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 show that the addition of DMF strengthens the HB network of water when the volume fraction of DMF (VDMF) is less than 0.4. However, the tetrahedral structure of water is destroyed when VDMF reaches 0.4, and water molecules and DMF molecules form two DMF-water complexes, namely DMF·3H2O and DMF·2H2O. While VDMF reaches 0.8, the DMF-water complex is transformed into DMF·H2O structure due to the instability of DMF·nH2O (n = 2, 3). In addition, the newly formed HB C=O···H-C, rather than the weak HB C-H···O, leads to the red shift of C–H stretching vibration mode.