onal bipyramid could be refined with an occupancy factor of 0.08. The second position of the cluster can be explained by a rotation of the molecule and formally by the occupation of another face of the In, tetrahedron; its In atoms exhibit normal distances to quarternary C atoms, so that the rest of the molecular structure seems to be little influenced by the disorder. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. . Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road,

Key Words: Tetraindane(4) / Indium(1) / Co-Co bond I Indium alkyl bridge tetrahedro-Tetrakis[tris(trimethylsilyl)methyl]tetraindane(4) of the oxygen atom of the bridging carbonyl group to the (1) reacts with octacarbonyldicobalt to yield two products, coordinatively unsaturated In atom of a second molecule depending on the stoichiometric ratio of the starting com-across a center of symmetry. Another compound (3) is formed pounds: By replacement of one bridging carbonyl group a by the replacement of both bridging carbonyl ligands, which dicobalt monoindium derivative 2 is formed, which contains exhibits a strongly distorted Co,In, tetrahedron with normal a Co-Co bond [256.81(5) pm] bridged by one carbonyl and Co-In bond lengths of 253.44(6) pm, but long Co-Co one monoalkylindium group. While 2 is a monomer in ben-[280.14(6) pm] and In-In distances [336.18(6) pm]. zene solutions, it dimerizes in the solid state by an interaction

The monomeric fragment In−C(SiMe3)3 with a monovalent indium atom is isolobal with carbon monoxide. It is probably formed as a reactive intermediate on heating solutions of the tetrahedral cluster compound In4[C(SiMe3)3]4 (1) in hexane and reacts with Fe3(CO)12 and Fe2(CO)9 to yield by the substitution of bridging CO ligands three novel iron indium compounds, Fe3(CO)10(μ-InR)2 (2), Fe2(CO)8(μ-InR) (3), and Fe2(CO)6(μ-CO)(μ-InR)2 (4), which all were characterized by crystal structure determinations (2:  C30H54Fe3In2O10Si6, monoclinic, P21/n, a = 1436.1(2) pm, b = 1992.9(3) pm, c = 1764.8(3) pm, β = 107.02(2)°. 3:  C18H27Fe2InO8Si3, monoclinic, C2/c, a = 1527.8(3) pm, b = 960.3(2) pm, c = 3755.4(8) pm, β = 90.17(3)°. 4:  C27H54Fe2In2O7Si6, triclinic, P1̄, a = 959.3(1) pm, b = 1506.7(2) pm, c = 1561.4(1) pm, α = 86.11(1)°, β = 88.76(1)°, γ = 73.57(1)°). While both products 2 and 4 are isostructural with the pure carbonyls with two or three bridging groups, respectively, compound 3 has only one bridging InR group besides eight terminal carbonyl ligands. The Fe−In bond lengths are quite similar (255.9−260.5 pm), but the Fe−Fe distances differ significantly with 286.7(1) pm for the bridged Fe−Fe bond in 2, 289.3(1) pm in 3, and 275.87(5) pm in 4. They all are much elongated compared to the starting carbonyl complexes.

Nur schwache Thallium‐Thallium‐Wechselwirkungen liegen in den Thallium‐Tetraedern der kristallinen Alkylthallium(I)‐Verbindung Tl[C(SiMe3)3] vor, die aus Cyclopentadienylthallium(I) und Tris(trimethylsilyl)methyllithium leicht zugänglich ist. In Lösung lassen sich nur Monomere der thermisch außerordentlich empfindlichen Verbindung nachweisen.