Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

Because of the low symmetry of carboxylate ions, RCO₂^-, the differing
types of carboxylate coordination cannot be distinguished on the basis of the
number of infrared or Raman active vibrations. Instead, attempts have
been made to relate values of the carbon-oxygen stretching frequencies to
the nature of the carboxylate coordination. In many cases (section C),
the proposed correlations or critical comments on them are based on a relatively
small number of complexes, the structures of which have often not
been determined crystallographically, hence a more definitive evaluation is
needed. Infrared spectra are available for a wide range of acetato complexes
and a useful number of trifluoroacetato complexes of known structure. In
this review, we use these data to assess critically the value of carbon-oxygen
stretching frequencies in diagnosing the nature of carboxylate coordination.