Sn2O(CN2) was obtained from a solid-state metathesis. Its crystal structure incorporates a Sn2+ ion with a 5s2 lone pair and was analyzed in relation to that of SnO by electronicstructure calculations and a COHP bonding analysis.
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.
Two binary transition metal cyanamides, Zr(CN2)2 and Hf(CN2)2, were prepared by solid-state metathesis (SSM) reactions and separately controlled by differential thermoanalysis (DTA). The crystal structure of Hf(CN2)2 was solved and refined from a single-phase crystal powder by X-ray diffraction (XRD) in the space group Pbcn. Zr(CN2)2 was characterized by isotypic indexing. The crystal structure of M(CN2)2 compounds with M = Zr, Hf is closely related to that of LiY(CN2)2, but reveals large cavities due to the absence of lithium ions. Hf(CN2)2 exhibits thermoelastic properties characteristic of a flexible framework material. The calculated phonon energies, elastic tensor, and thermal expansion tensor are presented; the volumetric coefficient of thermal expansion is predicted to be near-zero under ambient conditions (αV = -3.5 × 10-6 K-1).
The low-temperature modification of Sr(OCN) was prepared and assigned as α-SCY after the high-temperature phase (now called β-SCY) and its frequency-doubling properties were reported recently. The crystal structure of α-SCY was solved and refined by single-crystal X-ray diffraction. Both modifications of SCY crystallize in noncentrosymmetric space groups, with the low-temperature phase (α-SCY) adopting the lower symmetry structure (Cc). Atomic positions in α-SCY (Cc) reveal only small deviations in comparison to those in the structure of β-SCY (R3c). The reversible phase transition between both modifications of SCY was studied by means of temperature-dependent powder X-ray diffraction. NLO measurements of both SCY modifications are reported in comparison to the commercial frequency-doubling material KTiOPO (KTP).
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