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Vapour pressure measurements on M(CO)5PX3 (M = Cr, Mo, W; X = F, Cl, Br)
~-m/t~ At'~rn.~ (1978) 261-267 ~) Els~ar Scicnlific Publishing Company. An~c~dam - Printed in The h~harbnds
VAPOUR PRESSURE X = F.C!, Sr)
MEASUREMENTS
ON M(CO)sPX 3 (M
--- C r , M o , W ;
G . B O X H O O R N . A . (7. JESSE. J. M. F ~ I ' I ~ G
. 4 m w j ~ r h Clermisrh ~ m ' i m n . J . (T&- Aoedx-dam~)
A . ~ A- O S K A M ° It. ran "l I l o f f ln~itm~r. Unirersily o f Ann-terdm~..4rn~erdam
(P.o:Emed 7 January I,Fi~
ABSTRACT
T h e v a p o u r prc~mr¢~ a n d the cnthalpies o f sublimation for the complexes M(CO)sPX3 (M = Cr. Mo. W; X = F. CI. Br) were determined by the Knudsen effusion m e t h o d . T h e monosubslltuted complexes ha~e c o m p a r a b l e enthalpies o f sublimation as have been found for the hexacarbonyls. i~'~I~tOOUCTIO.~ In the course o f a study o f the photochemical behaxiour o f M ( C O ) ~ P X j (M = Cr, Mo. ~,V; X = F. CI. Br) in A r m a t r i c ~ at l 0 K. it appeared to be necessary [o k n o w the ~-apour pressures o f these carbonyl complexes ~ i t b high accuracy. I. Recently thermochemical investigations have bccn carried out in o u r laboratory o n (acac)M(subslitutcd ol¢fin) z and ( a c a c ) M ( C O ) : ; M = R h ( I ) . l r ( I ) z. T h e ~apour pressures
a n d cnthalpies o f sublimation o f these complexes were determined by the Knudscn effusion n ~ t h o d , which [cchniquc has been sho,vn to be suitable for complexes ,~ith low ~apour p r ~ u r e s : - a_ Therefore. in this paper Ii~ report the v a p o u r pressures a n d the enthalpies o f sublimation for the M(CO)sPX3 complexes, determined by the K n u d s e n effusion method.
T h e M(CO)sPX3 complexes ~ r c synthcsiscd, using standard literature m e t h o d s • - io ,~ith slLeht modifications, as has been described in a previous paper I i T h e thermochemical mea_~uremcnts ~ r e m a d e using a Merrier Therrnoanalyscr type I. with a K n u d s c n cell placed o n the balance_ T h e installation a n d construction o f the K n u d s e n cell has been published elsewhere=- ~. "l'he diameters o f the orifice ,s~TC 0.1 a n d I m m a n d the sample ,,eights x~aried between 100 a n d 200 m ~ T h e vacuum ~ s better than 3 >: I 0 - 4 Pa a n d the temperature ~ l s kept ° To whom ~
slmuld bc addressed.
262 constant to :~ 0.1 K. The re:curacy in dm;AI was about I :< I 0 - *: kg s c c - *. ~,Vilh 111¢ aid o f the K nudsen equation ( ! )
~lm •¢l~p
I | / ??~RT
(J)
----- v a p o u r p r e s s u r e , z i n n i A ! - - r 3 l e o r w e i 2 h !
I_~K~_<.q --
calibrated oril'ce a r e a ,
R = ~
~ t . T ----- t e m p e r a t u r ~ : t l = molecular ~ei~_ht. the equilibrium v : z p o u r pressures wcr~ calculatcd. A plot o f the tcmpcraturc a~zinst In prcssurc rcsu!tcd in a curve according to eqn- (2_) Inp=
A --~4-
B
(2)
T h e cnthalp~r o J ' s u b l i r n a t i o n ~ c 5 c ~ l c u l a l c d f r o m Ih~'~ eqU.'lfion- T h e s t a n d a r d dc~'iation
for th~ d H , ~ u c s was delermincd by a lcast squares analysis. Bcnzoic acid, supplied b y M e r r i e r . q~c5 u s e d a s a s t a n d a r d . RE3LqL'I'S A~.~D ~
0
~
Th~ orifice calibration o f the Knudsen cell v,i t h a n orifice diameter o f I m m has b a r n publishcd by Jesse ct aL z. F o r the Knudscn cell u~th a diameter o f 0-1 ram. the calibration o f the orifice area b y mea.~ring bo1_7_~,~ acid i~ W e n in Table !_ O n l y d a t a (A. B) rqx~rtcd by Wicdemann ~ wcrc usc~. M o ~ of Ihe M(CO),PX~ complcxcs TABLE I
zae/d
~
Tcmp-
Ifr'~
294-1 294.9 297~ 29~7
21 ~--3
3O6.7 .~DS_I
9.1 !12
~312~ 312-9 31~3
16.$ !7"3 217
316.5 31&.:s 3~0-~
?Jo 2~S& 397
37
dF~mc~cr 0-! mm-
b Ca~h~d
m-hh d~,~ from W E d c m a n ~ .
fPa) t ~ Io*U
fm~) (>: l ~ J )
!+1 I-6 I~ Z~ 3.S 4.5 5~ $.7 ,~.4 ~.7 11.3 !2-.5 12J 12-S 19.4 .3!.!
7.3 7-.7 7.4 7.6 6.9 7-6 7.S 7_4 7.4 7.3 7.1 7.6 7.5 7.4 7.6 7.0
263
CraC(~PCI 3 U°aCC15PC13
W(CCI5PC 1 3 ~
1(~ 3-2 310
3.4 3-6 ~__a 270 290Temperat ure [K]
4_0 250
F-,8- i. vapom- prcs~um~of the complc~esC~CO);t'CI:: Mo(CO)--PCI=:W(CO)~I)C~ have low th£~qrnodynamic stability. It is therefore n ~ , ~ a n j to in,~estigate the existence o f the complexes in the gas phase. From all M(CO)~PX~ molecules, pholoclcctron spectra were recorded ~ i l h a volafilc samplc inlet B-stcm ' t Rcccntly, the I R!clcctronic malriX isolation spectra n v.-c~c studied at I0 K. From these m ~ u r e m e n t s and the photocloL'tron SlX~lra it is deduced that thcs~ complexes exist in [hc .~as phase and that decomposition d o ~ not occur. Vapour pressure m,'~_surcments o f Mo(CO)~PBrj. however, m?..,~not carried oul, ~ u s c parlial dccompo~tion could not be avoided. The vapour pressure curves arc sho~vn in Rgs. I-3. The m~_sured vapour pre~mres and cnthalpies o f sublimation o f the complexes are compilcd in Tablc 2. The M(CO)sPX~ complexes havc similar enthalpics o f sublimation, a~ have been found for M(CO)h (Table 3: rcf. I~.a, b). The trends in the monosubslitutcd complexes and in the hcxacarbony!s provod to bc so irre~._ular that, up till nov,., no explanation could be given for the bcha~our oF the enthalpics o f sublimation. Therd'ore, further [hermochemical measurements are needed.
I0 (~s P Ci3
\c c%.pe
.cr(co~
PF 3
.,,To m~
3! 0
2'30
270.. T ~ m l ~ r a | u r ~ LKI
250
F'-~ ~ Vapour ~rcssurcs o f ~ ~ c n c c o I s P l ~ C r ( C O ~ ' C I ~ Cn~COh~'Br~- A l a ~ c r ram d ~ ~ dur/n~ d ~ ~ hours o f m ~ s m ~ m m ~ was o i ~ ! rot the M(CO)A~I~ c o m p ~~. _~r~ p f ~ due to a soh~nt impu~v.
265
~w (~C t%( PCI3 C O~PF3
"W O =S mb 0
"e~
32 310
34
3.8
290
T
38
270 Temper;~lure [K]
4;.0 250
Fit.- ~- Va4pour pressures or II~ ~ m ~ T~V(CO):.PF~ ",V(CO):I~-IL~:Vh'(CO).~PBra. A hiD'~r rate o f w e i ~ loss during uhe f u ~ hours o f d~c ~ t s ~ ~ : d for the ~ltCO):.PF~ complexer,. probably duc to a sol,~nt impurity-
266 TABLE 2
d Tony.
W,-Q.&r
Prr,J~m~
(E)
.!~_~
(Pa)
dH. ( k J mole" U
( :~ I0"-~-) C~CO~PF-~
251.8
~
0-7
M ~ ~
2550 263.0 2Z~'/ 269.7 275-7
47 140 173 359 753
I-4 4-2 $~ 10-9 23-1
O(CO)~PCI~*
2~0-8 261-9 263-9
66 74 99 136 212 395 846
1.8 2.0 ~7 3-S 5-9 !1~ Z4-1 49.0
3 ~ / ~ 329-385
_270.5 275-9 21~0-9
I'~01
C~CO~.PBr~ ~ r ~. 462.753
~-0 2"/5-I 278-1 281-1 2&3-1 283.3 :~-!
9 20 29 56 69 51 ~
0-2 0-.~
AH~ ~ 85.5 ~ ?-9
A ~ 9~0 ~ ~00 B ~ ~4-6
J H ~ ~ 7 & 9 ~ I-8
A u 9600 ~ ~ 0
d H s ~ 79-9 ~ I-9
/ 1 1 , = 9 5 4 0 - - 130 B ~ J4.2
~lHs ~ 79.3 ~ I-I
A~9310~ B == 3~-9
~ H s ~ "77.4 :~ I,.7
O-7 1.4 I-7 I~ -"
286-'7 290-7 294.9 29S-I ~4~.-7 • ~'/-0
84 134 20~ 321 495 779
3.3 5-1 8-O 12-4 19-6
M ~ 3"/3-3~-3
264-7 267.3 ~.2 277? 272..5 2"/5. I 27ELI 2S0.& 281.3 28"/.1
43 61 87 115 159 165 ~.~.-I 335 ~4 509 9"/5
I-I I-7 2.3 3.0 4-2 4.4 5*9 8-9 ! 1-9 13.6 26-4
V~CO)~PF-~
2~'LI 263A, 267.'7
I$ 36 65
0-4 0.9 1.6
~= 411.S'~5
A ~ 10300 -~ ~ 0
I$0
267 T A B L E 2 (~nntinurd)
Inp . . . . .
T~"~p!a~
(kg ~rc-~)
A
~- B
T
( Pa ) ( :< I O " )
.IH,
(kJ mole- ~)
( :~ Io-**-) ~V(CO}:PCI-,"
A! ~- 461 ~-?.35
W(CO~PBr:P AI =~ 594-6O3
~ I 261.9 265-7 27O-0 2T~_5 275-3 2~3 288-1 ?~5.7 289.4 294.O 29~-? 303:/
47 61 92
196 291 429
O~ 0-2 OA 0-~
.,4 ~ 1 0 4 0 0 ~; 2 0 0 B ~ 35-~
.IH,~ '~ 8 6 - 2
" I-7
:Ills ~
:~ 5-3
I-2
1059
1.7 4-3
19~
8-1
I0 13 22 43 ~0
O~
A ~ 9--'~J0 ~: 6 4 0
0-3
B ~ 28-6
T/~
0.5
0-9 1.3
Orif, c~ d i a n ~ r 0.1 tomb Orifice d i~m~cr I mm•" Moiocular vci~hm$ in TABLE 3
~tl(CO)s
Cannor r ! el. ' ~
Pilclwr r l el. '~"
Cr(COI~ Mo(CO~ w(CO)~
71~ 70-,~ sl~
71~ 73.~ ~(,_5
I
G. Boxhoom and A . Oskam. Inorx. Chim. Acta. 29 (1978} Z43. A- C. J c s ~ , J. M. EmslinS, D. J- Sluflccns and K. V ~ ~himActa. 25 (1978) 69. 3 H- G- V i ' ~ ~himAc!a. 3 {1972) 3554 L- ~ . l a ~ . ! ~ Gi~!i and G . Bm~di, J . L ~ m - P h i - , 59 (!973) 3875 W. Strohmcicr an d F. J- Mfillar. C/~rm- BET-. 10"1(1969) .~08. 6 l ~ J . CIm4c an d P . J . H o b c m ~ n , lnmT- Chore-,4 (196~ 1771. ? J_ Mfill~r. i~. U-trade! and B- M ~ Chem. Bet.. 104 (1971) 700g R- Poi!blau~ and M- B i ~ n c , Bull. Soc. Chim. Fr.. 29 (1962) 1301. 9 D.J. i ~ ~ a n d T . L Bro~-n. In~rt . Cl~rm., 7 ¢196~ 959. 10 E- O- Fro:her an d L K n a u ~ . Chrm. Brr.. liP. ¢1969) 223. I I 14L ~ G. ~ am~l A- ~ lnorl- Clu'm- A~'fa- 2B i1978) 263I:~a J- A - Cmmor, I-IL.A - ~kinncr and Y . Virmani. J. Clarm. ~ r . . Faraday Trm~r I, (1972) 1754, and n:fs- d ~ n ~ . b G- IPiich~. M- J. W a r e and D . A. Pitlam. J . ~ o m m o n Ale.*., 42 (1975) 223, a n d ref~ flzrein. 2
VAPOUR PRESSURE X = F.C!, Sr)
MEASUREMENTS
ON M(CO)sPX 3 (M
--- C r , M o , W ;
G . B O X H O O R N . A . (7. JESSE. J. M. F ~ I ' I ~ G
. 4 m w j ~ r h Clermisrh ~ m ' i m n . J . (T&- Aoedx-dam~)
A . ~ A- O S K A M ° It. ran "l I l o f f ln~itm~r. Unirersily o f Ann-terdm~..4rn~erdam
(P.o:Emed 7 January I,Fi~
ABSTRACT
T h e v a p o u r prc~mr¢~ a n d the cnthalpies o f sublimation for the complexes M(CO)sPX3 (M = Cr. Mo. W; X = F. CI. Br) were determined by the Knudsen effusion m e t h o d . T h e monosubslltuted complexes ha~e c o m p a r a b l e enthalpies o f sublimation as have been found for the hexacarbonyls. i~'~I~tOOUCTIO.~ In the course o f a study o f the photochemical behaxiour o f M ( C O ) ~ P X j (M = Cr, Mo. ~,V; X = F. CI. Br) in A r m a t r i c ~ at l 0 K. it appeared to be necessary [o k n o w the ~-apour pressures o f these carbonyl complexes ~ i t b high accuracy. I. Recently thermochemical investigations have bccn carried out in o u r laboratory o n (acac)M(subslitutcd ol¢fin) z and ( a c a c ) M ( C O ) : ; M = R h ( I ) . l r ( I ) z. T h e ~apour pressures
a n d cnthalpies o f sublimation o f these complexes were determined by the Knudscn effusion n ~ t h o d , which [cchniquc has been sho,vn to be suitable for complexes ,~ith low ~apour p r ~ u r e s : - a_ Therefore. in this paper Ii~ report the v a p o u r pressures a n d the enthalpies o f sublimation for the M(CO)sPX3 complexes, determined by the K n u d s e n effusion method.
T h e M(CO)sPX3 complexes ~ r c synthcsiscd, using standard literature m e t h o d s • - io ,~ith slLeht modifications, as has been described in a previous paper I i T h e thermochemical mea_~uremcnts ~ r e m a d e using a Merrier Therrnoanalyscr type I. with a K n u d s c n cell placed o n the balance_ T h e installation a n d construction o f the K n u d s e n cell has been published elsewhere=- ~. "l'he diameters o f the orifice ,s~TC 0.1 a n d I m m a n d the sample ,,eights x~aried between 100 a n d 200 m ~ T h e vacuum ~ s better than 3 >: I 0 - 4 Pa a n d the temperature ~ l s kept ° To whom ~
slmuld bc addressed.
262 constant to :~ 0.1 K. The re:curacy in dm;AI was about I :< I 0 - *: kg s c c - *. ~,Vilh 111¢ aid o f the K nudsen equation ( ! )
~lm •¢l~p
I | / ??~RT
(J)
----- v a p o u r p r e s s u r e , z i n n i A ! - - r 3 l e o r w e i 2 h !
I_~K~_<.q --
calibrated oril'ce a r e a ,
R = ~
~ t . T ----- t e m p e r a t u r ~ : t l = molecular ~ei~_ht. the equilibrium v : z p o u r pressures wcr~ calculatcd. A plot o f the tcmpcraturc a~zinst In prcssurc rcsu!tcd in a curve according to eqn- (2_) Inp=
A --~4-
B
(2)
T h e cnthalp~r o J ' s u b l i r n a t i o n ~ c 5 c ~ l c u l a l c d f r o m Ih~'~ eqU.'lfion- T h e s t a n d a r d dc~'iation
for th~ d H , ~ u c s was delermincd by a lcast squares analysis. Bcnzoic acid, supplied b y M e r r i e r . q~c5 u s e d a s a s t a n d a r d . RE3LqL'I'S A~.~D ~
0
~
Th~ orifice calibration o f the Knudsen cell v,i t h a n orifice diameter o f I m m has b a r n publishcd by Jesse ct aL z. F o r the Knudscn cell u~th a diameter o f 0-1 ram. the calibration o f the orifice area b y mea.~ring bo1_7_~,~ acid i~ W e n in Table !_ O n l y d a t a (A. B) rqx~rtcd by Wicdemann ~ wcrc usc~. M o ~ of Ihe M(CO),PX~ complcxcs TABLE I
zae/d
~
Tcmp-
Ifr'~
294-1 294.9 297~ 29~7
21 ~--3
3O6.7 .~DS_I
9.1 !12
~312~ 312-9 31~3
16.$ !7"3 217
316.5 31&.:s 3~0-~
?Jo 2~S& 397
37
dF~mc~cr 0-! mm-
b Ca~h~d
m-hh d~,~ from W E d c m a n ~ .
fPa) t ~ Io*U
fm~) (>: l ~ J )
!+1 I-6 I~ Z~ 3.S 4.5 5~ $.7 ,~.4 ~.7 11.3 !2-.5 12J 12-S 19.4 .3!.!
7.3 7-.7 7.4 7.6 6.9 7-6 7.S 7_4 7.4 7.3 7.1 7.6 7.5 7.4 7.6 7.0
263
CraC(~PCI 3 U°aCC15PC13
W(CCI5PC 1 3 ~
1(~ 3-2 310
3.4 3-6 ~__a 270 290Temperat ure [K]
4_0 250
F-,8- i. vapom- prcs~um~of the complc~esC~CO);t'CI:: Mo(CO)--PCI=:W(CO)~I)C~ have low th£~qrnodynamic stability. It is therefore n ~ , ~ a n j to in,~estigate the existence o f the complexes in the gas phase. From all M(CO)~PX~ molecules, pholoclcctron spectra were recorded ~ i l h a volafilc samplc inlet B-stcm ' t Rcccntly, the I R!clcctronic malriX isolation spectra n v.-c~c studied at I0 K. From these m ~ u r e m e n t s and the photocloL'tron SlX~lra it is deduced that thcs~ complexes exist in [hc .~as phase and that decomposition d o ~ not occur. Vapour pressure m,'~_surcments o f Mo(CO)~PBrj. however, m?..,~not carried oul, ~ u s c parlial dccompo~tion could not be avoided. The vapour pressure curves arc sho~vn in Rgs. I-3. The m~_sured vapour pre~mres and cnthalpies o f sublimation o f the complexes are compilcd in Tablc 2. The M(CO)sPX~ complexes havc similar enthalpics o f sublimation, a~ have been found for M(CO)h (Table 3: rcf. I~.a, b). The trends in the monosubslitutcd complexes and in the hcxacarbony!s provod to bc so irre~._ular that, up till nov,., no explanation could be given for the bcha~our oF the enthalpics o f sublimation. Therd'ore, further [hermochemical measurements are needed.
I0 (~s P Ci3
\c c%.pe
.cr(co~
PF 3
.,,To m~
3! 0
2'30
270.. T ~ m l ~ r a | u r ~ LKI
250
F'-~ ~ Vapour ~rcssurcs o f ~ ~ c n c c o I s P l ~ C r ( C O ~ ' C I ~ Cn~COh~'Br~- A l a ~ c r ram d ~ ~ dur/n~ d ~ ~ hours o f m ~ s m ~ m m ~ was o i ~ ! rot the M(CO)A~I~ c o m p ~~. _~r~ p f ~ due to a soh~nt impu~v.
265
~w (~C t%( PCI3 C O~PF3
"W O =S mb 0
"e~
32 310
34
3.8
290
T
38
270 Temper;~lure [K]
4;.0 250
Fit.- ~- Va4pour pressures or II~ ~ m ~ T~V(CO):.PF~ ",V(CO):I~-IL~:Vh'(CO).~PBra. A hiD'~r rate o f w e i ~ loss during uhe f u ~ hours o f d~c ~ t s ~ ~ : d for the ~ltCO):.PF~ complexer,. probably duc to a sol,~nt impurity-
266 TABLE 2
d Tony.
W,-Q.&r
Prr,J~m~
(E)
.!~_~
(Pa)
dH. ( k J mole" U
( :~ I0"-~-) C~CO~PF-~
251.8
~
0-7
M ~ ~
2550 263.0 2Z~'/ 269.7 275-7
47 140 173 359 753
I-4 4-2 $~ 10-9 23-1
O(CO)~PCI~*
2~0-8 261-9 263-9
66 74 99 136 212 395 846
1.8 2.0 ~7 3-S 5-9 !1~ Z4-1 49.0
3 ~ / ~ 329-385
_270.5 275-9 21~0-9
I'~01
C~CO~.PBr~ ~ r ~. 462.753
~-0 2"/5-I 278-1 281-1 2&3-1 283.3 :~-!
9 20 29 56 69 51 ~
0-2 0-.~
AH~ ~ 85.5 ~ ?-9
A ~ 9~0 ~ ~00 B ~ ~4-6
J H ~ ~ 7 & 9 ~ I-8
A u 9600 ~ ~ 0
d H s ~ 79-9 ~ I-9
/ 1 1 , = 9 5 4 0 - - 130 B ~ J4.2
~lHs ~ 79.3 ~ I-I
A~9310~ B == 3~-9
~ H s ~ "77.4 :~ I,.7
O-7 1.4 I-7 I~ -"
286-'7 290-7 294.9 29S-I ~4~.-7 • ~'/-0
84 134 20~ 321 495 779
3.3 5-1 8-O 12-4 19-6
M ~ 3"/3-3~-3
264-7 267.3 ~.2 277? 272..5 2"/5. I 27ELI 2S0.& 281.3 28"/.1
43 61 87 115 159 165 ~.~.-I 335 ~4 509 9"/5
I-I I-7 2.3 3.0 4-2 4.4 5*9 8-9 ! 1-9 13.6 26-4
V~CO)~PF-~
2~'LI 263A, 267.'7
I$ 36 65
0-4 0.9 1.6
~= 411.S'~5
A ~ 10300 -~ ~ 0
I$0
267 T A B L E 2 (~nntinurd)
Inp . . . . .
T~"~p!a~
(kg ~rc-~)
A
~- B
T
( Pa ) ( :< I O " )
.IH,
(kJ mole- ~)
( :~ Io-**-) ~V(CO}:PCI-,"
A! ~- 461 ~-?.35
W(CO~PBr:P AI =~ 594-6O3
~ I 261.9 265-7 27O-0 2T~_5 275-3 2~3 288-1 ?~5.7 289.4 294.O 29~-? 303:/
47 61 92
196 291 429
O~ 0-2 OA 0-~
.,4 ~ 1 0 4 0 0 ~; 2 0 0 B ~ 35-~
.IH,~ '~ 8 6 - 2
" I-7
:Ills ~
:~ 5-3
I-2
1059
1.7 4-3
19~
8-1
I0 13 22 43 ~0
O~
A ~ 9--'~J0 ~: 6 4 0
0-3
B ~ 28-6
T/~
0.5
0-9 1.3
Orif, c~ d i a n ~ r 0.1 tomb Orifice d i~m~cr I mm•" Moiocular vci~hm$ in TABLE 3
~tl(CO)s
Cannor r ! el. ' ~
Pilclwr r l el. '~"
Cr(COI~ Mo(CO~ w(CO)~
71~ 70-,~ sl~
71~ 73.~ ~(,_5
I
G. Boxhoom and A . Oskam. Inorx. Chim. Acta. 29 (1978} Z43. A- C. J c s ~ , J. M. EmslinS, D. J- Sluflccns and K. V ~ ~himActa. 25 (1978) 69. 3 H- G- V i ' ~ ~himAc!a. 3 {1972) 3554 L- ~ . l a ~ . ! ~ Gi~!i and G . Bm~di, J . L ~ m - P h i - , 59 (!973) 3875 W. Strohmcicr an d F. J- Mfillar. C/~rm- BET-. 10"1(1969) .~08. 6 l ~ J . CIm4c an d P . J . H o b c m ~ n , lnmT- Chore-,4 (196~ 1771. ? J_ Mfill~r. i~. U-trade! and B- M ~ Chem. Bet.. 104 (1971) 700g R- Poi!blau~ and M- B i ~ n c , Bull. Soc. Chim. Fr.. 29 (1962) 1301. 9 D.J. i ~ ~ a n d T . L Bro~-n. In~rt . Cl~rm., 7 ¢196~ 959. 10 E- O- Fro:her an d L K n a u ~ . Chrm. Brr.. liP. ¢1969) 223. I I 14L ~ G. ~ am~l A- ~ lnorl- Clu'm- A~'fa- 2B i1978) 263I:~a J- A - Cmmor, I-IL.A - ~kinncr and Y . Virmani. J. Clarm. ~ r . . Faraday Trm~r I, (1972) 1754, and n:fs- d ~ n ~ . b G- IPiich~. M- J. W a r e and D . A. Pitlam. J . ~ o m m o n Ale.*., 42 (1975) 223, a n d ref~ flzrein. 2