Unusual core engineering on a copper hydride nanoball.

A neutral polyhydrido copper cluster, [Cu 27 H 15 {S 2 CN n Bu 2 } 12 ] (abbreviated as [Cu 27 H 15 ]), was prepared by the reaction of dithiocarbamates (dtc), Cu(I) salts and NaBH 4 . 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 Cu 24 rhombicuboctahedral outer cage and an inner Cu 3 triangular kernel. The two core-shell clusters, [Cu 27 H 15 {S 2 CN n Bu 2 } 12 ] and previously published [Cu 28 H 15 (S 2 CN n Bu 2 ) 12 ] + (abbreviated as [Cu 28 H 15 ] + ), are only differentiated by one copper atom in their inner core. Importantly, we demonstrate core engineering with the controllable reversible transition between an irregular Cu 4 tetrahedron and a Cu 3 triangle, whilst maintaining their outer Cu 24 shell intact. The 15 hydride atoms in [Cu 27 H 15 ], coordinated in three different modes, are co-incident with the hydride positions in [Cu 28 H 15 ] + . The degradation of [Cu 27 H 15 ] in solution or the addition of one eq. of Cu(I) ions leads to the conversion of [Cu 27 H 15 ] into [Cu 28 H 15 ] + , while the reverse transformation can be achieved by the addition of either formic acid or a reducing agent to [Cu 28 H 15 ] + . A dicationic species was observed in the ESI mass spectrum, and the composition is formulated as [Cu 56 H 30 (S 2 CN n Bu 2 ) 24 ] 2+ , a dimer of [Cu 27 H 15 (S 2 CN n Bu 2 ) 12 + Cu + ] 2 2+ . The dimeric species was further explored by DFT calculations, suggesting that the lowest energy structure consists of a [Cu 28 H 15 ] + and a [Cu 27 H 15 ] cluster connected through one Cu + atom bridge. As a result, [Cu 27 H 15 ] is considered an intermediate species in the formation of the more stable [Cu 28 H 15 ] + nanoball.