A new supramolecular heterosynthon [C-IOC(carboxylate)] at work: Engineering copper acetate cocrystals

A carboxylateiodine supramolecular heterosynthon can be reliably applied in cocrystal engineering, using metal carboxylates as building blocks. Analysis of the energy framework of the exemplary paddlewheel crystal [Cu(OAc)2MeOH]2 indicates a robust 1D chain and even 2D layer long-range synthon modules, which can be intactly transferred into cocrystals. However, this approach allows the identification of a "weak link"-i.e. layers where the C-HOC hydrogen bonds between ([Cu(OAc)2(MeOH)]2)n polymeric chains will be subject to substitution by IOC halogen bonds during interaction with halogen bond donor co-formers. In contrast to the O-HOC/C-HOC catemeric crystals of pure acetic acid, the crystal design exercise based on the IOC(carboxyl) supramolecular synthon afforded a 1:1 cocrystal of 1,4-C6F4I2 and CH3COOH, where the discrete centrosymmetric dimers of acetic acid are stabilized by IOC(carboxyl) halogen bonds.