Two new 1,2,4,5-cyclohexanetetracarboxylate-bridged frameworks with metal hydroxide subunits. Synthesis, structures, magnetism and adsorption

Abstract

The hydrothermal synthesis, X-ray crystal structures and thermal and magnetic properties of a layered coordination polymer, [Ni_3.9Mn_1.1(μ₃-OH)₂(L^I)₂(H₂O)₁₀]·2H₂O (1) (L^I = 1e,2a,4a,5e-cyclohexanetetracarboxylate), and a porous 3D coordination polymer, [Ni₄(μ₂-OH)₂(μ₆-H₂L^IV)₂(pymc)(4,4′-bpy)(H₂O)₂](OH)·9H₂O (2) (pymc = 2-pyrimidinecarboxylate, 4,4′-bpy = 4,4′-bipyridine, L^IV = 1e,2e,4e,5e-cyclohexanetetracarboxylate), are reported in this paper. The structure of 1 has packed separated layers, each layer being formed of M₃(μ₃-OH)₂ chains bridged by M(L^I)₂viahydrogen bonds. The magnetic properties are characterized by Néel transitions to fully compensated antiferromagnets at 2.9 K and show that 1 is a metamagnet resulting from the ferrimagnetic M₃(μ₃-OH)₂ chains and other two metal atoms. Complex 2 is a 3D microporous coordination framework with 2D channels. The conformation of the 1,2,4,5-cyclohexanetetracarboxylate ligands (H₄L) of complex 2 changes from L^I (e,a,a,e) to L^IV (e,e,e,e). The magnetic measurement indicates spin-canted antiferromagnetic behaviour, and the adsorption measurements show that 2 can selectively adsorb CO₂ gas over N₂ gas.