J. Phys. Chem. 1981, 85,2393-2398
2393
1. Thermal Decomposltfon and Interaction with Chemistry of R u ( N H ~ ) ~in~Zeolites. + Oxygen, Water, arid Nitric Oxide Jos J. Verdonck, Robert A. Schoonheydt,’ and Peter A. Jacobs Centrum voor Oppervlaktescheikundeen ColloMale Schelkunde, Katholieke Unlversltelt Leuven, De Croylaan 42, 8-3030Leuven (Heverlee), tBeigium (Received: February 10, 1981; In Final Form: April 14, 1981)
As derived from in situ W-visiblenear-IR reflectance and IR transmission spectroscopy, Ru(NH3)2+exchanged in the supercages of zeolites X and Y hydrolyzes in vacuo and in the presence of zeolite-sorbed water to (Ru-red). In air a mixture of Ru-red and [ R U ( N H ~ ) ~ O Hand ] ~ +[(NH3)5RuORu(NH3)40R~(NH3)5]6+ [(NH3)5RuORu(NH3)40R~(NH3)5]7+ (Ru-brown)is obtained. These complexes are thermally unstable, and 2(01,0H,H20)4,3. Oxygen suppresses the formation above 373 K the only identifiable complex is RU(NO)(NH~)~ of the trimeric Ru complexes and interacts with Ru(NH3)pat 373 K or higher to form the nitrosyl complex. NO rea& at room temperature with Ru(NH3)2+to form [RU(NH~)&]~+, [RU(NH~)~NO]~+, and NH4+. There are slight differences between X and Y zeolites due to differences in basicities of the supercages, X being more basic than Y. In both cases after heating in vacuo or in NO the same nitrosyl complex is obtained as in other atmospheres. This chemistry of R u ( N H ~ )in~ ~ a zeolite + matrix is the same as its aqueous solution chemistry.
Introduction Supported ruthenium catalysts have gained considerable interest from the scientific community in recent years. Ru metal particles stabilized on Y-type zeolites were found to be active as well as selective catalysts for energy-related reactions such as the Fischer-Tropsch synthesis and the water-gas shift conversion.l4 Usually, the preparation of Ru metal containing zeolites involves the exchange of an ammine complex and its decomposition and/or reduction to the catalytic form.5 I:n the course of this process intermediates are formed which control the reduction to metallic particles and which may have catalytic activity on their own. Such an intermediate carbonyl complex was found to be active as a low-temperature water-gas shift catalysts4 Zeolites exchanged with hexaaquoruthenium(II1) and pentammine(dinitrogen)ruthenium(II) have been characterized by IR, near-IR-visible-UV, and Mossbauer spectroscopy.gg It has been firmly established that pentaammine(dinitrogen)ruthenium(II) in air oxidizes to Ru-red with formation of NH4+.9Heat treatment in vacuo gives activated Ru, possibly in the form of small clusters such as Runoor RU,,+.~V~ The redox behavior of liu(NH3):+ in the supercages of Y-type zeolites has also been extensively ~tudied.~JO However, the characterizationof the various Ru complexes, formed in the course of the catalyst activation, has not been performed. We report here on the activation of Ru(NH~)~ in~the + supercages of X- and Y-type zeolites (1) Nijs, H. H.; Jacobs, P. A.; IJytterhoeven, J. B. J.Chem. Soc., Chem. Commun. 1979.180. (2)Jacobs, P.-A,; Verdonck, J.; Nijs, R.; Uytterhoeven, J. B. Adu. Chem. Ser. 1979,No. 178,15. (3)Jacobs, P. A. In “Catalysin by Zeolites”;Imelik, B.,Naccache, C., Ben Taarit, Y.; Vedrine, J., Coudurier, G., Praliaud, H., Eds.; Elsevier: Amsterdam, 1980;p 293. (4)Verdonck, J. J.; Schoonheydt, R. A.; Jacobs, P. A. h o c . Int. Congr. Catal. 7th 1980,Paper B16. (5) Verdonck, J. J.; Jacobs, P. A.; Genet, M.; Poncelet, G. J. Chem. Soc., Faraday Tram. 1 1980,76, 403. (6) Coughlan, B.;Carroll, W. M.; McCann, W. A. Chem. Ind. (London) 1976,521.(7) Leing, K. R.; Leubner, R. L.; Lunsford, J. H. Inorg. Chem. 1975, 14,1400. (8)Clausen, C. A., III; Good, M. L. Inorg. Chem. 1977,16,816. (9)Madhusudhan,C. P.; Patil, M. D.;Good, M. L. Inora. Chem. 1979, 18,2384. (IO) Pearce, J. R.; Mortier, W. J.; Uytterhoeven, J. B.J. Chern. Soc., Faraday Tram. 1 1979,75,1395.
0022-3654/81/2085-2393$01.25/0
TABLE I: Cation Content of Hexaamineruthenium(II1)-ExchangedZeolites sample RuNa-Y-40 RuNa-X-10 RuNa-X-3 0 RuNa-X- 50
Ru, mequiv g1.75 0.56 1.75 2.91
Na, mequiv g2.7 2 5.76 4.27 2.93
’
in vacuo and in oxygen, water, and nitric oxide atmospheres. The transformations were followed by UV-visible-near-LR reflectance and IR transmission spectroscopy.
Experimental Section Samples and Materials. Na-Y and Na-X zeolites with 56 and 86 A1 atoms per unit cell, respectively, were from Union Carbide. They were pure phases as derived from their X-ray diffractograms. Comparison of the peak intensities to those of standard samples revealed an excellent degree of crystallinity. The samples were stirred overnight in 1N NaC1, washed CP-free, dried at room temperature, and stored in a desiccator over a saturated NH&l solution. They were exchanged with Ru(NH3)&13solutions containing the stoichiometric amounts of complex to obtain exchange levels between 0 and 50% of the cation exchange capacity. The exchange was performed overnight at room temperature with a so1id:liquid ratio of 1 g dm”. The samples were washed Cl--free, dried in air at room temperature, and stored as indicated for the Na forms. Ru and Na were determined with atomic absorption spectrometry after HF/H2S04dissolution of the zeolite. Table I shows typical results, illustrating the quantitative uptake of the complex from solution up to exchange levels of 50%. The number after the sample symbol is the percent exchange. Samples were made in small aliquots and used as soon as possible after preparation, because the hexaamine was unstable especially on X-type zeolites. Ru(NH3)&13was from Strem Chemicals, and ita purity checked by visible-UV spectroscopy prior to use. The gases O2and NO were ultrahigh-purity gases from Matheson. Before use NO was further purified by passing it through a liquid-air trap. The reflectance reference B&04 was a Merck White Standard DIN5033. RefEectance Spectroscopy. Reflectance spectra in the range 2000-210 nm were recorded on a Cary 17 instrument with type I reflectance attachment and BaS04 as a ref@ 1981 American Chemical Society
2394
The Journal of Physical Chemistry, Vol. 85,No.
IS, 1981
Verdonck et ai.
TABLE 11: SDectroscoDs of Ru ComDlexes UV-visible-near-IR band maxima, cm-' ( n m ) complex
obsd 3 8 000 30 500 1 2 830 18 200 2 5 600 38 750 3 3 000
(265) (325) (780) (550) (390) (258) (300)
21 740 ( 4 6 0 ) 29 4 0 0 ( 3 4 0 ) 4 5 450 ( 2 2 )
[Ru(NHJ,N,O]
2+
IR
lit.
ref
cm-'
assignment
ref
36 400 ( 2 7 5 ) 31 300 ( 3 1 9 ) 13 200 ( 7 5 8 ) 18 800 ( 5 3 2 ) 26 7 0 0 ( 3 7 5 ) 40 800 ( 2 4 5 ) 33 900 (295) 21 100 (474) 24 000 ( 4 1 7 ) 30 400 ( 3 2 9 ) 3 3 200 ( 3 0 1 ) 4 5 450 ( 2 2 0 ) 3 5 600 ( 2 8 1 ) 27 200 ( 3 6 8 ) 36 7 6 0 ( 2 7 2 ) 42 920 (233)
13
1360
&,(HNH)
14
17 13
1913-1925
u(N0)
21
21
2100 1855
u(N-N) (NO)
18 22
21 20
1169-1202 2250
u(N0,)
22 20
16
u
("0)
1 0 IO'j
-
100:
a
v
2
1 Flgure 1.- Quartz reflectance flow cell: (1)greaseless stopcocks; (2) Suprasil window.
erence. The spectra were tape-recorded and computerprocessed to obtain the Kubelka-Munk function against wavenumber (cm-l) after subtraction of the base lineal1 Spectra in the range 700-210 nm were obtained with the parent hydrated Na form of the zeolite as the reference and plotted as such. The vacuum treatment of the samples was performed in a quartz cell with Suprasil window and pretreatment balloon.12 The amount of sample used was -3 g. The samples were evacuated in the range 295-573 K in steps of -25 K below 373 K and in steps of -50 K above 373 K. At each temperature the evacuation time was 86.4 ks. The flow treatments were conducted in the U-type quartz cell with Suprasil window shown in Figure 1. A flow of 0.243 cm3s-l was conducted over the sample. The temperature range studied was 295-573 K with intervals of 50 K. The treatment time at each interval was 3.6 or 7.2 ks. Room-temperature reflectance spectra were recorded against hydrated Na-Y between 700 and 200 nm. The spectra were not converted to the Kubelka-Munk function but plotted as such. Infrared Spectroscopy. Self-supporting wafers of the samples (-5 mg cm-2) were prepared and fitted in a homemade IR cell allowing in situ pretreatment in vacuo and gas adsorption. The IR spectrometer was either a (11) KortIim, G. "Reflectance Spectroscopy"; Springer: West Berlin,
1969. (12) Velghe F.; Schoonheydt, R. A.; Uytterhoeven, J. B. Clays Clay Miner. 1977, 25, 375.
J
1u2
1631 , , _ ,
5
2 00 ,
12 8
,
,
,
,
20
,
,
,
! :
278
300 nm
, , , , . . , . ~ , , , 1, , , . !
35
4;s
1, 10-3,'cm.l
Flgure 2. Reflectance spectra of Ru-Y zeolites: (1) Ru-Y-20, airdried; (2) evacuated at 319 K; (3)Evacuated at 338 K; (4) evacuated at 373 K; (5) evacuated at 401 K; (6) Ru-Y-40 evacuated at 348 K; (7 and 8) Ru-Y-40 evacuated at room temperature and at 323 K, respectively (spectra recorded on nm scale with hydrated Na-Y as reference; no conversion to Kubelka-Munk function was performed).
Beckman IR 12 instrument or a Perkin-Elmer 580B. Both were used in the double-beam mode in either absorption or transmission. The spectral range between 1200 and 2500 cm-' was scanned. Gain and slit width were adjusted to maximum resolution (-1 cm-l at 1800 cm-'). Spectra were recorded of the samples as such and after evacuation in steps of 50 K up to 553 K. The samples were kept at each temperature for 3.6 ks before recording the spectra. For the decomposition in 02,H20, and NO atmospheres, the samples were kept at each temperature for 1.8 ks prior to recording the spectra. Typical pressures were 6.67 X lo3 Pa for NO and O2 and the room-temperature vapor pressure of water (2.67 X lo3 Pa). Results The spectroscopic characteristics of the Ru complexes which come into play are summarized in Table 11. Vacuum Decomposition of Ru(NH3)G3+in FaujasiteType Zeolites. A freshly prepared R u ( N H ~ ) ~ -sample Y has a reflectance spectrum characteristic of R u ( N H ~ ) ~ ~ +
RU(NHJ:+
The Journal of Physical Chemistry, Vol. 85, No. 16, 1981 2395
in Zeolites
1
I
IT
IPd
I
TABLE 111: Intensity Decrease of the NH Overtone
in Ru(NH,),-Y-20 Z', K 319 338 37 3 401 a Assumed value.
F(Rm)
NH,:Ru
4.2 x 2.7 X lo-' 1 . 7 X lo-' 1.5 X lo-'
6a 3.9b 2.4
2.1
The Theoretical value for Ru-red is
4.7.
1
A
w;,,+ v, I
2000
1800
"
1400
1200
Cm-1
Flgure 3. Room-temperature IR spectra of Ru-Y-40: (a) evacuated at room temperature; (b) evacuated at 348 K for 3.6 ks; (c) evacuated at 443 K for 3.6 ks; (d) evacuated at 498 K for 3.6 ks; (e) evacuated at 553 K for 1.8 ks.
(Figure 2). The typical band system comprises a broad band at 38 000 cm-' (265 nm) with a shoulder around 30 500 cm-l(325 nm). These bands are believed to be respectively a LMCT band and a d-d band but the assignment is still tentati~e.'~When recorded against BaS04the resolution is poor at small exchange levels. With hydrated Na-Y as a standard, both bands are well resolved (spectrum 7). In the near-IR the usual combination and overtone bands of H 2 0 and NH3 are clearly visible. The characteristic symmetric deformation of coordinated NH3 in Ru(NH3)(+, shown in Figure 3, is at 1360 cm-', in good agreement w t h nm the literature value.14 The complex is unstable. When the sample is left in the air for several weeks (a matter of FI ure 4. Reflectance spectra of Ru-Y-40 in a flow of O2 (0.243 cm' s- ): (1) 323 K for 7.2 ks; (2) 373 K for 7.2 ks; (3) 423 K for 7.2 days for Ru(NH&-X), the color changes to pink and wine ks; (4) 473 K for 7.2 ks. red. The decomposition process, giving rise to these color changes, is accelerated by evacuation and gentle heating The numbers are upper limits because no correction was a t 330-340 K. The accompanying spectral changes are made for NH4+. Thus, even at the maximal Ru-red conshown in Figures 2 and 3. Thus, the 38000-cm-l band centration, the NH3:Ru ratio is lower than 4.7, indicating broadens because of low-frequency and high-frequency that more strongly deamminated complexes are present shoulders, and its maximum shifts to 36000 cm-l(278 nm, on the surface. The conclusion is that the 32000- and spectrum 8). Upon heating the spectrum of Ru-red, 38 750-cm-' bands are due to lattice-bonded Ru complexes [ (NH3)5R~11*OR~N(NH3)40R~111(NH3)5]6+, is generated with one or two NH, in the coordination sphere. These (spectrum 3), giving the sample its characteristic wine red residual coordinated NH3 molecules have their symmetric color. The observed band maxima of Ru-red are sumstretching deformation at 1330 cm-l (Figure 3). The libmarized in Table I1 and agree with published literature erated NH3 is converted either to NH4+(1457 cm-') or to values.15J6 There are additional bands in spectrum 3 of NO (1875 cm-l). This NO is coordinated, forming a RuFigure 2: a shoulder at 8700 cm-' (1150 nm), absent on (11)-NO+ moiety. Whereas the reflectance spectra are Ru(NH,)~-Y-~O, and a band around 32000 cm-l(315 nm). almost featureless above 400 K, the IR spectra show that The latter is resolved into two components on Ru(Nevacuation up to -573 K is required to eliminate all of H3),-Y-40 (33000 cm-' (300 nm) and 35500 cm-' (282 nm)) the NH3, NO, and NH4+. with a supplementary band at 43250 cm-l(230 nm). This Interaction with 02,H 2 0 ,and Air. Heating an IR film is shown in spectrum 6 of Figure 2. of Ru(NH,),-Y or -X in O2 or in air produces IR spectra It is evident that several Ru complexes are present, but remarkably similar to those of Figure 3. Thus, the 1360a quantitative estimate is not possible. In any case, Ru-red cm-' band of R u ( N H ~ )is~ shifted ~+ to lower wavenumbers is completely destroyed by evacuation at 401 K, whereas and NH4+ is produced together with a nitrosyl complex the 32 000- and 38 750-cm-' (260-nm) bands become more (vNo = 1875 cm-l). This is the same as the one obtained intense. These bands are due to an ammine complex with by vacuum decomposition. There are quantitative diftwo or fewer NH3 molecules in the first coordination sphere ferences in that relatively more NH4+is formed in air and of Ru. The evidence comes from Table 111, in which are more NO in an O2atmosphere. shown the NH3:Ru ratios calculated from the intensity In the latter case the formation of Ru-red is completely decrease of the NH overtone. The initial assumption is suppressed. After generation of an intermediate, ill-dethat on an evacuated white sample the NH3:Ru ratio is 6. fined reflectance spectrum at 323 K (Figure 4), a stable species is produced absorbing at 21 300 cm-' (470 nm), (13) Guenzburger, D.;Gamier, A.; Danon, J. Inorg. Chim. Acta. 1977, 29 400 cm-' (340 nm), and 38 500 cm-' (260 nm). A similar 21,119. spectrum is produced after heating at 473 K in H20vapor: (14! Nakamoto, K. "Infrared and Raman Spectra of Inorganic and Coordination Compounds", 3rd ed.; Wiley: New York, 1978,; p 199. 21 300 cm-l(470 nm), 33000 cm-' (300 nm), and 40800 cm-' (15) Earley, J. E.; Fealey, T. J. Chem. SOC.,Chem. Commun. 1971,331. (245 nm). It is also seen that the two high-frequency bands (16) Earley, J. E. Fealey, T. Inorg. Chem. 1973,12, 323. are at almost the same frequencies as for vacuum-decom(17) Broomhead, J. A.; Basolo, F.; Pearson, R. G. Inorg. Chen. 1964, 3,826. posed Ru(NH,)~~+ zeolites (Figure 2). It results that in
B
2396
The Journal of Physical Chemistry, Vol. 85, No. 16, 1981
Verdonck et al.
Figure 6. Room-temperature reflectance spectra of Ru-Y-40 in a He flow with 5% NO: (1) 86.4 ks at room temperature; (2) 7.2 ks at 323 K; (3) 7.2 ks at 373 K; (4) 7.2 ks at 423 K.
-
The other bands in the spectrum are interpreted straightforwardly as the deformation of H20 around 1650 c m-1 cm-l and of NH4+at 1457 cm-l.14 The band at 1360 cm-l Flgure 5. Roomtemperature IR spectra of Ru-Y-40 after contact with is the symmetric deformation of coordinated NH, in RuNO and degassed at (a) 305, (b) 314, (c) 324, (d) 333, (e) 372, (f) 424, (NH3)63+,l4The 1330-cm-l band is of the same nature and and (9) 480 K. involves a NH, coordinated to Ru3+ in an environment different from Ru(NH3),3+. The assignments proposed on these widely different atmospheres the same Ru species the basis of the IR spectra are confirmed by reflectance is formed thermally stable up to 473 K and destroyed spectroscopy (Figure 6). Thus, the R u ( N H ~ ) ~ band ~+ above 473 K. Futhermore, the IR results have shown that system is partially replaced by bands at 220,340 (strongly it is a nitrosyl complex. overlapping with the bands of the hexaammine), and 455 The behavior of R u ( N H ~ ) in ~ ~the + different gaseous nm (broad). The first one can be ascribed to [Ruatmospheres below 373 K depends on its environment. (NH3)5N2]2+ (Table 11). It is thermally stable only up to Thus, in H20 vapor at 373 K, and intense spectrum of 323 K just like the corresponding 2120-cm-l vibration of Ru-red is produced together with a band at 33 000 cm-' (300 nm), very close to the spectrum of [ R U ( N H ~ ) ~ O H ] ~ +the coordinated N2 For the 460- and 340-nm bands there are two possible assignments: [ R U ( N H ~ ) ~ N Oand ]~+ (Table 11). cis-[Ru(NH3)4(NO)(OH)]2+. The corresponding vibrations Interaction with NO. When NO is adsorbed on a freshly of coordinated NO are also present in the IR spectra of prepared RU(NH,)~--Yzeolite, previously degassed at room Figure 5 1918 and 1875 cm-l, respectively, with the former temperature, the sample turns immediately yellow and the as the most intense band. This indicates that below 330 NO:Ru ratio is 1. In the presence of Ru-red the N0:Ru K [Ru(NH3),N0I3+is predominant. In fact it is doubtful ratio is less than 1. This simple overall behavior masks whether C~S-[R~(NH~),(NO)(OH)]~+ is present at all. Ina complicated chemistry which was unraveled by IR and deed, the 1875-cm-' band persists up to 480 K in vacuo, UV-visible-near-IR spectroscopy. The interaction of NO a temperature at which the number of coordinated NH3 with Ru(NH3)2+in Y-type zeolites produces the IR spectra is much less than 4. Furthermore the same nitrosyl viof Figure 5. The characteristic bands are assigned acbration was observed after vacuum heating and heating cording to Table 11. The 2120-cm-' band is the typical in O2 and air. We believe therefore that the 1875-cm-l stretching vibration of coordinated N2 in the mononuclear band corresponds to the same Ru"-NO+ moiety as dedinitrogen complex [ R U ( N H , ) ~ N ~ ] ~Other + . ~ ~possible scribed previously. The corresponding reflectance speccomplexes such as [ R U ( N H , ) ~ ] ~ ( N and ~ ) ~ +[Rutrum, 22 700 cm-' (440 nm), 30 000 cm-' (330 nm), 40 800 (NH3)5N20]2+ can be ruled out. The first one has a broad, cm-' (245 nm), is also very similar to those obtained in relatively weak absorption in the region 2100-2060 cm-' vacuo, air, Oz, or H20. In some cases a trace of Ru-red is due to bicoordinated N2while the coordinated N20 absorbs also formed at 373 K (545-nm band in spectrum 3 of Figure at 2250 cm-l (weak) and 1160 cm-' ( s t r ~ n g ) .The ~ ~ band ~~ at 1918 cm-l is the NO vibration in [ R u ( N H ~ ) ~ N O ] ~ + 6). . ~ ~The features of the Ru-X-40 IR and reflectance spectra in a flow of NO are the same as those of Ru-Y-40. Only the relative amount of dinitrogen complex is different: the (18) Allen, A. D.; Bottomley, F.;Harris, R. 0.; Reinsalu, V. P.; Senoff, 2120 cm-':1918 cm-I band intensity ratio is lower on RuC. V. J. Am. Chem. Soc. 1967,89, 5595. X-40 than on Ru-Y-40. The interaction of NO with Ru(19) Harrison, D. F.; Weissberger, E.; Taube, H. Science 1968,159,320. (20) Bottomley, F.; Crawford,J. R. J. Am. Chem. SOC.1972,94,9092. (NH3)S3+is also much slower on X- than on Y-type zeolites. ' 20'00 ' 16'00 1200 2400 1800 1400
(21) Bottomley, F.;Brooks, W. V. F.; Clarkson, S.G.; Tong, S. B. J. Chem. SOC.,Chem. Commun. 1973, 919. (22) Bottomley, F.;Crawford, J. R. J.Chem. SOC.,Dalton Trans. 1972,
2145.
( 2 3 ) Schreiner,A. F.; Lin, S.W.; Haueen, P. J.; Hopcus, E. A.; Hamm, D. J.; Gunter, J. D. Inorg. Chem. 1972,11,880. (24) Pell, S.;Armor, J. N. Znorg. Chem. 1973, 12, 873.
Discussion The results presented in this paper can be summarized as follows: (1) At low temperatures (2' < 373 K) the chemistry of Ru(NH3):+ in the supercages of faujasite-type
The Journal of Physical Chemistry, Vol. 85, No. 16, 1981 2397
RU(NH~)~'+ in Zeolites
TABLE IV: Spectral Data of the HT Nitrosyl Complex in Comparison with Those of Acidonitrosylammines
bands. cm-' visible-UV region 'A,
species
+
3Tlg, lA1g
%g
in 0, in H;O in NO
C~.S-[RU(NH,),(OH)(NO)]~+ trans-[ Ru(NH,),(OH)(NO) ] '+
2 1 300 21 300 22 700 21 7 0 0 23 300
lT1g
29 4 0 0 3 3 000 30 000 30 300 29 900
zeolites depends on the environment. Ru-red is formed in air, in HzO, and in vacuo. Its formation is suppressed by 0, and NO. (2) At high temperatures (T > 373 K) a nitrosyl complex with the Ru"-NO+ moiety is formed independently of the environment. Its concentration is environment dependent in the following order NO > 0, > H 2 0 > vacuo. (3) The vacuum and air decomposition of R u ( N H ~ ) ~is~ qualitatively + similar to that of [Ru(NH3)5N2]2+ in that NH4+and Ru-red are formed in the low-temperature (LT) range and a nitrosyl complex in the high-temperature (HT) range.7~~ (4) The LT chemistry of R u ( N H ~ ) in ~ ~the + supercages of faujasite-type zeolites can be explained on the basis of its known aqueous solution chemistry. These statements are substantiated in the following paragraphs. LT Chemistry of R u ( N H ~ ) ~In ~+ the . initial stages of the vacuum decomposition, the 265-nm band of Ru(NH3),3+shifts to 278 nm; this is indicative of the formation of [RU(NH~)~(OH)]~+ (A, at 295 n m 9 according to
-
+
P 4 O H ) --* e,(Ru)
NO vibrations
ref
1875 1875 1875 1861 1878 1855 1845
24 21 22 24
38 500 40 800 40 800 44 500 sh 4 3 900
products, [Ru(NH3)5N2I2+,[ R U ( N H ~ ) ~ N Oand ] ~ +NH4+, , are formed by the following reactions: Ru(NH~)+ ~ +NO [Ru(NH3)5N0I3+ NH3 (4)
+
-+
R u ( N H ~ )+ ~ +NO
+
-
[Ru(NHJ~(NH~NOH) J3+ (5)
[Ru(NH3)5(NH2NOH)J3++ NH, [ R u ( N H ~ ) ~ N+~NH4+ ] ~ + + HzO (6) Equation 4 represents a ligand substitution reaction. In eq 6 a ligand-ligand interaction occurs, which can be viewed as follows: Ru
Reaction 4 occurs also in acid solution, while the dinitrogen complex is formed in basic solution.25 The proposed mechanism for the formation of the dinitrogen complex Ru-red is formed as follows: in basic solution is via a concerted or stepwise attack of NO and OH- on [ R u ( N H ~ ) ~with ] ~ ' formation of amido + H,O [Ru~~'(NH,),OH]~+ intermediates. Our mechanism, summarized in eq 5 and trans-[R~~(NH~)~(0H)~]~+ + l / z H +~ NH3 (2) 6 is similar but does not involve OH- explicitly. HT Chemistry of Ru(NH3)2+.Except for band intensity 2[Ru"'( NH3)50H]2++ trans-[Ru'"( NH3)4( OH),] differences, both IR and reflectance spectroscopy show the [RU~~'(NH~)~ORU~(NH~)~ORU~~~(NH~)~]~+ + 2H20 (3) same nitrosyl complex independent of the atmospheric conditions. Futhermore, this nitrosyl complex was found These are essentially basic hydrolysis reactions. It is by Madhusudhan et alq8after decomposition of Rutherefore no surprise that the rate of Ru-red formation is (NH3)5N?+. The pertinent spectroscopic data are sumfaster on the more basic X-type zeolites. The formation marized in Table IV. of NH4+and Ru-red by vacuum and air decomposition of The decrease of vNo follows the increasing n-electron [ R u ( N H ~ ) ~ Nis~ ]now ~ + also recognizedg in contrast to donor ability of the trans ligands and to a lesser extent of previous interpretations.'" It is shown then by our results the cis ligands. Considering that one or two NH3 are that both [ R U ( N H ~ ) ~ Nand , ] ~ +[ R u ( N H ~ ) ~decompose ]~+ retained in the coordination sphere, the cis and trans ligin a similar way. ands are predominantly 0-containing molecules from HzO A mixture of Ru-red and Ru-brown is obtained when the or the lattice. The fact that the frequency of the NO hydrolysis (reactions 1-3) proceeds slowly in air at room vibration is close to the values reported for cis- and temperature. The same mixture is obtained after exchange tr~ns-[Ru(NH,)~(0H)(N0)]~+ supports this conclusion of Ru-red in air. In both cases Ru-red is the major species. (Table IV). The reflectance spectra can be interpreted In some cases a band at 1150 nm (Figure 1)was found and ascribed to Ru-brown: [ (NH3)5R~OR~(NH3)40Ru- along the lines proposed by Schreiner et al.23for the ruthenium acidonitrosylammines. The assignment in Table (NH3)5]7+,the one-electron oxidation product of Ru-red. IV is based on an assummed octahedral first coordination It may have been formed by traces of O p However, heating sphere of Ru(I1). The band maxima in Table IV do not in O2 did not result in the formation of Ru-brown or any exactly coincide with those reported by Schreiner et aLZ3 polynuclear complex formation below 373 K. The same Several factors contribute to the differences: (1)Weak, is true for NO, but in H20 at 373 K a very intense Ru-red broad bands for which it is difficult to determine the exact spectrum is obtained. Thus, water is necessary for its position, especially when they overlap with other bands. formation (reactions 1-3), and any molecule which faThis is especially true for 21 300- and 30 000-cm-l bands. vorably competes with HzO to enter the coordination The latter band may be split into unresolved components sphere or to react with coordinated NH3 suppresses the due to the deviation from octahedral symmetry. (2) The formation of Ru-red. This is most pronounced with NO because this molecule reacts with Ru(NH3IG3+ already at room temperature. The (25) Pell, S.;Armor, J. N. J. Am. Chem. SOC.1973, 95, 7625.
+
R u ( N H ~ ) , ~ +H20
[Ru(NH~)~OH]'+ + NH4+
-
(1)
-
,+
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J. Phys. Chem. 1981, 85, 2398-2403
number of lattice oxygens, H20, and NH3 in the coordior in vacuo, H20 is the oxidizing agent. The overal reaction nation sphere. The 40 800-cm-’ charge-transfer band is involves the liberation of N2 and H2besides formation of -3100 cm-’ below the pa(0H) e,(Ru) band in transthe nitrosyl moiety. At high temperatures H2is consumed [RU(NH,),(OH)(NO)]~+.~~ Such a bathochromic shift can in the reduction of Ru to the metallic state.6 be ascribed to environmental effects.26 This 40 800-cm-’ Conclusion band is therefore highly suggestive for OH- in the coordination sphere. Whether other 0-containing ligands are R U ( N H ~ )has ~ ~ a+ rich chemistry in the supercages of present in the coordination sphere is not evident from the faujasite-type zeolites. In water, in air, and in vacuo it experiments. Therefore, the following general formula has hydrolyzes to Ru-red or a mixture of Ru-red and Ruto be written: Ru1*(NO+)(NH3)1,2(OH,H20,0~)3,4. brown. The latter occurs only in the presence of O2 and Only a fraction of the Ru is present in the form of this HzO. In the atmospheres of pure O2 and NO, the Ru-red nitrosyl complex. Two arguments substantiate this formation is largely suppressed. O2 interacts with Rustatement: (i) its concentration is dependent on the en(NH3)$+at 373 K while NO interacts at room temperature with formation of [RU(NH~)~NO]~+, [ R U ( N H ~ ) ~ Nand ~]~+, vironment; (ii) from previous results5it is clear that Ru(0) is present after vacuum decomposition at 523 K. At this NH4+. All of these complexes are destroyed by heating above 373 K. The only identifiable stable complex in the temperature the 1875-cm-’ band is still present in the IR spectrum, although with strongly reduced intensity (Figure high temperature regime is R U ~ + ( N O + ) ( N H ~ ) ~ , ~ ( O ~ , OH,H20)4,3.Ita spectroscopic characteristics are very close 3). to those of the acidonitrosylammines. In an O2 atmosphere, O2 is the NH3 oxidizing agent following a reaction similar to the air-oxidation of RuAcknowledgment, This research was supported by the (“3)63+ to [RU(NH&NO]~+.~ In an atmosphere of water Belgian Government (Ministerie voor Wetenschapsbeleid, Geconcerteerde Onderzoeksakties). R.A.S. and P.A.J. are (26) Maes, A.; Schoonheydt, R. A.; Cremers, A.; Uytterhoeven, J.B. J . indebted to the National Fonds voor Wetenschappelijk Phys. Chem. 1980,84, 2795. Onderzoek (Belgium) for a grant as “Onderzoeksleider”. (27) Pell, S. D.; Armor, J. N. J . Am. Chem. SOC. 1976, 97, 5012.
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Dibenzoyl Peroxide Induced Photodecarboxylation of Amino Acids and Peptides. A Spin-Trapping Study Ionel Rosenthal,’ Magdl M. Mossoba, and Peter Rlesr’ Laboratory of Pathophysiology, Natlonal Cancer InstitUte, National,Institutes of Health, Bethesda, Maryland 20205 (Received: March 4, 1981)
In a new photochemical reaction the radicals produced from several amino acids and peptides by UV irradiation at 313 nm in dimethyl sulfoxide solutions in the presence of dibenzoyl peroxide were characterized by spin trapping using 2-methyl-2-nitrosopropane. The most predominant reactions were the decarboxylation of the amino acids and of the carboxyl-terminalresidue in peptides. An unusual behavior was exhibited by the valine moiety which consistently yielded H-atom abstraction radicals. No radicals derived from dimethyl sulfoxide could be detected under our reaction conditions.
Introduction The photochemical reactions of proteins and their constituents have been extensively studied because of the biological significance of these compounds. Since the photochemical processes are in general of homolytic nature, the ESR technique has been used for defining the primary events in the interaction between light and amino acids.2 Thus, the direct photolyses of amino acids and peptides have been studied by ESR in frozen aqueousg4 solutions and in the solid state.’ (1) On sabbatical leave from the Department of Technology, Agricultural Research Organization, Volcani Center, Bet-Dagan, Israel. (2) Box, H. C. “Radiation Effects: ESR and Endor Analysis”; Academic Press: New York, 1977. (3) Neubacher, H.; Schnepel, G, H. Radiat. Res. 1977, 72, 48. (4) Meybeck, A,; Meybeck, J. Photochem.Photobiol. 1972, 16, 359. (5) Meybeck, A.; Windle, J. J. Photochem. Photobiol. 1969, 10, 1. (6) Schnepel, G. H.; Neubacher, H. Radiat. Enuiron. Biophys. 1976, 13, 49. (7) Jones, R. B.; Looney, F. D.; Whelan, D. J. Photochem. Photobiol. 1962, 7, 65.
In recent years, the method of spin trapping has been developed for stabilizing transient free radicals. The method consists of the chemical addition of the short-lived free radical to an unsaturated double bond to yield a new and stable free radical at room t e m p e r a t ~ r e . The ~ ~ ~spin trap 2-methyl-2-nitrosopropane (MNP) has been used extensively for trapping and identification of free radicals derived from amino acids and pyrimidine bases.1° The pertinent chemical reaction for this process is R. + (t-Bu)N=O R(t-Bu)N-O c* R(t-Bu)N+-OFollowing this procedure, biologically significant free radicals can be detected at physiological temperatures, without suppressing thermally activated processes and solvation interactions with the ambient medium. In the present ESR and spin-trapping study we report the results of a new reaction that is the room-temperature
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(8) Lagercrantz, C. J . Phys. Chem. 1971, 75, 3466. (9) Janzen, E. G. Free Radicals Biol. 1980,4,116. (10) Riesz, P.; Rustgi, S. Radiat. Phys. Chem. 1979, 13, 21.
This article not subject to U S . Copyright. Published 1981 by the American Chemical Society
