Conformations of calix[4]arenes - an investigation based on CSD data. Part I. Cone conformers of methylene- and heteroatom-bridged calix[4]arenes
Abstract
Conformations of calix[4]arenes with methylene and heteroatom bridges from the Cambridge Structural Database (CSD) were investigated with the help of the previously introduced parameters alfa, beta and delta. The usefulness of these parameters in describing the conformations of the scaffolds of the above mentioned compounds was demonstrated.
The dependence of the values of these parameters on inter- and/or intramolecular interactions present in the structure was investigated in order to discover how the geometry of the calix[4]arene moiety depends on the above listed effects. Structures with C4v symmetry in the cone group have both beta and delta close to 0°.
With deformation of the calix[4]arene symmetry towards C2v (flattened cone structures), the beta parameter increases. Deformation towards Cs symmetry is best reflected by increase of the parameter.
Parameter alfa reflects the degree of 'opening' of the calix[4]arene cavity; structures with four OH groups at the lower rim tend to have lower alfa and therefore more open structure.