STRUCTURE INVESTIGATION OF METAL COMPLEXES BY MEANS OF X-RAY EMISSION AND PHOTOELECTRON SPECTROSCOPY

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STRUCTURE INVESTIGATION OF METAL COMPLEXES BY MEANS OF X-RAY EMISSION

AND PHOTOELECTRON SPECTROSCOPY

A. Meisel, R. Szargan, K.-H. Hallmeier, I. Uhlig, J.-A. Momand

To cite this version:

A. Meisel, R. Szargan, K.-H. Hallmeier, I. Uhlig, J.-A. Momand. STRUCTURE INVESTI- GATION OF METAL COMPLEXES BY MEANS OF X-RAY EMISSION AND PHOTOELEC- TRON SPECTROSCOPY. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-981-C9-988.

�10.1051/jphyscol:19879175�. �jpa-00227290�

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JOURNAL DE PHYSIQUE

Colloque C9, suppl6ment au n012, Tome 48, decembre 1987

STRUCTURE INVESTIGATION OF METAL COMPLEXES BY MEANS OF X-RAY EMISSION AND PHOTOELECTRON SPECTROSCOPY

A. MEISEL, R. SZARGAN, K.-H. HALLMEIER, I. UHLIG and J.-A. MOMAND

Sektion Chemie der Karl-Marx-Universitdt Leipzig, Talstrasse 35, DDR-7010 Leipzig, G.D.R.

The ability of the Ni L a , R , S hD, O Ko, and Ni 2p spectra to dis- tinguish between chemical states of atoms and their various en- vironments is applied for structural characterization of nickel coordination compounds. In addition to the well documented

in-

fluences of metal oxidation state and the electronegativity, the dependence of the energy shifts and intensity ratios upon the coordination geometry and the chelate ligand structure is discussed.

INTHODUCTION

A large number of experimental and theoretical studies during the last twenty years has shown that much could be learned about chemical bonding from X-ray emission (XES) and X-ray photoelectron spectroscopy ( X P S ) , Much of this work was associated with electronic structure calculations which have been used to interpret the experiments as well as to establish the validity of theoretical models

/I/.

The potential of XES and X P S for probing the electronic structure of transition metal compounds has been demonstrated also in numerous contributions to the conference pro- ceedings of this series,

The intention of our early experiments /2-4/ was to find the cor- rect explanation for the fine structure of X-ray emission bands using semiempirical as well. as ab initio and SU Xu MO calculations.

New instrumentation for fluorescence excitation in the ultrasoft X-ray region enabled us now to record all the X-ray emission bands of interest with high resolution, necessary for identification of the electronic charge fractions contributing to the individual molecular orbitals,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879175

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C9-982 JOURNAL DE PHYSIQUE

Most of t h e U S i n v e s t i g a t i o n s a r e combined w i t h t h e r e s u l t s of p h o t o e l e c t r o n s p e c t r o s c o p y because core-hole i n i t i a l and f i n a l s t a t e s involved i n b o t h methods and complementary valence band i n f o r m a t i o n a r e a v a i l a b l e . A n i n t e r e s t i n g and even now c o n t r o - v e r s i a l t o p i c of t h e XPS r e s e a r c h i s concerned w i t h t h e o r i g i n of s a t e l l i t e s t r u c t u r e i n c o r e e l e c t r o n emission. The s a t e l l i t e s o c c u r i n g 5 eV o r more h i g h e r in b i n d i n g e n e r g i e s t h a n t h e main peaks 2p and 2p i n heavy t r a n s i t i o n metals and t h e i r compounds a2d2not prea&ted by l i g a n d f i e l d t h e o r y and can be a t - t r i b u t e d t o two-bound h o l e f i n a l s t a t e s . To account f o r t h e s a - t e l l i t e s , i n t e r a c t i o n of 3d w i t h t h e l i g a n d p o r b i t a l s has been examined. With N i compounds, s c r e e n i n g by ligand-to-metal cha g e t r a n s f e r c a u s e s t h e main l i n e which i s t o be a t t r i b u t e d t o 3d §

4

valence e l e c t r o n c o n f i g u r a t i o n w i t h a h o l e

L

i n an a p p r o p r i a t e g l i g a n d l e v e l / 5 * 6 / . The s a t e l l i t e l i n e i s due t o unscreened 3d c o r e h o l e e l e c t r o n e m i s s i o n w i t h a IIOMO-LUPIO t r a n s i t i o n /7/. I n every c a s e t h e metal 3d

-

l i g a n d p mixing i n f l u e n c e s s u b s t a n t i a l l y t h e s a t e l l i t e s t r u c t u r e .

The scope of t h i s r e p o r t i s l i m i t e d t o t h e i n t e r p r e t a t i o n of t h e X B S and XPS i n t e n s i t y d i s t r i b u t i o n i n terms of d e t a i l s of chemical bonding. The e f f e c t s of composition and geometry of t h e coordina- t i o n s p h e r e and t h e o x i d a t i o n s t a t e of t h e N i i o n i n complex compounds w i t h mono- and b i d e n t a t e l i g a n d s , t h e l a t t e r c h e l a t i n g v i a N, O , I?, and S, on t h e O i ~ n , S hB, and N i Lx,R emission bands and t h e N i 2p s p e c t r a a r e analysed. I n o r d e r t o confirm t h e i n t e r p r e - t a t i o n by l i g a n d - f i e l d arguments and t h e c a l c u l a t i o n of component peak a r e a s , t h e molecular o r b i t a l e n e r g i e s and t h e e l e c t r o n i c charge f r a c t i o n s of t h e i n d i v i d u a l molecular o r b i t a l s have been c a l c u l a t e d by means of a n i t e r a t i v e SH'T method.

The N i L and O K emission bands a r e l o c a t e d in t h e s o f t X-ray region. T h e r e f o r e , t h e s p e c t r o m e t e r SMF-1 has t o e x h i b i t s e v e r a l s o p h i s t i c a t e d parameters such a s a high-vacuum system, v e r y t h i n window f o i l s a t t h e flow c o u n t e r (kr and C H ~ ) , and a high-power X-ray tube w i t h primary c u r r e n t s up t o 1 A t o g e n e r a t e s u f f i c i e n t secondar X-ray i n t e n s i t y . I n t h e p r e s e n t measurement HbAY (2d = 2.612 run7 was used a s a n a l y s i n g c r y s t a l . The samples were cooled by l i q u i d n i t r o g e n i n s i d e of t h e secondary anode t o prevent high- temperature decomposition, and e x c i t e d by X-rays from t h e t u b e o p e r a t e d a t 6 kV w i t h c u r r e n t s between 200 mk and 1 A. The s e l f - a b s o r p t i o n e f f e c t s which a r e t o be expected i n t h e short-wavelength r e g i o n of t h e bands, a r e assumed t o be s m a l l because Che 1 C i Lci band p r o f i l e o f t h e metal c o i n c i d e s w i t h t h e band p r o f i l e o b t a i n e d by u s by primary e x c i t a t i o n a t low v o l t a g e between 2 and 3 kV / 8 / . The energy s c a l e s were c a l i b r a t e d u s i n g t h e N i La, energy of t h e metal /y/ and t h e O K g energy of L i S O /lo/. The accuracy of t h e energy v a l u e s was b e t t e r t h a n 0.2 e5. bepending on t h e s l i t w i d t h t h e e x p e r i m e n t a l broadening of t h e peaks was i n t h e c a s e of N i L3,R i n t h e range 0.1

-

0.9 eV, and f o r 0 h a 0.3

-

^0.6 ^eV. ^From

t h e band p r o f i l e f i t w i t h a d e c o n v o l u t i o n program (hiarquardt 's approach) ~ a u s s / L o r e n t z ( 1 /1 ) components have been o b t a i n e d .

The XPS experiments have been c a r r i e d o u t by means of t h e s p e c t r o - meter VG ESCA 3 u s i n g unmonochromatized Al r i ~ r a d i a t i o n . The bind- i n g e n e r g i e s a r e r e f e r e n c e d t o t h e C 1 s peak a t 285 eV.

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HSSULTS ANI) UISCUSSION X-ray Emission Spectra

The X-ray emission process in the investigated ~ ~ ( 1 1 ) con~poynds corresponds to an electron transition from the d to the d con- figuration. Hear the top of the valence band the X-ray emission intensity is expected to be dominated by transition of d electrons, The metal 3d orbitals can mix with linear combinations of 2p

states of the surrounding ligands. Because of the distorted tetrahedral and planar local geometries, dipole selection rules allow numerous final states to contribute to the

L

emission band with a n upper part dominated by the Ni 3dn levels and a lower part with some d contributions to mainly g bonded orbitals localized preferably on the ligands (d, and d6 respectively, see Fig. 1 ) .

Pig. 1 Comparision of the experimental Ni L emission bands of tetrahedral and planar ( P C ~ ) 2 ~ i ~ 1 with calculated 3d charge fractions of luolecul& orbigals ( ~ y = cyclohexyle ) Fig. 2 S liR, Ni La,D, and 0 K m emission bands of the X i chelate of monothiodibenzoylmethane aligned to the corresponding ionization potentials

IP

For the further discussion it is useful to examine the intensity ratio I(LB)/I(L~) too. hvestigating different &h oxides Galakhov et al. / 1 1 / pointed out that this value rises if the number of unpaired electrons increases. This finding correlates with the growing exchange interaction betwean the core hole and the electrons

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JOURNAL DE PHYSIQUE

i n an u n f i l l e d 3d s h e l l and consequently w i t h t h e magnetic proper- t i e s of t h e compounds.

Fig. 2 shows t h e S K U , N i Ln,U, and 0 !L& X-ray emission bands of t h e N i c h e l a t e w i t h monothiodibenzoylmethane a l i g n e d by t h e appro- p r i a t e c o r e i o n i z a t i o n p o t e n t i a l s ( b i n d i n g energy p l u s 5 e ~ ) . The s i m i l a r e n e r g i e s of t h e low-energy La component and t h e La maximum on t h e one hand and t h e high-energy S hB s t r u c t u r e and i t s band ma- ximumonthe o t h e r hand i n d i c a t e t h e common o r i g i n of t h e r e s p e c t i v e f i n a l s t a t e s o r i g i n a t i n g from S 3p

-

^{N i}3d o r b i t a l mixing.

The s h o u l d e r a t t h e high-energy s i d e of t h e S h B maximum i n d i c a t e s c l e a r l y t h e S 3p

-

^{N i}3d donor-acceptor i n t e r a c t i o n , The t h i r d X i La component ( a t 854 e ~i s ) i n t e r p r e t e d a s a m u l t i p l e - i o n i z a t i o n s a t e l l i t e s t r u c t u r e .

The most i n t e n s i v e component i n t h e O koc band r e p r e s e n t s t h e " l o n e p a i r " e l e c t r o n s and a l s o x s t a t e s of t h e C

-

⁰bond /12/. The i n - f l u e n c e of t h e changed l o c a l geometry of t h e metal on t h e N i L&,D emission bands of t e t r a h e d r a l and p l a n a r ( P C ~ ) 2 N i ~ 1 2 i s demon- s t r a t e d i n Fig. 1. For comparison, t h e energ2es and metal 3d popu- l a t i o n s of t h e r e s p e c t i v e molecular o r b i t a l s fronr our i t e r a t i v e EH'l' c a l c u l a t i o n a r e shown. In b o t h c a s e s t h e N i L& band e x h i b i t s t h r e e s t r u c t u r e s : The high-energy component should be a m u l t i p l e - i o n i z a t i o n s a t e l l i t e ; t h e o t h e r two components i n c l u d i n g t h e peak maximum a r e reproduced by t h e two groups of d6 and d K s t a t e s ( s e e above). The e x p e r i m e n t a l l y o b t a i n e d s p l i t t i n g of t h e L a components A E i s 1.8 eV ( t e t r a h e d r a l ) and 1.6 eV ( p l a n a r ) . The d i f f e r e n c e be@en t h e s e v a l u e s i s s a t i s f a c t o r i l y reproduced by t h e c a l c u l a - t i o n a s t h e s e p a r a t i o n of t h e g r a v i t y c e n t r e s of t h e 5 and X s t a t e s ( s e e Table 1 ) . The t h e o r e t i c a l v a l u e s f o r t h e i n t e n s i t i e s of t h e low-energy component do n o t a g r e e w i t h t h e experiment, r e f l e c t i n g some l i m i t a t i o n of t h e s i m p l e EH'r procedure.

Comparing t h e e n e r g i e s of t h e La peak maxima we found a high- energy s h i f t of 0.3 eV f o r t h e p l a n a r compound i n analogy t o o t h e r t e t r a h e d r a l and p l a n a r s p e c i e s of compounds w i t h t h e same l i g a n d s . The i n t e n s i t y r a t i o I ( L D ) / I ( L & ) changes in a s i m i l a r way e x h i b i t -

i n g h i g h e r v a l u e s i n t h e s p e c t r a of t e t r a h e d r a l compounds

a able

^{1 ) .}

C o n f i g u r a t i o n

--

t e t r a h e d r a l

p l a n a r

Loc components &EAlB/"

A B C

/

exp. c a l c .

~ ( L a ) / e v 849.2 851.0 853.9

1

^1.8 ^2.7

Irel

i

~ X P -

f

3 1 100 Irel ( c a l c . ) 38 100

T a b l e 1 Experimental and c a l c u l a t e d d a t a of t h e N i LM,D s p e c t r a of ( P c ~ ) N i C I Z

3 2

X-ray P h o t o e l e c t r o n S p e c t r a

I n Tables 2 and 3 t h e N i 2p e n e r g i e s of s e v e r a l complex compounds a r e g i v e n t o g e t h e r w j C f i t h e r e l a t i v e i n t e n s i t i e s of t h e main components i n t h e s a t e l l i t e r e g i o n . Pig. 3 shows t h e s t r o n g dependence of t h e s p e c t r a on t h e chemical environment.

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Compound

(PCy3 I2NiCl2 tetrah.,paramagn.

( P C ~ ) NiC12

3

2

planar, diamagn.

(PCy ) NiBr2

3

2

tetrah. ,paramagn.

( PCy3 ) 2NiBr2 planar, diamagn.

W .o. C

^:

3 . N%

oc tah., paramagn.

'2

planar, d2amagn.

H 3 C a

L

planar, diamagn.

0.

N:i paramagn.

4

Ni 2p 3/2

& niax

/.VAE,,,/~V &

'max

856.4 5.1 0.60

Table 2 bhergies and intensity ratios of the Ni 2p and La spectra of complex compounds ( B and A

are

refered to peak

maximum

and the low-energy shoulder of Ni La resp.)

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JOURNAL DE PHYSIQUE

Table 3 k k e r g i e s and i n t e n s i t y r a t i o s of N i 2p-, N 1 s - and S 2p- s p e c t r a of complex compounds

Compound

/

1-

C,HI Ph N ,N

Y Y

I-C,H,

&

p l a n a r , diamagn.

4

P h y y S-

c

H,

9 s

%

N i 2p 3/2

/eV Ifssat/ev Isat/Imax

max

854.6

- -

d54.7

s

2~

Ii I s

(Se 3d)

399.2 163.1

- -

398.6

55.4 402.1

3 9 8 . 5

402.2 162.1

401.4 161.6

402.5 162.5

-

^163.6

-

^163.3

Se

'0uvN12[."(:~j,"l]

853.9

5.4 0.24

o c t a h e d r . , paramagn.

m s

CH, p i a n a r

,

^paramagn.

l a

8

CH3 ,NLN-SO,-P~-CH,

t e t r a h e d r . , param.

854.9

855.5

855.1

- -

5.6 0.32

856.0

8.2 0.14

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Fig. 3 N i 2p p h o t o e l e c t r o n spec- t r a of t h e diamagnetic monomere N i c h e l a t e of 7-methylchinoline- -8-01 ( 1 ) and t h e paramagnetic c h e l a t e j o f 2-methylchinoline-8-01

( 2 ) and a c e t y l p y r i d i n e - p - t o l y l - -sulfonylhydraxone ( 3 )

Summarizing t h e f e a t u r e s we f i n d t h e f o l l o w i n g c o n n e c t i o n s between t h e parameters of t h e s p e c t r a and t h e bonding which confirm e a r l i e r r e s u l t s /14-16/ and r e v e a l some new a s p e c t s :

-

^Ina l l paramagnetic Ni(11) compounds one o r more s a t e l l i t e s on t h e high-binding energy s i d e of t h e main l i n e w i t h v a r y i n g i n - t e n s i t y a r e observed.

-

There i s n o s a t e l l i t e emission i n p l a n a r N i ( 1 1 1 ) and N ~ ( I V ) compounds.

-

^The averaged energy d i f f e r e n c e of t h e N i 2p main l i n e s of p l a n a r N i compounds w i t h o x i d a t i o n s t a t e s I I ~ & ~ I V w i t h a s u l f u r c o o r d i n a t i o n p h e r e i s 1.6 eV

.

-

The X i 2p l i n e s of compounds w i t h t e t r a h e d r a l o r o c t a h e d r a l c0- o r d i n a tioa/gphere around t h e N i i o n a r e s h i f t e d by ligand-f i e l d e f f e c t s about 1.7 eV t o h i g h e r b i n d i n g energy w i t h r e s p e c t t o t h e l i n e of comparable compounds w i t h p l a n a r geometry.

-

The energy d i f f e r e n c e between t h e 2p main l i n e and t h e s a t e l - l i t e i s l a r g e r f o r ( P C ) N i B r p t h a n 3 & - ( P C ~ & l i i c l Z by 0.9 eV.

This i s i n accordance t a %he s x t u a t i o n found ?or C u d i h a l i d e s / 5 / : The more e l e c t r o n e g a t i v e $he l i g a n d i s , t h e l a r g e r e energy d i f f e r e n c e between t h e 36 c o n f i g u r a t i o n and t h e 3dtBk c o n f i g u r a t i o n w i t h a h o l e i n a n a p p r o p r i a t e l i g a n d l e v e l i s , t h e s m a l l e r i s t h e s e p a r a t i o n AS between t h e main l i n e and t h e s a - t e l l i t e . These f i n d i n g s c o n t r a d i c t t o t h e i n c r e a s i n g s a t e l l i t e s e p a r a t i o n A E w i t h i n c r e a s i n g l i g a n d e l e c t r o n e g a t i v i t y and HONO- LUhiO s e p a r a t i o n i n numerous t r a n s i t i o n metal compounds

/7/.

For l a c k of o p t i c a l d a t a and t h e o r e t i c a l r e s u l t s f o r t h e complex compounds s t u d i e d by u s , t h i s f a c t remains open f o r d i s c u s s i o n .

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JOURNAL

DE

PHYSIQUE

CONCLUSIONS

It has been demonstrated that the X-ray emission bands of the metal ion and all ligator atoms give more detailed information on the va- lence level structure of Ni complexes with mono- and bidentate li- gands than studies of XPS valence bands. Otherwise, the XPS data of core eleatrons are more suitable to recognize the coordination geo- metry of the metal ion than the XES data. Therefore, the potential of both XES and XPS for structure investigations of transition me- tal compounds should remain useful for a long time.

Wewould like to thank Prof. Dr. E. Uhlig (~ena), Prof. Dr. E.Uhle- mann (potsdam), Prof. Dr. L. Beyer, Dr. F. Dietze, and

Dr. W.

Dietzsch ( ~ e i p z i ~ ) for contributing the Ni compounds. Helpful dis- cussion with Dr. J. Reinhold ( ~ e i ~ z i ~ ) is gratefully appreciated.

REFERENCES

A. Meisel, G. Leonhasdt, and

R .

Szargan, Xantgenspektren und chemische Bindung, Akademische Verlagsgesellschaft, Leipzig 1977

A.

Meisel,

R.

Szargan,

G.

Leonhardt, and H.J. Kohler, J. Physique

22,

~ 4 - 3 0 1 (1971)

H .

Szargan, H. Sommer, and A. Meisel, in:Inner Shell and X-ray Physics (eds. D.J. Fabian, H. Kleinpoppen, and L.M. Watson, Plenum Press, New York 1981), p.717

A. Meisel, H. Szargan, K.H. Hallmeier, and

M.

Lahdeniemi, in Ref. 3, P O 707

G.

van der Laan,

C.

Westra,

C.

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2, 4369 (1981

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(

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LON. Mazalov, and E.A. hravtsova, Zh. Strukt. him. z, ⁸⁴ ⁽¹⁹⁸⁶⁾

13 J,