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 [Rh7(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 N2 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.