Energetic coordination compounds (ECCs) show promising
properties
to be used as potential substitutes for highly toxic lead-containing
primary explosives. The concept is to combine the three building blocks:
(i) ligand, (ii) transition metal, and (iii) anion, acting as (i)
fuel, (ii) matrix, and (iii) oxidizer (e.g., ClO4
–, NO3
–, ClO3
–) or energetic component (e.g., DN–, N3
–, picrate, styphnate, trinitrophloroglucinate).
By variation of the ligands, the complexes’ properties can
be adjusted toward their desired performance and sensitivities. In
the present study, 1-vinyl-5H-tetrazole (1-VTZ, 1) and 1-allyl-5H-tetrazole (1-ATZ, 2) were used as nitrogen-rich endothermic ligands to form
3d metal (Mn2+, Fe2+, Cu2+, Zn2+, Co2+, Ni2+)-based ECCs. The influence
of the introduction of an unsaturated C–C bond (1-ETZ vs 1-VTZ and 1-PTZ vs 1-ATZ) on the performance
and sensitivity of the complexes is discussed, as is the lengthening
of the alkenyl chain (1-VTZ vs 1-ATZ). For further
insights, the novel complexes were compared to literature-known complexes
based on N1-substituted C2- and C3-derived tetrazole
ligands, respectively. The ligand 1-VTZ (1) was prepared
by elimination of hydrogen chloride from 1-(2-chloroethyl)-5H-tetrazole in methanolic KOH solution. 1-ATZ (2) was obtained by a heterocyclization reaction of allylamine with
triethyl orthoformate and sodium azide in an acetic acid medium. All
compounds were intensively characterized with analytical methods such
as XRD, IR, EA, DTA, TGA, and sensitivity measurements (IS and FS).
The energetic performances were visibly evaluated in fast heating
experiments. Furthermore, PETN initiation and laser ignition experiments
were carried out for promising ECCs.