Figure 4. Charge transfer diagrams.

Shown are calculated charge density difference plots for the interaction between a Cu cation and benzonitrile (PhCN), using (a) the formal charge approach, (b) the reduced charge approach, and (c) the formal charge approach incorporating two ethanol (EtOH) solvent molecules (two views of the same complex are provided for clarity). EtOH donates electron density to Cu²⁺, lowering its effective charge. Electronic charge density depletion from the aromatic ring is significantly reduced in the presence of EtOH, as in the case of the reduced charge model shown in (b). Red represents electron charge accumulation and blue electron charge depletion; an isovalue of 0.005 e Å⁻³ was used to construct the surfaces.