Structural aspects of the metal ion complexes of the conjugates of calix[4]arene: crystal structures and computational models

In this review, the structural aspects of the metal ion complexes of calix[4]arene and its derivatives have been discussed. Aspects, such as the coordination geometry about the metal ions and conformational mobility of the arms of the calix[4]arene as well as the calix[4]arene platform were discussed and compared appropriately. Structures derived based on the computational modeling of the metal ion complexes of the calix[4]arene derivatives have also been reviewed. The complexation of the metal ions with the derivatives was observed mainly through the heteroatoms which were further strengthened by cation⋯π interactions extended from the phenyl moieties of calix[4]arene. Solvent molecules play an important role in preorganizing the cavity to optimize the binding of metal ions. Conformational changes were observed in the arms upon metal ion binding. However, conformational changes were also observed in the calix[4]arene moiety, particularly when no arms were built on these platforms for coordination. This review covers the structural information of ∼125 metal ion complexes from a list of 145 literature references and thus covers the relevant literature in its entirety starting from the year 1989. Thus the present review covers the metal ion complexes of the calix[4]arene and its derivatives, viz., alkali and alkaline earth, transition (first, second and third row), main group and lanthanides, that may be of use in designing the conjugates of calix[4]arene for their possible applications