VAPOR-PHASE FAR-INFRARED STUDIES OF ETA-BONDED METAL-CARBONYLS, (1,3-BUTADIENEIRON TRICARBONYL, CYCLOPENTADIENYLMANGANESE TRICARBONYL AND METHYLCYCLOPENTADIENYLMANGANESE TRICARBONYL)

Far-infrared spectra of 1,3-butadieneiron tricarbonyl, C4H6Fe(CO)(3), cyclopentadienyl-manganese tricarbonyl, C5HMn(CO)(3) and methylcyclope ntadienylmanganese tricarbonyl, CH3C5H4Mn(CO)(3) in the vapour phase h ave been reported first time in the region 500-100 cm(-1). An assignme nt of the frequencies on the basis of local symmetry of Fe(CO)(3) frag ment explain most of the observations, but the Fe-CO stretching modes of E symmetry are split. The C4H6 vibrations are assigned on the basis of C-S symmetry. For CpMn(CO)(3) and MeCpMn(CO)(3) particular referen ce is made to the assignment of the metal-ring modes. This assignment has been discussed in term of previous assignment given for (in liquid phase and Nujoll mull) other eta-cyclopentadienyl and related compoun ds, including ferrocene, dimethylferrocene, benzenechromium tricarbony l and toluenechromium tricarbonyl. (C) 1997 Elsevier Science B.V.