Analytical Sciences

Solvation Number and Conformation of N,N-Dimethylacrylamide and N,N-Dimethylpropionamide in the Coordination Sphere of the Cobalt(II) Ion in Solution Studied by FT-IR and FT-Raman Spectroscopy

Mitsunori ASADA, Takushi MITSUGI, Takahiro OGURA, Kenta FUJII, Yasuhiro UMEBAYASHI, and Shin-ichi ISHIGURO

Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi, Fukuoka 812-8581, Japan

The solvation number and conformation of N,N-dimethylacrylamide (DMAA) in the coordination sphere of the cobalt(II) ion in solution were studied, and compared with those of N,N-dimethylpropionamide (DMPA) by means of FT-Raman and FT-IR spectroscopy. Both solvents are present as either the planar cis or nonplanar staggered conformer in equilibrium, and the former is more stable in the bulk. As these solvents solvate the metal ion through the carbonyl O atom of the acryl (DMAA) or propionyl (DMPA) group, the solvation structure around the metal ion is highly congested to reduce the solvation number and/or to lead to a conformational geometry change of solvent. It turns out that the solvation number of the cobalt(II) ion is 4 for both DMAA and DMPA at 298 K, and that DMPA changes its conformation upon solvation, whereas DMAA hardly changes. The enthalpy of conformational change ΔH° for DMPA is 5 kJ mol^-1 in the bulk, and is -9 kJ mol^-1 in the coordination sphere of the cobalt(II) ion. On the other hand, the ΔH° value for DMAA is 9 kJ mol^-1 in the bulk.

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