Reactions of cis-[pt(s~lfoxide)~cl~] with silver salts and synthesis of hydroxo-bridged platinum(i1) complexes with sulfoxides

Transcription

1 Reactions of cis-[pt(s~lfoxide)~cl~] with silver salts and synthesis of hydroxo-bridged platinum(i1) complexes with sulfoxides FERNANDE D. ROCHON, PI-CHANG KONG, AND LOUISE GIRARD Dkpartement de chimie, Universite' du Quebec d Montre'al, C.P. 8888, succ. A, Montrkal (Que'.), Canada H3C 3P8 Received August 8, 1985 ' FERNANDE D. ROCHON, PI-CHANG KONG, and LOUISE GIRARD. Can. J. Chem. 64, 1897 (1986). Platinum(I1) compounds of the type ~is-[pt(l)~x~] where L = tetramethylenesulfoxide (TMSO), ethylmethylsulfoxide (EMSO), di-n-propylsulfoxide (DPSO), benzylmethylsulfoxide (BMSO), and dibenzylsulfoxide (DBSO) and X = C1- and I- have been synthesized. The reactions of these compounds with a silver salt were studied in aqueous solution. Monomers of the type ci~-[pt(l)~(c10~)~] = TMSO, EMSO, and DBSO), ~is-[pt(ems0)~(s0~)1 and hydroxy-bridged oligomers were isolated. Dimers, C~S-[P~(L)~(OH)]~(NO~)~ = TMSO, DPSO), and C~S-[P~(EMSO)~(OH)]~SO~ and possibly a trimer (c~s-[p~(emso)~(oh)]~)~(so~)~ wcre characterized. The compounds were studied by infrared spectroscopy and by 'H nmr. FERNANDE D. ROCHON, PI-CHANG KONG et LOUISE GIRARD. Can. J. Chem. 64, 1897 (1986) Des complexes de platine(ii), ~is-[pt(l)~x~l ou L = tctramcthylenesulfoxyde (TMSO), CthylmCthylsulfoxyde (EMSO), di-n-propylsulfoxyde (DPSO), benzylmcthylsulfoxyde (BMSO) et dibenzylsulfoxyde (DBSO) et X = C1- et 1.- ont CtC synthctiscs. La reaction de ces composcs avec un sel d'argent a CtC CtudiCe en solution aqueuse. Des monomeres de types ci~-[pt(l)~(clo~)~l = TMSO, EMS0 et DBSO), C~S-[P~(EMSO)~(SO~)] ainsi que des oligomkres A ponts hydroxo ont CtC isolcs. Les dimeres ~is-[pt(l)~(0h)]~(n0~)~ = TMSO, DPSO) et ci~-[pt(ems0)~(0h)1~~ et possiblement un trimere (c~s-[p~(emso)~(oh)]~)~(so~)~ ont CtC caractcriscs. Les complexes ont CtC Ctudies par spectroscopie infrarouge et par rmn protonique. Introduction Pt-C1 vibrations. Since some of the ligands (L) absorb in this Sulfoxide ligands have two potential donor sites but the region the corresponding iodo compounds were synthesized to preference of Pt(I1) for the sulfur donor site is well known and confirm the v(pt-c1) assignments. Compounds with ethylall reported neutral complexes are exclusively sulfur bonded in methylsulfoxide (EMSO) were also synthesized since cisthe solid state (1). Platinum, being a soft metal, does not form [Pt(EMS0)2C12] has not yet been reported. strong bonds with oxygen unless it is deprotonated or partly These compounds were well characterized since they were ionized as in DMF. the starting material for a study of their reactions with a silver When K2PtC14 reacts with a sulfoxide ligand (L), trans- salt to prepare oligomeric species. Dimeric species of DMSO [Pt(L)2C12] is probably first formed and is eventually isomer- has been recently synthesized (4). The crystal structure of a ized to the cis configuration (2). There are three factors affecting hydroxo-bridged platinum compounds [(DMS0)2Pt(OH)2Ptthe formation and the stability of the two isomers. First, the (DMS0)2](C104)2, isolated from an aqueous solution of trans effect of sulfoxide ligands is fairly large. Therefore the ~is-[pt(dms0)~](c10~)~ (two 0-bonded and two S-bonded trans isomer should be first formed. The second factor is the DMSO (1)) was recently reported (4). However, this method enhanced (d-d)n bonding which is more effective in the cis was found to be inadequate for the synthesis of dimers with geometry (1) and finally the steric hindrance between two large other sulfoxides. We have developed a new method involving ligands in cis position. In the Pd(1I) complexes, the enhanced the precipitation of the chloride ligands of ~is-[pt(l)~cl~] with a (d-d)n bonding in the cis geometry is probably not sufficient to silver salt. The method is similar to the one used to prepare overcome the interligand repulsions which are larger in the cis amine hydroxo-bridged oligomers (5, 6). Usually, sulfoxide configuration, and all the compounds have the trans structure. and amine platinum complexes behave quite differently. But we In the corresponding Pt(I1) complexes (d-d)n bonding is found that in this case, reactions were very similar. This study of apparently more effective and cis structures are obtained for all the reactions of ~is-[pt(l)~x~l (X = C1 or I -) with several the complexes except with a very sterically demanding ligand silver salts is described below. like diisoamylsulfoxide (1). Experimental The synthesis of ~is-[pt(l)~cl~] where L = tetramethyl- Elemental analyses were done by Galbraith Inc. The infrared spectra enesulfoxide (TMSO), di-n-propylsulfoxide (DPSO), benzylwere measured as Nujol mulls on a P.E. 621 spectrometer. A 60 MHz methylsulfoxide (BMSO), and dibenzylsulfoxide (DBSO) has Varian EM 360C was used to record the 'H nmr spectra. The reactions been reported (1, 3). But we have found that the published with silver salts were done in the dark. Special care was taken with method does not produce isomerically pure compounds espe- silver perchlorate, since it is explosive when mixed with combustible cially for bulky groups like DPSO, BMSO, and DBSO. For material. However, it was not considered a potential hazard when used example, the aqueous reaction between K2PtC1, with DPSO in the following experiments. will produce in the first 10 min yellow insoluble transcis -[Pt(EMS0J2Cl2] [Pt(DPSO)2C12] which has to be filtered out in order to obtain An aqueous solution (volume 15 rnl) containing 3 mmol of purified isomerically pure, very pale yellow coloured ~~s-[pc(dpso)~c~~]. K2PtC14 and 9 mmol EMS0 was stirred overnight. The white The formation of ~~~~S-[P~(DPSO)~CI,] in the few first minutes precipitate was filtered, washed with water, ethanol, and ether, and has already been observed (2). We have therefore modified then dried. The yield can be increased by concentrating the filtrate to the published methods in order to obtain pure ~is-[pt(l)~cl~]. 10 ml and letting the solution stand at room temperature. After a few Cis and trans-compounds can be identified by their stretching days, the crystals were filtered, washed with water, ethanol, ether, and then dried. Total yield: 67%, mp 126 C. Anal. calcd.: C 16.00, H 3.58; '~evision received May 6, found: C 16.26, H 3.83.

2 1898 CAN. J CHEM. \ C~S-[P~(DPSO)~C/~] A 40 ml aqueous solution containing 2 mmol of K2PtC14 and 4.4 rnmol DPSO was stirred for 15 min. The mixture was filtered and the filtrate was stirred overnight at room temperature. The very pale yellow precipitate was filtered, washed with hot water, ethanol, and ether, and then dried. Yield: 70%, mp 105 C. Anal. calcd.: C 26.97, H 5.28; found: C 27.07, H C~S-[P~(TMSO)~CG] An aqueous solution (15 ml) containing 3 mmol of purified K2PtC14 and 6.6 mmol TMSO was stirred at room temperature for I8 h. The white precipitate was filtered, washed with a great quantity of hot water, and dried. Yield: 90%, mp 194 C. Anal, calcd.: C 20.26, H 3.40; found: C 20.33, H cis -[Pt(BMS0J2C12] Method 1: BMSO (6 mmol, finely powdered) were added to an aqueous solution containing 3 mmol of K2PtC14. The mixture was stirred at room temperature for 48 h and then filtered. The precipitate was washed with hot water, ethanol, and ether, and then dried. The yellow compound was dissolved in DMF and stirred for 3-4 days. The DMF was then evaporated, and the residue dissolved in acetone. Ether was added to the solution and the pale yellow precipitate filtered and dried. Yield: 6796, mp 140 C (lit. (3) C). Anal. calcd.: C 33.45, H 3.51; found: C 33.41, H Method2 : BMSO (6 mmol) and K2PtC14 (3 mmol) were dissolved in 40 ml of DMF. The mixture was stirred for 3 days and heated at 70 C for 5 h each day. The DMF was evaporated at reduced pressure at 40 C. The product was washed withether, ethanol, and water, and then dried. Yield: 60%. cis-[pt(dbs0)2c12] This compound was prepared by the methods described for cis- [Pt(BMS0)2C12]. Yield: 70% (method l), mp 141 C (lit. (3) 142 C). Anal. calcd.: C 46.28, H 3.88, C1 9.76; found: C 45.92, H 3.86, C cis-[pt(lj212] L = TMSO, EMSO, DBSO KI (4 mmol) was added to 1 mmol of K2PtC14 dissolved in 15 ml H20. After stirring for 4 min, 2 mmol of L were added and the mixture was stirred in the dark for 24 h. The compound was filtered, washed with hot water, ethanol, ether, and then dried. Yield: -80%. Anal. calcd. for ~is-[pt(ems0)~1~]: C 11.38, H 2.55; found: C 11.26, H C~S-[P~(EMSO)~(C~O~)~].~H~O ~is-[pt(ems0)~cl~l (1.325 mmol) and AgC104 (2.650 mmol) were mixed together in 15 ml H20. After 24 h of stirring, AgCl was filtered out. The ph of the filtrate which was about 1.5 was raised to 6.5 with NaOH. The solution was concentrated avoiding precipitation of the products. The solution was then passed through "Sephadex G-25" in order to eliminate NaClO4. The solution was then evaporated to dryness and the product dissolved in acetone. Ether was then added to precipitate the compound which was filtered and dried to yield a white hygroscopic compound. Yield: 30%, mp 160 C. Anal. calcd.: C 11.73, H 3.26, S 10.42; found: C 11.56, H 2.92, S ~is-[pt(tms0)~(cl0~)~]. H20 ci~-[pt(tms0)~cl~l (0.752 mmol) and AgC104 (1.504 mmol) were stirred together in water for 24 h and then filtered to remove AgC1. The filtrate was neutralized with KOH and evaporated to dryness. The residue was dissolved in acetone and filtered to remove KC104. The acetone filtrate was evaporated to dryness, washed with ether, and dried. A pale yellow hygroscopic compound was obtained. Yield: 3096, mp 100 C. Anal. calcd.: C 15.05, H 3.13, S 10.03; found: C 15.46, H 2.77, S ci~-[pt(bms0)~(cl0~)~] ci~-[pt(bms0)~1~] (0.263 mmol) and AgC104 (0.526 mmol) were mixed together in a H20-ethanol mixture. After stirring for 4 days, ethanol was evaporated and AgI filtered out. The filtrate was concentrated and refrigerated. The white precipitate was filtered, washed with very cold water, and dried. Yield: 30%, mp C. Anal.calcd.:C27.35,H2.85,S9.12;found:C27.62,H2.89,S8.76. C~S-[P~(EMSO)~SO~] ~is-[pt(ems0)~cl~l (1.870 mmol) and Ag2S04 (1.870 mmol) were mixed together in 15 rnl H20. The mixture was stirred overnight and filtered to remove AgCl. Ethanol (5 ml) was added to the filtrate which was then evaporated to dryness. The white product was washed with ethanol, ether, and dried. Yield: 90%, mp 125 C. C~~-[(TMSO),P~(OH}~P~(TMSO)~] (NO3 J2 ci~-[pt(tms0)~cl~l (3 mmol) was suspended in 20 ml of water. Slightly less than 6 mmol of AgN03 dissolved in water were added to the above suspension and the mixture was stirred in the dark for 24 h. The precipitate (AgCl) was filtered and the excess AgN03 (if present) was precipitated with 0.5 M NaCl. The ph of the filtrate (about 1.5) was increased to 6.5 with a 1 M NaOH. The solution was maintained at 40 C for a few days until crystallization occurred. Very pale yellow crystals were obtained upon filtration. Yield: 30%, mp 170 C. Anal. calcd.: C 19.92, H 3.55, , N 2.90; found: C 19.87, H 3.72, , N C~S-[(DPSO)~P~(OH)~P~(DPSO)~/ (N03j2 The above method was used. The mixture was stirred in the dark for 48 h (instead of 24h). Yield: 83%, mp 145 C. Anal, calcd.: C 26.56, H5.39, ;found: C26.24, H5.17, C~S-[(EMSO)~P~(OH)~P~(EMSO)~]SO~ aizd(ci~-[pt(ems0)~(oh)]~ 12- (S04)3 ~is-[pt(ems0)~c1~1 (4 mmol) was mixed with slightly less than 4 mmol of Ag2S04 in 15 ml H20. The mixture was stirred for 24 h and the AgCl formed was then filtered. The ph of the solution (1.4) was raised to 6.5 with Ba(OH)2. The mixture was stirred at room temperature overnight. (Heating at 40 C overnight will increase the proportion of the trimer.) The precipitate (BaS04) was then filtered and the filtrate evaporated to dryness under vacuum at 40 C. About 5-10 ml of absolute ethanol were added to the dry product to dissolve the yellow trimer. The white dimer, insoluble in ethanol, was filtered and dried. Yield: 33%, mp 115 C. The ethanol filtrate was evaporated to dryness. Ether was added to the product which was filtered and dried. The yellow compound is believed to be a trimer. Yield: 32%, mp 195 C (dec.). The yield of the dimer can be increase by reducing the heating to a minimum throughout the preparation procedure while the yield of the trimer can be increased by heating the aqueous mixture for several hours at 40 C. Anal. calcd. for [(EMSO)zPt(OH)2Pt(EMS0)JS04: C 16.22, H3.85, ;found: C 15.48, H4.17, Anal. calcd. for ([Pt(EMS0)20H]3)2(S04)3: C 16.22, H 3.85, S 18.04; found: C 15.70, H 3.74, S Results and discussion Complexes cis -[Pt(L)2X2] Five complexes of this type were synthesized. Four of these compounds (L = TMSO, DPSO (I), BMSO, and DBSO (3)) have been reported as yellow crystals. We have modified the method used by these authors and we have isolated pure cis compounds which are white or very pale yellow in coiour. The yellow compounds are believed to be the trans complexes which are formed at the beginning of the reaction. If the trans compounds stay in solution, they will isomerize to give the thermodynamically more stable cis species. If they precipitate, a mixture of cis and trans compounds will be obtained. To obtain pure cis-compounds, the reaction can be done in a solvent like DMF (BMSO and DBSO) or the first formed trans compounds can be filtered out. We were able to isolate pure tran~-[?t(bmso)~gl~] which is yellow. The infrared spectrum showed one v(pt-cl) at 349 cm- '. All cis compounds showed two v(?t-c1) vibrations (Table 1). All ~is-[pt(l)~cl~] compounds showed a v(s-0) vibration

3 ROCHON ET AL TABLE 1. Main infrared bands of the [Pt(L)2X2] complexes (cm-') Compound v(s-0) v(pt-cl) Other bands ( cm') TMSO 1020s 326m ci~-[pt(tms0)~cl~l 1150s, 1134s, 1119s 336s, 320s 515m, 368s, 335sh ~is-[pt(tms0)~1~] 1135s, 1125s 368m EMS0 1048s, 1015s 395w, 372w, 347w. 310w ci~-[pt(ems0)~cl s, 1121s 339s, 317s 439s, 418s DPSO 1010s 450w, 395w ~is-[pt(dps0)~cl~l 1120s 349m, 324m 510s, 456m, 440s BMSO 1038s 464m. 394m, 335m ~is-[pt(bms0)~cl~l 1116s 331s, 311m 477s. 440s, 381m, 364m ~is-[pt(bms0)~1~] 1115s 478s, 419m, 388m tran~-[pt(bms0)~cl~] 1110s 349s 480s, 430s, 383m, 370w DBSO 1015s 460s. 366m, 327m ~is-[pt(dbs0)~cl~l 1125s 328m, 311m 480s, 476s, 419m, 41 lm, 394w c~s-[pt(dbs0)~1~] 1100s 476s, 410m, 405m, 353w at a frequency higher than that in the free ligand, confirming that the binding site is the sulfur atom (3) (Table 1). The infrared spectra of the iodo compounds confirmed the v(pt-cl) assignments since some of the ligands absorb in that region. A crystal structure determination of cis-[pt(tmso),cl,] (7) DMSO ~is-[pt(dms0)~cl~l + 2AgC104 A ~is-[pt(dms0)~](c10~)~ + 2AgC1 DMSO was used as solvent and as ligand. We have tried this method with other sulfoxides (L) using DMF as solvent. But we have found the method inadequate. We have then tried the reaction in aqueous medium. Compounds of the type [Pt(L)2(C104)2] were isolated (L = EMSO, TMSO, and BMSO). H7O ci~-[pt(l)~cl~] + 2AgC104 A ~is-[pt(l)~(c10,),] + 2AgC1 The results of the elemental analyses showed that some of the compounds were hydrated even after drying under vacuum (see Experimental section). The coordination of the perchlorate ion to the platinum atom in the solid state can be determined by infrared spectroscopy. Group theory predicts one large band v3(cl-0) in the region cm-' for ionic C104- (T,) and two bands for coordinated monodentate C104 (C3L)(9). ~is-[pt(dms0)~(0h)]~(c10~)~ showed one v3 at 1076 cmpl while [Pt(BMS0)2(C104)2] showed two bands at 1130 and 1094 cm-'. The infrared spectra of [Pt(TMS0)2(C104)21.2H20 and [Pt(EMSO)2(C104)2].H20 showed the presence of water. Conductivity measurements of ci~-[pt(ems0)~(cl0~)~].2h20 showed that the compound is hydrolyzed in aqueous solution. The value found immediately after dissolving the compound in water was 182 and 229 cm2 mol-' after 24 h, indicating the presence of close to three ions (10). The different hydrolysed species could be cis-[pt(ems0)2(h20)21(c104)2, [Pt(EMSO)2(H2O)(OH)](ClB4), and possibly some dimeric species C~S-[P~(EMSO)~(OH)]~(C~O~)~. Perchlorate in aqueous solution does not coordinate to platinum as shown by 195~t nmr (11). Attempts to isolate oligomeric species by neutralizing the and ~is-[pt(dps0)~cl~] (8) confirmed the configuration of the complexes and the binding site of the ligands. Reactions of cis-[pt(lj2c12] with AgC104 Rochon, Kong, and Melanson (4) have synthesized a DMSO dimer by the following method: H204 [(DMSO)2Pt(OH)2Pt(DMSO)2] (C1O4)2 reszlting aqueous solution of ~is-[pt(l)~(c10~),] were not successful. Reactions with AgN03 The reactions between cis-[pt(l),c12], (where L = TMSO and DPSO) and AgN03 produced dimeric species [Pt(L)2- (OH)]2(N03)2. Nitrate dimers seem easier to crystallize than perchlorate dimers. The synthetic method is shown in Fig. 1. The reaction is slower for L = DPSO but the yield is higher (80% and 35% for L = TMSO). The quantity of AgN03 is critical since an excess will decompose the complexes. The mixture of cis-[pt(l),cl,] and AgN03 in water is stirred for 24 h (48 h for DPSO) in the dark before filtering the AgC1. The ph is then about 1.5. NaOH (1 M) is added until the ph is 6.5 to increase the proportion of monoaquo-monohydroxo species in order to favor dimerisation. The solution is kept at 40 C for 3-4 days and crystallization occurs. The method of separation is based on solubility differences of the species in solution. The dimer crystallizes first, but it is quite soluble in water. The dimer containing DPSO is less soluble and is therefore easier to separate than the TMSO analogue. A series of forced crystallizations can increase the yield of the TMSB dimer. During this process, a very pale yellow compound is first obtained. Later, a darker compound believed to be a trimer can be isolated. The crystal structure analysis of c~s-[p~(tmso),oh~~(no~)~ has confirmed the structure (12). The cation contains a centre of symmetry. The molar conductivities were measured in aqueous solutions. The results showed the presence of three ionic species. The experimental values were 238 Q- ' cm2 for C~S-[P~(TMSO)~OH]~(NO,) and 236 a-' cm2 for ~is-[pt(dps0)~0hl~(n0~)~.

4 1900 CAN. J. CHEM. VOL 64, 1986 The nitrate salt of the EMS0 dimer could not be isolated. expected dimer. About half of the sulfoxide molecules were This compound is very soluble and could not be separated from found free after the reaction. The ph of the solution after the NaN03 produced upon neutralisation with NaOH. reaction was acidic indicating the presence of deprotonated Thereactions of ci~-[pt(bms0)~c1~1 and ~is-[pt(dbs0)~cl~l hydroxo species. The product is very soluble in acidic media with AgN03 are very different probably for steric reasons. The but precipitates when the solution is neutralized. Therefore the reaction is very slow (= 1 week) and must be initiated by complex is probably ionic in acidic media but neutral at ph > 7. heating. The product of the reaction is also different from the The preliminary results seem to suggest the following reactions: ci~-[pt(bms0)~c1~1 + 2AgN03 H20 BMSO\ /OH\ /H20 7OoC, 7 days H20/Pt\OH/Pt\BMS0 (N03-)2 + 2BMSO + 2AgCI J. The infrared spectrum of the neutral compound showed the Reactions with Ag2S04 presence of 0-H vibrations but no ionic or coordinated NO3-. The method developed to synthesize the EMS0 dimer Several attempts to synthesize dimers C~S-[P~(BMSO)~(OH)]~~+ involve the following reactions: were not successful. The close proximity of two very bulky - sulfoxide ligands which contain phenyl groups situated above -2AgC1 and below the platinum plane, might prevent the expected ci~-[pt(ems0)~cl~l + Ag2S04 hydrolyzed species dimerisation. The platinum atom will prefer to lose a sulfoxide H2O i ligand to reduce the steric hindrance and dimerisation can then Ba(OH12 ph = 6.5 occur. The complex ~is-[lpt(dbs0)~cl~], which is even more sulfate oligomer + BaS04 4 bulky, will react similarly with AgN03, but slower. 3-4 days 6.5 FIG. 1. Synthetic method for hydroxy-bridged dimers. The complex ~is-[pt(ems0)~cl~l reacts in water with Ag2S04. After 24 h, AgCl is filtered out. The ph of the solution is 1.4 and is raised to 6.5 with Ba(OH)2. The next day, the barium sulfate is filtered out. The filtrate contains the hydroxo dimer and probably some trimeric species. If it is desired to increase the proportion of the trimer, the mixture can be heated at 40 C for several hours before filtering the BaS04. The dimer and the trimer can be separated with ethanol. The white dimer is insoluble in ethanol while the trimer is soluble. After evaporating the ethanol, the trimer can be recovered with ether. This complex is dark yellow. The dimer can be obtained pure, while the trimer is more difficult to purify. Both compounds are very soluble in water and are difficult to recrystallize. The results of the element analyses of the two compounds are shown in the Experimental section. The trimer might contain some higher oligomers. Conductance measurements do not give any informations on the different oligomeric species for this type of compounds. The molar conductivities depend on the molecular weights which change with the different oligomers. The dimeric species were confirmed by 195~t nmr which gave a signal at 6 = ppm which is 259 ppm higher (lower field) than c~s-[p~(emso)~(h~o)~] as expected. The trimer showed a weak and broad signal at -2906ppm (13). 'H nrnr and ir spectra The 'H nmr spectra of the oligomeric species were measured in D20. The results are shown in Table 2. The a protons in the complexes have been shifted to lower field by 0.56 to 0.73 ppm

5 ROCHON ET AL TABLE 2. 'H nmr of the oligomers (S(ppm)) Compound TMSO [ (TMSO)2Pt(oH) 12(No3 12 DPSO [(DPS0)2Pt(OH )12(N03)2 EMS0 [(EMSO)2Pt(OH)]2S04 ([(EMso)zPt(oH)13)2(s04)3 [Pt(EMSO)z(SO4)1* *See text. 2.97m 3.65m t 3~ = 8 Hz 3.44m m -3.55m m (wide) (wide) -0.7 FIG. 2. 'H nmr spectra of (a) the dimer [Pt(EMS0)20H]2S04 and (b) the trimer. upon complexation. These values show the great influence of Pt on its environment. This influence is still important on the protons in 6 and even y (DPSO) positions. The smaller influence of Pt on HP of TMSO (A6 = 0.03 ppm) can be explained by the cyclic nature of the ligand, since the protons cannot approach the Pt atom as much as those in aliphatic ligands. The dimer and trimer of EMS0 have similar chemical shifts, but the peaks are much broader for the trimer (Fig. 2). The widening of the peaks can be explained by different conformations of the cation which is stereochemically non-rigid in solution as observed for the ammine trimer [(NH,)~P~(OH) (6). The EMS0 trimer might contain some small quantities of the dimeric compound, The EMS0 complexes contain chiral sulfur centers, so that diastereoisomers may coexist as oberved for cis-[pt- (CH3SOCH2C6N5)2C12] (3) which showed, in chloroform 2.22m 2.25m m 1.02t 3~ = 8 Hz 2.07m ~=8Hz t 3~=8Hz 2.70s 1.47t 3~=8Hz 3.40, ~(195~t-~) = 25 Hz , (wide) 3.43, , ~ = 8 Hz ~('95~t-~) = 26 Hz 1 3 ~ ~ solution, two CH3-S resonances separated by 0.14 ppm. There seem to be two very close CH3-S resonances for the EMS0 dimer and trimer (Fig. 2). The separation between the two peaks is only 0.02 ppm. Therefore, two forms might coexist in aqueous solution. The 195~t-H' satellites of the CH,-S resonances are well defined in the spectrum of the dimeric compound (Fig. 2a). The 195~t-~1 coupling constant is 26 Hz and compares well with the values found in cis- [Pt(DMS0)2C12] (23 Hz), in ~~s-[p~(ch~soch~c~h~)~ (22.5 Hz), and in [Pt(CH3SOCH(CH3)2)2C12](23 Hz) (3). The monomeric compound c~s-[p~(emso)~so~] also contains two chiral centers with the possibility of the coexistence of dl and meso forms. But the nmr spectrum of the compound is consistent with the presence of one form, since a single CH3-S resonance was observed. Only one CH3-S resonance was also observed for c~s-[p~(ch~soch(ch~)~)~c~~] in chloroform solution (3). The 195~t nmr spectrum of c~s-[p~(emso)~so~] showed that the compound is hydrolysed in aqueous solution (13). The two main species are C~S-[P~(EMS~)~(SO~)(H~O)] and c~s-[p~(ems~)~(h~o)~]~+. A small quantity of the dimeric compound was also observed. Infrared spectroscopy is an important method to identify the different synthesized species. Monomers are characterized in the solid state by coordinated NO3- or S042-, while these are ionic in oligomers. Ionic NO3- (D3h) has four vibrational modes, three are ir active, two of which are more intense (9). These were observed at 1360 and -825 cm-' (Table 3) for the TMSO and DPSO dimers. Therefore these two compounds contain ionic nitrate ions. Ionic S042- (Td) has two vibrations active in infrared (v3 and v4) while chelating bidentate sulfate with lower symmetry (C2c) has all degenerated modes separated (9). All the modes are infrared-active. The main bands of the three EMS0 sulfate compounds are listed in Table 3. These results show that the dimer and the trimer contain ionic sulfate ions while the monomer contains coordinated S042-. Three v, and three v4 bands have been identified indicating C2L symmetry for the monomer. The v3 vibrations appear at higher frequencies indicating chelating bidentate S042- rather than a bridged bidentate complex (9). A unidentate S042- (C3L) complex would show two v3 and two v4 vibrations. Therefore

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