Abstract
The review summarises data on transition metal complexes with the so-called non-innocent ligands. The specific feature of these complexes is that the oxidation state of the central metal atom and the electronic structure of the ligands are impossible to determine a priori and unambiguously. The results of experimental studies (spectroscopic, electrochemical, X-ray diffraction) of complexes with various non-innocent ligands are analysed. Particular attention is given to their structures and redox properties.