Triazole ring is a five membered heterocyclic system containing three nitrogen and two carbon atoms. When a pyridine ring is fused, it is termed triazolopyridine. Five heterocyclic systems make up the generic class of triazolopyridines. Two of these systems are 1,2,4-triazoles, while three of them are 1,2,3-triazoles [[1], [2], [3]]. Triazole and its derivatives have garnered a lot of attention owing to their numerous applications in coordination chemistry, polymer science, magnetic materials, agrochemicals, biomimetic catalysts, artificial acceptors, functional materials and so on [4]. They also have intriguing optical characteristics, such as their fluorescent properties, which enable them to develop biosensors [5]. Triazole heterocyclic compounds can be employed as precursors of diazo compounds and related metal carbenoids because of their ability to spontaneously undergo electrocyclic ring opening [6]. In addition, these compounds offer diverse supramolecular interactions, making them a versatile functional unit for applications in anion recognition, catalysis and photochemistry [7]. Triazole scaffolds are exceptionally versatile and exhibit a wide range of biological activities due to their special structure, which enables them to bind with various enzymes and receptors in biological systems through weak interactions like coordination bonds, van der Waals force, hydrogen bonds, dipole-dipole interactions and so forth [4]. According to the literatures, triazole derivatives have a variety of pharmacological properties, including vasodilators, antimicrobial, hypotensive, anticancer, hypoglycaemic, antineoplastic, antiasthmatic, anticonvulsant, antipyretic, analgesic agents and so on [8,9]. The primary benefits of triazole derivatives over other drugs include their effective pharmacological activity, low toxicological profile, fewer side effects, large bioavailability, good drug-targeting and pharmacokinetics properties and greater curative effect [4]. Owing to the versatility of triazolopyridines, a great deal of effort has gone into developing effective synthesis methods. Typically, the synthesis of triazolopyridines from an oxidation of the hydrazone of a pyridine-2-aldehyde or ketone may be achieved by the Bower process, yielding [1,2,3]triazolo[1,5-a]pyridines. Due to the cheap price and low toxicology, using copper salts as a catalytic oxidant is an appealing option for developing cost-effective and ecologically benign catalytic oxidative processes [1,10].

We have reported the formation of a metastable intermediate tricopper(II) complex of 1,5-bis(di-2-pyridyl ketone) carbohydrazone, which underwent degradation of the carbonyl group and resulted in the formation of a copper complex of 3-(2-pyridyl)triazolo[1,5-a]-pyridine [Cu(L1a)2Cl2]⸱CH3OH⸱H2O⸱H3O+Cl− [11]. Literatures have shown the formation of similar copper complexes of triazolopyridine, [Cu(L1a)2(X)2], where X = H2O, NO3−, MeOH, ClO4− in the presence of Cu(II) ions [[12], [13], [14]]. With the anticipation of an intermediate dicopper complex and similar kind of degradation of carbonyl groups leading to a copper complex of triazolopyridine, we selected a novel Schiff base 1,10-bis(di(2-pyridyl)ketone) adipic acid dihydrazone (H2L1) having two carbonyl groups and treated with copper perchlorate. 2-pyridyl pendant groups introduced on both sides of adipic acid dihydrazide could proffer proton acceptor positions in the resultant moiety, in addition to provide two separate coordination pockets for the ligand. However, instead of the formation of a metastable intermediate dinuclear complex, the proligand is found to undergoes oxidative cyclisation by intramolecular NN bond formation using catalytic copper perchlorate to yield a pentacoordinate mononuclear triazolopyridine Cu(II) complex [Cu(L1a)2Cl]ClO4 (1).