10‐Azidotetrazolo[1,5‐a][1,10] Phenanthroline: A Case of Azido‐tetrazole Behavior in 1,10‐Phenanthroline with Unusual Molecular Structure

In our quest for novel An/Ln separating ligands, we have synthesized a heterocyclic precursor based on phenanthroline and identified it as 10‐azidotetrazolo[1,5‐a][1,10] phenanthroline. This asymmetric heterocyclic azide has been synthesized in four reaction steps in good yield and is well characterized via experimental methods. Thermal analysis shows that this compound is reasonably stable as an azide. The heterocycle shows fluorescent properties with a distinctive red shift of the emissions and excitation peaks. A single‐crystal XRD study shows that the molecule is planar and exhibits total molecular disorder with molecules in the crystal structure present in a major:minor conformation ratio of 0.91:0.09 and related by a 180° flip. In addition, quantum‐theoretical investigation suggests that such a product with one fused tetrazolo ring is the most stable one out of other alternatives. This molecule presents a relatively rare case of azido‐tetrazole tautomerism in 1.10‐phenanthroline.