Formation of one-, two-, and three-dimensional open-framework zinc phosphates in the presence of a tetramine

Abstract

Five new open-framework zinc phosphates, encompassing the entire hierarchy of open-framework structures, have been synthesized hydrothermally in the presence of triethylenetetramine. The structures include one-dimensional ladders, two-dimensional layers, and three-dimensional structures as well as a zinc phosphate where the amine acts as a ligand. [C₆N₄H₂₂]_0.5[Zn(HPO₄)₂] (I): monoclinic, space group P2₁/c (no. 14), a = 5.2677(1) Å, b = 13.3025(1) Å, c = 14.7833(1) Å, β = 96.049°, Z = 4. [C₆N₄H₂₂]_0.5[Zn₂(HPO₄ )₃] (II): triclinic, space group P_↑ (no. 2), a = 7.515(1) Å, b = 8.2553(1) Å, c = 12.911(1) Å, α = 98.654(1)°, β = 101.274(1)°, γ = 115.791(1)°, Z = 2. [C₆N₄H₂₂]_0.5 [Zn₂P₂O₈] (III): triclinic, space group P_↑(no. 2), a = 8.064(1) Å, b = 8.457(1) Å, c = 9.023(1) Å, α = 111.9(1)°, β = 108.0(1)°, γ = 103.6(1)°, Z = 2. [C₆N₄H₂₂] _0.5[Zn₃(PO₄)₂(HPO₄)] (IV): triclinic, space group P_↑(no. 2), a = 5.218(1) Å, b = 8.780(1) Å, c = 16.081(1) Å, α = 89.3(1)°, β = 83.5(1)°, γ = 74.3(1)°, Z = 2. [C₆N₄H₂₀]_0.5[Zn₄P₄ O₁₆] (V): monoclinic, space group P2₁/c (no. 14), a = 9.219(1) Å, b = 15.239(1) Å, c = 10.227(1) Å, β = 105.2(1), Z = 4. The structure of I is composed of ZnO₄ and HPO₄ tetrahedra, which are edge-shared to form four-membered rings, which, in turn, form a one-dimensional chain (ladder). In II, these ladders are fused into a layer. The structures of III and IV comprise networks of ZnO₄ and PO₄ tetrahedra forming three-dimensional architectures. In V, the amine molecule coordinates to the Zn and acts as a pillar supporting the zinc phosphate layers, which possess infinite Zn-O-Zn linkages. The 16-membered one-dimensional channel in IV and the ZnO₃N pillar, along with infinite Zn-O-Zn linkages in V, are novel features. The structure of the open-framework zinc phosphates is found to depend sensitively on the relative concentrations of the amine and phosphoric acid, with high concentrations of the latter favoring structures with lower dimensions.