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XANES OF MANGANESE COORDINATION COMPLEXES
C. Cartier, M. Verdaguer, S. Menage, J. Girerd, J. Tuchagues, B. Mabad
To cite this version:
C. Cartier, M. Verdaguer, S. Menage, J. Girerd, J. Tuchagues, et al.. XANES OF MANGANESE COORDINATION COMPLEXES. Journal de Physique Colloques, 1986, 47 (C8), pp.C8-623-C8-625.
�10.1051/jphyscol:19868117�. �jpa-00226015�
JOURNAL DE PHYSIQUE
Colloque C8, supplement au n o 1 2 , Tome 47, decembre 1986
XANES OF MANGANESE COORDINATION COMPLEXES
C. CARTIER*, M. VERDAGUER* * * * , S . MENAGE* , J. J . GIRERD* ,
J. P. TUCHAGUES* * * and B . MABAD' ^
" ~ a b o r a t o i r e SET, (CNRS - U A 420), Bdtiment 4 2 0 ,
F-91405 Orsay Cedex, France
* * E c o ~ ~ Normale Superieure, Le Parc, F-92211 saint-cloud, France
* * * ~ a b o r a t o i r e de Chimie de Coordination, 205, route de Narbonne, F-31400 Toulouse, France
R6sumQ
Nous avons Qtudid les spectres XANES de complexes du Mn(II),Mn(III), Mn(1V) , dont
la structure et les proprietes electroniques sont parfaitement connues. Nous distin- guons trois zones : preseuil, seuil et post-seuil. Nous discutons les variations ob- servees en fonction du degre d'oxydation, de la g6ometrie et de la nuclearits. Les preseuils prdsentent une structure que nous comparons d la levee de ddggnerescence des orbitales d obtenue par spectroscopie visible et proche infra-rouge. Un deplace- ment important du seuil est observd lorsque la nuclearit6 et/ou la ggometrie varie.
Les differences dans la partie post-seuil, pour le chromophore Kn(III)O6 sont lieec d la stereochimie de l'octaedre.
Abstract
XiZNES of Mn compounds of known structure and electronic properties ~ M ~ ( I I ) , Mn(I111, Mn (IV) I is reported. Preedge, Edge and Post-Edge zone are detailed. Dependence on oxidation state, geometry and nuclearity are discussed. Preedge structure is obser- ved and compared with d-orbital splitting obtained from visible NIR spectroscopy. An important Edge shift has been observed with nuclearity and/or geometry change. Post- Edge differences due to stereochemistry are observed for the Mn(1II)O6 chromo~hore.
C u and Fe Coordination Chemistry has been much studied for the l a s t ten years. .Mn Coordination Chemistry has been much l e s s develop@. The sane observation can be made f o r the correlated f i e l d of X-ray absorption studies of coordination molecules.
We have thus begun X-Ray absorption study of .Nn containing rmlecules. The f i r s t objective is fundanental research on X-Ray absorption. The second one IS to help biophysicists studying by X-Ray spectroscopy Mn ions i n water evolving photosyn- t h e t i c apparatus (1). It seems important t o asset X-Ray spectroscopy of 1% i n order to be able to extract r e l i a b l e informations from study of the c q l i c a t e d biologi- c a l system.
We used very simple Mn containing molecules with w e l l established electronic pro- perties. The studied cmpunds are l i s t e d in Table I together with references t o their synthesis and structure.
ExFerimental conditions
Xanes Data were recorded a t LURE on EXAFS I Spectrameter. The mncchromator was S i 4 0 0 channel c u t ; the ring storage energy was 1.72 GeV and we used a 0.5 mn entrance slit. A 8 )lrn M n metallic f o i l was recorded just before each experimental spectrum.
We s e t mrmalization a t the top of the edge and energy origin a t the f i r s t - of the derivative of the n a e t a l . Second derivatives were calculated £ran smothed exp?rimental curves.
Spectra are given i n Fig. 3-4 for compunds 2, 3, 4_, 6, 7 , - - 9. -
Preedge
W e l l defined p r e e d e s were observed ror a l l the products. Preedge for @n(111jl are given i n Figure 1. For Mn(II1) we recorded visible-NIR data on d-d transitions.
The structure of the preedge i s related in general t o the t -e gap. We looked for 29 9
a quantitative correspondence betwen X-Ray data and visible NIR ones using a simple
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868117
JOURNAL DE PHYSIQUE
Table I : Compounds studied chromophore
~n(5N0 -sal-N(1,5,9,13)
2 Mn(1I)N 0
4 2
Mn (bipy) (NCS) Mn ( 11) N6
Mn (acac) Mn(III)06
K Mn (ox) 3. 3H20
3 Mn(III)06
KMnEDTA.2H20 Mn(III)N204
(Menane) 2Mn20(CH3C02) (C10 ) H 0
4 2' 2 Mn(III)N303 K Mn ( t ~ u j 2cat) 3. 6CH3CN
2 Mn (IV) O6
Mn sal N(1,4,7,10) (C1O4I2 Mn (IV) N402 Mn O(CH3C02) 6.CH CO H.CH CO
3 3 2 3 2 Mn(IV)O
6
synthesis 2 3 5 7 9 11 12 13 14
structure 2 4 6 8 10 11 12 13 14
SD ORBITALS
4
t 14
Figure 1 : Preedge for compound 4. - t: t l
3
Figure 2 : Comparison between preedge transitions predicted from visible-NIR data and obser-
ved ones in X-ray aborption for 3, 4 and - - 5. -
f
mnoelectronic picture. Three transitions are w t e d i n X-Ray absorption frcnn the scheme of d mlecular orbitals deduced f r m visible N I X data. This is i n agreement with experiment. But the third transition for c x x p u n d s 3 and 5 is f o d systemati- cally a t higher energy than predicted : ~lectron-electro'i; in=-actions are probably non negligible i n the multiplets of the ground and of the excited states in this phenarrt-Jlon. C m p r i s o n between X-Ray data and visible ones are i l l u s t r a t e d in Fig. 2 .
EeE In Fig. 3 we ccsnpare the spectra of Mn (11) , Pln(II1) , LMn(IV) w i t h the same nucleari- ty (here mnoners) . As expected the absorption is displaced toward higher energy when the oxidation s t a t e increases. Surprisingly for c a p u n d s 3 [ $ ( I I I ~ 6 CMn (111) -0-Mn (11111 and 9 ()PO-Mn (111) 3 ] we found t h a t the edge is displaced
- - -
a t lcwer energy when one goes from 2 to 2. (See figure 4 ) . 'Itrlo explanations can be propsed :
1) an e f f e c t of distances. The mean radius of the f i r s t s h e l l is for 2 , 1.981, for
6, 2.083, for 9 , 2.193. Thus the 4p orbitals a r e m r e destabilized i n 2 , than in 6 ,
- - -
than i n 9 . -
2. a delocalization effect.
The 4p excited state muld be delocalized i n 2 and stillmre in 9, thus gaining stabilisation energy.
Post-Edge
Spectra of 2 (Figure 4) and 4 (figure 3) allow to ccanpare Mn (111) O6 chrmphore with different outer shells. The Post-Edge structure is deeply affected by changes is the shells. Multiple scattering occurs in this region and we intend to perform theoretical calculations to fin3 how structural information can be extracted from this part of the XANES sJ?ctra on the first coordination s~here and outer ones.
Figure 3 : Comparison of absor~tion of 2,4 and 7.
- - -
Figure 4 : Spectra of 3, 6 and 9.
- - -
Conclusion
Preedge, Edge and Post-Edge zones of XANES spectra contain m y infomtions since they are sensitive to oxidation and spin states, local geometry (bonds, angles aM3.
synn~try),outer geametry and nuclearity. We are currently extending the program to other -11 characterized Mn systems towards the s~mthesis of plausible d e l s of biological. active sites.
REmmENx.5
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