Class: Intercalation Solid, Synthetic
Related Structures: Lithium intercalated hafnium nitrogen chloride, SmSI
Notable Properties: Superconductivity, Electrochromism
Zirconium nitrogen chloride is a layered structure with a double layer of ZrNCl. The chloride anions order similarly to the cadmium iodide structure type though the geometry at the Zr centers is now seven coordinate. Nitride centers occupy pseudo-tetrahedral site. As synthesized (from ZrH2 and NH4Cl heated to 650 °C), ZrNCl is a 3 eV bandgap semiconductor. However, the solid can be reduced post-synthetically via reductive intercalation of lithium.
By reduction with n-butyllithium in THF the nonstoichiometric phase LixZrNCl(THF)y can be synthesized to yield a rare case of what is formally trivalent zirconium. Upon reduction the material goes from electronically insulating to metallic at room temperature and transitions to a superconductor at about 13 K (link). Hafnium forms an isostructural phase that is superconducting below 25.5 K (link). These materials represented the first case of superconductivity in a metal nitride and displays a particularly dramatic change in electronic properties for an intercalation reaction.
Formula: LixZrNCl(THF)2x 0 < x < 0.13 (structure reported without THF upto x = 0.43)
Space Group: R-3m
Lattice Parameters: a = 3.59; c = 27.839
Similar phases: LixZrNBr(THF)2x and LixHfNCl(THF)2x
Reaction Notes: Reductive intercalation (assumed reversible)