Technetium electrochemistry. 7. Electrochemical and spectroelectrochemical studies on technetium(III) and -(II) complexes containing polypyridyl ligands

The redox properties of a series of technetium(III/II) complexes of the general formula cis(X), trans(P)-[TcIII/IIX2(PRwR')2L]10+, where X = Cl or Br, PR2R' = dimethylphenylphosphine or ethyldiphenylphosphine, and L = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), or 1,10-phenanthroline (phen), were investigated in 0.1 M TEAP/acetonitrile by cyclic voltammetry at a platinum-disk electrode. These complexes exhibit diffusion-controlled, 1-equiv Tc(IV)/Tc(III) redox couples and also Tc(III)/Tc(II) redox couples. Spectropotentiostatic experiments on three complexes of this class in 0.5 M TEAP/DMF confirm the 1-equiv character of the Tc(III)/Tc(II) couple. The electrochemical behavior of Tc(II) complexes of the general formula trans(P)-[TcX(PR2R')2terpy]+, terpy = 2,2':6',2 double-prime-terpyridine, was also investigated under the same conditions as above. These complexes exhibit diffusion-controlled, 1-equiv Tc(III)/Tc(II) redox couples and Tc(II)/Tc(I) redox couples. Spectropotentiostatic experiments on trans(P)-[TcCl(PMe2Ph)2terpy]+ confirm the 1-equiv character of the Tc(III)/Tc(II) couple but show that the Tc(II)/Tc(I) couple is not reversible on the spectropotentiostatic time scale