The use of light is one of the most promising ways to reversibly control various physical properties of organic and metal-organic compounds and opens up the possibility for the generation of new information storage devices. [1,2] Among these materials, iron(ii) spin-crossover complexes are particularly interesting as they are known to exhibit a light-induced low-spin (LS) to high-spin (HS) transition.[3] However, this light-induced excited spin state trapping (LIESST) phenomenon is only efficient at cryogenic temperatures (typically below 50 K) because at higher temperatures the photoinduced HS state relaxes rapidly to the ground state. This is a serious limitation for the development of optical switches based on spin-crossover materials.A possible approach to overcome this problem consists of working within the thermal hysteresis loop, in which the metastable HS or LS states have "infinite" lifetimes.[4] Such hysteresis phenomena have been found in many spin-crossover solids and can be related to long-range elastic interactions between the spin-state-changing molecules.[5] It should be emphasized that the hysteresis loop can be finetuned by chemical methods to situate it around room temperature.[6] The first light-induced LS!HS transition in the hysteresis region was recently observed by means of optical reflectivity when an 8-ns laser pulse was applied at 170 K to [Fe(pm-bia) 2 (NCS) 2 ] (pm-bia = N-2'-pyridylmethylene-4-aminobiphenyl), but the reverse phenomenon could not be detected.[2a] Herein, we report spectroscopic evidence for a bi-directional, light-induced spin transition at room temperature in [Fe(pyrazine){Pt(CN) 4 }] (Figure 1) by applying a one-shot laser pulse of irradiation.The synthesis of a hydrated form of the above-mentioned compound has been reported elsewhere.[7] Subsequent research has demonstrated that the spin-crossover behavior of this hydrated form ([Fe(pyrazine){Pt(CN) 4 }]·n H 2 O; n % 2-3) depends dramatically on the water content. Thermogravimetric analysis revealed that heating the sample at 420 K for 30 minutes is necessary to remove the water of crystallization. The dehydrated form [Fe(pyrazine){Pt(CN) 4 }] exhibits "improved" spin-crossover behavior in that the transition becomes complete and is centered at room temperature. Moreover, the hysteresis loop becomes wider, square-shaped, and reproducible over several cycles. This compound preserves its spin state (HS or LS) for several months if it is kept in a dry atmosphere at room temperature (295 K). Figure 2 shows the temperature dependence of the c M T value (c M is the molar magnetic susceptibility) for

In this work, we have studied, by means of Raman spectroscopy, water-additives interactions in the case of alkaline halogenides aqueous solutions. We have obtained some parameters describing the evolution of water structure vs concentration or the nature of the added salts. These parameters show, as previously described, a more important effect of anions than cations. Next, the evolution of the dynamical properties of the solution depends on the size of the ions. Moreover, the development of a new band in the isotropic part of the salts solutions spectra is attributed to water–ions interactions involved in the dynamics of hydration shells.