The quantum crystallography approach used here reveals the fine features of the interatomic interactions of different nature in [Co(NH3)5NO2]ClNO3 and [Co(NH3)5ONO]ClNO3 crystals and provides a better insight into the role of the crystalline environment in the intramolecular nitro–nitrito linkage photoisomerization.

This work presents a new iterative refinement method, comparable to Hirshfeld atom refinement, using the Hansen–Coppens multipole model charge density description to obtain accurate atomic coordinates and atomic displacements based on CRYSTAL17 periodic boundary calculations. The refinement, performed using the Python code ReCrystal, allows the user to explore the full periodic charge density in the crystalline solid state for charge density analysis of weak interactions.

Single-crystal X-ray structures measured at around 20 K to high resolution were refined with structure-specific restraints from quantum chemical molecule-in-cluster and full-periodic computations, which permits benchmarking levels of theory of varying sophistication. Restraints can then `augment' low-quality crystal structures, with other possible applications.

The temperature dependence of accurate structure factors of l-alanine and taurine was measured at the SPring-8 BL02B1 beamline. The quality of the structure factors is evaluated by charge density and quantum crystallographic studies. The effects of small amounts of twinning on the charge density study for taurine are also described.

Recent methodological developments and their applications in quantum crystallography are reviewed, with an eye towards near-future advancements in this research field.