Synthesis, X-ray structure, Hirshfeld surface analysis and antimicrobial assessment of tetranuclear s-triazine hydrazine Schiff base ligand

The unexpected tetranuclear [Cu₄(DPPT)₂Cl₆] complex was obtained by self-assembly of CuCl₂.2H₂O and (E)-2,4-di(piperidin-1-yl)-6-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)-1,3,5-triazine, (HDPPT) in ethanol. In this tetranuclear [Cu₄(DPPT)₂Cl₆] complex, the organic ligand acts as mononegative chelate bridging two crystallographically independent Cu(II) sites. The DPPT⁻ anion acts as a bidentate ligand with respect to Cu(1), while it is a tridentate for Cu(2). The Cu(1)N₂Cl₃ and Cu(2)N₃Cl spheres have square pyramidal and square planar coordination geometries with some distortion, respectively. Two of the chloride ions coordinating the Cu(1) are bridging between two crystallographically related Cu(1) sites connecting two [Cu₂(DPPT)Cl₃] units together, leading to the tetranuclear formula [Cu₄(DPPT)₂Cl₆]. The packing of the [Cu₄(DPPT)₂Cl₆] complex is dominated by C-H…Cl contacts, leading to one-dimensional hydrogen-bond polymeric structure. According to Hirshfeld surface analysis of molecular packing, the non-covalent interactions H…H, Cl…H, Cl…C, C…H, and N…H are the most significant. Their percentages are 52.8, 19.0, 3.2, 7.7, and 9.7%, respectively. Antimicrobial assessment showed good antifungal activity of the Cu(II) complex against A. fumigatus and C. albicans compared to Ketoconazole as positive control. Moreover, the [Cu₄(DPPT)₂Cl₆] complex has higher activity against Gram-positive bacteria than Gentamycin as positive control. The opposite was observed when testing the tetranuclear [Cu₄(DPPT)₂Cl₆] complex against the Gram-negative bacteria.