A water-based and high space-time yield synthetic route to MOF Ni2(dhtp) and its linker 2,5-dihydroxyterephthalic acid

Abstract

2,5-Dihydroxyterephthalic acid (H₄dhtp) was synthesized on an 18 g scale by carboxylation of hydroquinone in molten potassium formate. The hydrated form of the Ni₂(dhtp) MOF (also known as CPO-27-Ni and MOF-74(Ni)) was obtained in 92% yield by refluxing for 1 h a water suspension of the H₄dhtp linker with an aqueous solution of nickel acetate. The ensuing characterization of the material (XRD, HRTEM, TGA, N₂ adsorption at 77 K – S_BET = 1233 m² g⁻¹) confirmed the formation of a metal–organic framework of at least equal quality to the ones obtained from the previously reported routes (CPO-27-Ni and MOF-74(Ni)), with a different morphology (namely, well-separated 1 μm platelets for the herein reported water-based route). The temperature dependence of the magnetic susceptibility was measured and satisfactorily simulated assuming a Heisenberg (H = −2JΣS_iS_i+1) ferromagnetic intrachain interaction (J = +8.1 cm⁻¹) and an antiferromagnetic interchain interaction (J′ = −1.15 cm⁻¹). Overall, the reaction in water appears to follow easily distinguishable steps, the first being the deprotonation of H₄dhtp by an acetate counterion, leading to a soluble nickel adduct of the linker, en route to the MOF self-assembly.