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April 1, 2026Open Access

Pressure-Induced Reduction of Dicyanamide by Samarium(II) in a Coordination Polymer

HWHannah B. WineingerColorado School of Mines THTyler W. HinesColorado School of Mines KMKacy MendozaColorado School of Mines

Key Points

To investigate the pressure-induced reduction of dicyanamide by samarium(II) in a coordination polymer.
Synthesis of the samarium(II) coordination polymer using SmI2, tetrabutylammonium dicyanamide, and 2.2.2-cryptand.
Spectroscopic studies using UV-vis-NIR and Raman spectroscopy under varying pressure.
High-pressure single-crystal diffraction to observe structural changes.
A pressure-induced two-electron reduction of dicyanamide to cyanide and cyanamide occurs between 5 and 8 GPa.
A phase change is observed at 2.6 ± 0.1 GPa, characterized by a smaller Sm2+···N≡C bond angle and shorter Sm2+···C distance.
The findings provide mechanistic insights into reduction processes facilitated by pressure.

Abstract

A samarium(II) coordination polymer, Sm(2.2.2-cryptand)(dca)I (dca- = dicyanamide), has been prepared from the reaction of SmI2 with tetrabutylammonium dicyanamide and 2.2.2-cryptand. The structure consists of Sm(2.2.2-cryptand)2+ cations bridged by dicyanamide to form corrugated 1D chains. Single crystals of this compound have been studied spectroscopically using UV-vis-NIR and Raman spectroscopy as a function of pressure to reveal a pressure-induced two-electron reduction of dicyanamide by Sm2+ to cyanide and cyanamide and Sm3+ between 5 and 8 GPa. High-pressure single-crystal diffraction studies reveal a phase change at 2.6 ± 0.1 GPa, where a polymorph exhibiting a smaller Sm2+···N≡C bond angle and shorter Sm2+···C distance was observed. These observations provide mechanistic insight into the reduction of dicyanamide into cyanide and cyanamide by pressurized samarium(II).

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