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Mass spectrometric investigation of the thermal decomposition of tetrakis(N,N-diethyldithiocarbamato)tin(IV) in vacuum
MXSS SPECTROMEI’RIC IS\‘EsTIGATIOS OF -THE THERM-AL DECO~IPOSITIOS OF TETR_~~S(S~-DIETH~-LDITHIOCARBA!bLXTO)TIS(I\~) IS \7ACL’~-M
ISTRODL-CI’IOS
of a recenrl study [ 11, ii: wzs necm 10 co_spare the behaviox tci~~(S~~ie~vldifhiocub~at~~~i~(I~?! [Sn(Er,dr~)~] with rhar of bk(S,S~e~?;ldithio~hamato)rin(II) [Sn(Et=dtc)=J. (Sore that hers (Er,&c) represents (C+H,),SCs in any of its resonance forms.) One of the mass spectrometric techniques used is known in our laborarory as Programmed Probe _Analysk (PP_.) [2]. Similar techniques have been used by Risby and Yergey [3] and Price et al_ [4]. During the course of the earEer work, it becztze clear that. the behaviour of Sn(Et=dtc),, when esamined by this rtinique, was onl- qualitatively reproducible ar?d was subject 10 apparently random effects, the cause of which was not Bnoxn at. thar time. Furthermore, the PPA profile was inconsistent with our prc\~ously proposed mechanism for the thermal decomposition of Sn(Et=dtc); [5,6] and it revealed the previously unsuspected presence of an involatile ~ktcrmediate di-;l+ulphidobis[ bk(X,Xdiethgldithiocarbamato)tin(IV)] [S,Sn,(Er,dtc)4] [7] _ Beca~e of this new evidence we have proposed a re\ised mechanism. Ke have also studied the random effects and have attempted to esplain their cause in *he light of the new mechanism. The experiments are not described in chronoIn
36
logical order sequence.
but an attempt has been made to present the results in a logical
ESPZRDIEST_AL
_\!ass specxomexic ar.aIysts, including PP..., were carried out using tI;e d:kect inssrrion probe of a JELL JMS D-100 mass spectrometer, fitted with a combined electron impact;‘chemical ionkxion (EI!CIj source_ In CI, methane 1t-s used as the reagent gas. _A full description of the PPA technique has been given previous!>- [2]_ _A linear heating rate of 12_3’C,‘min was us-cd in 2U esperimenrs. Sn!Etldrc)z and SniErIdtc)G were zynthesised by the procedures describe2 nre\- [ 1.51. The ample of Sn(Er:d:c), obtained consisti of microscopic Cll;Sh!S_ To obtain macro-crys:aLhne sarn_cles, Sn(Et2dtc]; was recrysiilked from boiling acetone_ The sfacdard compound, ieiraeihylthiur-zm dkulphfde (TETD! was prepared b:- the reaction given br \-on Braun [S]. Tetnethyl‘;hluram monosulphide (TETM) wx prepared from TET’D by the reaction .TETD + CS- - TETX + SCX- [9 ]_
RESL-LTS
XSD
DISCUSSIOS
In order IO minimke confusion, a flow diagram of the pro_po:;ed decomposition schzne of Sr~(Er~d!c)~ in vacuum is presented (Fig. 1 j without justi-
z-2
.
_c _
Fig_ I. ‘Tke_zzs! c!eco_mpos~-; .-_on scheme for !kiE:=dzc); in xxucm. < 1) Primu?; decompcv sirion jllW24O=C)_ (2) Recombination at low iemper;irures (ZO-_12O=C)_ (3) Deco-mixsi:Ior. iabove iZO=C) TETD - TETl! + { &_ (4:) Rezciioxz ; S, + 9 s1( Erldrcjl - sSs:(Ezzdtc);, highly Giicient eren at iOO’C_ (5) Decom_xsitioG (260-3PO=Cj_
fication at this stage. In the figure, arrows with the leners MS denorc that, under PPX conditions, the subskznce is 21 least priiall_v vohtiie and a mass spectrum was obtained. Other abbreviations are those rlready used In r:he text. Typical PPA profile appropriare to &is decomposidon _sshe_meare given in Figs. 2 and 3. The fusr. peak (ca. 1iO-24O’Cj ik formed by ioz ?rom Sn(Ertdtc)z, TETD and TElX and encompses tie produc:lon of rhese compounds and the involatile S_Snz(Et=dtc)+ The second peali is fanned by- ions from Sn(Et_d*~)~ and &, the decomposirion products of ~Sn~(Er,d~c~~,_ The decomposition will be discussed in detail later. Jkss speclml considercttins
The characteri-sation of the above compounds is &gel>- based on IheIr EI mass spectra, especially on the idencifka:ion of rhe molsalar Ion. I; i% h-s appropriate at this s+age 10 comment briefl_v on aspwts pf the EI ma spectra of these and sknilar compounds_ In generai, x-hen reporting ;he m~csc spectra of potentially ihermali_v unsxb!e compounds, Ii k Lm-potianr 10 recognke the possibiiity that ptiic-ulu iox may arise from :?xznaI de-cornposition prod~ucts rather than from frue mass spexral frqmz=~zrion_ Th;% or example the pence of ink-zst peaY?k F f2c: i?2s oficn been over!ooked_ at miz ‘i6 (CSJ in the massspectra of_meraJ dkhlocarbzmares and ~~12~6 co=pounds, =peciaUy if the mokcular ion is absent or weak, is hIg;?!~- s-xgexiv2 thai thermal decomposition has occurred. In one ae 2: leas:, x-e hzw es-eined compounds whose spectra were repor;& 10 conxk 2 12rgc p22.X 2: .x_‘z 'i6 [lo], u&g conditions less likely to ca-tic thermal de.~darI-an and fonnd rke FLTI~T~rhat in all caseq the peak at m_:z 76 was v2_9- _zzil_ CrSomxzrel_v Cons of our apparatlxs a% thar rime prevented us from esa.crl_v duplica:kg the ri37ew 01 reporkd esperimenrs. Anile we have not czried out 2n esfi2ucx-e rhe liier;r,Ume conce_rning ihese compounds, we are ax-are of a zxxmber of p2pers in which we believe the reposed mass specxa indicate :ht_mxl
3s
decomposition.
However it is not appropriate
paperIn the studies reported
to discuss rhse
here, ihe peak ai. m/z ‘i6 in the rns
resuis
in this
spectrrlm of
Sn(Et,dtc), is of low abundance 2nd supports the suggestion that the mm spectrum of the complex has been obtained, although the molecukr ion 3% absent. The peaks obsen-& in the spectrum %xn easily be rationaked in terms of the known struc:ure of the complex However, as will be discussed, rhe obserr-eci spectrum is thaf of a misture of the decomposition products of Sa(EiZdtc)4, i.e. Sn(Et2dtc)2, TETM and ‘TETD. Cl ma_= spectra can be *useful when the presence of thermal li-agments -k suspkxtcd. For esa-mple, in recent studies of metal dishiocazbz?ales in which 2-hydrox>-!eth-1 groups zre slubstituted on rhe nitrogen atom [ 111, compkte thermal decomposition is observed wder PPA conditions. -This resuks in a whereas CI produces simpler specira in \-e&q-complex EI rnzss qectrum. which molecular ions of decomposition products can be disti?gG%hed. In the yit.;en! stud_\-. the lack of a _molecular ion in ihe CI -mass spectrum of EniEr-dk), buggests rhsr complete decomposiGon OCCUS. However, under rhc &ndfrions of the= esperimenis and in contrast to the 2-h\_-drosyIethy!~~bnirured dirhiocarbxnates above, the decomposition products appear to xr?dergo Ion-mo!ecule reacfiorx other thar! those expected from reaciiors with rhe reagefii gas. For example, ai low sznp!e PreszJreS, a molecukr ion is obsex& for TETJI brrr as the deco_mpcsit!on proceeds ad the sarr?p!e pre=-llre kcrsses. this Ion k in compeclrion wirh [SI + HI* ad [>I + llS]* lo?-_;.the !siter pre,cuzxb!y derived from the rescrion TETJI’- + TE’TM 131 i ‘1161‘ + (Er,dtc)-_
:
.
1 -. i
_-. ._---
:
Fig. 5. Fig_ G_
Ectmnco~sp~;cnomena
re!c!ed
to IliejCksf
PP_4 peck
__..----
1-i
reached its masimum. Tne phenomenon has been observed frequently, ROL only in this study and for a variety of compounds. It is most noticeable in highly crystal!ine samp!ts. Single ion monitoring (SIN) in which rhe mass spectrometer is adjusted to monitor one ion peak continuoud?;, reveals that in the exe of cobalt(II1) diKhiocarbzmates recrystallised from chloroform., ihe spikes were caused by- the e\-olution of chIoroform occiuded in rhe cn-stals [ 131. However, in the current studies, SIM revealed thzt the spikes are sudden pulses of volatE!;ked decomposition products. Samples rhat are known to melt before significant volatilisaiion, e.g. Sn(Ei:dic),, do not eshibir rhis behar-iour. N-e believe that. in the latter c2se, the spikes may occur where decomposition 2nd vol2ti!issrion of rhe products takes place within a solid matris 2nd rhsi high inremal pressures may be generated which evenrually lead to the rupture of rhe marris wirh the relexe of 2 pulse of gas. The problelm is markedly reduced w-her! crysralline samples are ground to a fine powder. EXtt.cnt~orls ~OTLS _-I second problem encountered during these analyss w-as the apparentl_v rr?ndom appearance of ions of metal diihiocarbamates which were not necessxi!>- related to ihe anal\-& in hand. The>- do not app22r in a PPA e.xperimen! wi-irhan empty probe nor are they p2rt of the machine background. Their cause N-E ewnically rrxed io metal-metal eschange reaciiors in\-o!ving mesa! dithiocaroamate comp!exes or fo che1aiir.g rezctions of rhiu_r;lm dikulphides wirh residues of precous s2rnples. For example, if 2 sample of TETD or Sg(E$dtc)z k analysed immediaiely after any rkkelare observed. Tnese re2cconi~.inir,g co,crp!ex, brezse ions of Si(Et=dicl: of the ior? IiOns zre ciearlv. simikr to the reeciiom with ihe meti pm source observed by Terlouw 2nd De Ridder [14] 2nd Giver! et al. [IS]. I= he general case, the possibility aJ.s o exists that with polar lhtermed&es, some reactions may occur with active sites 2s reported by Kegm2.w [IS]. III our xork, these effects were minim&xl by 2llowiEg TETD to flow into the ion source until the estrarreous ions were reduced to an 2cceprab!e level azd by using relatively kge _samp!es (It--SO pg). &king the source also reduces these effects. Lcc.6 ofrcprodrrcibil’it~ nf the first PP_4 _zak The mosi disturbing phenomenon was a lack of reproducibility of the profile of rhe first peak. _A repmducible PP_A profile, especi2&- if supported! 1 thermo_m\imetric (TG) and differential thermal 2zxzlys~k by mass specrra_, iDT.4) r-&s, indicates rha: rhe same compound is bekg anzlysed. In the analysis of Sn(Ei=drcj;, a freh sample, prepared by a preriou_Fly published method [5]. gave a FP_A proftie similar to ihat shown in Fig. S. The sample consisted of a very fiie precipitate filtered from zcetone 2nd N-2shed. Esaminacfon of rhe m-a spectra obtained during ihis PPA peak showed all three intermediate, Sn(Etzdtc)z, TETD and TETM. L-sing the abundulces of the molecular ions as a measure of relative propotions, the latter compounds were present in appro.simaiely equal zmounti. \ken the Same sample was crystalked from acetone, well-shaped relaiivelr large crystals were obtained. The PPA profde of this sample ~2s
4! s i m i l a r t o t h a t s h o w n i n F i g . ,3 a n d t h e m a s ~ s p e c t r a l e v - d e n c e i n d ~ _ c a t e d ~ h a z TETM was produced in much greater quant:..ty. "Ihese resui~ sugges-:c-d zhaz the two samples were different. Repeated .~v,~,~'e¢is._... _ f r o m o t h e r _-~,~,--~-~'~-~..~. (chloroforrn, cyclohexane, ethanol a n d w a t e r D s" o w e d [ h a : -,he r e s u k s o b tained from PPA analyses were not reproducible, f_,,-es'.'n s a m o l e s , tend;-n~.~ ~ o ~ v e . D r o f f l e s s i m i l a r t o t h a ~ s h o w n i n F i g . "~'_,recr-,-s~a!Hsed_ s a m o l e s _ ~ e n.d.. ;. '. ~ ~ -:o be similar to Fig. 3, with TET.M dominam. The r a n g e o f va.,q.a~:on o b s e _ , - v e d for the proportion o f T K T D t o T E T M w a s 2 : 1 ,.o 1 - 1 0 . The crucial experiment was the PPA an~vsis o f a cr:,_-s~a!Hne ~ , v ~ p l e
.~'ound to a fine p o w d e r . "Fne T E T D ~o T E T . M ra~io ;.ncreased fro.'-n i - ! 0 *.o ! " 2 a n d increases of this order w e r e n o t e d for oiher p o w d e r e d c.,-,-st.-q-ne smn~.pl~. It lhus appears [hal the lack of reproducib:,l, ily :-sre'-a:ed -'.opanicle size. -l-ne e x p e r i m e n t s described a b o v e w e r e e a r n e d out w-.:h ---a m D .~ _:~" - Of -... ~e order of 3 0 ~ug for p o w d e r s a n d o n e small crys.:al for c~'stai-iine ma-:efi~ ~approx. 5 0 ~g). %%-non sa_rnples larger lhan I 0 0 :.~g w e r e u ~ d . ihe P P A profiles w e r e only qualitatively s~.milar to [hose obse,'x'ed for _ ~ m ~ ! s.--~Dle_< a n d n o p a t t e m could be di~ce_,-n_ed to a c c o u n t for the change. Th~_s w a s ~ s o true for the m a s s specir?l results, -,:h~.ch frequen:!y ind'[cated .he presence of t w o m a x ; . m a in the d e c o m p o s i t i o n Droduc-:s. R e , e a r e d analyses of d:.,fferen -: quant;n-es of the _
reacrion is be!iewd \.ei:h ei. al. [ 121.
to be quantitative,
a finding consistent with the results of
Tire meckanisn? of tizenr:nI decomposition ?“ne primar\- decomposition of Sn(Erldrc); is iniriated by a reducrfo~ ro Sz(Erzdtc)2 wiih the formation of TETD. Three [17-191 of rhe four pa_pers [ 17--201 in which the reduction of the meral atom of the dirhiocrrba=a:e comples has been reported to occur during t;he primary decomposition. 230 reported the iormation of TETD. Ir? the case of the decomposition of copper dithiocarbamaie compleses [ 30] rhe siruarion is more comples [ 211. The formation of TETD ma- be unimolecu!ar as suggested by HusebJ-e and Sl-neren [ 221 for Te( Et:dtc),. This involves rhe formarion of a bond between the sulphur ato_ms lying cIosest to each other on adjacent ligands. probab!y the monodentare ligands, zs indicated by a CQ-skllographic srud>by Harreld and Schlemper [33] on Sn- the combination of (Et,dtc) radicals. Ho\;-ever. neither rhe reFd!ts reposed here nor those obrainab!e b_v e!ecrron spin resonance spectroscopic (ESR) srudk are !ikely 10 confirm either mechanism, since .TMD is known [ 2-11 to produce several ESR signals above iis melting point. The formarion of S2Sn2(Etzdrc)G involves seveti sreps. The initiation of the rezcrion results from the decomposirion of TETD which espels a srr!phur atom. Ii is likei>. that the su!phur is convened inro allorropes ranging from SI to S,. Cock et ai. [25] have shown rhar S: is rapidly converted into Ss in the gas phase but rhis reaction may be much slower in the decomposition matti. The sulphur alloiropes ma>- react xirh Sn(Er,drc j= in a number However it is possible rhai the of sreps before finall>- forming S,Sn,(Er,dk),. reaction is initiated by the espulsion of aulphur from TETD. effected by a co!Iision with Sny Ec:d:c): since sulphur abstraction from ihiuram disulphides by a reaction with metal compleses is known [26,2i]. Tine species may react fuxher KO produce S2Sn2(Er2drc)G. As a consequence of the decompositicr. of S2Snl(Et2dtc); at temperatures abo\-e 26O’C, the second peak in the PP_\ profile is produced [ 71. -4s prerious!y noted, th2 size of rhis peak relative to the firsi. peak \-aried with the cr)-sral dimensions of the sample. Ofirer
considemfions
.T%e suggestions made in ihis paper are at \.aria.nce with the repon: thar Sn{Et,dtc), sublimes ac 150’ C_~O_l mm Hg [ 281. On heating Sn~Ec~dk)~ apparatus unri! rhe residue (190-zoo= c/o .5 mm Hg) in a sublimation become creamy white, an orangeyellow !iquid and a red solid collect OR :he cold f;mger. The w-hire solid r&due is readily shown to be SISn2!Etzdtc); [ 71. On anal>-sing ihe liquid using PP..., ihe presence of TETN, TETD m_d Sn(Ei,dtc)2 is detected in the remperature rar.ge lOO-165’C. This temperature range, being lower than that iF. which these compounds are evohed during the PPA of Sn(Et,dfc), (17~-24O=C), indicates ihat ihermzl deccmposition occurs during sublimation.
43
The PP..\ analysis of the red solid indicated thzr the szhs*;a?ce is inde2d Sn( Ettdtc)4, which suggests that this compound sublimes, togerher w-irh the more volatile decomposition intermediates. HOW-~\-2rthe ebsencs of 2 molecular ion and, more significantly, of an [M - (Er:drc) j’ ion 1191 in borh the CI and EI rns spectra of Sn(Et=dic), indicate fina:. it is not volatile. ‘Thus it is suggested that the Sn(Etzdic)4 rssulrs from a recombination reaction (shown dotted in Fig. 1) between the primary decomposition inrcrmediates, TETD and Sn(Etzdtc)z and which takes pkce on the cold finger of ihe xublimation apparatus. Under PPX condiiiow this ;vould not. occur. In order ro vetif:- rhlis suggestion, fmdy ground Sn(Etzdfc)z and TETD v..2re mised and heated to 110-15O’C for 15 min under nirrog2n. .Tne r-idue was g-round and analysed by PP.% The largesr peaks corrspond ro rhe starting materials and appeared at the especred lower temperatuws. However, in the range ZOO-XO’C, the prof;_le and mass sp2ctn are corktenrwith rhe decomposition of Sn(Etzdrc);. The especfed pezk for SzSnz(Ei,dtc), was much larger than anticipated: not surpriiir&some of :he TETD had decomposed and allowed the Sn(Et=dtc)and Ss r2acfion to occur.
Arhough the thermal decomposition of Sn(Er=dtc); in vacuum has been sho\\n to be relatil-el_v simple. its elucidation is cornpiicat.ed by various phenomena It. is appar2nt that crystal size pla_vs 2 dominant role in the overall decomposition pathway of the complex It is concluded that these phenomena may be obsen-ed in the decomposition of metal complex= generally. In prek
The authors are grateful to Dr. P.J. Derrick for helpful discussions. Acknowledgement is made to the Australian Rsearch Grants Committee for the pro+,ion of the EI[CI source for the JEOL D-100 mass spectrometer. One of us, G.K.B., thanks La Trobe I.kiversit\- for the aw-ud of a Postgraduate Research Scholarship.
REFERESCES G.-K Ra+-spies, J.F. Smith, J-0. Hill and R-J. lkyre, Tke.?r?ochi.~. _XC~J.2: (1975) 307. J.F. Srnirh,b-n. J. 3ti Spectrorn.Ion Pn>--r,36 (197s) 149. TX Risby 2nd AL; Yergey, AnJ. Chea., 50 (191s) 327X. D. Rice, S.S Fate--i, R Nlitcheal, J.H. YLZppia?r. D. Dolhm-ore md _X Sdctlb; in D. F%ice 2nd J.F.J. Tadd (Editors), DyrsznIc 3Lrr Spa=t_ro.xeu\-, \.ol 5. IIeydeq Urdon, 19i’6, Ch. 20.
44 5 G . K . B . ~ t s p : . e s , J . F . S m i t h , J.O. Hill a n d R . J . . M a g e ~ , The..,'m...oc.him. Ac~,a, 19 ( 1 9 T $ ) 561. 6 G . K . B . - - ~ p i e s , J.F.S..~;.th ~nd J.O. Hill, T:.~e.rrnochiw... A c ~ , 19 ( 1 9 T S ) 5 7 3 - G . K . B . , - a ~ p i e s , J.F. S,~..i-h, J.O. HR| a n d P.J. D e r r ~ k , J. T h e r m ~ Anal., 16 ( 1 9 T 9 ) 3,69. J. yon Braun, Ber.. -~5 ( 1 9 0 2 ) S I T . 9 J.H. K a r c h m e r (EdPor), "Ice .-Ina!.vl;.calC'nemLstry." of Sulfur .~nd its C o m p o u n d a , P - ~ If. Wiley, N e w York, 19:2, Ch. !0.!2. 10 F.I. On,.m -ka and W.R. Boos, A n a l Che.-~..." 5 (1973) 967. 11 S Pr~kas.h, G.K.B.~-'.s-9.ies. J.O. Hill and R.J. Magee. in prep~r~:,on. !"2 .M. Ve~.:h, O. Recktenw-~Id ~nd E. Humpfer. Z. Naturforsch. B, 33 (!97~) ~=' 13 P. Oliver, P h D "l-nesis. I~ Trobe Unive.,'s~_zy,.Melbourne, 1979. 14 J.K. Terlouw and J.J. de Ridder. O r ~ . . M ~ s Spec'.rom., 5 (l-a'E]) 1127. IS K.W. Given. B..M..M-~t~son, G . L .Me"_ss!erand L.H.P.;gno!e~, J. Lnor~. Nucl. Che..-n..39 ~ I g T T ) 1309. 1G A. Ii"e~m-~nn. _AnR!_ Chem.. 50 (19TS) $30. ! T O. Foss..Acta Cne.-n. Sc-~nd., 7 ( 1 9 5 3 ) 2°_6. 1~ D . C . B . ~ d l e v , I.F. Re=dall =Rd K . D . ~ i e s , J. C.hem. Soc. D-~.',oR T~r-S /19T3~ -°225 .~.nd ~ p . 20SOS. 19 A.V. Dubrov:.n, K..M. Du.,-.~cva znd V.L Spi~_s_vP.. R ,i/.ss.J. L~o.--~. Cy',em., 23 ('--97S) !T01. 20 S.V. L~._~.onov. L.A. Kosareva, A . F . _M~.~l-:kova -',.,,-d A . A . Shkly-',ev, R " ~ . J. I~o.~. Chem., 2 2 ( 1 9 T T ) ! 2 9 9 . 21 G.K.B.~_tspies. J.F. ~Lmi~h a n d J.O. Hill. unpub!i_s.hed r e s u ! ~ . 22 S H u s e b y e a n d -~E. t~,'aeren. A c t a C-.~em. ~ n d . , 27 (3973) 7 6 3 . 23 C_S_ Hm~eld a n d E.O_ S c h l e m p e r , A c t a Crys:allogr.. Sec'.. B, 27 ( 1 9 7 ! ) 1 9 6 4 . 24 P. NichoLs aEd _M.W_ G.~-n:, L~ T r o b e URiversit3"..Melbourne, p ~ v a t e co..-rn~unic-~=io=. 2,~ D.L. C o c k e , G. Ahe.-.d a n d d. B l o c k . Adv-~r,.ces in -M~,ss S p e c z r o m e ~ - , V o L T-A. H e y d e c , L o n d o n . 197S. p. 7 0 3 . 26 P.J.H__A__M. van tier L e e m p u t , J. ~l.l,e,.,.se. J . A . C r ~ a n d L. G r o e n , Rec. Troy. C~,',_~-. P~3s-B.zs. 9S { ! 9 7 9 ) 4 1 3 . 2T J..A..McClevcr~y a n d N . J . . M o r r i s o n , J. C h e m . ~oc. D~!.'on Tra.~_s., ( 1 9 T 6 ) 2 1 6 9 . 2S D.C.B.--adley a n d M.H. Gi~l-:z. J. C'r'.em. Soc. _A, ( 1 9 6 9 ) ! I S f i .
ISTRODL-CI’IOS
of a recenrl study [ 11, ii: wzs necm 10 co_spare the behaviox tci~~(S~~ie~vldifhiocub~at~~~i~(I~?! [Sn(Er,dr~)~] with rhar of bk(S,S~e~?;ldithio~hamato)rin(II) [Sn(Et=dtc)=J. (Sore that hers (Er,&c) represents (C+H,),SCs in any of its resonance forms.) One of the mass spectrometric techniques used is known in our laborarory as Programmed Probe _Analysk (PP_.) [2]. Similar techniques have been used by Risby and Yergey [3] and Price et al_ [4]. During the course of the earEer work, it becztze clear that. the behaviour of Sn(Et=dtc),, when esamined by this rtinique, was onl- qualitatively reproducible ar?d was subject 10 apparently random effects, the cause of which was not Bnoxn at. thar time. Furthermore, the PPA profile was inconsistent with our prc\~ously proposed mechanism for the thermal decomposition of Sn(Et=dtc); [5,6] and it revealed the previously unsuspected presence of an involatile ~ktcrmediate di-;l+ulphidobis[ bk(X,Xdiethgldithiocarbamato)tin(IV)] [S,Sn,(Er,dtc)4] [7] _ Beca~e of this new evidence we have proposed a re\ised mechanism. Ke have also studied the random effects and have attempted to esplain their cause in *he light of the new mechanism. The experiments are not described in chronoIn
36
logical order sequence.
but an attempt has been made to present the results in a logical
ESPZRDIEST_AL
_\!ass specxomexic ar.aIysts, including PP..., were carried out using tI;e d:kect inssrrion probe of a JELL JMS D-100 mass spectrometer, fitted with a combined electron impact;‘chemical ionkxion (EI!CIj source_ In CI, methane 1t-s used as the reagent gas. _A full description of the PPA technique has been given previous!>- [2]_ _A linear heating rate of 12_3’C,‘min was us-cd in 2U esperimenrs. Sn!Etldrc)z and SniErIdtc)G were zynthesised by the procedures describe2 nre\
RESL-LTS
XSD
DISCUSSIOS
In order IO minimke confusion, a flow diagram of the pro_po:;ed decomposition schzne of Sr~(Er~d!c)~ in vacuum is presented (Fig. 1 j without justi-
z-2
.
_c _
Fig_ I. ‘Tke_zzs! c!eco_mpos~-; .-_on scheme for !kiE:=dzc); in xxucm. < 1) Primu?; decompcv sirion jllW24O=C)_ (2) Recombination at low iemper;irures (ZO-_12O=C)_ (3) Deco-mixsi:Ior. iabove iZO=C) TETD - TETl! + { &_ (4:) Rezciioxz ; S, + 9 s1( Erldrcjl - sSs:(Ezzdtc);, highly Giicient eren at iOO’C_ (5) Decom_xsitioG (260-3PO=Cj_
fication at this stage. In the figure, arrows with the leners MS denorc that, under PPX conditions, the subskznce is 21 least priiall_v vohtiie and a mass spectrum was obtained. Other abbreviations are those rlready used In r:he text. Typical PPA profile appropriare to &is decomposidon _sshe_meare given in Figs. 2 and 3. The fusr. peak (ca. 1iO-24O’Cj ik formed by ioz ?rom Sn(Ertdtc)z, TETD and TElX and encompses tie produc:lon of rhese compounds and the involatile S_Snz(Et=dtc)+ The second peali is fanned by- ions from Sn(Et_d*~)~ and &, the decomposirion products of ~Sn~(Er,d~c~~,_ The decomposition will be discussed in detail later. Jkss speclml considercttins
The characteri-sation of the above compounds is &gel>- based on IheIr EI mass spectra, especially on the idencifka:ion of rhe molsalar Ion. I; i% h-s appropriate at this s+age 10 comment briefl_v on aspwts pf the EI ma spectra of these and sknilar compounds_ In generai, x-hen reporting ;he m~csc spectra of potentially ihermali_v unsxb!e compounds, Ii k Lm-potianr 10 recognke the possibiiity that ptiic-ulu iox may arise from :?xznaI de-cornposition prod~ucts rather than from frue mass spexral frqmz=~zrion_ Th;% or example the pence of ink-zst peaY?k F f2c: i?2s oficn been over!ooked_ at miz ‘i6 (CSJ in the massspectra of_meraJ dkhlocarbzmares and ~~12~6 co=pounds, =peciaUy if the mokcular ion is absent or weak, is hIg;?!~- s-xgexiv2 thai thermal decomposition has occurred. In one ae 2: leas:, x-e hzw es-eined compounds whose spectra were repor;& 10 conxk 2 12rgc p22.X 2: .x_‘z 'i6 [lo], u&g conditions less likely to ca-tic thermal de.~darI-an and fonnd rke FLTI~T~rhat in all caseq the peak at m_:z 76 was v2_9- _zzil_ CrSomxzrel_v Cons of our apparatlxs a% thar rime prevented us from esa.crl_v duplica:kg the ri37ew 01 reporkd esperimenrs. Anile we have not czried out 2n esfi2ucx-e rhe liier;r,Ume conce_rning ihese compounds, we are ax-are of a zxxmber of p2pers in which we believe the reposed mass specxa indicate :ht_mxl
3s
decomposition.
However it is not appropriate
paperIn the studies reported
to discuss rhse
here, ihe peak ai. m/z ‘i6 in the rns
resuis
in this
spectrrlm of
Sn(Et,dtc), is of low abundance 2nd supports the suggestion that the mm spectrum of the complex has been obtained, although the molecukr ion 3% absent. The peaks obsen-& in the spectrum %xn easily be rationaked in terms of the known struc:ure of the complex However, as will be discussed, rhe obserr-eci spectrum is thaf of a misture of the decomposition products of Sa(EiZdtc)4, i.e. Sn(Et2dtc)2, TETM and ‘TETD. Cl ma_= spectra can be *useful when the presence of thermal li-agments -k suspkxtcd. For esa-mple, in recent studies of metal dishiocazbz?ales in which 2-hydrox>-!eth-1 groups zre slubstituted on rhe nitrogen atom [ 111, compkte thermal decomposition is observed wder PPA conditions. -This resuks in a whereas CI produces simpler specira in \-e&q-complex EI rnzss qectrum. which molecular ions of decomposition products can be disti?gG%hed. In the yit.;en! stud_\-. the lack of a _molecular ion in ihe CI -mass spectrum of EniEr-dk), buggests rhsr complete decomposiGon OCCUS. However, under rhc &ndfrions of the= esperimenis and in contrast to the 2-h\_-drosyIethy!~~bnirured dirhiocarbxnates above, the decomposition products appear to xr?dergo Ion-mo!ecule reacfiorx other thar! those expected from reaciiors with rhe reagefii gas. For example, ai low sznp!e PreszJreS, a molecukr ion is obsex& for TETJI brrr as the deco_mpcsit!on proceeds ad the sarr?p!e pre=-llre kcrsses. this Ion k in compeclrion wirh [SI + HI* ad [>I + llS]* lo?-_;.the !siter pre,cuzxb!y derived from the rescrion TETJI’- + TE’TM 131 i ‘1161‘ + (Er,dtc)-_
:
.
1 -. i
_-. ._---
:
Fig. 5. Fig_ G_
Ectmnco~sp~;cnomena
re!c!ed
to IliejCksf
PP_4 peck
__..----
1-i
reached its masimum. Tne phenomenon has been observed frequently, ROL only in this study and for a variety of compounds. It is most noticeable in highly crystal!ine samp!ts. Single ion monitoring (SIN) in which rhe mass spectrometer is adjusted to monitor one ion peak continuoud?;, reveals that in the exe of cobalt(II1) diKhiocarbzmates recrystallised from chloroform., ihe spikes were caused by- the e\-olution of chIoroform occiuded in rhe cn-stals [ 131. However, in the current studies, SIM revealed thzt the spikes are sudden pulses of volatE!;ked decomposition products. Samples rhat are known to melt before significant volatilisaiion, e.g. Sn(Ei:dic),, do not eshibir rhis behar-iour. N-e believe that. in the latter c2se, the spikes may occur where decomposition 2nd vol2ti!issrion of rhe products takes place within a solid matris 2nd rhsi high inremal pressures may be generated which evenrually lead to the rupture of rhe marris wirh the relexe of 2 pulse of gas. The problelm is markedly reduced w-her! crysralline samples are ground to a fine powder. EXtt.cnt~orls ~OTLS _-I second problem encountered during these analyss w-as the apparentl_v rr?ndom appearance of ions of metal diihiocarbamates which were not necessxi!>- related to ihe anal\-& in hand. The>- do not app22r in a PPA e.xperimen! wi-irhan empty probe nor are they p2rt of the machine background. Their cause N-E ewnically rrxed io metal-metal eschange reaciiors in\-o!ving mesa! dithiocaroamate comp!exes or fo che1aiir.g rezctions of rhiu_r;lm dikulphides wirh residues of precous s2rnples. For example, if 2 sample of TETD or Sg(E$dtc)z k analysed immediaiely after any rkkelare observed. Tnese re2cconi~.inir,g co,crp!ex, brezse ions of Si(Et=dicl: of the ior? IiOns zre ciearlv. simikr to the reeciiom with ihe meti pm source observed by Terlouw 2nd De Ridder [14] 2nd Giver! et al. [IS]. I= he general case, the possibility aJ.s o exists that with polar lhtermed&es, some reactions may occur with active sites 2s reported by Kegm2.w [IS]. III our xork, these effects were minim&xl by 2llowiEg TETD to flow into the ion source until the estrarreous ions were reduced to an 2cceprab!e level azd by using relatively kge _samp!es (It--SO pg). &king the source also reduces these effects. Lcc.6 ofrcprodrrcibil’it~ nf the first PP_4 _zak The mosi disturbing phenomenon was a lack of reproducibility of the profile of rhe first peak. _A repmducible PP_A profile, especi2&- if supported! 1 thermo_m\imetric (TG) and differential thermal 2zxzlys~k by mass specrra_, iDT.4) r-&s, indicates rha: rhe same compound is bekg anzlysed. In the analysis of Sn(Ei=drcj;, a freh sample, prepared by a preriou_Fly published method [5]. gave a FP_A proftie similar to ihat shown in Fig. S. The sample consisted of a very fiie precipitate filtered from zcetone 2nd N-2shed. Esaminacfon of rhe m-a spectra obtained during ihis PPA peak showed all three intermediate, Sn(Etzdtc)z, TETD and TETM. L-sing the abundulces of the molecular ions as a measure of relative propotions, the latter compounds were present in appro.simaiely equal zmounti. \ken the Same sample was crystalked from acetone, well-shaped relaiivelr large crystals were obtained. The PPA profde of this sample ~2s
4! s i m i l a r t o t h a t s h o w n i n F i g . ,3 a n d t h e m a s ~ s p e c t r a l e v - d e n c e i n d ~ _ c a t e d ~ h a z TETM was produced in much greater quant:..ty. "Ihese resui~ sugges-:c-d zhaz the two samples were different. Repeated .~v,~,~'e¢is._... _ f r o m o t h e r _-~,~,--~-~'~-~..~. (chloroforrn, cyclohexane, ethanol a n d w a t e r D s" o w e d [ h a : -,he r e s u k s o b tained from PPA analyses were not reproducible, f_,,-es'.'n s a m o l e s , tend;-n~.~ ~ o ~ v e . D r o f f l e s s i m i l a r t o t h a ~ s h o w n i n F i g . "~'_,recr-,-s~a!Hsed_ s a m o l e s _ ~ e n.d.. ;. '. ~ ~ -:o be similar to Fig. 3, with TET.M dominam. The r a n g e o f va.,q.a~:on o b s e _ , - v e d for the proportion o f T K T D t o T E T M w a s 2 : 1 ,.o 1 - 1 0 . The crucial experiment was the PPA an~vsis o f a cr:,_-s~a!Hne ~ , v ~ p l e
.~'ound to a fine p o w d e r . "Fne T E T D ~o T E T . M ra~io ;.ncreased fro.'-n i - ! 0 *.o ! " 2 a n d increases of this order w e r e n o t e d for oiher p o w d e r e d c.,-,-st.-q-ne smn~.pl~. It lhus appears [hal the lack of reproducib:,l, ily :-sre'-a:ed -'.opanicle size. -l-ne e x p e r i m e n t s described a b o v e w e r e e a r n e d out w-.:h ---a m D .~ _:~" - Of -... ~e order of 3 0 ~ug for p o w d e r s a n d o n e small crys.:al for c~'stai-iine ma-:efi~ ~approx. 5 0 ~g). %%-non sa_rnples larger lhan I 0 0 :.~g w e r e u ~ d . ihe P P A profiles w e r e only qualitatively s~.milar to [hose obse,'x'ed for _ ~ m ~ ! s.--~Dle_< a n d n o p a t t e m could be di~ce_,-n_ed to a c c o u n t for the change. Th~_s w a s ~ s o true for the m a s s specir?l results, -,:h~.ch frequen:!y ind'[cated .he presence of t w o m a x ; . m a in the d e c o m p o s i t i o n Droduc-:s. R e , e a r e d analyses of d:.,fferen -: quant;n-es of the _
reacrion is be!iewd \.ei:h ei. al. [ 121.
to be quantitative,
a finding consistent with the results of
Tire meckanisn? of tizenr:nI decomposition ?“ne primar\- decomposition of Sn(Erldrc); is iniriated by a reducrfo~ ro Sz(Erzdtc)2 wiih the formation of TETD. Three [17-191 of rhe four pa_pers [ 17--201 in which the reduction of the meral atom of the dirhiocrrba=a:e comples has been reported to occur during t;he primary decomposition. 230 reported the iormation of TETD. Ir? the case of the decomposition of copper dithiocarbamaie compleses [ 30] rhe siruarion is more comples [ 211. The formation of TETD ma- be unimolecu!ar as suggested by HusebJ-e and Sl-neren [ 221 for Te( Et:dtc),. This involves rhe formarion of a bond between the sulphur ato_ms lying cIosest to each other on adjacent ligands. probab!y the monodentare ligands, zs indicated by a CQ-skllographic srud>by Harreld and Schlemper [33] on Sn
considemfions
.T%e suggestions made in ihis paper are at \.aria.nce with the repon: thar Sn{Et,dtc), sublimes ac 150’ C_~O_l mm Hg [ 281. On heating Sn~Ec~dk)~ apparatus unri! rhe residue (190-zoo= c/o .5 mm Hg) in a sublimation become creamy white, an orangeyellow !iquid and a red solid collect OR :he cold f;mger. The w-hire solid r&due is readily shown to be SISn2!Etzdtc); [ 71. On anal>-sing ihe liquid using PP..., ihe presence of TETN, TETD m_d Sn(Ei,dtc)2 is detected in the remperature rar.ge lOO-165’C. This temperature range, being lower than that iF. which these compounds are evohed during the PPA of Sn(Et,dfc), (17~-24O=C), indicates ihat ihermzl deccmposition occurs during sublimation.
43
The PP..\ analysis of the red solid indicated thzr the szhs*;a?ce is inde2d Sn( Ettdtc)4, which suggests that this compound sublimes, togerher w-irh the more volatile decomposition intermediates. HOW-~\-2rthe ebsencs of 2 molecular ion and, more significantly, of an [M - (Er:drc) j’ ion 1191 in borh the CI and EI rns spectra of Sn(Et=dic), indicate fina:. it is not volatile. ‘Thus it is suggested that the Sn(Etzdic)4 rssulrs from a recombination reaction (shown dotted in Fig. 1) between the primary decomposition inrcrmediates, TETD and Sn(Etzdtc)z and which takes pkce on the cold finger of ihe xublimation apparatus. Under PPX condiiiow this ;vould not. occur. In order ro vetif:- rhlis suggestion, fmdy ground Sn(Etzdfc)z and TETD v..2re mised and heated to 110-15O’C for 15 min under nirrog2n. .Tne r-idue was g-round and analysed by PP.% The largesr peaks corrspond ro rhe starting materials and appeared at the especred lower temperatuws. However, in the range ZOO-XO’C, the prof;_le and mass sp2ctn are corktenrwith rhe decomposition of Sn(Etzdrc);. The especfed pezk for SzSnz(Ei,dtc), was much larger than anticipated: not surpriiir&some of :he TETD had decomposed and allowed the Sn(Et=dtc)and Ss r2acfion to occur.
Arhough the thermal decomposition of Sn(Er=dtc); in vacuum has been sho\\n to be relatil-el_v simple. its elucidation is cornpiicat.ed by various phenomena It. is appar2nt that crystal size pla_vs 2 dominant role in the overall decomposition pathway of the complex It is concluded that these phenomena may be obsen-ed in the decomposition of metal complex= generally. In prek
The authors are grateful to Dr. P.J. Derrick for helpful discussions. Acknowledgement is made to the Australian Rsearch Grants Committee for the pro+,ion of the EI[CI source for the JEOL D-100 mass spectrometer. One of us, G.K.B., thanks La Trobe I.kiversit\- for the aw-ud of a Postgraduate Research Scholarship.
REFERESCES G.-K Ra+-spies, J.F. Smith, J-0. Hill and R-J. lkyre, Tke.?r?ochi.~. _XC~J.2: (1975) 307. J.F. Srnirh,b-n. J. 3ti Spectrorn.Ion Pn>--r,36 (197s) 149. TX Risby 2nd AL; Yergey, AnJ. Chea., 50 (191s) 327X. D. Rice, S.S Fate--i, R Nlitcheal, J.H. YLZppia?r. D. Dolhm-ore md _X Sdctlb; in D. F%ice 2nd J.F.J. Tadd (Editors), DyrsznIc 3Lrr Spa=t_ro.xeu\-, \.ol 5. IIeydeq Urdon, 19i’6, Ch. 20.
44 5 G . K . B . ~ t s p : . e s , J . F . S m i t h , J.O. Hill a n d R . J . . M a g e ~ , The..,'m...oc.him. Ac~,a, 19 ( 1 9 T $ ) 561. 6 G . K . B . - - ~ p i e s , J.F.S..~;.th ~nd J.O. Hill, T:.~e.rrnochiw... A c ~ , 19 ( 1 9 T S ) 5 7 3 - G . K . B . , - a ~ p i e s , J.F. S,~..i-h, J.O. HR| a n d P.J. D e r r ~ k , J. T h e r m ~ Anal., 16 ( 1 9 T 9 ) 3,69. J. yon Braun, Ber.. -~5 ( 1 9 0 2 ) S I T . 9 J.H. K a r c h m e r (EdPor), "Ice .-Ina!.vl;.calC'nemLstry." of Sulfur .~nd its C o m p o u n d a , P - ~ If. Wiley, N e w York, 19:2, Ch. !0.!2. 10 F.I. On,.m -ka and W.R. Boos, A n a l Che.-~..." 5 (1973) 967. 11 S Pr~kas.h, G.K.B.~-'.s-9.ies. J.O. Hill and R.J. Magee. in prep~r~:,on. !"2 .M. Ve~.:h, O. Recktenw-~Id ~nd E. Humpfer. Z. Naturforsch. B, 33 (!97~) ~=' 13 P. Oliver, P h D "l-nesis. I~ Trobe Unive.,'s~_zy,.Melbourne, 1979. 14 J.K. Terlouw and J.J. de Ridder. O r ~ . . M ~ s Spec'.rom., 5 (l-a'E]) 1127. IS K.W. Given. B..M..M-~t~son, G . L .Me"_ss!erand L.H.P.;gno!e~, J. Lnor~. Nucl. Che..-n..39 ~ I g T T ) 1309. 1G A. Ii"e~m-~nn. _AnR!_ Chem.. 50 (19TS) $30. ! T O. Foss..Acta Cne.-n. Sc-~nd., 7 ( 1 9 5 3 ) 2°_6. 1~ D . C . B . ~ d l e v , I.F. Re=dall =Rd K . D . ~ i e s , J. C.hem. Soc. D-~.',oR T~r-S /19T3~ -°225 .~.nd ~ p . 20SOS. 19 A.V. Dubrov:.n, K..M. Du.,-.~cva znd V.L Spi~_s_vP.. R ,i/.ss.J. L~o.--~. Cy',em., 23 ('--97S) !T01. 20 S.V. L~._~.onov. L.A. Kosareva, A . F . _M~.~l-:kova -',.,,-d A . A . Shkly-',ev, R " ~ . J. I~o.~. Chem., 2 2 ( 1 9 T T ) ! 2 9 9 . 21 G.K.B.~_tspies. J.F. ~Lmi~h a n d J.O. Hill. unpub!i_s.hed r e s u ! ~ . 22 S H u s e b y e a n d -~E. t~,'aeren. A c t a C-.~em. ~ n d . , 27 (3973) 7 6 3 . 23 C_S_ Hm~eld a n d E.O_ S c h l e m p e r , A c t a Crys:allogr.. Sec'.. B, 27 ( 1 9 7 ! ) 1 9 6 4 . 24 P. NichoLs aEd _M.W_ G.~-n:, L~ T r o b e URiversit3"..Melbourne, p ~ v a t e co..-rn~unic-~=io=. 2,~ D.L. C o c k e , G. Ahe.-.d a n d d. B l o c k . Adv-~r,.ces in -M~,ss S p e c z r o m e ~ - , V o L T-A. H e y d e c , L o n d o n . 197S. p. 7 0 3 . 26 P.J.H__A__M. van tier L e e m p u t , J. ~l.l,e,.,.se. J . A . C r ~ a n d L. G r o e n , Rec. Troy. C~,',_~-. P~3s-B.zs. 9S { ! 9 7 9 ) 4 1 3 . 2T J..A..McClevcr~y a n d N . J . . M o r r i s o n , J. C h e m . ~oc. D~!.'on Tra.~_s., ( 1 9 T 6 ) 2 1 6 9 . 2S D.C.B.--adley a n d M.H. Gi~l-:z. J. C'r'.em. Soc. _A, ( 1 9 6 9 ) ! I S f i .