Different shapes: Tetravalent, hexavalent, and dodecavalent silica particles were obtained by the growth of the silica core of binary tetrapods, hexapods, and dodecapods, respectively. The surface of the multivalent particles can be regioselectively functionalized, thereby leading to particles with anisotropic geometry and chemistry.

Abstract: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)](BF 4 ). 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.

The past decade has been witness to the development of new chemical and physical methods allowing the synthesis of colloidal particles of different shapes with a good size and shape selectivity.

The coherent-domain morphology was determined for a crystalline powder of the 1D polymeric spin-crossover [Fe(Htrz) 2 (trz)](BF 4 ) {Htrz = 1H-1,2,4-triazole, trz = deprotonated triazolato(-) ligand} compound. This morphology is in adequacy with the crystal packing and proved that the long axis of the domain corresponds to the iron-triazole chains axis, which gives information on the crystal-growth process. Furthermore, thermal cycling clearly demonstrated that the coherent-domain [a] CNRS, Univ. Bordeaux, ICMCB, UPR 9048,

Photoswitching of the [Fe(Htrz) 2 (trz)](BF 4) spin crossover polymeric material has been investigated by means of confocal Raman spectroscopy upon continuous laser irradiation outside and inside its thermal hysteresis loop. In both cases, the evolution of HS and LS Raman marker bands show that light excitation can trigger the LS to HS transition, but the long-lived HS state can be populated only within the hysteresis loop. Local sample heating can explain this light-induced effect leading to a narrowing of the thermal hysteresis loop for laser intensities higher than 0.02 mW/lm 2 , in strong accordance with previous time-resolved pump-probe experiments on similar materials.

The inside cover picture shows the reduction of the size of coherent domains in a spin‐crossover metal coordination polymer upon thermal cycling. The length of the domains displays a continuous decrease when the number of successive high‐spin/low‐spin/high‐spin sequences increases. This observation reveals an irreversible structural fatigability, indicating a potential break in the 1D‐chain morphology, and therefore sheds new light on a deeply investigated family of switchable materials. Details are discussed in the article by P. Guionneau et al. on .

Nanoparticles of gold were successfully grafted onto nanoparticles of a 1D polymeric spin-crossover material leading to singular SCO@Au hybrid particles. The result is equally obtained using a large range of gold-particle sizes, from 4 to 45 nm, which first allows definition of the best experimental conditions, notably in terms of gold-particle concentration, and then demonstrates the robustness and the efficiency of the method.

Spin-crossover (SCO) triazole-based coordination polymers can be synthesized by micelle techniques, which almost always lead to rod-shaped nanoparticles. In order to notably reach new morphologies, we explore here the potentiality of the spray-drying (SD) method to get SCO materials. Three SCO coordination polymers and a mononuclear complex are investigated. In all cases, the SD method obtains particles definitely showing SCO. The features of the latter are yet always different from those of the referenced materials, in the sense that SCO is more gradual and incomplete, in adequacy with the poor crystallinity of the powders obtained by SD. In the case of coordination polymers, the particles are preferentially spherical. Indications of possible polymorphism and/or new materials induced by the use of the SD method are evidenced. In the case of the mononuclear complex, the SD method has allowed reproducing, in a quick and easy way, the well-known bulk compound. This exploratory work demonstrates the relevance of the concept and opens the way to a systematic scrutiny of all the experimental parameters to tune the size, morphology, and properties of the SD-synthesized SCO particles.