Structural Types in Oxide-Bridged Manganese Chemistry - ACS

Chapter 12

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 12, 2016 | http://pubs.acs.org Publication Date: June 21, 1988 | doi: 10.1021/bk-1988-0372.ch012

Structural Types in Oxide-Bridged Manganese Chemistry Toward a Model of the Photosynthetic Water Oxidation Center George Christou and John B. Vincent Department of Chemistry, Indiana University, Bloomington, IN 47405

A survey is presented of the structural types encountered during synthetic efforts in oxide-bridged manganese chemistry. These materials have resulted from efforts to model the Mn aggregate at the water oxidation center (WOC) of green plants. Complexes with Mn nuclearities i n the range 2-12 are currently known, and their structural parameters are compared with those deduced by study of the WOC. The 'short' (ca 2.7Å) Mn...Mn separation of the latter has been seen to date only i n synthetic species containing two oxide bridges between a Mn2 pair, whereas, the 'long' (ca 3.3Å) separation is compatible with at most only one oxide bridge. Particular emphasis is given to the dinuclear and tetranuclear complexes which most closely reproduce features observed or deduced i n the WOC, and the potential correspondence of these complexes to the various S states of the latter is discussed. n

I t i s now w e l l e s t a b l i s h e d t h a t m a n g a n e s e (Mn) i s a n e s s e n t i a l c o m p o n e n t o f t h e p h o t o s y n t h e t i c w a t e r o x i d a t i o n c e n t e r (WOC) ( 1 ) . A v a r i e t y o f t e c h n i q u e s h a v e b e e n a p p l i e d t o i t s s t u d y , a n d some p e r t i n e n t c o n c l u s i o n s c a n be b r i e f l y summarized: ( i ) t h e WOC c o n t a i n s b e t w e e n 2-4 Mn a t o m s ( 2 , 3 ) ; ( i i ) Mn...Mn s e p a r a t i o n s o f ç a 2.7Â a n d p o s s i b l y ç a 3.3À a r e p r e s e n t ( 3 , 4 ) ; ( i i i ) t h e Mn a t o m s a r e b r i d g e d b y 0 " ( o r OH") g r o u p s w i t h Mn-0 d i s t a n c e s o f ç a 1.75Â, a n d p e r i p h e r a l l i g a t i o n i s p r o v i d e d b y O / N - b a s e d g r o u p s ( f r o m a m i n o a c i d s i d e c h a i n s ) a t d i s t a n c e s o f ç a 1.98À ( 4 ) ; ( i v ) t h e Mn a g g r e g a t e c a n a d o p t v a r i o u s oxidation levels (theS s t a t e s ) i n v o l v i n g c o m b i n a t i o n s o f Mn o x i d a t i o n s t a t e s o f I I , I I I , and/or I V ( 1 ) ; and (v) t h e S l e v e l i s EPR-active and d i s p l a y s a spectrum containing a Mn-hyperfine-structured ("multiline") s i g n a l a t g«2 ( 2 ) . Fuller details o f the native manganese assembly c a n be found elsewhere i n t h i s volume. 2

n

2

0097-6156/88/0372-0238$06.00/0 © 1988 American Chemical Society

Que; Metal Clusters in Proteins ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

12.

CHRISTOU AND VINCENT

Oxide-Bridged Manganese Chemistry

One c o n s e q u e n c e o f t h e i n t e n s e e f f o r t b e i n g c o n c e n t r a t e d o n t h e WOC h a s b e e n a g r e a t e r l e v e l o f e x p l o r a t i o n b y i n o r g a n i c c h e m i s t s o f t h e c h e m i s t r y o f h i g h e r o x i d a t i o n s t a t e Mn. The o b j e c t i v e i s t h e s y n t h e s i s o f Mn/O c o m p l e x e s w h i c h p o s s e s s t h e appropriate s t r u c t u r a l features, o x i d a t i o n l e v e l s , and spectro s c o p i c a n d p h y s i c a l p r o p e r t i e s t o a l l o w them t o be c o n s i d e r e d s y n t h e t i c m o d e l s o f t h e WOC i n i t s v a r i o u s S s t a t e s . Their attainment should r e s u l t i n a greater l e v e l o f understanding o f the s t r u c t u r a l changes and g e n e r a l mechanism o f a c t i o n o f t h e n a t i v e s i t e d u r i n g t h e w a t e r o x i d a t i o n c y c l e , i n c l u d i n g mode o f s u b s t r a t e (H2O) b i n d i n g a n d c o n v e r s i o n t o O2. The p u r p o s e o f t h i s c h a p t e r i s t o r e v i e w t h e c u r r e n t s t a t u s o f t h i s model approach and t o d e s c r i b e t h e s t r u c t u r a l t y p e s o f d i s c r e t e o x i d e - b r i d g e d Mn a g g r e g a t e s w h i c h h a v e b e e n synthesized t o date. F o r c o m p l e t e n e s s , a l l known n u c l e a r i t i e s w i l l be d e s c r i b e d , i n terms o f i n c r e a s i n g n u c l e a r i t y . Space r e s t r i c t i o n s p r e c l u d e a c o m p l e t e s u r v e y a n d we s h a l l concentrate mainly on the s t r u c t u r a l features o f these m a t e r i a l s ; the reader i s r e f e r r e d t o t h e o r i g i n a l l i t e r a t u r e f o r more d e t a i l , s u c h as variable-temperature magnetic s u s c e p t i b i l i t y , e l e c t r o c h e m i c a l and EPR data.


n

Dinuclear

Complexes

The p o s s i b i l i t y o f a d i n u c l e a r u n i t i n t h e WOC h a s p r o m p t e d much e f f o r t a t t h i s n u c l e a r i t y and a v a r i e t y o f d i n u c l e a r oxideb r i d g e d c o m p l e x e s a r e now k n o w n , c o n t a i n i n g e i t h e r o n e o r t w o b r i d g i n g 0 " groups. T h e y h a v e b e e n made e m p l o y i n g a v a r i e t y o f procedures, i n c l u d i n g d i r e c t a s s e m b l y f r o m a p p r o p r i a t e mono n u c l e a r reagents and appropriate m o d i f i c a t i o n o f preformed d i nuclear materials. E x a m p l e s o f t h e l a t t e r a p p r o a c h i n c l u d e chem i c a l o x i d a t i o n o f [Mn 0(0 CMe) (TACN) ] to the t r i c a t i o n with S 0 " (10), and i t s h y d r o l y t i c a l l y - i n d u c e d o x i d a t i o n t o [Mn 0 (0 CMe)(TACN) ] ( 1 3 ) . Some r e p r e s e n t a t i v e s t r u c t u r e s a r e r e p r o d u c e d i n F i g u r e s 1 a n d 2. A s c a n b e s e e n f r o m T a b l e I , three types o f b r i d g i n g arrangements have been encountered; l i n e a r Mn-O-Mn, b e n t Mn-O-Mn a n d Μ η ( μ - 0 ) . The c o m p l e x e s w i t h l i n e a r o x i d e b r i d g e s c o n t a i n n o o t h e r b r i d g i n g ligands and are c h a r a c t e r i s t i c o f species w i t h extensive Mn-0 π-bonding. T h e l i n e a r a r r a n g e m e n t n e c e s s i t a t e s a l a r g e Mn...Mn s e p a r a t i o n a n d o b s e r v e d d i s t a n c e s a r e i n t h e 3.42-3.54Â range. I n c o n t r a s t , complexes w i t h a s i n g l e bent oxide b r i d g e i n v a r i a b l y c o n t a i n a d d i t i o n a l b r i d g i n g l i g a n d s , and s t r u c t u r a l l y c h a r a c t e r i z e d m a t e r i a l s p o s s e s s t h e t r i p l y - b r i d g e d [Μη(μ-Ο)(μ0 CMe) Mn] ' core. T h e TACN a n d M e - T A C N s p e c i e s d i s p l a y a n e l e c t r o c h e m i c a l l y r e v e r s i b l e one-electron couple r e l a t i n g the Mn /Mn Mn l e v e l s , and examples o f b o t h have been i s o l a t e d and s t r u c t u r a l l y c h a r a c t e r i z e d . The [ M n 0 ( 0 C M e ) ] species h a v e a c h a r a c t e r i s t i c Mn...Mn s e p a r a t i o n i n t h e r a n g e 3.08-3.23Â. Interestingly, the Mn Mn complex has t h e l o n g e r r a t h e r than t h e s h o r t e r Mn...Mn s e p a r a t i o n t h a t o n e m i g h t h a v e e x p e c t e d . 2

2 +

2

2

2

2

2

2

8

2

2

2

2

2

2

2 +

2

3 +

2

I I I

2

3

I I I

I V

2

2 + 7 3 +

2

I I ] [

2

2

I V

The d i - μ - o x i d e - b r i d g e d c o m p l e x e s h a v e b e e n o b s e r v e d i n t w o types: ( i ) w i t h no a d d i t i o n a l b r i d g i n g l i g a n d s , a n d ( i i ) w i t h a n a d d i t i o n a l b r i d g i n g MeC0 " group. The f o r m e r h a s b e e n s e e n w i t h both Mn Mn and M n oxidation states, while the l a t t e r only 2

I I 1 :

I V

I V

2


239


240

METAL CLUSTERS IN PROTEINS

C2L 3 +

F i g u r e 1. The s t r u c t u r e o f [ M n 0 ( 0 C M e ) ( M e - T A C N ) ] ; t h e other [Mn 0(0 CMe) ] complexes i n Table I d i f f e r s t r u c t u r a l l y o n l y i n the i d e n t i t y of the t e r m i n a l l i g a n d s . (Reproduced w i t h p e r m i s s i o n f r o m r e f . 10. C o p y r i g h t 1986 VCH V e r l a g s g e s e l l s c h a f t ) 2

2

2

2

2

3

2

2

\ 2 +

F i g u r e 2. The s t r u c t u r e o f [ M n 0 ( 0 C M e ) ( T A C N ) ] ; t h e d a s h e d l i n e i n d i c a t e s the imposed t w o - f o l d a x i s . (Reproduced w i t h perm i s s i o n f r o m r e f . 13. C o p y r i g h t 1987 R o y a l S o c i e t y o f C h e m i s t r y ) 2

2

2

2


12.

Oxide-Bridged Manganese Chemistry 241


f o r Mn Mn . T h e l a t t e r a l s o d i s p l a y s l i g h t l y s h o r t e r Mn...Mn s e p a r a t i o n s ( 2 . 5 9 , 2.67Â) t h a n t h e f o r m e r (2.70-2.75Â) . The [Mn 02(phen) ] p a i r allows a useful s t r u c t u r a l comparison of the e f f e c t o f o x i d a t i o n l e v e l on e x a c t l y i s o s t r u c t u r a l s p e c i e s , and a g a i n the h i g h e r o x i d a t i o n s t a t e y i e l d s the s l i g h t l y l o n g e r Μη.,.Μη s e p a r a t i o n ( 2 . 7 5 v s . 2.70Â). 3 + , 4 +

2

4


TABLE I .

Structural

P a r a m e t e r s (Â) o f D i n u c l e a r

Complex Linear Oxide Bridges I i : [

[Mn2 [Mn [Mn

Mn. . .Mn

6

0(CN)io] " 0(phthal) ] 0(TPP) ] 2

I V

2 +

2

Mn-0

ref

3.446(4) 1.723(4) 3.42(1) 1.71(1) 3.537(4) 1.743(4),1.794(4)

l : [ 1

2

Complexes

2

5 6 7

Bent Oxide Bridges I I ] [

[Mn [Mn [Mn [Mn2 2

I I I

2

0(02CMe)2(TPB)2] 0(0 CMe) (bipy) Cl ] 0(0 CMe)2(TACN)2] ' 0(0 CMe)2(Me3-TACN)2] 2

2

2

I i : i :

2

2 +

2

I I I

I V

2

Di-/z-oxide [Mn [Mn [Mn [Mn [Mn [Mn

a.

2

Bridges

^'^0 (bipy)4] ^'^0 (phen) ] ^"'^0 (0 CMe)(TACN) ] ^ ' 0 (0 CMe) ( b i p y ) C 1 ^'^0 (phen) ] ' 0 (pic) ] 2

3

+

3

+

2

2

2

2

4

2

1 1

I

2

2

2

4 +

2

i V

2

2 +

2

V

2

2

3 +

3.159(1) 1.773(2) , 1.787(2) 8 3.153(1) 1.777(12),1.788(11) a 3.084(3) 1.80(1) 9 3 . 2 3 0 ( 3 ) 1 . 8 2 6 ( 6 ) , 1 . 8 1 4 ( 6 ) 10

4

I V

2

4

2

]

2.716(2) 1.784-1.856 2.700(1) 1.808-1.820 2.588(2) 1.817(5) , 1.808(4) 2.667(2) 1. 7 9 3 - 1 . 8 4 3 2.748(2) 1.794-1.805 2.747(2) 1.819(3)

11 12 13 a 12 a

unpublished

S h o u l d t h e WOC s i t e p r o v e t o b e d i n u c l e a r ( o r t w o s e p a r a t e d d i n u c l e a r u n i t s ) , t h e q u e s t i o n a r i s e s as t o w h i c h known d i n u c l e a r c o m p l e x e s c a n be c o n s i d e r e d good m o d e l s . As n o t e d above, t h e Mn...Mn s e p a r a t i o n s o f T a b l e I r e f l e c t t h e i d e n t i t y o f t h e b r i d g e and a r e n o t ( s e r i o u s l y ) dependent on t h e m e t a l o x i d a t i o n s t a t e s . T h u s , o n l y t h e M n 0 - c o n t a i n i n g c o m p l e x e s p o s s e s s Μη.,.Μη s e p a r a t i o n s i n t h e ç a 2.7Â r a n g e s u g g e s t e d b y EXAFS d a t a o n t h e WOC. T h i s c a n b e t a k e n a s some e v i d e n c e t h a t a similar Mn 0 unit m i g h t be p r e s e n t i n t h e l a t t e r . In accord with t h i s , a s t r i k i n g s i m i l a r i t y h a s b e e n n o t e d b e t w e e n t h e EXAFS s p e c t r u m o f [Mn 0 (bipy) ] ( a n d i t s p h e n a n a l o g u e ) a n d t h e EXAFS s p e c t r u m o f t h e WOC ( 1 4 ) . S t r o n g c o r r e s p o n d e n c e was f o u n d b e t w e e n t h e number, t y p e a n d d i s t a n c e s o f t h e l i g a n d atoms i n t h e f i r s t c o o r d i n a t i o n s p h e r e o f t h e Mn f r o m b o t h s o u r c e s . I t w o u l d t h u s seem that i t i s the Mn 0 complexes which r e p r e s e n t s t r u c t u r a l models o f t h e WOC. T h e Mn Mn complexes d i s p l a y a Mn-hyperfines t r u c t u r e d EPR s i g n a l i n t h e g - 2 r e g i o n f o r w h i c h 16 h y p e r f i n e l i n e s a r e c l e a r l y r e s o l v a b l e ( 1 , 13, 1 5 ) . The l a t t e r b e a r s 2

2

2

2

3 +

2

2

4

2

2



242

s i m i l a r i t y to the S m u l t i l i n e s i g n a l suggesting t h a t the M n ^ ^ M n ^ c o m p l e x e s r e p r e s e n t m o d e l s o f t h e S2 l e v e l a n d , theref o r e , t h a t the M n * complexes m i g h t c o r r e s p o n d t o S3; a r e v e r s i b l e o n e - e l e c t r o n r e d o x c o u p l e h a s b e e n o b s e r v e d b e t w e e n t h e s e two o x i d a t i o n l e v e l s i n the s y n t h e t i c complexes. M o d e l s f o r So and Si would then presumably require M n ^ M n and Mn dinuclear c o m p l e x e s , b u t no d i ^ - o x i d e b r i d g e d s p e c i e s a t t h e s e o x i d a t i o n s t a t e s a r e c u r r e n t l y known and must r e p r e s e n t o b j e c t i v e s o f f u t u r e work. A c o m p l e x w i t h a Mn2***(0H>2 c o r e h a s b e e n r e p o r t e d (Mn...Mn = 2.72Â) ( 1 6 ) , b u t t h e r e i s some d e b a t e a s t o w h e t h e r t h i s m i g h t r e a l l y be a M n ^ 0 2 s p e c i e s . S h o u l d t h e l o n g e r (ça 3.3À) Mn...Mn s e p a r a t i o n s u g g e s t e d b y t h e E X A F S d a t a o n t h e WOC t u r n o u t t o be r e a l , t h i s c o u l d e i t h e r b e i n t e r p r e t e d a s two o f t h e a b o v e Mn2Û2 u n i t s s e p a r a t e d b y c a 3.3Â (no e x a m p l e c u r r e n t l y known) o r , a l t e r n a t i v e l y , a s i n g l e M n 0 u n i t w i t h one o r two a d d i t i o n a l ( a n d w e l l s e p a r a t e d ) Mn a t o m s a t c a 3.3Â f r o m t h e c e n t r a l Mn2Û2 u n i t (vide infra). The i m p o r t a n t p o i n t , h o w e v e r , i s t h a t two d i s t i n c t l y d i f f e r e n t Mn...Mn s e p a r a t i o n s w o u l d n o t b e p o s s i b l e f o r two i s o l a t e d M n 0 2 u n i t s or a h i g h l y symmetrical t r i n u c l e a r or t e t r a n u c l e a r species. O v e r a l l , the c u r r e n t s t a t u s of d i n u c l e a r m o d e l l i n g studies suggests that Mn 0 complexes r e p r e s e n t a good m i n i m a l r e p r e s e n t a t i o n of the WOC. 2

1

V

2

1 1 1


2

2

2

2

2

2

Trinuclear

2

Complexes

A l l r e p o r t e d t r i n u c l e a r complexes possessing oxide b r i d g e s which have been c h a r a c t e r i z e d t o date have been p r e p a r e d from Mn0 ~ i n either aqueous o r non-aqueous media, and possess the "basic carboxylate" s t r u c t u r e v i z . a μ - o x i d e - c e n t e r e d Mn3 triangle. Both M n M n 2 and M n s s p e c i e s a r e c u r r e n t l y known, and their p e r t i n e n t s t r u c t u r a l parameters are l i s t e d i n Table I I . 4

3

I I

1 1 1

TABLE I I .

S t r u c t u r a l Parameters

Complex Mn 0(0 CMe) (py)3 3

2

1 1 1

3

2

6

2

3

2

6

2

[Mn 0(02CPh)6(ImH)3]

+

3

a.

room t e m p e r a t u r e b.

of Trinuclear

Complexes

Mn-0 Mn...Mn 1.941(1) 3.363(1) 1.9364(18) 3.351(1) 1.863-2.034 n.r. 1.798-2.154 3.214-3.418 1.888(4)-1.881(8) 3.259(1)3.270(1)

a

6

Mn 0(0 CMe) (py)3 Mn 0(0 CMe)6(3-Cl-py)3 Mn 0(0 CPh) (py)2(H 0) 3

(À)

-50°C

c.

unpublished

n.r.

- not

ref 17 18 19 18 c

reported

A r e p r e s e n t a t i v e s t r u c t u r e i s s h o w n i n F i g u r e 3. In a l l cases, Mn...Mn s e p a r a t i o n s a r e * l o n g ' (ça 3 . 3 À ) , s i m i l a r t o v a l u e s f o u n d f o r t h e m o n o - o x i d e - b r i d g e d Mn complexes d e s c r i b e d above. Even i n t h e t r a p p e d - v a l e n c e c o m p l e x M n 0 ( 0 C P h ) ( p y ) 2 ( H 0 ) (18) shown i n F i g u r e 3, w h e r e t h e Mn3 u n i t i s i s o s c e l e s r a t h e r t h a n e q u i l a t e r a l , t h e Mn...Mn s e p a r a t i o n s a r e n o t d i s t i n c t l y d i f f e r e n t , a n d n o s e p a r a t i o n i s f o u n d i n t h e ça 2.7À range. I t could thus be c o n c l u d e d t h a t an MneO-type u n i t c a n n o t r e p r e s e n t t h e c o m p l e t e 2

3

2

6

2


12.


Oxide-Bridged Manganese Chemistry

243

Mn a g g r e g a t e f o u n d i n t h e WOC; t h i s c o n c l u s i o n i s a d m i t t e d l y b a s e d o n l y o n t h e s y n t h e t i c t r i n u c l e a r c o m p l e x e s c u r r e n t l y known. Tetranuclear

Complexes

The p o s s i b i l i t y o f a t e t r a n u c l e a r u n i t i n t h e WOC h a s a l s o prompted intense e f f o r t a t t h i s n u c l e a r i t y . The f i r s t c h a r a c t e r i z e d t e t r a n u c l e a r Mn/O c o m p l e x w a s [ M n 0 e ( T A C N ) ] , r e p o r t e d b y Wieghardt and coworkers (20). T h i s compound p o s s e s s e s a c e n t r a l Mn 0e c o r e w i t h a n a d a m a n t a n e - l i k e s t r u c t u r e (shown i n F i g u r e 4) a n d a l l Mn c e n t e r s i n t h e +4 o x i d a t i o n l e v e l . T h e Mn...Mn s e p a r a t i o n s ( T a b l e I I I ) a r e a l l i n t h e ç a 3.2Â r a n g e a n d a r e t h u s a g a i n t o o l o n g t o m o d e l t h e ç a 2.7Â s e p a r a t i o n s e e n i n t h e WOC. N o t e t h a t e a c h Mn...Mn e d g e o f t h e c e n t r a l M n tetrahedron i s b r i d g e d b y o n l y o n e μ - O " g r o u p ; t h e o b s e r v e d Mn...Mn s e p a r a t i o n i s thus c o n s i s t e n t w i t h those observed i nd i n u c l e a r and t r i n u c l e a r complexes p o s s e s s i n g o n l y one μ - 0 ~ group between a Mn pair. I n 1 9 8 7 , t e t r a n u c l e a r o x i d e - b r i d g e d Mn c o m p l e x e s b e c a m e a v a i l a b l e w h i c h p o s s e s s t w o d i s t i n c t t y p e s o f Mn...Mn s e p a r a tions. V i n c e n t et al. s h o w e d t h a t t h e t r i n u c l e a r c o m p l e x e s c o n taining [Mn 0] ' cores w i l l react with 2,2'-bipyridine (bipy) to g i v e complexes c o n t a i n i n g t h e [ M n 0 ] ' ' core i n high yield. With [Mn 0 ( 0 C M e ) 6 ( p y ) 3 ] , t h e p r o d u c t was [Mn 0 (0 CMe) (bipy) ] shown i n F i g u r e 5 ( 2 1 ) . A l l Mn a r e i n t h e +3 o x i d a t i o n l e v e l , a n d t h e M n 0 c o r e c a n b e c o n s i d e r e d a s a 4 +


4

4

4

4

2

2

2

6 +

7 +

3

6 +

4

I ] [ I

7 +

8 +

2

+

3

2

+

4

2

2

7

2

4

TABLE I I I .

S t r u c t u r a l Parameters

Complex

2

(Â) o f T e t r a n u c l e a r

3.21(l)

4 +

[Mn 0 (TACN) ] [Mn 0 (0 CMe) (bipy) ] 4

4

6

4

2

2

7

2.848(5)

+

2

2.7787(12)

[Mn 0 (0 CMe) (bipy) ] 4

2

2

6

2

ref

Mn-0

Mn...Mn (long)

Mn...Mn (short)

Complexes

a

3.2993.385 3.288(1) 3.481(1)

1.79(l)

a

1.8041.930 1.8507(20)° 1.8560(21) 2.1032(21) 1.7972.002 1.δοδΙ.966

20 21 22

b

c

2

[Mn 0 Cl (0 CMe) (ImH)] " 4

3

6

2

3

[Mn 0 Cl (0 CMe) (py) ] 4

a.

3

4

2

3

3

2.8062.818 2.8145(15)

average d i s t a n c e s , b. M n ( I I I ) - 0 ,

3.2463.323 3.269(1)

c. M n ( I I ) - 0 ,

d.

23 d

unpublished

2

" b u t t e r f l y " w i t h a μ - 0 ~ b r i d g i n g each t r i a n g u l a r face. An a l t e r n a t i v e way o f v i e w i n g t h e s t r u c t u r e e m p h a s i z e s i t s M n 0 p a r e n t h o o d ; t h e p r o d u c t c a n be c o n s i d e r e d as two t r i a n g u l a r u n i t s s h a r i n g a n edge. Extension o f t h eb i p y r e a c t i o n t o t h e mixedv a l e n c e t r i n u c l e a r complexes l e a d s t o p r o d u c t s whose o x i d a t i o n l e v e l depends on t h e i d e n t i t y o f t h e c a r b o x y l a t e group. Thus, Mn 0(0 CPh) (py)2(H 0) reacts with bipy to yield Mn 0 (0 CPh) 3

3

3

2

6

2

4

2


2

7


244


Figure 3. The structure of Mn 0(0 CPh) (py) (H 0) illustrating the unique terminal ligand asymmetry; Mn(3) is the Mn" center possessing a terminal H

Structural Types in Oxide-Bridged Manganese Chemistry - ACS

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