Metalloid cluster compounds [1] of the general formula M n R m (n > m; R = ligand such as Si(SiMe 3 ) 3 or N(SiMe 3 ) 2 ) are ideal model compounds for molecular entities in the gray area between molecules and the solid state. [2] This borderland is of particular interest especially for metals or semi-metals, as drastic changes in the physical properties take place during the reduction from salt-like oxidized compounds (e.g. oxides, halides: non-conducting) to the elemental bulk phase (metal: conducting; semi-metal: semiconducting).[3] As the dimensions of metalloid clusters are in the nanometer range, the synthesis of metalloid clusters also opens the possibility of obtaining structural information on small nanoparticles, an important prerequisite for structure-property relations in this expanding area. [4] In the case of germanium, several different synthetic routes have been introduced in recent years, leading to a number of metalloid clusters, which exhibit new and unusual structures as well as exceptional bonding properties. Hence, by a reductive elimination reaction [Ge 10 (SitBu 3 ) 6
I]+ is obtained, [5] whereas the metalloid clusters [Ge 5 {CH-(SiMe 3 ) 2 } 4 ][6] and [Ge 6 (C 6 H 3 Dipp 2 ) 2 ] (Dipp = 2,6-iPr 2 C 6 H 3 ) [7] have been synthesized by reductive coupling reactions. The most fruitful route to metalloid germanium clusters to date uses the disproportionation reaction of dissolved metastable Ge I halides, which thus allows the synthesis of clusters with eight [Ge 8 {N(SiMe 3 ) 2 } 6 ], [8] [Ge 8 {(OtBu) 2 C 6 H 3 } 6 ], [9] nine [Ge 9 {Si(SiMe 3 ) 3 } 3 ]À , [10] ten [Ge 10 Si{Si(SiMe 3 ) 3 } 4 -(SiMe 3 ) 2 Me] À , [11] [Ge 10 {Fe(CO) 4 } 8 {Na(thf) 3 } 6 ], [12] and up to fourteen [Ge 14 {E(SiMe 3 ) 3 } 5 {Li(thf) 2 } 3 ] (E = Si, Ge) [13,14] germanium atoms in the cluster core.Among metalloid main-group clusters in general [Ge 10 {Fe(CO) 4 } 8 {Na(thf) 3 } 6 ] is an exceptional example as it is the only metalloid cluster which is exclusively stabilized by transition-metal-based ligands. This shows that the influence of transition-metal ligands on metalloid clusters is nearly unexplored. Furthermore, such metalloid clusters stabilized with transition-metal-based ligands might open an access to new metastable binary materials.[15] However, transitionmetal reagents have already been used in the chemistry of germanium clusters; either as ligands in direct synthesis to gain fully substituted clusters, such as [Ge 6 {Cr(CO) 5 X compounds (X = À1: M = Cu, Ag, Au;[23, 24] X = 0: M = Zn, Cd, Hg [25] ). We now present a second example of a metalloid maingroup cluster exclusively stabilized by transition-metal-based ligands, showing a unique arrangement of the tetrel atoms in the cluster core. After work up of a reaction mixture of a metastable GeBr solution (CH 3 CN, THF, nBu 3 N (2:2:1); 0.28 m) with solid K[FeCp(CO) 2 ] (Cp = cyclopentadienyl) we obtained black crystals of the metalloid germanium cluster [Ge 12 {FeCp(CO) 2 } 8 {FeCp(CO)} 2 ] (1). The molecular structure of 1, as shown in Figure ...