Selective complexation of 1-ethyl-5-nitro-1,2,3-triazole (entz) with copper(II) salts: Preparation and characterization of [Cu(entz)2Cl2] and [Cu(entz)4(H2O)2](ClO4)2

Treatment of a mixture of isomeric N-ethyl-4(5)-nitro-1,2,3-triazoles with copper(II) chloride or copper(II) perchlorate was found to yield crystalline complexes with 1-ethyl-5-nitro-1,2,3-triazole (entz), namely [Cu(entz)2Cl2] or [Cu(entz)4(H2O)2](ClO4)2, respectively. The obtained complexes, being the rare examples of coordination compounds of vicinal nitrotriazoles, have been characterized by X-ray diffraction and thermal methods. Both compounds present mononuclear complexes with entz сoordinating through N3 atom of heterocycle. The complexes are readily decomposed under action of aqueous ammonia generating pure 1-ethyl-5-nitro-1,2,3-triazole with high yield. Succession of complexation and decomplexation reactions was shown to be a simple procedure for isolation of 1-ethyl-5-nitro-1,2,3-triazole from isomeric mixtures formed under alkylation of 4-nitro-1,2,3-triazole.