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Reactivity of manganese(II) complexes of derivatives of 2-methylpyridine-N-oxide towards sulfur dioxide
Pergamon
REACTIVITY OF MANGANESE(I1) COMPLEXES OF DERIVATIVES OF 2-METHYLPYRIDINE-N-OXIDE TOWARDS SULFUR DIOXIDE* M. FONDO,
M. R. BERMEJO,? E. GOMEZ
Departamento de Quimica Santiago de Compostela,
A. SOUSA,t FORNEAS
J. SANMARTiN
and
InorgBnica, Facultade de Quimica, Universidade de Santiago de Compostela, Galicia, E- 15706 Spain and C. A. McAULIFFEt
Department
of Chemistry, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 IQD, UK (Received
8 Januar?, 1996 ; accepted 2 Fehruur?, 1996)
Abstract-The metallic complexes [Mn(2-PyCO),,X,(H,O),](2-PyCO = 2_methylpyridineN-oxide, n = l-3. X = Cl, Br, I and NO, and x = O--3) have been synthesized and their reactions with sulfur dioxide, both in the solid state and as toluene slurries at room temperature, have been investigated. Furthermore, the reactivity of these complexes with sulfur dioxide at high temperature has been studied by thermogravimetric analysis (TGA), the temperature range of study depending critically on the melting point of the initial complexes. All the complexes, except the chloride derivative, react with sulfur dioxide at room temperature. Increase in the temperature, in general, disfavours this reaction and the amount of sulfur dioxide fixed decreases at high temperature. Finally, desorption studies have been carried out in order to discover whether the reaction of the precursors with sulfur dioxide is reversible. Copyright 0 1996 Elsevier Science Ltd
Aside from its renown as a source of acid precipitation, sulfur dioxide is remarkable in possessing coordination properties that are more diverse than those of any other small molecule. The diversity of the coordination modes established for SO,‘,’ has stimulated numerous studies, predominately focused on the second and third row transition metal complexes. We have extended our investigations on the coordination chemistry of first row transition metal complexes containing phosphine and arsine oxide
ligands’ ’ with sulfur dioxide, to complexes with pyridine-N-oxide derivatives as ligands. In this paper we report the synthesis and characterization of mono, bis and tris complexes of 2methylpyridine-N-oxide (2-PyCO) with manganese halides and nitrate and their reactivity towards sulfur dioxide in the solid state and as toluene slurries at room temperature and in the solid state at high temperature.
EXPERIMENTAL Preparation *Dedicated to the Royal University of Santiago de Compostela in the year of its V century. t Authors to whom correspondence should be addressed.
of the precursors
The syntheses were performed in absolute ethanol, using the metal salts MnCl,, MnBr,*4H,O,
3881
M. FOND0
3882
MnI, and Mn(NO& * 6H,O and the 2-methylpyridine-N-oxide without further purification. These complexes were obtained by a method preThe salt (2 mmol) was disviously described.‘,” solved in ethanol (25 cm’) at room temperature and the ligand (in 1 : 2 or 1 :4 ratios) was added. The mixtures were stirred for 24 h and the powder isolated by filtration, washed with diethyl ether and dried. The solution of nitrate derivative in the molar ratio 1 : 4 generates an oil which, on trituration with diethyl ether, results in powder formation. The solutions of chloride, iodide and nitrate derivatives in molar ratios 1 : 2 and 1 : 4 yield only the ligand : metal 1 : 1 adduct ; the solutions of the bromide derivatives yield the precursors 1 : 2 and 1 : 3 (Table 1).
et al.
results in an increase in the temperature of the sample until its melting point is reached, whilst a gas flow of 50 cm3 min-’ is maintained. The relative proportions of SO, and nitrogen are controlled with Rosemount mass/flow meters at the time the temperature is decreasing. The uptake of SO, was monitored for samples (0.040.08 g) using a series of temperature/partial programmes. (iv) High temperature SO, desorption. Sulfur dioxide desorption studies were performed on the same thermogravimetric balance by heating the sample (0.02-0.5 g) until its melting point and maintaining it under a nitrogen stream for 12-24 h, or by heating the compound in a Rotaflo tube until its melting point, under reduced pressure for 7 h. The resultant complexes were studied by elemental analyses. Elemental analyses were performed by the USC and UMIST Microanalytical Services. Infrared spectra were obtained as KBr pellets or as Nujol spectroresults using a Nicolet PC5 FT-IR photometer in the range 2100400 cm-‘.
Reactions with sulfur dioxide (i) Solid state at room temperature. A sample (0.1-0.3 g) of the complex, contained in a Rotaflo tube, was exposed to sulfur dioxide for several days until a constant mass was achieved. The compounds were managed and isolated under an inert atmosphere. Full details of this procedure have been published previously.” (ii) Toluene slurries. Slurries were prepared using dry distilled toluene (Na, benzophenone) and performed in a pre-dried round-bottomed flask fitted with a side-arm and ground-glass tap. Manganese precursors (0.054.30 g) were added to the flask and the slurry saturated with sulfur dioxide. The flask was then sealed and the contents stirred for ca 7 days, after which the products were isolated by standard Schlenk techniques and dried in a stream of argon. Full details of the synthesis have been previously described.6c.8” (iii) Solid state at high temperature. The absorption of sulfur dioxide at high temperature was studied using a CAHN Instruments TG131 thermogravimetric balance. The programmed scheme
RESULTS
AND DISCUSSION
Metal complexes The synthesis of the metal complexes has been performed by a method previously described,“.” with little change, the salts were not dehydrated previously and the reaction was performed at room temperature, not in hot ethanol. The elemental analyses, IR data and some physical properties for these compounds are shown in Tables 1 and 2. The IR spectrum of 2-methylpyridine-N-oxide has been studied by Karayannis et a1.,12assigning v(N0) at 1244 cm-’ and 6(NO) at 851 cm-‘. All the metallic precursors show a negative shift (2454 and 3-8 cm-‘) in v(N0) and s(NO), reflecting a decrease in the strength of the N-O bond, as
Table 1. Analytical data for the metal complexes Analyses” (%) Metal complex Mn(2-PyCO)Cl,(H,O) Mn(2-PyCO)zBrz(HZO)x Mn(2-PyCO)&,(H@), Mn(2-PyC0)21, Mn(2-PyCO),(NQ),(H@) u Calculated
C
H
N
28.5(28.5) 29.3(29.5) 36.0(36.2) 27.0(27.3) 35.3(34.7)
3.2(3.5) 4.2(4.1) 4.5(4.5) 2.5(2.6) 3.7(3.8)
5.6(5.6) 5.4(5.7) 6.7(7.0) 5.4(5.3) 13.3(13.4)
values in parentheses.
Reactivity
of manganese(II)
Table 2. IR data and some physical
properties
complexes
3883
for the metal complexes IR” (cm-‘)
___~ Metal complex Mn(2-PyCO)CI,(H,O) Mn(2-PyCO)ZBr2(H20),* Mn(2-PyCO),Br,(H,0)1* Mn(2-PyCO)J,
Mn(2-PyCO),(N0,)2(H,0) “All spectra performed
Colour
M.p. (C)
\)(NO)
fi(NO)
v(NOJ
White Yellow Ochre Brown Pale yellow
z 300 163-165 102-103 126128 17cL172
1198s 1220s 1194s lI9Os 1209s
845s 846s 841s 871s 847s
13oos, 815s
in Nujol except those marked
with an asterisk which have been obtained
expected. Only for the iodine derivative there is a displacement of 6(NO) towards higher frequency observed with respect to the free ligand ; this fact is probably due to the removal of electronic charge from the nitrogen atom of the pyridine ring resulting in a higher concentration of charge in the N-O bond, as proposed by Ahuja and Rastogi.” The nitrate complex shows bands at 1300 and 8 15 cm ’ assignable to the nitrate ion acting as a monodentate group.” Previous work with this ligand and copper compounds indicates that the 1 : 1 adducts are tetrahedral dimers.” with one chloride acting as a bridge, and the 1 : 2 adducts are monomers.‘” Nevertheless, no 1 : 3 adducts have been reported previously.
The reactivity of the same metallic precursor with sulfur dioxide in the solid state and as toluene slurries at room temperature is quite different, as the SO, adducts obtained from the two states are quite different. Thus, the medium of the reaction appears to play an important role in the reactivity of these
Table 3. Analytical
precursors with sulfur dioxide, as has been observed previously.x In spite of the marked differences in the adducts formed, there are some common aspects in the reactivity of the precursors towards sulfur dioxide at room temperature. All the metal complexes studied, except the chloride derivative, show reactivity towards sulfur dioxide in the solid state and in toluene slurries at room temperature. The nitrate derivatives fix most SO, and show a displacement of the nitrate group by the sulfate, this fact is confirmed by the elemental analyses (Tables 3 and 5) and by the new bands at frequencies lower than 900 cm ’(Tables 4 and 6). In the two mediums one mole of sulfur dioxide is oxidized to sulfate. perhaps as a consequence of the reduction of the nitrate group to nitrogen oxides, in agreement with other results found by us.’ These sulfate groups generate bands at 8855872, 661--644 and 615-540 cm -’ in the IR spectra, which accord with a sulfate group acting as a bidentate chelate.” The r(N0) and 6(NO) frequencies for the coordinated 2-methylpyridine-N-oxide were assigned in the ranges 120&1188 and 871-839 cm-‘. respectively, for the SO, adducts, and they do not suppose a significant displacement with respect to the initial metallic precursors.
data for the SO? adducts
in the solid state at room temperature Analyses”
Metal complex
SO> adduct
Mn(2-PyCO)Cl,(H,O) Mn(2-PyCO)ZBr,(H,0), Mn(2-PyCO),Brz(H,0)J Mn(2-PyCO),I, Mn(2-PyCO)z(N0J2(H20) ._______~_
No reaction Mn(2-PyCO),Br,(SO,)(Hzo)2 Mn(2-PyCO),Br,(SO&(H,O), Mn(2-PyCO),I,(SOJ1 Mn(2-PyCO)ZS0,(SOz)z(H10),
”Calculated
values in parentheses.
as KBr pellets.
( ‘70)
G
H
N
S
26.6(27.0) 29.7(29.8) 21.6(21.9) 26.6(27.0)
3.3(3.4) 4.0(3.7) 2.6(2.1) 3.5(3.4)
5.2(5.7) 5.8(5.8) 4.2(4.3) 5.4(5.3)
6.5(6.0) 9.1(8.8) 9.4(9.8) 17.7(18.0)
3884
M. FOND0 et al.
Reactions with surfur dioxide in the solid state at room temperature New adducts obtained after interaction with SO, in the solid state at room temperature fix between 1 and 3 moles of sulfur dioxide per mole of metallic precursor (Table 3). This reaction is accompanied by changes in colour and, sometimes, in aspect. Most of the SO, adducts are unstable in air and decompose when they are dissolved in alcohols. Infrared spectra. The ranges of frequencies for the different binding modes of the sulfur dioxide were compiled by Kubas and co-workers.2b The only new binding mode established later is the insertion of sulfur dioxide in a metal-halide bond, as reported by McAuliffe and co-workers.3 Although strong correlation between infrared stretches and SO, bonding modes exist, overlap between the infrared regions for each mode can occur and so this technique cannot unequivocally provide bonding assignments and must be used in conjunction with other data. The IR spectra of the adducts between 500 and 100 cm-’ are not useful and it was not possible to assign new bonds in this range owing to the great number of bands presented by the ligand in this zone. In the IR spectra of these adducts between 2000 and 500 cm-’ we could not assign new bands for most of the halide derivatives. Only for Mn(2PyCO)2Br,(S02)(H20)2 do we observe the appearance of two new bands at 1261 and 1065 cm-‘, assignable to S-O stretching modes; these bands suggest a possible yl’-S planar or a ligand-bound mode for this molecule of sulfur dioxide. The same behaviour is expected for the sulfur dioxide linked in Mn(2-PyC0),@0,)(S0,),(H,0),, which generates bands at 1240 and 1090 cm-‘. Sulfur dioxide desorption studies. Desorption studies are a very important tool, in combination with IR spectroscopy and analogy with other well characterized complexes, in postulating the possible binding mode of sulfur dioxide in SO, adducts. Kubas and co-workers2’ indicated that, in general, if the bonding mode is ligand bound, SO* must be lost by heating in a reversible process, in contrast with the irreversible process for the y’-S planar binding mode. The desorption of Mn(2-PyCO),Br2(S02)(H20), (see Table 7) yields the product Mn(2-PyCO) Br2(H20)2, showing that the SO, is linked in a labile manner. This lability and the IR bands at 126 1 and 1065 cm-’ accord with a ligand-bound binding mode. When we studied the desorption of the Mn(2PyCO),Br,(SO,),,, adduct, obtained from toluene slurry, which exhibits an IR band at 1240 cm-‘, we
Reactivity Table 5. Analytical
of manganese(H)
data for the SO, adducts
complexes formed
3885
in toluene slurries _~ Analyses”
Metal complexes
SO? adduct
Mn(?-PyCO)CI,(H20) Mn(2-PyCO)IBr2(H,0)J Mn(2-PyCO),Br,(HzO)X Mn(2-PyCO),12 Mn(3-PyCO),(NO,),(H,0)
No reaction Mn(2-PyCO)zBrz(SOz), . Mn(2-PyCO)Br,(SO,)(H20)L Mn(2-PyCO)IZ(SOl),(H,O) Mn(2-PyCO)SO,(SOJ(H,0)
“Calculated
a loss of sulfur dioxide too. The reversibility of the reaction and the IR spectra are in accord with a ligand-bound mode for one mole of sulfur dioxide. The comparison of the IR spectra of this compound with Mn(2-PyCO)z S04(S02)2(HZ0)3, contributes to strengthening the proposed ligand-bound mode for the SO, in this complex. Presumably all the adducts obtained in the solid state present the same ligand-bound mode. Such a supposition is supported by the ability of pyridine-N-oxide to form 1 : 1 adducts with the sulfur dioxide.lX Desorption studies for Mn(2-PyCO),Br,(SOz) (H,O), allow us to conclude that the reaction is reversible. RTSO,
Brl s
40(‘.7h Mn(2-PyCO),Br?(SO1).
So this metallic precursor could be used to reduce SO? in a gas stream at room temperature and to leave it again at 90 C. Reactions
C
H
N
s
27.4(27.2) 17.5(17.1) 13.1(12.8) 20.6(21 .O)
3.0(2.7) 2.4(2.6) 2.0(1.6) 2.6(2.6)
5.0(5.3) 3.2(3.3) 2.8(2.5) 4.3(4.1)
9. I(9. I ) 7.2( 7.6) 11.7(11.3) Ic).O( 18.7)
values in parentheses.
observed
Mn(2-PyCO),
~~~
(%)
n,ith su~ji~ dicuide in tolurne slurries
All the precursors. except Mn(2-PyCO): Br,(H,O), lose at least one mole of 2-methylpyridine-N-oxide when they react with sulfur dioxide in toluene slurries. This fact has been observed previously, “.20 indicating that, really, there is a displacement of the ligand by sulfur dioxide. Ir$Lared spectra. All the SO, adducts exhibit new bands between 2000 and 500 cm-’ assignable to S-O vibrations, and these bands are in accordance with different bonding modes for sulfur dioxide. The infrared spectra are not definitive enough to establish the coordination mode of the SOz. Nevertheless, this study, in combination with sulfur dioxide desorption studies, allows us to propose a
binding mode for the sulfur dioxide linked in these adducts. Su@r dioxide deesorption studirs. The desorption studies show that the sulfur dioxide is strongly bound in these adducts. It is quite robust and is present in the compounds even when they are heated to their melting points (Table 7). For the iodine derivative we observe a loss of halide and 2-PyCO but not loss of SO,. Figure I shows the desorption thermogram of Mn(2-Py CO)J2(S0,),(H20). It is shown that an increase in the temperature (from 120 to 130 ‘C) does not result in a decrease in weight. The elemental analyses of the final compound (Table 7) shows that it is a little impurified by the picoline ligand, but it is clear that all the sulfur dioxide remains in the compound. As all the ligand is lost, it is not possible to think about a ligand-bound sulfur dioxide mode and this SO, must be directly linked to the metal. As the bond Mn-SO2 is irreversible the q’-S pyramidal binding mode is not possible.” The loss of iodine suggests a decrease in the strength of the Mn-I bond, so it is possible that one of the sulfur dioxide molecules is inserted in the Mn-I bond. This fact is supported by an IR band at 1286 cm ‘. Owing to the irreversibility of the reaction, the band at 1320 cm ’ cannot be associated with a simple ligand bound so perhaps this inserted sulfur dioxide is. at the same time. interacting with the ligands. The third band at 1070 cm-.’ and the displacement of a mole of 2PyCO by a mole of SOz permit us to propose an II’S planar binding mode for this second molecule of sulfur dioxide. as was found by Conway ct (11.‘~~ The same q’-S planar bond must be present in Mn(2PyCO)SO,(SO,)(H,O), which also exhibits a band at 1071 cm-‘. When we studied the desorption of Mn(2-Py CO)Br,(S0,)(H,0)2 we only observed a loss of water and ligand. no bromide or SO, was lost. Again, the displacement of one mole of ligand by
3886
M. FOND0
et al.
-60 0.0112-
Time (hrs: min: set)
Fig. 1. Desorption thermogram for Mn(2-PyCO),I,(SO,),(H,O) : ( ?? ) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
the SO2 permits us to propose the vi-S planar binding mode for the sulfur dioxide linked in this compound. The band at 1070 cm-’ present in the iodine derivative is not assigned in this compound owing to the broad band centred at 1150 cm-’ (Figure 2). Different behaviour is shown by Mn(2-PyCO), Br,(S02),,5, which does not show a loss of ligand with respect to the precursor. The desorption study shows a partial loss of sulfur dioxide and ligand ; 1 mole of SO, is lost, together with a 2-PyCO ligand while 0.5 moles remain in the compound. This behaviour and the band at 1240 cm-’ allow us to
propose that the labile SO, is linked in a ligandbound mode, while the 0.5 moles are perhaps acting as a bridge between two metal centres ; these results have been obtained by us8 for other SO, adducts with manganese precursors. As a conclusion of the study at room temperature we observed that the sulfur dioxide is linked preferably to the ligand in those adducts with 2-methylpyridine-N-oxide. Nevertheless, when the reaction takes place in toluene slurry, the easier displacement of the ligand permits the sulfur dioxide to bind to the metal in an y’-S planar binding mode ; the
a
b
Fig. 2. Comparative IR spectra for (a) Mn(2-PyCO)1Br,(H,0)1
and (b) Mn(Z-PyCO)Br,(SO,)(H,O),.
Reactivity of manganese(I1) complexes insertion of SO, into the metal-halide be favoured for the iodine derivatives. found previously.‘,‘”
3887 bond must as we have
The interaction of the precursors with sulfur dioxide at high temperature has been performed using a thermogravimetric balance. These thermogravimetric analyses are particularly interesting because it is possible to study the thermal stability of the metallic complexes and the optimum temperature range over which SO, absorption occurs by these complexes. We have observed (Table 8) that the reaction of the metal complexes selected by us with SO, is temperature dependent and this process is disfavoured when the temperature increases. In this way. only the nitrate derivative Mn(2-PyCO)z(N0J7(H20) is able to absorb more than I mole of sulfur dioxide per mole ofprecursor. This reaction, at high temperature. presents three phenomena. 1. One mole of 2-methylpyridine-N-oxide is lost, being replaced by a molecule of SOz. The loss of one mole of pyridine ligand shows that the precursor is quite unstable towards temperature. 2. The molecule of sulfur dioxide is oxidized to sulfate, perhaps as a consequence of the reduction of the nitrate group. which is displaced. 3. The absorption of sulfur dioxide occurs very quickly. The compound being almost saturated at 140’C, after which the compound does not absorb a significant quantity of SO,, even when the temperature decreases to 30 C (Fig. 3). The only halide precursor that is able to fix and is the Mn(2-PyCO), sulfur dioxide retain Br2(H,0),. This compound can fix 0.5 moles of sulfur dioxide per mole of compound, but it does not react at a temperature higher than 120 C (Fig. 4) and the reaction is very slow, even when we study the reaction in the temperature range 80-30’ C (Fig. 5). The complex Mn(2-PyCO),Br,(H,O), decomposes when it is heated at 100 C for 30 min, losing ligand, and the resultant compound does not react with SO,. Different behaviour is shown by Mn(2PYCO)~I,, which shows a little increase in its weight when it is exposed to a sulfur dioxide stream in the temperature range 100-30 C. Nevertheless. when elemental analysis is performed, no sulfur dioxide is detected. Perhaps in this case the sulfur dioxide
“Calculated
values in parentheses.
Mn(2-PyCO),(NO,),(H,O)
No reaction
Mn(2-PyCO)~Brz(SWO No reaction No reaction Mn(2-PyCO)SO,(SOJ,
Mn(2-PyCO)Cl,(H,O) Mn(Z-PyCO),Br,(H,O), Mn(2-PyCO),Br,(H,O), Mn(2-PyCO),I,
Table 8. Analytical
SO, adduct
values in parentheses.
Metal complex
“Calculated
90 120 220-230 120-130
Mn(2_PyCO)Br,(H,O),
Mn(2-PyCO)zBr,(S0,)(H,0)z Mn(2-PyCO),BrDCW, Mn(2-PyCO)Br,(SOz)(H,0)z Mn(2-PyCO)L(SW,(H,0)
7h 7h 16 h 20 h
Time
obtained
20.2(20.0) 20.8(20.2) 10.6(10.8) 1.7(0.3)
C
25
5
28&30 15&30 9&30 100-30 160-30
Temp. range (“C) 5 3 4 2 11
h h h h h
20 50 20 30
Time min min min min
2.7(3.0) 2.6(2.0) 2.0(1.0) 0.2(0.0)
H
C
25.9(26.1)
(%)
6.2(6.0)
5.3(5.1)
3.9(3.0)
2.3(2.5)
H
N
3.9(3.9) 4.4(4.0) 2.0(2.1) 1.3(0.0)
N
Analyses” (%)
Analysed”
range presented
studies
31.1(31.0)
after SO, desorption
data for the SO2 formed in the solid state in the temperature
Mn(2-PyCO)Br#O& Mn(2-PyCO)0.,BrI(SW MnUOH)(SO,),
T (“C)
Complexes
data for the complexes
SO, adduct
Table 7. Analytical
15.3(14.5)
3.6(3.4)
S
O(O) 5.0(4.5) 9.5(9.6) lU(19.6)
S
3 9 K
8
s
Reactivity
of manganese(H)
complexes
3889
0.0385
170
120
0.0371
s % F 70
0.035L II 0:w:oa
1:10 5: 00: 00
ll:oo:oo
Time (hrs: min: set)
Fig. 3. Absorption thermogram for Mn(2-PyCO)z(N0,),(H,0) in the range 16&30’ C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time. 4 150
0.0398 b
0.0390-
- 120
Time (hrs: min: set)
thermogram for Mn(2-PyCO),Brz(HzO)? in the range 150-30°C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
Fig. 4. Absorption
is physically adsorbed and is lost when the compound is handled in air. As a result of the study at high temperature we can conclude that elevated temperatures disfavour the reactivity of these complexes towards sulfur dioxide, but the behaviour of these compounds indicates an advantage with respect to those precursors of manganese with phosphine and arsine oxide ligands :3~’there is a derivative of halide that
can react with sulfur dioxide perature than room temperature.
at a higher
tem-
CONCLUSIONS The reactivity of the manganese complexes, Mn(2-PyCO),X2(H,0),, with sulfur dioxide depends on the anion (halide or nitrate) and on the coordination number n. Furthermore. the reaction
M. FOND0
3890
et al. i
0.0305 1 r’
F----l
0.0296
:98
3 E s
E
0.0288
-62
's
-
3
E" g
-42
Time (hrs: mix set)
Fig. 5. Absorption thermogram for Mn(2-PyC0)2Br,(H,0)3 in the range 10@3O”C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
medium influence the ability of the complexes to react with sulfur dioxide. A third factor is the temperature, which disfavours the uptake of SO,. Finally we must point out that the precursor Mn(2PyC0)2Br,(H20), is able to fix SO2 in a reversible way, it absorbs SO2 at room temperature and evolves it above 90°C. REFERENCES 1. W. A. Schenk, Angew. Chem., Int. Ed. Engl. 1987, 26, 98. 2. (a) G. J. Kubas, Znorg. Chem., 1979, 18, 182 and
references therein ; (b) R. R. Ryan, G. J. Kubas, D. C. Moody and P. G. Eller, Struct. Bond. 1981,46,48. 3. J. A. Gott, J. Fawcett, C. A. McAuliffe and D. R. Russell, J. Chem. Sot., Chem. Commun. 1984, 1283. 4. K. Al-Farham, B. Beagley, 0. El-Sayrafi, G. A. Gott, C. A. McAuliffe, P. P. MacRory and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1990, 1243.
5. (a) S. M. Godfrey, D. G. Kelly and C. A. McAuliffe, J. Chem. Sot., Dalton Trans. 1992, 1305 ; (b) S. M. Godfrey, C. A. McAuliffe, G. C. Ranger and D. G. Kelly, J. Chem. SOL, Dalton Trans. 1993, 2809. 6. (a) C. A. McAuliffe, B. Beagley, G. A. Gott, A. G. MacKie, P. P. MacRory and R. G. Pritchard, Angew, Chem., Int. Ed. Engl. 1987, 26, 264 ; (b) B. Beagley, 0. El-Sayrafi, G. A. Gott, D. G. Kelly, C. A. McAuliffe, A. G. MacKie, P. P. MacRory and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1988, 1095; (c) B. Beagley, D. G. Kelly, P. P. MacRory, C. A. McAuliffe and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1990,2657.
7. S. M. Godfrey, D. G. Kelly, C. A. McAuliffe and R. G. Pritchard, J. Chem. SOL, Dalton Trans. 1995, 1095. *. (a) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Forneas, Acta them. &and. (in press) ; (b) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Foneas, Inorg. Chim. Acta (in press) ; (c) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Forneas, Synth. React. Inorg. Met-org. Chem. (in press). 9. M. R. Kidd, R. S. Sager and W. H. Watson, Inorg. Chem. 1967,6,947.
10. D. H. Brown, D. Kenyon and D. W. Sharp, J. Chem. Sot. (A), 1969, 1474.
11. D. S. Barratt, C. G. Benson, G. A. Gott, C. A. McAuliffe and P. Tanner, J. Chem. Sot., Dalton Trans. 1985, 2661.
12. N. M. Kardyannis, L. L. Pytewski and C. M. Mikulski, Coord. Chem. Rea. 1973, 11, 93. 13. I. S. Ahuja and P. Rastogi, J. Nucl. Chem. 1970,32,138 I. 14. G. J. Kleywegt, W. G. R. Weismeijer, G. J. Van Driel, W. L. Driessen and J. Reedijk, J. Chem. Sot., Dalton Trans. 1985, 2177. 15. R.
Whyman and W. H. Hatfield, Inorg. Chem. 1967,
6, 1859. 16. W. H. Watson, Znorg. Chem. 1969, 8, 1879. 17. R. W. Horn, E. Weisberger and J. P. Collman, Inorg. Chem. 1970,9,2367. 18. G. J. Kubas, A. C. Larson and R. R. Ryan, J. Org. Chem. 1989,44,3867. 19. V. C. Burschka, F. E. Bauman and W. A. Schenk, Z. Anorg. Allg. Chem. 1983, 502, 191. 20. P. Conway, S. M. Grant, A. R. Manning and F. S. Stephens, Znorg. Chem. 1983,22, 3714.
REACTIVITY OF MANGANESE(I1) COMPLEXES OF DERIVATIVES OF 2-METHYLPYRIDINE-N-OXIDE TOWARDS SULFUR DIOXIDE* M. FONDO,
M. R. BERMEJO,? E. GOMEZ
Departamento de Quimica Santiago de Compostela,
A. SOUSA,t FORNEAS
J. SANMARTiN
and
InorgBnica, Facultade de Quimica, Universidade de Santiago de Compostela, Galicia, E- 15706 Spain and C. A. McAULIFFEt
Department
of Chemistry, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 IQD, UK (Received
8 Januar?, 1996 ; accepted 2 Fehruur?, 1996)
Abstract-The metallic complexes [Mn(2-PyCO),,X,(H,O),](2-PyCO = 2_methylpyridineN-oxide, n = l-3. X = Cl, Br, I and NO, and x = O--3) have been synthesized and their reactions with sulfur dioxide, both in the solid state and as toluene slurries at room temperature, have been investigated. Furthermore, the reactivity of these complexes with sulfur dioxide at high temperature has been studied by thermogravimetric analysis (TGA), the temperature range of study depending critically on the melting point of the initial complexes. All the complexes, except the chloride derivative, react with sulfur dioxide at room temperature. Increase in the temperature, in general, disfavours this reaction and the amount of sulfur dioxide fixed decreases at high temperature. Finally, desorption studies have been carried out in order to discover whether the reaction of the precursors with sulfur dioxide is reversible. Copyright 0 1996 Elsevier Science Ltd
Aside from its renown as a source of acid precipitation, sulfur dioxide is remarkable in possessing coordination properties that are more diverse than those of any other small molecule. The diversity of the coordination modes established for SO,‘,’ has stimulated numerous studies, predominately focused on the second and third row transition metal complexes. We have extended our investigations on the coordination chemistry of first row transition metal complexes containing phosphine and arsine oxide
ligands’ ’ with sulfur dioxide, to complexes with pyridine-N-oxide derivatives as ligands. In this paper we report the synthesis and characterization of mono, bis and tris complexes of 2methylpyridine-N-oxide (2-PyCO) with manganese halides and nitrate and their reactivity towards sulfur dioxide in the solid state and as toluene slurries at room temperature and in the solid state at high temperature.
EXPERIMENTAL Preparation *Dedicated to the Royal University of Santiago de Compostela in the year of its V century. t Authors to whom correspondence should be addressed.
of the precursors
The syntheses were performed in absolute ethanol, using the metal salts MnCl,, MnBr,*4H,O,
3881
M. FOND0
3882
MnI, and Mn(NO& * 6H,O and the 2-methylpyridine-N-oxide without further purification. These complexes were obtained by a method preThe salt (2 mmol) was disviously described.‘,” solved in ethanol (25 cm’) at room temperature and the ligand (in 1 : 2 or 1 :4 ratios) was added. The mixtures were stirred for 24 h and the powder isolated by filtration, washed with diethyl ether and dried. The solution of nitrate derivative in the molar ratio 1 : 4 generates an oil which, on trituration with diethyl ether, results in powder formation. The solutions of chloride, iodide and nitrate derivatives in molar ratios 1 : 2 and 1 : 4 yield only the ligand : metal 1 : 1 adduct ; the solutions of the bromide derivatives yield the precursors 1 : 2 and 1 : 3 (Table 1).
et al.
results in an increase in the temperature of the sample until its melting point is reached, whilst a gas flow of 50 cm3 min-’ is maintained. The relative proportions of SO, and nitrogen are controlled with Rosemount mass/flow meters at the time the temperature is decreasing. The uptake of SO, was monitored for samples (0.040.08 g) using a series of temperature/partial programmes. (iv) High temperature SO, desorption. Sulfur dioxide desorption studies were performed on the same thermogravimetric balance by heating the sample (0.02-0.5 g) until its melting point and maintaining it under a nitrogen stream for 12-24 h, or by heating the compound in a Rotaflo tube until its melting point, under reduced pressure for 7 h. The resultant complexes were studied by elemental analyses. Elemental analyses were performed by the USC and UMIST Microanalytical Services. Infrared spectra were obtained as KBr pellets or as Nujol spectroresults using a Nicolet PC5 FT-IR photometer in the range 2100400 cm-‘.
Reactions with sulfur dioxide (i) Solid state at room temperature. A sample (0.1-0.3 g) of the complex, contained in a Rotaflo tube, was exposed to sulfur dioxide for several days until a constant mass was achieved. The compounds were managed and isolated under an inert atmosphere. Full details of this procedure have been published previously.” (ii) Toluene slurries. Slurries were prepared using dry distilled toluene (Na, benzophenone) and performed in a pre-dried round-bottomed flask fitted with a side-arm and ground-glass tap. Manganese precursors (0.054.30 g) were added to the flask and the slurry saturated with sulfur dioxide. The flask was then sealed and the contents stirred for ca 7 days, after which the products were isolated by standard Schlenk techniques and dried in a stream of argon. Full details of the synthesis have been previously described.6c.8” (iii) Solid state at high temperature. The absorption of sulfur dioxide at high temperature was studied using a CAHN Instruments TG131 thermogravimetric balance. The programmed scheme
RESULTS
AND DISCUSSION
Metal complexes The synthesis of the metal complexes has been performed by a method previously described,“.” with little change, the salts were not dehydrated previously and the reaction was performed at room temperature, not in hot ethanol. The elemental analyses, IR data and some physical properties for these compounds are shown in Tables 1 and 2. The IR spectrum of 2-methylpyridine-N-oxide has been studied by Karayannis et a1.,12assigning v(N0) at 1244 cm-’ and 6(NO) at 851 cm-‘. All the metallic precursors show a negative shift (2454 and 3-8 cm-‘) in v(N0) and s(NO), reflecting a decrease in the strength of the N-O bond, as
Table 1. Analytical data for the metal complexes Analyses” (%) Metal complex Mn(2-PyCO)Cl,(H,O) Mn(2-PyCO)zBrz(HZO)x Mn(2-PyCO)&,(H@), Mn(2-PyC0)21, Mn(2-PyCO),(NQ),(H@) u Calculated
C
H
N
28.5(28.5) 29.3(29.5) 36.0(36.2) 27.0(27.3) 35.3(34.7)
3.2(3.5) 4.2(4.1) 4.5(4.5) 2.5(2.6) 3.7(3.8)
5.6(5.6) 5.4(5.7) 6.7(7.0) 5.4(5.3) 13.3(13.4)
values in parentheses.
Reactivity
of manganese(II)
Table 2. IR data and some physical
properties
complexes
3883
for the metal complexes IR” (cm-‘)
___~ Metal complex Mn(2-PyCO)CI,(H,O) Mn(2-PyCO)ZBr2(H20),* Mn(2-PyCO),Br,(H,0)1* Mn(2-PyCO)J,
Mn(2-PyCO),(N0,)2(H,0) “All spectra performed
Colour
M.p. (C)
\)(NO)
fi(NO)
v(NOJ
White Yellow Ochre Brown Pale yellow
z 300 163-165 102-103 126128 17cL172
1198s 1220s 1194s lI9Os 1209s
845s 846s 841s 871s 847s
13oos, 815s
in Nujol except those marked
with an asterisk which have been obtained
expected. Only for the iodine derivative there is a displacement of 6(NO) towards higher frequency observed with respect to the free ligand ; this fact is probably due to the removal of electronic charge from the nitrogen atom of the pyridine ring resulting in a higher concentration of charge in the N-O bond, as proposed by Ahuja and Rastogi.” The nitrate complex shows bands at 1300 and 8 15 cm ’ assignable to the nitrate ion acting as a monodentate group.” Previous work with this ligand and copper compounds indicates that the 1 : 1 adducts are tetrahedral dimers.” with one chloride acting as a bridge, and the 1 : 2 adducts are monomers.‘” Nevertheless, no 1 : 3 adducts have been reported previously.
The reactivity of the same metallic precursor with sulfur dioxide in the solid state and as toluene slurries at room temperature is quite different, as the SO, adducts obtained from the two states are quite different. Thus, the medium of the reaction appears to play an important role in the reactivity of these
Table 3. Analytical
precursors with sulfur dioxide, as has been observed previously.x In spite of the marked differences in the adducts formed, there are some common aspects in the reactivity of the precursors towards sulfur dioxide at room temperature. All the metal complexes studied, except the chloride derivative, show reactivity towards sulfur dioxide in the solid state and in toluene slurries at room temperature. The nitrate derivatives fix most SO, and show a displacement of the nitrate group by the sulfate, this fact is confirmed by the elemental analyses (Tables 3 and 5) and by the new bands at frequencies lower than 900 cm ’(Tables 4 and 6). In the two mediums one mole of sulfur dioxide is oxidized to sulfate. perhaps as a consequence of the reduction of the nitrate group to nitrogen oxides, in agreement with other results found by us.’ These sulfate groups generate bands at 8855872, 661--644 and 615-540 cm -’ in the IR spectra, which accord with a sulfate group acting as a bidentate chelate.” The r(N0) and 6(NO) frequencies for the coordinated 2-methylpyridine-N-oxide were assigned in the ranges 120&1188 and 871-839 cm-‘. respectively, for the SO, adducts, and they do not suppose a significant displacement with respect to the initial metallic precursors.
data for the SO? adducts
in the solid state at room temperature Analyses”
Metal complex
SO> adduct
Mn(2-PyCO)Cl,(H,O) Mn(2-PyCO)ZBr,(H,0), Mn(2-PyCO),Brz(H,0)J Mn(2-PyCO),I, Mn(2-PyCO)z(N0J2(H20) ._______~_
No reaction Mn(2-PyCO),Br,(SO,)(Hzo)2 Mn(2-PyCO),Br,(SO&(H,O), Mn(2-PyCO),I,(SOJ1 Mn(2-PyCO)ZS0,(SOz)z(H10),
”Calculated
values in parentheses.
as KBr pellets.
( ‘70)
G
H
N
S
26.6(27.0) 29.7(29.8) 21.6(21.9) 26.6(27.0)
3.3(3.4) 4.0(3.7) 2.6(2.1) 3.5(3.4)
5.2(5.7) 5.8(5.8) 4.2(4.3) 5.4(5.3)
6.5(6.0) 9.1(8.8) 9.4(9.8) 17.7(18.0)
3884
M. FOND0 et al.
Reactions with surfur dioxide in the solid state at room temperature New adducts obtained after interaction with SO, in the solid state at room temperature fix between 1 and 3 moles of sulfur dioxide per mole of metallic precursor (Table 3). This reaction is accompanied by changes in colour and, sometimes, in aspect. Most of the SO, adducts are unstable in air and decompose when they are dissolved in alcohols. Infrared spectra. The ranges of frequencies for the different binding modes of the sulfur dioxide were compiled by Kubas and co-workers.2b The only new binding mode established later is the insertion of sulfur dioxide in a metal-halide bond, as reported by McAuliffe and co-workers.3 Although strong correlation between infrared stretches and SO, bonding modes exist, overlap between the infrared regions for each mode can occur and so this technique cannot unequivocally provide bonding assignments and must be used in conjunction with other data. The IR spectra of the adducts between 500 and 100 cm-’ are not useful and it was not possible to assign new bonds in this range owing to the great number of bands presented by the ligand in this zone. In the IR spectra of these adducts between 2000 and 500 cm-’ we could not assign new bands for most of the halide derivatives. Only for Mn(2PyCO)2Br,(S02)(H20)2 do we observe the appearance of two new bands at 1261 and 1065 cm-‘, assignable to S-O stretching modes; these bands suggest a possible yl’-S planar or a ligand-bound mode for this molecule of sulfur dioxide. The same behaviour is expected for the sulfur dioxide linked in Mn(2-PyC0),@0,)(S0,),(H,0),, which generates bands at 1240 and 1090 cm-‘. Sulfur dioxide desorption studies. Desorption studies are a very important tool, in combination with IR spectroscopy and analogy with other well characterized complexes, in postulating the possible binding mode of sulfur dioxide in SO, adducts. Kubas and co-workers2’ indicated that, in general, if the bonding mode is ligand bound, SO* must be lost by heating in a reversible process, in contrast with the irreversible process for the y’-S planar binding mode. The desorption of Mn(2-PyCO),Br2(S02)(H20), (see Table 7) yields the product Mn(2-PyCO) Br2(H20)2, showing that the SO, is linked in a labile manner. This lability and the IR bands at 126 1 and 1065 cm-’ accord with a ligand-bound binding mode. When we studied the desorption of the Mn(2PyCO),Br,(SO,),,, adduct, obtained from toluene slurry, which exhibits an IR band at 1240 cm-‘, we
Reactivity Table 5. Analytical
of manganese(H)
data for the SO, adducts
complexes formed
3885
in toluene slurries _~ Analyses”
Metal complexes
SO? adduct
Mn(?-PyCO)CI,(H20) Mn(2-PyCO)IBr2(H,0)J Mn(2-PyCO),Br,(HzO)X Mn(2-PyCO),12 Mn(3-PyCO),(NO,),(H,0)
No reaction Mn(2-PyCO)zBrz(SOz), . Mn(2-PyCO)Br,(SO,)(H20)L Mn(2-PyCO)IZ(SOl),(H,O) Mn(2-PyCO)SO,(SOJ(H,0)
“Calculated
a loss of sulfur dioxide too. The reversibility of the reaction and the IR spectra are in accord with a ligand-bound mode for one mole of sulfur dioxide. The comparison of the IR spectra of this compound with Mn(2-PyCO)z S04(S02)2(HZ0)3, contributes to strengthening the proposed ligand-bound mode for the SO, in this complex. Presumably all the adducts obtained in the solid state present the same ligand-bound mode. Such a supposition is supported by the ability of pyridine-N-oxide to form 1 : 1 adducts with the sulfur dioxide.lX Desorption studies for Mn(2-PyCO),Br,(SOz) (H,O), allow us to conclude that the reaction is reversible. RTSO,
Brl s
40(‘.7h Mn(2-PyCO),Br?(SO1).
So this metallic precursor could be used to reduce SO? in a gas stream at room temperature and to leave it again at 90 C. Reactions
C
H
N
s
27.4(27.2) 17.5(17.1) 13.1(12.8) 20.6(21 .O)
3.0(2.7) 2.4(2.6) 2.0(1.6) 2.6(2.6)
5.0(5.3) 3.2(3.3) 2.8(2.5) 4.3(4.1)
9. I(9. I ) 7.2( 7.6) 11.7(11.3) Ic).O( 18.7)
values in parentheses.
observed
Mn(2-PyCO),
~~~
(%)
n,ith su~ji~ dicuide in tolurne slurries
All the precursors. except Mn(2-PyCO): Br,(H,O), lose at least one mole of 2-methylpyridine-N-oxide when they react with sulfur dioxide in toluene slurries. This fact has been observed previously, “.20 indicating that, really, there is a displacement of the ligand by sulfur dioxide. Ir$Lared spectra. All the SO, adducts exhibit new bands between 2000 and 500 cm-’ assignable to S-O vibrations, and these bands are in accordance with different bonding modes for sulfur dioxide. The infrared spectra are not definitive enough to establish the coordination mode of the SOz. Nevertheless, this study, in combination with sulfur dioxide desorption studies, allows us to propose a
binding mode for the sulfur dioxide linked in these adducts. Su@r dioxide deesorption studirs. The desorption studies show that the sulfur dioxide is strongly bound in these adducts. It is quite robust and is present in the compounds even when they are heated to their melting points (Table 7). For the iodine derivative we observe a loss of halide and 2-PyCO but not loss of SO,. Figure I shows the desorption thermogram of Mn(2-Py CO)J2(S0,),(H20). It is shown that an increase in the temperature (from 120 to 130 ‘C) does not result in a decrease in weight. The elemental analyses of the final compound (Table 7) shows that it is a little impurified by the picoline ligand, but it is clear that all the sulfur dioxide remains in the compound. As all the ligand is lost, it is not possible to think about a ligand-bound sulfur dioxide mode and this SO, must be directly linked to the metal. As the bond Mn-SO2 is irreversible the q’-S pyramidal binding mode is not possible.” The loss of iodine suggests a decrease in the strength of the Mn-I bond, so it is possible that one of the sulfur dioxide molecules is inserted in the Mn-I bond. This fact is supported by an IR band at 1286 cm ‘. Owing to the irreversibility of the reaction, the band at 1320 cm ’ cannot be associated with a simple ligand bound so perhaps this inserted sulfur dioxide is. at the same time. interacting with the ligands. The third band at 1070 cm-.’ and the displacement of a mole of 2PyCO by a mole of SOz permit us to propose an II’S planar binding mode for this second molecule of sulfur dioxide. as was found by Conway ct (11.‘~~ The same q’-S planar bond must be present in Mn(2PyCO)SO,(SO,)(H,O), which also exhibits a band at 1071 cm-‘. When we studied the desorption of Mn(2-Py CO)Br,(S0,)(H,0)2 we only observed a loss of water and ligand. no bromide or SO, was lost. Again, the displacement of one mole of ligand by
3886
M. FOND0
et al.
-60 0.0112-
Time (hrs: min: set)
Fig. 1. Desorption thermogram for Mn(2-PyCO),I,(SO,),(H,O) : ( ?? ) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
the SO2 permits us to propose the vi-S planar binding mode for the sulfur dioxide linked in this compound. The band at 1070 cm-’ present in the iodine derivative is not assigned in this compound owing to the broad band centred at 1150 cm-’ (Figure 2). Different behaviour is shown by Mn(2-PyCO), Br,(S02),,5, which does not show a loss of ligand with respect to the precursor. The desorption study shows a partial loss of sulfur dioxide and ligand ; 1 mole of SO, is lost, together with a 2-PyCO ligand while 0.5 moles remain in the compound. This behaviour and the band at 1240 cm-’ allow us to
propose that the labile SO, is linked in a ligandbound mode, while the 0.5 moles are perhaps acting as a bridge between two metal centres ; these results have been obtained by us8 for other SO, adducts with manganese precursors. As a conclusion of the study at room temperature we observed that the sulfur dioxide is linked preferably to the ligand in those adducts with 2-methylpyridine-N-oxide. Nevertheless, when the reaction takes place in toluene slurry, the easier displacement of the ligand permits the sulfur dioxide to bind to the metal in an y’-S planar binding mode ; the
a
b
Fig. 2. Comparative IR spectra for (a) Mn(2-PyCO)1Br,(H,0)1
and (b) Mn(Z-PyCO)Br,(SO,)(H,O),.
Reactivity of manganese(I1) complexes insertion of SO, into the metal-halide be favoured for the iodine derivatives. found previously.‘,‘”
3887 bond must as we have
The interaction of the precursors with sulfur dioxide at high temperature has been performed using a thermogravimetric balance. These thermogravimetric analyses are particularly interesting because it is possible to study the thermal stability of the metallic complexes and the optimum temperature range over which SO, absorption occurs by these complexes. We have observed (Table 8) that the reaction of the metal complexes selected by us with SO, is temperature dependent and this process is disfavoured when the temperature increases. In this way. only the nitrate derivative Mn(2-PyCO)z(N0J7(H20) is able to absorb more than I mole of sulfur dioxide per mole ofprecursor. This reaction, at high temperature. presents three phenomena. 1. One mole of 2-methylpyridine-N-oxide is lost, being replaced by a molecule of SOz. The loss of one mole of pyridine ligand shows that the precursor is quite unstable towards temperature. 2. The molecule of sulfur dioxide is oxidized to sulfate, perhaps as a consequence of the reduction of the nitrate group. which is displaced. 3. The absorption of sulfur dioxide occurs very quickly. The compound being almost saturated at 140’C, after which the compound does not absorb a significant quantity of SO,, even when the temperature decreases to 30 C (Fig. 3). The only halide precursor that is able to fix and is the Mn(2-PyCO), sulfur dioxide retain Br2(H,0),. This compound can fix 0.5 moles of sulfur dioxide per mole of compound, but it does not react at a temperature higher than 120 C (Fig. 4) and the reaction is very slow, even when we study the reaction in the temperature range 80-30’ C (Fig. 5). The complex Mn(2-PyCO),Br,(H,O), decomposes when it is heated at 100 C for 30 min, losing ligand, and the resultant compound does not react with SO,. Different behaviour is shown by Mn(2PYCO)~I,, which shows a little increase in its weight when it is exposed to a sulfur dioxide stream in the temperature range 100-30 C. Nevertheless. when elemental analysis is performed, no sulfur dioxide is detected. Perhaps in this case the sulfur dioxide
“Calculated
values in parentheses.
Mn(2-PyCO),(NO,),(H,O)
No reaction
Mn(2-PyCO)~Brz(SWO No reaction No reaction Mn(2-PyCO)SO,(SOJ,
Mn(2-PyCO)Cl,(H,O) Mn(Z-PyCO),Br,(H,O), Mn(2-PyCO),Br,(H,O), Mn(2-PyCO),I,
Table 8. Analytical
SO, adduct
values in parentheses.
Metal complex
“Calculated
90 120 220-230 120-130
Mn(2_PyCO)Br,(H,O),
Mn(2-PyCO)zBr,(S0,)(H,0)z Mn(2-PyCO),BrDCW, Mn(2-PyCO)Br,(SOz)(H,0)z Mn(2-PyCO)L(SW,(H,0)
7h 7h 16 h 20 h
Time
obtained
20.2(20.0) 20.8(20.2) 10.6(10.8) 1.7(0.3)
C
25
5
28&30 15&30 9&30 100-30 160-30
Temp. range (“C) 5 3 4 2 11
h h h h h
20 50 20 30
Time min min min min
2.7(3.0) 2.6(2.0) 2.0(1.0) 0.2(0.0)
H
C
25.9(26.1)
(%)
6.2(6.0)
5.3(5.1)
3.9(3.0)
2.3(2.5)
H
N
3.9(3.9) 4.4(4.0) 2.0(2.1) 1.3(0.0)
N
Analyses” (%)
Analysed”
range presented
studies
31.1(31.0)
after SO, desorption
data for the SO2 formed in the solid state in the temperature
Mn(2-PyCO)Br#O& Mn(2-PyCO)0.,BrI(SW MnUOH)(SO,),
T (“C)
Complexes
data for the complexes
SO, adduct
Table 7. Analytical
15.3(14.5)
3.6(3.4)
S
O(O) 5.0(4.5) 9.5(9.6) lU(19.6)
S
3 9 K
8
s
Reactivity
of manganese(H)
complexes
3889
0.0385
170
120
0.0371
s % F 70
0.035L II 0:w:oa
1:10 5: 00: 00
ll:oo:oo
Time (hrs: min: set)
Fig. 3. Absorption thermogram for Mn(2-PyCO)z(N0,),(H,0) in the range 16&30’ C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time. 4 150
0.0398 b
0.0390-
- 120
Time (hrs: min: set)
thermogram for Mn(2-PyCO),Brz(HzO)? in the range 150-30°C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
Fig. 4. Absorption
is physically adsorbed and is lost when the compound is handled in air. As a result of the study at high temperature we can conclude that elevated temperatures disfavour the reactivity of these complexes towards sulfur dioxide, but the behaviour of these compounds indicates an advantage with respect to those precursors of manganese with phosphine and arsine oxide ligands :3~’there is a derivative of halide that
can react with sulfur dioxide perature than room temperature.
at a higher
tem-
CONCLUSIONS The reactivity of the manganese complexes, Mn(2-PyCO),X2(H,0),, with sulfur dioxide depends on the anion (halide or nitrate) and on the coordination number n. Furthermore. the reaction
M. FOND0
3890
et al. i
0.0305 1 r’
F----l
0.0296
:98
3 E s
E
0.0288
-62
's
-
3
E" g
-42
Time (hrs: mix set)
Fig. 5. Absorption thermogram for Mn(2-PyC0)2Br,(H,0)3 in the range 10@3O”C : (+) represents the temperature and (0) the curve of the variation of mass versus temperature and time.
medium influence the ability of the complexes to react with sulfur dioxide. A third factor is the temperature, which disfavours the uptake of SO,. Finally we must point out that the precursor Mn(2PyC0)2Br,(H20), is able to fix SO2 in a reversible way, it absorbs SO2 at room temperature and evolves it above 90°C. REFERENCES 1. W. A. Schenk, Angew. Chem., Int. Ed. Engl. 1987, 26, 98. 2. (a) G. J. Kubas, Znorg. Chem., 1979, 18, 182 and
references therein ; (b) R. R. Ryan, G. J. Kubas, D. C. Moody and P. G. Eller, Struct. Bond. 1981,46,48. 3. J. A. Gott, J. Fawcett, C. A. McAuliffe and D. R. Russell, J. Chem. Sot., Chem. Commun. 1984, 1283. 4. K. Al-Farham, B. Beagley, 0. El-Sayrafi, G. A. Gott, C. A. McAuliffe, P. P. MacRory and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1990, 1243.
5. (a) S. M. Godfrey, D. G. Kelly and C. A. McAuliffe, J. Chem. Sot., Dalton Trans. 1992, 1305 ; (b) S. M. Godfrey, C. A. McAuliffe, G. C. Ranger and D. G. Kelly, J. Chem. SOL, Dalton Trans. 1993, 2809. 6. (a) C. A. McAuliffe, B. Beagley, G. A. Gott, A. G. MacKie, P. P. MacRory and R. G. Pritchard, Angew, Chem., Int. Ed. Engl. 1987, 26, 264 ; (b) B. Beagley, 0. El-Sayrafi, G. A. Gott, D. G. Kelly, C. A. McAuliffe, A. G. MacKie, P. P. MacRory and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1988, 1095; (c) B. Beagley, D. G. Kelly, P. P. MacRory, C. A. McAuliffe and R. G. Pritchard, J. Chem. Sot., Dalton Trans. 1990,2657.
7. S. M. Godfrey, D. G. Kelly, C. A. McAuliffe and R. G. Pritchard, J. Chem. SOL, Dalton Trans. 1995, 1095. *. (a) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Forneas, Acta them. &and. (in press) ; (b) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Foneas, Inorg. Chim. Acta (in press) ; (c) J. Sanmartin, M. R. Bermejo, A. Sousa, M. Fondo, C. A. McAuliffe and E. Gomez-Forneas, Synth. React. Inorg. Met-org. Chem. (in press). 9. M. R. Kidd, R. S. Sager and W. H. Watson, Inorg. Chem. 1967,6,947.
10. D. H. Brown, D. Kenyon and D. W. Sharp, J. Chem. Sot. (A), 1969, 1474.
11. D. S. Barratt, C. G. Benson, G. A. Gott, C. A. McAuliffe and P. Tanner, J. Chem. Sot., Dalton Trans. 1985, 2661.
12. N. M. Kardyannis, L. L. Pytewski and C. M. Mikulski, Coord. Chem. Rea. 1973, 11, 93. 13. I. S. Ahuja and P. Rastogi, J. Nucl. Chem. 1970,32,138 I. 14. G. J. Kleywegt, W. G. R. Weismeijer, G. J. Van Driel, W. L. Driessen and J. Reedijk, J. Chem. Sot., Dalton Trans. 1985, 2177. 15. R.
Whyman and W. H. Hatfield, Inorg. Chem. 1967,
6, 1859. 16. W. H. Watson, Znorg. Chem. 1969, 8, 1879. 17. R. W. Horn, E. Weisberger and J. P. Collman, Inorg. Chem. 1970,9,2367. 18. G. J. Kubas, A. C. Larson and R. R. Ryan, J. Org. Chem. 1989,44,3867. 19. V. C. Burschka, F. E. Bauman and W. A. Schenk, Z. Anorg. Allg. Chem. 1983, 502, 191. 20. P. Conway, S. M. Grant, A. R. Manning and F. S. Stephens, Znorg. Chem. 1983,22, 3714.