Insertion of germanium atoms in high-nuclearity rhodium carbonyl compounds: synthesis, characterization and preliminary biological activity of the heterometallic [RhGe(CO)], [RhGe(CO)] and [RhGe(CO)] clusters

The reaction of the [Rh 7 (CO) 16 ] 3− cluster anion with Ge 2+ salts, in different stoichiometric ratios and under different atmospheres, leads to the formation of new heterometallic Rh-Ge clusters, representing the first known examples of Rh carbonyl compounds containing interstitial germanium atoms. More specifically, under N 2 the reaction progressively affords the new [Rh 13 Ge(CO) 25 ] 3− and [Rh 14 Ge 2 (CO) 30 ] 2− clusters in good yields, with the Ge atoms located in cubic and square-anti-prismatic cavities, respectively. However, under a CO atmosphere, the [Rh 13 Ge(CO) 25 ] 3− derivative undergoes a significant structural and chemical rearrangement giving the new compound, [Rh 12 Ge(CO) 27 ] 4− , where Ge is hosted in an icosahedral metal cage. All species have been characterized by IR spectroscopy and ESI mass spectrometry, and their structures have been elucidated by single-crystal X-ray diffraction. Additionally, preliminary biological tests on the [Rh 13 Ge(CO) 25 ] 3− and [Rh 14 Ge 2 (CO) 30 ] 2− clusters show that they are cytotoxic to various cell lines. The reaction of [Rh 7 (CO) 16 ] 3− with Ge 2+ salts led to the first Rh carbonyl clusters with interstitial Ge atoms.