July 5 , 1957
SYNTHESIS OF ETHYLENEDIAMINEPLATINUM(~~) AND (IV) BROMIDES AND IODIDES33 15
in the following order: Pt(1V) > Pt(I1) > Co(II1) plex itself on the ammonia deformation frequencies Pd(I1) > Cr(II1) > Cu(I1) > Ni(I1) > Co(I1). is seen also in the series of cobalt(II1) ammines Univalent silver is somewhat out of line, the am- (compounds 17, 16, 15 and 14). (The position of monia ligands in [Ag(NH&]+ having a rocking the rocking band a t 790 ern.-' in compound 17 is frequency slightly greater than that in [Cu- not accurately known as the NO2 group also ab(NH3)4]++. The presence of rocking frequencies sorbs strongly in this region). Both the rocking in the spectra of the hexammine Ni(I1) and Co(I1) and symmetrical deformation frequencies increase, complex ions indicates that the nitrogen-to-metal in general, with increasing positive charge on the bonds have covalent character; the relatively low complex. This increasing positive charge coincides frequencies along with the paramagnetism of these with increasing number of ammonia molecules in these Co(II1) complexes. complexes indicate sp3d2outer orbital type bonds. The replacement of the carbonate group in the The rocking frequencies show a large variation and are thus very sensitive to the nature and oxida- [Co(NH3)&03]+ ion (compound 24) by a sulfate tion state of the central metal ion. This is under- group (compound 27) has no effect on the rocking standable from the above discussion of the nature frequency, and replacement by an oxalate group (compound 28) has very little effect on either the of the rocking vibration. The symmetrical bending frequencies of coordi- rocking or the symmetric deformation frequencies. ions ~ (compounds 1s to 21 nated ammonia molecules show a similar variation I n the [ C O ( N H ~ ) & ] + with the nature of the N-L!I bond but the percen- and 26), an appreciable lowering of the rocking tage difference in frequency in going from the and symmetric deformation frequencies occurs Co(I1) to Pt(1V) ammines is not so great as for only where X is a hydroxyl group. The replacethe rocking frequencies. Moreover, the degenerate ment of an inner chlorine atom by a nitro group in frequencies show little variation with the nature the [Cr(NH3)&1]++ ion (compounds 10 and 11) of the N-M bond. These observations are also in results in an appreciable increase in the these deforaccord with the foregoing discussions of the natures mation frequencies. The spectra of these metal ammine complexes of the symmetric and degenerate deformation vibraare being determined in the cesium bromide region tions. The neutral Pt(NH3)zClZ molecule (12) has a in these laboratories t o study the nature of the lower rocking and a lower symmetric deformation lower frequencies, as reported in a previous paper.*j frequency than the [Pt(NH3)4]++ion (8) and a ( 2 5 ) D. M. Sweeny, I. Nakagawa, S. Mizushima and J. V. Quaglisimilar effect is observed in the Pd(I1) compounds ano, THISJ O U R N A L , 78, 889 (1956). (13 and 6). The effect of the charge of the com- NOTREDAME,INDIANA
>
[CONTRIBUTION FROM THE
DEPARTMENT OF
CHEMISTRY OF THE UNIVERSITY OF TEXAS]
The Synthesis o€ Certain Ethylenediamineplatinum(I1) and (IV) Bromides and Iodides1 BY GEORGEUT.WATTAND ROBERTE. MCCARLEY RECEIVED MARCH16, 1957 Methods for the synthesis of ethylenediamine coordination compounds of certain halides of platinum( 11) and ( I V ) in high yield and high purity are described. It is shown that [Pt(en)Brzl and its isomer [Pt(en)g]PtBra may be separated quantitatively owing t o the solubility of the former in liquid ammonia a t -33.5'.
In the course of studies on the lower oxidation states of platinum,2 we have had occasion to prepare numerous ethylenediamine coordination compounds of platinum halides. Although many of the corresponding chlorides have been synthesized and are well characterized, they are not desirable as starting materials for reactions in liquid ammonia owing to their generally low solubility. Accordingly, the necessary bromides and iodides were prepared. The syntheses described below either correspond to compounds not previously reported or represent new and/or improved procedures. Experimental Methods.-Platinum, when present as the only nonvolatile component, was determined by ignition t o the metal; otherwise, platinum was reduced t o the metal with ( 1 ) This work was supported in p a r t by the U. S. Atomic Energy Commission, Contract AT-(40-1)-1639. (2) G. W. W a t t and R. E. McCarley. THISJOURNAL, 79, in press (1957).
hydrazine, dissolved in aqua regia, and determined spectrophotometrically.a Halogens were determined as silver halide; where halogen was covalently bonded in complexes, i t was displaced with ethylenediamine prior to precipitation. All X-ray diffraction patterns were obtained using a Hayes unit, Cu Kor radiation, an Ni filter, a tube voltage of 35 kv., a filament current of 15 ma. and exposure times that varied with the nature of the sample. All of the X-ray diffraction data reported here are assembled in Table I and include only the six most intense lines for each compound for which such data are riot already available; more nearly cotnplete data are tabulated elsewhere.' For potentiometric titrations, the potential was measured with a Leeds and Northrup type K potentiometer, a platinum indicator electrode, and a saturated calomel reference electrode. Materials.-Unless otherwise indicated, all chemicals employed in this work were reagent grade materials that were used without further purification. Hexabromoplatinic acid was obtained by dissolving finely divided platinum in bromine and concentrated hydrobromic acid followed by boiling t o remove excess bromine and acid. Massive platinum was dissolved in aqua regia and the re(3) G. H. Ayres and A. s. Meyer, Jr., Anal. Chem., 23, 299 (1951). (4) R. E. McCarley, Dissertation, The University of Texas, 1956.
Ethylenediaminedibromopla tinum (I1j , [Pt(en)Br2].This compound was prepared by a method similar t o t h a t X-RAYDIFFRACTION DAra used by Basolo, et aZ.,' for the synthesis of the corresponding chloride. d , A. I/Io d , A. 1110 d , A. IjJIn A suspension of 10.5 g. (0.0140 mole) of potassium hexa&PtBrG ( enH2)PtBr6 [Pt(en)Br~l bromoplatinate(1V) in 50 ml. of water was reduced to potassium tetrabromoplatinate(I1) !qith 2.57 g. (0.0140 5.98 1.0 6.50 0.9 6.99 1.0 mole) of potassium oxalate l-hydrate,C and treated with 5.19 0.8 .5.97 1.0 6.46 0.5 1 : 10 aqueous ethylenediamine i n 0.1-nzl. portions at room ., 3.13 .6 5.49 0.4 4.94 . I temperature. After each addition, t h e reaction was allowed t o proceed t o completion (i.e., until t h e pH of the re2.99 .6 3.81 .6 3.83 .6 action mixture S 6) before the next portion was added. 2.59 .9 2.98 .7 3.49 .8 During the reaction of the first portion of ethylenediamine c 1.93 . ( 2.40 .7 3.12 .7 solution, iridescent green crystals [see ref. 21 separated and continued to form until 0.5 ml. of the base had been added. [ P t ( en),] P tBrl [Pt(en!,l Br2 [Pt(eniBrdl This product (0.85 8.) was removed by filtration and the 7.81 0.9 7.88 1.0 6.32 1.0 reaction was continued in t h e same manner. Upon addition of the next portion of the diamine, bright yellow cr3-s5.91 1.0 6.56 0.4 5.83 0.5 tals formed and after addition of 5 ml. of the diamine, 2.60 5.21 0.5 4.92 .6 5.28 .4 g. of this product was separated. Another crop (1.87 g.) 4.94 .5 1.03 .9 4.77 .8 of this same product was separated after adding an addi3.85 ,-I 3.76 .7 3.87 .1 tional 3 ml. of ethylenediamine solution. h final increxnental addition of 2 ml. of ethylenediamine solution provided 3.48 .7 3.53 .I) s ,07 .6 a mixture of yellow crystals contaminated with a pale green solid. (Subsequent work--see belov-has shown t h a t thi5 [Pt(en)CL [ P t ( en i I41 yellow product [Pt(en)Br2] is contaminated with a polyd , A. Ill0 d , A. I/In merization isomer. Conditions leading t o t h e formation 7.43 0.5 6.63 Strong of [Pt(en)Br,] while minimizing t h e formation of the isomer 6.73 1.0 5.82 Strong are embodied in the procedure given.) T h e total bield was 6.14 0.5 5.11 Very strong 4.47 e . or 77qn based on Dotassium hexabromoDlatinatei1~). Anal: Calcd: for [Pt(en)Br2]: Pt, 47.0; Br, 38.5. Fdund: 5.63 .i) 4.42 Medium P t , 46.9; Br. 38.7. 3.37 .9 3.84 Strong Ethylenediaminedibronioplatinum(I1) is soluble in liquid .7 3.31 \Yeak 3.02 ammonia a t -33.5" apparently without reaction. Evaporation of the solvent from the \-ellow solution urovided vellotr sulting solution was evaporated to dryness several times with crystals that gave an X-ra) diffraction pattern identical concentrated hydrobromic acid t o expel hydrogen chloride with that of the solid originally dissolved. When a mixture and oxides of nitrogen. of the yellow solid arid its green polymerization isomer is Potassium hexabromoplatinate(1V) was prepared from treated with liquid ammonia a t -33.5", the former dissolutions of hexabromoplatinic acid by the method of Weber.5 solves while the latter remains as a brown insoluble amEthylenediammonium hexabromoplatinate(1V) was moniate. Pure [Pt(en)Br,] was recovered from the amformed by slow addition of ethylenediamine t o a cold solu- monia solution; the ammonia-insoluble brown arninoniate tion of hexabromoplatinic acid. This brilliant red salt is was deammoniated at lo-, inm. at room temperature to only sparingly soluble in water. Anal. Calcd. for ( C Z H ~ O -provide the original green component of the mixture. S\.T2)2PtBrs:P t , 26.5; Br, 65.1. Found: Pt, 26.5; Br, 64.7. Yellow [Pt(en)Br2] is also readily soluble in S,r\'-dirnethylTetrabromoplatinate(I1) ion was, in some instances, pre- formamide, from which the bromide may be recrystallized pared by t h e reduction of potassium hexabromoplatinate- by addition of Tvater. If, however, these solutions are (IV) with potassium oxalate by the method of Bulman and heated t o cn. SO", decomposition resulting in deposition of ..lnderson.6 This reaction however is quite slow, and com- elemental platinum occurs. Bisethylenediambeplatinum(I1) Tetrabromoplatinateplete reduction is achieved only by evaporating the reaction mixture t o a small volume. (11), [Pt en)^] PtBr4.-A solution of tetrabromoplatinic acid \vas divided into two equal portions, ethylenediamine was Since, in other cases, it was desirable to form the free acid in the absence of extraneous by-product ions, conditions added t o one portion at 80-90" until all of the solid dissolved \vliereupon this was added to the other portion of the original were devised for the production of this ion by electrolytic reduction. X platinum wire cathode was immersed in 220 solution. The pale green crystals t h a t separated in quantitative yield were washed with mater and dried a t 110' for ml. of solution containing 3 g. of platinum as hexabromoplatinic acid. i\ platinum wire anode was immersed in a 2 hr. A n a l . Calcd. for [Pt(en)?]PtBr(: P t , 47.0; Br, solution of potassium chloride t h a t was connected to the 38.5. Found: P t , 47.1; Br, 38.5. -4s a means of providing evidence (other than that arising cathode compartment by a potassium chloride-agar bridge. The catholyte was stirred vigorously, the current was main- from the mode of synthesis) for the identity of the ionic tainedat ca. 0.1 amp., and thecathodepotentialwas followed components of this salt, precipitation of PtBr42-as the silver by means of a Leeds and Northrup No. 7664 pH meter salt proved unsuccessful a t or below room temperature owusing a saturated calomel reference electrode. During the ing t o incomplete reaction; precipitation a t elevated temcourse of the electrolysis, t h e color of the solution changed peratures is impractical because of formation of silver bromide. -bxordingly, the presence of two distinctly different progressivelb- from maroon-red t o the deep red-brown color characteristic of the tetrabromoplatinate(I1) ion. Concur- ionic species containing platinum(I1) was demonstrated by the potentiometric titration method of Grinbergand Ryabchirently, the potential gradually became more positive b u t there was no definite break in the time LIS. potential curve. kov.8 Thus, 0.2801 g. of the salt was suspended with effiAccordingly, the appearance of a deposit of platinum on cient stirring in 110 ml. of 1.0 il'hydrochloric acid solution the cathode that appeared after about 60 hr. was taken as :it 25" and titrated with 0.1384 N sodiuni bromate solution; the end-point for the reduction process. As evidenced by the the results are given in Fig. 1. About 4 hr. mas required nature of the products obtained upon treatment of the for the titration tn the first end-point, a t which stage all o f product solutions with ethylenediamine, reduction is in- the solid had dissolved and the color of the solution was palc complete unless time is allowed for deposition of a consid- yellow. Titration to the second end-point required only erable quantity of platinum on the cathode. The current 30 min.; the final solution had a n intense yellow color, and should be expected to contain [Pt(en)2Br?]PtCleand/or its efficiency is ca. 10cc. Synthesis of Platinum(I1) and (IV) Halides.-In several isomers. Evaporation of the solution t o a small volume yielded 0.1 g. of orange colored crystals. A n a l . Calcd. for of the cases t h a t follow, numerous procedural variables were studied, but only the final procedures t h a t gave optimum .. . results are described. ( 7 ) E'. Basoln, J . C .B a i l a r , J r , and R . R. T:m, T H I SJ O C R N A T , 72, TABLE I
( 5 ) H. C P. Weber, THISJ O U R N A L , 34, 1300 (1912). ( 6 ) E. Bdlman a n d A C Anderson, B e ? , 36, 1566 (1903)
" 4 3 4 3 (1950). ( 8 ) A. A , Grinberg and D. I. Ryabchikor, Conipt. r e n d . a r a d . sci. r . R . S . S , 14, 119 (1937).
July 5 , 1%7
SYNTHESIS OF ETHYLENEDIAMISEPLATINUM(II) AND
(Iv) BROMIDESAND
IODIDES
3317
[Pt(en)zBr~]PtC1~: P t , 45.0. Found: P t , 44.3. T h e calI I I I I 1 . culated end-points for oxidation of half and all of the plati0.9 num t o the 4+ oxidation state are 4.87 and 9.75 ml. of titrant, respectively. T h e end-points established by means of a differential plot are 4.68 and 9.75 ml. Bisethylenediamineplatinum(11)Bromide, [Pt (en)21 Brz.Although this compound should be formed readily by t h e PI action of ethylenediamine upon either [Pt(en)Brz] or [PtI ( e r ~ ) ~ ] P t Bthe r ~ ,reaction h i t h the latter was found t o be impractically slow. Accordingly, 1.87 g. of [Pt(en)Brzl was 0.E suspended in 30 ml. of water, treated with 1 ml. of ethylene0.E diamine and heated a t 80-90" for 4 hr. A small quantity of residual solid was removed by filtration, the filtrate was diluted with 500 ml. of ethanol, and cooled t o 0". The fine white crystals that sepoarated were filtered, washed with ethanol, and dried a t 110 . T h e yield was 1.96 g. or 92% based on [Pt(en)Br~]. Anal. Calcd. for [Pt(en)z]Brz: cn' P t , 41.1; Br, 33.6. Found: P t , 41.1; Br, 33.4. t trans-Bisethylenediaminedibromoplatinum(1V)Bromide, 0.5 [Pt(en)zBr~] Brf.-This synthesis was effected by a proce> dure similar t o that used by Schleicher, Henkel and Spiess for the preparation of [Pt(en)zBrz]Cl~.Thus, 0.424 g. of [Pt(en),]Br~was dissolved in 25 ml. of water and treated with 0.2 ml. of bromineat 50". After 15 rnin., the temperature was raised t o 100" and air was blown over the surface of the solution t o remove excess bromine. When the volume of the solution was reduced t o 10 ml., it was cooled t o 0.4 room temperature, treated with 1 ml. of concentrated hydrobromic acid solution, and finally diluted with 100 ml. of 2 : 1 ethanol-acetone mixture. The fine yellow crystals that separated were filtered, washed with ethanol and acetone, and dried in air.'!' Anal. Calcd. for [ P t ( e n ) ~ B r r ] B r ~ : P t , 30.7. Found: P t , 29.7. Ethylenediaminetetrabromoplatinum(1V), [Pt(en)Br4].! I I I 1 I Allthough this compound was formed successfully by the 0.3 6 8 10 12 2 4 oxidation of [Pt(en)Br?] with bromine, this procedure7~9was found t o be much less satisfactory than that which follows. NABRO, S O L N , M L An excess of SOYo aqueous ethylenediamine was added t o Fig. 1.-Potentiometric titration of [Pt(en)z]PtBrd with 2.99 g. of KzPtBrs in 100 ml. of water a t room temperature. After 3 hr., the solution was acidiced with hydrobromic sodium bromate. acid, heated t o go", then cooled to 10 . T h e orange-colored powder that separated was filtered, washed with water (en)Br?] slurried in 150 ml. of water was treated with 1.1913 followed by ethanol and ether, and dried in air. The yield mas 1.78 g. or i870 based on KzPtBrR. Anal. Calcd. for g. (0.0070 mole) of silver nitrate for 1 hr. a t 90". The pre[Pt(en)Brl]: P t , 34.0; Br, 55.6. Found: P t , 34.0; Br, cipitated silver bromide was removed by filtration and excess potassium iodide was added t o the filtrate. The fluffy 55.3. This substance is soluble in both iY,N'-dimethylformamide and ybutyrolactone, and dissolves in liquid yellow solid that separated immediately was filtered, washed ammonia owing t o the occurrence of reactions described with water and with ethanol and dried in air. The yield was 1.i3 g. or 96.7% based on [ P t ( e n ) B r ~ ] . Anal. Calcd. elsewhere.2 for [ P t ( e n ) I ~ ] :P t , 38.3; I , 49.8. Found: P t , 38.4; I, Ethylenediaminedichloroplatinum(I1) , [Pt(en) Cl,] .-Although another method of synthesis has been repqrted,' the 49.5. Platinum(1V) Iodide, PtI4.-In accordance with the profollowing procedure is both simple and efficient. T o 1.30 cedure described by Pigeon," PtIa was prepared in quantitag (0.00313 mole) of [Pt(en)Br?] suspended in 75 ml. of water \vas added t o 1.064 g. (0.00626 mole) of silver nitrate tive yield by heating 5.54 g. of platinum as HzPtCls with 19 and the mixture was acidified with 1 ml. of 6 N nitric acid. g. of K I a t 80". Anal. Calcd. for PtId: P t , 27.8. Found: After heating the reaction mixture a t 90' for 2 hr., the pre- P t , 27.8. Ethylenediaminetetraiodoplatinum(1V) , [Pt (en)14].cipitated silver bromide was filtered off, and the filtrate was Approximately 1 g. of PtI4 was dissolved in a slight excess of treated with excess potassium chloride solution. Golden yellow needles of the desired chloride separated after about aqueous potassium iodide solution to provide a solution of 5 rnin., whereupon the solution was cooled t o 0" and fil- KzPtIs which was treated dropwise with SOYo aqueous tered. The product was washed with water, ethanol, and ethylenediamine. A very fine maroon-red precipitate separated a t once and continued to form until the solution was dried for 12 hr. a t 110". T h e yield was 0.93 g. or 91% based on [Pt(en)Brz]. Anal. Calcd. for [Pt(en)C12]: colorless. Since analysis showed that this product was impure, it was treated with 100 ml. of y-butyrolactone a t room P t , 59.8; C1,21.7. Found: P t , 59.6; C1,21.7. temperature; this resulted in a deep red solution and a bronze Ethylenediaminediiodoplatinum(II), [Pt(en)14 .-This colored solid that was removed and discarded. The filtrate substance was prepared by a method analogous t o that used by Schleicher, et al.9 Thus, 1.4445 g. (0.0035 mole) of [Pt- was diluted fivefold with water and fine glisteniiig black crystals separated. This product was filtered, washed with water and with ethanol and dried in air; the yield was ca. 1 (9) A. Schleicher, H. Henkel and L. Spies, J. pvakt. Chern., 106, g. Anal. Calcd. for [Pt(en)14]:P t , 25.6; I , 66.5. Found: 31 (19221. P t , 25.5; I , 66.5. (10) It is assumed t h a t this product is the trans isomer since i t seems well established t h a t complexes of the type [Pt(en)r]Brs retain Ausns. TEXAS
1
g
their configuration upon oxidation [see F. Basolo, Chem. Reus., 62, 459 (195313.
(11) L. Pigeon, A i i n . Lhim. Phys., 2, 496 (1894).
