Acetic acid as a solvent for the synthesis of metal–organic frameworks based on trimesic acid

Abstract

Nowadays, there is a great interest in the design of new metal–organic frameworks (MOFs) synthetized by routes that can be transferred to industrial scale with low environmental impact. In this context, this work explores the use of a soft method for the synthesis of MOFs, in which neat acetic acid is used as the reaction media. Trimesic acid (H3BTC) was chosen as the organic linker source and combined with different metal acetates, all these precursor being moderately soluble in hot acetic acid. The metal acetate provides both the metallic cation and a base, the acetate, necessary to deprotonate the H3BTC. Three first row transition metals, Cu, Co and Ni, and one heavy metal, Bi, were chosen for the study. Results denoted that the metal acetate was determinant to direct the nature of the precipitated material. For instance, the precipitation of the well-known porous HKUST-1 was observed from Cu acetate and H3BTC in neat acetic acid, giving systems with hierarchical porosity. Contrarily, for Co and Bi the use of acetic acid as a solvent yielded two 2D non porous coordination polymers, [Co6(BTC)2(Ac)6(HAc)3] (1) and [Bi(HBTC)(Ac)] (3), respectively. These new compounds were structurally elucidated. Moreover, the magnetic behaviour was analysed for the Co compound (1). Finally, an amorphous phase was precipitated for Ni. In the latter case, the use of propionic acid, with a higher boiling point than acetic acid, led to the precipitation of a crystalline material.