Pressure-Induced Polymerization of LiN(CN)2

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• 作者：Derek W. Keefer ; Huiyang Gou ; Andrew P. Purdy ; Albert Epshteyn ; Duck Young Kim ; John V. Badding ; Timothy A. Strobel
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：December 1, 2016
• 年：2016
• 卷：120
• 期：47
• 页码：9370-9377
• 全文大小：478K
• ISSN：1520-5215

文摘

The high-pressure behavior of lithium dicyanamide (LiN(CN)₂) was studied with in situ Raman and infrared (IR) spectroscopies, and synchrotron angle-dispersive powder X-ray diffraction (PXRD) in a diamond anvil cell (DAC) to 22 GPa. The fundamental vibrational modes associated with molecular units were assigned using a combination of experimental data and density functional perturbation theory. Some low-frequency modes were observed for the first time. On the basis of spectroscopic and diffraction data, we suggest a polymorphic phase transformation at ∼8 GPa, wherein dicyanamide ions remain as discrete molecular species. Above ca. 18 GPa, dicyanamide units polymerize, forming a largely disordered network, and the extent of polymerization may be increased by annealing at elevated temperature. The polymerized product consists of tricyanomelaminate-like groups containing sp²-hybidized carbon–nitrogen bonds and exhibits a visible absorption edge near 540 nm. The product is recoverable to ambient conditions but is not stable in air/moisture.