Correlating Mechanical Sensitivity with Spin Transition in the Explosive Spin Crossover Complex [Fe(Htrz)3]n[ClO4]2n

Spin crossover complexes are known to undergo bond length, volume and enthalpy changes during spin transition. In an explosive spin crossover complex, these changes could affect the mechanical and initiation sensitivity of the explosive and lead to the development of a new class of sensitivity switchable materials. To explore this relationship, the well-known spin crossover compound [Fe(Htrz)3]n[ClO4]2n (1) was re-evaluated for its explosive properties and its mechanical impact sensitivity was correlated to spin transition. A variable temperature impact test was developed and used to evaluate the impact sensitivity of 1 in the low spin (LS, S=0), and thermally accessed high spin (HS, S=2) and mixed LS and HS states. For comparison, the structurally similar Ni compound, [Ni(Htrz)3]n[ClO4]2n (2), that does not undergo a spin transition at accessible temperatures, was synthesized and characterized and its explosive properties and variable temperature impact sensitivity measured. These results reveal a correl...