A macrocyclic tetraamido ligand 5,6:(3-pyrido)-12,12-diethyl-2,2,9,9-tetramethyl-3,8,11,13-tetraoxo-1,4,7,10-tetraazacyclotridecane, H(4)1, has been designed to incorporate Co-II and Co-III in the primary coordination site and has a secondary bidentate site, comprising pyridine-N and amido-O donor atoms, that coordinates Lewis acids. The complex PPh4[2] was obtained by deprotonation of H(4)1 with lithium diisopropylamide in the presence of CoCl2, followed by air oxidation and precipitation from water by addition of PPh4Cl. The X-ray crystal structure of PPh4[2] was obtained. The compound crystallizes in the space group PT (No. 2) with unit cell dimensions a = 12.936(4) Angstrom, b = 13.253(5) Angstrom, c = 13.288(2) Angstrom, alpha = 93.75(2)degrees, beta = 90.91(2)degrees, gamma = 91.53(3)degrees, V = 2272.1(1.2) Angstrom (3), and Z = 2. Lewis acids can be bound either reversibly as in the case of alkali and alkaline earth cations or irreversibly as found for [(bpy)(2)Ru](2+) (bpy is 2,2'-bipyridine) and [(Me(2)bpy)(2)Ru](2+) (Me(2)bpy is 4,4'-(CH3)(2)-2,2'-bipyridine). The Lewis acid in the secondary coordination site broadly modifies the chemistry at Co-III and Co-II in [2](-) and [2](2-), respectively. The axial binding affinity of the Co-III center for 1-CH3-imidazole was 1 to 2 orders of magnitude larger when divalent Lewis acids were in the secondary coordination site than that for [2](-). The reactivities of [2](2-), Ca2+/[2](2-), and [(bpy)(2)Ru[2]] toward O-2 were significantly different. The reaction of [2](2-) with O-2 rapidly generated [2](-), apparently by an outer-sphere electron-transfer pathway. In contrast, the oxidation of Ca2+/[2](2-) by O-2 was a complex reaction in which some of the Ca2+ was consumed and the final species depended on the amount of Ca2+ present at the start of the reaction. Finally, in the case of [(bpy)2Ru[2]], it appeared as though the dinuclear complex [(bpy)(2)Ru[2]](2)(mu -O-2) formed upon reaction with O-2.