Two Cu(ii) complexes of triadimefon: crystal structure, antifungal activities and structure–activity relationship†
Two Cu(II) complexes, [CuL2Cl2(EtOH)] 1 and [CuL4(NO3)2]·0.5H2O 2 (L = 1-(4-chlorophenoxy)-3,3-dimethyl-1-H(1,2,4-triazole-1-y)-2-butanone, triadimefon) have been synthesized and their structures were determined by single crystal X-ray diffraction (XRD). Crystal structural analysis shows that in complex 1, the copper cation lies on a crystallographic inversion center and is coordinated with two triazole groups, two chloride ligands and an ethanol molecule. In each unit cell, two pairs of adjacent [CuL2Cl2(EtOH)] molecules are linked by O–H⋯Cl hydrogen bonds to form a 2D plane. Complex 2 is octahedral with the metal cation bound to four triazole groups and two nitrate ligands. The geometry is elongated due to the more distant interactions between connecting nitrate O atoms and the Cu cation. The two complexes were screened for antifungal activities against five selected fungi using the mycelial growth rate method. The synergistic interactions between Cu2+ and triadimefon were also investigated by the Wadley approach, and the results reveal that the synergy levels for the ratio 1 : 4 of the molecular-level mixture of Cu2+ and triadimefon are better than that for the ratio 1 : 2. To better understand the structure–activity relationship, theoretical investigation of the electronic structure of the metal complexes has been carried out using density function theoretical (DFT) calculations. The results indicated that the Cu cation and the triazole originating from triadimefon are the active sites, and the decrease of the polarity of Cu2+ can contribute to the increased biocidal properties after complexation since it is responsible for the enhanced penetration of the metal complexes into the lipid membranes.