Gd12C6I17 – eine Verbindung mit kondensierten,C2-gefüllten Gd6I12-Clustern

Gd₁₂C₆I₁₇ — a Compound with Condensed, C₂-Containing Gd₆I₁₂ Clusters Gd₁₂C₆I₁₇ was isolated in black shining crystals from a reaction product of Gd, GdI₃ and graphite, heated in sealed tantalum capsules at 1170 K. The compound is monoclinic (C2/c; a = 1929.7(9), b = 1220.1(5), c = 1863.5(5) pm, = 90.37(3)°). The crystal structure is composed of linear units of 3 condensed Gd₆I₁₂ clusters (connection via trans-edges of the central Gd₆ octahedron), which are further linked via cis edges to form zig-zag chains. The centres of the Gd₆ octahedra are occupied by C₂ units. The distances d_{C? C} ≈ 145 pm correspond to a filling of the antibonding π* orbitals of the C₂ group, which, however, interact with empty d-orbitals of the metal atoms especially in the apices of the octahedra and thus loose their pure carbon character. The short Gd? C distances (d_{Gd? C} = 222 and 227 pm, respectively) are explained as due to multiple bonds. The occurrence of C₂ units and single C atoms, respectively, in lanthanide carbides and carbide halides is coupled to the electron concentration of the metal or cluster framework.