The molecular and electronic structures of the four members, [Cr(tpy)(2)](PF6)(n) (n = 3-0; complexes 1-4; tpy = 2,2':6',2 ''-terpyridine), of the electron transfer series [Cr(tpy)(2)](n+) have been determined experimentally by single-crystal X-ray crystallography, by their electro- and magnetochemistry, and by the following spectroscopies: electronic absorption, Xray absorption (XAS), and electron paramagnetic resonance (EPR). The monoanion of this series, [Cr(tpy)(2)](1-), has been prepared in situ by reduction with KC8 and its EPR spectrum recorded. The structures of 2, 3, 4, 5, and 6, where the latter two compounds are the Mo and W analogues of neutral 4, have been determined at 100(2) K. The optimized geometries of 1-6 have been obtained from density functional theoretical (DFT) calculations using the B3LYP functional. The XAS and low-energy region of the electronic spectra have also been calculated using time-dependent (TD)-DFT. A consistent picture of the electronic structures of these octahedral complexes has been established. All one-electron transfer processes on going from 1 to 4 are ligand-based: 1 is [CrIII(tpy(0))(2)](PF6)(3) (S = 3/2), 2 is [Cr-III(tpy(center dot))(tpy(0))](PF6)(2) (S = 1), 3 is [CrIII(tpy(center dot))(2)](PF6) (S =1/2), and 4 is [Cr-III(tpy(center dot center dot))(tpy(center dot))](0) (S = 0), where (tpy(0)) is the neutral parent ligand, (tpy(center dot))(1-) represents its one-electron-reduced ir radical monoanion, (tpy(2-))(2-) or (tpy(center dot center dot))(2-) is the corresponding singlet or triplet dianion, and (tpy(3-))(3-) (S =1/2) is the trianion. The electronic structure of 2 cannot be described as [Cr-II(tpy(0))(2)](PF6)(2) (a low-spin Cr(II) (d(4); S = 1) complex). The geometrical features (C-C and C-N bond lengths) of these coordinated ligands have been elucidated computationally in the following hypothetical species: [(ZnCl2)-Cl-II(tpy(0))](0) (S = 0) (A), [Zn-II(tpy(center dot))CI(NH3)](0) (S = 1/2) (B), [Zn-II(tpy(2-))(NH3)(2)](0) (S = 0 or 1) (C), and [Al-III(tpy(3-))(NH3)(3)](0) (S = 1/2 and 3/2) (D). The remarkable electronic structure of the monoanion has been calculated and experimentally verified by EPR spectroscopy to be [Cr-III(tpy(2-))(tpy(center dot center dot center dot))](1-) (S = 1/2), a complex in which the two dianionic tpy ligands differ only in the spin state. It has been clearly established that coordinated tpy ligands are redox-active and can exist in at least four oxidation levels.