Linear and Nonlinear Infrared Spectroscopies Reveal Detailed Solute–Solvent Dynamic Interactions of a Nitrosyl Ruthenium Complex in Solution

Abstract

In this work, the solvation of a nitrosyl ruthenium complex, [(CH)N][RuCl(qn)(NO)] (with qn = deprotonated 8-hydroxyquinoline), which is a potential NO-releasing molecule in the bio-environment, was studied in two bio-friendly solvents, namely deuterated dimethyl sulfoxide (dDMSO) and water (DO). A blue-shifted NO stretching frequency was observed in water with respect to that in dDMSO, which was believed to be due to ligand-solvent hydrogen-bonding interactions, one N═O···D and particularly three Ru-Cl···D, that show competing effects on the NO bond length. The dynamic differences of the NO stretch in these two solvents were further revealed by transient pump-probe IR and two-dimensional IR results: faster vibrational relaxation and faster spectral diffusion (SD) were observed in DO, confirming stronger solvent-solute interaction and also faster solvent structural dynamics in DO than in DMSO. Further, a significant non-decaying residual in the SD dynamics was observed in DO but not in DMSO, suggesting the formation of a stable solvation shell in water due to strong multi-site ligand-solvent hydrogen-bonding interactions, which is in agreement with the observed blue-shifted NO stretching frequency. This work demonstrates that small solvent molecules such as water can form a relatively rigid solvation shell for certain transition metal complexes due to cooperative ligand-solvent interactions and show slower dynamics.

Probing the local structure and dynamics of nucleotides using vibrationally enhanced alkynyl stretching

“…5 shows that the FFCF of the CC stretching of molecule 1a relaxes relatively faster in DMSO and THF than in MeOH. In the case of DMSO, the relaxation time is 0.88 ± 0.14 ps, which agrees roughly with our early work, 75 in which the solvent dynamics was probed by a Ru-NO complex and the time constant was 1.2 ps in d-DMSO. The result is also very close to those obtained by formamide in DMSO (1.17 ps) and dimethylformamide in DMSO (1.31 ps).…”