Metal-organic framework structures of Cd(II) built with two closely related podands that are further stabilized by water clusters

Abstract

Reaction of tris-(2-chloroethylamine) with either para-hydroxyethylbenzoate or meta-hydroxyethylbenzoate followed by hydrolysis affords the podands tris-(4-carboxy-2-phenoxy-ethyl)amine and tris-(3-carboxy-2-phenoxy-ethyl)amine, respectively. Aqueous solutions of Cd(NO₃)₂·6H₂O readily react with the podands in a 1:2 molar ratio in the presence of pyridine at room temperature to form the porous coordination polymers {[Cd(ptaH)]·5H₂O}_n (1) and {[Cd₂(mtaH)₂(H₂O)₂]·14H₂O}_n (2). Compound 1 crystallizes in the triclinic space group P↑ with a = 10.223(7), b = 11.465(8), and c = 12.331(8) Å, a = 93.43(1)°, β = 96.67(1)°, γ = 95.08(1)°, V = 1426.4(2) ų, Z = 2, ρ_calcd = 1.65 g cm^-3, T = 100 K, µ = 0.839 mm^-1, R₁ = 0.0741 (I > 2σ(I)), wR₂ = 0.1636, and GOF = 1.322. Compound 2 crystallizes in the monoclinic space group P2₁/c with a = 16.752(1), b = 18.568(1), and c = 21.610(2) Å, β = 107.36(10)°, V = 6415.8(8) ų, Z = 4, ρ_calcd = 1.58 g cm^-3, T = 100 K, μ = 0.759 mm^-1, R₁ = 0.0339 (I > 2σI)), wR₂ = 0.0861, and GOF = 1.040. Each of the coordination polymers looks like an infinite chain of metallocycles with different void spaces. These voids are occupied by supramolecularly assembled water molecules whose structures are commensurate with the metal-organic frameworks (MOFs).