Analogous copper nanoclusters (Cu) with two electron superatomic and mixed valence copper(II)/copper(I) and copper(I)/copper(0) characters.

The reported copper nanoclusters (Cu NCs) of either Cu or Cu or mixed valence (MV) Cu/Cu or Cu/Cu characters are found to be stabilized with a discrete set of ligand donors; hence, analogous Cu NCs with a common architecture supported by the same or nearly the same donor set that exhibit different MV states of Cu, such as Cu/Cu and Cu/Cu, are unknown. Such a series of highest nuclearity copper clusters supported by aromatic thiol-S donor ligands, namely [(L4)CuI15Cu(μ-S)](PF) (1), [(L4)CuI15Cu(μ-S)]ClO·8CH (2) and [(L4)CuI15Cu(DMF)](PF)·CHOH·2CH (3), where L = 2-((3-X-thiophen)-(2-yl-methylene)amino)-4-(trifluoromethyl)benzenethiol (X = H/Me), have been synthesized and their electronic structural properties have been examined and reported herein. The Cu NCs, 1 and 2, feature a central sulfido-S (S) bridged tetracopper SCu core inside a sphere-shaped CuS truncated octahedron. As 1 and 2 have a non-metal (chalcogen or halogen) central atom (here S) instead of a metallic Cu core inside the CuS shell, they are of the inverse coordination complex (ICC) category, rather than superatomic with a core-shell (the core is a metal and the shell is a metal-ligand framework) structure. The NC 1, in the presence of polar solvents, converts to a two electron superatomic Cu NC, 3. The NC 3 features a trigonal pyramidal-shaped Cu core inside a modified CuS, CuS shell. The transformation of 1 to 3 may be visualized as the replacement of the central sulfido-S by an extra Cu atom (generated from decomposed molecules of 1) and the shifting of a Cu atom of the SCu unit to the CuS shell, resulting in a CuS shell. The present work offers the first example of (i) an ICC that has Cu character (2), (ii) a superatomic Cu NC (3) stabilized by an aromatic thiol-S donor ligand and (iii) spontaneous ICC (1) → superatomic NC (3) conversion that does not require any reducing agent, but rather occurs in the presence of a dioxygen oxidant. The probable mechanisms for the reversible 1 ↔ 3 conversions have been discussed. The presence of S in 1 and 2 unveils the first evidence of benzene thiol C-S bond cleavage, to the best of our knowledge. The spectroelectrochemical studies shed light on the choice of Cu/Cu and Cu/Cu character of 1 and 2, respectively, which is supported by high resolution XPS and Cu LMM Auger spectroscopy.