Rare‐Earth Complexes with the 5,5′‐Bitetrazolate Ligand – Synthesis, Structure, Luminescence Properties, and Combustion Catalysis

A complete series of complexes of the lanthanides and yttrium (except radioactive Pm) with the 5,5′‐bitetrazolate (BT^2–) ligand were synthesized from sodium 5,5′‐bitetrazolate and available rare‐earth (RE) salts. Eight new complexes were structurally characterized by single‐crystal XRD. The [M(BT)(H₂O)₇]₂[BT]·6H₂O [M = Pr (1), Gd (2)] complexes are isomorphous and consist of [M(BT)(H₂O)₇]⁺ ions in which only one BT^2– ligand acts as a chelate for each metal center. The complexes [M(H₂O)₈]₂[BT]₃·4H₂O [M = Y (3), Dy (4), Ho (5), Tm (6), Yb (7), Lu (8)] are saltlike compounds that do not exhibit any significant metal–nitrogen contacts. Luminescence was very informative for the determination of the number of inner‐sphere coordinated water molecules in the solid samples. Despite its low luminescence intensity owing to its high hydrate composition, the deuterated europium complex exhibited an internal quantum yield of 44 %. The catalytic activities of the 5,5′‐bitetrazolate salts for the decomposition and combustion reactions of energetic materials were tested. Although no effect was found for nitramine (HMX) explosive, the impact of the salts on the thermolysis of ammonium perchlorate (AP) was established. The addition of 5 % [Dy(H₂O)₈]₂[BT]₃·4H₂O decreases the temperature at the maximum reaction rate by 100 °C. The catalytic effect during combustion is apparently masked by the inhibitory influence of water; however, for [Pr(BT)(H₂O)₇]₂[BT]·6H₂O, a 20 % increase in the AP burning rate was observed.