Shaping coordination polymers by ball milling

Abstract

Selective syntheses of known 1D-coordination polymers derived from the combination of 4,4′-bipyridine (bipy) or 1,2-bis-(4-pyridyl)ethylene (dpe) with Zn(OAc)₂·2H₂O were achieved under mechanochemical conditions by carefully controlling the mechanochemical parameters, including reaction stoichiometry and the nature of the solvent used in liquid assisted grinding. Ligand exchange reactions performed under grinding conditions showed the conversion of the dpe-containing polymers into bipy-containing polymers, whereas the reverse reactions proved unfeasible. A computational rationale for the observed reactivity is provided. The dimensionality growth of the dpe-containing 1D-coordination polymers into a three-dimensional pillared metal–organic framework was achieved by reaction with terephthalic acid. The same 3D-MOF was also obtained by a one-pot procedure, involving dpe, Zn(OAc)₂·2H₂O and terephthalic acid simultaneously ground in the presence of a small aliquot of N,N-dimethylformamide. All the reactions occurred in high yields affording pure products with a favorable environmental profile, as evidenced by the environmental factor (EF) and reaction mass efficiency (RME) calculated for selective reactions. This work highlights how mechanochemistry not only allows the efficient synthesis of coordination polymers but also their post-synthetic modifications by environmentally benign protocols.