C-H O hydrogen bonds involving carbonyl ligands

Careful analyses of numerous crystal structures of organotransition metal carbonyl complexes have revealed that weak organometallic hydrogen-bonds of the C-H- -0 type are abundant in these structures [102, 144]. This is not surprising because there are virtually countless metal carbonyl complexes known which con- 

As mentioned above, potential weak hydrogen-bond donors capable of interacting with CO ligands are abundant in a large variety of organometallic complexes. 

The tricobalt derivative (jU3-CH)Co3(CO)9, 90, is an instructive example of hydrogen-bonding in a 3-methylidene cluster complex [151], The triply bridging methylidene ligands interact in a trifurcated fashion with three carbonyl oxygens from two neighboring molecules. 

Various examples of bi- and trifurcated-acceptor interactions have been found in supramolecular structures of metal carbonyl complexes. In (/ -CO)(jU-CHCH3)-[(C5H5)Fe(CO)]2, 91, the bridging carbonyl ligand participates in two C-H- -O hydrogen-bonding interactions with C-H units of the cyclopentadienyl ligands. As a result the dinuclear molecules are self-assembled into polymeric chains [152]. 

Other structurally characterized metal carbonyl complexes with bi- and trifurcation at a carbonyl oxygen atom include, for example, the cycloheptatrienyl and cyclooctatetraene cobalt clusters Co4 CO)6ir -C ii9) r -C-J ii ), 92, Co4(CO)e-(t/ -CsHsXlti-CsHg), 93, and Co4(CO)8(Ai3-C8H8), 94 [153]. 

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