A DFT investigation on the electronic properties of octahaloditechnetate anions: Correlation between charge and bond strength

Irregular decrease in Tc-Tc bond length from the Tc2X82− ion to the Tc2X83− ion (X = Cl, Br) was reproduced by DFT calculations using the functional BH&HLYP and basis sets SDD/aug-CC-PVDZ. NBO analyses demonstrated that the decrease in formal charge on the Tc atoms from 3+ to 2.5+ probably resulted in an expansion in orbital size and weaker electrostatic repulsion, which led to better orbital overlap, stronger σ and π bonding and shorter Tc-Tc bond length.79