19F NMR and Structural Evidence for Spin-State Modulation of Six-Coordinate Cobalt(II) in a Weak Field Porphyrin Ligand(1).
The syntheses and characterization of [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenylporphinato]cobalt, Co(F(8)TPP), and [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphinato]cobalt, Co(F(28)TPP), are reported. Co(F(28)TPP).2tol (tol = toluene) crystallizes in the monoclinic space group C2/c-C(h)() (No. 15) with a = 22.1616(5) Å, b = 12.0274(3) Å, c = 19.9159(2) Å, beta = 110.645(1) degrees, V = 4967.6(2) Å(3), and Z = 4 {d(calcd) = 1.818 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.50 mm(-)(1)}, and Co(F(28)TPP).2THF crystallizes in the triclinic space group P&onemacr; (No. 2) with a = 11.0691(1) Å, b = 12.0451(1) Å, c = 12.9558(2) Å, alpha = 62.531(1) degrees, beta = 69.544(1) degrees, gamma = 76.181(1) degrees, V = 1429.71(3) Å(3) and Z = 1 {d(calcd) = 1.700 g/cm(3); &mgr;(a)(Mo Kalpha) = 0.45 mm(-)(1)}. A comparison of the X-ray crystal structure data from Co(F(28)TPP).2tol and Co(F(28)TPP).2THF indicates that the porphyrin core expands dramatically (0.08 Å) in the six-coordinate complex. Optical and (19)F NMR spectroscopic studies of Co(F(28)TPP) in the presence of added ligand demonstrate that spin-state modulation of the six-coordinate Co(II) center is facile. Partial population of the (4)E(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 (19)F NMR spectrum. Co(F(28)TPP) is the first example of a porphyrin which supports a high-spin cobalt ion.
Smirnov
Valeriy V.
VV
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0304.
Woller
Eric K.
EK
DiMagno
Stephen G.
SG