Complexes of technetium (IV) with triphenylphosphine, tripenylarsine and αα′dipyridyl have been isolated and studied. The experimental data is consistent with the formulation of the compounds as containing octahedrally co-ordinated technetium, TcCl4(Ph3P)2, TcCl4(Ph3As)2, [TcCl2(dipy)2]Cl2 and TcCl4(dipy). Technetium (IV) is reduced to technetium (III) with (bisdiphenyl-phosphine)ethane and the tervalent