Two Cu(II) complexes of 1,2,4-triazole fungicides with enhanced antifungal activities

Abstract Two Cu(II) complexes, namely, [Cu L 1 2 (OAc) 2 ]·MeOH 1 and [Cu L 2 2 (OAc) 2 ] 2 (OAc = CH 3 COO, acetate), were synthesized based on two 1,2,4-triazole fungicides of paclobutrazol ( L 1 ) and diniconazole ( L 2 ). The crystal structural analysis shows that the two obtained complexes have similar structures and both of them adopt octahedral coordination mode. The Cu(II) atoms in both the complexes lie on a crystallographic inversion center and are coordinated with two triazole groups and two acetate anions. To screen effective fungicides, the two complexes were investigated for antifungal activities against four selected fungi using mycelial growth rate method. The results demonstrate that the toxicity of complex 2 was 6.96–23.39 times greater than that of complex 1 , since complex 2 possesses both C C linkage and 2,4-dichlorobenzene moiety, and shows higher synergy levels for the molecular-level mixture of copper cation and L 2 . The results also show that both the synthesized complexes showed superior activities of 1.20–5.94 times to those of their ligands. The DFT calculation results of the title complexes and their ligands reveal that the complexes have a new active site of metal cation, smaller HOMO–LUMO energy gaps and lower polarity than their ligands, which should be responsible for the enhanced bioactivities after complexation.