Potential Constants of Iron Pentacarbonyl from Vibrational Spectra of Isotopic Species

Abstract

The vibrational spectra of Fe(12C16O)5, Fe(13C16O)5, and Fe(12C18O)5 have been observed. Most of the fundamentals have been assigned, with some changes from earlier results in the literature. Potential constants have been calculated by constraining many of the interaction constants to values estimated from analogous constants of the hexacarbonyls. The results indicate that the axial CO bonds are stronger than the equatorial CO bonds. This implies that the axial MC bonds are weaker than the equatorial MC bonds, though the calculated MC potential constants are not significantly different.

Infrared spectroscopy and structures of manganese carbonyl cations, Mn(CO)n+ (n = 1−9)

“…The Co(CO) 5 ϩ and the Fe(CO) 5 complexes both have trigonal bipyramid structures with singlet ground states. Co(CO) 5 ϩ has two carbonyl stretches at 2140 and 2150 cm Ϫ1 [44], while Fe(CO) 5 has these same vibrations at 2013 and 2034 cm Ϫ1 [15]. Like the Mn ϩ /Cr comparison in the present work, the ionized cobalt complex has a much smaller red shift in its vibrations than the isoelectronic iron neutral.…”

“…If this were the most important factor, then cation species should have greater red shifts in their vibrations than corresponding neutrals, opposite to the observed trend. On the other hand, back- were studied previously, which have CO stretching frequencies of 2094, 1946, and 1799 cm Ϫ1 respectively [15,20,22]. Here the neutral has inefficient backbonding, while this increases with charge for anions.…”

Characterization of the Fe Site in Iron−Sulfur Cluster-Free Hydrogenase (Hmd) and of a Model Compound via Nuclear Resonance Vibrational Spectroscopy (NRVS)

“…In contrast, the 502 cm −1 mode seems to have no IR intensity, and it is not a resolved feature in the Raman spectrum. Reference to the extensive body of work on Fe carbonyl bending and IR and Raman spectra [34][35][36][37][38][39][40][41] allows these features to be qualitatively assigned as Fe-C-O bending and stretching modes. The higher frequency pair is expected to involve primarily Fe-C-O bending, while the lower frequency pair primarily reflects Fe-CO stretching motion.…”

Solvent induced structural dynamics of ruthenium pentacarbonyl in benzene

“…Isolated M(CO) 5 compounds have 18 normal vibrational modes, but only the m 10 and m 6 carbonyl stretching modes, which represent the asymmetric in-plane equatorial carbonyl stretch and asymmetric axial carbonyl stretch, respectively, are IR active in the region near 2000 cm À1 [32][33][34][35][36][37][38][39][40]. However, when IPC forms a complex with a single solvent molecule, the totally symmetric m 1 vibrational mode becomes IR active due to the induced break in D 3h symmetry.…”