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.
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 CuWO 4 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. Sn 2 O(NCN) increases the photocurrent of CuWO 4 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 Sn 2 O (NCN) forms a core-shell structure Sn 2 O(NCN)@SnPO x during the PEC water oxidation in phosphate buffer. The electrochemical activation is similar to the behavior of Mn(NCN) but different from Co(NCN). † Electronic supplementary information (ESI) available. See
The formation of the new compound Sn 9 O 5 Cl 4 (CN 2 ) 2 is reported and placed in the context of several other recently discovered tin carbodiimide compounds (Sn(CN 2 ), Sn 2 O(CN 2 ), and Sn 4 Cl 2 (CN 2 ) 3 ), all of which contain divalent tin. The crystal structure of Sn 9 O 5 Cl 4 (CN 2 ) 2 , as determined by X-ray powder diffraction, includes an unusual [Sn 8 O 3 ] 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. Mossbauer spectroscopy shows tin to predominantly adopt the +2 oxidation state, and electronic structure calculations predict Sn 9 O 5 Cl 4 (CN 2 ) 2 to be a semiconductor.
Three tin oxide halides, Sn 7 O 4 Cl 6 , Sn 7 O 4 Br 6 , and Sn 4 OI 6 , were synthesized by solid-state reactions of SnO and SnX 2 (X=Cl, Br, I) at 300°C. Crystal structures were solved and refined from single crystal X-ray diffraction data, revealing the presence of cubane-like [Sn 4 O 4 ] units in the structures of Sn 7 O 4 Cl 6 and Sn 7 O 4 Br 6. The electronic structure of Sn 7 O 4 Cl 6 was analyzed by DFT band structure calculations and the electron localization function (ELF).
WO2I2, a compound important in the chemical transport reaction of elemental tungsten and the hitherto unknown W2O3I4 are reported with their layered structures. Increasing iodine content increases the metallicity of the compounds.
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