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) 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) and Rh14Ge2(CO)(30) 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) derivative undergoes a significant structural and chemical rearrangement giving the new compound, Rh12Ge(CO)(27), 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) and Rh14Ge2(CO)(30) clusters show that they are cytotoxic to various cell lines.