Atomically precise rhodium-indium carbonyl nanoclusters: synthesis, characterization, crystal structure and electron-sponge features

In this paper we present the investigation of the reactivity of [Rh 7 (CO) 16 ] 3− with InCl 3 , with the aim of expanding the more general study that allowed us to obtain, among other species, the icosahedral [Rh 12 E(CO) 27 ] n − ( n = 4 when E = Ge or Sn; n = 3 when E = Sb or Bi) family of clusters. Indeed, the study resulted in the isolation and characterization of the analogous In-centred icosahedral [Rh 12 In(CO) 28 ] 3− nanocluster ( 1 ), which is isoelectronic and isostructural with the [Rh 12 E(CO) 27 ] n − congeners. During the course of the reaction two more new species, namely the octahedral [Rh 6 (CO) 15 InCl 3 ] 2− ( 2 ) and the dimeric [{Rh 6 (CO) 15 InCl 2 } 2 ] 2− ( 3 ) have also been identified. The reaction between [Rh 7 (CO) 16 ] 3− and InCl 3 proved to be poorly selective; nevertheless, by fine tuning some reaction parameters it was possible to drive the reaction more towards one product or the other. Alternatively, [Rh 6 (CO) 15 InCl 3 ] 2− can be more selectively prepared by reacting either [Rh 5 (CO) 15 ] − or, less efficiently, [Rh 6 (CO) 15 ] 2− with InCl 3 . As for the dimeric [{Rh 6 (CO) 15 InCl 2 } 2 ] 2− species, this was only isolated by carrying out the reaction with [Rh 7 (CO) 16 ] 3− under inert atmosphere, as opposed to under CO. All clusters were characterized by IR spectroscopy and ESI-MS, and their molecular structures were fully established by single-crystal X-ray diffraction studies. The [Rh 12 In(CO) 28 ] 3− species was also analysed by EDS via SEM, and further investigated through in situ infrared spectroelectrochemistry and CV experiments to check its multivalence nature. Indeed, [Rh 12 In(CO) 28 ] 3− can reversibly undergo two monoelectronic oxidation and one bi-electronic reduction processes, behaving like an electron sponge and, thus, giving rise to the further [Rh 12 In(CO) 28 ] n − derivatives ( n = 1, 2 and 5). These results parallel the findings for the [Rh 12 E(CO) 27 ] n − series. The geometry variations of the metal framework associated with the changes in the cluster negative charge were investigated by means of DFT calculations. The reactivity of [Rh 7 (CO) 16 ] 3− with InCl 3 led to the isolation of three new clusters, including [Rh 12 In(CO) 28 ] 3− , which extends the [Rh 12 E(CO) 27 ] n − series (E = Sn, Ge, Sb, Bi). Its multivalence has been experimentally and theoretically unravelled.