New Open-Framework Zinc Oxalates Synthesized in the Presence of Structure-Directing Organic Amines

Two new open-framework zinc oxalates have been prepared by hydrothermal methods in the presence of structure-directing organic amines. The crystal data for these oxalates are as follows: I, [H3N(CH2)3NH3]2+[Zn2(C2O4)3]2-·3H2O, triclinic, space group P1̄ (no. 2), a = 9.261(1) Å, b = 9.455(1) Å, c = 12.487(1), α = 83.93(1)°, β = 88.01(1)°, γ = 61.03(1)°, V = 951.1(1) Å3, Z = 2, M = 524.8, Dcalc = 1.83 g cm-3, μ = 2.60 mm-1, Mo Kα, RF = 0.03; II, 2[C3H7NH3]+[Zn2(C2O4)3]2-·3H2O, monoclinic, space group C2/c (no. 15), a = 15.847(1) Å, b = 9.685(1) Å, c = 18.333(1), β = 115.5(1)°, V = 2539.1(2) Å3, Z = 4, M = 569.1, Dcalc = 1.60 g cm-3, μ = 1.97 mm-1, Mo Kα, RF = 0.07. In I, the linkages between the Zn and oxalate units gives rise to a layered architecture with 12-membered (6 Zn and 6 oxalates) honeycomb-like apertures wherein the amine and water molecules are located. In II, the Zn−oxalate layers are cross-linked by another oxalate unit giving rise to a three-dimensional structure with two distinct channels where the amine and water molecules reside; the largest aperture in II involves a 20-membered ring (10 Zn and 10 oxalates). There is extensive hydrogen bonding among the amine, water, and the framework. Adsorption studies indicate that water can be reversibly adsorbed in I.