Supramolecular chemistry and complexation abilities of diphosphonic acids

The solution and solid state complexation features for two classes of diphosphonic acids: with gem-phosphonic–phosphonate groups or with a CNC spacer between them are reviewed. In particular, the co-ordination and the supramolecular networks in their complexes are discussed. The structural analysis revealed a large variety of coordination units, dependent upon the topochemical nature of the ligands, the geometrical and charge preferences of the metal ions, and the influence of the counter ions. An amazing superstructural and supramolecular diversity is observed in the extended frameworks. The solution-solid state relationships are elucidated and the role of the hydrogen bonds for the metal complexation in solution is also revealed.