Chapter 11: Secondary Building Units and Framework Structures in Aluminium and Zinc Phosphates: The Connection Between

The area of metal phosphate frameworks, derived from phosphoric acid (H₃PO₄) and its esters ((RO)PO₃H₂), has developed into a major theme within the chemistry of framework and porous solids during the last decade. The analogous metal phosphonates which are derived from organophosphonic acids (RPO₃H₂) have however been extensively investigated since as early as 1970s owing to their important applications in various fields. While the majority of the metal phosphonates reported in the literature are layered compounds (made up of 2D [M(RPO₃)(H₂O)]_n sheets that are stacked one over other), a greater structural diversity exists in the case of metal phosphates. The known structural types vary from discrete zero-dimensional clusters, 1D chains, 2D sheets to 3D framework solids and zeolite-like porous compounds. Generation of such varied structures starting from both phosphoric acid and its esters is the focal point of this chapter. This article showcases, taking zinc and aluminum phosphates as examples, how the transformations of rationally synthesized molecular compounds to materials represent an important new direction in both structural inorganic chemistry and materials chemistry, enabling possible pathways for the rational design of newer materials.