Transition-metal carbonyl derivatives of the germanes. Part 13. Preparation, spectroscopic properties, and the crystal and molecular structure of bis[µ-carbonyl-bis(tricarbonylcobaltio)(Co–Co)]germanium (4Co–Ge), [Ge{Co₂(CO)₇}₂]; a new type of group 4–tetracobalt species

Abstract

Reaction between Gel₄ and [Co(CO)₄]⁻ or between GeH₄ and [Co₂(CO)₈] gives [Ge{Co₂(CO)₇}₂](1). The crystal and molecular structure of (1) has been obtained by X-ray methods. Crystals are triclinic, with a= 10.396(2), b= 16.495(3), c= 12.879(2)Å, α= 90.33(2), β= 97.68(2), γ= 95.03(2)°, space group P1, and Z= 4. The structure was solved by direct methods and refined by least-squares techniques to R= 0.056 for 2 852 reflections [I 5σ(l)]. The molecule exhibits approximate C₂ symmetry with the Ge atom bridging the Co–Co bonds of two Co₂(CO)₇ units. The Ge bridge is unsymmetric with unequal Ge–Co bond lengths (average 2.38, 2.34 Å); the corresponding µ-CO in each unit is asymmetrically disposed in the opposite sense. Infrared and mass spectral data for [Ge{Co₂(CO)₇}₂] are also discussed.