Lead cyanamide PbNCN was synthesized by solid-state metathesis between PbCl2 and Na2NCN in a 1:1 molar ratio, and its structure was confirmed from Rietveld refinement of X-ray data. Electronic-structure calculations...

Due to its unsurpassed capability to engage in various sp hybridizations or orbital mixings, carbon may contribute in expanding solid-state nitrogen chemistry by allowing for different complex anions, such as the known NCN 2À carbodiimide unit, the so far unknown CN 3 5À guanidinate anion, and the likewise unknown CN 4 8À ortho-nitrido carbonate (onc) entity. Because the latter two complex anions have never been observed before, we have chemically designed them using first-principles structural searches, and we here predict the first hydrogen-free guanidinates TCN 3 (T = V, Nb, Ta) and ortho-nitrido carbonates T' 2 CN 4 (T' = Ti, Zr, Hf) being mechanically stable at normal pressure; the latter should coexist as solid solutions with the stoichiometrically identical nitride carbodiimides and nitride guanidinates. We also suggest favorable exothermic reactions as useful signposts for eventual synthesis, and we trust that the decay of the novel compounds is unlikely due to presumably large kinetic activation barriers (C À N bond breaking) and quite substantial Madelung energies stabilizing the highly charged complex anions. While chemicalbonding analysis reveals the novel CN 4 8À to be more covalent compared to NCN 2À and CN 3 5À within related compounds, further electronic-structure data of onc phases hint at their physicochemical potential in terms of photoelectrochemical water splitting and nonlinear optics.

A detailed study of the electrochemical reaction mechanism between lithium and the trivalent transition‐metal carbodiimide Cr2(NCN)3, which shows excellent performance as a negative electrode material in Li‐ion batteries, is conducted combining complementary operando analyses and state‐of‐the‐art density functional theory (DFT) calculations. As predicted by DFT, and evidenced by operando X‐ray diffraction and Cr K‐edge absorption spectroscopy, a two‐step reaction pathway involving two redox couples (Cr3+/Cr2+ and Cr2+/Cr0) and a concomitant formation of Cr metal nanoparticles is apparent, thus indicating that the conversion reaction of this carbodiimide upon lithiation occurs only after a preliminary intercalation step involving two Li per unit formula. This mechanism, evidenced for the first time in transition‐metal carbodiimides, is likely behind its outstanding electrochemical performance as Cr2(NCN)3 can maintain more than 600 mAh g−1 for 900 cycles at a high rate of 2 C.

Bi2(NCN)3, the first binary pnictogen carbodiimide, and its ammonia derivative Bi2(NCN)3·NH3 have been prepared via nonaqueous liquid-state low-temperature ammonolysis. The crystal structure of Bi2(NCN)3·NH3 in space group Cc solved via single-crystal X-ray diffraction corresponds to a two-dimensional-like motif with layers of NCN2– alternating with honeycomb-like layers of edge-sharing distorted BiN6 octahedra, half of which are also coordinated by molecular ammonia occupying the octahedral holes. By contrast, Bi2(NCN)3 adopts a higher-symmetric C2/c structure with a single Bi position and stronger distortion but empty octahedral voids. In both cases, Bi3+ and its 6s2 lone pair are well mirrored by antibonding Bi–N interactions below the Fermi level. Density functional theory calculations reveal an exothermic reaction for the intercalation of NH3 into Bi2(NCN)3, consistent with the preferential formation of Bi2(NCN)3·NH3 in the presence of ammonia. A Bärnighausen tree shows both compounds to be hettotypic derivatives of the R3̅c M2(NCN)3 corundum structure that express highly distorted hexagonal-close-packed layers of NCN2– in order to accommodate the aspherical Bi3+ cations. Although Bi2(NCN)3 does not resemble the isovalent Bi2Se3 in forming two-dimensional layers and a topological insulator, theory suggests a driving force for the spontaneous formation of Bi2Se3/Bi2(NCN)3 sandwiches and a conducting surface state arising within the uppermost Bi2(NCN)3 layer.

The quaternary cyanamide Li 2 MgSn 2 (NCN) 6 was prepared by a solid-state metathesis reaction between Li 2 NCN, MgF 2 , and SnF 4 . Its trigonal structure was determined from powder X-ray diffraction data to be isotypic to that of Li 2 MnSn 2 (NCN) 6 with P31m symmetry. The new phase is well thought of as being derived from a [NiAs]-type MNCN structure with Sn 2 (NCN) 3 2 + corundum-like layers alternating with Li 2 Zr(NCN) 3 -like Li 2 Mg-(NCN) 3 2À layers. Structural anomalies in the shape of the cyanamide units are addressed via PXRD, IR spectroscopy as well as density-functional theory, all of them suggesting the presence of N�CÀ N 2À cyanamide units.