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Submitted on 1 Jan 1976
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ANOMALOUS SPIN STATES OF IRON (II) IN MÖSSBAUER EMISSION SPECTRA OF [57
Co(2-CH3-phen),] (ClO4)2.2 H2O AND [57Co(2-CH3O-phen)3] (ClO4)2.H2O
J. Fleisch, P. Gütlich
To cite this version:
J. Fleisch, P. Gütlich. ANOMALOUS SPIN STATES OF IRON (II) IN MÖSSBAUER EMISSION SPECTRA OF [57 Co(2-CH3-phen),] (ClO4)2.2 H2O AND [57Co(2-CH3O-phen)3] (ClO4)2.H2O.
Journal de Physique Colloques, 1976, 37 (C6), pp.C6-473-C6-474. �10.1051/jphyscol:1976694�. �jpa-
00216805�
JOURNAL DE PHYSIQUE CoIIoque C6, suppliment au no 12, Tome 37, Dkcembre 1976, page C6-473
ANOMALOUS SPIN STATES OF IRON (11) IN MOSSBAUER EMISSION SPECTRA OF C5 " Co(2-CH, -phen), ] (C104), . 2 Hz 0 AND
[57C0(2-CH30-phen),] (C104)2 . H 2 0 (*)
J. FLEISCH and P. GUTLICHInstitut fiir Anorganische Chemie und
Analytische Chemie, Universitat Mainz, D-6500 Mainz, FRG
R6sum6. - Dans un travail anterieur nous avions etudie les spectres d'emission Mossbauer de complexes [57Co(phen)~(NCS)~] et [57Co(bpy)~(NCS)2], observe les ttats anormaux 5T2 k tempe- rature suffisamment basse, ou les spectres d'absorption des composes correspondants du fer montrent la coexistence d'etats fondamentaux haut-spin (S = 2) et bas-spin (S = 0). Dans ce travail, l'6tude a Bte &endue a des systkmes contenant des ligands purement aromatiques.
I1 a kt6 ktabli par differentes methodes physiques que le complexe [Fe(2-CH3-phen)3](C104)2 prQente une transition haut-spin (ST2)
+
bas-spin-(~AI) dependant de la temperature, en liaison avec la valeur du param6tre 10 Dq du champ de ligand qui est du meme ordre de grandeur que I'knergie moyenne n d'appariement des spins. Nous avons recemment trouvk par spectromktrie d'absorption Mossbauer, spectroscopie dans I'infrarouge lointain et mesures de susceptibilite magnetique que le compose [Fe(2-CHsO-phen)3](C104)2HzO presentait aussi une transition de spin dependant de la temperature.Nous avons obtenu les spectres Mossbauer d'kmission de [57Co(2-CH3-phen)3](C104)2.2 H z 0 et de [57Co(2-CH30-phen)3](C104)2.H20 entre 4,6 et 293 K avec un absorbant standard de K4[Fe(CN)6] 3Hz0 maintenu k 293 K. Ces spectres prouvent I'absence de resonances provenant d'etat 1A1 qui est I'ktat predominant en absorption. M6me B la temperature de l'helium liquide, I'Btat ST2 est Ie seul visible sur les spectres d'6mission.
Le dtplacement isomkrique et I'effet quadrupolaire mesurBs en emission correspondent aux valeurs de la contribution haut-spin mesurees en absorption. L'influence de la temperature permet de dire que les etats haut-spin sont de nature 5A1 en symetrie D 3, B partir d'un calcul du champ de ligand tenant compte de la distorsion trigonale du couplage spin-orbite et de la covalence.
Abstract. - In a previous investigation we had studied the Mossbauer emission spectra of the complexes [57Co(phen)~(NCS)z](phen = 1.10-phenanthroline) and [57Co(bpy)2(NCS)~](bpy = a, a'-bipyridyl) and observed anomalous 5T2 states at sufficiently low temperatures, where the absorp- tion spectra of the corresponding iron compounds show the coexistence of high-spin ( S = 2) and low-spin (S = 0) ground states. In the present work we have extended these studies to systems with purely aromatic ligands.
It has been well established [I, 21 by various physical methods that the complex
shows a temperature dependent high-spin (ST?) % low-spin (1A1) transition, because the ligand field splitting parameter lODq and the mean spin pairing energy n are of the same order of magni- tude. We recently found [3] by variable temperature Mossbauer absorption spectroscopy, far infrared spectroscopy and magnetic susceptibility measurements that the compound
also shows a temperature dependent spin transition.
We have measured the Mossbauer emission spectra of [57Co(2-CH3-phen) 3](C104) 2.2Hz0 and [57Co(2-C~30-~hen)3](~10&.~20 versus K4[Fe(CN)6].3HzO (293 K) as absorber in the temperature range 293 - 4.6 K and compared with the corresponding absorption spectra of the synthesised complexes. The emission spectra demonstrate the absence of resonances arising from the 1A1 state, which is the dominating electronic state of iron (11) in the absorption spectra at the same temperature. Even at liquid helium temperature the 5T2 state is the only one visible in the emission spectra.
The isomer shift and the quadrupole splitting of the high-spin resonances in the emission spectra of [5 TCo(2-CH 3-phen) 3](C104)2.2H20 agree well with those of the high-spin resonances in the absorption spectra of the system [5 7Feo,o ICO 0.99(2-CH~phen) 3](C104) 2. x H20. From the calculated temperature dependence of the quadrupole splitting of the high-spin resonances in
(*) The paper will be published in Chem. Phys. Lett.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1976694
both emission and absorption spectra we have derived the nature of the electronic high-spin state to be 5A1 under D3 symmetry. The calculation was based on a ligand field model including trigonal distortion, spin-orbit coupling and covalency.
The mechanism of the formation of the anomalous spin states will be discussed.
References
[I] GOODWIN, H. A., SYLVA, R. N . , Austr. J. Chem. 21 (1968) 81.
[2] FLEISCH, J., GUTLICH, P., HASSELBACH, K. M., MULLER, W., J. Physique Collog. 35 (1974) C 6-12.
[3] FLEISCH, J., Dissertation, TH Darmstadt (1976).
