For a number of years, there existed a real gap between the science of metal complexes and that of electron spin resonance (ESR). Simple reasons account for this fact. At a certain stage of development the scientists engaged in investigations of metal complexes did not have access to ESR instrumen- tation, while on the other hand, ESR theoreticians rarely had an interest in exploring the chemical applications of metal complexes. More recently chemical physicists have started to make intensive efforts to bridge the gap by applying the ESR technique to a wide range of chemical problems,...