Controllable sensitivity mechanism in an energetic compound of [FeII(Rtrz)6] as a molecular switch

Abstract

Transition metal iron complexes can be designed for spin crossover compounds with low spin and high spin bistable (LS and HS) states, spin transition can be triggered by external excitation, which regulates stability (sensitivity) and magnetism of complexes. [FeII(Rtrz)6] systems are bulit with the nitrogen-rich group triazole as the ligand, potentially making them high-energy compounds that can be applied in pyrotechnics and especially good candidates as green initiator for weapon systems. In this paper, two kinds of mononuclear complexes [FeIIN6-1,2,4-triazole] (1) and [FeIIN6-1,2,3-triazole] (2) are constructed, and LS ⇌ HS transition occurs by altering the bond lengths of metal ligand at room temperature; therefor, complex 1 and 2 may be spin crossover energetic materials. The ground state of both complexes is the LS state (low sensitivity), and the stable trend is 1 > 2. The spin transport mechanism is calculated by the non-equilibrium Green's function formalism combined with density functional theory. The theoretical results show that both 1 and 2 can be used as molecular switches in a small bias range, but 2 cannot be used when the bias voltage is high. In short, complex 1 is an ideal molecular switch from HS state (high-sensitivity) to LS state (low-sensitivity), acting as a reversible on ⇌ off switch. The spin state transition of complex 1 can be induced with an electric field; therefore, it is expected to control the safety of primary explosives precisely in the long term.