The IR and Raman spectra for two isomorphic trinuclear μ3-oxo-formato complexes of iron and chromium were measured in the range 2000-110 cm-1.The assignments on the vibrations of the bridging and terminal coordinated formic ligands were made from the results of substitution reaction of the latter.A simplified model and a simplified general valence force field were used in normal coordinate analysis.The calculated frequencies agree well with the observed values,with a mean deviation of 1.1% for [Fe3O17C] and 0.9% for [Cr3O17C],confirming our assignments of their vibrational spectra.Two sets of the force constants have been calculated.In terms of the relationship among the vibrational frequencies,structure and some properties of the compounds,the rationality and reliability of the results were discussed.
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