The syntheses of cationic, four-coordinate cobalt(III) complexes, [Co(TC-3,3)](+) and [Co(TC4,4)](+), afforded by the tetraazamacrocyclic tropocoronand ligand [(TC-n,m)](2-), are described. The [Co(TC-4,4)](+) cation displays a unique geometry for tetracoordinate Co(III) between square-planar and tetrahedral. The reduction potentials and Lewis acidity of the [Co(TC-n,m)] tropocoronands, together with an extended Huckel MO analysis of the frontier orbitals, demonstrate electronic tuning through geometric variations imposed by the ligands.