Varying Bonding Modes of the Zintl Ion [Ge₉]^4– in Cu^I Complexes: Syntheses and Structures of [Cu(η⁴‐Ge₉)(PR₃)]^3– (R = <i>i</i>Pr, Cy) and [Cu(η⁴‐Ge₉)(η¹‐Ge₉)]^7–

Abstract

Abstract Three novel Cu‐capped Ge 9 clusters were synthesized from K 4 Ge 9 and phosphane‐stabilized copper(I) compounds CuCl(PR 3 ) with R = isopropyl ( i Pr) or cyclohexyl (Cy). Reactions in N , N ‐dimethylformamide (dmf) at ambient temperature resulted in the isolation of [Cu(η 4 ‐Ge 9 )(PCy 3 )] 3– as a [K([2.2]crypt)] salt ([2.2]crypt: 1,7,10,16‐tetraoxa‐4,13‐diazacyclooctadecane). From solutions of [Cu(η 4 ‐Ge 9 )(P i Pr 3 )] 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(η 4 ‐Ge 9 )(η 1 ‐Ge 9 )] 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(η 4 ‐Ge 9 )(η 1 ‐Ge 9 )] 7– is a unique example in which two differently bonded Ge 9 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 Ge 9 nido cluster binds to the copper atom by means of its open square face, whereas the second Ge 9 nido cluster is coordinated through one lone pair as a two‐electron σ donor. The key role of the flexible electron‐donor properties of [Ge 9 ] 4– in the reaction path towards the formation of intermetalliod clusters is discussed.