The encumbering m-terphenyl isocyanide ligand, CNArMes2 (Mes = 2,4,6-Me3C6H2), is used to stabilize homoleptic tetraisocyanide complexes of cobalt in the 1-, 0, and 1+ charge state. Most importantly, these complexes serve as isolable analogues of the binary carbonyl complexes [Co(CO)(4)](-), Co(CO)(4), and [Co(CO)(4)](+). Sodium amalgam reduction of CoCl2 in the presence of CNArMes2 provides the salt Na[Co(CNArMes2)(4)], which can be oxidized with 1 equiv of ferrocenium triflate (FcOTf) to the neutral complex, Co(CNArMes2)(4). X-ray diffraction, FTIR spectroscopy, and low-temperature EPR spectroscopy reveal that Co(CNArMes2)(4) modulates between D-2d- and C-2v-symmetric forms. DFT calculations are used to rationalize this structural modulation in terms of thermal access to low-energy b(2)-symmetric C-Co-C bending modes. Treatment of Na[Co(CNArMes2)(4)] with 2 equiv of FcOTf, followed by addition of Na[BAr4F], provides the salt [Co(CNArMes2)(4)]BAr4F, which contains a diamagnetic, square planar monovalent cobalt center. The molecular and electronic structures of [Co(CNArMes2)(4)]BAr4F are compared and contrasted to the reported properties of the carbonyl cation, [Co(CO)(4)](+).