[PPh,]x-C5H5 and HW(CO),-been recorded. In this complementary study of complex metal carbonyl compounds, assignments are suggested for metal-carbon-oxygen deformation, metal-carbon stretching, metal-ring, and metal-phosphorus stretching vibrations. It is thought that the latter occur in the range 240-200 cm-', frequencies for phosphite complexes being lower than for the corresponding phosphine derivatives.