Coordinated alkynes, bent geometry

The most distinctive structural feature of the heavier alkyne analogs is that, unlike typical triple-bonded carbon atoms, the group 14 elements are not linearly coordinated. For the digermyne, the bent geometry suggests that the Ge-Ge interaction is not a true triple bond, but that the molecule might be better viewed as a bis(germylene) ... 

Either picture qualitatively rationalizes two important structural features of the coordinated alkyne (1) the C=C bond order is decreased relative to that in the free ligand, and (2) its geometry is cis, bent. Analogy has been drawn between the structures of the coordinated alkyne and the excited state of the free ligand (Blizzard and Santry, 1968). Carbon-carbon bond lengths in coordinated alkynes range from 1.24 to 1.40 A, and the deformation angle... 

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