An EPR and ENDOR investigation of a series of Cu(II) transition metal complexes

Abstract

Copper complexes have an enormous potential as cytotoxic compounds. Understanding the subtle interactions of these complexes and the variable modes of coordination with biologically relevant bases is mandatory from a biological perspective. However, in this thesis the more specific context is to investigate in detail the electronic and structural aspects of various copper complexes including [Cu(acac)2], [Cu(acac)(N-N)]+ and the multidentate ligand based complex [Cu(aNbN-aN)], and their interaction with target nitrogen bases. Therefore, an in-depth study on the configurational aspects of adducts formed between [Cu(acac)2] and imidazole (Im) was performed using ENDOR, HYSCORE and DFT calculations, providing a detailed analysis of the decoded trans-equatorial [Cu(acac)2(Im)n = 2] conformation. Based on N-imine coordinated complexes, a series of square planar Casiopeina Cu2+ complexes, consisting of one acetylacetonate and one diamine ligand, have been investigated by EPR and ENDOR spectroscopy. These diimine ligands were selected in light of the fact that the size of the aromatic diimine ligand may influence the therapeutic activity. Subtle but not neglectable electronic and structural changes of these [Cu(acac)(N-N)]+ complexes were detected by using X-,Q- and W-band CW EPR and 1H and 14N ENDOR measurements, revealing distortion and strain effects in the ligand system. Multidentate ligand based complexes [Cu(aN-bN-aN)] formed with e.g. di(2-picolyl)amine, tris(2-pyridylmethyl)amine and tris(2-aminoethyl)amine have been investigated by EPR and ENDOR spectroscopy. The focus of this investigation is to utilise ENDOR spectroscopy to examine copper complexes bearing inequivalent coordination nitrogen nuclei. Interesting electronical and structural features have been observed, illustrating the nature of the multidentate mixed nitrogen ligand