Three stages of hydrogen bonding network in DMF-water binary solution

Three stages of hydrogen bonding (HB) network in N, N-dimethylformamide (DMF)-water binary solution were investigated by Raman spectroscopy with different mixing ratios at room temperature and atmospheric pressure. The results showthat the addition of DMF strengthens the HB network of water when the volume fraction of DMF (V-DMF) is less than 0.4. However, the tetrahedral structure of water is destroyed when V-DMF reaches 0.4, and water molecules and DMF molecules form two DMF-water complexes, namely DMF center dot 3H(2)O and DMF center dot 2H(2)O. While V-DMF reaches 0.8, the DMF-water complex is transformed into DMF center dot H2O structure due to the instability of DMF center dot nH(2)O (n = 2, 3). In addition, the newly formed HB C=O center dot center dot center dot H-C, rather than the weak HB C-H center dot center dot center dot O, leads to the red shift of C-H stretching vibration mode. (C) 2020 Elsevier B.V. All rights reserved.