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E L S E V I E R lnorganica Chimica Acta 279 1998) 2 4-29

S y n t h e s e s a n d X - r a y c r y st a l s tr u c tu r e s o fc is M n ( b i p y ) 2 C 1 2 2 H 2 0 E t O H a nd c is [ M n ( p h e n ) 2 C 1 2

( b i p y -- 2 , 2 ' - b i p y d d i n e ; p h e n = 1 , 1 0 - p h e n a n t h r o l i n e ) ; c a t a l y st s f o r th ed i sp r o p o r t io n a t io n o f h y d r o g e n p e r o x i d e

Sebas t ian M cCann a M alachy M cCann ~ * , Rev . M ichae l T . C asey a, Mau ra Jackm anM ichae l D evereux ~ , Vickie M cKe e ~Chemist~' Departme~t. St. P atrick 's C ollege. Maynooth, Co. l~'ildare, Irelandb Dublin Insti tute of Technology. Cathal Brugha Street. Dublin. Ireland

Schoo l of Chemisto, . Queen's Unitwrsio: Belfast , B19 SAG , UKReceived 20 May 1997. received in revi ~d form 24 June 1 997. accepted 25 Novem ber 1997

A b s t r a c t

MnCI~.4H:O reacts with 2,2 -bipyridine (bipy) to g ive c i s - [ M n ( b i p y ) 2 C l : (I) , and recrystall i~tion of I from ethanol gives c i s .[Mn(bipy)~Cl:] .2H~O.EtOH (2 ) . MnC I:.4H~O and l .lO-phenanthroline (phen) react to form c i s - [ M n ( p h e n ) ~ C l ~ l (3) . in each case,the X -ray crystal structures of 2 and 3 show the ma nga ne~(ll) a tom to have a similar distorted octahedral geometry, and in both casest ~ is extended ~= ~ stacking of the conjugated ring systems. Com pared with MnCl~ 4H~,O, I and 3 are m uch more efficient catalystsfor the d tsproportionation of hyd roge n peroxide. The catalytically activ e species are I~lleved t be IMn (hipy)~ (it~O), l ~ and[ M n p h e n ) ~ H ~ O ) ~ ] ~ * , respectively. 1 ~ 8 Elsevier Science S.A. All rights reserved.Ke)~,ord.v: Cfy~t~l ~fulur~; M a.~.n e~c omple~~; Bipyfldlne omple~e~; Ph en an lh ~l i~ ,~mplcx~,~:Calalyti~:di,~p~)p.flionatioa

I I n t r o d u c t i o n

A nu m be r o f m a nga ne se~ c on ta in ing non- ha e m c a ta l a ~have recenOy been isola ted and c h a r a c t e d s e d I I - 3 1 , a n dthese ca ta ly ~ the d ispropor t iona t ion of hydrogen peroxide ,a reac t ion wh ich is impor tant for ce l l de toxif ica t ion:2H~O~ ~* ~ + 2H~OPresently, the re is a lot of interest in preparin g and charac-t e ds ing b iom im e t i c m a nga noc nz ym e c om ple xe s in o r de r t ha tthe mode o f ac t ion o f the na tura l ca ta lases can be es tabl ished[ 4 1 2 ] , R e c e n t l y , we have been en gaged in the synthes is ands t r uc tu r a l c ha r a c t c r i sa t ion o f m a nga ne ~ ( l l ) c a r boxy la t ecomp lexes [ i~ 2 1 1 end, in par t icular , com plexes conta iningdicafl~oxylic acid ligan ds [ 17-21 ], A pz-ct~;u;n~-y~>~c.-.~,mentof the abi l i ty of the complexes to work as func t iona l b io-m i m i c s f o r m a n g a ~ c a t a l a ~ s s h o w e d t h at d i ca rb o x y la tecomplexes , conta ining the anc i l la ry che la t ing NN donor

ligand I , 10-phcnanthrolin~, (phe n) I 17-2 01. wt:t~ particu-la r ly ac t ive ca ta lys ts for the d isptopo t t iona t ion o f hydrogenperoxide . Conduc t iv i ty measurements , taken on aqueoussolut ions o t the ph enanthrol ine-carboxyla te complexes , sag .ges ted tha t there was ex tensive dissoc ia tion of the com plexesin wa te r w i th c onse que n t f o r m a t ion o f [ M n( phe n) ~ -( H a O ) a I : *, Th us, i t appe ars l ikely that i t is this dication thatis pr imar i ly responsible for the ca ta ly t ic breakdow n o f per -oxide by these m odel comp lexes , a l thoug h the na ture of thede-coordina ted f ree ca rboxyla te anions a lso appears toinf luence the ra te of peroxide decom posi t ion. A s an a id toour u nders tanding of the reac t iv ity of the ca rboxyla te -phen.anthrol ine com plexes , w e have now synthes ised and charac-t e ri s ed m a n ga ne ~ ( l l ) c h lo ride c om ple xe s c on tain ing the NNdono r ligands 2 ,2 -b ipyr idyl (b ipy) and I , lO-phenanthro-line, and investigated their catalytic activity towards per-oxide,:2 E x l ~ d m e n t a l

C ~ ~ aurar el : 3 3 3 -I - 7 0 8 7 6 7 : f ax : + 3 5 3 - I - 7 0 8 3 8 1 5 ; C he m ic a l s we r e pu r c ha se d f r om c om m e r c ia l sou rc e s a ndused wi thout fur ther pur i f ica t ion. Inf ra red spec t ra were ) : , ~ I ~ M ~ t - ~ f r e t r ~ r I ~ E ls evi er S ~ i~ nce S , A, A l l r igh ts r c ~ r ved .P tt 0 0 2 0 - 1 6 9 3 ( 9 ~ ) 0 0 0 3 1 - 0

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S . ~ c f o n n e l a l. / I n o r g a n k a f h i m i c a A ( ,t a 2 7 9 ( t 9 9 8 ) 2 4 - 2 9 2 5

r e c o r d e d a s K B r di s c s i n t h e r e g i o n 4 0 0 0 - 4 0 0 c m - o n aN i c o l e t I m p a c t 4 0 0 D F r - | R S p e c t r o m e t er . M a g n e t i c s u s c ep -t i b i l i t y m e a s u r e m e n t s w e r e m a d e a t r o o m t e m p e r a t u r e u s i n ga J o h n s o n M a t t h e y M a g n e t i c S u s c e p t i b i l it y B a l a n c e a n d c o n -d u c t i v i t y m e a s u r e m e n t s w e r e t a k e n a t 2 5 ( : u s i n g a n A G BS c i e n t if i c L t d . m o d e l 1 0 c o n d u c t i v i t y m e t e r . E l e m e n t a l a n a -l y s e s w e r e c a r r i e d o u t b y t h e M i c r o a n a l y t i c a i L a b o r a t o r y ,U n i v e r s i t y C o l l e g e C o r k , I r e l a n d .2 . I . C o , s i a l d a t a

C r y s t a l d a t a f o r c i s - [ M n ( b i p y ) , C l : 1 . 2 H , O . E t O H ( 2 )a n d cis-[ Mn( phen) _ , CI . ,. ( 3 ) a r e sum m a r i s ed in Tab le I .2 . 2 . D a m c o l l e c t i o n a n d l) r o c e s s i n g

B o t h d a t a s e t s w e r e c o l l e c t e d o n a S i e m e n s P 4 d i f f r a c t o -m e t e r u s i n g g r a p h i t e m o n o c h r o m a t e d M o K c t r a d i a ti o n . U n i tc e l l p a r a m e t e r s w e r e d e t e r m i n e d b y n o n - l i n e a r l e a s t -s q u a r e sr e f inem ent o f 33 r e f l ec t ions ( 10 < 2 0 < 25) : c r ys ta l s t ab i l i tyw a s m o n i t o r e d b y r e c o r d i n g 3 c h e c k r e f l e c t i o n s e v e r y I 0 0r e f l ec t ions , and no s ign i f i can t in tens i ty changes wer e

o i 'bser ved . The da ta wer e cor r ec ted f o r Lor e n tz and po la r i s a -t i o n e f f e c t s a n d e m p i r i c a l a b s o r p t i o n c o r r e c t i o n s w e r eapp l ied .2 . 3 . S t r u c t u r e a n a l y s i s a n d r e f i n e m e n t

T h e s t r u c t u r e s w e r e s o l v e d b y d i r e c t m e t h o d s ( T R E F[ 221 and r e f ined by fu l l m a t r ix l ea s t - squa r es on F- ', u s inga l l t h e r e f le c t io n s . A l l n o n - h y d r o g e n a t o m s w e r e r e f in e d w i t ha n i s o t r o p i c a t o m i c d i s p l a c e m e n t p a r a m e t e r s a n d h y d r o g e na t o m s , b o n d e d t o t h e c a r b o n a t o m s o f b i p y r i d i n e o r p h e n a n -th r o l ine , wer e inse r t ed a t ca lcu la ted pos i t ions wi th i so t r op icd i s p l a c e m e n t p a r a m e t e r s r i d i n g o n U u o f t h e i r c a r r i e r a to m s .i n t h e c a s e o f c i s - l M n ( b i p y ) : C l . , ] . 2 H , O . E t O H ( 2 ) , t h eh y d r o g e n a t o m s o n t h e s o l v a te w a t e r m o l e c u l e s w e r e l o ca t e df r o m d i f f e r e n c e m a p s a n d n o t f u r t h e r r e f i n e d ; t h o s e o f t h ed i sor de r ed , pa r t i a l occupancy e thano l so lva te wer e no tinc luded . Al l p r ogr am s used in the s t r uc tu r e r e f inem ent a r ec o n t a i n e d i n t h e S H E L X L - 9 3 p a c k a g e 1 2 3 I .2 .3 .1 . ( ' i s - l Mn(b i : ) y ) ,C l , . l )T o a s o l u t i o n o f 2 , 2 ' - b i p y r i d i n e ( 0 . 9 8 4 g . 6 . 3 m m o l ) i ne t ha n o l ( 3 0 c m a ) w a s a d d e d M n C I , . 4 H , O ( 0 . 5 g , 2 .5 2 7

T a b l eC r y s t a l d a t a

cL~'-IM n ( bip y ) :(?1~ I ' 2 Ho,O . E t O H ( 2 ) ( 'i ~ -I M n ( p h e n ) , C I : I ( 3 1

i ] .m l ' f i r ic a l h ) r n m i a C ~ . F I = , ~ C I : M r I N ~ O , C . . sH , , ,C I ~ M n N , ~P o r i i l l l l ii w e i g h t 4 1 ) 3 .2 6 . IX ( ) , 2 5C ~ , ~ t l il d l ; s c r i p t i o n y e l l m v i i h ic k y e l l o w b l o c kT e m l ~ r i i t n r e ( K ) 1 5 3 ( 2 ) 1 5 ~ l 2 )W i l v e l e n l l ih I ~ ) 0 . 7 1 0 7 3 I ) 7 1 0 7 J( ' i y ~ l i l l < ~ ) , ~ l e ii n l i l n l l c , l h i i i l l o i i t ~ : l i i l i ~ l l i i t . ' e ~ r l l l l ( . / , .o I ~ l l ) I l l , l O l l ( l ) ) t ) . 4 ~ l ) l l ( I I ) )b i A 1 3 J J 2 1 J ) I ~ I q l 1 2 )c ( A I I I , . t 24 ( 6 ) 14 , J 541 2 )~ t ( 1 123 , (~4 ( 41 914 ,62 ( I tV (~ ) 24 l )1 ( 2 ) 2 ( ) ,' I I , I ( 4 IZ 4 4[ ~ n x i t y I c a l c n h l te d , g i t ~ ) 1 , 3 { 1 4 I , S t ) Oi t i ( n l n l i ) 0 . 7 9 9 0 , 9 3 4b'(O fiO ) I0 1 6 ~Jl414 i ~ s t i i l s i z e ( m m ) ( ) . 6 2 5 X 0 . 3 2 5 x l ) . 2 7 5 0 . 4 2 0 .2 1 4 ,,< O , 1 80 r i i l ll l e I ' o r d i i t l l c o l l e c t i o n I ) 2 . 3 6 t o 2 5 . 0 0 5 2 , I 0 t o 2 5 . 1X )I n d e x r a n g e s 0 < h < 22 - 0 < h < I I- I < k < 1 5 - I < k < 1 8

1 3 < / < I I - 1 7 < 1 < 1 6R e f l e c t i o n s o l l e c t e d 2 3 7 0 40314I n d e p e n d e n t r e f l e c t i o n s 2 1 1 3 t R , ,, , = O . O I 7 ) ) 355 5 ( R., , ~ ( i ,03214 IA b s o r p t i o n c o r r e c t i o n s e m i o e m p i r i c a l { I~/-SCiillS ~emi-cnlpir ical ( i /v~clin~ )M a x . a n d m i n . l r a n s m i s s i o r l 0 . 9 2 ~ a i l d 0 .1 ,1 8 6 0 . I, I0 4 a v l d 0 3 4 5R e l i n e l n e r l t m e t h o d f u l l m a t r i x l e a s t - s q u a r e s o n I : f u l l - n i a t r i x I c a s l - s q u a n . '5 ( m i f. ':D a l a l r e s t r a i n ts l p a r a n i e l e r s 2 1 1 3 / 0 / 1 4 2 3 5 5 5 / 0 / 2 8 0G o o d n e s s o o f o l i t o n F : 1 . 0 8 9 . 0 2 7F i n a l R i n d i c e s I I > 2 ~ r ( i ) i Ri ~ ( ) .0431) R i ~ 1),(15,18

l l' R 2 ~ O . I O ) I u R , = O . 1 2 5 2R i n d i c e s ( a l l d i l l q R i = 0 . I ). 5 ( )5 R , = 0 . ( ) 9 2 5w R 2 = O . 1 1 4 1 w R 2 = O . 1 4 5 8L a r g e s t d i f f . p e a k a l i d h o l e ( e A ~ ' ) 0 . 9 7 5 l i l l d - - 0 . 5 9 7 0 . 6 7 0 a n d - 0 . 6 4 3

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2 ~ S. McC ann e l al . / Inorganica Chi mi c a A c t a 279 1998)2 4 2 9re too l ) and the mix tu re was warmed gen t ly and s t i r red fo r0 .$ h , " r i t e p rec ip i~ te d ye l low p roduct wa s f i lt e red o f f andthe f i l t ra te was concen t ra ted by ro ta ry evapora t ion to g ivem o re o f t h e y e l l o w s o li d . Th e c o m b i n e d s o li d s w e re w a s h e dwi th two sm al l po r t ions o f e thano l and then d r ied in vacuo .Yie ld : 0 .75 g (68%). Ana l . Calc.: C, 54.8; H, 3 .7: N, 12.8 .Found: C, 54.6: H. 3 .7; N, 12.1%. IR : 3060, 1 600 , 1490,1440, 1315 , 1245, 11 50, I 00, 1060, 1020, 820, 775, 735,650 . 625 cm-~. / . t~ , - r=6 .17 BM ( 20 .7 C ) . AM(H20)= 2Y-- ;S c m " t o o l - t . Th e c o m p l e x w a s s o l u b le i n w a t e r , m e t h a n o land e thano l , and in so lub le in ch lo ro fo rm and e thy l ace ta te .Recrys ta l l i sa tion o f the . sol id f rom e thano l gave c rys ta l s o ffo rm u la cis- [ M n ( b ipy ) ,C l , 1 .2H , ,O. EtOH ( 2 ) wh ich we resu i tab le fo r X-ray ana lys i s ,

2 .3 .2. c i s - IM n(phe n):C l : l (3 )To a so lu t ion o f I . 0 -phenan th ro l ine ( I , 139 g , 6. 3 2 m m o l )i n m e t h an o l ( 5 c m ~ ) w a s a d d e d a s o lu t io n o f M n C I2 . 4 H , O

(0 .5 g . 2 .53 re too l ) in methano l ( lO cm~) . The resu l t ingye l low suspens ion was s t i r red fo r 0 .5 h a t room tempera tu re .The ye l low so l id was f i l t e red o f f , washed wi th th ree smal lpo r t ions o f methano l and then d r ied in vacuo . Yie ld : .0 g( g i ) . A m d . Calc.: C. 59.3 . H. 3 .3: N, 1 .5 . Found : C, 59.1:H . 3 .3 ; N . 1 .3 % . IR: 3050. 1 620 , 1580, 1 515. 1430, 1345,1220, I 145, I 100, 845. 780, 730 , 640 c m = ~. # ~ ,= 5 .84 B M( 20 .3 C ) , A m(H ~ O ) ~ 202 S e ra : reel ~. Th e c o m p l e x w a sso lub le in w ater , methano l and e thano l , an d in so lub le in ch lo -ro lbnB and e thy l ace ta te. R ecrys la l l i sa tion o f the sol id I~ommethano l gave c rys ta ls o f 3 w h ich we re su itab le fo r Xorayanalysis,

3 , 4 , i l y d ~ , , ~ , e n p e r ~ , , t i d e d i , ~ l u v p o r t h . . a i ~ m , ~ t m t i ,

Aqueo us H~O~ (35 t~ w t , /wt , , 30 c m ~. 342 re too l ) was~dded to a sol id mixtu re com pris ing the com plex ( ( I ) IO, Irag , 2 ,07 10 : s ree l ; ( 3 ) 10 ,5 r ag . ~.,39 10 reel : I0 ,1rag , ~ ,10 l0 =~' ree l MnCI= , .4H~O) and imidazo le ( lO 0rag ) . The com bina t ion w as s t i rred and then nos ta l t ed a t 25C.Th e evo lved O: w a s m e a s u red vo lumet r i ca l l y .

3 , R e s u l t s a n d d b c u , ~ i o n

M n C I : , 4 H : O r e a c t e d w i t h 2 , 2 ' - b i p y r i d i n e t o g i v e Ih eye l low so l id c i ,~ 'qMn(b ipy)~Cl : ] (1 ) in g~od y ie ld , and~ r y s t a l l i t a t k m o f I f rom e thano l gave c rys ta l s o f c / s -I M n ~ , b i p y ) ~ C I ~ I , 2 H , O , E t O H ( 2 ) . T h e re a c t io n o fMnCI= , 4H~O wi th I , I (bphenan th ro l ine p roduced the ye l lowc~m~plex c / s - |Mnqph en)~Cl= , ] (3 ) , The p repara t ions o f I[ 241 and 31251 have been repor ted p rev ious ly us ing s imi la rsynthet ic s t rategies ,

C

CIo

C9

C1C8

C3 C~Fig, . S tructure of c i s- I M n ( b ip y ) 2 C I , I " 2 1 t , O - E tO H ( 2 ) ( w a te r an d e th -an o l m o lecu le s o mi u ed f o r c l a r ity ).Tab le 2S e lec l cd b o n d l en g th s ( A ) a n d a n g l e s ( '~) for 2M n ~ N ( 2 ) 2 , 2 ? 5 ( 3 )M n = N ( I ) ,,..='~~87( .~ )M n = C 2 . 4 8 3 4 ( I I )N ( 2 ) ' =M n ~ N ( 2 } 1 6 2. 6t~ ( 1 3 }N ( 2 ) ' = M n ~ N ( I1 9 5 , 3 1 ( I 0 )N ( 2 ) ~ M n ~ N ( I ) 7 1 , 9 3 ( lo tN( I ) = M B = N ( I ) ' ~ 7 , 6 1 ( 1 4 )N ( 2 ) '=M.~=CI ~ )8 ,18 ( 7 IN( 21 = M n ~ " l ~ ).~ ,7 7 ( 7N ( I ) = M n = ( ' l I h ~ 5 , h 7 tN ( I ) ' , , = M . :C I ~ 1 , ( d ( ~

The X oruy crysta l s t ructure s o1 '1 ~ ( Figs . I and 2) and 3(F igs , 3 and 4 ) were ob ta ined and a re d i scussed toge t l )e r~ l ow . Se lec ted bond len g |hs and ang les fo r 2 and 3 a re li s tedin Tab les 2 and 3 , respec t ive ly , in each s t ruc tu re , the manganese a tom i s s ix -coord inme bu t the geom etD ~ s fa r removedl h~ m ~ | a h e d ra l , p r i n c ip a l l y d u e t o t h e ' h i l C o f t h e b i p y r id i n eand phenan thml ine l igands , The manganese ion in c i s .I M n (b i p y ) , C l ~ I ' 2 H , O . E IO H ( :2 ) s i t s o n a t w o d b l d a x i s ,w h e re a s c i s , I M n(p he n) ~Cl~ I (3 ) has no in te rna l c rys ta l log ra p h i c s y m m e t ry , In sp i te o f th i s, the geom et r ies o f the twocomplexes a re very s imi la r ( see super imposed p ic lu re~ inFig, 5), Th ere are sma ll d ifG.,rences in the t i l t ~, " he plan eso f the con juga ted i igands , w h ich c :~ :~ p robab ly be accoun tedfo r by pack ing in te rac t ions , l a bo th cases , there i s ex tended

T h e . ~ l ~ t u r e o f t h e c L ~ -I M n ( b i p y ~ : C I , I i ~ M i o n o f c i s - I M n ( b i p y )~ C I : I , ? . H : O , E I O H ( 2 ~ q , ~ pa c c g r o u p C 2 / ( '~ i s b a s i c a l l y t h e ~ a m c a s t h atI ~ V i o u s l y ~ l ~ H e d b y L u m n ~ ~ m d L i n d c l l 1 2 (~ 1 I o r ('e .s olM n ( h i p y L ,C I : I( Sl~aC e g r o u p P 2 ~ l c ) , ~ th o u g h th e r e a r e s o m e d i f f e r en ces in th e s p ec i f i edb o n d l en g th s an d an g le s q e , g , C I - M n - C I an ~ ,l e in 2 i s 9 2 , 7 2

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, M c C m m e l a /, / b u ~ r g m ~ i ca C l f f m h ~ l A ~ t r ~ 27 9 i ~ '~ '~ ,~) 2 , . / -29 2?

c u l e a n d a h a l f - o c c u p a n c y e t h a n o l m o l e c u l e ( d i s o r d e r e dabou t a two- foh l ax is ) . The e tha lo l and w ater a rc hyd rogen -b o n d e d ( O l w - O 2 1 2 . 7 7 5 ( 8 ) A ) . F u r t h e r m o r e . t h e w a t e rm o l e c u l e a l s o i n t e r a c t s w t h t h e c h l o r i d e l i g a n d s ( O l w - C I3 . 2 9 3 ( 3 ) a n d 3 . 2 5 8 ( 3 ) A ) u n d e r t r a n s fo r m a t i o n s ( o f t h eC i) x , - y , i / 2 + - and x, y , I + : , r espec t ive ly .

A q u e o u s s o l u t i o n s o f r i s - I M n ( b i p y ) : C l : l ( 1 ) a n d ( 'i sI Mn( phen )~CI~ I (3 ) were h igh ly condu ct ive . Th is im p l iedtha t there was ex tens ive d is soc ia t ion o f the ch lo r ide i igands

Fig, 2, ~r~r slackingof the conjugated r ing systems n 2 . t lpon d issolu tion of the com plex es in wa ter and con seq uentf l~ rmat ion o f the r espec t ive d ica t ions IMn(b ipy )~o

'i re 'n " s ta lck ing o f the con jug a ted r ing sys tems , charac te r i sed ( t1~O)~ I ~ ' and J Mn( phen )~( H ,O)~ I : ' A l though co rnby the inteq~ lan ar dis tan ce s ill1 he i '~|nge 3,3o~3.5/A ( see sta ck - i '~lexes I and 3, by them~e lve.~, we re quite illel ' fectiv for theing p lo ts in Figs . 2 and 4) . The re is no solve nt in the h lt t ice d ispropt) r t ion ation of t1~O, , they hoth v ig t~rously cataly ,~edo1' ~ i so J M ~11 phell ) ~CI~ J ( 3) but the i lsym me tr ic u nit o1 ' r i s o the b rea kd ow n o1' the pero xide in the i ' )re. ,,ellc of ~dded imi d ~J MII( b ipy ) fl?l~ I ' 2 i i ,O . EIOH (2 ) t 'ont{lins a Wll te l mole,o a/ ol c ( Fig. ~ ) , It shou ld bc no ted that th e im idaz()lc I~l, ,,c by

F i g . 4 . n '- 'r r s l a c k i n g o 1 h e c , m j u g a t e d r i n g s y s t c m ~ i n 3 .

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S. Mcf .~mn et aL I Inor, ~nica Chimica Acta 279 1998) 24 -29

Table 3Selecled bond lengths t /k) and angles () for 3 3 0 0 0 I M n ( p h e n h C h lM n - N 2 A ) 2 . 2 8 1 4 )M n - N { l ) 2 . 2 9 9 4 )M n - N 2 B ) 2 . 34 1 4 )Mn-N IA) 2.371 4 )M n . . C I { l ) 2 . 4 3 9 6 ( 1 4 )Mn-C I 2) 2.4544 13)N ( 2 A ) - M n - - N ( I B ? 1 5 9 .1 0 ( 1 4 )N ( 2 A ) - M , P N ( 2 B ) 8 8 . 9 3 ( 1 4 )N ( I B ) - M n - N ( 2 B ) 71.63 14)N ( 2 A ) - M n - - N ( I A ) 7 1 . 2 8 ( 1 3 )N I B ) - M n - N ( I A ) 97.88 13)N 2 B ) ~ M ~ N I A ) 8 2 . 4 3 1 3 )N 2 A ) - M n - . C l I [ 0 2 . 9 1 1 0 )N ( I B ) - M n - - C I ( 1 9 4 . 1 1 ( l I )N ( 2 B ) , - M w 4 ~ I ( 1 1 6 0 . 9 3 ( 1 0 )N { I A ) - M n ~ C I ( l ) 8 7 . 2 4 ( 1 0 )N 2 A ) - M n , - C I 2 ) 9 0 , 6 3 9 )N ( l B ) ~ M n . ~ I ( J ) 9 7 . 0 0 ( 1 0 )N ( 2 B ) - - M n - 4 ~ I ( 2 ) 9 0 .5 9 { 1 6 )N I A ) = M n . - C I 2 ) 1 6 0 . 6 3 1 0 )e l ( I ) = M n = C i ( 2 ) 1 0 3 .9 9 ( 5 )

jd

t. J

Fig, ~, Structures2 an~ 3 s u p e f i m ~ (water and ethanol mol~ule sof 2omi tted for cl~tly),

i t , l l c a uses on ly a ve r y s l igh t d isp r oport iona tion o f pe rox ideand tha t th is s luggish reac tion is grea t ly enhan ced w hen thema nga ne .~ ( I i ) comp lexes I and 3are inc luded in the reac tionmixture . Such an enhancem ent in the ra te o f peroxide dispro-por tiona tion in the p ~ n c e o f a dde d ba se ha s a l so be e nreported by other w ork e~ 18.9,12,2T and, signif icanOy, bet-n3cycl ic bases a te kn own to be present in the v ic in i ty of theac t ive s ites of m anganoenzy mes 128 ] .

The num be r o f H :O~ m ole c u le s b r oke n down by e a c hmanganese a tom, in comp lexes I and 3 , dur in g the f ir s t min -u te o f t he r e a ct ion wa s e s~ n t i a l ly t he sa m e ( 5322 a nd 5382 ,

"-" 2500q2 0 0 0

a> 1 5 0 0 ooo

( ~ 5 0 0

I M n ( b i p y h C l J

M n C I z 4 H 2 0~ q ~ ~ m ~ l em gm mm

o 2 4 6 8 1t i m e ( r a i n )

Fig.6. Kineticcurves for the catalyticdisproponionation f hydrogenper-ox ide by c i s - [Mn(b ipy )~C l~ l I ) , c i s - l M n p h e n ) ~ C I , I (3) and MnCIo,,4H,O , in the pte~nce o f imidazole,respec t ive ly) 2 Af te r 25 min, about 75% of the peroxide hadbeen conver ted to O: . A f te r a reac tion t ime of i . 5 h . about90% of the peroxide had dispropor t iona ted and th is impl iedtha t any s ide reac t ions involved in the consum ption of H.~O2molecHes were ins ignif icant . In contras t , under the sameexper imenta l condi t ions , the s imple manganese( l l ) sa l tMnCI~. 4H 20 was found to be considerably less ac t ive thanI a nd 3 as a d ispropor t iona t ion ca ta lys t (9 i 8 H,O , m oleculesbroken down b y each m anganese a tom dur in g the fi rs t min-ute ) . These resulL~ substant ia te ea r l ie r f indings 1131 w hichshowed tha t maximum ca ta lyt ic ac t iv i ty towards peroxideo c c u r s whe n t h e concentra t ion of f re e m a n g a n e s e ions i sminimi .~d, i . e . when the meta l i s l iga ted by bipyr idyl andphenanthrol ine . Fur thermo~, a brown suspension of in t ln~anese oxide was noted to I b r m d u r i n g t h e M n C h . 4 H ~ Ocatalysed reaction, wh ereas w ith catalysts I and 3 the reactionsolut ion remained essent ia l ly colour less or pa le y e l low bothdur ln8 and a f te r the reac tion wi th peroxide . Thus , i t i s evidenttha t the presence of b identa te che la t ing NN donor l igands ,such as 2 ,2 ' -b ipyr id ine and I , 10-phenanthrol ine , in the coor -dina t ion sphere of the m eta l aot only s ign if icant ly enhancesthe abi l i ty of the mang anese to d ispropor t iona te H:O.~ buta iso inhibi ts the format ion of insoluble manganese oxide .These resul ts cor robora te our o th er f indings f rom ca ta lyt ics tud ie s on a num be r o f m a nga ne se ( l i ) d i c a r boxy la t ecomplexes .

F ina l ly , c is~ lM n(bip y) . ,Cl , l ( I ) has previously [301been used as a ca ta lys t for the l iquid-phase oxida t ion of i so .propylbenzene by molecula r oxygen, indica t ing the addi-tional po tential , scope for t h i s a nd r e l a t e d m a nga ne se ( l l )reagents i n organic synthes is .

~' It w as previously estab l ished 1291 that Ihe &'compo sition of hydrogenperoxide (0, I M ~ueo us ,so lution by c i s . [ Mn( b ip y ) . ,CI~ ( I } is zero orderand, a t pH 7 ,09, the rate constant k was (1,35 : i :0 ,02 ) x iO~ mole H~O.,rnin ~ ~, The o veral l rate cons tant was calculated from the kinetic curve andreferred to one mole of hydrogen peroxide decomposed by one m ole ofcatalyst per minute.The pre ~n t disproportionation tudies were carriedoutwith a muchhigherconcentrationof hydrogenperoxide ( I 1.6 M) and alsoin the presenceof the helerocycl ic base iraid~ole.

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