Characterization of Alkyne-Substituted Clusters

1H NMR spectroscopy plays an important role in the identification of all organometallic compounds. In cluster complexes this technique has been particularly useful for establishing the presence of hydride ligands 

Infrared v(C-C) Stretching Frequencies in Triosmium Alkyne and Alkene Clusters 

For any cluster complex which incorporates an organic-based ligand, 1H NMR is one of the most powerful tools for characterizing the organic species, investigating the existence of isomers in solution (216), or determining the nature of any fluxional processes which may occur (294, 377). Aspects of the use of this technique may be found in most research papers on organometallic and cluster chemistry. 

Of special relevance to the investigation of alkyne-substituted clusters is the observation of a low-field resonance, generally in the range —1 to + 1.5t, for a proton attached to a carbon atom which is either a or n bonded to the metals. Values of the chemical shift for this signal for 23 tri- and tetranuclear osmium clusters were presented by 

Sappa et al. in their review (17). This constitutes quite a powerful diagnostic probe for such complexes. The reason for the appearance of this signal at such a low field may be due to the fact that the proton is bonded to a carbon which is partially carbenic in character. 

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