdrawing groups such as F or CN in ZX 3 molecule tends to increase the absolute value of interaction energy, while a reverse trend is seen for the electron-donating groups (OH and CH 3 ). According to quantum theory of atoms in molecule, all strong SETB interactions indicate a partially covalent character. The analysis of the intermolecular orbital interactions in the title complexes also indicates that the amount of charge transfer from the single-electron occupied p orbital of radical methyl to the empty p orbital of Z atom increases in the order CN [ NC [ H [ CH 3 [ F [ Cl [ Br [ OH.
