MOSSBAUER PARAMETERS AND STRUCTURE CORRELATIONS IN 5-COORDINATE IRON COMPLEXES

Iron-57 Mossbauer spectroscopy data are reported for [Fe(ButNC)5], [Fe(CO)4 (ButNC)] and [(PPh3)2N[Fe(CO)4(CN)] complexes in order to examine the bonding character and geometrical changes of several iron penta-coordinate complexes. The small quadrupole splitting value of 0.88 mm s-1 measured for the distorted trigonal bipyramidaI [Fe(ButNC)5] differs significantly from these found for regular geometries. As a consequence of this unusual result, a new correlation method of analysis was proposed for 13 known structures of five-coodinate [FeL5], axially substituted [Fe(CO)4L'] and [{Fe(CO)4}(n)L']n- complexes (L = CO or ButNC), on the basis of deviations from the idealized trigonal bipyramidal structure and changes in the quadrupole splittings. Furthermore, correlations involving Mossbauer data and IR carbonyl stretching frequencies were used to answer more detailed electronic and stereochemical questions.11131629163