Open-framework zinc phosphates synthesized in the presence of structure-directing organic amines

Abstract

Four open-framework zinc phosphates have been synthesized in the presence of structure-directing organic amines. Crystal data: compound I, [NH₃(CH₂)₂NH₃·Zn₂(HPO₄)₂(H₂PO₄)₂], monoclinic, space GROUP=P2₁/c (No. 14), a=16.420(2) Å, b=7.826(1) Å, c=14.640(1) Å, β=116.47(1)°, V=1684.05(2) ų, Z=4, M=578.8(1), D_calc=2.22 g cm⁻³, MoKα, R_F=0.05; compound II, [NH₃(CH₂)₂NH₃·Zn(HPO₄)₂], monoclinic, space GROUP=P2₁/c (No. 14), a=5.161(1) Å, b=15.842(2) Å, c=12.027(2) Å, β=92.36(2)°, V=982.41(1) ų, Z=4, M=319.45(1), D_calc=2.16 g cm⁻³, MoKα, R_F=0.06; compound III, [NH₃CH₂CH(OH)CH₂NH₃·Zn₂(HPO₄)₃], monoclinic, space GROUP=P2₁/c (No. 14), a=8.615(1) Å, b=9.648(1) Å, c=17.209(1) Å, β=93.02(1)°, V=1428.4(2), Z=4, M=510.8(1), D_calc=1.79 g cm⁻³, MoKα, R_F=0.03; compound IV, [NH₃(CH₂)₆NH₃·Zn₃(HPO₄)₄H₂O], monoclinic, space GROUP=C2/c (No. 15), a=16.815(1) Å, b=8.970(1) Å, c=15.080(1) Å, β=97.25(1)°, V=2256.4(1), Z=4, M=734.3(1), D_calc=2.16 g cm⁻³, MoKα, R_F=0.05. The compounds are made up of ZnO₄ and PO₄ tetrahedra that share vertices. The connectivity between the ZnO₄ and PO₄ units gives rise to layers in I, III, and IV and a chain architecture in II. The structure-directing organic amine holds the chains and the layers in position through multi-point hydrogen bonding. The layers in I and III consist of bifurcated 12-membered rings, and those in IV, of 8-membered rings. The phosphate units occur either as hydrogen phosphate (HPO₄) or dihydrogen phosphate (H₂PO₄) moieties. These and other novel features in these materials suggest that further exploration may lead to many new solids with interesting structures. As a guide to understanding the formation of different ring structures in Zn phosphates and allied materials, a possible pathway involving the basic 4-membered ring is suggested.