Coordination behavior of the tetraza macrocycle isocyclam

A polemic in answer to R. G. Swisher et al (ibid., 1980, 19, 1336) who claim that isocyclam (1,4,7,11-tetraazacyclotetradecane) in its Ni complex, [NiL]2+, is tridentate. On the basis of the exothermicity of formation of [NiL]2+, its NMR, and its acid-base properties, the planar L is tetradentate and does not contain a free basic N atom.