Formation of the Unprecedented [Ge ₉ Ga–GaGe ₉ ] ⁴⁻ Cluster Anion through Nido‐[Ge ₉ ] ⁴⁻ Cluster Extension with GaCp*

From a reaction of K 4 Ge 9 , GaCp*, and [18]crown‐6 in ethylenediamine, the new compound [K([18]crown‐6)] 4 [Ga 2 Ge 18 ]·4en has been obtained, containing the novel [Ge 9 Ga–GaGe 9 ] 4− cluster anion. The compound crystallizes in space group P (no. 2) with a = 12.103(3) Å, b = 12.863(3) Å, c = 17.369(3) Å, α = 82.48(2)°, β = 81.51(2)°, γ = 76.35(2)°, V = 2585.7(11) Ǻ 3 , and Z = 1. From electrospray ionization mass spectrometry, the main peak indicates a [GaGe 9 ] − group, that is, one half of the cluster anion. Quantum chemical calculations corroborate the experimental observations, confirming the location of the Ga atoms as bridging units within the dimeric 20‐atom cluster. Alternative structural arrangements with Ga atoms in different positions are significantly less favorable in energy. The paramagnetic monomer [GaGe 9 ] 2− is energetically disfavored relative to dimer formation. The [Ge 9 Ga–GaGe 9 ] 4− is only the second example of a germanium cluster dimer featuring a homoatomic bond between two Ga atoms with oxidation state +2, following the previously reported [Ge 9 Zn–ZnGe 9 ] 4− comprising Zn with formal oxidation state +1.