Voltammetric and UV to near-IR spectroelectrochemical characterization of the meso, meso'-buta-1, 3-diyne-bridged octaethylporphyrin dimers M (OEP) (. mu. -C4) M (OEP) (M2 = H4, cobalt2, nickel2, copper2, zinc2, palladium2, platinum2, Co/Ni, and Ni/Zn), in their neutral, mononegative, and dinegative oxidation states | Synapse