Raman Spectra of Metal Carbonyl Compounds. III. Raman Spectrum, Vibrational Analysis, and Bond Structure of Nickel Tetracarbonyl

Abstract

The Raman spectrum of Ni(CO)₄, excited by He‐lines 5875.6 and 6678.1 A, has been restudied. A new frequency assignment is proposed, based upon measurements of intensities and the state of polarization of the observed Raman shifts, and taking into account the results previously obtained on the Raman spectra of Fe(CO)₅, Fe(CO)₄^2—, and Co(CO)₄^—. Assuming a simplified quadratic valence force function containing seven potential constants, a normal coordinate analysis has been carried out. The force constants as calculated by means of this model satisfactorily reproduce the observed frequencies. The numerical values of the constants, as compared with those of the isoelectronic anions Co(CO)₄^— and Fe(CO)₄^2—, provide direct evidence for partial multiple M—C bonding and conjugation between M—C and C–O bonds in metal carbonyl compounds and lead to approximate evaluations of bond numbers.