Pressure-Induced Polymerization of LiN(CN)₂

Abstract

The high-pressure behavior of lithium dicyanamide (LiN(CN)) 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 sp-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.

High‐Pressure Behavior of Lead Cyanamide PbNCN

“…Instead, we observe a flattening of the corrugated double layers. A similar behavior has been suggested in a recent study on LiN(CN) 2 where an anisotropic behavior was proposed up to 4 GPa and no polymerization was observed up to 22 GPa …”

“…2018, 1881-1885 www.zaac.wiley-vch.de proposed up to 4 GPa and no polymerization was observed up to 22 GPa. [20] To understand why this happens during the compression from 0 to 13 GPa, we provide COHP plots of the cells (Figure 3c). Again, starting from 0 to 5 GPa, we see only miniscule changes in the COHP plots, resulting in a slightly more covalent system and a reduction of the bandgap from 1.7 to 1.5 eV.…”

From Molecules to Carbon Materials—High Pressure Induced Polymerization and Bonding Mechanisms of Unsaturated Compounds

“…A trimerization process involving three cyanide groups from different dicyanamide ions to form a tricyanomelaminate ring was reported in some nitride compounds [72][73][74]. The behavior of LiN(CN) 2 under high pressure was studied by Raman spectroscopy, infrared spectroscopy and XRD [75]. Infrared and Raman spectrum data show that LiN(CN) 2 begins to undergo a phase transition at 7.5-9 GPa, but the original peaks related to molecular crystal does not change significantly in frequency and intensity, suggesting that this is a new polymorph.…”

“…(f) Neutron PDF (G(r)) of K3Fe(CN)6 recovered from different pressures. (g) Phase transition and chemical reaction process of K3Fe(CN)6 under high pressure [71].A trimerization process involving three cyanide groups from different dicyanamide ions to form a tricyanomelaminate ring was reported in some nitride compounds[73][74][75]. The behavior of LiN(CN)2 under high pressure was studied by Raman spectroscopy, infrared spectroscopy and XRD…”

Comparative studies of vibrational properties and phase transitions in perovskite‐like frameworks of [(C3H7)4N][M(N(CN)2)3] with MMn, Co, Ni

“…The tentative assignment of the dca modes is proposed on the basis of experimental and calculated vibrational modes prepared for simple dicyanamides salts: sodium, lithium, and ammonium. [26][27][28] Likewise, the analysis of phonon properties of the TPrA + ion is based on our DFT calculation.…”