Two-Step Solvothermal Preparation of a Coordination Polymer Containing a Transition Metal Complex Fragment and a Thiostannate Anion: [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (en, Ethylenediamine)
CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 5 1845-1848
Xiao-Mei Gu,† Jie Dai,*,†,‡ Ding-Xian Jia,† Yong Zhang,† and Qin-Yu Zhu† Department of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215006, P. R. China, and State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P.R. China Received March 25, 2005;
Revised Manuscript Received May 15, 2005
ABSTRACT: A two-step solvothermal synthetic method was used for preparation of a one-dimensional compound, [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (1), in which the Mn(II) ions are bridged by thiostannate [Sn2S6]4- anions and linear coordinating ethylenediamine (en) molecules. At first, a clear yellow solution containing [Sn2S6]4- anions was previously obtained from a SnCl4/S/en mixture under solvothermal conditions. Then MnCl2‚6H2O was added to the resulted solution, and the solvothermal reaction went on for additional days. Finally pale-yellow crystals of 1 were obtained. Using the same starting materials and in the same molar ratio, however, we obtained a colorless [Mn(en)3]2Sn2S6 (2) by the one-step, one-portion solvothermal reaction from a MnCl2/SnCl4/S/en mixture. Introduction The synthesis of new chalcogenidostannates ([SnxQy]n-, Q ) S, Se, and Te) has attracted much attention due to the rich structural diversity of these compounds based on corner- and edge-sharing of SnQm (m ) 4, 5, 6) polyhedrons and potential applications of these compounds in microporous materials or non-oxygen molecular sieves,1 semiconductors or chemical sensors,2 and photoluminescent or magnetic materials.3 Hydrothermal or solvothermal synthesis is a very effective method and has been popularly used in inorganic synthesis, especially for inorganic polymers. During the past decades, organic-inorganic hybrid thiostannates have been synthesized by such techniques in the presence of organic amines or ammonium salts. Among these thiostannates, one of the typical structures of the anions is a dimeric ion [Sn2S6]4-. Its counterions are protonated amines or ethylenediamine-coordinated transition metal cations.4 Another fundamental structure is a twodimensional polyanion assembled by broken-cube units [Sn3S7]2-, for example, SnS-1 and SnS-3.5 These compounds are usually charge-balanced by alkylammonium ions. Although other structures, such as one-dimensional or three-dimensional organic-inorganic thiostannates, have also been characterized, the diversity in structures of these hybrid thiostannates is not as rich as that of the pure inorganic thiostannates, which were usually prepared by the molten salt (flux) method.6 Despite the fact that hydrothermal or solvothermal synthetic methods have been widely used, the development of a rational approach to the synthesis of designable compounds still remains a major challenge.7 The most widely used hydrothermal or solvothermal synthesis or crystal growth is a one-portion and one-step reaction. The reaction mechanisms can be affected by a * To whom correspondence should be addressed. E-mail: daijie@ suda.edu.cn. † Suzhou University. ‡ Nanjing University.
variety of factors, and therefore, to predict the final products is difficult. In our recent study of the synthesis of thiostannates, we found that the product of a twostep solvothermal synthetic method was different from that of the one-step, one-portion solvothermal reaction, even using the same starting materials. By the two-step solvothermal reaction, a one-dimensional compound, [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (1), was prepared, in which the thiostannate [Sn2S6]4- anions are bridged by Mn(II) ions and en molecules (en ) ethylenediamine). Experimental Section All analytically pure starting materials were purchased and used without additional purification. FT-IR spectra were recorded with a Nicolet Magna-IR 550 spectrometer in dry KBr pellets. Elemental analysis was carried out on a MOD 1106 elemental analyzer. Synthesis of [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (1). To a solution of 5 mL of ethylenediamine, SnCl4‚5H2O (0.526 g, 1.5 mmol) and S8 powder (0.3848 g, 1.5 mmol) were added. After being stirred for 5 min, the mixture was transferred to a Teflon-lined steel autoclave, the volume of which is about 15 mL (the filling rate of the autoclave is about 40%). The sealed autoclave was heated to 160 °C and maintained isothermal for 2 days. After it cooled to room temperature, a bright yellow solution was obtained. To the resulting solution (2 mL), MnCl2‚ 6H2O (0.076 mg, 0.6 mmol) and en (1 mL) were added, and the mixture was reacted for an additional 7 days at 160 °C. Transparent pale-yellow crystals formed (95 mg, yield 45% based on Sn). Anal. Calcd: C, 14.30; H, 4.80; N, 16.67%. Found: C, 14.52; H, 5.03; N, 16.72%. Synthesis of [Mn(en)3]2Sn2S6 (2). This compound was synthesized by a reported procedure.4f Synthesis of (Hen)4Sn2S6 (3). The reactant mixture of SnCl4‚5H2O (0.526 g, 1.5 mmol) and S8 (0.3848 g, 1.5 mmol) dissolved in 6 mL of ethylenediamine was transferred to a Teflon-lined steel autoclave, the volume of which is about 15 mL. Then the sealed autoclave was heated to 160 °C and maintained at this temperature for 2 days. After it cooled to room temperature, a bright yellow solution was obtained. The solution was transferred to a flask and left aside. A large number of colorless platelet crystals of (Hen)4Sn2S6 appeared
10.1021/cg050109o CCC: $30.25 © 2005 American Chemical Society Published on Web 08/16/2005
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after months (yield 56%, based on Sn). Anal. Calcd (C8H36N8Sn2S6): C, 14.25; H, 5.38; N, 16.62%. Found: C, 14.21; H, 5.32; N, 16.52%. Crystal Structure Determination. All measurements were carried out on a Rigaku Mercury CCD diffractometer at 193 K with graphite monochromated Mo KR (λ ) 0.710 73 Å) radiation. X-ray crystallographic data were collected and processed using CrystalClear (Rigaku). The structure was solved by SHELXS-97 (Sheldrick, G. M., University of Go¨ttingen) and refined using SHELXL-97 (Sheldrick, G. M., University of Go¨ttingen). The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using the riding model. A summary of the experimental details is given as following: [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (1), Mw ) 840.14 (C10H40Mn2N10S6Sn2), triclinic, space group P1 h (No. 2) with a ) 9.0097(8), b ) 9.7735(5), and c ) 10.8421(2) Å and R ) 60.379(14)°, β ) 67.235(16)°, and γ ) 70.250(18)°, and V ) 752.38(8) Å3. T ) 193 K, Z ) 1, Dcalcd ) 1.845 g‚cm-3, F(000) ) 416, and µ ) 2.896 mm-1. A total of 8255 reflections collected of which 3352 reflections were unique. R1 for 3243 reflections (I > 2σ(I)) 0.0218; wR2 for all 3352 data 0.0468; GOF 1.118.
Results and Discussion Recently, thiostannate [Mn(en)3]2Sn2S6 (2) was synthesized by our group using a one-step solvothermal reaction from a MnCl2/SnCl4/S/en mixture under mild solvothermal conditions at about 150-180 °C.4f The compound consists of discrete [Sn2S6]4- anions and [Mn(en)3]2+ cations. For the aim of preparation of an inorganic-organic composite polymer or network, the factors of the reaction, such as molar ratio and temperature, had been changed, but compound 2 was the only pure product isolated. When the above reaction system reacted in the absence of MnCl2 (a SnCl4/S/en system), a clear solution was obtained. The resulting solution was left for about one or two months at room temperature under ambient conditions, and colorless crystals of (Hen)4Sn2S6 (3) were isolated in high yield. The crystal structure of 3 was determined by single-crystal X-ray diffraction and was isostructural with the compound described by Dehnen’s group,8 but they used a different synthetic route. However the experimental results show that the dimeric anion [Sn2S6]4- should be the main product of the reaction system. In the presence of sizesuited [Mn(en)3]2+ cations, the compound 2 crystallized immediately during the reaction. But the protonated en cations are not well size-suited for the [Sn2S6]4- dimeric anion; therefore, the period of the crystallization of 3 takes a very long time. These phenomena inform us that preparation of new polymeric compounds with [Sn2S6]4anions might be possible by adding suitable transition metals as connecting ions to the solution of [Sn2S6]4-, a solution obtained from the SnCl4/S/en system after solvothermal reaction and before the crystallization of 3. With this idea, a novel one-dimensional thiostannate, [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ (1), was prepared using a two-step solvothermal reaction. The only difference in the syntheses of 1 and 2 was the reaction procedures. The colorless [Mn(en)3]2Sn2S6 (2) was obtained by a one-step reaction from a MnCl2/ SnCl4/S/en mixture, whereas the [{Mn(en)2}2(µ-en)(µSn2S6)]∞ (1) was obtained in a different procedure. At first, a clear yellow solution containing [Sn2S6]4- anions was previously obtained from a SnCl4/S/en mixture under solvothermal conditions. Then MnCl2 was added to the resulting solution, and the solvothermal reaction
Gu et al.
Figure 1. ORTEP representation of the structure of 1 with labeling scheme and 50% probability ellipsoids. Hydrogen atoms are omitted for clarity. Table 1. Selected Distances (Å) and Angles (deg) for the Title Compound (1) distances Sn(1)-S(1) 2.3433(7) Sn(1)-S(2) 2.3380(6) Sn(1)-S(3) 2.4513(8) Sn(1)-S(3)a 2.4581(6) S(1)-Mn(1) 2.5683(9) Mn(1)-N(1) 2.284(2) Mn(1)-N(2) 2.2983(19) Mn(1)-N(3) 2.266(2) Mn(1)-N(4) 2.338(2) Mn(1)-N(5) 2.302(2) a
angles S(1)-Sn(1)-S(2) S(3)-Sn(1)-S(3)a Sn(1) -S(3)-Sn(1)a Mn(1)-S(1)-Sn(1) N(5)-Mn(1)-S(1) N(1)-Mn(1)-N(2) N(3)-Mn(1)-N(4) N(1)-Mn(1)-N(3) N(2)-Mn(1)-N(5) C(5)-N(5)-Mn(1)
114.73(2) 93.33(3) 86.67(?) 108.28(2) 84.75(6) 76.60(7) 75.38(8) 160.05(7) 164.84(8) 118.24(15)
Symmetry code: 2 - x, 1 - y, 1 - z.
Figure 2. One-dimensional structure of 1, showing the connection of the polyhedrons.
continued for an additional 7 days. Finally pale-yellow crystals of 1 were obtained. An ORTEP view of the structure of 1 is given in Figure 1. The Mn(II) ion is six-coordinated by two chelating en molecule, one linearly coordinated en molecule, and a [Sn2S6]4- anion. The octahedral coordination sphere of Mn(II) is distorted, and the two chelating en molecules are in cis conformation. The Mn-N bond distances of 1 (Table 1) vary from 2.266(2) to 2.338(2) Å lying within the range of the distances in other compounds containing the [Mn(en)3]2+ cation.9,10 No remarkable difference is observed for the bond distances of Mn-Nc (c ) chelate) and Mn-Nb (b ) bridge). The Sn-St (t ) terminal) bond lengths of the [Sn2S6]4- anion are 2.3432(7) and 2.3380(6) Å for Sn(1)S(1) and Sn(1)-S(2), respectively, and the Sn-Sb bond lengths are 2.4513(8) and 2.4581(6) Å for Sn(1)-S(3) and Sn(1)-S(3)a, respectively. These data are in agreement with corresponding bond distances of the discrete [Sn2S6]4- anions;4 however, the slightly elongated Sn(1)S(1) distance might be due to the influence of the coordination of S(1) atom to Mn(II) ion. The distance of the coordination bond of Mn(1)-S(1) is 2.5683(9) Å. Figure 2 shows the one-dimensional structure of 1 in a polyhedron model. The octahedral-coordinated Mn(II) ions are connected to the neighboring Mn(II) ions by an en bridge and a [Sn2S6]4- bridge, in which two SnS4
Two-Step Preparation of [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞
Figure 3. Packing structure of the one-dimensional chains in the unit cell box.
tetrahedra share a common edge. It is unfamiliar for organic-inorganic hybrid thiostannates that the [Sn2S6]4anion acts as a bridge that coordinates to metal centers. Usually the [Sn2S6]4- ion is a discrete anion in crystals.4 The only example that has been found is [{Co(tren)}2(µ-Sn2S6)]4e in which the anion coordinates to the metal center. All the [{Mn(en)2}2(µ-en)(µ-Sn2S6)]∞ chains are parallel to each other along the direction [1,-1/2,0] (Figure 3). In the en-coordinated compounds, the en molecule usually acts as a chelate ligand. The bridging coordination of en is seldom found. Within the chalcogenidometalates of the group 13-15 elements, only a few examples were documented in which the en coordinates to two metal centers as a bridge, for example, [Mn(en)3]2[Mn4(en)9(SbSe4)4]‚H2O11 and (enH)[{Mn(en)2(enH)}2(µ-en)(Ge2Se7)2].12 Repeated corner bridging of tetrahedral [SnS4]4anions leads to the formatiom of the infinite [SnS32-]∞ one-dimensional (1-D) chains that have been found in structures of K2SnS3‚2H2O, Tl2SnS3, BaSnS3, and SrSnS3, summarized by W. S. Sheldrick.6 With the exception of K2SnS3‚2H2O,13 which was isolated from aqueous solution, the other compounds were prepared by the high-temperature flux technique. To the best of our knowledge, the only reported 1-D thiostannate consisting of organic components is an unusual polymer, [SnS2‚en].14 The basic structure of the compound is an infinite [SnS32-]∞ chain as mentioned above. To the Sn(IV) center, an additional en ligand is chelated. Compound 1 is a new type 1-D polymer of thiostannate with organic linkages. The results of this work reveal that although all the starting materials and the reaction temperature are the same for the one- and two-step reactions, the products may be different. In the two-step reaction, the thiometalate anions tend to coordinate to the metal ions as a bridge. Another example of this phenomena is a polymeric lanthanide thioantimonate [Sm(en)3(H2O)(µSbS4)]∞ prepared using the two-step method.15 In the one-dimensional structure of [Sm(en)3(H2O)(µ-SbS4)]∞, the SbS43- anions coordinate to metal centers as a bridge. But the one-step reaction only gives a compound of [Sm(en)4]SbS4‚0.5en with discrete cations and anions.15 However in that communication, the phenomenon has not been discussed because only one example had been found. The mechanism of the reaction is still unclear, and it should relate to the concentration of the thioantimonate and the competitive coordination of the thioantimonate and the en molecules to metal centers. The concentra-
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tion of the thioantimonate is very low at the beginning of the one-step reaction, since the starting materials are SnCl4 and S, so at an early stage the transition metal ions might be coordinated by en or exist as SnSx and MnSx species. For the two-step reaction, there is a high concentration of the thiometalates at the time that the metal cation is added to the system, which has been confirmed by the result of the SnCl4/S/en system (compound 3). This is the main difference between the twostep reaction and the one-step reaction. In summary, this work discusses a two-step solvothermal method to prepare a coordination polymer containing thiostannate and compares the reaction result with that of the method of one-step reaction. The strategy can be used for preparation of other chalcogenidostannates having polymeric structure. Acknowledgment. This work was supported by the National Natural Science Foundation (Grants 20071024 and 20371033), P.R. China. The authors are also grateful to the Key Laboratory of Organic Synthesis of Jiangsu Province, Suzhou University, for financial support. Supporting Information Available: Crystallographic data of 1 in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
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