Binuclear and Mixed Metal Binuclear Chelates of Schiff-Base

32 Binuclear and Mixed Metal Binuclear Chelates of Schiff-Base Derivates of

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1, 3, 5-Triketones RICHARD L. LINTVEDT, BARBARA TOMLONOVIC, DAVID E. FENTON, and MILTON D. GLICK Wayne State University, Detroit, Mich. 48202

Some new binucleating, Schiff-base ligands were prepared by reacting the 1,3,5-triketones 1-phenyl-1,3,5-hexanetrione and 2,2-dimethyl-3,5,7-octanetrione with ethylenediamine in 1:1 molar ratios. The products, abbreviated H (BAA) en and H (PAA) en respectively, contain two different coordination sites which enable them to bind selectively to two different metal ions. Several heteronuclear complexes were prepared and characterized; these included NiZn(BAA) en, NiCu(BAA) en, NiVO(BAA) en, and NiUO (BAA) en. A single-crystal x-ray structure was determined for NiZn(BAA) en. The Cu(II) chelates of these ligands have unusually strong antiferromagnetism; Cu (PAA) en is diamagnetic at room temperature, has no EPR signal, and gives a high resolution NMR spectrum. Cu (PAA) en undergoes electrochemical reversible reduction vs. SCE at —0.61 V in a one-step, two-electron reduction per molecule. 4

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'Sphere has been considerable interest recently in the physical properA

ties of p o l y n u c l e a r t r a n s i t i o n m e t a l complexes.

T h i s interest covers

a w i d e r a n g e of areas i n c l u d i n g m e t a l l o e n z y m e s , h o m o g e n e o u s catalysis, e l e c t r i c a l c o n d u c t i v i t y , a n d m a g n e t i c exchange interactions.

Until

now

m u c h of the r e s e a r c h i n v o l v e d i n v e s t i g a t i n g a n i s o l a t e d e x a m p l e of a n interesting polynuclear complex.

Although many compounds w i t h inter-

e s t i n g a n d i m p o r t a n t properties w e r e d i s c o v e r e d i n this m a n n e r , i t is n o t a systematic m e t h o d of either p r e p a r i n g n e w m a t e r i a l s or u n d e r s t a n d i n g the p h y s i c a l p r i n c i p l e s r e s p o n s i b l e for t h e i r p r o p e r t i e s . 407 In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

408

INORGANIC

COMPOUNDS WITH

UNUSUAL PROPERTIES

I d e a l l y , one w o u l d l i k e to p r e p a r e m a n y closely r e l a t e d complexes, e a c h one d e s i g n e d to v a r y a p a r a m e t e r r e l a t e d to the p r o p e r t i e s u n d e r investigation.

I t is p r o b a b l e that o n l y t h r o u g h s u c h m o l e c u l a r d e s i g n

w i l l a t h o r o u g h u n d e r s t a n d i n g of the p r o p e r t i e s a n d r e a c t i v i t y of p o l y n u c l e a r complexes

be a c h i e v e d .

A s u r p r i s i n g l y l i t t l e s t u d i e d class

of

p o l y n u c l e a r t r a n s i t i o n m e t a l complexes w h i c h presents a n excellent o p p o r t u n i t y for m o l e c u l a r d e s i g n of h u n d r e d s of n e w c o m p o u n d s consists of t h e β-polyketonate chelates a n d t h e i r d e r i v a t i v e s . T h e g e n e r a l i z e d s t r u c


t u r e of the β-polyketone l i g a n d s m a y be d e p i c t e d as a h o m o l o g o u s i n w h i c h the w e l l k n o w n 1,3-diketones are the s i m p l e s t m e m b e r s .

1,3-diketone

0

0

0

series The

1,3,5-triketone

0

1,3,5,7-tetraketone organic molecules may be altered i n various ways i n c l u d i n g v a r y i n g R a n d R ' , r e p l a c i n g h y d r o g e n s o n the b a c k b o n e carbons w i t h other g r o u p s , r e p l a c i n g the k e t o n i c oxygens w i t h other e l e c t r o n p a i r donors s u c h as N , S, Se, a n d P , a n d i n c r e a s i n g the n u m b e r of ketone groups ( i.e. i n c r e a s ing n).

V e r y little i n f o r m a t i o n a b o u t s u c h m o l e c u l e s , m u c h less t h e i r

m e t a l d e r i v a t i v e s , is f o u n d i n the l i t e r a t u r e . S o m e r e l a t i v e l y h i g h m o l e c u l a r w e i g h t β-polyketones h a v e b e e n r e p o r t e d .

F o r example, Harris and

c o - w o r k e r s ( J , 2; also see references c i t e d i n 2) p r e p a r e d /?-polyketones i n a h o m o l o g o u s series u p to a n d i n c l u d i n g a

1,3,5,7,9,11,13,15-octaketone,

a n d t h e r e are reports of β-polyketone p o l y m e r s w i t h m o l e c u l a r w e i g h t s of a b o u t 2000 ( 3 ) . W h e n one considers the chelates p r e p a r e d f r o m the β-polyketones, i t is i m p o r t a n t to r e a l i z e t h a t these l i g a n d s are r e a d i l y e n o l i z a b l e a n d t h a t t h e y f o r m p o l y a n i o n i c species i n the presence of a base (e.g. T h e c o n j u g a t e d sp

2

Reaction 1).

t y p e carbons i n the p o l y a n i o n s i m p a r t a r i g i d p l a n a r i t y

to the system so that c h e l a t i o n of m e t a l ions results i n p l a n a r , p o l y n u c l e a r m o l e c u l e s i n w h i c h the metals share b r i d g i n g oxygens. homologous

series of l i g a n d s , a h o m o l o g o u s

T h u s , b y use of a

series of chelates m a y

In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

be

32.

LiNTVEDT

l

ET

I J

AL.

Binucîear Schiff Base

409

Ligands

base

(D


p r e p a r e d i n w h i c h the m a j o r s t r u c t u r a l features are constant. T h e

first

three m e m b e r s of s u c h a series of d i v a l e n t m e t a l c o m p l e x e s are 1, 2, a n d 3. I n these structures Β represents a n a d d u c t l i g a n d , e.g. H 0 o r p y r i d i n e , 2

w h i c h m a y or m a y not b e present d e p e n d i n g o n t h e m e t a l i o n . T h e r e are a f e w p a p e r s o n 1,3,5-triketonate chelates (4, 5, 6, 7, 8, 9,10) one r e p o r t o n t r i n u c l e a r 1,3,5,7-tetraketonate

chelates

(Ji).

knowledge, no higher homologs have been reported.


but only To

our

410

INORGANIC

COMPOUNDS WITH

UNUSUAL PROPERTIES

Recently single-crystal x-ray structure determinations for binuclear 1,3,5-triketonates of C u ( I I )

(12, 13), N i ( I I ) ( 7 ) , a n d C o ( I I ) (6) h a v e

c o n f i r m e d t h e g e n e r a l structures 1, 2, a n d 3 a n d t h e fact t h a t t h e l i g a n d s are essentially p l a n a r . I n d e e d , i n t h e N i ( I I ) a n d C o ( I I ) chelates w h e r e Β is p y r i d i n e , t h e b a c k b o n e carbons, t h e k e t o n i c oxygens, a n d t h e m e t a l ions are c o p l a n a r w i t h i n e x p e r i m e n t a l error. T h e C - C a n d C - O distances r e v e a l that t h e π electrons i n t h e l i g a n d s are d e l o c a l i z e d a n d f u r t h e r s u p p o r t t h e b e l i e f that t h e carbons are best r e p r e s e n t e d as sp . T h e other 2

important

s t r u c t u r a l features

are: (a)

the bridging

oxygen-to-metal


distance is v e r y s i m i l a r to t h e t e r m i n a l o x y g e n - t o - m e t a l distance, ( b ) t h e O -M-O b

b

a n g l e is a b o u t 7 5 ° , a n d ( c ) t h e M - O - M angle is a b o u t 1 0 2 ° . b

T h e p r i m a r y interest i n t h e β-polyketonate chelates so f a r has b e e n to investigate m a g n e t i c exchange b e t w e e n t h e m e t a l ions w i t h i n t h e same molecule. Temperature-dependent magnetic susceptibility was measured o n b i n u c l e a r triketonates of d -d l

and d - d 9

9

l

( 8 ) , d*-d

s

(4, 5, 9, 12, 13) systems.

(14), d -d 7

7

(6), d*-d* (7),

I n a l l cases, q u i t e s t r o n g a n t i f e r r o -

m a g n e t i c exchange is o b s e r v e d w i t h t h e strongest b e i n g t h e d -d 9

chelates.

Cu(II)

9

T h e s i m i l a r g e o m e t r y of t h e m e t a l ions a n d b r i d g i n g oxygens

i m p l i e s that differences i n t h e strengths of exchange a r e c a u s e d b y d i f ferences i n t h e s y m m e t r y of t h e e x c h a n g i n g electrons ( 1 5 ) . S i n c e t h e u n p a i r e d (d ) ry

electron i n C u ( I I ) is d i r e c t e d at t h e k e t o n i c o x y g e n a n d

is a b l e to p a r t i c i p a t e d i r e c t l y i n σ b o n d i n g , i t is l o g i c a l t h a t d -d 9

9

ex

c h a n g e is t h e strongest y e t o b s e r v e d i n t h e first-row t r a n s i t i o n m e t a l ions. M o r e quantitative information about unpaired electron symmetry a n d exchange s t r e n g t h awaits p r e p a r a t i o n of n e w complexes, m o r e m a g n e t i c measurements, a n d additional structural information. A n o t h e r area of c o n s i d e r a b l e interest i n p o l y n u c l e a r m e t a l c o m p l e x c h e m i s t r y f o r w h i c h the β-polyketones seem w e l l s u i t e d is t h a t o f m i x e d m e t a l a n d m i x e d v a l e n c e complexes.

W h e n one is seeking f u n d a m e n t a l

d a t a o n h o w t h e m o l e c u l a r s t r u c t u r e a n d p r o p e r t i e s of s u c h

compounds

relate to b u l k p r o p e r t i e s , i t is n o t sufficient to b e content w i t h u n c e r t a i n ties c o n c e r n i n g p u r i t y a n d t h e positions of t h e different ions.

I n this

p a p e r w e r e p o r t o n a s y s t e m a t i c a p p r o a c h to t h e p r e p a r a t i o n of some h e t e r o n u c l e a r , m o l e c u l a r chelates, i.e. m o l e c u l e s c o n t a i n i n g t w o o r m o r e

4


32.

LINTVEDT ET


AL.

411

Ligands

different m e t a l ions. T h e l i g a n d s u s e d i n this i n v e s t i g a t i o n are Schiff-base d e r i v a t i v e s of 1,3,5-triketones a n d e t h y l e n e d i a m i n e . T h e s e m o l e c u l e s c o n t a i n t w o different c o o r d i n a t i o n sites, one w i t h t w o n i t r o g e n a n d o x y g e n donors, the other w i t h f o u r oxygen donors

(4).

two

T h e binucîear

chelates of these l i g a n d s h a v e r a t h e r u n u s u a l properties w h e t h e r the t w o m e t a l ions are s i m i l a r or different.


Experimental T h e 1,3,5-triketones w e r e p r e p a r e d b y the m o d i f i e d C l a i s e n - t y p e c o n d e n s a t i o n d e s c r i b e d b y M i l e s , H a r r i s , a n d H a u s e r (16). Abbreviations are b a s e d o n the t r i v i a l n a m e s : l - p h e n y l - l , 3 , 5 - h e x a n t r i o n e is b e n z o y l a c e t y l a c e t o n e ( H B A A ) a n d 2,2-dimethyl-3,5,7-octanetrione is p i v a l o y l a c e t y l a c e t o n e ( H P A A ). 2

2

H ( B A A ) e n . T h e c o n d e n s a t i o n of e t h y l e n e d i a m i n e a n d H B A A w a s effected b y the a d d i t i o n of 2.0 m l (0.03 m o l e ) e t h y l e n e d i a m i n e t o 11.0 g (0.054 m o l e ) H B A A i n a m i n i m u m of m e t h a n o l . T h e s o l u t i o n w a s h e a t e d to b o i l i n g a n d c o o l e d at — 5 ° C . T h e c r u d e crystals w e r e c o l l e c t e d a n d r e c r y s t a l l i z e d f r o m acetone. T h e y e l l o w crystals m e l t at 171 ° C . Y i e l d s are t y p i c a l l y 8 0 - 9 0 % . A n a l . : c a l c d for C H N 0 : C 72.19, H 6.52, Ν 6.45; f o u n d : C 71.84, Η 6.45, Ν 6.66. 4

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H ( P A A ) e n . T h e p r e p a r a t i o n of this l i g a n d w a s s i m i l a r to t h a t of H ( B A A ) e n w i t h y i e l d s of about 9 0 % . T h e off-white, m i c a - l i k e crystals m e l t at 1 4 5 ° - 1 4 6 ° C . A n a l . : c a l c d for C o H N 0 : C 67.34, Η 9.20, Ν 7.14; f o u n d C 66.98, Η 9.40, Ν 7.12. 4

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N i H ( B A A ) e n . T h i s mononuclear complex was prepared b y m i x i n g e q u i m o l a r q u a n t i t i e s of H ( B A A ) e n d i s s o l v e d i n hot acetone a n d N i ( C > H 0 ) · 4 H 0 d i s s o l v e d i n a s m a l l a m o u n t of h o t w a t e r . W h e n the r e a c t i o n m i x t u r e w a s c o o l e d , the c r u d e p r o d u c t p r e c i p i t a t e d a n d i t was then r e c r y s t a l l i z e d f r o m acetone. T h e r e d crystals m e l t at 1 7 4 ° C . A n a l : c a l c d for C H N 0 N i : C 63.84, Η 5.38, Ν 5.73, N i 12.0; f o u n d : C 63.56, H 5.32, Ν 5.73, N i 11.9. 2

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2 C

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C u ( B A A ) e n . T w o solutions w e r e p r e p a r e d : one c o n t a i n e d 2.0 g (0.01 m o l e ) H ( B A A ) e n i n 40 m l a c e t o n e - 1 6 0 m l C H C 1 , the other 4.0 g (0.02 m o l e ) C u ( C H 0 ) · H 0 i n 125 m l m e t h a n o l . T h e w a r m l i g a n d s o l u t i o n was t h e n a d d e d to the w a r m , s t i r r e d m e t a l i o n s o l u t i o n d u r i n g a b o u t 30 m i n . T h e r e a c t i o n m i x t u r e was h e a t e d 1 h r u n t i l the v o l u m e decreased to about 100 m l . T h e p r e c i p i t a t e d p r o d u c t w a s filtered, a i r d r i e d , a n d w a s h e d three times w i t h 30 m l portions of acetone a n d o n c e w i t h 30 m l C H C 1 . T h e green p r o d u c t does not m e l t b e l o w 3 3 5 ° C . A n a l . : c a l c d for C H N 0 C u : C 56.21, H 4.35, Ν 5.04, C u 22.88; f o u n d : C 56.22, Η 4.43, Ν 5.21, C u 22.6. 2

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C u ( P A A ) e n . T h e crude product was prepared b y m i x i n g stoichio m e t r i c q u a n t i t i e s of H ( P A A ) e n a n d C u ( C H 0 ) · H 0 ( 1 : 2 m o l a r r a t i o ) i n h o t m e t h a n o l . A f t e r several m i n u t e s of h e a t i n g a n d t h e n c o o l i n g , the c r u d e p r o d u c t p r e c i p i t a t e d ; i t was t h e n r e c r y s t a l l i z e d f r o m h o t C H C 1 . T h e s m a l l green crystals m e l t at 2 6 4 ° C . A n a l . : calcd for C H N 0 C u : C 51.20, Η 6.21, Ν 5.43; f o u n d : C 50.46, Η 6.13, Ν 5.38. 2

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412

INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES

N i C u ( B A A ) e n . T h e mononuclear complex N i H ( B A A ) e n was u s e d as a l i g a n d b y d i s s o l v i n g it i n acetone a n d s l o w l y a d d i n g a n e q u i m o l a r q u a n t i t y of C u ( C H 0 ) · H 0 d i s s o l v e d i n a m i n i m u m v o l u m e of H 0 . A f t e r c o n c e n t r a t i o n a n d c o o l i n g , the h e t e r o n u c l e a r chelate p r e c i p i t a t e d . T h e c r u d e p r o d u c t was r e c r y s t a l l i z e d f r o m p y r i d i n e , w a s h e d w i t h c o l d acetone, a n d d r i e d u n d e r v a c u u m . Y i e l d is a b o u t 8 5 % b a s e d o n N i H o ( B A A ) e n . T h e d a r k r e d - b r o w n p r o d u c t does not m e l t b e l o w 3 3 5 ° C . A n a l . : c a l c d f o r C H N , 0 N i C u : C 56.70, H 4.39, Ν 5.09, C u 11.54; f o u n d : C 56.85, Η 4.47, Ν 5.12, C u 11.50. 2

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2 4

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N i Z n ( B A A ) e n · 2 H 0 . T h i s c o m p o u n d w a s p r e p a r e d b y the same m e t h o d that was u s e d for N i C u ( B A A ) e n . T h e c r u d e p r o d u c t w a s r e c r y s t a l l i z e d f r o m b e n z e n e to g i v e a g o l d e n b r o w n p o w d e r w i t h a b o u t 6 0 % y i e l d . T h e c o m p o u n d does not m e l t b e l o w 3 0 0 ° C . A n a l . : c a l c d for C H N 0 N i Z n : C 53.06, Η 4.70, Ν 4.76, N i 9.97; f o u n d : C 53.41, H 4.30, Ν 4.96, N i 10.2. R e c r y s t a l l i z a t i o n f r o m p y r i d i n e gave l a r g e s i n g l e crystals of a p y r i d i n e a d d u c t , N i Z n ( p y ) ( B A A ) e n · 2 p y , i n w h i c h one p y r i d i n e is c o o r d i n a t e d to the Z n a t o m . T h e u n c o o r d i n a t e d p y r i d i n e s are easily r e m o v e d b y w a s h i n g w i t h acetone. A n a l . : c a l c d for C H N 0 N i Z n ( C H N ) : C 58.94, H 4.63, Ν 6.65; f o u n d : C 58.51, Η 4.72, Ν 6.61. 2

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2

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N i U 0 ( B A A ) e n . T h i s c o m p o u n d w a s p r e p a r e d b y the same m e t h o d t h a t w a s u s e d for N i C u ( B A A ) e n . T h e c r u d e p r o d u c t w a s r e c r y s t a l l i z e d f r o m acetone to g i v e a d a r k r e d p o w d e r w h i c h does not m e l t b e l o w 3 3 0 ° C . A n a l . : c a l c d for C H N > 0 N i U : C 41.24, Η 3.19, Ν 3.70, U 31.43, N i 7.75; f o u n d : C 40.68, H 3.82, N 3.50, U 31.4, N i 7.4. 2

2

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2 4

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N i V O ( B A A ) e n . T h e same p r o c e d u r e was u s e d to p r e p a r e this c o m p o u n d . R e c r y s t a l l i z a t i o n f r o m acetone y i e l d e d d a r k r e d crystals w h i c h d o not m e l t b e l o w 3 0 0 ° C . A n a l . : c a l c d for G > H N 0 N i V : C 56.35, H 4.37, Ν 5.06; f o u n d : C 56.15, Η 4.43, Ν 5.06. 2

G

2 4

2

5

S p e c t r a . S p e c t r a w e r e r e c o r d e d u s i n g the f o l l o w i n g spectrometers: a b s o r p t i o n spectra, a C a r y - 1 4 ; mass spectra, a n A t l a s C - 4 mass s p e c t r o m e ter; E S R , a V a r i a n E - 4 ; a n d N M R , a V a r i a n A 6 0 A . T h e fluorescence spectra w e r e r e c o r d e d u s i n g a n A m i c o B o w m a n spectrofluorometer. Magnetic Susceptibility Measurements. T h e magnetic susceptibility of the solids w a s m e a s u r e d b y t h e F a r a d a y m e t h o d w i t h H g [ C o ( S C N ) ] u s e d as the c a l i b r a n t . C o r r e c t i o n s for d i a m a g n e t i s m w e r e m a d e u s i n g Pascal's constants. S o l u t i o n measurements w e r e m a d e i n C H C 1 b y N M R techniques (17). 4

3

X - r a y S t r u c t u r e D e t e r m i n a t i o n . A three-dimensional single-crystal s t r u c t u r e w a s d e t e r m i n e d o n crystals o b t a i n e d b y r e c r y s t a l l i z a t i o n of N i Z n ( B A A ) e n f r o m p y r i d i n e . T h e crystals w e r e m o n o c l i n i c I 2/c w i t h lattice parameters of a = 2 8 . 4 0 3 ( 6 ) A , b = 8.465(3) A , c = 3 0 . 2 2 0 ( 9 ) A , β = 1 0 5 . 8 6 ( 2 ) ° , a n d Ζ = 8. I n t e n s i t y d a t a w e r e c o l l e c t e d b y t h e 0-20 scan technique w i t h graphite-monochromated M o - Κ α radiation on a Syntex F2 diffractometer. O f the 5055 d a t a w i t h sin θ/λ < 0.54, 2559 h a d I > 3 σ ( Ι ) a n d these w e r e u s e d i n the s o l u t i o n a n d refinement of t h e structure. T h e s t r u c t u r e was s o l v e d b y P a t t e r s o n — F o u r i e r m e t h o d s a n d refined b y f u l l - m a t r i x ( i s o t r o p i c ) a n d b l o c k - d i a g o n a l ( a n i s o t r o p i c ) least squares refinement. T h e c o n v e n t i o n a l d i s c r e p a n c y factors at the present state of refinement are R = 0.056 a n d R — 0.071. 2

X

w


32.

LiNTVEDT

Results

and

ET

AL.


413

Ligands

Discussion

T h e d i a m i n e Schiff-base d e r i v a t i v e s of 1,3,5-triketones are a n i n t e r esting a n d versatile class of l i g a n d s . F r o m the d e r i v a t i v e s p r e p a r e d so far, i t appears t h a t the d i a m i n e condensations analogous to those of the 1,3-diketones.

that o c c u r

are

fairly

F o r e x a m p l e , amines c o n d e n s e

v e r y r e a d i l y at the c a r b o n y l c a r b o n of a n a c e t y l g r o u p b u t n o t at the c a r b o n y l c a r b o n of a b e n z o y l or p i v a l o y l g r o u p w h e t h e r i t b e a d i k e t o n e or a t r i k e t o n e . T h e r e f o r e , i n a n u n s y m m e t r i c a l l y s u b s t i t u t e d 1,3,5-triketone i n w h i c h the 1-substituent is - C H a n d the 5-substituent is C H Downloaded by UCSF LIB CKM RSCS MGMT on November 25, 2014 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch032

3

or

ter£-C H , 4

9

6

5

a d i a m i n e condenses e x c l u s i v e l y at the m e t h y l e n d . U n d e r

a v a r i e t y of e x p e r i m e n t a l c o n d i t i o n s , c o n d e n s a t i o n w a s n o t o b s e r v e d at the c e n t r a l c a r b o n y l c a r b o n . A s a result of this specificity, b i n u c l e a t i n g l i g a n d s c a n be p r e p a r e d i n w h i c h there are t w o c o o r d i n a t i v e l y different sites for m e t a l ions. S i n c e one site furnishes t w o i m i n e - t y p e nitrogens a n d t w o oxygens a n d the other f u r n i s h e s f o u r o x y g e n d o n o r s , t h e m e t a l s o c c u p y i n g these sites experience different l i g a n d field effects.

Several

studies h a v e d e m o n s t r a t e d t h a t m a g n e t i c exchange b e t w e e n m e t a l ions in

t h e triketonates is s t r o n g l y a n t i f e r r o m a g n e t i c

(4-15).

Therefore,

i n the Schiff-base t r i k e t o n a t e , i t is possible to investigate t h e p r o p e r t i e s of binucîear complexes i n w h i c h s t r o n g l y c o u p l e d metals are i n s i g n i f i c a n t l y different l i g a n d fields. Heteronuclear Complexes.

T h e presence of t w o c o o r d i n a t i v e l y d i s -

t i n c t sites i n the l i g a n d i m p l i e s t h a t c e r t a i n m e t a l ions h a v e a p r e f e r e n c e

heteronuclear p o s i t i o n a l isomers

homonuclear complexes


414

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

f o r one of the sites a n d different m e t a l ions a p r e f e r e n c e for t h e other site.

B y u s i n g these preferences,

w e can prepare pure compounds i n

w h i c h t w o different m e t a l ions are c o n t a i n e d w i t h i n the same m o l e c u l e . I n a d d i t i o n , the positions of t h e m e t a l ions w i t h i n t h e m o l e c u l e

are

p r e d i c t a b l e because of the c o o r d i n a t i o n specificity. I f c o n d i t i o n s are n o t completely

favorable,

however,

i m p u r i t i e s i n the f o r m

isomers a n d h o m o n u c l e a r chelates m a y b e f o r m e d .

of

positional

T h e characterization

a n d i d e n t i f i c a t i o n of a p u r e p r o d u c t w h e n a l l p o s s i b i l i t i e s exist is not t r i v i a l , a n d even s t r u c t u r e d e t e r m i n a t i o n is not u n a m b i g u o u s w h e n the


t w o metals h a v e s i m i l a r a t o m i c n u m b e r s .

T h u s , the a p p r o a c h t a k e n to

t h e systematic p r e p a r a t i o n of p u r e h e t e r o n u c l e a r c o m p l e x e s m u s t b e v e r y d e l i b e r a t e , a n d c h a r a c t e r i z a t i o n m u s t i n c l u d e s e v e r a l different p h y s i c a l measurements. O u r a p p r o a c h to the p r e p a r a t i o n of p u r e h e t e r o n u c l e a r chelates is to e s t a b l i s h the s e l e c t i v i t y of the t w o c o o r d i n a t i o n sites i n a l i g a n d s u c h as H ( B A A ) e n 4

2

by

d e t e r m i n i n g the s t r u c t u r e of

some

mononuclear

chelates. O n c e these are u n a m b i g u o u s l y c h a r a c t e r i z e d , t h e y are u s e d as l i g a n d s to b i n d a s e c o n d m e t a l i o n w i t h a p r o v e n p r e f e r e n c e

for t h e

a v a i l a b l e site. T h e t w o metals are chosen so as to m i n i m i z e c o m p e t i t i o n for the same site w i t h i n the m o l e c u l e . M O N O N U C L E A R

complexes w i t h

CHELATES

the

OF

Three w e l l characterized

H (BAA) EN. 2

4

general formula M [ H ( B A A ) e n ] , 2

2

where

is

M

N i ( I I ) , C u ( I I ) , and V O ( I I ) , were prepared. Single-crystal x-ray struct u r e d e t e r m i n a t i o n s of the C u ( I I )

(18)

and V O ( I I )

(19)

complexes

r e v e a l e d t h a t the m e t a l ions o c c u p y t h e site w i t h f o u r o x y g e n

donors

u n d e r the p r e p a r a t i v e c o n d i t i o n s used. A l t h o u g h the presence of a s m a l l a m o u n t of t h e other p o s i t i o n a l i s o m e r c a n n o t

be

discounted,

sample

h o m o g e n e i t y a n d c r y s t a l l i z a b i l i t y are i n d i c a t i o n s t h a t a significant q u a n t i t y is not present i n the c r y s t a l l i n e p r o d u c t w h i c h is i s o l a t e d i n h i g h yields. A s t r u c t u r e d e t e r m i n a t i o n of the other m o n o n u c l e a r chelate, N i [ H 2

( B A A ) e n ] , was d e e m e d not necessary because of its u n a m b i g u o u s c h a r 2

a c t e r i z a t i o n b y s p e c t r a l a n d m a g n e t i c measurements.

T h e v i s i b l e spec-

t r u m of N i [ H ( B A A ) e n ] is essentially i d e n t i c a l to t h a t of N i ( A c a c ) e n 2

2

2

w h i c h is k n o w n to c o n t a i n s q u a r e p l a n a r N i ( I I ) .

T h e I R spectrum con-

tains a n intense u n c h e l a t e d c a r b o n y l b o n d at 1700 c m "

1

w h i c h indicates

t h a t the n i c k e l a t o m is c o o r d i n a t e d to t w o nitrogens a n d t w o

oxygens.

In addition, N i [ H ( B A A ) e n ]

—266 X

2

10" cgs w h i l e x 6

g

2

is d i a m a g n e t i c w i t h X

g

obs. =

c a l c u l a t e d f r o m Pascal's constants is —246 X

10'

6

cgs,

w h i c h is f u r t h e r p r o o f of s q u a r e p l a n a r g e o m e t r y a b o u t t h e N i . T h e spectral properties

of

Ni[H (BAA) en] 2

2

are n o t a sensitive

m e a s u r e of p u r i t y w i t h respect to the t w o p o s i t i o n a l isomers, b u t the d i a m a g n e t i s m of t h e c o m p o u n d m a y b e u s e d to j u d g e p u r i t y .

I f the N i


32.

LiNTVEDT

ET

AL.

Binuclear

415

Schiff Base Ligands

w e r e c o o r d i n a t e d to f o u r oxygens, its e n v i r o n m e n t w o u l d b e v e r y s i m i l a r to that f o u n d i n bis ( b e n z o y l a c e t o n a t o ) n i c k e l ( I I ) , w h i c h is p a r a m a g n e t i c b y v i r t u e of the fact that it attains h i g h e r c o o r d i n a t i o n n u m b e r s t h r o u g h solvent c o o r d i n a t i o n or o l i g o m e r i z a t i o n ( 2 0 ) . paramagnetic N i (II) measurements.

E v e n a s m a l l a m o u n t of a

species w o u l d b e easily d e t e c t e d b y s u s c e p t i b i l i t y

O n the basis of the experiments p e r f o r m e d

so f a r , i t

appears t h a t p u r e isomers of m o n o n u c l e a r c o m p l e x e s are r e a d i l y p r e p a r e d u n d e r a g i v e n set of e x p e r i m e n t a l c o n d i t i o n s a n d t h a t t h e c o o r d i n a t i o n sites e x h i b i t a significant d e g r e e of specificity t o w a r d different m e t a l ions.


PREPARATION

AND CHARACTERIZATION OF

HETERONUCLEAR CHELATES.

O n c e i t w a s e s t a b l i s h e d that the t w o sites i n Schiff-base d e r i v a t i v e s of 1,3,5-triketones m a y specifically c o o r d i n a t e different m e t a l ions, i t b e c a m e feasible to p r e p a r e p u r e m i x e d m e t a l c o m p l e x e s i n w h i c h t h e p o s i t i o n of the t w o m e t a l ions is k n o w n . A s a m a t t e r of p r e p a r a t i v e c o n v e n i e n c e i n t h e e a r l y stages o f this w o r k , w e chose to use N i [ H ( B A A ) e n ] as a 2

2

l i g a n d to b i n d a different m e t a l i o n w h i c h has a p r e f e r e n c e for the a v a i l a b l e o x y g e n d o n o r site ( R e a c t i o n 2 ) .

T h e major r a t i o n a l e f o r u s i n g the

N i c o m p l e x as a l i g a n d is as f o l l o w s :

(a)

a p p r e c i a b l y s o l u b l e i n most (b)

we

observed

this m o n o n u c l e a r c o m p l e x is

o r g a n i c solvents i n c l u d i n g

t h a t this c o m p l e x

hydrocarbons;

has e x t r e m e l y l i t t l e t e n d e n c y

to

i s o m e r i z e to the other p o s i t i o n a l i s o m e r i n w h i c h N i is b o n d e d to f o u r oxygens; a n d ( c ) the d i a m a g n e t i s m of N i [ H ( B A A ) e n ] is a c o n v e n i e n t 2

2

p r o p e r t y for j u d g i n g w h e t h e r or not the m e t a l ions change p o s i t i o n d u r i n g the r e a c t i o n since t h e N i is e x p e c t e d to b e p a r a m a g n e t i c i n the o x y g e n donor position. Mass

T h e h e t e r o n u c l e a r chelates Z n ( p y ) ( B A A ) e n ,

Spectra.

2

NiCu-

( B A A ) e n , a n d N i V O ( B A A ) e n are sufficiently v o l a t i l e that mass s p e c t r a 2

2

can be obtained.

I n e a c h case, s t r o n g p a r e n t i o n peaks are

observed

m i n u s a n y a d d u c t e d l i g a n d s . T h e h i g h mass regions of t h e N i Z n ( B A A ) e n 2

a n d N i V O ( B A A ) e n s p e c t r a are s u r p r i s i n g l y s i m p l e — o n l y t h e p a r e n t i o n , 2

the p a r e n t i o n m i n u s t w o mass u n i t s , a n d the d o u b l y c h a r g e d ions a r i s i n g f r o m these t w o species are o b s e r v e d i n a p p r e c i a b l e c o n c e n t r a t i o n a b o v e m/e =

105. W i t h b o t h these chelates, the loss of t w o mass u n i t s b y the


416

INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES

p a r e n t i o n is a v e r y f a v o r a b l e process ( R e a c t i o n 3 ) .

T h e most l o g i c a l

e x p l a n a t i o n of the strong P - 2 peaks is that t w o h y d r o g e n atoms a r e lost +

f r o m t h e e t h y l e n e d i a m i n e g r o u p w h i c h results i n a c o m p l e t e l y u n s a t u r a t e d m o l e c u l a r i o n . T h i s e x p l a n a t i o n for the P - 2 p e a k is b e i n g i n v e s t i +

g a t e d f u r t h e r b y isotope studies.


-2H

Ni

M

m/e

M

m/e

Zn

550, 552, 554, 556

Zn

548, 550, 552, 554

VO

553, 555

VO

551, 553

(3) [p-2H]

2 +

M

m/e

M

m/e

Zn

275, 276, 277, 278

Zn

274, 275, 276, 277

VO

276.5, 277.5

VO

275.5, 276.5

It is o b v i o u s that the peaks a r o u n d mass 275 are c a u s e d b y d o u b l y c h a r g e d ions since the half-mass a n d full-mass peaks are a l l q u i t e intense. T h e i m p o r t a n c e of the d o u b l y c h a r g e d ions is c e r t a i n l y the result of t h e presence of t w o m e t a l centers, each of w h i c h c o u l d l o g i c a l l y s t a b i l i z e a p o s i t i v e charge. T o p u r s u e this p o i n t , the mass s p e c t r u m of the m o n o n u c l e a r chelate N i [ H ( B A A ) e n ] w a s r e c o r d e d . 2

2

T h e r e is n o

evidence

of f o r m a t i o n of d o u b l y c h a r g e d ions b y this c o m p o u n d , w h i c h constitutes strong i n d i r e c t e v i d e n c e that the m a x i m u m p o s i t i v e c h a r g e is d e t e r m i n e d b y the n u m b e r of m e t a l atoms present. T h e s p e c t r u m of N i C u ( B A A ) e n is s i m i l a r to those of Z n a n d V O , 2

b u t i t is m o r e c o m p l e x i n that P - C u a n d r e l a t e d fragments are q u i t e +

intense. T h e p r i m a r y reason for r e c o r d i n g t h e mass s p e c t r a w a s to s u p p o r t t h e c o n c l u s i o n that these c o m p o u n d s are p u r e h e t e r o n u c l e a r chelates r a t h e r t h a n m i x t u r e s of h e t e r o - a n d h o m o n u c l e a r m o l e c u l e s .

Since no


32.

LiNTVEDT

ET

Binuclear

AL.

Schiff Base

Ligands

417

peaks a t t r i b u t a b l e to species s u c h as N i ( B A A ) e n a n d Z n ( B A A ) e n 2

2

2

2

w e r e o b s e r v e d , t h e mass s p e c t r a s u p p o r t t h e c o n c l u s i o n t h a t t h e samples consist of p u r e heteronuclear m o l e c u l e s . Magnetic

Properties.

A l t h o u g h the a n a l y t i c a l a n d mass s p e c t r a l d a t a

i n d i c a t e t h a t the h e t e r o n u c l e a r chelates are p u r e , t h e y g i v e n o c l u e as to w h e t h e r some of t h e m e t a l ions h a v e r e v e r s e d t h e i r positions d u r i n g preparation.

S i n c e one of o u r p u r p o s e s is to b e a b l e to p r e p a r e p u r e

m i x e d m e t a l c o m p o u n d s i n w h i c h positions of the m e t a l ions are k n o w n , such a reversal w o u l d constitute a n i m p u r i t y i n the b u l k sample.


m a g n e t i c p r o p e r t i e s of these N i m i x e d m e t a l c o m p o u n d s d o ,

The

however,

e n a b l e one to d e t e r m i n e the m e t a l i o n positions w i t h some c e r t a i n t y

Figure 1.

Molecular structure of

NiZn(py)(BAA)2en


418

INORGANIC

COMPOUNDS WITH

UNUSUAL PROPERTIES

since N i ( I I ) is square p l a n a r a n d d i a m a g n e t i c w h e n c o o r d i n a t e d to the t w o nitrogens a n d the t w o c e n t r a l oxygens.

I n the a l t e r n a t i v e p o s i t i o n ,

the N i ( I I ) is e x p e c t e d to b e p a r a m a g n e t i c , as d i s c u s s e d above. T h e m a g n e t i c s u s c e p t i b i l i t i e s of a l l the h e t e r o n u c l e a r complexes p r e p a r e d f r o m N i [ H ( B A A ) e n ] are consistent w i t h a d i a m a g n e t i c , s q u a r e 2

2

p l a n a r N i ( I I ) . T h e m a g n e t i c m o m e n t s of N i C u ( B A A ) e n a n d N i V O 2

( B A A ) e n c o r r e s p o n d to one u n p a i r e d e l e c t r o n p e r m o l e c u l e , N i Z n ( p y ) 2

( B A A ) e n is d i a m a g n e t i c , a n d N i U 0 ( B A A ) e n has a s m a l l p a r a m a g 2

2

2


n e t i s m that m a y result f r o m some o r b i t a l c o n t r i b u t i o n . Structure

of NiZn(py)(BAA) en. 2

S i n g l e crystals w e r e p r e p a r e d b y

c r y s t a l l i z i n g N i Z n ( H 0 ) ( B A A ) e n f r o m p y r i d i n e , a n d the structure w a s 2

2

p r o v e n to b e as d e p i c t e d i n F i g u r e 1. It is i n t e r e s t i n g t h a t a l t h o u g h x - r a y techniques

cannot

distinguish between

N i a n d Z n atoms,

the

four-

c o o r d i n a t e a t o m m u s t be N i since the c o m p o u n d w o u l d be p a r a m a g n e t i c if N i were

five-coordinate.

five-coordinate

I n a d d i t i o n , the c o o r d i n a t i o n sphere of t h e

a t o m is v e r y s i m i l a r to t h a t f o u n d i n Z n ( A c a c ) p y

(21).

2

T h e N i a n d its four d o n o r atoms ( t w o nitrogens a n d t w o o x y g e n s ) f o r m a p l a n e i n w h i c h no a t o m is d i s p l a c e d m o r e t h a n 0.03 A p l a n a r i t y . T h e Z n is i n a t y p i c a l l y

five-coordinate

from

environment i n w h i c h

the m e t a l a t o m is d i s p l a c e d 0.32 A f r o m the least-squares p l a n e of the f o u r d o n o r oxygens.

T h e average distances i n the c o o r d i n a t i o n spheres of the

t w o m e t a l atoms are d e p i c t e d i n F i g u r e 2, a n d the i m p o r t a n t angles i n the m e t a l c o o r d i n a t i o n spheres are s h o w n i n F i g u r e 3. The

geometry

of

the M

ring

i n the

Schiff-base

ligand

( B A A ) e n ~ does not differ g r e a t l y f r o m that f o u n d i n the h o m o n u c l e a r 4

2

complexes

that c o n t a i n s i m p l e triketonate l i g a n d s (see

T a b l e I.

Comparisons of M

/°\

Table I).

The

M Ring Structure in

S e v e r a l Binucîear C o m p l e x e s Metal-Metal Distance, A

Complex

0

Ni (DBA) (py) Co (DBA) (py) Cu (BAA) (py) Cu (DAA) (py) NiZn(py) (BAA) en 2

2

4

2

2

4

2

2

2

2

2

2

2

3.17 3.27 3.06 3.05 3.12

O-M-0 Angle,

°

78.5 77.3 75.9 77 79.7,68.8*

M-O-M Angle,

°

101.5 102.7 103.6 103 104.9

Ref. 7 6 12 13

" D B A is the dianion of l,5-diphenyl-l,3,5-pentanetrione whose trivial name is dibenzoylacetone. D A A is the dianion of 2,4,6-heptanetrione whose trivial name is diacety lace tone T h e angle 68.8° is for O - Z n - O , and 79.7° is for O - N i - O . b



32.

LiNTVEDT

ET

Binuclear

AL.

419

Schiff Base Ligands

N(2)

0(3)

0(4)

N(l)

0(2)

O(l)

Figure

2.

Distances (in A) in the spheres of Ni and Zn

coordination

s t r u c t u r a l s i m i l a r i t i e s l e a d one to c o n c l u d e that a n y of s e v e r a l m e t a l ions m a y b e i n t r o d u c e d w i t h o u t s i g n i f i c a n t l y d i s t o r t i n g the p a r t of the m o l e c u l e i n w h i c h m e t a l - m e t a l interactions take p l a c e .

Therefore, from the

s t a n d p o i n t of m a g n e t i c superexchange studies, a great m a n y h o m o - a n d h e t e r o n u c l e a r c o m p l e x e s c a n b e i n v e s t i g a t e d u n d e r c o n d i t i o n s of s i m i l a r c o o r d i n a t i o n geometry.

very

T h i s fact s h o u l d p r o v e v e r y u s e f u l i n the

q u a n t i t a t i v e e x p e r i m e n t a l testing of

current theory

describing

super-

exchange mechanisms. F i n a l l y , the structure of N i Z n ( p y ) ( B A A ) e n lends c o n v i n c i n g s t r u c 2

t u r a l s u p p o r t to t h e c o n t e n t i o n t h a t the c o o r d i n a t i v e l y different sites i n t h e l i g a n d d e t e r m i n e p r e d i c t a b l y the positions of the t w o m e t a l atoms. T h i s i n f o r m a t i o n , together w i t h m a c r o s c o p i c measurements

(particularly

m a g n e t i c s u s c e p t i b i l i t y ) to i n d i c a t e b u l k p u r i t y , demonstrates t h a t i t is N(2)

0(3)

0(4)

N(l)

0(2)

O(l)

Figure

3.

Bond angles in the coordination of Ni and Zn

spheres


420

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

p o s s i b l e to take a n e x t r e m e l y systematic a p p r o a c h to t h e synthesis heteronuclear molecular

of

complexes.

H o m o n u c l e a r Chelates of H ^ P A A ^ e n . was s h o w n that the r e a c t i o n of

1:1

I n the a b o v e d i s c u s s i o n , i t

m o l a r ratios of C u ( I I )

and H 4

( B A A ) e n at e l e v a t e d t e m p e r a t u r e s i n M e O H y i e l d s C u [ H ( B A A ) e n ] 2

2

with Cu(II)

c o o r d i n a t e d to f o u r oxygens.

2

U n d e r different p r e p a r a t i v e

c o n d i t i o n s , h o w e v e r , o t h e r p r o d u c t s are o b t a i n e d (see

Reactions 4 a n d 5 ) .

CHCl -MeOH 3

H (PAA) en + 2Cu(OAc)


4

2

• Cu (PAA) en +

2

2

4HOAc (4)

2

hot

.C(CH )

H C

3

3

T T

_

A N

H (PAA) en 4

2

+

CHCl -MeOH

Γ ^V,

3

lCu(OAc)

'

3

(5)

Η

2

0

C

N

L

CH

0

Ο

C(CH ) 3

3

3

purple solution A n a l o g o u s c o m p o u n d s w e r e p r e p a r e d i n w h i c h the tert-butyl replaced by phenyl.

These

new

w h i c h s h o u l d p r o v e u s e f u l i n the s t u d y of p o l y n u c l e a r MAGNETIC

PROPERTIES.

g r o u p is

compounds have unusual properties complexes.

T h e b i n u c l e a r C u ( I I ) c o m p o u n d s of Schiff-

base triketonate ligands a l l exhibit extremely strong antiferromagnetism. T h e s o l i d a n d s o l u t i o n m a g n e t i c p r o p e r t i e s of C u ( P A A ) e n a n d 2

related triketonate C u ( P A A ) 2

Table II.

0

2

β

The

the high

T , °K

2

Cu (PAA) 9

9

2

2

Cut(PAA) en %

(BM)

(inCHCl ) 3

M a g n e t i c resonance i n C H C 1 or C D C 1 EPR NMR 3

2

i n Table II.

M a g n e t i c Properties of C u ( P A A ) a n d C u ( P A A ) e n

Parameter M a g n e t i c moment solid solution

2

are c o m p a r e d

300 77 ambient

0.22 0.00 0.18

0.42 0.21 0.00

very weak signal b r o a d absorptions

no s i g n a l s h a r p absorptions

3

Determined by N M R .

r e s o l u t i o n N M R s p e c t r u m a n d t h e absence of a n E P R s i g n a l for C u 2

( P A A ) e n p r o v e t h a t the c o m p l e x is d i a m a g n e t i c at r o o m t e m p e r a t u r e . 2


32.

LiNTVEDT

ET


AL.

421

Ligands

T h u s , the a n t i f e r r o m a g n e t i s m is s t r o n g e n o u g h to p a i r c o m p l e t e l y t h e electrons o n the t w o C u ( I I )

ions.

T h i s means that t h e g r o u n d state

s i n g l e t - e x c i t e d state t r i p l e t s e p a r a t i o n is at least 1400 Bleaney-Bowers

method

(22).

cm"

by

1

the

Strong antiferromagnetism i n planar

binucîear C u ( I I ) complexes is not u n c o m m o n , b u t to o u r k n o w l e d g e n o s u c h complexes

have been

reported i n w h i c h h i g h resolution N M R

spectra are o b t a i n e d a n d there is no E P R s i g n a l . Since trace amounts of p a r a m a g n e t i c C u ( I I ) b r o a d e n N M R peaks t r e m e n d o u s l y a n d are easily o b s e r v e d b y E P R , not o n l y is the m a g n e t i c exchange i n C u ( P A A ) e n 2

2


v e r y strong, b u t the c o m p o u n d is u n u s u a l l y free of C u ( I I ) i m p u r i t i e s . E v e n at v e r y h i g h i n s t r u m e n t a l gains, n o E P R s i g n a l is observed. T h e absence of a n E P R s i g n a l at r o o m t e m p e r a t u r e i n C H C 1

makes

3

p o s s i b l e a series of u n u s u a l m i x e d m e t a l E P R experiments i n w h i c h a m e t a l other t h a n C u is d o p e d i n t o C u ( P A A ) e n . I n t r o d u c t i o n of a t r a c e 2

2

of t h e n e w m e t a l i o n i n t o the d i a m a g n e t i c C u ( P A A ) e n d i s r u p t s t h e 2

2

m a g n e t i c exchange i n the s u b s t i t u t e d m o l e c u l e s , t h e r e b y g i v i n g rise to a Cu(II)

E P R s i g n a l that is a t t r i b u t a b l e to the m i x e d m e t a l m o l e c u l e s .

T h e metal ion doped into C u ( P A A ) e n may be diamagnetic, paramag2

2

n e t i c , E P R a c t i v e , or E P R i n a c t i v e . I n e a c h case, a s i g n a l appears w h e n ever the d o p e d m e t a l replaces a C u ( I I ) i n C u ( P A A ) e n . 2

2

I n t r o d u c i n g Z n ( I I ) i n t o C u ( P A A ) e n , for e x a m p l e , gives the s i g n a l 2

2

i n F i g u r e 4 (the s p e c t r u m w a s r e c o r d e d i n C H C 1 T h e sample was prepared by m i x i n g a C H C 1 and

3

3

at r o o m t e m p e r a t u r e ) .

s o l u t i o n of H ( P A A ) e n 2

a methanol solution that contained C u ( I I )

acetate

4

and

acetate i n 9 5 : 5 m o l a r r a t i o ; t h e p r o d u c t w a s t h e n c o l l e c t e d crystallized from C H C 1 .

Zn(II) and re-

T h e s p e c t r u m gives a n a d d e d b o n u s i n t h a t

3

s u p e r h y p e r f i n e s p l i t t i n g of 1 5 - 2 0 g is o b s e r v e d .

S i n c e this is t h e m a g n i -

t u d e of c o p p e r - n i t r o g e n s p l i t t i n g a n d it is almost i d e n t i c a l to the p u r p l e i s o m e r of C u [ H ( P A A ) e n ] , i t c a n be stated w i t h some confidence t h a t 2

2

the o x y g e n - c o o r d i n a t e d

Cu(II)

is the one r e p l a c e d b y Z n ( I I ) .

The

green isomer of C u [ H ( B A A ) e n ] , w h i c h w a s d e m o n s t r a t e d s t r u c t u r a l l y 2

to

2

contain oxygen-coordinated

Cu(II),

has a s i m p l e E P R s p e c t r u m

w i t h o u t s u p e r h y p e r f i n e s p l i t t i n g . A n a l o g o u s experiments w i t h a v a r i e t y of other m e t a l ions s h o u l d f u r n i s h m u c h i n f o r m a t i o n a b o u t h e t e r o n u c l e a r complexes w i t h p o t e n t i a l l y strong superexchange i n t e r a c t i o n s . SPECTRAL

PROPERTIES.

Absorption

Spectra.

T h e spectral properties

of binucîear C u ( I I ) complexes w h i c h e x h i b i t strong m a g n e t i c

exchange

are not w e l l k n o w n . E x p e r i m e n t a l l y there is some a d v a n t a g e to s t u d y i n g the polyketonates

a n d t h e i r Schiff-base

d e r i v a t i v e s since

comparisons

can b e m a d e b e t w e e n the p o l y n u c l e a r m o l e c u l e s a n d the w e l l k n o w n m o n o n u c l e a r diketonates. F o r e x a m p l e , C u ( P A A ) e n c a n b e e n v i s i o n e d 2

as r e s u l t i n g f r o m a f u s i o n of chelates ( R e a c t i o n 6 ) .

2

d i k e t o n a t e a n d Schiff-base

diketonate

S i n c e the l i g a n d fields a n d m e t a l i o n geometries


422

INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES

b e f o r e a n d after f u s i o n are q u i t e s i m i l a r , s p e c t r a l changes i n g o i n g f r o m m o n o - to b i n u c l e a r m o l e c u l e s c a n b e a t t r i b u t e d to t h e f o r m a t i o n of the Downloaded by UCSF LIB CKM RSCS MGMT on November 25, 2014 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch032

o x y g e n - b r i d g e d system a n d the resultant c h a n g e i n e n e r g y levels.

The

v i s i b l e spectra of m o n o - a n d b i n u c l e a r complexes are c o m p a r e d i n T a b l e

Figure 4. First derivative EPR spectrum of Zn(U)-doped Cu (PAA) en compared with that of the purple isomer Cu \H (PAA) eri\ 2

2

2


2

32.

LiNTVEDT

ET

423

Binucîear Schiff Base Ligands

AL.

I I I . I t is clear that n e w absorptions a n d / o r shifts i n s p e c t r a l transitions take p l a c e i n g o i n g f r o m the m o n o - to the binucîear complexes.

Although

T a b l e I I I . T h e V i s i b l e S p e c t r a of Some R e l a t e d M o n o - a n d Binucîear C u ( I I ) C o m p l e x e s ( i n C H C l ) 3

Complex

Wavelength,

Cu(Acac) Cu(Acac )en Cu (PAA) en Cu (PAA )

nm (emax) 650

2

540 ( 1 9 8 ) 650 (160) 645 (282)

2

2


512 (75) - 4 7 5 (75)

2

2

2

β

(38)

β

a

745 (50) 735 (65)

From Ref. 23.

it is p r e m a t u r e to consider m a k i n g assignments, these d a t a do i n d i c a t e t h a t a d d i t i o n a l s p e c t r a l studies are w a r r a n t e d . Emission

T h e emission spectra from transition metal com

Spectra.

plexes c a n b e a n e x t r e m e l y u s e f u l a i d i n s t u d y i n g m o l e c u l a r

electronic

states.

fluorescence

T h e binucîear c o m p l e x

C u ( P A A ) e n has a s h a r p 2

2

e m i s s i o n at 427 n m . T h i s is u n u s u a l since C u ( I I )

compounds rarely, if

ever, are o b s e r v e d to emit. It is significant t h a t n e i t h e r C u ( A c a c ) Cu(Acac) en

emits u n d e r the e x p e r i m e n t a l c o n d i t i o n s

2

Cu (PAA) en. 2

2

u s e d to

study

I n d e e d , there are no reports i n the l i t e r a t u r e of e m i s s i o n

f r o m either of these chelates u n d e r a n y e x p e r i m e n t a l c o n d i t i o n s . fluorescence

nor

2

spectra

of

the protonated

The

ligand, H ( P A A ) e n , and 4

2

of

C u ( P A A ) e n are c o m p a r e d i n T a b l e I V . T h e e x c i t a t i o n w a v e l e n g t h i n 2

2

Table I V .

Substance

F l u o r e s c e n c e S p e c t r a of H ( P A A ) e n a n d C u ( P A A ) e n ( i n 3-Methylpentane at 7 7 ° K ) 4

Excitation,

H (PAA) en

370

Cu (PAA) en

365 385

4

2

2

2

nm

Emission,

2

2

Comparative Half-band Widths at Half Height, nm

nm

-385 -400 ~420 427 427

b o t h t h e l i g a n d a n d the c o m p l e x

corresponds

2

- 4 - 7 -12 1.5 1.5 to a s t r o n g

absorption,

p r e s u m a b l y a n i n t r a l i g a n d ΤΓ--»7Γ* b a n d . W h e n C u ( P A A ) e n is e x c i t e d 2

2

at either 365 or 385 n m , s h a r p e m i s s i o n occurs at 427 n m . N o

phospho

rescence was o b s e r v e d d o w n to a b o u t 800 n m . ELECTROCHEMISTRY.

T h e c y c l i c v o l t a m m o g r a m f o r the r e d u c t i o n of

C u ( P A A ) e n in dimethylformamide 2

2

T h e r e d u c t i o n occurs at E i

/ 2

=

( D M F ) is p r e s e n t e d i n F i g u r e 5.

—0.61 V vs. S C E , a n d i t is r e v e r s i b l e .


424

INORGANIC

2e"


REVERSIBLE

COMPOUNDS

WITH

REDUCTION -

UNUSUAL PROPERTIES

Cu^PAAfeen

ο

-.45

-50

-.55

-.60

-:65

-.70

-.75

VOLTS

Figure

5.

Cyclic

voltammogram for the reduction (PAA) en in DMF

of

Cu s

2

O n the basis of

electrolysis e x p e r i m e n t s , i t was d e t e r m i n e d that t h e

process i n v o l v e s the a d d i t i o n of t w o electrons p e r m o l e c u l e . T h i s is q u i t e w h i c h generally

reduce

i r r e v e r s i b l y i n a one-step, t w o - e l e c t r o n r e d u c t i o n g i v i n g C u ( 0 )

u n c h a r a c t e r i s t i c of s i m p l e C u ( I I )

compounds

(24).

S e v e r a l of the b i s ( l , 3 , 5 - t r i k e t o n a t o ) d i c o p p e r ( I I ) p o l a r o g r a p h i c a l l y i n o u r laboratories

(25).

chelates w e r e s t u d i e d

These

reductions

are a l l

i r r e v e r s i b l e , b u t t h e y are s i m i l a r to t h a t of C u ( P A A ) e n i n t h a t t h e y 2

2

consist of t w o - e l e c t r o n r e d u c t i o n s . D u r i n g the electrolysis i n w h i c h a s o l u t i o n of C u ( P A A ) e n i n D M F 2

2

w a s q u a l i t a t i v e l y r e d u c e d , t h e color c h a n g e d f r o m green to y e l l o w b u t n o p r e c i p i t a t e f o r m e d . T h u s it seems l i k e l y t h a t a stable C u ( I ) was f o r m e d .

complex

T h e r e v e r s i b i l i t y of the r e d u c t i o n i n d i c a t e s t h a t p e r h a p s

species s u c h as [ C u ( P A A ) e n ] ' or C u [ H ( P A A ) e n ] are f o r m e d i n ?

2

2

2

2

2


32.

LINTVEDT

ET AL.

Binuclear

Schiff Base

425

Ligands

s o l u t i o n . T h e n a t u r e o f these solutions w i l l b e i n v e s t i g a t e d f u r t h e r since the electrochemical

d a t a suggest that chelates

s u c h as C u ( P A A ) e n 2

2

m a y b e u s e f u l e l e c t r o n transfer reagents.


Literature Cited 1. 2. 3. 4. 5. 6.

Wittek, P. J., Harris, T. M., J. Am. Chem. Soc. (1973) 95, 6865. Murphy, G. P., Harris, T. M., J. Am. Chem. Soc. (1972) 94, 8253. Oda, R., Munemiya, S., Okano, M., Makromol. Chem. (1961) 43, 149. Baker, D., Dudley, C. W., Oldham, C., J. Chem. Soc. A (1970) 2605. Murtha, D. P., Lintvedt, R. L., Inorg. Chem. (1970) 1532. Kuszaj, J. M., Tomlonovic, B., Murtha, D. P., Lintvedt, R. L., Glick, M. D., Inorg. Chem. (1973) 12, 1297. 7. Lintvedt, R. L., Borer, L. L., Murtha, D. P., Kuszaj, J. M., Glick, M. D., Inorg. Chem. (1974) 13, 18. 8. Lintvedt, R. L., Mack, J., "Abstracts of Papers," 6th Central Regional Meeting, ACS, April 1974, INORG 613. 9. Sagara, F., Kobayashi, H., Ueno, K., Bull. Chem. Soc. Jpn. (1968) 41, 266. 10. Taguchi, Y., Sagara, F., Kobayashi, H., Ueno, K., Bull. Chem. Soc. Jpn. (1970) 43, 2470. 11. Andrelczyk, B., Lintvedt, R. L.,J.Am. Chem. Soc. (1972) 94, 8633. 12. Tomlonovic, B., Glick, M. D., Lintvedt, R. L., unpublished data. 13. Blake, A. B., Fraser, L. R., J. Chem. Soc. Dalton Trans. (1974) 2554. 14. Borer, L. L., Ph.D. Thesis, Wayne State University, 1972. 15. Glick, M. D., Lintvedt, R. L., Prog. Inorg. Chem. (1975) in press. 16. Miles, M. L., Harris, T. M., Hauser, C. R., J. Org. Chem. (1965) 30, 1007. 17. Evans, D. F., J. Chem. Soc. (1959) 2003. 18. Gavel, D., Kuszaj, J., Lintvedt, R. L., Glick, M. D., "Abstracts of Papers," 166th National Meeting, ACS, Aug. 1973, INORG 156. 19. Gavel, D., Glick, M. D., Lintvedt, R. L., unpublished data. 20. Fackler, Jr., J. P., J. Am. Chem. Soc. (1962) 84, 24. 21. Belford, R. L., Chasteen, N. D., Hitchman, Μ. Α., Hon, P. K., Pfluger, C. E., Paul, I.C.,Inorg. Chem. (1969) 8, 1312. 22. Bleaney, B., Bowers, K. D., Proc. R. Soc. London (1952) A214, 451. 23. Holm, R. H., J. Am. Chem. Soc. (1960) 82, 5632. 24. Lintvedt, R. L., Russell, H. D., Holtzclaw, H. F., Inorg. Chem. (1966) 5, 1603. 25. Handy, R. F., Ph.D. Thesis, Wayne State University, 1972. RECEIVED January 30, 1975.


Binuclear and Mixed Metal Binuclear Chelates of Schiff-Base

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