Abstract：Due to the important application of cyanamide compounds in organic synthesis, the design and mechanism research of various cyanamide compounds have become a hot topic. The structure is the basis for functional material design. In order to explore the structural stability of a prototype of cyanamide compounds-dicyandiamide, we study the high-pressure Raman investigation of dicyandiamide at pressures of 24GPa.Under compression, most of the Raman lines move toward to high wave-number region, indicating that the reduced bond length of the functional group in dicyandiamide is shortened. Furthermore, the intensity of four Raman bands located at 502, 524, 934 and 2 157 cm-1 respectively change greatly with pressure (N—H, NCN, CNC, CN). At the same time, spectral phenomena such as new appearance of Raman peaks, disappearance of original Raman peaks and splitting of some Raman peaks are observed, indicating a pressure-induced electronic density rearrangement occurs in the dicyandiamide. Through the analysis of Raman frequency-pressure curves of dicyandiamide. It is observed that the slope of most curves suddenly changes at 5 GPa, and it could be concluded that a first-order phase-transition happens at about 5 GPa. Furthermore, there is no significant change in the slope of the CN and CN frequency-pressure curves, indicating that the two functional groups have similar pressure responses before and after the phase transition. In contrast, the slope of N—H bending vibration changes significantly, indicating that this functional group has a complex response to pressure, which is attributed to the inter-molecular hydrogen bond between dicyandiamide molecules. In addition, the intensity of the N—H stretching mode decreases gradually with the increase of pressure, and the frequency shows an abnormal blue shift, which indicates that the N-H bond length extends and the intermolecular hydrogen bond of dicyandiamide is enhanced in the new structural phase. At ambient conditions, dicyandiamide has two kinds of isomers, imino and amino forms. The characteristic peak of the imino form is 2 157 cm-1 and that of the amino form is 2 203 cm-1. According to the characteristic Raman line intensity evolution of the two isomers, it is found that the amino form of dicyandiamide transforms into an imino form gradually and disappears at 11 GPa. This study shows that high pressure Raman spectroscopy is an effective method to study the structural phase-transition and isomer identification of cyanamides, which provides an experimental basis for the design and synthesis of functional materials.
陶玉瑞，王洪波，王海华，周 密. 高压下双氰胺相变和异构转变研究[J]. 光谱学与光谱分析, 2022, 42(10): 3046-3051.
TAO Yu-rui, WANG Hong-bo, WANG Hai-hua, ZHOU Mi. Pressure-Induced Phase and Isomer Transition of Dicyandiamide. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(10): 3046-3051.
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