Varying bonding modes of the zintl ion [Ge₉]^4- in Cu¹ complexes: Syntheses and structures of [Cu(η⁴- Ge₉)(PR₃)]^3- (R =iPr, Cy) and [Cu(η⁴-Ge₉)(η₄-Ge₉)] ^7-

Three novel Cu-capped. Ge₉ clusters were synthesized, from K₄Ge₉ and phosphane-stabilized copper(I) compounds CuCl(PR₃) with R = isopropyl (iPr) or cyclohexyl (Cy). Reactions in N,N-dimethylformamide (dmf) at ambient temperature resulted in the isolation of [Cu(η-Ge₉PCy₃)]^3- as a [K([2.2]crypt)] salt ([2.2]crypt: l,7,10,16-tetraoxa-4, 13-diazacyclooctadecane). From solutions of [Cu(eta;⁴-Ge₉(PiPr₃)]^3- in liquid ammonia, the anion was isolated when the reaction mixture was stored at -70 ^°C. Under the same reaction conditions but at a temperature of -40^°C the cluster [Cu(η⁴-Ge₉)(η- Geg)]^7- crystallized in the presence of [2.2.2]crypt (4, 7, 13, 16, 21, 24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosan) or [2.2]crypt. The ligand-free intermetalloid cluster [Cu(η⁴Ge₉-Ge ₉)]^7- is a unique example in which two differently bonded Ge₉ units are linked by a transition-metal atom. This cluster complex, remarkably demonstrates the ability of homoatomic polyanions to bind in different modes to the same transition-metal atom.. One Ge₉ nido cluster binds to the copper atom by means of its open square face, whereas the second Ge₂ nido cluster is coordinated through one lone pair as a two-electron a donor. The key role of the flexible electron-donor properties of [Ge₉]^4- in the reaction path towards the formation of intermetalliod clusters is discussed.