A new intermolecular charge transfer (CT) band at 305 nm has been observed in the UV-visible spectrum between ReH5(PPh3)(3) and the hydroquinone form of p-chloranil in a mixed CH2Cl2-n-hexanes solution. Formation constants (1600 dm(3)/mol at 25 degrees C) have been measured according to a Benesi-Hildebrand treatment and the thermodynamic parameters (-Delta H degrees = 25.8 kJ/mol; -Delta S degrees = 25 J/mol; -Delta G degrees = 18 kJ/mol) have been calculated for this strong CT complexation.