Vibrational heavy atom effect on relaxation and solvent shell dynamics in group VIII trimetallic carbonyls

Infrared pump-probe and two-dimensional infrared (2D-IR) spectroscopies were used to study the vibrational dynamics of a homologous set of trimetallic dodecacarbonyls with increasingly heavy atomic masses in tetrahydrofuran solution. The vibrational lifetimes showed some evidence of the vibrational heavy atom effect (VHAE) but were not consistent across the sample set. Spectral diffusion was measured by 2D-IR spectroscopy to investigate whether the changes produced by the VHAE had influenced other aspects of vibrational dynamics. The triiron species was found to be more dynamic on very fast timescales and may exhibit evidence of a transient bridging CO structure. Centerline slope analysis of the high-frequency CO peak for each complex revealed that the vibrational dynamics were subtly but consistently slowed for the compounds with heavier metal atoms.