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

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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)A, 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 A); 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.