LiSb(edta) (H,O): a convenient precursor to LiSbS, and LiSb03 Bertrand Marrot, Chantal Brouca-Cabarrecq and Alain Mosset" CEMESf CNRS, 29 rue Marvig, 31055 Toulouse Cedex, France The synthesis and crystal structure of the edta complex LiSb(edta)( HzO) are reported (H,edta =ethylenediaminetetraacetic acid). The compound crystallizes in the monoclinic system. Sb(edta) entities are connected by cyclic [Li(COO)], dimers resulting in parallel layers stacked in the [1lo] direction. Pyrolysis of this complex under sulfur vapour between 700 and 850 "C leads to the mixed sulfide 0-LiSbS,. Pyrolysis in air above 660 "Callows the preparation of the mixed oxide LiSb03. Much research has been carried out in attempts to find new fast ion conducting materials for applications in solid-state batteries or other ionic devices.These compounds are mainly oxides, but sulfides also have been investigated extensively and a number of compounds have been shown to possess interesting electrical properties. For instance, AgIn,S8 shows high ionic conduction, while AgSbSz and Cu3BiS3 exhibit mixed electronic-ionic conduction. Li3,Sb6 -,s, presents elec- tronic behaviour for x=+ and mainly ionic behaviour for x=4.1-4 Improvements in conductivity of several orders of magni- tude can be obtained through substitutions as shown e.g. for Li,GeO,. This material is a moderately good conductor (lo-, K1cm-l at 300°C) but high conductivity (10-1!X1cm-' at 300°C) is found in Li3,,Zn,.,,Ge04.5 We intend to apply this idea to the chemistry of the group 15 metals antimony and bismuth, and to study not only mixed oxides but also mixed sulfides.Indeed, investigation of the phase diagrams of the systems M2S-M',S3 (M=Li, Na, Cu, Ag; M' =Sb, Bi) shows numerous, extremely stable sulfides, some of which occur as minerals (e.g. pyrargyrite, emplectite, pavonite). These systems are interesting because the trivalent nature of the group 15 element and the stereoactivity of the electron lone pair could lead to a great diversity of structural types and, perhaps, to frameworks optimized for ionic conduction. One of the goals in modern solid-state chemistry is to find new synthesis routes at low temperatures through so-called soft chemistry. Different methods can be used to prepare sulfides with complicated stoichiometries.The coprecipitation method has problems of reproducibility and stoichiometry control owing to the different solubilities of cation salts. The all-alkoxide sol-gel method is very promising, and has been used successfully for the preparation of CaLa,S, .6 However, the alkoxide precursors are unstable towards moisture, expens- ive and sometimes difficult to prepare in the case of heterobime- tallic compounds. Our approach to the problem is to use edta coordination complexes as starting products. The ligand itself and several sodium salts are commercially available and are rather cheap. A large number of metallic and heterobimetallic complexes are known and are easy to prepare in aqueous media.The great majority are extremely stable under ambient conditions and can be stored. Further, the sulfurization process using sulfur vapour is more efficient on organometallic compounds because of the formation of carbon disulfide, a very powerful sulfid- ing agent. In this paper, we report the initial results of this study. A new edta complex, LiSb(edta)(H,O), has been prepared and its structure has been solved. Results of pyrolyses under air and sulfur vapour are reported. They prove the feasability of the synthesis method in the case of the bimetallic, i.e. non-substituted, sulfides and oxides. Experimental Crystals of LiSb(edta)(H,O) were prepared by the following procedure. Antimony oxide, Sb203 (20 mmol), and H,edta (40mmol) were dissolved in 150ml of water and heated at reflux for 1 h.Lithium acetate (40 mmol) was then added and refluxing was continued for a further 2 h. The pH of the resulting solution was 4.5. After cooling, the solution was evaporated slowly at room temperature. After 30 days, suitable colourless single crystals were obtained. The chemical formula was established by elemental analysis (see Table 1).Diffracted intensities were measured on a CAD- 4 Enraf-Nonius automatic diffractometer. The space group was determined from the examination of systematic reflection conditions. The crystal structure was solved using the Patterson method and difference Fourier syntheses. All hydrogen atoms were located. Refinement calculations were performed using SHELX76 with a weighting scheme w =k/[02(F)+k'F2].Crystal data, measurement and refinement parameters are given in Table 2. Scattering factors for neutral atoms and f,f' were taken from the International Tables for X-Ray Crystallography.8 X-Ray powder diffraction measurements were recorded on a Seifert diffractometer using Cu-Kar. radiation. Diffraction patterns for single phases were indexed by comparison to the JCPDS library and using the LAZY PULVERIX program.' Pyrolyses were conducted in a Thermolyne tube furnace. The apparatus used for sulfide preparation is schematically drawn in Fig. 1. To avoid the presence of oxygen and moisture, the furnace was flushed with dry nitrogen for 14 h. Samples, placed in a mullite boat, were heated to 200°C in a dry nitrogen flow and then, at a fixed temperature for 2 h, in a flow of nitrogen and sulfur vapour (partial pressure = 10 Torr).During cooling, the sulfiding atmosphere was stopped when the sample temperature reached 200°C but the nitrogen flow was maintained. Table 1 Elemental analysis of the edta complex element experimental (Yo) Sb 26.42( 9) Li 1.56(3) C 27.88( 6) H 3.29(5) N 6.63(6) 0" 34.22 a Obtained by difference to 100%. calculated for LiSb(edta)(H,O) (%) 27.99 1.59 27.62 3.24 6.44 33.1 1 J. Muter. Chem., 1996, 6(5), 789-793 789 Table 2 Crystal data, intensity measurements and refinement para- Table 3 Final least-squares atomic parameters with estimated standard meters for LiSb(edta)(H,O) deviations for SbLi(edta)(H,O) formula mass 434.9 ~~ ~space group min z 4 0.24512( 5) 0.24332(2) 0.06845(4) 1.46(1)44 7.348( 1) 0.5107( 15) 0.0471 (6) 0.6459( 11) 2.27(2) blA 16.833(6) 0.3285(6) 0.2227(2) -0.125 2.21(4) CIA 10.822(2) 0.4484( 6) 0.1350( 3 J -0.2502(4) 2.62(5) Bl" 92.84(2) 0.18 16( 6) 0.1200( 3) 0.1565( 5) 2.47(5)VIA' 1336.9(6) 0.2995( 6) 0.0207( 3) 0.2734( 5) 2.81(5) diffractometer Enraf-Nonius CAD4 0.3356(6) 0.2697( 2) 0.2521 (4) 2.10(6) radiation, monochr. Mo-Ka, graphite 0.4590( 7) 0.3582(3) 0.3814(5) 2.78(4) T/K 293 0.1355(6) 0.3896( 3) 0.0242 (4) 2.13( 5) crystal size/mm3 0.25 x 0.125 x 0.05 0.2087( 6) 0.4937(2) -0.091 3( 5) 2.28(5) picm -21.2 0.1427( 7) 0.9870(4) 0.8980(4) 3.73(8) D,/g cm-3 2.16 0.5049( 7) 0.1668( 3) 0.0808(5) 1.39(8) F(000) 856 0.4772( 7) 0.3356( 3) 0.0463( 5) 1.46( 9) scan mode w scan 0.6711(9) 0.2191 (4) 0.0928 (7) 1.8( 1) data collection limits O< 04 30" 0.6486(8) 0.2929( 4) 0.0157(6) 1.8(1) -ll<h<ll; O<k<24, 0.5051( 10) 0.1 172(4) -0.0342( 7) 1.9(2) 0<1<16 0.4240( 8) 0.1609(4) -0.1470( 6) 1.7(2) number of reflections total 4147, unique 3892, 0.5012( 10) 0.1 129(4) 0.1903(7) 1.8( 1) with I z 3a(I) 2051 0.31 16( 9) 0.0805( 4) 0.2085(6) 2.1(1) no.of variables, R, R, 251, 0.033, 0.032 0.5018(9) 0.3778 (4) 0.168 1 (7) 1.7(2) pmaxin final AF synthesisle k3 1.61 0.4298( 8) 0.3336( 4) 0.2767(6) 1.7(2) 0.4308( 9) 0.3936(4) -0.053 l(6) 1.7(2) 0.2426(9) 0.4296( 3) -0.0391 (5) 1.6(2) Results and Discussion Description of the crystal structure of LiSb(edta) (H,O) Final positions and equivalent isotropic thermal parameters are given in Table 3, and selected bond angles and distances appear in Table 4.As shown in Fig. 2, the ethylenediaminetetraacetate ligand is coordinated to five metallic centres, one antimony atom and four lithium atoms. Among the eight oxygen and two nitrogen atoms of the ligand, only one oxygen atom [0(6)] is not involved in the coordination scheme. The six-coordination around Sb results in the formation of five chelated rings: four glycinate rings fused equatorially, G( 1) [Sb-N(2)-C(9)- C(10)-0(7)] and G(2) [Sb-N(l)-C(5)-C(6)-0(3)], or axially, R(l) [Sb-O(l)-C(4)-C(3)-N(l)] and R(2) [Sb-O(5)-C(8)-C(7)-N(2)], to the ethylenediamine E ring [Sb-N( 1)-C( l)-C(2)-N(2)].The resulting confor- mation is E,G/R according to the notation suggested by Porai- Koshits and co-workers,l0''' a conformation frequently ob- served in six-coordinate edta complexes. The five-membered rings deviate greatly from planarity, with dihedral angles (NCCN or NCCO) of 53.8, 21.8, 20.2, 16.8 and 8.6" for E, G(l),G(2), R( 1) and R(2), respectively. The three dicoordinate carboxylate groups show a classical dissymmetry* in the C-0 distances with a mean 'shyt' distance of 1.23( 1) A and a mean Fig. 2 ORTEP view of the edta coordination to antimony and lith- 'long' distance of 1.28(2) A. The only no?-coordinated oxygen ium atoms atom gives a C-0 distance of 1.215A. According to the + H20 NaOH Fig.1 Diagram of the sulfiding apparatus. 1, Sulfur mullite boat; 2, sample mullite boat. 790 J. Muter. Chem., 1996, 6(5),789-793 Table 4 Interatomic distances (A)and angles(") Sb-N( 1) Sb-O(1) Sb-O(5) Li-0(2) Li-0(7) 2.3007( 3) 2.2385( 4) 2.1119( 3) 1.9277(4) 1.9574( 3) N(l)-C( 1) N(2)--C(2) C(l)-C(2) C(4)-0(2) C(6)-0(4) C(8)-0(6)C( 10)-O( 8) 1.5053( 2) 1.501 1 (2) 1.5012(4) 1.2204( 2) 1.23 19( 3) 1.21 53( 2) 1.2390( 3) N( 1)-Sb-O( 1) N( l)-Sb-0(7) N(2)-Sb-O( 3) O(l)-Sb-0(3) 0(3)-Sb-0(5) 0(2)- L1- 0(4) O(4)- L1- O(7) 72.71( 1) 141.35( 1) 142.70( 1) 108.20( 1) 82.15( 1) 11 1.67( 1) 105.56( 1) N( 1 )-Sb-O(3) N( 1)-Sb-N(2) N(2)-Sb-O( 5) O(l)-Sb-0(5) O(3)- Sb- O(7) O(2)-Li-O( 7) 0(4)-Li-0(8) C( 1)-N( 1)-C(3) C(2)-N(2)-C( 7) N( 1)-C( 1)-C(2) C( 3)-C(4)-0( 1) N( l)-C(5)-C(6) O(3)-C( 6)-0(4) C( 7)- C( 8)-O(6) C(9)-C( 10)-0(7) 11 1.28( 1) 110.79( 1) 11 1.63 ( 1) 116.10( 1) 112.00(1) 127.25( 1) 120.36(2) 115.84(2) C( 1)-N( 1)-C(5) C( 2)-N( 2)- C( 9) C( l)-C(2)-N(2) C( 3)-C(4)-0( 2) C( 5)-C( 6)-O( 3) N(2)-C( 7)-C( 8) O(5)-C(8)-O(6) C( 9)- C( 10)- O(8) standard notation for coordinated carboxylates, the classifi- cation is a-2-a for C(4) and C(6), 1-a for C(8) and a-3-sa for C( 10).12 The six-coordination of the antimony atom corresponds to an extremely irregular polyhedron.Two facts explain this characteristic: the stereoactivity of the Sb"' electron lone p?ir and the wide range of Sb-0 distances (from 2.112 to 2.628 A). The longest Sb-0 distance is observed for the p2-0(7) atom.The lithium atom shows a distorted tetrahedral surrounding; the greatest deviation appears for 0(2)-Li-0(7) (96.15'). The coordination of the edta ligand to five metal atoms results in an intricate three-dimensional network. The main characteristic is the formation of lithium cyclic dimers, localized on centres of symmetry, through the coordination of the C( ly) carboxylate group. The lithium-lithium distance is 3.53 A. This type of association of M' metal atoms (M=Li, Na, Ag) is not uncommon in the crystal structures of edta com-plexes. It has already been observed, for example, in Na,In(edta)(SO,)(H,O), (Na-Na= 3.43 A), LiNi(Hedta) Fig. 3 ORTEP view of a layer 2.3282( 4) Sb-Li 4.033( 1) 2.3402( 7) Li-Li 3.530( 1) 2.6281 (8) 1.9723( 3) 1.9126(2) 1.4996( 3) 1.4937( 3) 1.5001(2) 1.48OO( 3) 1.5214( 2) 1.283 1 (3) 1.5185(2) 1.2726( 2) 1.5089( 2) 1.2987(3) 1.5240( 2) 1.2625 (2) 70.22( 1) 76.67(2) 76.01( 1) 145.63( 1) 147.13( 1) 96.15( 2) 115.59(2) N( 1)-Sb-0(5) N(2)- Sb- O(1) N(2)-Sb-O(7) O(l)-Sb-0(7) 0(5)-Sb-0(7) 0(2)-Li-0(8) O(7)- Li-O( 8) 80.87( 1) 76.79( 1) 64.87( 2) 94.05( 1) 93.07( 1) 108.66( 1) 117.60( 1) 109.44( 1) 108.75(1) 110.18( 1) 119.50( 1) 115.30( 1) 114.76(2) 122.70( 1) 117.66( 1) C(3)-N( 1)-C(5) C( 7)- N(2)- C (9) N( l)-C(3)-C(4) O(l)-C(4)-0(2) C(5)-C( 6)- O(4) C(7)-C(8)-0( 5) N(2)-C(9)-C( 10) O(7)-C( 10)-O(8) 108.68(2) 109.86( 2) 112.32( 2) 124.37( 1) 117.43( 1) 116.94( 1) 11 1.54( 1) 126.50( 1) 1 (a) () f 24ii h i+! Y 2? 5 15 20 25.._.-id (b) I Fig. 4 Experimental (a) and calculated (b) X-ray patterns for LiSb(edta)(H,O). All the experimental peaks were indexed but this indexation is only shown for the 35 strongest peaks on the experimen- tal pattern. (H20) (Li- Li =3.74 A), Na,Mo,O,(edta)( JNa-Na = 3.74 A) and AgCu(Hedta)(H,O), (Ag-Ag=2.86 The three-dimensional structure can be described in terms of parallel layers. Fig. 3 shows such a layer. For the sake of clarity, only the atoms involved in the connections between metal atoms have been included. Fused rings built from four lithium dimers and four antimony atoms can be seen. In these rings, alternating long Sb-Li distances [through the C(6) carboxylate group] and short Sb- Li distances C4.03 A through the p2-o(7) atom] are found.Alternatively, the struc- ture of the layer can be described as a pseudo-hexagonal J. Muter. Chem., 1996, 6(5), 789-793 791 arrangement of lithium dimers These layers are stacked in the [ 1lo] direction and connected through Sb' atoms X-Ray powder data Large quantities of the edta complex can be prepared con-veniently using the above procedure with rapid evaporation at 25 "C The as-prepared microcrystalline powder is identical to the single crystals, as shown by comparison of the exper- imental diffraction pattern with the pattern calculated for the crystal structure (Fig 4) Preparation of LiSbSz The hexagonal form of the bimetallic sulfide, P-LiSbS2, has been obtained at 800°C by pyrolysis of the edta precursor in a sulfiding atmosphere This phase can be obtained free from impurities between 700 and 850°C The sulfide is slightly hygroscopic but it can be stabilized by subsequent drying at 3 1 1 ? 5 10 15 20 25 -60I 5 10 15 20 25 II -Fig.5 X-Ray patterns for LiSbS, (a)experimental, (b)calculated from the crystal structure (c)JCPDS file no 40-1330 for P-LiSbS," 792 J Muter Chem , 1996, 6(5),789-793 100 10 I0 00 a0 a 3DOID a01 32 43s 14 4 a I 1IZ IZt 02 I21 I2 0 I 0 2 Bldegrees Fig. 6 Guinier-Lenne pattern of the precursor pyrolysis in air (a)incre-asing temperature, (b)plateau at 1000 "C, (c) decreasing temperature 120"C for 20 min The structural characterization was made by powder X-ray diffraction A comparison between the exper- imental pattern [Fig 5(u)] and the pattern calculated from the crystal structure17 [Fig 5(b)] shows an unambiguous indexation, which does not, however, correspond to the JCPDS file (no 40-1330)18 given for P-LiSbS, [Fig 5(c)] In this original work," the bimetallic sulfide was prepared by reaction, in a silica tube, of a mixture of Sb2S3 and Li2S and slow cooling from the melt Thus, the phase registered as the p phase in the JCPDS file does not correspond to the crystal structure and, most probably, was spoiled by oxygen owing to reaction between L1,S and the tube Indeed, in some of our expenmental runs, the obtained sulfide corresponds to the JCPDS file but contains up to 64 mass% of oxygen This result seems to originate from the sulfur vapour pressure being too low during the sulfiding procedure Preparation of LiSb03 The mixed oxide can also be prepared from the edta precursor by pyrolysis in air above 660°C Fig 6 shows the thermal behaviour as registered on a Guinier-Lenne camera The precursor is heated slowly to 1000 "C (0 17 "C min-l), kept at this temperature for 10 h and then cooled to room temperature Above 3OO0C, the precursor is destroyed totally and the product is amorphous At 660"C, the mixed oxide LiSbO, crystallizes This is in good agreement with the TG analysis which shows a gradual loss of water below 300 "C, a decompo- sition of the organic part leading to Sb20, + Li2C03 at 410 "C (experimental loss 49 1%, calc loss 49 5%) and finally the formation of the mixed oxide above 550°C (experimental loss 59 6%, calc loss 59 4%) Conclusions This study demonstrates that edta coordination complexes can be convenient precursors for mixed oxides and sulfides In a first stage, non-substituted materials were prepared The same procedure will be used to prepare these compounds with appropriate substitutions in the antimony site in order to control and improve the ionic conductivity This can be achieved easily through coprecipitation from the aqueous solution by adding a solvent like acetone l9 References 1 J Flahaut, L Domange, M Guittard, M Ourmitchi and J Kamsu, Bull SOC Chim Fr , 1961,2382 2 V Valiukenas, R Jasinskaite, A Orliukas and A Sakalas, Liet Fiz Rinkinys, 1980,20,49 3 N F Lugakov, E A Movchanskii and I N Pokrovskii, Fiz Tverd Tela Poluprovodn , 1974,23 4 J Olivier-Fourcade, L Izghouti, E Philippot and M Maurin, Rev Chim Miner, 1983,20,186 5 A. 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