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

Abstract

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.