[Cu6(NGuaS)6]2+and its oxidized and reduced derivatives: Confining electrons on a torus

What is it about?

The hexanuclear thioguanidine mixed-valent copper complex cation [Cu6(NGuaS)6]+2 (NGuaS = o-SC6H4NC(NMe2)2)and its oxidized/reduced states are theoretically analyzed by means of density func-tional theory (DFT) (TPSSh+D3BJ/def2-TZV). A detailed bonding analysis using overlap populations is performed. We find that a delocalized Cu based ring orbital serves as an acceptor for donated S p elec-trons. The formed fully delocalized orbitals give rise to a confined electron cloud within the Cu6S6 cage which becomes larger upon reduction. The resulting strong electrostatic repulsion might prevent the fully reduced state. Experimental UV/Vis spectra are explained using time-dependent density functional theory (TD-DFT) and analyzed with a natural transition orbital (NTO) analysis. The spectra are dominated by MLCTs with-in the Cu6S6 core over a wide range but LMCTs are also found. The experimental redshift of the reduced low energy absorption band can be explained by the clustering of the frontier orbitals.

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