Laser Initiation of Fe(II) Complexes of 4‑Nitro-pyrazolyl Substituted Tetrazine Ligands

The synthesis and
characterization of new 1,2,4-triazolyl and 4-nitro-pyrazolyl
substituted tetrazine ligands has been achieved. The strongly electron
deficient 1,2,4-triazolyl substituted ligands did not coordinate Fe­(II)
metal centers, while the mildly electron deficient 4-nitro-pyrazolyl
substituted ligands did coordinate Fe­(II) metal centers in a 2:1 ratio
of ligand to metal. The thermal stability and mechanical sensitivity
characteristics of the complexes are similar to the conventional explosive
pentaerythritol tetranitrate. The complexes had strong absorption
in the visible region of the spectrum that extended into the near-infrared.
In spite of having improved oxygen balances, increased mechanical
sensitivity, and similar absorption of NIR light to recently reported
Fe­(II) tetrazine complexes, these newly synthesized explosives were
more difficult to initiate with Nd:YAG pulsed laser light. Specifically,
the complexes required lower densities (0.9 g/cm3) to initiate
at the same threshold utilized to initiate previous materials at higher
densities (1.05 g/cm3).