Unusual core engineering on a copper hydride nanoball

A neutral polyhydrido copper cluster, [Cu27H15{S2CNnBu2}12] (abbreviated as [Cu27H15]), was prepared by the reaction of dithiocarbamates (dtc), Cu(I) salts and NaBH4. The isolated cluster provides insights into core engineering, demonstrating its novel ability to reversibly add or remove one copper atom from the cluster core. Single-crystal X-ray analysis reveals that the new core-shell structure exhibits a Cu24 rhombicuboctahedral outer cage and an inner Cu3 triangular kernel. The two core-shell clusters, [Cu27H15{S2CNnBu2}12] and previously published [Cu28H15(S2CNnBu2)12]+ (abbreviated as [Cu28H15]+), are only differentiated by one copper atom in their inner core. Importantly, we demonstrate core engineering with the controllable reversible transition between an irregular Cu4 tetrahedron and a Cu3 triangle, whilst maintaining their outer Cu24 shell intact. The 15 hydride atoms in [Cu27H15], coordinated in three different modes, are co-incident with the hydride positions in [Cu28H15]+. The degradation of [Cu27H15] in solution or the addition of one eq. of Cu(I) ions leads to the conversion of [Cu27H15] into [Cu28H15]+, while the reverse transformation can be achieved by the addition of either formic acid or a reducing agent to [Cu28H15]+. A dicationic species was observed in the ESI mass spectrum, and the composition is formulated as [Cu56H30(S2CNnBu2)24]2+, a dimer of [Cu27H15(S2CNnBu2)12 + Cu+]22+. The dimeric species was further explored by DFT calculations, suggesting that the lowest energy structure consists of a [Cu28H15]+ and a [Cu27H15] cluster connected through one Cu+ atom bridge. As a result, [Cu27H15] is considered an intermediate species in the formation of the more stable [Cu28H15]+ nanoball.