Synthesis, Structure, and Electronic Properties of Sn9O5Cl4(CN2)2.

The formation of the new compound Sn9O5Cl4(CN2)2 is reported and placed in the context of several other recently discovered tin carbodiimide compounds (Sn(CN2), Sn2O(CN2), and Sn4Cl2(CN2)3), all of which contain divalent tin. The crystal structure of Sn9O5Cl4(CN2)2, as determined by X-ray powder diffraction, includes an unusual [Sn8O3] cluster, in which tin atoms form the motif of a hexagonal bipyramid. An additional tin atom and two oxygen atoms connect these clusters into chains. Mössbauer spectroscopy shows tin to predominantly adopt the +2 oxidation state, and electronic structure calculations predict Sn9O5Cl4(CN2)2 to be a semiconductor.

Synthesis, Structure, and Electronic Properties of Sn(CN2) and Sn4Cl2(CN2)3.

A solid-state metathesis reaction between equimolar amounts of Li2(CN2) and SnCl2 revealed the formation of two new compounds, Sn4Cl2(CN2)3 and Sn(CN2). Thermal analysis of this reaction indicated that Sn4Cl2(CN2)3 forms exothermically near 200 °C and subsequently transforms into Sn(CN2) at higher temperatures. The crystal structures of both compounds are presented. According to optical measurements and band structure calculations, Sn(CN2) can be considered as a semiconductor with a band gap on the order of 2 eV. The presence of Sn2+ ions in the structure of Sn(CN2) with a toroidally shaped lone pair is indicated by electron localization function calculations. The structure of Sn(CN2) is shown to be related to the structures of FeS2 and CaC2.

W2O3I4 and WO2I2: metallic phases in the chemical transport reaction of tungsten.

The crystal structures of the hitherto unknown phase W2O3I4 and of WO2I2, a compound that is known to play an important role in the chemical vapor transport of elemental tungsten are reported. We demonstrate that WO2I2 transforms into W2O3I4, and then into WO2 with increasing temperature. Crystals of WO2I2 appear as thin platelets, showing metallic luster; crystals of W2O3I4 appear as black colored needle-shaped platelets. Both compounds adopt layered structures; electronic band structure calculations reveal metallic conductivity for W2O3I4 and surprisingly also for WO2I2.

Increased photocurrent of CuWO4 photoanodes by modification with the oxide carbodiimide Sn2O(NCN).

Tin(ii) oxide carbodiimide is a novel prospective semiconductor material with a band gap of 2.1 eV and lies chemically between metal oxides and metal carbodiimides. We report on the photochemical properties of this oxide carbodiimide and apply the material to form a heterojunction with CuWO4 thin films for photoelectrochemical (PEC) water oxidation. Mott-Schottky experiments reveal that the title compound is an n-type semiconductor with a flat-band potential of -0.03 V and, as such, the position of the valence band edge would be suitable for photochemical water oxidation. Sn2O(NCN) increases the photocurrent of CuWO4 thin films from 32 µA cm-2 to 59 µA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) in 0.1 M phosphate buffer (pH 7.0) under backlight AM 1.5G illumination. This upsurge in photocurrent originates in a synergistic effect between the oxide and oxide carbodiimide, because the heterojunction photoanode displays a higher current density than the sum of its individual components. Structural analysis by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveals that Sn2O(NCN) forms a core-shell structure Sn2O(NCN)@SnPOx during the PEC water oxidation in phosphate buffer. The electrochemical activation is similar to the behavior of Mn(NCN) but different from Co(NCN).