The thiotrithiazyl iodated polyhalides

Z inorg, nucL Chem. Vol. 42, pp. 5-7 Pergamon Press Ltd., 1980. Printed in Great Britain

THE THIOTRITHIAZYL IODATED POLYHALIDES H. VINCENT, Y. MONTEIL and M. P. BERTHET Laboratoire de Physicochimie Min&ale associg au C.N.R.S. No. 116, 43 Boulevard du 11 Novembre 1918, 69621 Villeurbanne, France (First received 19 March 1979; in revised form 9 April 1979) Abstract--We have prepared a series of simple and mixed trihalides containing iodine (S4Nd~, S4N312Br,S4N3IBr2), by metathesis between an appropriate caesium trihalide and $4N3CI. The action of 12 on $3N3C13 gives the analogous salt $4N3ICI_,. In the other hand, we have also prepared the compound S4N3Br~by metathesis between alkaline tribromides and $4N3C1. All these compounds are characterized by IR spectra and X-ray diffraction patterns; we have also studied their stabilities. The iodated mixed trihalogenides are more stable than the compounds $4N313and S4N3Br3. All the iodated trihalogenides are more stable than S4Nd.

INTRODUCTION S-N compounds and their halogenated derivatives have recently attracted considerable interest due to the very interesting electric properties of the polymeric sulfur nitride, (SN)x[I-4], and of some of its brominated derivatives, which were also obtained by the bromination of $4N415-7]. The effect of ICI and IBr on $4N4 gives the polymers [SN(ICI)o.4]x and [SN(IBr)o.4]x comparable with (SNBro.4)x obtained by brominatlon[8]. There have been a few studies on thiazyl iodides. Only one compound $4N3I, stable at a temperature lower than 0°C, is known[9]. We have studied the effect of iodine on $4N4 as well as the effect of bromine on $4N4. Contrary to the observations in the literature, we have noticed that iodine reacted on $4N4; we have worked in solution, in an inert solvent, at its boiling temperature. However the reaction is very slow, after a few days the sulfur nitride is only partly attacked. The reaction products precipitate in small amounts. The insoluble substance has a very dark red colour. Its composition is not well determined, it approximates (SNIo.33)x; it varies slightly according to the time of the thermal treatment. X-Rays show it to be amorphous. It is not studied any longer. We tried other methods to obtain defined iodated compounds. We studied the action of hydrogen iodide on the thiazyl chlorides S3N3C13, 83N2C12 and S4N3CI. HI acts in the same way as HBr, it causes the destruction of the cycle of the chlorinated compounds and the formation of the salt $4N3C12I, stable at room temperature[10]. We have also obtained this salt by the action of iodine on $3N3C13 in a carbon disufide solution. For the first time we have now prepared and characterized a series of simple and mixed trihalides containing iodine. The general method which has been used to prepare these compounds consists of a metathesis between an alkaline polyhalide and $4N3CI. The polyhalides of caesium which are the most stable have been chosen for this reaction. In the same series, we have prepared the compound S4N31]r3 which was found during the bromination of $4N4[11] and which Street[12] has obtained by action between liquid bromine and $4N4 in a sealed tube. EXPERIMENTAL

Reactions between halogens and halides can be achieved in a suitable solvent or by a gas-solid reaction, provided that the

reaction temperature is lower than the decomposition temperature of the polyhalide[13]. In solution, solvents liable to halogenation or reactions of solvolysis must be avoided. Then we will have to use aqueous solutions for polyiodides, because iodine reacts hardly with water. More inert solvents such as halogenated hydrocarbides are not suitable, because they cannot dissolve halogenides. On the other hand solvents such as methanol, anhydrous acetic acid and formic acid seem to be the most suitable ones. The method consists in adding an excess of halogen to a solution of an appropriate halogenide. The polyhalogenide precipitates with a good degree of purity and car, be purified by recrystallization. A decrease of the yield is caused by the dissociation of the trihalogenide giving the halogen and the corresponding halogenide. CsBr~. 3g of finely powdered CsBr was treated by dry gaseous bromine in a desiccator. Bromine in excess was absorbed by KOH. The reaction was over if there was no CsBr on the X-ray diffraction pattern of the reaction product. Calc. for CsBr~: Br, 64.3; Found: Br, 63.9. IR spectrum (cm ~): v~ = 136 (m), v~= 210 is). Csl3. 2.6g Csl was dissolved in 100ml of water and 3.0g I2 was added. To make 12dissolve easier the solution was heated to 50°C. As the temperature decreased CsL precipitated. It was filtered in a dry box, dried under vacuum during 5 rain, then washed by CS2 to dissolve the iodine excess which precipitated at the same time as CsL. Calc. for CsK: 1, 74.1. Found: I, 73.3. IR spectrum (cm t): vl - 100 (s), v3 = 145 (s), v2 = 66 (w). Csl2Br. 3g CsBr and 4g 12 were put in 10Oral of a waterethanol mixture, (50 vol.%): CsBr does not dissolve in pure ethanol. The solution was refluxed during 2 or 3 min. After cooling, the solution must be evaporated till it is dry to precipitate a mixture of CsI2Br and l> The iodine excess was eliminated by a long washing by CS> Calc. for CsI~Br: I, 54.4: Br, 17.1. Found: I, 53.8; Br, 16.7. IR spectrum (cm ~): v~--:115 (s), .v~- 167 (s). CslBr2. 3g Csl was dissolved in 100ml of anhydrous formic acid. After the complete dissolution of Csl, 3.2g bromine was added which corresponds to a light excess in relation to the CslBr2 formation. The CslBr2 trihalide is obtained by the evaporation of the solution. Calc. for CslBrz: I, 30.2: Br, 38.5. Found: 1, 29.1: Br, 37.4. IR spectrum (cm ~): v , - 140 Is), ~,~188 (m), v2 = 90 Im). S4N~X~. The S4N~CI has been prepared by Jolly's method[14] which consists in making the sulfur dichloride S:C1, react on the thioditbiazyl dichloride: 3S~N,CI: + S~CI2 S4N~CI+ 3SC1: S~N,CIz was prepared from ammonium chloride and sulfur dichloride. The S4N~C1compound is not very sensitive to moisture and ice-cold water does not hydrolize it, it is soluble in ionic solvents such as anhydrous formic acid.

6

H. VINCENT et al.

The different compounds S4N3X3 have been prepared by dissolving about 5g of S4N3CIin 100mL of formic acid to which we have added the stoechiometric quantity of CsX3 and 20% excess. S4N3X3 has been obtained by filtration. All the products S4N3X3 are sensitive to moisture. This is the reason why they were handled in a glove-box. S4N~ICI,has been prepared from S3N3Cl3. A solution of iodine in CS2 was added to a saturated solution of S3N3C]3 in CC14.The I2 addition was slowly done at room temperature. A dark precipitate appeared immediately and the solution was getting clearer. The iodine solution was added till the resulting solution remained dark and a few iodine crystals were added. Then the mixture was refluxed during 2hr. A dark product very well crystallized was obtained by filtration. S4N3Br3 Calc.: S, 31.22; N, 10.24; Br, 58.54. Found: S, 30.8; N, 10.2; Br, 58.3. X-ray diffraction pattern, d(~,): 4.50(s), 3.477(s), 3.386(m), 3.303(s). S4NdBr~, Calc.: S, 28.00; N, 9.19; I, 27.79; Br, 35.01. Found: S, 27.6; N, 9.25; I, 26.9; Br, 34.7. X-ray diffraction pattern, d(/~): 4.49(s), 3.566(s), 3.431(m), 3.345(s). S4N312BrCalc.: S, 25.40; N, 8.33; I, 50.40; Br, 15.87. Found: S, 25.1; N, 8.2; I, 50.6; Br, 15.6. X-ray diffraction pattern, d(/~): 4.51(s), 3.613(m), 3.470(m), 3.388(s). $4N313 Calc.: S, 23.23; N, 7.62; I, 69.15. Found: S, 22.9; N, 7.6; I, 68.8. X-ray diffraction pattern, d(,~): 3.434(s), 3.057(s), 2.557(s). $4N31CI2Calc.: S, 34.78; N, 11.41; CI, 19.29; I, 34.51. Found: S, 33.6; N, 11.10; CI, 18.35; I, 33.15. X-ray diffraction pattern, d(,~): 3.483(m), 3.270(s), 2.784(s). Halogens were titrated by potentiometry, nitrogen by the Kjeldahl's method and sulfur as barium sulfate. IR spectra (CsBr or CsI discs) were obtained by using a Perkin-Elmer 457 between 250 and 400cm-~. In the frequency range 10-400cm-1 polyethylene discs were used with a Beckman IR 720. Thermal gravimetric analysis as performed under dynamic vacuum with a Setaram B.70. The weight of samples was 50-100 mg. Powder data were obtained in a Debye-Scherrer camera. The preparation of samples was done in a dry box. RESULTS AND DISCUSSION

There have been a few studies on caesium trihalides. Only the structure of CsI3 and CsIzBr have been determined by X-rays diffraction [15, 16]. We have characterized them by their X-ray patterns and their spectra in far-IR. It has not been possible to obtain the Raman spectra of these compounds which are very dark; only the lighter tribromide of caesium might be suitable for such measures. Its Raman spectrum has not been obtained because of its decomposition by the laser effect. The four trihalides obtained present at least two strong absorption bands u, and v3; this indicates that the three

halogens are arranged either in an asymetric or a nonlinear way. In the CsI3 compound the three iodine atoms are not linear, they make an angle of 176°[15]. The 12Br ion is asymmetric, its structure has been determined by radiocrystallography[16]. In the CsIBr2, of unknown structure, the anion must have a symmetric arrangement, because we know that the heavier atom generally stands in the central position[17, 18]. At the same time we notice the two bands u, and u3 so that the anion is not linear. As far as we know, the tribromide of Cs has not been studied by IR spectroscopy. For the (BuhNBr3 compound, only the band u3 at 193 cm ' has been observed, whereas in Me4NBr3 Raman spectroscopy gives a single band at 162 cm ' due to the symmetric stretching vibration m[19]. The two bands observed for CsBr3 viz. u, = 136cm ~(m) and u3 = 210cm ~(s) show that in this compound the Br3 anion is not linear. It is natural that the constitution of the cation affects the anion structure; this is the reason why the 13 anion is not linear in CsI3 whereas this same anion is linear in (CH3hNI3 [20]. The trihalides of caesium react quantitatively with the thiotrithiazyl chloride. The compound S4N3CI whose structure is unknown, reacts in water at 0°C or in formic acid in the same way as an ionic compound. With the trihalides of caesium we get a metathesis according to: S4N3+C1

+

Cs+X3 -..~S4N3X3+ Cs+C1

The compound S4N3X3 precipitates from the reaction medium. The structure of the 54N3 ÷ ion has been determined using a single crystal of thiotrithiazyl nitrate [21,22]. 54N3 + has a plane structure and a pseudo-aromatic character caused by the fact that the SN bonds are similar and have an intermediate length between a simple and a double bond which gives it a high stability. It has the two characteristics which allow the formation of polyhalides: large ionic radius and small charge. The S4N3ICI_, has been only prepared by the action of iodine on the thiotrithiazyl trichloride in a solution of carbon tetrachloride. In Table 1 the IR spectra of the thiotrithiazyl trihalides have been put together. There is a great number of analogies between the different spectra. Above 200 cm they are also similar with the IR spectrum of the known thiotrithiazyl nitrate[23]. It seems reasonable, therefore to assume the existence of a similar type of ring structure S4N3+ of all these compounds. The frequencies vary

Table 1. IR spectra of thiotrithiazyl trihalides S4N3br 3

S4N31Br 2

S4N312Br

S 4 N 313

1160

vs

1175

s

1167

S

1165

s

1170

1010

vs

1015

vs

1007

vs

1020

vs

1018

s

677

m

m

676

m

672

m

678

ra

6"78

S 4 N 31C 12

m

565

m

572

w

565

w

565

m

570

w

475

s

475

vs

420

s

460

vs

475

vs

325

m

321

S

322

m

313

s

327

m

254

w

255

w

250

w

250

w

276

w

204

m

197

m

186

m

183

m

185

m I<,5

~37

w

141

m

182

m

~36

m

m

13R

w

120

w

The thiotrithiazyl iodated polyhalides slightly in the different solid spectra according to the anion size. In particular, the very strong band at 1010 cm ~ in S4N3Br3 is displaced 10 cm J in S4N313. The influence of the anion does not seem to be important here. In the far-IR we notice, for the trihalides ions, that the ,. band has about the same frequency, viz. u~ = (138_+4)cm '. The z,3 band is situated between 186cm and 165 cm '. The two bands ~,~ and ~'3 indicate that the anions studied have an asymmetric or a nonlinear structure. This analogy of IR spectra is found again in the X-ray patterns of these polyhalides. Only $4N313 is completely different from the others. The thermal stability of the different thiotrithiazyl trihalides was studied by thermal gravimetric analysis, The S4N3Br~ and $4N313 compounds are less stable than the trihalides containing a mixed anion. On the other hand, the iodated trihalides of thiotrithiazyl are more stable than the monoiodide $4N3I. The thiotrithiazyl tribromide decomposes above 35°C according to the reaction: S4N~Br~-~ S4N~Br + Br2 The thiotrithiazyl triodide decomposes above 42°C according to: S4Nd~-~ $4N3I + I2 but the decomposition goes on because $4N3I is instable. The decomposition products are $4N4, iodine and sulfur. The most stable iodide is S4N3IBr2. In the IBr2 anion, iodine is placed between the two bromine atoms, which explains the formation of S4N3Br above 95°C. Later on S4N3Br decomposes: 2S4N~Br ~ $4N4 + 2NSBr + 2S The anion of $4N3IC12 is similar to IBrz . The iodine always takes the central position and the chlorine atoms take the place of the bromine atoms which explains the weaker thermal stability of this compound. Its complete decomposition starts at 60°C, and there is a formation of $4N4 from the beginning of the decomposition which can be written: 4S4N3IC12 ~ 3S4N4 + 4S + 4C1~ + 212. In the S4N312Br compound, the I2Br ion is not symmetric. S4N312Br decomposes above 60°C, a temperature which is lower than the decomposition temperature of S4N3IBr~. This is in agreement with Popov's results [13]

who has noticed that the IX2 ions (X = CI or Br) are more stable than I2X ions. By T.G.A. of S4N312Br we have observed two mass losses. The first at 60°C results in an iodine emission. After this emission the residue is composed of S4N~Br: S4N312Br ~ S4N~Br + I, The second mass loss relates to the S4N,Br decomposition above 110°C.

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