Quaternary selenostannates Na2−xGa2−xSn1+xSe6 and AGaSnSe4 (A=K, Rb, and Cs) through rapid cooling of melts. Kinetics versus thermodynamics in the polymorphism of AGaSnSe4
Introduction
The structural chemistry of complex chalcogenides containing tetravalent group 14 elements (i.e., Si, Ge, Sn) has been relatively well investigated [1], [2], [3]. Due to the strong preference of these elements for tetrahedral geometry, most compounds possess crystal structures consisting of a variety of edge- or corner-shared MQ4 (M=Si, Ge, Sn; Q=S, Se, Te) tetrahedra. These include (i) [MQ4]4− tetrahedra [4], [5], (ii) the [M2Q7]6− unit formed by the corner-sharing of two tetrahedra [6], (iii) the adamantane-like [M4Q10]4− unit formed by the sharing of three corners of each tetrahedron [7], and (iv) the [M2Q6]4− dimers formed by the edge-sharing of two tetrahedra [8]. Several quaternary selenostannates are known with transition metals such as Cu, Ag, Au, and Mn [9], [10].
Fewer reports exist with group 13 elements (e.g., Al, Ga, and In). From the viewpoint of synthetic methodology, selenostannates have been generally prepared in flux medium at intermediate temperature or by direct combination reactions followed by slow cooling to achieve crystallization. The latter technique results in thermodynamically stable phases in the range of crystallization temperature. In an attempt to avoid thermodynamically stable phases and favor kinetically stable or even metastable phases we opted to take the exact opposite approach. That is a fast reaction, followed by rapid quenching to induce rapid crystallization. In this regard, we have explored a flame melting–rapid cooling method in which the reactants are thoroughly melted by a torch flame and then rapidly quenched into room temperature or even liquid N2 temperature. This approach can produce cooling rates in the order of 200°C/min and can be useful (although it does not guarantee) in accessing kinetically stable phases that cannot be prepared by conventional slow cooling processes. Such a tactic has been little exploited. Recently, we reported some interesting metastable compounds (e.g., KBiP2Se6 and KSbP2Se6) [11], KSb5S8[12], and β-KInSnSe4[13] that have been trapped through rapid melt cooling. These materials exhibit phase transitions to more thermodynamically stable configurations simply by annealing below the melting point.
Here we report several quaternary alkali-metal gallium selenostannates synthesized through this flame melting–rapid cooling method, and also describe their crystal structures and optical properties. Na2−xGa2−xSn1+xSe6 (I) has a three-dimensional framework structure consisting of trimeric (Sn,Ga)3Se9 units and tunnels where the Na atoms reside. The structures of KGaSnSe4 (II), RbGaSnSe4 (III), and CsGaSnSe4 (IV) are layered in which one-dimensional chains consisting of edge-shared (Sn,Ga)2Se6 dimers and (Sn,Ga)Se4 tetrahedra are linked side-by-side. We show that in KGaSnSe4, RbGaSnSe4, cooling of the melts does not produce the thermodynamically stable product. In fact the latter is inaccessible under melt-cooling conditions; instead a proper solid-state annealing protocol is necessary to obtain the so-called γ-form of these compounds. The implications of these results are discussed.
Section snippets
Experimental
Chemicals were used as obtained without further purification: (i) Ga metal (3 mm shots 99.999%, CERAC, Inc.) (ii) Sn metal (99.8%, −325 mesh, CERAC, Inc.), and (iii) Se (99.99%, Noranda Advanced Materials, Quebec, Canada) A2Se (A=Na, K, Rb, and Cs) were prepared by reaction of stoichiometric amounts of alkali-metal and selenium in liquid ammonia [14]. All manipulations were carried out under a dry nitrogen atmosphere inside a glovebox.
Red crystals of Na2−xGa2−xSn1+xSe6 (I), yellowish-brown
Structure of Na0.9Ga0.9Sn0.6Se3
The Ga and Sn sites in the lattice are mixed occupancy sites and compared to the ideal composition of “NaGaSn0.5Se3” there exist a slight excess of tin atoms on metal sites M(1) and M(2). As a result, the concentration of Na and Ga is slightly decreased from the ideal concentration to maintain charge neutrality. As illustrated in Fig. 1, the structure of I is non-centrosymmetric and polar and contains a three-dimensional network of corner-shared (Sn,Ga)Se4 tetrahedra. The network consists of
Conclusion
The quaternary selenostannates, Na2−xGa2−xSn1+xSe6 and AGaSnSe4 (A=K, Rb, and Cs), were prepared with a flame melting–rapid cooling method. The structure of Na2−xGa2−xSn1+xSe6 can be described as three-dimensional polar network of trimeric (Sn,Ga)3Se9 units with Na atoms in one-dimensional tunnel. This phase is found to require a fast crystallization condition to form and it is regarded to be only kinetically stable. In light of this, it is evident that the flame melting–rapid cooling method is
Acknowledgements
Financial support from the National Science Foundation (DMR-0127644) is gratefully acknowledged. This work was supported in part by Korea Research Foundation Grant (KRF-2003-042-C00065).
References (20)
- et al.
Coord. Chem. Rev
(1998)et al.J. Solid State Chem
(1999) - et al.
Z. Anorg. Allg. Chem
(1976) - et al.
Inorg. Chem
(1993) - et al.
Chem. Mater
(1993) - et al.
Chem. Mater
(2000) - et al.
Prog. Inorg. Chem
(1995) Angew. Chem. Int. Ed. Engl
(1983)et al.J. Solid State Chem
(1978)Rev. Chim. Miner
(1970)et al.Inorg. Chem
(2001)Acta Crystallogr. E
(2002)et al.J. Solid State Chem
(2002)- et al.
J. Solid State Chem
(1971) - et al.
Z. Anorg. Allg. Chem
(1973) - et al.
Z. Anorg. Allg. Chem
(1973)
Cited by (24)
AGaSnS<inf>4</inf> (A = Rb, Cs): Three sulfides and their structure diversity
2020, Journal of Solid State ChemistryCitation Excerpt :The Rb1, Rb2 atom coordinate with seven or eight S atoms with the bond distances of 3.360–3.687 and 3.339–3.823 Å, respectively (Table S2, Fig. S3). The structures o-CsGaSnS4 and m-RbGaSnS4 are similar with those of Cs2ZnGe3S8 [12], Cs2MnGe3Se8 [13], AGaSnSe4 [17] and TlInSiS4 [26]. All of them have a two-dimensional layered structure that is constructed by the neighboring corner-sharing [M1M2Q7] chains linked via edge-shared [M2Q6] dimers, although they eventually crystallize in different space group.
Synthesis, structure, magnetic and optoelectric properties of layered NaM<inf>0.5</inf>Sn<inf>0.5</inf>S<inf>2</inf> (M= Mn, Fe)
2018, Journal of Alloys and CompoundsCitation Excerpt :Chalcogenides, especially, quaternary thiostannates have abundant structures [1–9] and diverse applications such as thermoelectric materials [10–12], non-linear optic materials [1,13–16], battery anodes [17], photovoltaic materials [18–24], ion conducting materials [25] and ion-exchange materials [26].
Syntheses, structures, and optical properties of the indium/germanium selenides Cs<inf>4</inf>In<inf>8</inf>GeSe<inf>16</inf>, CsInSe<inf>2</inf>, and CsInGeSe<inf>4</inf>
2014, Journal of Solid State ChemistryCitation Excerpt :The M/Q layers in CsInGeSe4 are found in the structures of several other AMM'Q4 compounds. These compounds, which crystallize in diverse space groups, include TlMM'S4 (M=Al, Ga, In, M'=Si, Ge) [27,28], KInGeS4 [8], β-KInSnSe4 [29], and AGaSnQ4 (A=Na, K, Rb, Cs, Tl, Q=S, Se) [8,30,31]. However, insofar as we can determine, CsInGeSe4 is isostructural only to CsGaSnSe4 [31].
Solvothermal syntheses of three new one-dimensional ternary selenidostannates: [DBNH][M<inf>1/2</inf>Sn<inf>1/2</inf>Se<inf>2</inf>] (M = Mn, Zn, Hg)
2013, Journal of Solid State ChemistryCitation Excerpt :On the other hand, hybridize transition metals with group 13 and 14 metals may regulate the chemical and physical properties of 1D chain. 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) has been frequently used in the solvothermal syntheses of metal chalcogenides [66,67], mostly because protonated DBNH+ cations can act as templates or structure directing-agents in the constructions of chalcogenides, and moreover, DBN can provides strongly alkaline environment in the synthesis procedure. In this paper, we report the solvothermal syntheses, crystal structures, and characterizations of three one-dimensional chain-like mixed-metal ternary selenidostannates: [DBNH][M1/2Sn1/2Se2] (M=Mn (1), Zn (2), Hg (3)); DBN=1,5-diazabicyclo[4.3.0]non-5-ene).
- 1
Present address: Department of Applied Chemistry, Center for Optoelectronics and Microwave Thin-Film Devices, College of Natural Sciences, Konkuk University Chungju Campus, Chungju, Chungbuk 380-701, South Korea.