The syntheses and characterization of [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenylporphinato]cobalt, Co(F28TPP), and [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphinato]cobalt, Co(F28TPP), are reported. Co(F28TPP). 2tol (tol = toluene) crystallizes in the monoclinic space group C2/c-C-h (No. 15) with a = 22.1616(5) Angstrom, b = 12.0274(3) Angstrom, c = 19.9159(2) Angstrom, beta = 110.635(1)degrees, V= 4967.6(2) Angstrom(3), and Z = 4 {d(calcd) = 1.818 g/cm(3); mu(a)(Mo K alpha) = 0.50 mm(-1)}, and Co(F28TPP). 2THF crystallizes in the triclinic space group P (1) over bar (No. 2) with a = 11.0691(1) Angstrom, b = 12.0451(1) Angstrom, c = 12.9558(2) Angstrom, alpha = 62.531(1)degrees, beta = 69.544(1)degrees, gamma = 76.181(1)degrees, V = 1429.71(3) Angstrom(3) and Z = 1 {d(calcd) = 1.700 g/cm(3); mu(a)(Mo K alpha) = 0.45 mm(-1)}. A comparison of the X-ray crystal structure data from Co(F28TPP). 2THF and Co(F28TPP). 2THF indicates that the porphyrin core expands dramatically (0.08 Angstrom) in the six-coordinate complex. Optical and F-19 NMR spectroscopic studies of Co(F28TPP) in the presence of added ligand demonstrate that spin-state modulation of the six-coordinate Co(II) center is facile. Partial population of the E-4(g), State is accessed upon coordination of the cobalt center with THF sigma-donor ligands, while six-coordinate complexes with 1-methylimidazole result in complete conversion to the high spin state, as evinced by 280 ppm downfield chemical shifts for the beta-fluorine resonances in the F-19 NMR spectrum. Co(F28TPP) is the first example of a porphyrin which supports a high-spin cobalt ion.