Experimental and Theoretical Evidences of p-Type Conductivity in Nickel Carbodiimide Nanoparticles with a Delafossite Structure Type

Perovskite-Like Carbodiimides AB(NCN)3: Synthesis and Characterization of MnHf(NCN)3 and FeHf(NCN)3

Two novel ternary air-stable transition-metal carbodiimides, MnHf(NCN)3 and FeHf(NCN)3, were synthesized via solid-state metathesis using either ZnNCN or Na2NCN as the carbodiimide source and the corresponding binary metal chlorides. These two phases are the first examples of transition-metal carbodiimides with an AB(NCN)3 composition, akin to ubiquitous ABO3 perovskite oxides. The crystal structure of MnHf(NCN)3 was determined and refined from powder X-ray diffraction (XRD) data in the non-centrosymmetric space group P6322 allowing for chirality, the assignment of which is supported by second-harmonic generation (SHG) measurements. FeHf(NCN)3 was found to crystallize isotypically, and the presence of iron(II) in a high spin state was confirmed by 57Fe Mößbauer spectroscopy. The structures are revealed to be NiAs-derived and can be described as a hexagonal stack of NCN2- anions with metal cations occupying 2/3 of the octahedral voids. Both IR spectroscopic measurements and DFT calculations agree that the NCN2- unit is a bent carbodiimide with C2v symmetry, necessary to account for the size difference present in such a vacancy-ordered structure. Magnetic studies reveal predominantly strong antiferromagnetic interactions but no long-range order between the paramagnetic Mn2+ centers, likely due to the dilution of Mn2+ over the octahedral sites or perhaps even due to some degree of magnetic frustration. The optical and electrochemical properties of MnHf(NCN)3 were then studied, revealing a wide band gap of 3.04 eV and p-type behavior.

Mechanistic Insights on the Formation of a Carbodiimide Ion from Urea in La2O2NCN Synthesis Based on the "Proanion" Strategy

This study affords mechanistic insights into the formation mechanism of carbodiimide ions (NCN2-) from urea during the synthesis of La2O2NCN by employing the "proanion" strategy without using NH3 gas. It is a safer, cost-effective, and environmentally friendly approach. Urea, acting as a proanion, decomposes upon heating, facilitating conversion to NCN2-. This work meticulously examines the phase transitions and identifies intermediate species formed during the reaction using in situ X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric-differential thermal analysis-mass spectrometry. The findings present a detailed mechanism in which urea initially decomposes at 140 °C, releasing HNCO, which reacts with La(OH)3 to immobilize NCO- species on the surface of La(OH)3. As the temperature reaches approximately 400 °C, these NCO- anions transform into NCN2- anions by releasing CO2 gas, resulting in the formation of an amorphous phase rich in NCN2-. Following further heating to 600 °C, La2O2NCN crystallizes, enhancing its crystallinity as the temperature increases. These findings elucidate the formation mechanism of La2O2NCN, introduce the "proanion method" for the alternative synthesis of metal (oxy)carbodiimides, and expand their potential for applications as functional materials.

Controlled phase and crystallinity of FeNCN/NC dominating sodium storage performance

FeNCN is a potentially fast-charging sodium ion anode due to the presence of lots of broad tunnels and its high electronic conductivity. However, FeNCN has been rarely investigated due to its complicated synthetic process and unclear synthetic mechanism, which affect the precise control of its phase and crystallinity. In this work, phase- and crystallinity-controlled FeNCN polyhedrons grown on nitrogen-doped carbon (FeNCN/NC) are successfully fabricated by adjusting the growing time and temperature. Moreover, the synthesis mechanism is disclosed in this paper. High-crystallinity FeNCN grows along the [001] direction, which exposes sufficient broad channels on the {010} planes and significantly improves the diffusion rate of sodium ions. Moreover, high-crystallinity FeNCN exhibits higher mechanical strength, which reduces its pulverization rate and endows it with durable cycling stability. When applied as an anode in a sodium-ion battery, high-crystallinity FeNCN/NC exhibits a high rate capability of 332 mA h g^-1 at 5.0 A g^-1 and a stable cycling performance of 368 mA h g^-1 after 300 cycles at a high current density of 1.0 A g^-1. This work confirms that the sodium-ion storage performance of FeNCN can be further improved by tuning its crystallinity.

Metathetic synthesis of lead cyanamide as a p-type semiconductor

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.

[(Ba19Cl4)(Ga6Si12O42S8)]: a Two-Dimensional Wide-Band-Gap Layered Oxysulfide with Mixed-Anion Chemical Bonding and Photocurrent Response

Mixed-anion compounds play an essential part in modern structural chemistry. In this Communication, an unprecedented hexanary oxysulfide, [(Ba₁₉Cl₄)(Ga₆Si₁₂O₄₂S₈)] (FJ-1), was synthesized at 1073 K by a standard solid-state method, which is a new phase in the AE/M^III/M^IV/O/Q/X (AE = alkaline-earth metal; M^III = group 13 metal; M^IV = group 14 metal; Q = chalcogen; X = halogen) system. FJ-1 adopts a new structure type and crystallizes in the orthorhombic system with space group Cmcm. In the structure, unique two-dimensional [Ga₆Si₁₂O₄₂S₈]^34- layers formed by the familiar [SiO₄] species and unusual heteroligand [GaO₂S₂] and [GaO₃S] tetrahedra extend the intralayer linking. Significantly, a photoelectrochemical test revealed that FJ-1 is photoresponsive under ultraviolet illumination. Moreover, density functional theory calculations were employed to gain insight into the relationship between the electronic structure and optical properties. Such work will be conducive to the structural diversity of gallium coordination chemistry by exploration of the new mixed-anion functional chalcohalides.