| Summary: | The binary cluster [Co@Sn9]4– (1) was extracted directly from ethylenediamine (en) solutions of an intermetallic precursor with nominal composition “K5Co3Sn9”, and its reactions with various organometallic reagents were explored. Reaction with Ni(PPh3)2(CO)2 gives [Co@Sn9Ni(CO)]3– (2), a Co-centered closo-Sn9Ni bicapped square antiprism. Analogous reactions with Ni(COD)2, Pt(PPh3)4, and Au(PPh3)Ph led to the isolation of [Co@Sn9Ni(C2H4)]3– (3), [Co@Sn9Pt(PPh3)]3– (4), and [Co@Sn9AuPh]3– (5), respectively. 3 is structurally similar to 2 but significantly distorted from a closo-cluster with one open square face. The coordination of [CoSn9]3– by PtPPh3 (4) or AuPh (5) induces a structural transformation in the CoSn9 core, from a monocapped square antiprism (C4v) to a tricapped trigonal prismatic structure (pseudo-C3v), with the transition metal fragment capping a triangular face. The four trimetallic anions presented here represent a new family of ternary functionalized Zintl clusters incorporating a d9 transition metal center. All clusters were characterized by single-crystal X-ray diffraction and electrospray ionization mass spectrometry (ESI-MS).
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