Transformations of low-dimensional zinc phosphates to complex open-framework structures. Part 1: zero-dimensional to one-, two- and three-dimensionalstructures

Zero-dimensional 4-membered zinc phosphate monomers, [C6N2H18][Zn(HPO4)(H2P O4)(2)], I, and [C6N4H21][Zn(HPO4)(2)(H2PO4)], II, transform under simple r eaction conditions to one-, two- and three-dimensional structures. Monomer II, on heating with zinc acetate dihydrate (Zn(OAc)(2)) in aqueous solution , gives a layered phosphate [C6N4H21][NH4][Zn-6(PO4)(4)(HPO4)(2)]H2O, III. A novel three-dimensional structure [C6N4H21](4)[Zn-7(PO4)(6)](3), IV, with channels comprising Zn7O6 clusters is obtained on heating II in water unde r hydrothermal conditions. The monomer I transforms to a one-dimensional la dder, [C3N2H5][Zn(HPO4)], V, on heating with imidazole and to a three-dimen sional structure, [C4N2H12][Zn-2(H2O)(PO4)(HPO4)](2), VI, on heating with p iperazine under ordinary conditions. I also transforms to a layered zinc ph osphate, [C6N2H18][Zn-3(H2O)(4)(HPO4)(4)], VII, on heating in water. In add ition to the monomer, II, compounds III-VI have been obtained for the first time. The structures formed by the transformations of the monomers also ex hibit unique structural features. Thus, in the ladder structure, V, the imi dazole molecule is linked to the Zn center similar to the phosphate unit in a typical ladder structure, while in the layered phosphate, III, one-dimen sional tubules are linked via ZnO4 tetrahedra and the three-dimensional str ucture, IV, possesses Zn7O6 clusters. Isolation of several related solids e ncompassing a variety of architectures through the transformations of zero- dimensional monomeric phosphates demonstrates not only that the 4-membered ring is a basic structural building unit in these open-framework materials, but also sheds light on the building-up process involved in their formatio n.