Effect of Solvent Polarity on the Vibrational Dephasing Dynamics of the Nitrosyl Stretch in an FeII Complex Revealed by 2D IR Spectroscopy

The vibrational dephasing dynamics of the nitrosyl stretching vibration (νNO) in sodium nitroprusside (SNP, Na2[Fe(CN)5NO]·2H2O) are investigated using two-dimensional infrared (2D IR) spectroscopy. The νNO in SNP acts as a model system for the nitrosyl ligand found in metalloproteins which play an important role in the transportation and detection of nitric oxide (NO) in biological systems. We perform a 2D IR line shape study of the νNO in the following solvents: water, deuterium oxide, methanol, ethanol, ethylene glycol, formamide, and dimethyl sulfoxide. The frequency of the νNO exhibits a large vibrational solvatochromic shift of 52 cm–1, ranging from 1884 cm–1 in dimethyl sulfoxide to 1936 cm–1 in water. The vibrational anharmonicity of the νNO varies from 21 to 28 cm–1 in the solvents used in this study. The frequency–frequency correlation functions (FFCFs) of the νNO in SNP in each of the seven solvents are obtained by fitting the experimentally obtained 2D IR spectra using nonlinear response theor...