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 of HSE06 density-functional type reveal PbNCN to be an indirect semiconductor with a band gap of 2.4 eV, in remarkable quantitative agreement with the measured value. Mott–Schottky experiments demonstrate PbNCN to be a p-type semiconductor with a flat-band potential of 2.3 eV vs. the reversible hydrogen electrode (RHE) which is commonly used to estimate the value of the valence band edge position. Moreover, thin films of powderous PbNCN were assembled into a photoelectrode for photoelectrochemical water splitting. On the example of p-type PbNCN, this study provides the first experimental evidence that MNCN compounds can be applied as photocathodes for reductive reactions in photoelectrochemical cells.

In this work, we describe the synthesis and structure of the quaternary transition-metal cyanamides Na₂MnSn₂(NCN)₆ and Li₂MnSn₂(NCN)₆. These phases crystallise isotypically in layered structures, with P1m symmetry, that comprise hexagonal close-packed arrays of NCN²⁻ anions with metal cations in 5/6 of the octahedral holes, thereby reflecting low-symmetry modifications of the hierarchical [NiAs]-type MNCN structure. The distinct coordination requirements of the metal cations template an ordered decoration across the octahedral sites with corundum-like [Sn₂(NCN)₃]²⁺ layers alternating with [A₂Mn(NCN)₃]²⁻ layers which resemble a portion of the Li₂Zr(NCN)₃ structure. This motif is also mirrored in the form of the NCN²⁻ anions which adopt N–CN²⁻ cyanamide shapes with clear single- and triple-bond character. Distortion-mode analysis reveals the importance of K₁ octahedral twist and K₂ cyanamide tilt displacements in stabilising these phases, the latter of which is only accessible because of the extended nature of the NCN²⁻ anion. These are the first examples of non-binary transition-metal cyanamides to be discovered and this study highlights how the additional flexibility of the NCN²⁻ anion affords a novel structure-type not observed in oxide chemistry.

The ternary carbodiimide BaZn(NCN)₂ was prepared by a solid-state metathesis reaction between BaF₂, ZnF₂, and Li₂NCN in a 1:1:2 molar ratio, and its crystal structure was determined from Rietveld refinement of X-ray data. BaZn(NCN)₂ represents the aristotype of the LiBa₂Al(NCN)₄ structure which is unique to carbodiimide/cyanamide chemistry and is well regarded as being constructed from ZnN₄ tetrahedra, sharing edges and vertices through NCN²⁻ units to form corrugated layers with Ba²⁺ in the interlayer voids. Structural anomalies in the shape of the cyanamide units are addressed via IR spectrometry and DFT calculations, which suggest the presence of slightly bent N=C=N²⁻ carbodiimide units with C_2v symmetry. Moreover, chemical-bonding analysis within the framework of crystal orbital Hamilton population (COHP) reveals striking similarities between the bonding interactions in BaZn(NCN)₂ and SrZn(NCN)₂ despite their contrasting crystal structures. BaZn(NCN)₂ is only the second example of a ternary post-transition metal carbodiimide, and its realization paves the way for the preparation of analogues featuring divalent transition metals at the tetrahedral Zn²⁺ site.

The ternary cyanamide NaSc(NCN)₂ was prepared by a solid‐state metathesis reaction between Na₂NCN and ScCl₃ at 600 °C. The orthorhombic crystal structure was determined from powder X‐ray diffraction data to be isotypic to that of LiY(NCN)₂ with Pbcn symmetry. As such the structure of NaSc(NCN)₂ is well thought of as being derived from [NiAs]‐type MNCN binaries with a hexagonally close‐packed array of NCN^2–. In this hettotypic form, however, the Na⁺ and Sc³⁺ cations occupy the octahedral holes in a 1:1 ordered fashion forming corrugated rows within the octahedral planes that alternate along the stacking direction. Furthermore, the significant cation size differential induces a pronounced tilting of the cyanamide anion away from the [100] direction. Electronic structure calculations indicate an indirect band gap of 3.41 eV (SCAN functional), in broad agreement with the measured value of 4.19 eV, which characterizes NaSc(NCN)₂ as a wide‐band‐gap semiconductor.