The coordination core of Ag(i) N-heterocyclic carbene (NHC) complexes with anticancer properties as revealed by synchrotron radiation X-ray absorption spectroscopy

Abstract

An X-ray absorption structural study has been carried out on three N-heterocyclic carbene (NHC) complexes of group 11 metals (Ag, Au), which were previously shown to possess promising anticancer properties. Extended X-ray Absorption Fine Structure (EXAFS) data concerning the Au complex, besides confirming the structure already available by crystallography, allowed the comparison between the crystalline and the amorphous state of the same compound. The EXAFS study conducted on the most biologically active complex, {[Im^B]₂AgCl}, revealed the occurrence of an unusual coordination geometry, where two ligand molecules and one chlorine atom interact with the Ag core to form a three coordinate complex. The present analysis firmly underlines the reliability of the EXAFS approach when X-ray diffraction data are not available. The suitable strategy, also including the statistical evaluation of the results, which has permitted us to build up the structural model for fitting the Ag complex starting from the Au one, is highlighted here.