Uncovering the role of non-covalent interactions in solid-state photoswitches by non-spherical structure refinements with NoSpherA2.

We present a charge density study of two linkage isomer photoswitches, [Pd(Bu 4 dien)(NO 2 )]BPh 4 ·THF (1) and [Ni(Et 4 dien)(NO 2 ) 2 ] (2) using Hirshfeld Atom Refinement (HAR) methods implemented via the NoSpherA2 interface in Olex2. HAR is used to explore the electron density distribution in the photoswitchable molecules of 1 and 2, to gain an in-depth understanding of key bonding features and their influence on the single-crystal-to-single-crystal reaction. HAR analysis is also combined with ab initio calculations to explore the non-covalent interactions that influence physical properties of the photoswitches, such as the stability of the excited state nitrito-( η 1 -ONO) isomer. This insight can be fed back into the crystal engineering process to develop new and improved photoswitches that can be optimised towards specific applications.