Synthesis, Structure, and Optical Properties of Antiperovskite-Derived

Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Synthesis, Structure, and Optical Properties of AntiperovskiteDerived Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I) Chalcohalides Ruiqi Wang,† Xian Zhang,† Jianqiao He,‡ Kejun Bu,‡ Chong Zheng,§ Jianhua Lin,*,† and Fuqiang Huang*,†,‡ †

Beijing National Laboratory for Molecular Sciences and State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China ‡ CAS Key Laboratory of Materials for Energy Conversion and State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, People’s Republic of China § Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States S Supporting Information *

ABSTRACT: Six isostructural antiperovskite-derived chalcohalides, Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I), crystallizing in the space group Pnma, have been synthesized by solid-state reactions. The crystal structure features a 3D framework with the [XBa5]9+ disordered square pyramids as building blocks and [MQ3]3− units filling the interspace. [XBa5]9+ disordered square pyramids are edge-sharing along [010], derived from the fusing of the two pyramids in octahedral [XBa6]11+. Surprisingly, Ba2AsS3X (X = Cl, Br, I) show almost the same optical band gap of 2.80 eV, and Ba2AsSe3X (X = Br, I) also have a similar band gap of 2.28 eV. The optical band gap of Ba2SbS3I is 2.64 eV. First-principles calculations reveal that the optical absorption is attributed to the transitions between Q np at the valence band maximum (VBM) and M np−Q np at the conduction band minimum (CBM). These compounds also possess interesting photoluminescence properties with splitting emission peaks on excitation at 200 nm.

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INTRODUCTION Heteroanionic compounds, which contain at least two different anions in one structure, have shown many novel physical and chemical properties such as superconductivity,1,2 SHG effects,3 photocatalysis,4 hard-ray detectors,5 and photovoltage.6,7 As a class of heteroanionic compounds, chalcohalides include many compounds with abundant structural diversities and potential applications. Ferroelectricity of trinary chalcohalides SbSI was found in 1962.8 BiSI can act as the photoelectrode in photoelectrochemical (PEC) processes or as the absorber in thin film solar cells.6,7 BiTeI with a unique layered structure exhibits a giant Rashba effect and low lattice thermal conductivity. 9−11 Ba 3 AGa 5 Se 10 Cl 2 (A = K, Cs, Rb), 3 (Sb7S8Br2)(AlCl4)3,12 and NaBa4Ge3S10Cl13 showed strong second harmonic generation (SHG) properties. In addition, other properties such as upconversion luminescence14,15 and phase transitions16,17 are also found in some chalcohalides. Recently some antiperovskite-type chalcohalides, with the position of cations and anions inverted with respect to perovskite, were synthesized such as Ba3(MQ)4Cl (M = Ga, In, Q = S, Se),13,18 Ba3(GaS4)Br,13 Ba3(FeS4)X (X = Cl, Br), and Ba3(FeSe4)Br.19 These structures consist of a 3D octahedral framework of [Ba3X]5+ filled by [MQ4]5− tetrahedra. Some novel physical properties were found in these © XXXX American Chemical Society

compounds. For example, an unexpected antiferromagnetic phase transition was observed in Ba3(FeS4)Br, even though the shortest Fe−Fe distance exceeds 6 Å.19 Chalcohalides Hg3Q2I2 (Q = S, Se, Te) possess a defect antiperovskite structure with ordered vacancies and are demonstrated to be promising candidates for hard radiation detectors.20,21 However, antiperovskite-type chalcohalides and their related compounds are much rarer, and their optical properties have not been investigated fully. Herein we report the syntheses and structures of six new antiperovskite-derived chalcohalides Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I). The crystal structure features a framework with the [XBa5]9+ disordered square pyramids as building blocks and [MQ3]3− units filling the interspace. The edge-sharing [XBa5]9+ disordered square pyramids are derived from the fusing of the two pyramids in octahedral [XBa6]11+. These compounds show interesting optical properties, such as consistent band gaps and splitting photoluminescence emission. Electronic structures are calculated using first-principles theory. Received: November 8, 2017

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DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Table 1. Crystallographic Data and Details of the Structure Refinement for Ba2AsS3X (X = Cl, Br, I), Ba2SbS3I, and Ba2AsSe3X (X = Br, I)a formula wt a (Å) b (Å) c (Å) V (Å3) cryst color ρc (g cm−3) μ (mm−1) F(000) Rint R1 (I > 2σ(I)) wR2 (all data) GOF

Ba2AsS3Cl

Ba2AsS3Br

Ba2AsS3I

Ba2SbS3I

Ba2AsSe3Br

Ba2AsSe3I

481.23 11.8589(4) 6.8211(2) 9.6627(3) 781.62(4) pale yellow 4.089 15.247 840 0.0482 0.0149 0.0267 1.190

525.69 12.064(2) 6.8683(7) 9.671(2) 801.4(2) pale yellow 4.357 19.524 912 0.0427 0.0145 0.0216 1.037

572.68 12.3889(7) 6.9845(3) 9.7057(5) 839.84(7) pale yellow 4.529 17.549 984 0.0406 0.0204 0.0356 1.073

619.51 12.5170(5) 7.1019(4) 9.8228(5) 873.19(7) pale yellow 4.712 16.146 1056 0.0252 0.0140 0.0262 1.217

666.39 12.2603(5) 7.1176(3) 9.9900(4) 871.77(6) yellow 5.077 29.756 1128 0.0228 0.0140 0.0285 1.003

713.38 12.602(2) 7.2070(9) 10.017(2) 909.8(2) yellow 5.208 27.516 1200 0.0330 0.0152 0.0241 1.203

All compounds crystallize in the space group Pnma. R = ∑||Fo| − |Fc||/∑|Fo|, wR2 = {∑[w(|Fo|2 − |Fc|2)2]/∑(w|Fo|4)1/2, and calculated w = 1/ [σ2(Fo2) + (0.0255P)2] where P = (Fo2 + 2Fc2)/3.

a

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using the Kubelka−Munk equation.23 Photoluminescent properties of the six compounds were measured using a Hitachi F7000 fluorescence spectrophotometer at room temperature. The excitation wavelength was 200 nm, while the range of the emission wavelength was from 250 to 700 nm. Electronic Structure Calculations. In order to investigate the electronic structures of these compounds, first-principles calculations were carried out within density functional theory (DFT) using the projector augmented wave (PAW) method24 implemented in the Vienna ab initio simulation package (VASP).25−27 The Perdew− Burke−Ernzerhof (PBE) version of the generalized gradient approximation (GGA) was used to describe the exchange correlation functional.28 The cutoff energy of the plane-wave basis was set to 370 eV. During the structural optimization, the crystal structures and the lattice parameters were set as the values observed in experiments, while the positions of atoms were relaxed until the atomic forces on each atom were less than 0.01 eV/Å. A Monkhorst−Pack k-point grid of 8 × 14 × 10 was used for Brillouin zone (BZ) sampling for the six compounds.

EXPERIMENTAL SECTION

Synthesis. Single crystals of the six compounds were obtained by solid-state reactions. All operations were carried out in an Ar-protected glovebox. The reagents BaS and BaSe were synthesized by heating a mixture of Ba pieces and S or Se powder at 873 K under vacuum. With the synthesis of Ba2AsS3Cl as an example, the starting materials BaS (0.1016g, 0.6 mmol), As2S3 (0.0492g, 0.2 mmol), and BaCl2 (0.0416g, 0.2 mmol) were mixed and fully ground. They were loaded in a carbon-coated fused silica tube. The tube was frame-sealed under vacuum (10−3 mbar), heated to 1023 K for 12 h, held for 48 h, and cooled to 573 K in 72 h. Pale yellow single crystals were obtained after this procedure. Single crystals of the other five compounds were synthesized under almost the same conditions, except that Ba pieces and I2 were used as starting materials when the iodine-containing compounds were synthesized. Single-Crystal X-ray Crystallography. Single crystals suitable for X-ray diffraction were chosen. Data collection was performed on an Agilent Super Nova Diffractometer equipped with mirror-monochromated Mo Kα radiation. The structures of the six compounds were solved by direct methods and refined by full-matrix least squares on F2 using the SHELXTL program package.22 Multiscan absorption corrections were performed. All six compounds are isostructural. The crystal data and refinement details are summarized in Table 1. Selected interatomic distances are presented in Table S1 in the Supporting Information. Powder X-ray Diffraction and Scanning Electron Microscopy. Powder X-ray diffraction (PXRD) data were collected on ground crystalline samples of these six compounds with a flat sample geometry using a Bruker D2 phaser diffractometer equipped with a monochromated source of Cu Kα radiation (λ = 0.15406 nm) at 4 kW (40 kV, 100 mA). The patterns were recorded in a slow-scanning mode with 2θ from 5 to 80° with a scan rate of 1.2° min−1. Images and semiquantitative energy dispersive X-ray spectroscopy (EDS) analyses of the six compounds were obtained using a Phenom Pro scanning electron microscope (SEM) equipped with a PGT energy-dispersive X-ray analyzer. Single crystals were placed on the surface of a doublesided carbon tape which was attached on the aluminum SEM substrate. EDS data were collected using an accelerating voltage of 15 keV with a 60 s accumulation time. The atomic ratios of four elements in each compound are all close to their corresponding chemical compositions, and the detailed compositions are given in Table S2 in the Supporting Information. Optical Measurements. Optical diffuse-reflectance measurements were performed at room temperature using a UV-4100 spectrophotometer operating from 1000 to 250 nm. BaSO4 was used as a 100% reflectance standard. The powdered samples were spread on a compacted base of BaSO4 powder. The generated reflectance versus wavelength data were used to calculate the band gaps of the materials

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RESULTS AND DISCUSSION Syntheses. Due to the differences in electronegativities, charge densities, and polarizabilities between chalcogen ions and halogen ions, attempts to synthesize chalcohalidea often end in phase separation. Thus, the number of chalcohalides is very limited, and the chemistry of chalcohalides is not well developed. Here the six chalcohalides Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I) were synthesized by solid-state reactions at 1023 K. The powder X-ray diffraction data of the six as-synthesized products all match well with the simulated patterns obtained from the single-crystal data (Figure 1 and Figure S1 in the Supporting Information). The crystal morphologies were studied with a SEM, and the images are shown in Figure S2 in the Supporting Information. Semiquantitative EDS confirmed the presence of all the elements in each compound and the Ba:M:Q:X ratios are close to the expected 2:1:3:1 (Table S2 in the Supporting Information). Crystal Structure. The six isostructural compounds Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I) crystallize in an antiperovskite-derived structure type. They each contain four formula units in the space group Pnma; the detailed cell parameters are shown in Table 1, and the selected bond lengths and angles are shown in Table S1 in the Supporting Information. In Ba2AsS3Cl, there are two independent Ba sites (4c Wyckoff position), one independent As site (4c), two B

DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX

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respectively. The stereochemically active 4s2 lone pair of As3+ possesses an orientation toward Ba1 with a Ba−As distance of 3.4038(4) Å, which implies a relatively strong interaction. Along the series, the lengths of As−S bonds increase from 2.2296(7) and 2.228(2) Å in Ba2AsS3Cl to 2.236(2) and 2.240(2) Å in Ba2AsS3I. The As−Se bonds of Ba2AsSe3I (2.3804(4) and 2.3750(5) Å) are also longer than those of Ba2AsSe3Br (2.3733(4) and 2.3703(6) Å). The Sb−S distances in Ba2SbS3I are 2.4080(7) and 2.389(2) Å. The M−Q bond lengths are consistent, for example, with those of 2.243(2)− 2.267(2) Å for As−S in CsCu2AsS3,29 2.345(2)−2.388(2) Å for As−Se in RbAg2As3Se6,30 and 2.4444(8)−2.4659(8) Å for Sb− S in KCu2SbS3.31 Ba2MQ3X series compounds are isostructural with the mineral mutnovskite, Pb2AsS3(Cl,Br,I), while Ba2+ (radius 1.61 Å), being larger than Pb2+ (1.49 Å), leads to extension of cell volumes.32 To omit the distortion effect of the halide atoms on the coordination environment of Pb in mutnovskite, we also solved the structure of Pb2AsS3I, which was synthesized via a metal flux method. Ba2+ in Ba2AsS3I and Pb2+ in Pb2AsS3I both reside upon the Wyckoff position 4c with symmetry element m perpendicular to the b axis. They possess the same coordination as shown in Figure S3 in the Supporting Information. The Pb2−S1 distance of 3.720(2) Å (×2) is obviously longer than the corresponding Ba2−S1 distance of 3.445(2) Å. The Pb1−S1 distance of 3.319(2) Å (×2) is also longer than the corresponding Ba1−S1 distance of 3.190(2) Å. The shortest Ba−As distance of 3.5259(9) Å in Ba2AsS3I is comparable with the shortest Pb−As distance of 3.444(2) Å. Optical Measurements. The optical absorption properties of these compounds were investigated by UV−vis diffuse reflectance spectroscopy, as depicted in Figure 3a, and the band gaps were determined by an extrapolation method, as shown in Figure 3b. Ba2AsS3X (X = Cl, Br, I) are all pale yellow, which is consistent with their experimental optical band gap of 2.80 eV. Ba2AsSe3X (X = Br, I) is yellow with an optical band gap of 2.28 eV. Ba2SbS3I is pale yellow with an optical band gap of 2.64 eV. The similar band gaps of Ba2AsS3X (X = Cl, Br, I) and Ba2AsSe3X (X = Br, I) indicate that the band edges of these compounds are mainly contributed by the states of the As−Q bonds, while the states of the more ionic halogens are located deeper in the valence band, as illustrated in Figure 3c. The band gaps of Ba2MQ3X are larger than those of some related compounds such as binary As2S3 (2.44 eV),33 As2Se3 (1.85 eV),34 and Sb2S3 (1.72 eV),35 ternary NaAsS2 (2.19 eV),33 γNaAsSe2 (1.75 eV),34 and Ba3Sb4.66S10 (2.14 eV),36 and chalcohalides Ba4Sb3S8Cl (2.09 eV),37 Ba3KSb4S9Cl (1.99 eV),38 and [Sb7S8Br2](AlCl4)3 (2.03 eV).12 The optical absorptions of these compounds all originate from the transitions between chalcogen np states and 15 group metal ns−np states. Therefore, the larger band gaps of the title compounds result from the highly isolated [MQ3]3− units instead of 0D large clusters (Ba4Sb3S8Cl, [Sb7S8Br2](AlCl4)3), 1D chains (NaAsS2, γ-NaAsSe2, Ba3KSb4S9Cl), or 2D layers (As2S3, As2Se3, Sb2S3, Ba3Sb4.66S10). The photoluminescence emission spectra of these compounds excited at 200 nm, interestingly, have multiemission character, as shown in Figure 4. For Ba2AsS3X, the top of each peak split into two peaks centered at 386 and 468 nm (Figure 4a). For Ba2AsSe3X in Figure 4b the split is more obvious, and the centers of the two peaks are at 355 and 500 nm, respectively. The asymmetry of the emission peak of Ba2SbS3I also reveals multiemission character, while the intensity of the

Figure 1. Simulated (black) and experimental (red) PXRD patterns of Ba2AsS3Cl.

independent S sites (4c, 8d) and one independent Cl site (4c). The structure features a framework of the [ClBa5]9+ disordered square pyramids filled by [AsS3]3−, as depicted in Figure 2a.

Figure 2. (a) Schematic diagram of framework of the [ClBa5]9+ disordered square pyramids filled by [AsS3]3−. (b) Transformation from the [ClBa6]11+ octahedron to two edge-sharing [ClBa5]9+ disordered square pyramids. (c) Coordination environment of [AsS3]5−.

[ClBa5]9+ disordered square pyramids are edge-sharing along [010], derived from the fusing of the two pyramids in octahedral [ClBa6]11+, as shown in Figure 2b. The [ClBa5]9+ chains along [010] are connected with each other through corner sharing to form the 3D framework. The As3+ ions form 3-fold trigonal pyramids AsS3 containing two S1 atoms and one S2 atom. The As−S1 bond (2.2296(7) Å) is slightly longer than the As−S2 bond (2.228(2) Å), as shown in Figure 2c. The S1−As−S1 and S1−As−S2 (×2) angles are 97.93 and 99.82°, C

DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (a) UV−vis diffuse reflectance spectra and (b) plot of F1/2(R) vs energy using the Kubelka−Munk equation for Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I). (c) Schematic DOS of Ba2AsS3Br, Ba2AsS3I, and Ba2AsSe3Br.

Figure 4. Emission spectra of (a) Ba2AsS3X (X = Cl, Br. I), (b) Ba2AsSe3X (X = Br, I), and (c) Ba2SbS3I excited at 200 nm and (d) normalized emission spectra of Ba2AsS3I, Ba2SbS3I, and Ba2AsSe3I.

Electronic Structures. In order to investigate the electronic structures of these compounds, DFT calculations were performed. The band structure and density of states (DOS) of Ba2AsS3Cl are shown in Figure 5, and the calculation results of the other compounds are shown in Figures S4−S8 in the Supporting Information. The calculation reveals that Ba2AsS3X (X = Cl, Br, I) and Ba2AsSe3X (X = Br, I) are all indirect band

peak around 350 nm is lower than that of the peak at 468 nm (Figure 4c). The normalized emission spectrum is shown in Figure 4d. Regardless of the halogens, compounds with the same chalcogen anions possess almost the same emission spectrum, which implies that the splitting of peaks is not related to the halogen anions. D

DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX

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and its related structures can provide more new materials for optical applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02812. XRD, SEM, EDS, bond lengths and angles, and electronic structures (PDF) Accession Codes

CCDC 1583958−1583963 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for J.L.: [email protected]. *E-mail for F.H.: [email protected].

Figure 5. (a) Band structure (left) and DOS (right) of Ba2AsS3Cl. (b) Partial DOSs of As, S, and Cl.

ORCID

semiconductors with the valence band maximum (VBM) at the Γ point and the conduction band minimum (CBM) at the U point, and the calculated band gaps are 2.37 and 1.62 eV, respectively. In contrast, Ba2SbS3I is a direct band semiconductor whose VBM and CBM are both located at the Γ point, and the calculated band gap is 2.15 eV. The PDOS of Ba2AsS3Cl reveals that the VBM is mainly contributed by the S 3p states, and the S 3p and As 4p states contribute equally to the CBM. The partial DOS of Cl atoms is located near −3 eV below the Fermi level (Figure 5b). The partial DOS of As 4s is mainly located at −9 eV, manifesting the interaction between Ba and the 4s2 lone pair (Figure S9 in the Supporting Information). The band structures of the other five compounds are similar. This DOS composition near the Fermi level can explain the origin of the similar optical absorptions of Ba2AsS3X (X = Cl, Br, I) and Ba2AsSe3X (X = Br, I). The band edges of these compounds are mainly contributed by the states of the As−Q bonds, while the PDOSs of the more electronegative chalogen are located deeper below the Fermi level in comparison to those of chalcogenide. The optical absorption is mainly contributed by the electron transition between the states of the chalcogen and VA metal, with little participation of halogen states.

Fuqiang Huang: 0000-0001-7727-0488 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Innovation Program of the CAS (Grant KJCX2-EW-W11), “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (Grants XDB04040200), NSF of China (Grants 91122034, 51125006, 51202279, 61376056, and 21201012), and Science and Technology Commission of Shanghai (Grant 12XD1406800).

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REFERENCES

(1) de La Cruz, C.; Huang, Q.; Lynn, J.; Li, J.; Ratcliff, I. W.; Zarestky, J. L.; Mook, H.; Chen, G.; Luo, J.; Wang, N. Magnetic order close to superconductivity in the iron-based layered LaO1‑xFxFeAs systems. Nature 2008, 453, 899−902. (2) Zhao, J.; Huang, Q.; De La Cruz, C.; Li, S.; Lynn, J.; Chen, Y.; Green, M. A.; Chen, G.; Li, G.; Li, Z. Structural and magnetic phase diagram of CeFeAsO1−xFx and its relation to high-temperature superconductivity. Nat. Mater. 2008, 7, 953−959. (3) Yu, P.; Zhou, L. J.; Chen, L. Noncentrosymmetric inorganic open-framework chalcohalides with strong middle IR SHG and red emission: Ba3AGa5Se10Cl2(A = Cs, Rb, K). J. Am. Chem. Soc. 2012, 134, 2227−2235. (4) Zhang, K. L.; Liu, C. M.; Huang, F. Q.; Zheng, C.; Wang, W. D. Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst. Appl. Catal., B 2006, 68, 125−129. (5) Johnsen, S.; Liu, Z.; Peters, J. A.; Song, J. H.; Nguyen, S.; Malliakas, C. D.; Jin, H.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G. Thallium Chalcohalides for X-ray and γ-ray Detection. J. Am. Chem. Soc. 2011, 133, 10030−10033. (6) Hahn, N. T.; Rettie, A. J. E.; Beal, S. K.; Fullon, R. R.; Mullins, C. B. n-BiSI Thin Films: Selenium Doping and Solar Cell Behavior. J. Phys. Chem. C 2012, 116, 24878−24886. (7) Hahn, N. T.; Self, J. L.; Mullins, C. B. BiSI Micro-Rod Thin Films: Efficient Solar Absorber Electrodes? J. Phys. Chem. Lett. 2012, 3, 1571−6. (8) Fatuzzo, E.; Harbeke, G.; Merz, W. J.; Nitsche, R.; Roetschi, H.; Ruppel, W. Ferroelectricity in SbSI. Phys. Rev. 1962, 127, 2036.

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CONCLUSION A new series of six chalcohalides, Ba2MQ3X (M = As, Sb; Q = S, Se; X = Cl, Br, I), were synthesized by a solid-state method, and their structures were determined. These compounds possess the same crystal structures and similar electronic structures. The crystal structure is derived from an antiperovskite which features a framework of the [ClBa5]9+ disordered square pyramids filled by [AsS3]3−. [ClBa5]9+ disordered square pyramids are edge-sharing along [010], derived from the fusing of the two pyramids in octahedral [ClBa6]11+. They possess relatively large band gaps. First-principles calculations reveal that the states of halogens are located deep in the valence band; thus, the optical absorption and photoluminescence are mainly contributed by the states of the M−Q bonds. The interesting optical properties of these compounds imply that antiperovskite E

DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.7b02812 Inorg. Chem. XXXX, XXX, XXX−XXX