The synthesis, spectroscopic properties, and electrochemistry of six different alkyl- and aryl-substituted Co(III) corroles are presented. The investigated compounds contain methyl, ethyl, phenyl, or substituted phenyl groups at the eight beta -positions of the corrole macrocycle and four derivatives also contain a phenyl group at the 10-meso position of the macrocycle. Each cobalt corrole undergoes four reversible oxidations in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate and exists as a dimer in its singly and doubly oxidized forms. The difference in potential between the first two oxidations is associated with the degree of interaction between the two corrole units of the dimer and ranges from an upper value of 0.62 V, in the case of (Me(6)Et(2)Cor)Co, to a lower value of about 0.17 V, in the case of four compounds which have a phenyl group located at the 10-meso position of the macrocycle. These Co(III) corroles strongly coordinate two pyridine molecules or one carbon monoxide molecule in CH2Cl2 media, and ligand binding constants were evaluated using spectroscopic and electrochemical methods. The structure Of (MC(4)Ph(5)Cor)Co(py)(2) was also determined by X-ray diffraction. Crystal data: (Me(4)Ph(5)Cor)Co(py)(2). 3CH(2)Cl(2).H2O, orthorhombic, a = 19.5690(4) Angstrom, b = 17.1070(6) Angstrom, c = 15.9160(6) Angstrom, V =5328.2(5) Angstrom (3), space group Pna2(1), Z = 2, 35 460 observations, R(F) = 0.069.