First Synthesis of Group‐14 Polyanions by Extraction of a Binary Alloy with dmf and a Novel Conformation of the (Ge 9 −Ge 9 ) 6− Dimer: Crystal Structures of [K 6 (Ge 9 −Ge 9 )](dmf) 12 , [Rb 6 (Ge 9 −Ge 9 )](dmf) 12 and [K 2.5 Cs 3.5 (Ge 9 −Ge 9 )](dmf) 12 .

Crystals of the title compounds [K 6 (Ge 9 −Ge 9 )](dmf) 12 ( 1 ) and [Rb 6 (Ge 9 −Ge 9 )](dmf) 12 ( 2 ) have been synthesized by dissolving binary phases of the formal composition K 4 Ge 9 and Rb 4 Ge 9 , respectively, in N,N‐dimethylformamide (dmf) and subsequent cooling to −36 °C. [K 2.5 Cs 3.5 (Ge 9 −Ge 9 )](dmf) 12 ( 3 ) was obtained as a by‐product during the reaction of K 2 Cs 2 Ge 9 with sulphur in dmf. Single crystal structure analyses of 1 , 2 and 3 show that all compounds contain dimeric [Ge 9 −Ge 9 ] 6− units. The dimers are connected via the alkali metal atoms in form of [(A + ) 3 (μ 2 −dmf) 6 ] chains and build a two‐dimensional square net of the composition $^{2}_{\infty}\rm \{A_{6}(dmf)_{12}[Ge_{9}-Ge_{9}]\}$ with A = K and Rb for 1 and 2 , respectively. [(Cs + −K + −Cs + )(μ 2 −dmf) 6 ] linkages bridge the dimers in 3 under formation of $^{2}_{\infty}\rm \{K_{2.5}Cs_{3.5}(dmf)_{12}[Ge_{9}-Ge_{9}]\}$ . 1 crystallized in the tetragonal space group I 4 with a = b = 34.003(5), c = 17.366(4) Å, V = 20078(6) Å 3 , Z = 8, compound 2 in the triclinic space group $I{\bar 4}$ with a = 13.501(3), b = 14.766(3), c = 21.426(4) Å, α = 88.11(3)°, β = 86.76(3)°, γ = 75.54(3)°, V = 4129(1) Å 3 ; Z = 2 and 3 in the monoclinic space group C 2/ c with a = 21.459(4), b = 17.153(3), c = 22.939(5) Å, β = 93.37(3)°, V = 8429(3) Å 3 , Z = 4. The dimer consists of two Ge 9 clusters, whose shapes are best described as C 2ν ‐distorted monocapped square antiprisms. The clusters are connected via an exo Ge–Ge bond with its orientation either co‐linear to the shorter diagonal of the open rectangular of the antiprism or radial with respect to the cluster centre in a new type of [Ge 9 −Ge 9 ] 6− dimer.