Energetic ionic liquids (EILs) are a subset of the rapidly growing field of ionic liquid research.

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The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex, [Fe II 3 (npt) 6 (EtOH) 4 (H 2 O) 2 ](ptol) 6 $4EtOH (1), and of its Co II (2 and 3) and Ni II (4) analogues, are reported here. The complexes were synthesized by reacting a 1,2,4-triazole-based ligand, 4-(4 0 -nitrophenyl)-1,2,4-triazole (npt), with the p-tolylsulfonate (ptol) metal salts in methanol or ethanol. Structural analyses revealed that all complexes are iomorphous and consist of a linear trinuclear core where metal centres are bridged by triazole groups. For 1, dc susceptibility measurements exhibit gradual spin transition with T 1/2 ¼ 148 K which corresponds to HS / LS crossover for the triazole bridged central Fe II ion. This spin transition was confirmed by Single-Crystal X-Ray Diffraction data of 1 at 100 K and 181 K, where the low temperature measurement revealed a decrease in volume for the central Fe II ion, which is in agreement with a HS / LS transition.

A nitrogen-rich ligand bis(1H-tetrazol-5-yl)amine (H 3 bta) was employed to isolate a new Fe III complex, Na 2 NH 4 [Fe III (Hbta) 3 ]·3DMF·2H 2 O (1). Single crystal X-ray diffraction revealed that complex 1 consists of Fe III ions in an octahedral environment where each metal ion is coordinated by three Hbta 2− ligands forming the [Fe III (Hbta) 3 ] 3− core. Each unit is linked to two one-dimensional (1-D) Na + /solvent chains creating a two-dimensional (2-D) network. In addition, the presence of multiple hydrogen bonds in all directions between ammonium cation and ligands of different [Fe III (Hbta) 3 ] 3− units generates a three-dimensional (3-D) network. Magnetic measurements confirmed that the Fe III center undergoes a Spin Crossover (SCO) at high temperature (T 1/2 = 460(10) K). ■ INTRODUCTIONThe design and study of switchable materials have been the focus of significant attention because of potential applications in the field of nanoelectronics. 1,2a Among the most exciting category of molecular units exhibiting switchable behavior, Spin Crossover (SCO) and Spin Transition (ST) complexes of 3d 4 to 3d 7 transition metal ions have been extensively studied for the past decade. 2,3 While the SCO phenomenon consists of a thermal equilibrium (i.e., Boltzmann distribution) between the low spin (LS) ground state and the high spin (HS) state with intermediate-field ligands, ST complexes display a phase transition allowing the system to commute between the two magnetic states with, in some cases, bistable properties (thermal hysteresis effect). 3 It has been well established that these phenomena can be induced by external stimuli such as temperature or pressure variations as well as light irradiation or the application of a magnetic field. 4 The type of LS↔HS phenomenon (SCO vs ST) is controlled by the cooperativity of the material network that is weak and strong for SCO and ST systems, respectively. Such cooperativity is due to the intermolecular elastic interactions, which enable a domino effect spreading the magnetic and structural changes accompanying the LS↔HS conversion. Among all transition metal complexes that exhibit these switchable properties, pure Fe III complexes are less common than other systems. 5,6 Furthermore, only a small portion of these Fe III complexes exhibit a spin-crossover around or above room temperature. 5n−q Indeed, there are few examples of high-temperature (above 300 K) SCO or ST compounds reported thus far, all of which are tris(pyrazol-1-yl)methane, Fe II -based complexes. 7 In addition to the metal center, the ligand plays an important role in the SCO and ST properties. Nitrogen rich (N-rich) chelates are known to act as intermediate-field ligands because of their ability to populate/depopulate d orbitals of higher energy which renders the LS as well as the HS states accessible, a prerequisite for

5,5'-bis(1H-tetrazolyl)amine (BTA), a nitrogen rich molecular solid has been investigated under compression at room temperature [corrected]. Powder x-ray diffraction using synchrotron radiation and micro-Raman spectroscopy were carried out to pressures up to 12.9 GPa. BTA conserves the crystalline structure of its room condition phase up to the highest pressure, i.e., an orthorhombic unit cell (Pbca). A fit of the isothermal compression data to the Birch-Murnaghan equation of state reveals the high compressibility of BTA. An analysis of the volume change with pressure yields a bulk modulus and its derivative similar to that of high-nitrogen content molecular crystals. Upon laser heating to approximately 1100 K, the sample decomposed while pressurized at 2.1 GPa, resulting in a graphitic compound. Finally, numerical simulations demonstrate that the minimum energy conformation is not experimentally observed since a higher energy conformation allows for a more stable dense packing of the BTA molecules.