Matrix-isolation IR spectra of halogen-P and halogen-π complexes of phosphines and iodotrifluoroethylene (C

The CC stretching mode of iodotrifluoroethylene (ITFE) serves as a marker for halogen-bonding (XB) interactions in complexes with phosphines. The formation of C-I⋯P XB-complexes becomes evident from a strong red-shift of this marker band. The formation of C-I⋯π bound clusters, which were kinetically trapped in the cryogenic environment, was confirmed by a slightly smaller red-shift of the marker band.