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Synthesis, crystal structure and optical property of a novel metal chalcohalide: ZnHg3Se2Cl4
Author’s Accepted Manuscript Synthesis, crystal structure and optical Property of a novel metal chalcohalide: ZnHg3Se2Cl4 Guodong Zhang, Wei-Wei Xiong, Lina Nie, Qichun Zhang www.elsevier.com/locate/yjssc
PII: DOI: Reference:
S0022-4596(15)30040-2 http://dx.doi.org/10.1016/j.jssc.2015.06.032 YJSSC18960
To appear in: Journal of Solid State Chemistry Received date: 11 May 2015 Revised date: 16 June 2015 Accepted date: 20 June 2015 Cite this article as: Guodong Zhang, Wei-Wei Xiong, Lina Nie and Qichun Zhang, Synthesis, crystal structure and optical Property of a novel metal chalcohalide: ZnHg3Se2Cl4, Journal of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2015.06.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title Page
Title: Synthesis, Crystal Structure and Optical Property of a Novel Metal Chalcohalide: ZnHg3Se2Cl4 Authors: Guodong Zhang,a Wei-Wei Xiong,a Lina Nie,a Qichun Zhang*a,b Affiliation: aSchool of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore b
Division of Chemistry and Biological Chemistry, School of Physical and
Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
*Corresponding author: E-mail: [email protected]; Tel: +65-6790 4705. Fax: +6567904705
1
ABSTRACT:
A novel chalcohalide ZnHg3Se2Cl4 has been synthesized through a solid state
method and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the acentric space group Cmc21 (No. 36) with cell parameters a =7.3262(8) Å, b = 12.518(2) Å, c = 11.3324(14) Å. The compound consists of 12-membered Hg6Se6 rings edge-sharing with six neighbored rings to construct a 2D layered network and the ZnCl4 tetrahedra are sandwiched between layers. TG-DTA measurement shows that the compound is thermally stable up to 300 °C. The band gap of the crystal is about 2.23 eV, and the crystal exhibits a broad transparent range from 0.56 to 13.8 µm.
Keywords: Chalcohalide; Crystal structure; Solid state synthesis
* Corresponding author. E-mail: [email protected] Phone: +65-67904705. Fax: +6567904705
2
1. Introduction New crystalline chalcohalides and chalcogenides have received extensive research interests [16] not only because of their diverse structures but also technologically promising properties such as thermoelectric, phase-change transitions, upconversion luminescence, nonlinear optics, magnetism, and x-ray or γ-ray detections [7-15]. Among them, ternary or quaternary metal chalcohalides are hybrid materials, whose compositions and band gaps usually lie between those of binary chalcogenides and binary halides, providing them much richer structural features and more chances to tune their band gaps [16-28]. In particular, mercury (II)-related chalcohalides are much attractive because mercury ions usually possess diverse coordination geometries varying from linear to octahedral, thus it has a greater tendency to form all kinds of architectures covering 0D, 1D, 2D, and 3D topologies [16, 17, 20-27]. In fact, some interesting structural factors of mercury (II) chalcohalides have been report. For example, Hg2SnS2Br2 [21, 22] and CuHgSI [24] contain one-dimensional chains, in which, the short Hg-S bonds lead to [-Hg-S-] helical chains. Hg4In2Q3Cl8 (Q= S, Se, Te) are a new class of 1 D chalcohalides, which feature the novel quaternary cationic nano-belts [26]. The compound ZnHg3S2Cl4 is a case of 2D layered network, in which Hg6S3Cl3 forms a novel 12-membered ring, and these rings connected with each other by sharing the edges to form a layer structure [25]. The compounds Hg2PbI2S2 [20], Hg7InS6Cl5 [16], and TlHg6Q4Br5 (Q=S, Se) [27], are four cases of different 3D frameworks. Herein, we report a novel mercury-related chalcohalide: ZnHg3Se2Cl4, which is synthesized by using high temperature solid-state reaction method. The crystal structure, band gap, and thermal stability were characterized by single crystal XRD, optical absorption spectrum, and thermogravimetric measurement.
3
2. Experimental section 2.1 Synthesis of ZnHg3Se2Cl4 The title compound was prepared through a typical solid state reaction from a mixture containing Hg2Cl2 powder (4N, 2 mmol, 944 mg; note: much attention should be paid due to the toxicity of mercury and extreme care must be taken when handling sample and products.), Zn powder (5N, 1 mmol, 65 mg), and Se powder (3N, 2 mmol, 158 mg) which were loaded into an fused silica tube (12mm i.d.) and sealed under high vacuum (~10-3 Pa). The mixture was heated to relatively low temperature 200 °C within 20h, and kept at this temperature for 60 h, followed by a shutdown of the furnace. The yellow-green powder was obtained in a quantitative yield. To obtain the single crystals for structural characterization, the above reaction was performed as following: the mixture was heated to a higher temperature of 600 °C within 24h, kept at this temperature for 60 h, and then slowly cooled to 200 °C in 120 h, followed by cooling to room temperature by turning off the furnace. The yellow-green plate crystals (~30% yield based on Hg2Cl2) were sublimed and crystallized on the top part of tube wall, while the other binary and ternary phases stayed at the bottom of the tube. 2.2 Characterization For phase identification, X-ray diffraction patterns of polycrystalline materials were performed at room temperature by a Bruker D8 Advance X-ray powder diffractometer using Cu- Kα radiation (λ = 1.54186 Å). The data were recorded in the operation angle 2θ ranging from 10° to 65° with a step size of 0.02° and a counting time of 6.5 s. The elemental analysis of the title compound was performed with the aid of scanning electron microscope (JEOL 6360) equipped with an energy-dispersive X-ray spectroscope (EDX, Oxford INCA). The thermal stability of
4
ZnHg3Se2Cl4 was tested on a TGA Q500 instrument in a flowing nitrogen atmosphere. The temperature range from 300 to 873 K was applied with a heating rate of 10 °C/min. The UV-Vis absorption spectrum was obtained at room temperature on a Model UV-2501 PC using BaSO4 plates as standard (100% reflectance). The absorption (α/S) data were calculated from the reflectance using the Kubelka-Munk function: α/S = (1-R)2/2R, in which, α is the absorption coefficient, R is the reflectance and S is the scattering wavelength. The band gap values were obtained by extrapolating the linear regions of (α/S)2 versus energy plot to (α/S)2=0. The IR spectra were measured on a Perkin-Elmer Fourier-transformed infrared (FTIR) spectrophotometer using KBr pellets in the range 500-4000 cm-1 (2.5-20 µm).
3 Results and discussion 3.1 Synthesis of ZnHg3Se2Cl4 Adopting the similar synthesis procedure described the references 17 and 27, polycrystalline powder of the title compound was prepared in a quantitative yield under relatively low temperature of 200 °C. The PXRD pattern of polycrystalline powder the as-obtained compound was shown in Fig. S3 and the results indicate that the as-obtained compound is a pure phase and it can be stable in air for months. Note that the larger crystals show an orange color, which might arise from the point defect related absorptions near band gap (Fig. S1). 3.2 Structure of ZnHg3Se2Cl4 The single crystal X-ray diffraction data were collected on a Bruker APEX II CCD diffractometer at 293 K. The title compound with the formula ZnHg3Se2Cl4 crystallizes in a crystal system orthorhombic with a noncentrosymmetric space group of Cmc21 (No. 36), which consists of HgSe2Cl2, HgSe2 and ZnCl4 units connected with each other to form the novel 3D
5
framework (Fig. 1). The asymmetric unit of the title compound contains one crystallographically independent Zn atom, two Hg atoms, two Se atoms, and three Cl atoms. Despite the similar chemical formula, the title compound and the reported compound ZnHg3S2Cl4 are subtly different due to the size effects originated from anions [25]. In the structure of ZnHg3S2Cl4, every Hg atom connected with one S atom and one Cl atom [25], while in title compound, the Hg2 atom is two-coordinated by Se atoms with a zig-linear geometry, while the split Hg1 atom is four-coordinated by two Se atoms and two Cl atoms to form the HgSe2Cl2 unit. From the other view, the Hg atoms and Se atoms connect with each other to form an interconnected 12-membered Hg6Se6 rings with chair-like configuration. This chair-like ring is distorted in the title compound, which is also found in the compounds Hg3Q2MX6 (Q = S, Se; M = Zr, Hf; X = Cl, Br) [29] Hg4In2Q3Cl8 (Q= S, Se, Te) [26], and Hg3Q2Bi2Cl8 (Q=S, Se, Te) [17]. Each ring is edge-sharing with six neighboring rings to construct a 2D layered network. The bond lengths of Hg-Se fall in the range of 2.3517(6)-2.7614(10) Å, and the bond angles of Hg-Se-Hg are between 95.368(6)-98.638(7) °, which is similar with that in compounds Hg3Se2Bi2Cl8 [17], Hg4In2Se3Cl8 [26], Cl6HfHg3Se2 [29], Cl6Hg3Se2Zr [29]. Zn atoms adopt ZnCl4 tetrahedral geometry which is sandwiched in the [Hg6Se6]n layered networks by Hg1-Cl2 bonds (Fig. 1b). The ZnCl4 tetrahedrons further connect with each other by the Zn-Cl1 (in adjacent unit) bond to form a [ZnCl4]n chain, which penetrates through the Hg6Se6 ring by the Cl2-Hg1A bonds. The neighboring [ZnCl4]n chains further connect to form a 2-D network along ac-plane through Hg1 atoms. The bond lengths of Zn-Cl fall in the range of 2.1984(7)2.3857(13) Å, and the bond angles of Cl-Zn-Cl are between 104.988(17)-118.072(12)°. Interestingly, there are four sets of split sites: Hg1A/Hg1B, Zn1A/Zn1B, Se1A/Se1B and
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Se2A/Se2B with the ratios of 19.1/81.0, 37.5/62.5, 63.7/36.3 and 47.7/52.3. This accounts for the relatively high R1 value. 3.3 Characterizations of ZnHg3Se2Cl4 The elemental analysis performed by energy-dispersive X-ray spectroscope (Fig. S2) shows the atomic ratio of Zn/Hg/Se/Cl is 11/30/19/40, which matches very well with the calculated one from single crystal structure determination. The thermal stability was tested by TGA measurement. As shown in Fig. 2, the compound is thermally stable up to about 300 °C with a sharp weight loss between 330 to 400 °C. The UV-vis diffuse reflectance spectrum for the compound was shown in Fig. 3. The absorption edge near the UV side for the title compound is about 556 nm, corresponding to the calculated band gap of 2.23 eV, which is consistent well with its yellow-green color, as shown in the inset of Fig. 3. Fig. S4 shows the FTIR spectrum of compound ZnHg3Se2Cl4. It exhibits a wide transparent range from 500-4000 cm-1 with a slight absorption at 720 and 550 cm-1. Totally, the UV-vis and FTIR spectrum shows a wide transparence in the visible and IR region from 0.56 to 13.8 µm.
4 Conclusions In summary, a quaternary chalcohalide, ZnHg3Se2Cl4 has been successfully synthesized by high temperature solid-state method. The crystal structure is characterized by a 2D layered network, which contains interconnected 12-membered Hg6Se6 rings and the sandwiched ZnCl4 tetrahedra between the layers. The optical absorption spectrum shows the band gap of the compound is 2.23 eV. The TGA result shows that the compound is thermally stable up to about 300 °C.
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Supporting Information Crystallographic files in CIF format, experimental methods, and additional tables and figures. Figure S1. Photograph of ZnHg3Se2Cl4 crystal.
Acknowledgment Q. Z. acknowledges financial support from AcRF Tier 1 (RG133/14) and Tier 2 (ARC 20/12 and ARC 2/13) from MOE, and the CREATE program (Nanomaterials for Energy and Water Management) from NRF, Singapore.
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Chem. 2011, 50, 5679-5686. (b) Xiong, W. W.; Li, P. Z.; Zhou, T. H.; Tok, A. I. Y.; Xu, R.; Zhao, Y.; Zhang, Q. Inorg. Chem. 2013, 52, 4148. [5]
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[12] Li, H.; Malliakas, C. D.; Peters, J. A.; Liu, Z.; Im, J.; Jin, H.; Morris, C. D.; Zhao, L.-D.; Wessels, B. W.; Freeman, A. J.; Kanatzidis, M. G., Chem. Mater. 2013, 25, 2089. [13] Wibowo, A. C.; Malliakas, C. D.; Liu, Z.; Peters, J. A.; Sebastian, M.; Chung, D. Y.; Wessels, B. W.; Kanatzidis, M. G., Inorg. Chem. 2013, 52, 7045. [14] 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., J. Am. Chem. Soc. 2011, 133, 10030. [15] Johnsen, S.; Liu, Z.; Peters, J. A.; Song, J.-H.; Peter, S. C.; Malliakas, C. D.; Cho, N. K.; Jin, H.; Freeman, A. J.; Wessels, B. W.; Kanatzidis, M. G., Chem. Mater. 2011, 23, 3120. [16] Liu, Y.; Wei, F.; Yeo, S. N.; Lee, F. M.; Kloc, C.; Yan, Q.; Hng, H. H.; Ma, J.; Zhang, Q., Inorg. Chem. 2012, 51, 4414. [17] Wibowo, A. C.; Malliakas, C. D.; Chung, D. Y.; Im, J.; Freeman, A. J.; Kanatzidis, M. G., Inorg. Chem. 2013, 52, 2973. [18] Wang, L.; Hwu, S.-J., Chem. Mater. 2007, 19, 6212. [19] Feng, K.; Yin, W.; Lin, Z.; Yao, J.; Wu, Y., Inorg. Chem. 2013, 52, 11503. [20] Blachnik, R.; Buchmeier, W.; Dreisbach, H. A., Acta Crystallographica Section C 1986, 42, 515. [21] Blachnik, R.; Lytze, K.; Reuter, H., J. Solid State Chem. 1996, 126, 95-98. [22] Ruiz, E.; Payne, M. C., Chem. Eur. J. 1998, 4, 2485.
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[23] Beck, J.; Rompel, M., Zeitschrift für anorganische und allgemeine Chemie 2003, 629, 421. [24] Moro’oka, M.; Ohki, H.; Yamada, K.; Okuda, T., J. Solid State Chem. 2004, 177, 1401. [25] Chen, W.-T.; Kuang, H.-M.; Chen, H.-L., J. Solid State Chem. 2010, 183, 2411. [26] Liu, Y.; Kanhere, P. D.; Hoo, Y. S.; Ye, K.; Yan, Q.; Rawat, R. S.; Chen, Z.; Ma, J.; Zhang, Q., RSC Advances 2012, 2, 6401. [27] Wibowo, A. C.; Malliakas, C. D.; Chung, D. Y.; Im, J.; Freeman, A. J.; Kanatzidis, M. G., Inorg. Chem. 2013, 52, 11875. [28] Wang, L.; Hung, Y.-C.; Hwu, S.-J.; Koo, H.-J.; Whangbo, M. H., Chem. Mater. 2006, 18, 1219. [29] Beck, J.; Hedderich, S., J. Solid State Chem. 2003, 172, 12.
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Figure Captions Figure 1. (a) Ball-and-stick projection model of title compound on to the ac plane with atomic labels, and (b) view of the layer of title compound along the c direction. Hg2, Se1, Se2, and Zn1 atoms in the structure split into Hg1A/Hg1B, Zn1A/Zn1B, Se1A/Se1B and Se2A/Se2B. Figure 2. TGA analysis of compound ZnHg3Se2Cl4. Figure 3. UV-vis absorption spectrum of compound ZnHg3Se2Cl4.
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Figure 1
Figure 2
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Figure 3
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Graphical Abstract
Research highlights: 1. A novel chalcohalide ZnHg3Se2Cl4 was synthesized by solid state method. 2. The structure contains 12-membered Hg6Se6 rings and ZnCl4 tetrahedra. 3. The band gap of the as-prepared compound is about 2.23 eV.
15
PII: DOI: Reference:
S0022-4596(15)30040-2 http://dx.doi.org/10.1016/j.jssc.2015.06.032 YJSSC18960
To appear in: Journal of Solid State Chemistry Received date: 11 May 2015 Revised date: 16 June 2015 Accepted date: 20 June 2015 Cite this article as: Guodong Zhang, Wei-Wei Xiong, Lina Nie and Qichun Zhang, Synthesis, crystal structure and optical Property of a novel metal chalcohalide: ZnHg3Se2Cl4, Journal of Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2015.06.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title Page
Title: Synthesis, Crystal Structure and Optical Property of a Novel Metal Chalcohalide: ZnHg3Se2Cl4 Authors: Guodong Zhang,a Wei-Wei Xiong,a Lina Nie,a Qichun Zhang*a,b Affiliation: aSchool of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore b
Division of Chemistry and Biological Chemistry, School of Physical and
Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
*Corresponding author: E-mail: [email protected]; Tel: +65-6790 4705. Fax: +6567904705
1
ABSTRACT:
A novel chalcohalide ZnHg3Se2Cl4 has been synthesized through a solid state
method and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the acentric space group Cmc21 (No. 36) with cell parameters a =7.3262(8) Å, b = 12.518(2) Å, c = 11.3324(14) Å. The compound consists of 12-membered Hg6Se6 rings edge-sharing with six neighbored rings to construct a 2D layered network and the ZnCl4 tetrahedra are sandwiched between layers. TG-DTA measurement shows that the compound is thermally stable up to 300 °C. The band gap of the crystal is about 2.23 eV, and the crystal exhibits a broad transparent range from 0.56 to 13.8 µm.
Keywords: Chalcohalide; Crystal structure; Solid state synthesis
* Corresponding author. E-mail: [email protected] Phone: +65-67904705. Fax: +6567904705
2
1. Introduction New crystalline chalcohalides and chalcogenides have received extensive research interests [16] not only because of their diverse structures but also technologically promising properties such as thermoelectric, phase-change transitions, upconversion luminescence, nonlinear optics, magnetism, and x-ray or γ-ray detections [7-15]. Among them, ternary or quaternary metal chalcohalides are hybrid materials, whose compositions and band gaps usually lie between those of binary chalcogenides and binary halides, providing them much richer structural features and more chances to tune their band gaps [16-28]. In particular, mercury (II)-related chalcohalides are much attractive because mercury ions usually possess diverse coordination geometries varying from linear to octahedral, thus it has a greater tendency to form all kinds of architectures covering 0D, 1D, 2D, and 3D topologies [16, 17, 20-27]. In fact, some interesting structural factors of mercury (II) chalcohalides have been report. For example, Hg2SnS2Br2 [21, 22] and CuHgSI [24] contain one-dimensional chains, in which, the short Hg-S bonds lead to [-Hg-S-] helical chains. Hg4In2Q3Cl8 (Q= S, Se, Te) are a new class of 1 D chalcohalides, which feature the novel quaternary cationic nano-belts [26]. The compound ZnHg3S2Cl4 is a case of 2D layered network, in which Hg6S3Cl3 forms a novel 12-membered ring, and these rings connected with each other by sharing the edges to form a layer structure [25]. The compounds Hg2PbI2S2 [20], Hg7InS6Cl5 [16], and TlHg6Q4Br5 (Q=S, Se) [27], are four cases of different 3D frameworks. Herein, we report a novel mercury-related chalcohalide: ZnHg3Se2Cl4, which is synthesized by using high temperature solid-state reaction method. The crystal structure, band gap, and thermal stability were characterized by single crystal XRD, optical absorption spectrum, and thermogravimetric measurement.
3
2. Experimental section 2.1 Synthesis of ZnHg3Se2Cl4 The title compound was prepared through a typical solid state reaction from a mixture containing Hg2Cl2 powder (4N, 2 mmol, 944 mg; note: much attention should be paid due to the toxicity of mercury and extreme care must be taken when handling sample and products.), Zn powder (5N, 1 mmol, 65 mg), and Se powder (3N, 2 mmol, 158 mg) which were loaded into an fused silica tube (12mm i.d.) and sealed under high vacuum (~10-3 Pa). The mixture was heated to relatively low temperature 200 °C within 20h, and kept at this temperature for 60 h, followed by a shutdown of the furnace. The yellow-green powder was obtained in a quantitative yield. To obtain the single crystals for structural characterization, the above reaction was performed as following: the mixture was heated to a higher temperature of 600 °C within 24h, kept at this temperature for 60 h, and then slowly cooled to 200 °C in 120 h, followed by cooling to room temperature by turning off the furnace. The yellow-green plate crystals (~30% yield based on Hg2Cl2) were sublimed and crystallized on the top part of tube wall, while the other binary and ternary phases stayed at the bottom of the tube. 2.2 Characterization For phase identification, X-ray diffraction patterns of polycrystalline materials were performed at room temperature by a Bruker D8 Advance X-ray powder diffractometer using Cu- Kα radiation (λ = 1.54186 Å). The data were recorded in the operation angle 2θ ranging from 10° to 65° with a step size of 0.02° and a counting time of 6.5 s. The elemental analysis of the title compound was performed with the aid of scanning electron microscope (JEOL 6360) equipped with an energy-dispersive X-ray spectroscope (EDX, Oxford INCA). The thermal stability of
4
ZnHg3Se2Cl4 was tested on a TGA Q500 instrument in a flowing nitrogen atmosphere. The temperature range from 300 to 873 K was applied with a heating rate of 10 °C/min. The UV-Vis absorption spectrum was obtained at room temperature on a Model UV-2501 PC using BaSO4 plates as standard (100% reflectance). The absorption (α/S) data were calculated from the reflectance using the Kubelka-Munk function: α/S = (1-R)2/2R, in which, α is the absorption coefficient, R is the reflectance and S is the scattering wavelength. The band gap values were obtained by extrapolating the linear regions of (α/S)2 versus energy plot to (α/S)2=0. The IR spectra were measured on a Perkin-Elmer Fourier-transformed infrared (FTIR) spectrophotometer using KBr pellets in the range 500-4000 cm-1 (2.5-20 µm).
3 Results and discussion 3.1 Synthesis of ZnHg3Se2Cl4 Adopting the similar synthesis procedure described the references 17 and 27, polycrystalline powder of the title compound was prepared in a quantitative yield under relatively low temperature of 200 °C. The PXRD pattern of polycrystalline powder the as-obtained compound was shown in Fig. S3 and the results indicate that the as-obtained compound is a pure phase and it can be stable in air for months. Note that the larger crystals show an orange color, which might arise from the point defect related absorptions near band gap (Fig. S1). 3.2 Structure of ZnHg3Se2Cl4 The single crystal X-ray diffraction data were collected on a Bruker APEX II CCD diffractometer at 293 K. The title compound with the formula ZnHg3Se2Cl4 crystallizes in a crystal system orthorhombic with a noncentrosymmetric space group of Cmc21 (No. 36), which consists of HgSe2Cl2, HgSe2 and ZnCl4 units connected with each other to form the novel 3D
5
framework (Fig. 1). The asymmetric unit of the title compound contains one crystallographically independent Zn atom, two Hg atoms, two Se atoms, and three Cl atoms. Despite the similar chemical formula, the title compound and the reported compound ZnHg3S2Cl4 are subtly different due to the size effects originated from anions [25]. In the structure of ZnHg3S2Cl4, every Hg atom connected with one S atom and one Cl atom [25], while in title compound, the Hg2 atom is two-coordinated by Se atoms with a zig-linear geometry, while the split Hg1 atom is four-coordinated by two Se atoms and two Cl atoms to form the HgSe2Cl2 unit. From the other view, the Hg atoms and Se atoms connect with each other to form an interconnected 12-membered Hg6Se6 rings with chair-like configuration. This chair-like ring is distorted in the title compound, which is also found in the compounds Hg3Q2MX6 (Q = S, Se; M = Zr, Hf; X = Cl, Br) [29] Hg4In2Q3Cl8 (Q= S, Se, Te) [26], and Hg3Q2Bi2Cl8 (Q=S, Se, Te) [17]. Each ring is edge-sharing with six neighboring rings to construct a 2D layered network. The bond lengths of Hg-Se fall in the range of 2.3517(6)-2.7614(10) Å, and the bond angles of Hg-Se-Hg are between 95.368(6)-98.638(7) °, which is similar with that in compounds Hg3Se2Bi2Cl8 [17], Hg4In2Se3Cl8 [26], Cl6HfHg3Se2 [29], Cl6Hg3Se2Zr [29]. Zn atoms adopt ZnCl4 tetrahedral geometry which is sandwiched in the [Hg6Se6]n layered networks by Hg1-Cl2 bonds (Fig. 1b). The ZnCl4 tetrahedrons further connect with each other by the Zn-Cl1 (in adjacent unit) bond to form a [ZnCl4]n chain, which penetrates through the Hg6Se6 ring by the Cl2-Hg1A bonds. The neighboring [ZnCl4]n chains further connect to form a 2-D network along ac-plane through Hg1 atoms. The bond lengths of Zn-Cl fall in the range of 2.1984(7)2.3857(13) Å, and the bond angles of Cl-Zn-Cl are between 104.988(17)-118.072(12)°. Interestingly, there are four sets of split sites: Hg1A/Hg1B, Zn1A/Zn1B, Se1A/Se1B and
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Se2A/Se2B with the ratios of 19.1/81.0, 37.5/62.5, 63.7/36.3 and 47.7/52.3. This accounts for the relatively high R1 value. 3.3 Characterizations of ZnHg3Se2Cl4 The elemental analysis performed by energy-dispersive X-ray spectroscope (Fig. S2) shows the atomic ratio of Zn/Hg/Se/Cl is 11/30/19/40, which matches very well with the calculated one from single crystal structure determination. The thermal stability was tested by TGA measurement. As shown in Fig. 2, the compound is thermally stable up to about 300 °C with a sharp weight loss between 330 to 400 °C. The UV-vis diffuse reflectance spectrum for the compound was shown in Fig. 3. The absorption edge near the UV side for the title compound is about 556 nm, corresponding to the calculated band gap of 2.23 eV, which is consistent well with its yellow-green color, as shown in the inset of Fig. 3. Fig. S4 shows the FTIR spectrum of compound ZnHg3Se2Cl4. It exhibits a wide transparent range from 500-4000 cm-1 with a slight absorption at 720 and 550 cm-1. Totally, the UV-vis and FTIR spectrum shows a wide transparence in the visible and IR region from 0.56 to 13.8 µm.
4 Conclusions In summary, a quaternary chalcohalide, ZnHg3Se2Cl4 has been successfully synthesized by high temperature solid-state method. The crystal structure is characterized by a 2D layered network, which contains interconnected 12-membered Hg6Se6 rings and the sandwiched ZnCl4 tetrahedra between the layers. The optical absorption spectrum shows the band gap of the compound is 2.23 eV. The TGA result shows that the compound is thermally stable up to about 300 °C.
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Supporting Information Crystallographic files in CIF format, experimental methods, and additional tables and figures. Figure S1. Photograph of ZnHg3Se2Cl4 crystal.
Acknowledgment Q. Z. acknowledges financial support from AcRF Tier 1 (RG133/14) and Tier 2 (ARC 20/12 and ARC 2/13) from MOE, and the CREATE program (Nanomaterials for Energy and Water Management) from NRF, Singapore.
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Figure Captions Figure 1. (a) Ball-and-stick projection model of title compound on to the ac plane with atomic labels, and (b) view of the layer of title compound along the c direction. Hg2, Se1, Se2, and Zn1 atoms in the structure split into Hg1A/Hg1B, Zn1A/Zn1B, Se1A/Se1B and Se2A/Se2B. Figure 2. TGA analysis of compound ZnHg3Se2Cl4. Figure 3. UV-vis absorption spectrum of compound ZnHg3Se2Cl4.
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Figure 1
Figure 2
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Figure 3
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Graphical Abstract
Research highlights: 1. A novel chalcohalide ZnHg3Se2Cl4 was synthesized by solid state method. 2. The structure contains 12-membered Hg6Se6 rings and ZnCl4 tetrahedra. 3. The band gap of the as-prepared compound is about 2.23 eV.
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