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Submitted on 1 Jan 1979
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AFTER EFFECTS OF EC-DECAY 57Co - LABELLED TRIS (OXINATO) COBALT (III) AND TRIS
(β -DIKETONATO) COBALT( I I I )
K. Endo, M. Harada, Y. Sakai, H. Sano
To cite this version:
K. Endo, M. Harada, Y. Sakai, H. Sano. AFTER EFFECTS OF EC-DECAY 57Co - LABELLED
TRIS (OXINATO) COBALT (III) AND TRIS (β-DIKETONATO) COBALT( I I I ). Journal de
Physique Colloques, 1979, 40 (C2), pp.C2-420-C2-422. �10.1051/jphyscol:19792147�. �jpa-00218520�
JOURNAL DE PHYSIQUE Colloque C2, suppl&nent au n O 3, Tome 40, mars 1979, page C2-420
AFTER
EFFECTS OF EC-DECAY 5 7 ~ oTRIS(OXINATO) COBALT(I
- ~ ~ ~ ~ ~I I)
~ ~ ~ AND T R IS
(B-DI KETONATO) COBALT( I I I
)K. Endo, M. Harada, Y. Sakai and H. Sano
Department of Chemistry, Faculty o f Science, Tokyo Metropolitan University, Fukasawa, Setagaya, Tokyo, 158, Japan
Resum&.-Lesspectres Mksbauer dlBmission du tris(oxinato)cobalt(III) et du tris(8-dicetonato)cobalt (111) diamagnstiques (S=O) marques au 7 ~ o ont dt& compar6s aux spectres d'absorp tion de 5 7 ~ e (oxine) 3
et 57~e(acac) 3 paramagngtiques (S=5/2) diluss de Al(oxine) 3 et Co(acac) 3, respectivement
.
La structure magnstique hyperfine a arailt dans les spectres drQrnission de Co(dbm)s (dbm = dibenzoylmsthanate) et Co(oxine)s marquss au "CO 3 78 K, tandis que les spectres des autres compos6s n'ont pas montrd de telle structure magnstique hyperfine.Abstract
.-
The emission ~6ssbauer spectra of diamagnetic (S=O) 57~o-labelled tris (oxinato)cobalt (111) and tris(B-diketonato)cobalt(III) were compared with the absorption spectra of paramagnetic (S=5/2) 57~e(oxine) 3 and 57~e(acac) 3 diluted with diamagnetic A1 (oxine) 3 and Co(acac) 3, respectively. Magnetic hfs appears in the emission spectra of 57~o-labelled Co(dbm)3 (dbm = dibenzoylmethanate) and Co(oxine)s at 78 K, whereas the spectra of other complexes show essentially no such magnetic hfs.Emission Ifhssbauer spectroscopic studies have shown that the decayed 5 7 ~ e species exist in one or more anomalous charge states within the lifetime of the nuclear excited state. These chemical states were affected by the matrices /l/. It is expected in a diamagnetic compound doped with 5 7 ~ o species that the concentration of the paramagnetic 5 7 ~ e species produced through EC-decay is low enough to show the magnetic hyperfine structure (hfs) in the emission spectrum, because of the reduced spin-spin interac- tion. However, the emission spectra studied have so far shown no such magnetic hfs. The absence of magne- tic hfs in the diamagnetic 57~o-labelled cobalt(II1) compounds was ascribed to the spin-spin interaction due to mainly the organic radicals produced in the vicinity of the decayed atom by Sano /2/.
In the present paper, we have studied the absor- ption spectra of paramagnetic (S=5/2) 57~e(o~ine) 3
and 57~e(acac)3 diluted with diamagnetic (S=O) A1 (oxine)3 and Co(acac)s, respectively, and the emis- sion spectra of diamagnetic 57~o-labelled Co(acac) 3, Co(dpm) 3, Co(oxine) 3 and Co(dbm) 3, in order to con- firm the proposal. The latter two compounds have n-conjugated systems which are considered to reduce the local radiolytic radical formation.
1. Experimental
.-
57~o-lavelled compounds : 7 ~ o - labelled C~(oxine)~ was prepared from an ethanol so-red in a cold run. The preparations of 57~o-labe11ed Co(acac) 3 (acac = acetylacetonate), Co(dbm) 3 (dbm =
dibenzoylmethanate), Co(dpm)3 (dpm = dipivaloylme- thanate) were essentially the same as those reported by Hamond et al. /4/.
Mixed crystals : ( 5 7 ~ e , Al) ( ~ x i n e ) ~ was prepa- red from the aqueous solution containing "Fec13,, A1C13 and the ligand. The pH value was adjusted to be 5-6 with CH3COOH and CH3COONa. The preparation of ( 5 7 ~ e , Co)(acac)a was the same as reported in reference 121. The X-ray diffraction analysis proved these samples to be mixed crystals. The details of MESS- bauer spectroscopic measurements were the same as those reported elsewhere /1,2/.
2. Results and discussion-.- 2.1. Absorption spec- tra.- The absorption spectrum of Fe(oxine)3 gives
---
the I.S. value of 0.44 m m / ~ and the Q.S. value of 0.96 mm/s at 78 K, whereas the spectrum of ( 5 7 ~ e , Al) (oxine)3 shows magnetic hfs at 78 K as shown in figure 1. We observed similar results on M(II1)
(acac) 3 (M = Fe,Co) ; the spectrum of Fe(acac) 3 shows a single broad line (I.S. = 0.25 mm/s)
,
while the spectrum of 57~e(acac) 3 diluted with diamagnetic Co(a~ac)~ gives magnetic hfs, both at 78 K. The in- ternal magnetic fields ofthe high spin compounds were estimated to be 518 kOe for ( 5 7 ~ e , Al) (oxine)3 and 540 kOe for (57~e, CO) (acac) 3 .lution containing 50 mg of CoC12 6H20, about 1 mCi
2.2. Emission spectra.- The emission spectra of of 5 7 ~ o and 95 mg of the ligand by following the
7~o-labelled CO (acac) 2 , CO (dpm) 3, CO (oxine) 3 and method described in reference / 3 / . The purity was
Co(dbm)3 at 78 K are shown in figure 2. The spec- checked by elemental analysis of the compound prepa-
trum of 57~o(dpm)3 showed greater yield of Fe(I1)
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792147
species than 57~o(acac) 3. The higher yield of 5 7 ~ e (11) species may be explained by assuming a higher probability of bond rupture releasing more electrons through the local radiolysis initiated by the EC- decay in dpm ligands. The cobalt(II1) compounds used in the present study are diamagnetic (S=O) and the corresponding Fe(II1) compounds are paramagnetic (S=5/2). The concentration of paramagnetic 5 7 ~ e spe- cies produced in the host Co(II1) compound is consi- dered to be low enough to show magnetic hfs because of the reduced spin-spin interaction.
Fig. 1 : Absorption Mi;ssbauer spectra of mixed crys- tals of (a) 3% Mol. ( 5 7 ~ e , Al)(oxine)s, and 3% Mol.
( 5 7 ~ e , CO) (acac) 3 at 78 K.
Therefore, the absence of magnetic hfs in those spec- tra can be explained in terms of the enhanced spin- spin interaction of the 5 7 ~ e species with the para- magnetic species produced through EC-decay in the vicinity of '%e. These species may inclitde mainly organic radicals of the immediate neighbor(ligand) and, to a lesser extent, the radicals of Co(II1) com- plexes and paramagnetic Co(II)(S=7/2) or excited Co(II1) (S= I) in the surrounding molecuies
.
The spectrum of 57~o(oxine) 3 shows apparently broader line width than that of 57~o(acac)3 at 78 K.
Furthermore, the spectrum of 5 7 ~ o (dbm) 3 more clearly exhibits magnetic hfs at 78 K. These trends are de- finitely shown in the spectra at 4.2 K as seen in figure 3.
Fig. 3 : Emission IGssbauer spectra of 57~o-labelled (a) Co(dpm)3. (b) Co(oxine),, and (c) Co(dbm)s at 4.2 K.
The results indicate that Co(dbm)s and Co(oxine)3 have a role in reducing the amount of the paramagne- tic species or in rapid quenching of the radical species, since Co(dbm)s and Co(oxine)s have T-elec- tron system in ligands compared with Co(acac)3 and Co(dpm)s. The greater contribution of the magneti- cally split component found in the spectra of CO (dbm)3 may be explained by the fact that Co(dbm)3 has more R-electron system than Co(~xine)~. The ex- perimental findings indicate that the conjugated m-system is apparently stable in the local radioly- sis to be induced by the EC-decay and the following Auger process.
Fig. 2 : Emission Mgssbauer spectra of 57~o-labelled (a) Co(dpm) 3, (b) Co(acac) s, (c) Co(oxine)s, and (d) Co(dbm)s at 78 K.
JOURNAL DE PHYSIQUE
R e f e r e n c e s
/ l / Sano, H. and Hashimoto, F., B u l l . Chern. Soc. Jpn., 38 (1965) 1565; Sano, H. and Kanno, M , , Chem.
Commun. (1969) 601. Sano, H. and Ohnuma, T . , B u l l . Chem. Soc. Jpn.,
48
(1975) 2 6 6 ./ 2 / Sano, H . , J . R a d i o a n a l . Chem.
2
(1977) 105.1 3 1 Ablob, A . , Memories P r e s e n t e s Soc. Chem. (1933) 234.
/ 4 / Hamond, G.S., Nonhebel, D.C. and Wu. C.S., I n o r g . Chem.
