On the path to kinetic solid-state chemistry: Activation energy-controlled stepwise synthesis and crystal structure of LiSc(NCN)2

Rationally designing new materials is a crucial objective in modern solid-state chemistry, employing different synthetic strategies to vary a reaction's energetic aspects and, hence, effectively control its direction. In that context, and aided by density-functional-based enthalpy diagrams, we have developed a solid-state cyanamide metathetic method allowing to synthetically scan its activation energy profile, thus yielding milder reaction conditions and preventing potential product decomposition. This approach has led to the preparation of the ternary cyanamide LiSc(NCN)₂ via solid-state metathesis between Na₂NCN, ScCl₃ and LiCl, essentially by the existence of an intermediate, Li_xNa_1–xSc(NCN)₂, and the subsequent stepwise exchange of Na⁺ with Li⁺ ions. Both LiSc(NCN)₂ and the solid solution crystallize in an orthorhombic crystal structure with Pbcn symmetry, similar to the rest of the LiM(NCN)₂ cyanamide family with M = Al, In, Yb and Y. Structural analysis of the coordination environment around the NCN²⁻ group reveals a relaxation in the distortion of this unit and also an inversion of the cyanamide orientation as Na⁺ ions are progressively replaced with Li⁺, thus making the formation of the targeted compound highly favorable.