Redox reactivity of photogenerated pentacarbonylchromium species: formation of [Cr(III)(o-semiquinone)3] complexes

Abstract

The metal hyperfine parameters \AZ\ = 645 X 10"4 cm"1 and \ ^\ = 697 X 10"4 cm"1 of the CuF2 molecule17 are almost isotropic and far higher than those of K2Zn[Cu]F4, or almost all other copper(II) complexes, clearly implying a significant unpaired spin density in the copper 4s orbital. The gxy value of 2.601 suggests an orbital contribution µ = 0.112 for CuF2, yielding "best fit" estimates of the hyperfine constants Az = 684 X 10"4 cm"1 and Axy = 657 X 10"4 cm"1 using a value of K = -1.5. This implies an occupancy of the 4s orbital of ~33%, some 10 times that in K2Zn[Cu]F4. Simple theory suggests that the 3dza/4s mixing coefficient in tetragonally distorted complexes is proportional to the difference in metal-ligand bonding between the axial and in-plane ligands,26 so that a significantly greater 4s participation is indeed expected for the linear CuF2 molecule compared with the axially compressed CuF64" ion.Acknowledgment. The receipt of a Humboldt research fellowship to M.A.H. is gratefully acknowledged.

Electron Exchange and the Photophysics of Metal−Quinone Complexes. 1. Synthesis and Spectroscopy of Chromium−Quinone Dyads

“…Their synthetic route involves a redox reaction between a Cr II starting material (Cr(CTH)Cl 2 ) and the parent quinone. The approach is similar to that used for forming tris-semiquinone complexes, e.g., Cr 0 plus 3 equiv of quinone to yield a Cr(SQ) 3 complex. , An advantage of this synthetic strategy is the lability of the Cr II synthon toward loss of the chloride ligands. However, chromatographic work revealed that in our hands several other products are also formed in this reaction.…”

Synthesis and Ligand-Based Mixed Valency ofcis-andtrans-CrIII(X4SQ)(X4Cat)(L)n(X = Cl and Br,n= 1 or 2) Complexes: Effects of Solvent Media on Intramolecular Charge Distribution and Ligand Dissociation of CrIII(X4SQ)3

“…Since no chemical and spectroscopic studies of Cr III (SQ) 3 in polar solvents have yet been reported, the electronic absorption spectra of Cr III (Cl 4 SQ) 3 were determined in dichloromethane,5a carbon disulfide, cyclohexane, nitromethane, acetone, and benzonitrile to investigate the conversion of Cr III (X 4 SQ) 3 to 1 − 6 . As shown in Figure (top), the spectra obtained for the solvents with a low dielectric constant (ε r at 293 K), cyclohexane (ε r = 2.02), carbon disulfide (ε r = 2.64), and dichloromethane (ε r = 9.02), were found to be similar to each other.…”