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 [Rh7(CO)16]3− with InCl3, with the aim of expanding the more general study that allowed us to obtain, among other species, the icosahedral [Rh12E(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 [Rh12In(CO)28]3− nanocluster(1), which is isoelectronic and isostructural with the [Rh12E(CO)27]n− congeners. During the course of the reaction two more new species, namely the octahedral [Rh6(CO)15InCl3]2− (2) and the dimeric [{Rh6(CO)15InCl2}2]2− (3) have also been identified. The reaction between [Rh7(CO)16]3− and InCl3 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, [Rh6(CO)15InCl3]2− can be more selectively prepared by reacting either [Rh5(CO)15]− or, less efficiently, [Rh6(CO)15]2− with InCl3. As for the dimeric [{Rh6(CO)15InCl2}2]2− species, this was only isolated by carrying out the reaction with [Rh7(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 [Rh12In(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, [Rh12In(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 [Rh12In(CO)28]n− derivatives (n = 1, 2 and 5). These results parallel the findings for the [Rh12E(CO)27]n− series. The geometry variations of the metal framework associated with the changes in the cluster negative charge were investigated bymeans of DFT calculations.