Cu(II)‐promoted cyclization of hydrazonophthalazine to triazolophthalazine; Synthesis and structure diversity of six novel Cu(II)‐triazolophthalazine complexes

A novel route for the synthesis of Cu(II)-triazolophthalazine complexes using the Cu(II)-promoted cyclization dehydrogenation reactions of hydrazonophthalazines under reflux was presented. Two hydrazonophthalazines were cyclized to the corresponding triazolophthalazine ligands, 3-pyridin-2-yl-3,10b-dihydro-[1,2,4]triazolo[3,4-a]phthalazine (TPP) and 3-(3,10b-dihydro-[1,2,4]triazolo[3,4-a]phthalazin-3-yl)-benzoic acid (TP3COOH), followed by in situ complexation with Cu(II) yielding six novel Cu(II)-triazolophthalazine complexes depending on the reaction conditions. The molecular and supramolecular structures of the Cu(II)-triazolophthalazine complexes were discussed. The metal sites have rectangular pyramidal geometry in the [Cu(TPP)Cl2]2; 1 and [Cu(TP3COOEt)Cl2(H2O)]2; 4 dinuclear complexes, distorted square planar in [Cu(TP3COOMe)2Cl2]; 3, [Cu(TP3COOH)2Cl2]; 5 and [Cu(TP3COOH)2Cl2]·H2O; 6 and a distorted octahedral in [Cu(TPP)(H2O)2(NO3)2]; 2. Hirshfeld analysis showed that the O…H, C…H, Cl…H (except TP3COOH and 2), N…H and π-π stacking interactions are the most important intermolecular contacts. The π-π stacking interactions are the maximum for TP3COOH and complex 6 with net C…C/C…N contacts of 19.4% and 15.4%, respectively. The orbital–orbital interaction energies of the Cu-N/Cu-Cl bonds correlated inversely with the corresponding Cu-N/Cu-Cl distances, respectively. The charge transfer processes between Cu(II) and ligand groups were also discussed. The charge densities of the Cu(II) centers are reduced to 0.663–0.995 e due to the interactions with the ligand groups coordinating it.