OctaDist is an interactive and visual program for determination of structural distortion in octahedral coordination complexes such as spin crossover complexes, single-ion magnets, perovskites or metal–organic frameworks. OctaDist computes the octahedral distortion parameters initially designed in the context of the spin-crossover phenomenon and denoted ζ, Σ, and Θ from standard structural files. The program also provides additional tools for molecular analyses and visualization. It emphasizes performance, flexibility, ease of use, application programming interface (API) consistency, and clear documentation. The modules and classes in OctaDist can be easily customized to include new algorithms or analytical tools. OctaDist is cross-platform supported for modern operating systems and is available as open-source distributed under the GNU General Public License version 3.

Light-Induced Excited Spin-State Trapping has been studied since 1982 in solution and 1984 in solid state as it offers a reversible way of photoswitching the electronic configuration of spin crossover systems. Since then, the lifetime of the photo-induced state was deeply investigated through kinetics measurements. In 1998, a fast and easy way to record the limit temperature above which the photo-induced state is erased, denoted T(LIESST), was introduced. This procedure has been widely used in the spin crossover community due to its easiness and its efficiency to provide detailed information on the photo-induced state. Correlations between T(LIESST) and structural parameters have been proposed for instance. However, it intrinsically contains drawbacks that can lead to misinterpretation of behaviours and can lead to an over estimation of its scope. This review aims to present and discuss not only the correct way to measure T(LIESST) but also the essential contributions it has brought and the limits not to be exceeded in its interpretation.

The substitution of sulphur by selenium leads to spin-crossover single-crystals exhibiting a large hysteresis centred at room temperature.

The spin-crossover (SCO) materials based on iron (II) and triazole ligands can change their spin state under an external perturbation such as temperature, pressure or light irradiation, exhibiting notably large hysteresis in their physical properties’ transitions. If these aspects are investigated for decades, it is only in the recent years that the design of SCO particles has attracted the attention of the scientific community with increasing interest focusing on the possibility of getting wide ranges of sizes and shapes of nanoparticles. In this context, we rationalized the reverse-micellar synthesis, thanks to the scrutiny of the experimental parameters, to produce SCO particles with controlled size and shape. This approach has been performed for the reference one-dimensional (1D) polymeric spin-crossover compound of formula [Fe(Htrz)₂(trz)](BF₄). A synergetic effect of both time and temperature is revealed as being of paramount importance to control the final particle size. Consequently, under well-defined experimental conditions, we can now offer rod-shaped SCO particles with lengths ranging from 75 to 1000 nm.

Crystal packing energy calculations are applied to the [Fe(PM-L)₂(NCS)₂] family of spin crossover (SCO) complexes (PM-L = 4-substituted derivatives of the N-(2-pyridylmethylene)-4-aminobiphenyl ligand) with the aim of relating quantitatively the cooperativity of observed SCO transitions to intermolecular interactions in the crystal structures. This approach reveals a linear variation of the transition abruptness with the sum of the magnitudes of the interaction energy changes within the first molecular coordination sphere in the crystal structure. Abrupt transitions are associated with the presence of significant stabilising and destabilising changes in intermolecular interaction energies. While the numerical trend established for the PM-L family does not directly extend to other classes of SCO complex in which the intermolecular interactions may be very different, a plot of transition abruptness against the range of interaction energy changes normalised by the largest change shows a clustering of complexes with similar transition abruptness. The changes in intermolecular interactions are conveniently visualised using energy difference frameworks, which illustrate the cooperativity pathways of an SCO transition.