Insertion of germanium atoms in high-nuclearity rhodium carbonyl compounds: synthesis, characterization and preliminary biological activity of the heterometallic [Rh13Ge(CO)25]3-, [Rh14Ge2(CO)30]2- and [Rh12Ge(CO)27]4- clusters

The reaction of the [Rh-7(CO)(16)](3-) cluster anion with Ge2+ 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 [Rh13Ge(CO)(25)](3-) and [Rh14Ge2(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 [Rh13Ge(CO)(25)](3-) derivative undergoes a significant structural and chemical rearrangement giving the new compound, [Rh12Ge(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 [Rh13Ge(CO)(25)](3-) and [Rh14Ge2(CO)(30)](2-) clusters show that they are cytotoxic to various cell lines.