Inorganic carbodiimide

[1] Adolph Frank and Nikodem Caro were the first to synthesize calcium cyanamide (CaNCN) and to develop a route for its production at the industrial level in 1898.

One can find detailed reports by E. Drechsel on the preparation of Ag2NCN, CaNCN, BaNCN, K2NCN and Li2NCN between 1875 and 1898 (before even XRD invention).

[3][4] The preparation of  Cd, Zn, Tl, Cu, Pb and Hg carboimides has been described during the 1950s.

Starting from 2000s, rare earth metal carbodiimides Ln2(NCN)3 (Ln = La, Ce, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Tm)[5] and transition metal carbodiimides TNCN (T= Mn, Fe, Co, Ni, Cu) and Cr2(NCN)3have been reported.

Recently, metal carbodiimides are explored as anode materials for lithium and sodium ion batteries and found to present better specific capacities compared to conventional graphite and hard carbon electrode materials.

The Lewis diagram for NCN 2- showing the symmetric carbodiimide form (1) and the asymmetric cyanamide form (2)
Crystal structure of TNCN, M= Fe, Co, Ni
Electrochemical performance of FeNCN as anode material for Li-ion batteries