Abstract:
Here we report electrochemical, spectroscopic, and crystallographic characterization of a redox series of cobalt complexes in five sequential oxidation states. A simple bidentate phosphine ligand,
cis-1,2-bis(diphenylphosphino)ethylene (dppv), allows for isolation of the 3+, 2+, 1+, 0, and 1– oxidation states of cobalt─the only known example of transition-metal complexes with redox-innocent ligands in five oxidation states. Electrochemistry of [Co(dppv)
2]
2+ reveals three reversible reductions and one reversible oxidation. Complexes in each oxidation state are characterized using single-crystal X-ray diffraction. The coordination number and geometry of the complex changes as a function of the oxidation state: including acetonitrile ligands, the Co
3+ complex is
pseudo-octahedral, the Co
2+ complex is square-pyramidal, the Co
+ complex is pseudo-square-planar, and the Co
0 and Co
– complexes approach
pseudo-tetrahedral, illustrating structures predicted by crystal-field theory of inorganic transition-metal complexes.
Publisher's Version