Structural Reassessment of [W(CO)₅(TCNE)]: N (σ) Coordination Instead of an Olefin (π) Complex

The blue title compound, long assumed to be an olefin complex on the basis of an apparently single unresolved CN stretching band in the IR spectrum, has been identified by experiment and through DFT analysis as a σ complex with the tungsten atom coordinated to one of the nitrile N centers. The previously reported data are reinterpreted in light of the new structural assignment, and spectroelectrochemical results (UV–vis, IR, EPR) are presented.