Two new ternary materials NaGaS 2 (1) and the Fedoped phase of NaGaS 2 , NaFe 0.135 Ga 0.865 S 2 (2), have been synthesized by employing polysulfide flux. Single crystal XRD analyses of 1 and 2 show that the structure is built up of adamantane-like Ga 4 S 10 super tetrahedral fundamental building units. These admantane-like units are connected through their corners to form [GaS 2 ] ∞ − layers that are stacked one over the other with Na ions residing in between the layers to balance the charge. Both the materials have the remarkable ability to absorb atmospheric water molecules and moisture from undried solvents as verified by TG analysis and FT-IR and XPS studies. The process of water absorption leads to stable distinct material) with restacked layers different from original crystal structure. This structural transformation is reversible as the transformed structures 1•H 2 O and 2•H 2 O can be returned to their original structures 1 and 2, respectively, upon heating. DFT calculation study reveals that a spontaneous exergonic hydration reaction takes place as outlined in NaGaS 2 + H 2 O → NaGaS 2 •H 2 O with the energy release, ΔE of −73.9 kJ mol −1 . DFT calculation predicts an increase in the unit cell parameters of b and c directions and shrinkage along the a direction of hydrated phase 1•H 2 O with an overall volume increase of 36.6%. Structural transformation affects their physical properties as the pristine compound 1 possess Na + ion conductivity of 2.88 × 10 −7 S cm −1 at 22 °C, whereas the hydrated compound 1•H 2 O displays ∼40 times increased ion conductivity of 1.25 × 10 −5 S cm −1 at the same temperature. DRS studies show very similar optical band gaps of ∼4 eV for compounds 1 and 1•H 2 O, respectively, in reasonable agreement with the DFT(HSE) band gap estimation but more than 1 eV above the DFT(PBE)-predicted band gaps of ∼2.4 eV. A sorption study indicates selective adsorption of water over MeOH, EtOH, and CH 3 CN with a maximum water uptake of 2.6 H 2 O per formula unit at P/P 0 = 0.9. A Karl Fischer titration study shows that NaGaS 2 (1) is certainly capable of adsorbing water from wet methanol and can be useful as a fast desiccating agent.

Herein, we report the syntheses, structure, Na-ion conductivity, and theoretical investigation of two moisture stable quaternary compounds, Na3ZnGaQ 4 (Q = S, Se). These compounds are synthesized using high-temperature solid-state synthesis routes employing polychalcogenide flux or by metathesis reactions. The crystal structure of these compounds is built up of a three-dimensional (3-D) network of corner-shared supertetrahedral (T2) units, where two such 3-D networks are interlocked. The d-block metal and the main group metal, Ga, occupy the same crystallographic site with a 1:1 ratio, making it a rare form of building unit. Band structure calculations show that both the compounds are wide band gap semiconductors with band gaps of 2.25 and 1.61 eV, respectively, for Na3ZnGaS4 (I) and Na3ZnGaSe4 (II), which are slightly underestimated compared to experimentally determined band gaps of 3.0 and 1.90 eV, respectively. I and II possess ionic conductivities of 3.74 × 10–4 and 0.12 mS/cm with activation energies of 0.42 and 0.38 eV, respectively, at 30 °C. Interestingly, I shows a significantly high ionic conductivity of 0.13 mS/cm at 30 °C upon exposure to air, which could be due to water adsorption on the surface or occlusion in the grain boundaries. Assuming the vacancy-assisted diffusion mechanism for ionic conductance, this difference is consistent with the difference on vacancy formation energies in these compounds, as predicted by DFT calculations. The bond valence sum map indicates that in both structures, the lowest energy diffusion path is one dimensional and it is along the c axis of the unit cell.

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Two new ternary thiogallates in the series A5GaS4 (A = Li(I), Na(II)) have been synthesized for the first time employing gas passing route using oxide precursors and high temperature solid...