UNEXPECTED ASSEMBLY OF HEXANUCLEAR MACROMOLECULAR COMPLEXES OBTAINED UNDER BALL-MILLING CONDITIONS

IUPAC defines a mechanochemical reaction as “a reaction that is induced by the direct absorption of mechanical energy” and lists mechanochemistry as one of the "Ten Chemical Innovations That Will Change Our World"[1]. The popularity of mechanochemistry is rapidly growing owing to its low environmental impact deriving from the reduced amount of solvent employed and the possibility of reaching new compounds isolable only under mechanochemical conditions [2]. Herein, we present the unexpected self-assembly of hexa-nuclear Zn-complexes synthesized using ball-mill grinding techniques, along with their solid-state structural characterization. The reaction between zinc acetate, isonicotinamide, and a 4-X-substituted benzoic acid (X = Cl, Br, I) were conducted by means of a vibrating ball mill resulting in the formation of species containing six tetrahedrally coordinated zinc nuclei arranged in a crown fashion, as depicted in Figure 1. Isonicotinamide and benzoate ligands act as monodentate ligands, while the acetate bridges two metal atoms. This unprecedented type of assembly is a clear example of how mechanochemistry can give access to unexpected reaction routes and new types of products that are difficult to isolate by solution based synthesis. 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.