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Cis and trans isomers of dichlorodiamminepalladium (II)
J. inorg, nucl. Chem.. 1966, Vol. 28, pp. 1965 to 1972. Pergamon Press Ltd. Printed in Northern Ireland
CIS A N D T R A N S ISOMERS OF DICHLORO-
DIAMMINEPALLADIUM
(I 1)
R . LAYTON,* D . W . SINK a n d J. R . DURIG Department of Chemistry, University of South Carolina, Columbia, South Carolina, U.S.A. (Received 21 October 1965; in revised form 30 December 1965) Abstract--The existence and characterization of cis and trans isomers of Pd(NH3)~CI2 have been re-investigated. A stable monoclinic trans compound has been prepared at low temperature. It has been shown that when trans-Pd(NH3)zCl~ is prepared at room temperature or above, it is a mixture of monoclinic and tetragonal dimorphs. The material previously reported to be cis-Pd(NH3)~Cl2 has been shown to be a complex mixture while the pure authentic cis-Pd(NH3)2C12 has been prepared and identified by its unique X-ray diffraction pattern and infra-red spectrum. INTRODUCTION
THREE distinct square planar palladium compounds with the empirical formula Pd(NH3)2C1~ have been reported. They are trans-Pd(NH3)2C12, cis-Pd(NH3)2C12, and the pink double salt, [Pd(NH3)4][PdC14]. The familiar yellow compound, prepared by acidifying a solution of Pd(NHahC1 z, was assigned the trans structure by DREWcl) on the basis of its chemical similarity to trans-Pt(NH3)zCl 2. In an early X-ray study of this compound, MANN identified several crystal modifications and habits, but the trans structure could not be definitely confirmed by his data. ~2) For some years the double salt, [Pd(NH3h][PdCI4] was mistaken for the cis isomer. (3) Eater GRUNBERGc4) reported that the "true" cis isomer could be prepared by treating (NH~)2PdC14 with NH~C~H30z in water. The cis assignment was based on the observation that the compound was different from the trans in solubility and conductivity and gave a rapid red coloration to acetone solutions of KI. The isomeric purity, the specific conditions for formation, and X-ray data were not then or subsequently reported. A thorough re-investigation of these compounds was initiated when the reported methods of preparing the eis and trans isomers of Pd(NH3),~C12 led to materials with astonishingly similar X-ray powder patterns which could not be indexed by MANN'S crystallographic data. Several infra-red investigations have been reported (5-8~ for * Present address: Saint Peter's College, Jersey City, New Jersey. ~a~ H. D. K. DREW and G. H. WYAT% J. chem. Soc. 56 (1934). ~2/F. G. MANN, D. CROWFOOT, D. C. GATTIKER and N. WOOSTER, J. chem. Soe. 1642 (1935). ~3~j. W. MELLOR, A Comprehensive Treatise on Inorganic arm Theoretical Chemistry, Vol. XV, pp. 663-665. Longman, Green, London (1936). ~4, A. GRUNBERG and A. SCHULMAN, Dokl. Akad. Nauk S S S R N.S. 215 (1933). ~:'~D. B. POWELL and N. SHEPPARD, J. chem. Soc. 3108 (1956). *~;)E. P. BERTIN, I. NAKAGAWA, S. MIZUSHIMA, T. J. LANE and J. V. QUAGLIANO, J. Am. chem. Sac. 80, 525 (1958). ~ R. C. LEECH, D. B. POWELL and N. SHEPPARD, Speetrochim. Acta 21, 559 (1965). s p. j. HENDRA and N. SADASlVAN, Speetrochim. Acta 21, 1271 (1965). 1965
1966
R. LAYTON,D. W. SINKand J. R. DtralO
trans-Pd(NH3)2Cl 2 but only in the study by BERTINet al. was the infra-red spectrum of the corresponding cis compound reported. These authors tr) indicate that the most distinguishing feature between the two spectra was a weak shoulder at 1265 cm -1 found on the high frequency side of the NH a symmetric deformation vibration. However, the most drastic change in the spectra of the two molecules should be found in the skeleton stretching vibrations which is beyond the frequency range of the previous infra-red investigations, tr) By assuming the NH 3 group to be a point mass or to be freely rotating, one readily notes that trans-Pd(NH3)2Cl 2 belongs to the point group D2h while cis-Pd(NHa)2C1 z has only Cz~ symmetry. With the neglect of lattice coupling, symmetry dictates that one Pd-N stretching frequency should be found for the trans isomer while both a symmetric and antisymmetric Pd-N stretching vibration are expected for the cis isomer. Likewise, in the palladium chloride stretching region only the antisymmetric stretching frequency should be infra-red active for the trans-Pd(NH3)2Cl z but both the symmetric and antisymmetric Pd-Cl stretching vibrations should be observed in the infra-red spectrum of the cis isomer. With these expectations in mind we investigated the infra-red spectra and X-ray powder patterns of cis and trans isomers of Pd(NH3)2CI 2 prepared by previously reported methods.
DISCUSSION OF RESULTS The results of this study indicate that the cis-Pd(NHa)2C12 reported by GRUNBERG is in reality a mixture of cis and trans Pd(NH3)zCI2 along with smaller amounts of [Pd(NHz)4][PdCla] and (NH4)2PdC14. This conclusion has been reached by comparing X-ray and infra-red data of the pure components to that of GRUNBERG'Sproduct. This required the crystallographic identification of the trans-Pd(NHz)zC12 polymorphs. Trans-Pd(NHa)2C12 The trans isomer has been found to exist in at least two crystal modifications: a low temperature monoclinic form and a high temperature tetragonal modification. Pure monocllnic trans-Pd(NH3)2C12 was prepared by slow crystallization from an aqueous solution of (NH~)2PdC14 and (NH4)2CzHzO 2 at 5°C. The X-ray powder data for this compound are given in Table 1. These lines can be adequately indexed using the monoclinic cell parameters given in Table 1. Supporting this indexing is the recent work by PORAI-KoSHITSta) on the corresponding platinum compound (trans-Pt(NH3)2Cl2) which was found to be monoclinic with a = 5.46 A, b = 6.05 A, c = 8.07 A, fl-----93o47' with two molecules per unit cell. The calculated density for two molecules per unit cell is 1.86 g/cm3. The experimental density is 2.06 g/cm3. This value is high, possibly due to some contamination by the tetragonal modification which is more abundant at higher temperatures (see section on mixtures). The infra-red spectrum is given in Fig. 1 and the frequencies and assignments are given in Table 2. Neglecting lattice coupling, the spectrum is typically trans with one Pd-N stretching vibration at 496 cm -1 and one Pd-C1 stretching frequency at 333 cm -~. In the region above 700 cm -1 the spectrum compares quite favourably with that reported previously, t5,6) A very weak shoulder is noted on the 1247 cm -1 band and the central maximum is somewhat lower than that reported by BERTIN et al., tn) but compares quite favourably with the infra-red results reported by POWELL and tg~ M. A. PORM-KOSHITS,Trudp Inst. Kristall. 229 (1954).
Cis and
trans isomers of dichlorodiamminepalladium
(II)
1967
TABLE 1.--X-RAY DATA FOR traIIs-DICHLORODIAMMINEPALLADIUM (II) Monoclinic modification Cell parameters: a = 6.00/~,, b = 6.24/~, c = 10.1 A, f4 = 95 ° 20'
Line
I/lo
hkl
d(obs.) (~)
d(calc.) (~)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
5 100 2 1 31 1 1 1 1 1 1 1 1 5 1 1 1 1
100 010 002 111 112, 112 200 210, 210,210 121,004 0i4, 01~ 023 220 22~ 024 030 204 031,124 130 205,203
6'18 5'93 5"02 3"88 3'24 3.06 2'76 2"50 2'43 2"35 2"14 2"06 2-01 1"98 1"94 1"92 1"91 1'75
6-24 5"98 5'03 3-87 3-17 3'12 2"77 2'51 2'40 2"34 2"16 2-04 2.02 1"99 1.96 1'92 1-90 1'75
SHEPPARD(5) on a yellow powder sample. The higher frequencies also compared quite favourably with the bands reported by POWELLand SHEPI'ARD.(5) The tetragonal modification has not been obtained in the pure state. However, the existence of another modification of trans Pd(NH3)2C12 has been demonstrated by heating [Pd(NH3)4][PdC14] at 170 °. After 140 hr, the weight is unchanged and the infra-red spectrum (see Fig. 1) is identical to monoclinic t r a n s Pd(NH3)2C12. The X-ray pattern, which had rather broad and diffuse lines, included ten lines which could not be indexed with the monoclinic cell parameters. However, these ten lines can be satisfactorily indexed, considering the quality of the pattern, using tetragonal 25
3
4
S f z u
5
~ . ~ - ~
WAVELENGTH IMJCRONSI 6 7 ~---
_
/- -
~
,
8
9
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~-
,[
i
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I 3000
2500
2000
1800
1600 1400 FREQUENCY (CM~i
1200
I000
800
6O0
4OO
FIG. 1.--Trans dichlorodiamminepalladium (II). The spectrum was recorded at 24°C with a frequency scan time of 85 cm-1/mm, chart speed of 18 cm-1/mm above 2000 cm -~ and a scan time of 50 cm-1/mm, chart speed of 4 c m - t / m m below 2000 cm -1. The amplifier gain was 5.0 and the normal slit programme was employed.
1968
R. LAYTON,D. W. SINK and J. R. DURIG TABLE2.--INFRA-RED FREQUENCIES FOR trans- AND CiS-DICHLORODIAMMINEPALLADIUM(II) Trans-Pd(NHa)2Cl2
Cis-Pd(NH3)~C12
frequencies (cm-1)
frequencies (cm-1)
3320 3240 3181 1720 vb 1605 1460 vb 1255 sh 1247 788 sh 753 496
3314 3237 3177 1700vb 1610 1480 vb 1269 1248 788 sh 752 495 476 327 306
333
Assignment NH3 stretching NH8 stretching NH3 stretching NH3 antisymmetric deformation NH3 symmetric deformation NHa rocking Pd-N antisymmetric stretching Pd-N symmetric stretching Pd-CI antisymmetric stretching Pd-C1 symmetric stretching
parameters (a = 6.70, b = 6.19/~). While the existence o f a tetragonal f o r m has been previously reported, ~2) these cell parameters are unique. Extended heating (6 weeks) o f [Pd(NH3)4][PdC14] produces another set of lines which could not be identified or indexed. The infra-red spectrum still corresponded to trans-Pd(NH3)2C12. Cis-Pd(NH3)2C12 W h e n K2PdC14 is treated with (NH4)2C2H303, both in anhydrous ethanol, a yellow precipitate is formed. The material corresponds to Pd(NHz)2C12 and has the unique X - r a y diffraction pattern given in Table 3. These lines can be indexed using TABLE3.~X-RAY DATA FOR ciS-DICHLORODIAMM1NEPALLADIUM(II) Cell parameters: a = 12"7/~, c = 6"02/~ Line
I/Io
hkl
d(obs.)
d(calc.)
1 2 14 3 4 5 6 7 8 9 10 11 12 13
47 100 35 51 27 42 20(B) 33 33 12 15 5 5 5
200 001 111 131 400 140 141 500,340 222 051 052,342 233 003 333
6.36 6.02 5.01 3.34 3-21 3.11 2.77 2-53 2.51 2-35 1.94 1.73 2.01 1.66
6.36 6.02 5.00 3.34 3.18 3.08 2.74 2.54 2-51 2-34 1.94 1.74 2.01 1.67
tetragonal cell parameters with the unit cell containing eight molecules (density; calc.; 2.86; found, 2.84). The infra-red spectrum is also unique, showing two
Cis and trans isomers of dichlorodiamminepalladium(II)
1969
bands in both the Pd-N stretching region (495 and 476 cm -1) and the Pd-C1 stretching region (327 and 306 cm -1) as dictated by the C2, symmetry of the cis isomer. Slight changes are also noted in the high frequency portion of the spectrum. The NH 3 symmetric deformation vibration, found at 1248 cm -1, has an additional pronounced band at 1269 cm -1. Weak absorption is found on both the high and low frequency side of the NH a antisymmetric deformation vibration at 1610 cm-L Similar absorption on the wings of the corresponding band of the trans complex has been attributed to partially hindered rotation of the - - N H z group. (7) The same explanation can account for the breadth of the 1610 cm -1 band in the cis complex but no temperature studies were made to substantiate this explanation. An alternative explanation has been given by NAKAMOTOet al, (1°) for the broad bands of the NH a antisymmetric deformation vibration in dihalogenodiammineplatinum (II) complexes. The splitting observed in the platinum analogues ranged from 140 to 65 cm -1 and has been attributed the hydrogen-5d-electron and ligand-ligand interactions. As pointed out by these authors the 4d-orbitals of the palladium atom are spatially less extensive but there still should be sufficient overlap to account for the weak splitting noted in the palladium compounds. The bands are very broad but are extremely pronounced in the concentrated pellets. Currently we see no way of distinguishing between the two possible explanations for these broad shoulders. Freshly prepared eis-Pd(NHa)2C12 isomerizes to trans-Pd(NHa)2C12 within 40 hr as evidenced by the change of the infra-red absorption to the spectrum characteristic of the trans isomer. However, the eis isomer can be stabilized by suspending the solid in ethanolic HC1 at --20°C for 12 hr. After the compound was isolated from this medium, the infra-red spectrum and X-ray pattern remained unchanged for at least 2 months. Mixtures
When trans-Pd(NHa)2C12 is formed at temperatures above 5°C, or rapidly separated from solution, the product is a mixture of the monoelinic and tetragonal forms. The X-ray diffraction patterns are a composite of those found for monoclinic and tetragonal trans-Pd(NHa)2Cl ~ while the infra-red spectra are identical to that shown in Fig. 1. The cis isomer of Pd(NHa)zC12 is reported to precipitate from an aqueous solution of (NH4)2PdC1 ~ and NH4C2HaO 2. Since the conditions were not specified in the original paper, the preparation was attempted at different temperatures and various mole ratios of starting materials. At low temperatures (0-5°C) the trans isomer was obtained (see above). At room temperature a product was obtained corresponding to GRUNBERG'Sdescription in about 70 per cent yield with a 4-10 mole excess of NH4C2HaO z. The experimental evidence discussed below clearly demonstrates that this material is a mixture with the approximate composition of 60-70%, trans-Pd(NHa)2Cl2, 20-30% cis-Pd(NH3)oC12, 5-10% Pd(NH3)4PdC14 and 0.1-1 !'~, (N H4)2PdCI4. All the lines in the X-ray powder pattern are accounted for by monoclinic and tetragonal trans-Pd(NH3)2CL., cis-Pd(NH3).~C12 and [Pd(NH3)4][PdC14]. The minor component, (NH~)zPdC14, cannot be detected in the X-ray powder pattern, but was plainly visible under the microscope (100 ×) as red clumps dispersed in the extremely (10)
K. NAKAMOTO,P. J. MCCARTHY, J. FUJITA,R. A. CONDRATEand G. T. BEHNKE,Inorg. Chem. 4, 36 (1965).
1970
R. LAYTON,D. W. SINK and J. R. DtrRIG
fine yellow needles. T h o r o u g h washing with cold water r e m o v e d the clumps a n d (NHa)zPdC14 was recovered f r o m the washings by e v a p o r a t i o n . The a m o u n t of cis-Pd(NH3)2C12 was estimated by treating the mixture with alcoholic HCI for several days. U n d e r these conditions, the cis isomer was converted to (NH4)2PdC14 which was then recovered a n d weighed. The trans isomer did n o t react. The p i n k salt, Pd(NH3)4PdC14, was f o u n d as a residue when the mixture was treated with a q u e o u s pyridine solutions. The infra-red spectrum of the mixture was similar to that o b t a i n e d for the cis isomer, i n that it h a d two b a n d s in the P d - N stretching region, b u t the relative intensities o f the b a n d s were reversed. This is because b o t h the cis a n d trans isomers have a b s o r p t i o n m a x i m a at 495 cm -1. I n the Pd-C1 stretching region, there was only a single b r o a d b a n d observed. EXPERIMENTAL Materials. All materials, except the palladium complexes were reagent grade and used without further purification. Analysis. Palladium was determined by hydrogen reduction for solid samples and precipitation of the dimethylglyoximate from solution samples. Nitrogen was determined by the Dumas and Kjeldahl methods and chloride as AgC1. X-ray data. Powder patterns were obtained with a Norelco (North American Phillips) generator, wide range diffractometer, and standard Debye-Scherrer Camera (114 cm) using either a copper or chromium target tube. Infra-red spectra. The infra-red spectra were recorded from 4000 to 250 cm-1 and in some cases from 600 to 250 cm-1 using a Perkin-Elmer Model-521 SpectrophotometerJ TM Above 600 cm-I the spectrophotometer was calibrated using the usual materials while below 600 cm-1 atmospheric water vapour and the assignments of RANDALLet al. ~2~ were used. The samples were examined in KBr disc and all spectra were checked as Nujol nulls.
Aqueous reaction of K2PdC14 with NH4C2HaO2 at 5°C--trans-Pd(NH3)zCl~ Solutions of K2PdC14 (1"2993 g in 100 ml of water) and NH4CaHsO~ (1.2812 g in 30 ml of water) were cooled to 5°C, mixed, and placed in a freezer at 5°C. Yellow crystals began to form after 3 hr. After 24 hr the product was filtered, washed with cold water and air-dried. The yield was 0.466 g, or 60 per cent based on K~PdC14. Anal Calcd. for Pd(NHa)2C12: Pd, 50"38; CI, 33"54. Found: Pd, 50'29; C1, 33"90. Density, 2'06 g/cm 3. The infra-red spectrum is given in Fig. 1 and X-ray diffraction data are presented in Table 1. Aqueous reaction of K2PdCI~ with NH4C2HzO2 at room temperature A number of reactions were run to define the conditions for the preparation of cis-Pd(NHs)2C12 according to GRUNBERO.t4~ The following is typical while the others differed only in that the mole ratio of KzPdC14 to NH4C2H~O~ varied from 1:0"51 to 9:1. Potassium tetrachloropalladate (4.00 g, 0"0123 moles) was dissolved in 100 ml of water and 3"80 g (0.049 moles) of NH4C2H30~ was added with stirring. A dull yellow precipitate began to form almost immediately and was collected after 1 hr. The product was washed successively with cold water and ethanol and air-dried. Anal Found: Pd, 50.01~ The Pd content of the other samples vary between 48.8 and 50.0 per cent. The infra-red spectrum is similar to that given in Fig. 2 except that the bands at 495 cm-x and 474 cm-x are reversed in relative intensity. After 6 months at room temperature, the band at 474 cm-1 had disappeared. ~11~We are pleased to acknowledge the financial support by National Science Foundation of an institutional grant, GP-1681, for the purchase of the Perkin-Elmer Model 521 Infra-red Spectrophotometer. c12~H. M. RANDALL,D. M. DENNISON,N. GINSBUROand L. R. WEBER,Phys. Rev. 52, 160 (1937).
Cis and trans isomers of dichlorodiamminepalladium (II)
25
3
4
5
WAVFtENGTH {MICRONS) 6 7
8
9
"
ZE
12
15
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20
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20 I 41300
30 40
i
', t "h i'
',
_~a0 I -
10
1971
41 3500
3(]00
2500
2000
1800
1600 1400 FREQUI~NCY ,',CM~i
1200
Fl~. 2.--Cis dichlorodiamminepalladium (II). Instrumental conditions the same as described in Fig. 1. The X-ray diffraction pattern is similar to that in Table I, but it also includes lines from Table 3. Microscopic examination (100 × ) reveals that the material consists of yellow needles, red "clumps" of much smaller needles, and occasional dark red octahedra. The product (0.1016 g) was suspended in 50 ml of ethanol containing 1'0 ml of conc. HCI. After 21 days the mixture was filtered and 0-0682 g (67.2%) of trans-Pd(NH3)2Cl= was recovered. The red filtrate gave only (NH4)~PdC14 upon evaporation. Both compounds were identified by X-ray diffraction. Under identical conditions trans-Pd(NHa)=C12 was recovered unchanged. Similar results were found with 0.2 N aqueous HCI. Trans-Pd(NH3)2Cl2treatedsimilarlywasrecoveredquantitatively unchanged. A 0.7210 g sample (previously washed with cold water and dried at 60°C in vacuum) was suspended for 2 hr in a solution prepared by mixing 75 ml of ethanol and 10 ml of pyridine. The residue was stirred with cold water leaving 0.0222 g of pink material which was shown to be [Pd(NHa)4I[PdCId by X-ray diffraction. Reaction of K2PdC14 with NH4C2HaO2 in ethanol~cis-Pd(NHa)2Cl2 Finely divided ammonium tetrachloropalladate was dissolved in 75-100-ml portions of anhydrous ethanol by heating the solvent to boiling. This was repeated until the total volume was 900 ml. Traces of the metal, resulting from reduction in the hot ethanol solution, were removed and the solution cooled to --15°C in an ice-salt slurry. A small aliquot was removed to determine approximate concentration of the solution. A yellow-green precipitate appeared rapidly upon addition of an excess of cold alcoholic solution of NH4C2H~O2. A 4:1 molar ratio NH4C2H~O~ to (NH4)~PdCl4 was used. The product was collected 15 min after mixing the solutions, washed with cold ethanol, and air-dried. The infra-red spectrum is similar to that given in Fig. 2 with bands at 495 (w), 476 (w), 327 (m), and 306 (m). Periodic recording of the spectrum showed that the band at 476 cm -1 decreased in intensity until it completely disappeared after 40 hr. Simultaneously, the broad band at 325 cm- 1 sharpened considerably. The X-ray diffraction was too diffuse for interpretation. An unweighed portion of the damp product was placed in a 5;0 ml Kjeldahl flask and decomposed with aqueous 50 ~/oKOH. The released NH3 was caught in saturated boric acid solution and titrated with standard HC1. The solution remaining in the Kjeldahl flask was carefully decanted from palladium metal which had settled to the bottom. The metal was thoroughly washed and washings added to the decantate. Chloride was determined by precipitation of silver chloride after acidification of the solution with nitric acid. The palladium was dissolved in a small amount of aqua regia, fumed 3 times with HC1 and precipitated and weighed as the dimethylglyoxime complex. Results: NH~, 0.315 mmoles; Pd, 0.162 mmoles; CI-, 0.325 mmoles. The ratio Pd:NH~:C1 is 1:2:2. A sample of the above product was suspended in 50 ml of ethanol containing 1 ml of conc. HC1. After standing for 12 hr at --20°C, the material was filtered, washed with cold ethanol, and air-dried. The infra-red spectrum is given in Fig. 2. As a result of this treatment, the spectrum is sharpened considerably as is the X-ray pattern which is given in Table 3. ]4
1972
R. LAYTON, D. W. SINK and J. R. DURIG
Anal Calcd. for Pd(NH3)2CI2: Pd, 50'38; C1, 33"54. Found: Pd, 50'45; C1, 33'49. Density, 2-84 g/em3. Reaction of Pd(NHz)aCl~ with HCI An aqueous solution of Pd(NH3)~C12 was prepared by dissolving PdCI~ in warm dilute HC1 and adding aqueous NHa until the precipitated [Pd(NH3)4][PdCId redissolved. The solution was cooled to 5-10°C and acidified with cold dilute HCI producing a bright yellow product. The material was filtered, washed with water and alcohol and dried in a vacuum. Anal Calcd. for Pd(NH3),CI~: Pd, 50.38; N, 13"26; CI, 33"54. Found: Pd, 50-28; N, 13.88; C1, 33-83. Density, 2.56/cms. The X-ray diffraction pattern is the same as given in Table 1 along with the strongest lines found for heated Pd(NH3)4PdC14(below). The infra-red spectrum is identical to that of the trans-Pd(NHs)~Cl2 Heated Pd(NHs)4CI~ When heated at ll0°C, the white Pd(NH3)4CI~ changed to yellow within 1 hr. After 12 hr the product gave an X-ray diffraction pattern and an infra-red spectrum identical to that obtained for the product of Pd(NH3)4C1, with HC1. Identical results are found when Pd(NH3)aClz is heated at 60°C in a vacuum. Anal Calcd. for Pd(NHs)2CI~: Pd, 50-38; C1, 33"54. Found: Pd, 50.23; C1, 33"38. Heated [Pd(NH3)~][PdC1,] Salmon pink [Pd(NH3)4][PdCId was heated at 170°C for 4½ days. During that time the colour changed to yellow without change in weight. The X-ray pattern shows the lines in Table 1. The infra-red spectrum is identical to that for the trans-Pd(NH3)~Cl2. Anal. Calcd. for Pd(NH3)2CI~: Pd, 50.38; CI, 33'54. Found: Pd, 50'17; CI, 33"27. X-ray diffraction data. The following data refer to lines remaining after the lines in Table 1 have been removed. The data included are in the following order: d(obs.), intensity, hkl and d(calc.) assuming a tetragonal cell with a = 12"7/~, c = 6"02/~. 7.70, 12, 100, 6"70; 6"19, 11, 001, 6.19; 4-63, 100, 110, 4"73; 3'79, 80, 111, 3.76; 2"87, 42, 012, 2.81; 2.48 (broad and diffuse), 11,121, 2.69; 2'44 (broad and diffuse), 25, 112, 2.59; 2"37, 30, 220, 2'37; 2.31, 25, 202, 2-27; 2'04, 9, 003, 2.06. Acknowledgement The authors gratefully acknowledge the financial support given this work by the National Science Foundation.
CIS A N D T R A N S ISOMERS OF DICHLORO-
DIAMMINEPALLADIUM
(I 1)
R . LAYTON,* D . W . SINK a n d J. R . DURIG Department of Chemistry, University of South Carolina, Columbia, South Carolina, U.S.A. (Received 21 October 1965; in revised form 30 December 1965) Abstract--The existence and characterization of cis and trans isomers of Pd(NH3)~CI2 have been re-investigated. A stable monoclinic trans compound has been prepared at low temperature. It has been shown that when trans-Pd(NH3)zCl~ is prepared at room temperature or above, it is a mixture of monoclinic and tetragonal dimorphs. The material previously reported to be cis-Pd(NH3)~Cl2 has been shown to be a complex mixture while the pure authentic cis-Pd(NH3)2C12 has been prepared and identified by its unique X-ray diffraction pattern and infra-red spectrum. INTRODUCTION
THREE distinct square planar palladium compounds with the empirical formula Pd(NH3)2C1~ have been reported. They are trans-Pd(NH3)2C12, cis-Pd(NH3)2C12, and the pink double salt, [Pd(NH3)4][PdC14]. The familiar yellow compound, prepared by acidifying a solution of Pd(NHahC1 z, was assigned the trans structure by DREWcl) on the basis of its chemical similarity to trans-Pt(NH3)zCl 2. In an early X-ray study of this compound, MANN identified several crystal modifications and habits, but the trans structure could not be definitely confirmed by his data. ~2) For some years the double salt, [Pd(NH3h][PdCI4] was mistaken for the cis isomer. (3) Eater GRUNBERGc4) reported that the "true" cis isomer could be prepared by treating (NH~)2PdC14 with NH~C~H30z in water. The cis assignment was based on the observation that the compound was different from the trans in solubility and conductivity and gave a rapid red coloration to acetone solutions of KI. The isomeric purity, the specific conditions for formation, and X-ray data were not then or subsequently reported. A thorough re-investigation of these compounds was initiated when the reported methods of preparing the eis and trans isomers of Pd(NH3),~C12 led to materials with astonishingly similar X-ray powder patterns which could not be indexed by MANN'S crystallographic data. Several infra-red investigations have been reported (5-8~ for * Present address: Saint Peter's College, Jersey City, New Jersey. ~a~ H. D. K. DREW and G. H. WYAT% J. chem. Soc. 56 (1934). ~2/F. G. MANN, D. CROWFOOT, D. C. GATTIKER and N. WOOSTER, J. chem. Soe. 1642 (1935). ~3~j. W. MELLOR, A Comprehensive Treatise on Inorganic arm Theoretical Chemistry, Vol. XV, pp. 663-665. Longman, Green, London (1936). ~4, A. GRUNBERG and A. SCHULMAN, Dokl. Akad. Nauk S S S R N.S. 215 (1933). ~:'~D. B. POWELL and N. SHEPPARD, J. chem. Soc. 3108 (1956). *~;)E. P. BERTIN, I. NAKAGAWA, S. MIZUSHIMA, T. J. LANE and J. V. QUAGLIANO, J. Am. chem. Sac. 80, 525 (1958). ~ R. C. LEECH, D. B. POWELL and N. SHEPPARD, Speetrochim. Acta 21, 559 (1965). s p. j. HENDRA and N. SADASlVAN, Speetrochim. Acta 21, 1271 (1965). 1965
1966
R. LAYTON,D. W. SINKand J. R. DtralO
trans-Pd(NH3)2Cl 2 but only in the study by BERTINet al. was the infra-red spectrum of the corresponding cis compound reported. These authors tr) indicate that the most distinguishing feature between the two spectra was a weak shoulder at 1265 cm -1 found on the high frequency side of the NH a symmetric deformation vibration. However, the most drastic change in the spectra of the two molecules should be found in the skeleton stretching vibrations which is beyond the frequency range of the previous infra-red investigations, tr) By assuming the NH 3 group to be a point mass or to be freely rotating, one readily notes that trans-Pd(NH3)2Cl 2 belongs to the point group D2h while cis-Pd(NHa)2C1 z has only Cz~ symmetry. With the neglect of lattice coupling, symmetry dictates that one Pd-N stretching frequency should be found for the trans isomer while both a symmetric and antisymmetric Pd-N stretching vibration are expected for the cis isomer. Likewise, in the palladium chloride stretching region only the antisymmetric stretching frequency should be infra-red active for the trans-Pd(NH3)2Cl z but both the symmetric and antisymmetric Pd-Cl stretching vibrations should be observed in the infra-red spectrum of the cis isomer. With these expectations in mind we investigated the infra-red spectra and X-ray powder patterns of cis and trans isomers of Pd(NH3)2CI 2 prepared by previously reported methods.
DISCUSSION OF RESULTS The results of this study indicate that the cis-Pd(NHa)2C12 reported by GRUNBERG is in reality a mixture of cis and trans Pd(NH3)zCI2 along with smaller amounts of [Pd(NHz)4][PdCla] and (NH4)2PdC14. This conclusion has been reached by comparing X-ray and infra-red data of the pure components to that of GRUNBERG'Sproduct. This required the crystallographic identification of the trans-Pd(NHz)zC12 polymorphs. Trans-Pd(NHa)2C12 The trans isomer has been found to exist in at least two crystal modifications: a low temperature monoclinic form and a high temperature tetragonal modification. Pure monocllnic trans-Pd(NH3)2C12 was prepared by slow crystallization from an aqueous solution of (NH~)2PdC14 and (NH4)2CzHzO 2 at 5°C. The X-ray powder data for this compound are given in Table 1. These lines can be adequately indexed using the monoclinic cell parameters given in Table 1. Supporting this indexing is the recent work by PORAI-KoSHITSta) on the corresponding platinum compound (trans-Pt(NH3)2Cl2) which was found to be monoclinic with a = 5.46 A, b = 6.05 A, c = 8.07 A, fl-----93o47' with two molecules per unit cell. The calculated density for two molecules per unit cell is 1.86 g/cm3. The experimental density is 2.06 g/cm3. This value is high, possibly due to some contamination by the tetragonal modification which is more abundant at higher temperatures (see section on mixtures). The infra-red spectrum is given in Fig. 1 and the frequencies and assignments are given in Table 2. Neglecting lattice coupling, the spectrum is typically trans with one Pd-N stretching vibration at 496 cm -1 and one Pd-C1 stretching frequency at 333 cm -~. In the region above 700 cm -1 the spectrum compares quite favourably with that reported previously, t5,6) A very weak shoulder is noted on the 1247 cm -1 band and the central maximum is somewhat lower than that reported by BERTIN et al., tn) but compares quite favourably with the infra-red results reported by POWELL and tg~ M. A. PORM-KOSHITS,Trudp Inst. Kristall. 229 (1954).
Cis and
trans isomers of dichlorodiamminepalladium
(II)
1967
TABLE 1.--X-RAY DATA FOR traIIs-DICHLORODIAMMINEPALLADIUM (II) Monoclinic modification Cell parameters: a = 6.00/~,, b = 6.24/~, c = 10.1 A, f4 = 95 ° 20'
Line
I/lo
hkl
d(obs.) (~)
d(calc.) (~)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
5 100 2 1 31 1 1 1 1 1 1 1 1 5 1 1 1 1
100 010 002 111 112, 112 200 210, 210,210 121,004 0i4, 01~ 023 220 22~ 024 030 204 031,124 130 205,203
6'18 5'93 5"02 3"88 3'24 3.06 2'76 2"50 2'43 2"35 2"14 2"06 2-01 1"98 1"94 1"92 1"91 1'75
6-24 5"98 5'03 3-87 3-17 3'12 2"77 2'51 2'40 2"34 2"16 2-04 2.02 1"99 1.96 1'92 1-90 1'75
SHEPPARD(5) on a yellow powder sample. The higher frequencies also compared quite favourably with the bands reported by POWELLand SHEPI'ARD.(5) The tetragonal modification has not been obtained in the pure state. However, the existence of another modification of trans Pd(NH3)2C12 has been demonstrated by heating [Pd(NH3)4][PdC14] at 170 °. After 140 hr, the weight is unchanged and the infra-red spectrum (see Fig. 1) is identical to monoclinic t r a n s Pd(NH3)2C12. The X-ray pattern, which had rather broad and diffuse lines, included ten lines which could not be indexed with the monoclinic cell parameters. However, these ten lines can be satisfactorily indexed, considering the quality of the pattern, using tetragonal 25
3
4
S f z u
5
~ . ~ - ~
WAVELENGTH IMJCRONSI 6 7 ~---
_
/- -
~
,
8
9
~---
/
10
12
15
/ ~ . ~ J ~ ,
20
x~'~-'~-~
.
30 40
"-'~-~,
/
]
,,f
i I,
~-
,[
i
i
'11 r
I 3000
2500
2000
1800
1600 1400 FREQUENCY (CM~i
1200
I000
800
6O0
4OO
FIG. 1.--Trans dichlorodiamminepalladium (II). The spectrum was recorded at 24°C with a frequency scan time of 85 cm-1/mm, chart speed of 18 cm-1/mm above 2000 cm -~ and a scan time of 50 cm-1/mm, chart speed of 4 c m - t / m m below 2000 cm -1. The amplifier gain was 5.0 and the normal slit programme was employed.
1968
R. LAYTON,D. W. SINK and J. R. DURIG TABLE2.--INFRA-RED FREQUENCIES FOR trans- AND CiS-DICHLORODIAMMINEPALLADIUM(II) Trans-Pd(NHa)2Cl2
Cis-Pd(NH3)~C12
frequencies (cm-1)
frequencies (cm-1)
3320 3240 3181 1720 vb 1605 1460 vb 1255 sh 1247 788 sh 753 496
3314 3237 3177 1700vb 1610 1480 vb 1269 1248 788 sh 752 495 476 327 306
333
Assignment NH3 stretching NH8 stretching NH3 stretching NH3 antisymmetric deformation NH3 symmetric deformation NHa rocking Pd-N antisymmetric stretching Pd-N symmetric stretching Pd-CI antisymmetric stretching Pd-C1 symmetric stretching
parameters (a = 6.70, b = 6.19/~). While the existence o f a tetragonal f o r m has been previously reported, ~2) these cell parameters are unique. Extended heating (6 weeks) o f [Pd(NH3)4][PdC14] produces another set of lines which could not be identified or indexed. The infra-red spectrum still corresponded to trans-Pd(NH3)2C12. Cis-Pd(NH3)2C12 W h e n K2PdC14 is treated with (NH4)2C2H303, both in anhydrous ethanol, a yellow precipitate is formed. The material corresponds to Pd(NHz)2C12 and has the unique X - r a y diffraction pattern given in Table 3. These lines can be indexed using TABLE3.~X-RAY DATA FOR ciS-DICHLORODIAMM1NEPALLADIUM(II) Cell parameters: a = 12"7/~, c = 6"02/~ Line
I/Io
hkl
d(obs.)
d(calc.)
1 2 14 3 4 5 6 7 8 9 10 11 12 13
47 100 35 51 27 42 20(B) 33 33 12 15 5 5 5
200 001 111 131 400 140 141 500,340 222 051 052,342 233 003 333
6.36 6.02 5.01 3.34 3-21 3.11 2.77 2-53 2.51 2-35 1.94 1.73 2.01 1.66
6.36 6.02 5.00 3.34 3.18 3.08 2.74 2.54 2-51 2-34 1.94 1.74 2.01 1.67
tetragonal cell parameters with the unit cell containing eight molecules (density; calc.; 2.86; found, 2.84). The infra-red spectrum is also unique, showing two
Cis and trans isomers of dichlorodiamminepalladium(II)
1969
bands in both the Pd-N stretching region (495 and 476 cm -1) and the Pd-C1 stretching region (327 and 306 cm -1) as dictated by the C2, symmetry of the cis isomer. Slight changes are also noted in the high frequency portion of the spectrum. The NH 3 symmetric deformation vibration, found at 1248 cm -1, has an additional pronounced band at 1269 cm -1. Weak absorption is found on both the high and low frequency side of the NH a antisymmetric deformation vibration at 1610 cm-L Similar absorption on the wings of the corresponding band of the trans complex has been attributed to partially hindered rotation of the - - N H z group. (7) The same explanation can account for the breadth of the 1610 cm -1 band in the cis complex but no temperature studies were made to substantiate this explanation. An alternative explanation has been given by NAKAMOTOet al, (1°) for the broad bands of the NH a antisymmetric deformation vibration in dihalogenodiammineplatinum (II) complexes. The splitting observed in the platinum analogues ranged from 140 to 65 cm -1 and has been attributed the hydrogen-5d-electron and ligand-ligand interactions. As pointed out by these authors the 4d-orbitals of the palladium atom are spatially less extensive but there still should be sufficient overlap to account for the weak splitting noted in the palladium compounds. The bands are very broad but are extremely pronounced in the concentrated pellets. Currently we see no way of distinguishing between the two possible explanations for these broad shoulders. Freshly prepared eis-Pd(NHa)2C12 isomerizes to trans-Pd(NHa)2C12 within 40 hr as evidenced by the change of the infra-red absorption to the spectrum characteristic of the trans isomer. However, the eis isomer can be stabilized by suspending the solid in ethanolic HC1 at --20°C for 12 hr. After the compound was isolated from this medium, the infra-red spectrum and X-ray pattern remained unchanged for at least 2 months. Mixtures
When trans-Pd(NHa)2C12 is formed at temperatures above 5°C, or rapidly separated from solution, the product is a mixture of the monoelinic and tetragonal forms. The X-ray diffraction patterns are a composite of those found for monoclinic and tetragonal trans-Pd(NHa)2Cl ~ while the infra-red spectra are identical to that shown in Fig. 1. The cis isomer of Pd(NHa)zC12 is reported to precipitate from an aqueous solution of (NH4)2PdC1 ~ and NH4C2HaO 2. Since the conditions were not specified in the original paper, the preparation was attempted at different temperatures and various mole ratios of starting materials. At low temperatures (0-5°C) the trans isomer was obtained (see above). At room temperature a product was obtained corresponding to GRUNBERG'Sdescription in about 70 per cent yield with a 4-10 mole excess of NH4C2HaO z. The experimental evidence discussed below clearly demonstrates that this material is a mixture with the approximate composition of 60-70%, trans-Pd(NHa)2Cl2, 20-30% cis-Pd(NH3)oC12, 5-10% Pd(NH3)4PdC14 and 0.1-1 !'~, (N H4)2PdCI4. All the lines in the X-ray powder pattern are accounted for by monoclinic and tetragonal trans-Pd(NH3)2CL., cis-Pd(NH3).~C12 and [Pd(NH3)4][PdC14]. The minor component, (NH~)zPdC14, cannot be detected in the X-ray powder pattern, but was plainly visible under the microscope (100 ×) as red clumps dispersed in the extremely (10)
K. NAKAMOTO,P. J. MCCARTHY, J. FUJITA,R. A. CONDRATEand G. T. BEHNKE,Inorg. Chem. 4, 36 (1965).
1970
R. LAYTON,D. W. SINK and J. R. DtrRIG
fine yellow needles. T h o r o u g h washing with cold water r e m o v e d the clumps a n d (NHa)zPdC14 was recovered f r o m the washings by e v a p o r a t i o n . The a m o u n t of cis-Pd(NH3)2C12 was estimated by treating the mixture with alcoholic HCI for several days. U n d e r these conditions, the cis isomer was converted to (NH4)2PdC14 which was then recovered a n d weighed. The trans isomer did n o t react. The p i n k salt, Pd(NH3)4PdC14, was f o u n d as a residue when the mixture was treated with a q u e o u s pyridine solutions. The infra-red spectrum of the mixture was similar to that o b t a i n e d for the cis isomer, i n that it h a d two b a n d s in the P d - N stretching region, b u t the relative intensities o f the b a n d s were reversed. This is because b o t h the cis a n d trans isomers have a b s o r p t i o n m a x i m a at 495 cm -1. I n the Pd-C1 stretching region, there was only a single b r o a d b a n d observed. EXPERIMENTAL Materials. All materials, except the palladium complexes were reagent grade and used without further purification. Analysis. Palladium was determined by hydrogen reduction for solid samples and precipitation of the dimethylglyoximate from solution samples. Nitrogen was determined by the Dumas and Kjeldahl methods and chloride as AgC1. X-ray data. Powder patterns were obtained with a Norelco (North American Phillips) generator, wide range diffractometer, and standard Debye-Scherrer Camera (114 cm) using either a copper or chromium target tube. Infra-red spectra. The infra-red spectra were recorded from 4000 to 250 cm-1 and in some cases from 600 to 250 cm-1 using a Perkin-Elmer Model-521 SpectrophotometerJ TM Above 600 cm-I the spectrophotometer was calibrated using the usual materials while below 600 cm-1 atmospheric water vapour and the assignments of RANDALLet al. ~2~ were used. The samples were examined in KBr disc and all spectra were checked as Nujol nulls.
Aqueous reaction of K2PdC14 with NH4C2HaO2 at 5°C--trans-Pd(NH3)zCl~ Solutions of K2PdC14 (1"2993 g in 100 ml of water) and NH4CaHsO~ (1.2812 g in 30 ml of water) were cooled to 5°C, mixed, and placed in a freezer at 5°C. Yellow crystals began to form after 3 hr. After 24 hr the product was filtered, washed with cold water and air-dried. The yield was 0.466 g, or 60 per cent based on K~PdC14. Anal Calcd. for Pd(NHa)2C12: Pd, 50"38; CI, 33"54. Found: Pd, 50'29; C1, 33"90. Density, 2'06 g/cm 3. The infra-red spectrum is given in Fig. 1 and X-ray diffraction data are presented in Table 1. Aqueous reaction of K2PdCI~ with NH4C2HzO2 at room temperature A number of reactions were run to define the conditions for the preparation of cis-Pd(NHs)2C12 according to GRUNBERO.t4~ The following is typical while the others differed only in that the mole ratio of KzPdC14 to NH4C2H~O~ varied from 1:0"51 to 9:1. Potassium tetrachloropalladate (4.00 g, 0"0123 moles) was dissolved in 100 ml of water and 3"80 g (0.049 moles) of NH4C2H30~ was added with stirring. A dull yellow precipitate began to form almost immediately and was collected after 1 hr. The product was washed successively with cold water and ethanol and air-dried. Anal Found: Pd, 50.01~ The Pd content of the other samples vary between 48.8 and 50.0 per cent. The infra-red spectrum is similar to that given in Fig. 2 except that the bands at 495 cm-x and 474 cm-x are reversed in relative intensity. After 6 months at room temperature, the band at 474 cm-1 had disappeared. ~11~We are pleased to acknowledge the financial support by National Science Foundation of an institutional grant, GP-1681, for the purchase of the Perkin-Elmer Model 521 Infra-red Spectrophotometer. c12~H. M. RANDALL,D. M. DENNISON,N. GINSBUROand L. R. WEBER,Phys. Rev. 52, 160 (1937).
Cis and trans isomers of dichlorodiamminepalladium (II)
25
3
4
5
WAVFtENGTH {MICRONS) 6 7
8
9
"
ZE
12
15
', /
20
[')j
20 I 41300
30 40
i
', t "h i'
',
_~a0 I -
10
1971
41 3500
3(]00
2500
2000
1800
1600 1400 FREQUI~NCY ,',CM~i
1200
Fl~. 2.--Cis dichlorodiamminepalladium (II). Instrumental conditions the same as described in Fig. 1. The X-ray diffraction pattern is similar to that in Table I, but it also includes lines from Table 3. Microscopic examination (100 × ) reveals that the material consists of yellow needles, red "clumps" of much smaller needles, and occasional dark red octahedra. The product (0.1016 g) was suspended in 50 ml of ethanol containing 1'0 ml of conc. HCI. After 21 days the mixture was filtered and 0-0682 g (67.2%) of trans-Pd(NH3)2Cl= was recovered. The red filtrate gave only (NH4)~PdC14 upon evaporation. Both compounds were identified by X-ray diffraction. Under identical conditions trans-Pd(NHa)=C12 was recovered unchanged. Similar results were found with 0.2 N aqueous HCI. Trans-Pd(NH3)2Cl2treatedsimilarlywasrecoveredquantitatively unchanged. A 0.7210 g sample (previously washed with cold water and dried at 60°C in vacuum) was suspended for 2 hr in a solution prepared by mixing 75 ml of ethanol and 10 ml of pyridine. The residue was stirred with cold water leaving 0.0222 g of pink material which was shown to be [Pd(NHa)4I[PdCId by X-ray diffraction. Reaction of K2PdC14 with NH4C2HaO2 in ethanol~cis-Pd(NHa)2Cl2 Finely divided ammonium tetrachloropalladate was dissolved in 75-100-ml portions of anhydrous ethanol by heating the solvent to boiling. This was repeated until the total volume was 900 ml. Traces of the metal, resulting from reduction in the hot ethanol solution, were removed and the solution cooled to --15°C in an ice-salt slurry. A small aliquot was removed to determine approximate concentration of the solution. A yellow-green precipitate appeared rapidly upon addition of an excess of cold alcoholic solution of NH4C2H~O2. A 4:1 molar ratio NH4C2H~O~ to (NH4)~PdCl4 was used. The product was collected 15 min after mixing the solutions, washed with cold ethanol, and air-dried. The infra-red spectrum is similar to that given in Fig. 2 with bands at 495 (w), 476 (w), 327 (m), and 306 (m). Periodic recording of the spectrum showed that the band at 476 cm -1 decreased in intensity until it completely disappeared after 40 hr. Simultaneously, the broad band at 325 cm- 1 sharpened considerably. The X-ray diffraction was too diffuse for interpretation. An unweighed portion of the damp product was placed in a 5;0 ml Kjeldahl flask and decomposed with aqueous 50 ~/oKOH. The released NH3 was caught in saturated boric acid solution and titrated with standard HC1. The solution remaining in the Kjeldahl flask was carefully decanted from palladium metal which had settled to the bottom. The metal was thoroughly washed and washings added to the decantate. Chloride was determined by precipitation of silver chloride after acidification of the solution with nitric acid. The palladium was dissolved in a small amount of aqua regia, fumed 3 times with HC1 and precipitated and weighed as the dimethylglyoxime complex. Results: NH~, 0.315 mmoles; Pd, 0.162 mmoles; CI-, 0.325 mmoles. The ratio Pd:NH~:C1 is 1:2:2. A sample of the above product was suspended in 50 ml of ethanol containing 1 ml of conc. HC1. After standing for 12 hr at --20°C, the material was filtered, washed with cold ethanol, and air-dried. The infra-red spectrum is given in Fig. 2. As a result of this treatment, the spectrum is sharpened considerably as is the X-ray pattern which is given in Table 3. ]4
1972
R. LAYTON, D. W. SINK and J. R. DURIG
Anal Calcd. for Pd(NH3)2CI2: Pd, 50'38; C1, 33"54. Found: Pd, 50'45; C1, 33'49. Density, 2-84 g/em3. Reaction of Pd(NHz)aCl~ with HCI An aqueous solution of Pd(NH3)~C12 was prepared by dissolving PdCI~ in warm dilute HC1 and adding aqueous NHa until the precipitated [Pd(NH3)4][PdCId redissolved. The solution was cooled to 5-10°C and acidified with cold dilute HCI producing a bright yellow product. The material was filtered, washed with water and alcohol and dried in a vacuum. Anal Calcd. for Pd(NH3),CI~: Pd, 50.38; N, 13"26; CI, 33"54. Found: Pd, 50-28; N, 13.88; C1, 33-83. Density, 2.56/cms. The X-ray diffraction pattern is the same as given in Table 1 along with the strongest lines found for heated Pd(NH3)4PdC14(below). The infra-red spectrum is identical to that of the trans-Pd(NHs)~Cl2 Heated Pd(NHs)4CI~ When heated at ll0°C, the white Pd(NH3)4CI~ changed to yellow within 1 hr. After 12 hr the product gave an X-ray diffraction pattern and an infra-red spectrum identical to that obtained for the product of Pd(NH3)4C1, with HC1. Identical results are found when Pd(NH3)aClz is heated at 60°C in a vacuum. Anal Calcd. for Pd(NHs)2CI~: Pd, 50-38; C1, 33"54. Found: Pd, 50.23; C1, 33"38. Heated [Pd(NH3)~][PdC1,] Salmon pink [Pd(NH3)4][PdCId was heated at 170°C for 4½ days. During that time the colour changed to yellow without change in weight. The X-ray pattern shows the lines in Table 1. The infra-red spectrum is identical to that for the trans-Pd(NH3)~Cl2. Anal. Calcd. for Pd(NH3)2CI~: Pd, 50.38; CI, 33'54. Found: Pd, 50'17; CI, 33"27. X-ray diffraction data. The following data refer to lines remaining after the lines in Table 1 have been removed. The data included are in the following order: d(obs.), intensity, hkl and d(calc.) assuming a tetragonal cell with a = 12"7/~, c = 6"02/~. 7.70, 12, 100, 6"70; 6"19, 11, 001, 6.19; 4-63, 100, 110, 4"73; 3'79, 80, 111, 3.76; 2"87, 42, 012, 2.81; 2.48 (broad and diffuse), 11,121, 2.69; 2'44 (broad and diffuse), 25, 112, 2.59; 2"37, 30, 220, 2'37; 2.31, 25, 202, 2-27; 2'04, 9, 003, 2.06. Acknowledgement The authors gratefully acknowledge the financial support given this work by the National Science Foundation.