To better characterize the interactions between the N-phenyl and the benzimidazolyl-phenyl or benzimidazolyl-pentafluorophenyl rings, the natural charges of complexes Ru16-opt and Ru17opt have been computed by natural bond orbital (NBO) analysis (Figure ). In complex Ru16opt, the carbon atoms of both the N-phenyl and benzimidazolyl-phenyl rings display negative charges (in the range -0.217 to -0.260 and -0.227 to -0.250 for the N-phenyl and benzimidazolylphenyl groups respectively). Conversely, in complex Ru17-opt, while the carbon atoms of the Nphenyl rings display negative charges (in the range -0.228 to -0.254), those of the benzimidazolyl-pentafluorophenyl rings display positive charges (in the range 0.300 to 0.393). According to the Hunter and Sanders model applied to complex Ru16, the π electron density on both the Nphenyl and benzimidazolyl-phenyl rings creates a quadrupole moment with a partial negative A molecular orbital (MO) analysis of compounds Ru16-opt and Ru17-opt was also carried out in order to probe a potential intramolecular orbital interaction between the N-phenyl and the backbone-phenyl or -pentafluorophenyl rings. Indeed, when two aromatic rings are near enough to each other, their π orbital overlapping may provide an additional binding force to their stacking interaction (see Figures and for the most representative MOs). For both the Ru16-opt and Ru17-opt complexes, the HOMO-15 orbital is the only molecular orbital involving a small overlapping between the π orbitals of the ipso and ortho carbons of both the N-phenyl and the backbone-phenyl or -pentafluorophenyl rings, respectively. This small overlapping is slightly stronger for Ru17-opt than for Ru16-opt, as confirmed by an NBO analysis showing a slightly stronger second order stabilizing interaction between the N-phenyl and the second decker pentafluorophenyl rings in Ru17-opt ), compared to that between the N-phenyl and the second decker-phenyl rings in Ru16-opt ).