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Solvothermal synthesis of novel antimony sulphides containing [Sb4S7]2− units
Solid State Ionics 172 (2004) 601 – 605 www.elsevier.com/locate/ssi
Solvothermal synthesis of novel antimony sulphides containing [Sb4S7]2 units Paz Vaqueiro a,*, David P. Darlow a, Anthony V. Powell a, Ann M. Chippindale b a
b
Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, UK School of Chemistry, The University of Reading, Whiteknights Reading RG6 6AD, UK
Received 9 November 2003; received in revised form 9 January 2004; accepted 26 January 2004
Abstract Two new antimony sulphides have been prepared solvothermally and characterised by single-crystal X-ray diffraction. [Co(en)3][Sb4S7] (1) was prepared at 140 jC from CoS, Sb2S3 and S in the presence of ethylenediamine, whilst heating a mixture of Sb2S3, Co and S in tris(2aminoethyl)amine, N(CH2CH2NH2)3, at 180 jC results in the formation of [C6H20N4][Sb4S7] (2). Both materials contain [Sb4S7]2 chains formed from linkage of cyclic Sb3S36 units by SbS33 pyramids. In (1), the [Sb4S7]2 chains are linked by secondary Sb – S interactions to form sheets, between which the charge balancing [Co(en)3]2 + cations reside. The structure of (2) involves interconnection of pairs of [Sb4S7]2 chains through Sb2S2 rings to form isolated [Sb4S7]2 double chains which are interleaved by protonated template molecules. D 2004 Elsevier B.V. All rights resereved. PACS: 61.66.Fn; 81.20.Zx Keywords: Solvothermal synthesis; Antimony sulphide; Crystal structure
1. Introduction Solid-state materials are traditionally prepared using high-temperature routes. Products of such reactions are generally limited to thermodynamically stable phases, with relatively simple crystal structures of high density. The recent increased interest in soft-chemistry techniques is motivated by their potential to provide access to metastable phases which may have markedly different structural and physical properties from those of materials prepared using conventional synthetic techniques. Solvothermal synthesis is a particularly versatile low-temperature route, in which polar solvents, under pressure and at temperatures above their boiling point, are used [1]. Under solvothermal conditions, the solubility of the reactants increases significantly, enabling reaction to take place at considerably lower temperatures than in conventional synthetic techniques. This type of soft-chemistry approach is mild enough to allow ‘‘molecular’’ building blocks such as chains and rings to form and participate in the formation of polymeric structural
* Corresponding author. Fax: +44-131-451-3180. E-mail address: [email protected] (P. Vaqueiro). 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights resereved. doi:10.1016/j.ssi.2004.01.064
units [2]. Organic amines or alkylammonium cations may be employed as templates to exert a structure directing effect on the crystallisation process. This results in the formation of open-framework inorganic materials [3], such as zeolites, in which the organic template is retained in the pores and/or the interlamellar spaces. Whilst in oxide-based frameworks the primary building blocks are most commonly corner-shared tetrahedral TO4 units (T = Si4 +, P5 +, Al3 +), chalcogenide materials show a greater diversity of geometries. This is exemplified by the solvothermally synthesized tin sulphides, in which tin adopts a variety of coordinations, ranging from trigonal pyramidal to octahedral [4]. The diversity of coordination polyhedra and connectivity in the solvothermally synthesised chalcogenides results in a rich structural chemistry, in which new architectures may be identified. Much of our recent work has centered on the solvothermal preparation of antimony sulphides [5,6]. In these materials, the primary structural unit is the SbS33 trigonal pyramid [7]. Linkage of these units may generate a range of chain-like motifs, including [SbS2] chains, of which two types have been observed, involving vertex-linked [8] or edge-linked [9] SbS33 pyramids. [Sb4S7]2 chains, consisting of Sb3S63 rings connected through a SbS33 unit, have also been described [10].
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Here, we report the synthesis and structure determination of two new antimony sulphides, [Co(en)3][Sb4S7] (1) and [C6H20N4][Sb4S7] (2). Both materials contain [Sb4S7]2 chains, which are isolated in 1 and linked through Sb2S2 rings to form double chains in 2.
2. Experimental [Co(en)3][Sb4S7] (1) was prepared by heating a mixture of CoS (0.134 g, 1.5 mmol) and Sb2S3 (0.500 g, 1.5 mmol) in ethylenediamine (5 ml) in a Teflon-lined 23 ml stainless steel autoclave, at 140 jC for 7 days, followed by cooling to room temperature at a rate of 20 jC/h. [C6H20N4][Sb4S7] (2) was obtained from a mixture of Sb2S3 (0.500 g; 1.5 mmol), Co (0.104 g; 1.8 mmol) and S (0.096 g; 3 mmol) in 3.6 ml of tris(2-aminoethyl)amine (tren, Aldrich, 96%), which was loaded into a Teflon-lined 23 ml autoclave. The container was closed, heated at 180 jC for 14 days and then cooled to room temperature at 20 jC/h. After cooling to room temperature, the reaction mixtures were filtered and washed with ethanol and water. Products from both reactions consist of a mixture of crystals and black polycrystalline powder. Although the structure of 2 does not contain cobalt, experiments have demonstrated that this metal is essential to produce crystals of 2. Interestingly, a large number of needles of 2 were obtained when the reaction was carried out using technical grade triethylenetetramine (trien, Aldrich, 60%) as template instead of tren. NMR data for this amine indicated that it contains a small amount of tren. The majority of the crystals of 1 were coated with a black powder, removal of which proved impossible. This prevented reliable analytical data for 1 being obtained. Crystals of 2 were separated from the bulk sample by handpicking, for combustion and thermogravimetric analysis. Combustion analysis for the crystals of 2 gave C 8.98, H 2.45 and N 6.46% which compares favourably with the values calculated from the crystallographically determined formula [C6H20N4][Sb4S7] (C 8.38, H 2.33 and N 6.51%). Thermogravimetric analysis for finely ground crystals of 2, carried out under a nitrogen atmosphere and with a heating rate of 2 jC/min, resulted in a total weight loss of 18.7%. This value is in reasonable agreement with the calculated value for the removal of the tren molecules, 17.2%.
3. Crystal structure determination Crystals of 1 and 2 were mounted on glass fibres with cyanoacrylate adhesive and X-ray intensity data collected at room temperature using a Nonius KappaCCD diffractometer ˚ ). (graphite monochromated Mo Ka radiation, 0.71073 A Both data sets were processed using DENZO [11] and SCALEPACK [12], the structures solved by direct methods (SIR92) [13] and models refined using CRYSTALS [14]. Full crystallographic details are given in Table 1.
Table 1 Crystallographic data for [Co(en)3][Sb4S7] (1) and [C6H20N4][Sb4S7] (2) Formula
[Co(en)3][Sb4S7] (1)
[C6H20N4][Sb4S7] (2)
Mr Crystal Habit Crystal System Space group T (K) ˚) a (A ˚) b (A ˚) c (A a (j) b (j) c (j) ˚ 3) V (A Z l (mm 1) Measured data Unique data Observed data (I >3r(I )) Rmerg R Rw
950.65 yellow plate monoclinic P21/c 293 9.9319(2) 14.2181(3) 17.2781(3) 90 102.4533(9) 90 2382.48 4 5.778 9572 5428 3860 0.019 0.0267 0.0299
859.67 red needle triclinic P-1 293 5.9346(7) 9.1140(8) 19.636(2) 98.9880(4) 98.407(5) 94.489(5) 1032.23 2 5.883 4860 4330 1740 0.045 0.0565 0.0497
Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre, with the CCDC numbers 223571 and 223572.
4. Results 4.1. Structure of [Co(en)3][Sb4S7] (1) Each antimony atom is coordinated to three sulphur ˚ in atoms at distances in the range 2.329(2) –2.510(1) A approximately trigonal pyramidal geometry with S –Sb – S angles of 86.72(5) – 101.72(6)j. Three of the four crystallographically independent Sb atoms also have significant secondary Sb – S interactions at distances within the sum ˚ ) [15]. The of the van der Waals’ radii of Sb and S (3.80 A Sb(3) atom has three additional long contacts with S atoms ˚ , and is therefore in a in the range 3.546(1) – 3.580(1) A distorted octahedral coordination, whilst Sb(2) and Sb(4) exhibit two long additional contacts to S of 3.067(1) – ˚ leading to five coordination. 3.382(2) A The primary building unit of this structure is the SbS33 pyramid. Vertex linking of three SbS33 trigonal pyramids generates cyclic Sb3S63 units, termed semicubes [16]. These are linked by individual SbS33 trigonal pyramids to form infinite zig-zag [Sb4S7]2 chains, which are directed along [001] (Fig. 1). The secondary Sb –S interactions described above link the individual zig-zag chains to form [Sb4S7]2 layers which lie in the bc plane, as shown in Fig. 1. The resulting anionic [Sb4S7]2 sheets are separated by [Co(en)3]2 + cations. The Co – N distances lie in the range ˚ , which is typical for a Co2 + cation in 2.163(5) – 2.195(5) A octahedral coordination by nitrogen atoms [8,17]. The
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Fig. 1. View of [Co(en)3][Sb4S7] (1) along [100]. Bonds within the [Sb4S7]2 chains are shown as solid lines, while those in the [Co(en)3]2 + cations are shown as open lines. Dashed lines show the secondary Sb – S interactions, which link the chains to form a layer. Key: antimony, large solid circles; cobalt, large shaded circles; sulphur, large open circles; carbon, small solid circles and nitrogen, small open circles.
Fig. 2. View along the [100] direction showing the [Sb4S7]2 (2). Key as for Fig. 1.
double chains and the location of the tris(2-aminoethyl)amine molecules in [C6H20N4][Sb4S7]
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˚. distance between neighbouring [Sb4S7]2 layers is ca. 8 A 2+ All of the N atoms in the [Co(en)3] cations have sulphur ˚ , which suggests atoms at distances in the range 3.31– 3.73 A the possible presence of hydrogen bonding between the cations and the framework. 4.2. Structure of [C6H20N4][Sb4S7] (2) With the exception of Sb(2), each of the crystallographically unique antimony atoms is coordinated to three sul˚, phur atoms at distances in the range 2.367(6) – 2.520(5) A 3 which are typical for pyramidal SbS3 units [10]. The structure of [C6H20N4][Sb4S7] (2) also contains [Sb4S7]2 chains, similar to those found in 1. However, two of the vertices (S(4)) of the individual SbS33 trigonal pyramid are common to two chains, giving rise to a four-membered Sb2S2 ring that serves to link pairs of chains to form an [Sb4S7]2 double chain. The atom Sb(2), which forms part of the Sb2S2 ring, is coordinated to four sulphur atoms by ˚ ) and two long two short bonds (2.392(5) and 2.587(4) A ˚ bonds (2.739(5) and 2.759(5) A). Similar bonding distances have been previously observed for four-coordinated Sb atoms in Sb2S2 rings [9]. All of the Sb atoms exhibit significant secondary Sb –S interactions at distances within ˚) the sum of the van der Waals’ radii of Sb and S (3.80 A [15]. Interactions involving the atoms Sb(1) and Sb(3) link the double [Sb4S7]2 chains into layers, while a number of
additional secondary Sb –S interactions, which lie in the ˚ , are present within each double chain. range 3.12 – 3.44 A 2 Sheets of [Sb4S7] double chains are separated by double layers of diprotonated tris(2-aminoethyl)amine molecules, (Fig. 2). With the exception of N(3), each of the crystallo˚, graphically unique nitrogen atoms has N atoms at ca. 2.8 A which is shorter than the sum of the van der Waals’ radii ˚ ). Additionally, all N atoms have several neighbour(3.10 A ˚ . This ing S atoms at distances within the range 3.28– 3.44 A suggests that hydrogen bonding between template molecules and between the framework and the template, plays an important role in stabilising this structure.
5. Discussion The two materials described in this work contain [Sb4S7]2 chains, which are isolated in 1 and linked through Sb2S2 rings to form double chains in 2. Isolated [Sb4S7]2 chains have been reported for the materials [NH4]2[Sb4S7] [18], [C4N2H12][Sb4S7] [19] and [M(en)3][Sb4S7] (M = Mn, [20] Fe, [8] Ni [8]). The compound 1 described here is isostructural with [M(en) 3 ][Sb 4 S 7 ] [8,20]. Although [NH4]2[Sb4S7] and [C4N2H12][Sb4S7] also contain isolated [Sb4S7]2 chains, the conformations of the chains differ significantly from that observed in [M(en)3][Sb4S7]. In the latter, the chains exhibit a zig – zag conformation, whereas in
Fig. 3. Comparison of the structures of (a) [C6H20N4][Sb4S7] (2) and (b) SrSb4S76H2O24 showing the different orientations of the [Sb4S7]2 double chains. In the latter, Sb4S27 double chains are separated by chains of face-sharing Sr(OH2)8 units. Key: antimony, large solid circles; strontium, large shaded circles; sulphur, large open circles; carbon, small solid circles; nitrogen, small open circles and oxygen, small shaded circles.
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both [NH4]2[Sb4S7] and [C4N2H12][Sb4S7] the chains are linear, and show only relatively minor differences in conformation. Whilst in the linear chains all of the semicubes exhibit an identical orientation, in the zig – zag chains semicubes with two orientations, related by a rotation of 120j, alternate along the chain. The change in conformation leads to differences in secondary interactions between chains. A linear conformation is also apparent for the double [Sb4S7]2 chains in 2. Linkage of single [Sb4S7]2 chains by a variety of bridging units to form double chains has also been described. In [C2H10N2][Sb8S13] [21], pairs of single [Sb4S7]2 chains share one vertex of the individual SbS33 pyramids. The structure of [C2H8N]2[Sb8S12(S2)] [22] is very similar to that of [C2H10N2][Sb8S13], with the single chains connected by a S22- unit instead of a single sulphur atom. In [C3H12N2] [Sb10S16] [23], the single [Sb4S7]2 chains are connected through two edge-sharing SbS33 pyramids, which form a Sb2S2 ring. Double [Sb4S7]2 chains similar to those reported here for 2 have been observed previously in the structure of SrSb4S7 6H2O. [24]. However differences in the secondary interactions lead to variations in the packing of the double [Sb4S7]2 chains in the two structures (Fig. 3). In 2, secondary interactions between double chains involve only the Sb atoms in the semicubes, while in SrSb4S76H2O, O, the double chains are linked into sheets through secondary interactions involving the Sb atoms in the Sb2S2 rings. The wide range of compounds in which the [Sb4S7]2 chain may be identified indicates its importance as a building block in antimony-sulphide chemistry. Soft-chemistry techniques offer scope for the generation of new structure types by linking such chains through alternative bridging units.
Acknowledgements The authors wish to thank Dr A.R. Cowley, University of Oxford for assistance with the collection of single-crystal
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X-ray diffraction data. AVP and AMC thank The Royal Society of Edinburgh and The Leverhulme Trust for Research Fellowships, respectively.
References [1] R.I. Walton, Chem. Soc. Rev. 31 (2002) 230. [2] T. Jiang, A. Lough, G.A. Ozin, R.L. Bedard, J. Mater. Chem. 8 (1998) 733. [3] A.K. Cheetham, G. Fe´rey, T. Loiseau, Angew. Chem., Int. Ed. 38 (1999) 3268. [4] T. Jiang, G.A. Ozin, J. Mater. Chem. 8 (1998) 1099. [5] A.V. Powell, S. Boissie`re, A.M. Chippindale, Chem. Mater. 12 (2000) 182. [6] A.V. Powell, R. Paniagua, P. Vaqueiro, A.M. Chippindale, Chem. Mater. 14 (2002) 1220. [7] W.S. Sheldrick, J. Chem. Soc., Dalton Trans. (2000) 3041. [8] H.-O. Stephan, M.G. Kanatzidis, Inorg. Chem. 36 (1997) 6050. [9] K. Volk, P. Bickert, R. Kolmer, H. Scha¨fer, Z. Naturforsch., Teil B 34 (1979) 380. [10] W.S. Sheldrick, M. Wachhold, Coord. Chem. Rev. 176 (1998) 211. [11] Z. Otwinowski, DENZO, Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA, 1993. [12] Z. Otwinowski, SCALEPACK, Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA, 1993. [13] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori, M. Camelli, J. Appl. Crystallogr., Sect. A 27 (1994) 435. [14] D.J. Watkin, C.K. Prout, J.R. Carruthers, P.W. Betteridge, CRYSTALS Issue 10, Chemical Crystallography Laboratory, Univ. of Oxford, UK, 1996. [15] A. Bondi, J. Phys. Chem. 68 (1964) 441. [16] J.B. Parise, J. Chem. Soc., Chem. Commun. (1990) 1553. [17] P. Sobota, J. Utko, S. Szafert, Z. Janas, T. Glowiak, J. Chem. Soc., Dalton Trans. (1996) 3469. [18] G. Dittmar, H. Scha¨fer, Z. Anorg. Allg. Chem. 437 (1977) 183. [19] J.B. Parise, Y. Ko, Chem. Mater. 4 (1992) 1446. [20] W. Bensch, M. Schur, Z. Naturforsch. 52b (1997) 405. [21] K. Tan, Y. Ko, J.B. Parise, Acta Cryst. Sect. C. 50 (1994) 1439. [22] K. Tan, Y. Ko, J.B. Parise, J.N. Park, A. Darovsky, Chem. Mater. 8 (1996) 2510. [23] X. Wang, Eur. J. Solid State Inorg. Chem. 32 (1995) 303. [24] G. Cordier, H. Scha¨fer, C. Schwidetzky, Z. Naturforsch. 39b (1984) 131.
Solvothermal synthesis of novel antimony sulphides containing [Sb4S7]2 units Paz Vaqueiro a,*, David P. Darlow a, Anthony V. Powell a, Ann M. Chippindale b a
b
Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, UK School of Chemistry, The University of Reading, Whiteknights Reading RG6 6AD, UK
Received 9 November 2003; received in revised form 9 January 2004; accepted 26 January 2004
Abstract Two new antimony sulphides have been prepared solvothermally and characterised by single-crystal X-ray diffraction. [Co(en)3][Sb4S7] (1) was prepared at 140 jC from CoS, Sb2S3 and S in the presence of ethylenediamine, whilst heating a mixture of Sb2S3, Co and S in tris(2aminoethyl)amine, N(CH2CH2NH2)3, at 180 jC results in the formation of [C6H20N4][Sb4S7] (2). Both materials contain [Sb4S7]2 chains formed from linkage of cyclic Sb3S36 units by SbS33 pyramids. In (1), the [Sb4S7]2 chains are linked by secondary Sb – S interactions to form sheets, between which the charge balancing [Co(en)3]2 + cations reside. The structure of (2) involves interconnection of pairs of [Sb4S7]2 chains through Sb2S2 rings to form isolated [Sb4S7]2 double chains which are interleaved by protonated template molecules. D 2004 Elsevier B.V. All rights resereved. PACS: 61.66.Fn; 81.20.Zx Keywords: Solvothermal synthesis; Antimony sulphide; Crystal structure
1. Introduction Solid-state materials are traditionally prepared using high-temperature routes. Products of such reactions are generally limited to thermodynamically stable phases, with relatively simple crystal structures of high density. The recent increased interest in soft-chemistry techniques is motivated by their potential to provide access to metastable phases which may have markedly different structural and physical properties from those of materials prepared using conventional synthetic techniques. Solvothermal synthesis is a particularly versatile low-temperature route, in which polar solvents, under pressure and at temperatures above their boiling point, are used [1]. Under solvothermal conditions, the solubility of the reactants increases significantly, enabling reaction to take place at considerably lower temperatures than in conventional synthetic techniques. This type of soft-chemistry approach is mild enough to allow ‘‘molecular’’ building blocks such as chains and rings to form and participate in the formation of polymeric structural
* Corresponding author. Fax: +44-131-451-3180. E-mail address: [email protected] (P. Vaqueiro). 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights resereved. doi:10.1016/j.ssi.2004.01.064
units [2]. Organic amines or alkylammonium cations may be employed as templates to exert a structure directing effect on the crystallisation process. This results in the formation of open-framework inorganic materials [3], such as zeolites, in which the organic template is retained in the pores and/or the interlamellar spaces. Whilst in oxide-based frameworks the primary building blocks are most commonly corner-shared tetrahedral TO4 units (T = Si4 +, P5 +, Al3 +), chalcogenide materials show a greater diversity of geometries. This is exemplified by the solvothermally synthesized tin sulphides, in which tin adopts a variety of coordinations, ranging from trigonal pyramidal to octahedral [4]. The diversity of coordination polyhedra and connectivity in the solvothermally synthesised chalcogenides results in a rich structural chemistry, in which new architectures may be identified. Much of our recent work has centered on the solvothermal preparation of antimony sulphides [5,6]. In these materials, the primary structural unit is the SbS33 trigonal pyramid [7]. Linkage of these units may generate a range of chain-like motifs, including [SbS2] chains, of which two types have been observed, involving vertex-linked [8] or edge-linked [9] SbS33 pyramids. [Sb4S7]2 chains, consisting of Sb3S63 rings connected through a SbS33 unit, have also been described [10].
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Here, we report the synthesis and structure determination of two new antimony sulphides, [Co(en)3][Sb4S7] (1) and [C6H20N4][Sb4S7] (2). Both materials contain [Sb4S7]2 chains, which are isolated in 1 and linked through Sb2S2 rings to form double chains in 2.
2. Experimental [Co(en)3][Sb4S7] (1) was prepared by heating a mixture of CoS (0.134 g, 1.5 mmol) and Sb2S3 (0.500 g, 1.5 mmol) in ethylenediamine (5 ml) in a Teflon-lined 23 ml stainless steel autoclave, at 140 jC for 7 days, followed by cooling to room temperature at a rate of 20 jC/h. [C6H20N4][Sb4S7] (2) was obtained from a mixture of Sb2S3 (0.500 g; 1.5 mmol), Co (0.104 g; 1.8 mmol) and S (0.096 g; 3 mmol) in 3.6 ml of tris(2-aminoethyl)amine (tren, Aldrich, 96%), which was loaded into a Teflon-lined 23 ml autoclave. The container was closed, heated at 180 jC for 14 days and then cooled to room temperature at 20 jC/h. After cooling to room temperature, the reaction mixtures were filtered and washed with ethanol and water. Products from both reactions consist of a mixture of crystals and black polycrystalline powder. Although the structure of 2 does not contain cobalt, experiments have demonstrated that this metal is essential to produce crystals of 2. Interestingly, a large number of needles of 2 were obtained when the reaction was carried out using technical grade triethylenetetramine (trien, Aldrich, 60%) as template instead of tren. NMR data for this amine indicated that it contains a small amount of tren. The majority of the crystals of 1 were coated with a black powder, removal of which proved impossible. This prevented reliable analytical data for 1 being obtained. Crystals of 2 were separated from the bulk sample by handpicking, for combustion and thermogravimetric analysis. Combustion analysis for the crystals of 2 gave C 8.98, H 2.45 and N 6.46% which compares favourably with the values calculated from the crystallographically determined formula [C6H20N4][Sb4S7] (C 8.38, H 2.33 and N 6.51%). Thermogravimetric analysis for finely ground crystals of 2, carried out under a nitrogen atmosphere and with a heating rate of 2 jC/min, resulted in a total weight loss of 18.7%. This value is in reasonable agreement with the calculated value for the removal of the tren molecules, 17.2%.
3. Crystal structure determination Crystals of 1 and 2 were mounted on glass fibres with cyanoacrylate adhesive and X-ray intensity data collected at room temperature using a Nonius KappaCCD diffractometer ˚ ). (graphite monochromated Mo Ka radiation, 0.71073 A Both data sets were processed using DENZO [11] and SCALEPACK [12], the structures solved by direct methods (SIR92) [13] and models refined using CRYSTALS [14]. Full crystallographic details are given in Table 1.
Table 1 Crystallographic data for [Co(en)3][Sb4S7] (1) and [C6H20N4][Sb4S7] (2) Formula
[Co(en)3][Sb4S7] (1)
[C6H20N4][Sb4S7] (2)
Mr Crystal Habit Crystal System Space group T (K) ˚) a (A ˚) b (A ˚) c (A a (j) b (j) c (j) ˚ 3) V (A Z l (mm 1) Measured data Unique data Observed data (I >3r(I )) Rmerg R Rw
950.65 yellow plate monoclinic P21/c 293 9.9319(2) 14.2181(3) 17.2781(3) 90 102.4533(9) 90 2382.48 4 5.778 9572 5428 3860 0.019 0.0267 0.0299
859.67 red needle triclinic P-1 293 5.9346(7) 9.1140(8) 19.636(2) 98.9880(4) 98.407(5) 94.489(5) 1032.23 2 5.883 4860 4330 1740 0.045 0.0565 0.0497
Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre, with the CCDC numbers 223571 and 223572.
4. Results 4.1. Structure of [Co(en)3][Sb4S7] (1) Each antimony atom is coordinated to three sulphur ˚ in atoms at distances in the range 2.329(2) –2.510(1) A approximately trigonal pyramidal geometry with S –Sb – S angles of 86.72(5) – 101.72(6)j. Three of the four crystallographically independent Sb atoms also have significant secondary Sb – S interactions at distances within the sum ˚ ) [15]. The of the van der Waals’ radii of Sb and S (3.80 A Sb(3) atom has three additional long contacts with S atoms ˚ , and is therefore in a in the range 3.546(1) – 3.580(1) A distorted octahedral coordination, whilst Sb(2) and Sb(4) exhibit two long additional contacts to S of 3.067(1) – ˚ leading to five coordination. 3.382(2) A The primary building unit of this structure is the SbS33 pyramid. Vertex linking of three SbS33 trigonal pyramids generates cyclic Sb3S63 units, termed semicubes [16]. These are linked by individual SbS33 trigonal pyramids to form infinite zig-zag [Sb4S7]2 chains, which are directed along [001] (Fig. 1). The secondary Sb –S interactions described above link the individual zig-zag chains to form [Sb4S7]2 layers which lie in the bc plane, as shown in Fig. 1. The resulting anionic [Sb4S7]2 sheets are separated by [Co(en)3]2 + cations. The Co – N distances lie in the range ˚ , which is typical for a Co2 + cation in 2.163(5) – 2.195(5) A octahedral coordination by nitrogen atoms [8,17]. The
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Fig. 1. View of [Co(en)3][Sb4S7] (1) along [100]. Bonds within the [Sb4S7]2 chains are shown as solid lines, while those in the [Co(en)3]2 + cations are shown as open lines. Dashed lines show the secondary Sb – S interactions, which link the chains to form a layer. Key: antimony, large solid circles; cobalt, large shaded circles; sulphur, large open circles; carbon, small solid circles and nitrogen, small open circles.
Fig. 2. View along the [100] direction showing the [Sb4S7]2 (2). Key as for Fig. 1.
double chains and the location of the tris(2-aminoethyl)amine molecules in [C6H20N4][Sb4S7]
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˚. distance between neighbouring [Sb4S7]2 layers is ca. 8 A 2+ All of the N atoms in the [Co(en)3] cations have sulphur ˚ , which suggests atoms at distances in the range 3.31– 3.73 A the possible presence of hydrogen bonding between the cations and the framework. 4.2. Structure of [C6H20N4][Sb4S7] (2) With the exception of Sb(2), each of the crystallographically unique antimony atoms is coordinated to three sul˚, phur atoms at distances in the range 2.367(6) – 2.520(5) A 3 which are typical for pyramidal SbS3 units [10]. The structure of [C6H20N4][Sb4S7] (2) also contains [Sb4S7]2 chains, similar to those found in 1. However, two of the vertices (S(4)) of the individual SbS33 trigonal pyramid are common to two chains, giving rise to a four-membered Sb2S2 ring that serves to link pairs of chains to form an [Sb4S7]2 double chain. The atom Sb(2), which forms part of the Sb2S2 ring, is coordinated to four sulphur atoms by ˚ ) and two long two short bonds (2.392(5) and 2.587(4) A ˚ bonds (2.739(5) and 2.759(5) A). Similar bonding distances have been previously observed for four-coordinated Sb atoms in Sb2S2 rings [9]. All of the Sb atoms exhibit significant secondary Sb –S interactions at distances within ˚) the sum of the van der Waals’ radii of Sb and S (3.80 A [15]. Interactions involving the atoms Sb(1) and Sb(3) link the double [Sb4S7]2 chains into layers, while a number of
additional secondary Sb –S interactions, which lie in the ˚ , are present within each double chain. range 3.12 – 3.44 A 2 Sheets of [Sb4S7] double chains are separated by double layers of diprotonated tris(2-aminoethyl)amine molecules, (Fig. 2). With the exception of N(3), each of the crystallo˚, graphically unique nitrogen atoms has N atoms at ca. 2.8 A which is shorter than the sum of the van der Waals’ radii ˚ ). Additionally, all N atoms have several neighbour(3.10 A ˚ . This ing S atoms at distances within the range 3.28– 3.44 A suggests that hydrogen bonding between template molecules and between the framework and the template, plays an important role in stabilising this structure.
5. Discussion The two materials described in this work contain [Sb4S7]2 chains, which are isolated in 1 and linked through Sb2S2 rings to form double chains in 2. Isolated [Sb4S7]2 chains have been reported for the materials [NH4]2[Sb4S7] [18], [C4N2H12][Sb4S7] [19] and [M(en)3][Sb4S7] (M = Mn, [20] Fe, [8] Ni [8]). The compound 1 described here is isostructural with [M(en) 3 ][Sb 4 S 7 ] [8,20]. Although [NH4]2[Sb4S7] and [C4N2H12][Sb4S7] also contain isolated [Sb4S7]2 chains, the conformations of the chains differ significantly from that observed in [M(en)3][Sb4S7]. In the latter, the chains exhibit a zig – zag conformation, whereas in
Fig. 3. Comparison of the structures of (a) [C6H20N4][Sb4S7] (2) and (b) SrSb4S76H2O24 showing the different orientations of the [Sb4S7]2 double chains. In the latter, Sb4S27 double chains are separated by chains of face-sharing Sr(OH2)8 units. Key: antimony, large solid circles; strontium, large shaded circles; sulphur, large open circles; carbon, small solid circles; nitrogen, small open circles and oxygen, small shaded circles.
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both [NH4]2[Sb4S7] and [C4N2H12][Sb4S7] the chains are linear, and show only relatively minor differences in conformation. Whilst in the linear chains all of the semicubes exhibit an identical orientation, in the zig – zag chains semicubes with two orientations, related by a rotation of 120j, alternate along the chain. The change in conformation leads to differences in secondary interactions between chains. A linear conformation is also apparent for the double [Sb4S7]2 chains in 2. Linkage of single [Sb4S7]2 chains by a variety of bridging units to form double chains has also been described. In [C2H10N2][Sb8S13] [21], pairs of single [Sb4S7]2 chains share one vertex of the individual SbS33 pyramids. The structure of [C2H8N]2[Sb8S12(S2)] [22] is very similar to that of [C2H10N2][Sb8S13], with the single chains connected by a S22- unit instead of a single sulphur atom. In [C3H12N2] [Sb10S16] [23], the single [Sb4S7]2 chains are connected through two edge-sharing SbS33 pyramids, which form a Sb2S2 ring. Double [Sb4S7]2 chains similar to those reported here for 2 have been observed previously in the structure of SrSb4S7 6H2O. [24]. However differences in the secondary interactions lead to variations in the packing of the double [Sb4S7]2 chains in the two structures (Fig. 3). In 2, secondary interactions between double chains involve only the Sb atoms in the semicubes, while in SrSb4S76H2O, O, the double chains are linked into sheets through secondary interactions involving the Sb atoms in the Sb2S2 rings. The wide range of compounds in which the [Sb4S7]2 chain may be identified indicates its importance as a building block in antimony-sulphide chemistry. Soft-chemistry techniques offer scope for the generation of new structure types by linking such chains through alternative bridging units.
Acknowledgements The authors wish to thank Dr A.R. Cowley, University of Oxford for assistance with the collection of single-crystal
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X-ray diffraction data. AVP and AMC thank The Royal Society of Edinburgh and The Leverhulme Trust for Research Fellowships, respectively.
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