UNDERSTANDING MECHANOCHEMISTRY BY XRPD CHARACTERIZATION: FROM METAL COMPLEXES TO COORDINATION POLYMERS

Mechanochemistry has been recognized by IUPAC as one of the “Ten Chemical Innovations That Will Change Our World”.[1] Its popularity is rapidly increasing due to the possibility of transferring synthetic protocols from solution to solventfree conditions, as well as opening novel synthetic strategies.[2] Considering the microcrystalline nature of the mechanochemical products, powder X-ray diffraction analysis is the definitive methods to unambiguously determine the structure of the isolated materials. In this context, here we present two successful approaches where X-ray powder diffraction (XRPD) is effective for precisely identifying the obtained products. In the first example we focus our effort toward the mechanochemical synthesis of zinc “paddlewheellike” complexes and their structural characterization by means of XRPD. Here, the extensive range of possible coordination modes involving pyridine and carboxylate ligands has been fully elucidated by an in-depth XRPD analysis of the mechanochemical products. The second case deals with the solvent-directed synthesis of different coordination polymers deriving from zinc acetate and 1,2-Di(4-pyridyl)ethylene. The structural framework exhibited by the obtained polymers is selectively modulated by the small aliquot of solvent used during grinding, leading to the same reactivity observed in the solution-phase synthesis but with reduced reaction times and higher yields of reaction. Once again, powder X-ray diffraction turned out to be the best technique for monitoring the selective conversion of the reagents in the target products. References: [1] Fernando Gomollón-Bell, Chemistry International 2019, 41, 12– 17. [2] Tomislav Friščić, Cristina Mottillo, and Hatem M. Titi, Angewandte Chemie Int. Ed. 2020, 59, 1018– 1029.