Coumarin incorporated 1,2,4–triazole derived silver(I) N–heterocyclic carbene complexes as efficient antioxidant and antihaemolytic agents

Abstract Three series of structurally and electronically varied silver complexes of coumarin and allyl substituted N–heterocyclic carbene (NHC) ligands derived from 1,2,4–triazole core have been prepared and characterized. The ionic 1,2,4–triazolium salts have been prepared by successive N–alkylation method using allyl bromide and appropriately substituted 4–bromomethylcoumarin derivatives. Further, in–situ deprotonation method for triazolium salts was followed with different silver sources (silver oxide and silver acetate) and reaction conditions to obtain structurally diverse silver NHC coordination architectures. Furthermore, the structure of 4–bromomethyl–6–chlorocoumarin, a triazolium salt and two silver complexes has been established by single crystal X–ray diffraction technique. The silver NHC complexes displayed a linear coordination geometry with monoclinic crystal system. Supramolecular assembly of the salt and the complexes evidenced moderate π − π stacking interactions between adjacent coumarin rings. Since silver(I) NHC complexes are well known for medicinal properties, present complexes have been studied for their potent antioxidant and antihaemolytic abilities. Bis–NHC coordinated silver hexafluorophosphate complexes displayed DPPH radical scavenging activity with an IC50 value in the range 61 ± 14 to 131 ± 7 μM, while others displayed moderate to poor activity. Similarly, antihaemolytic activity has been carried out at 100 μM concentration, and the complexes exhibited lysis of red blood cells as low as 2.32 ± 0.05%.