Symmetry and topology code of the cluster self-assembly of framework MT structures of alumophosphates AlPO4(H2O)2 (metavariscite and variscite) and Al2(PO4)2(H2O)3 (APC)

Abstract

The supramolecular chemistry of alumophosphates, which form framework 3D MT structures from polyhedral AlО₄(Н₂О)₂ clusters with octahedral O coordination (of M polyhedra) and PO₄ and AlO₄ with tetrahedral O coordination (of T polyhedra), is considered. A combinatorial–topological modeling of the formation of possible types of linear (six types) and ring (two types) tetrapolyhedral cluster precursors М₂Т₂ from MT monomers is carried out. Different versions of chain formation from linked (MT)₂ rings (six types) are considered. The model, which has a universal character, has been used to simulate the cluster selfassembly of the crystal structure of AlPO₄(H₂O)₂ minerals (metavariscite, m-VAR, and variscite, VAR) and zeolite [Al₂(P_O4)₂(H₂O)₂] · H₂O (APC). A tetrapolyhedral linear precursor is established for m-VAR and a ring precursor (MT)₂ is established for VAR and APC. The symmetry and topology code of the processes of crystal structure self-assembly from cluster precursors is completely reconstructed. The functional role of the O–H···O hydrogen bonds is considered for the first time. The cluster self-assembly model explains the specific features of the morphogenesis of single crystals: m-VAR prisms, flattened VAR octahedra, and needleshaped APC square-base prisms.