We present recent results on the effect of solvent environment on the IR spectrum of trans-[Fe(CN)₄(CO)₂]^2- using ab initio methods. Gas-phase calculations have been carried out on the metal complex with explicit solvent molecules ranging from a few to a number that is representative of a primary solvation shell. Using a Natural Bond Analysis (NBO) method, we find that the presence of solvent molecules capable of hydrogen bonding to the cyano ligand of trans-[Fe(CN)₄(CO)₂]^2- results in an enhancement of the lone orbital electron density on the metal atom and a decrease in metal-ligand back bonding. Decrease in metal-ligand back bonding results in decreased population of the anti-bonding π* orbitals of the C-O bond. This leads to the strengthening of the C-O bond, the decreasing of the C-O bond length, and a blue shift in the CO band position. We show that the observed shift in the carbonyl peak position could be used to predict the number of nearest neighbor solvent molecules interacting with the metal complex.