A Research Paper Published in Angewandte Chemie International Edition

This work demonstrates a novel, unexpected phenomenon resulting from the interface of coordination chemistry and supramolecular chemistry based on halogen bonding. Halogen bonding enables the mechanochemical ball-milling isomerization of an otherwise persistent cis-coordinated metal complex into the corresponding trans-isomer. The importance of halogen bonding for enabling the cis→trans isomerization of the metal centre is evidenced by real-time in situ synchrotron powder X-ray diffraction monitoring of the ball-milling experiments that showed the transient appearance of a cis-geometry metal-organic halogen-bonded (MOXB) cocrystal, which is rapidly replaced by the corresponding trans-geometry one, with any excess non-halogen-bonded cis-geometry complex being retained throughout the milling experiment. The importance of cocrystallization for cis→trans isomerization is supported by periodic density-functional theory calculations which show that the process becomes notably more exothermic in the presence of the halogen bond donor. The presented work indicates that the formation of MOXB cocrystals can open the door to new, functional properties, different from those of parent solid-state coordination compounds.

This research was performed as part of the project New building blocks for the supramolecular design of complex multi-component molecular crystals based on halogen bonds (HaloBond IP-2019-04-1868), financed by the Croatian Science Foundation.