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Mössbauer study of anhydrous ferrous formate
Solid State Communications,
Vol. 9, pp. 241—243, 1971. Pergamon Press.
Printed in Great Britain
MöSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE*
J.
Pipman~’and M. Ron
Department of Physics, Technion
—
Israel Institute of Technology, Haifa, Israel
(Received 10 November 1970 by C.W. McCombie)
a-Fe(HCO 2)2~ obtained by dehydration of Fe(HCO 2) 2 ~ 20 was studied by M6ssbauer spectroscopy. As expected, a single environmental iron site was found, displaying a Q.S. of (1.86 ±0.03) mm/sec, midway between the two iron splittings in Fe(HCO 2) 2~2H20, whereas the !.S. remained almost unchanged. Measurements between 300 and 77°K show a line width increase of 20%.
IT WAS shown by X-ray studies 1 that Fe ++ formate dihydrate crystallizes in a monoclinic structure in which the iron ions are located at four inequivalent sites, differing in their local surrounding and spatial orientation. However, 1’2 have led to the further Mössbauer studies conclusion that there are only two inequivalent local environments of the metal ion sites — type I and II — with two electric field gradients, displaying two different quadrupole splittings,
was synthetized according to a known method ~ and identified by means of X-rays and Mössbauer spectroscopy. A 5 g sample of powdered ferrous formate dihydrate, placed in a glass tube, was introduced a furnace 245°C,resulting fast heatinginto of the sample,atand was held therein for 15 mm. The water vapor released during the dehydration was evacuated with a rotation pump. A poor vacuum was recorded during the dehydration process. The product was a brownish powder. It was identified by its X-rays diffraction pattern as a-Fe(HCO 2)2, in accordance with reference 4. The anhydrous salt was also prepared from the Fe(HCO2)2.2H20 by heating a sample of Ca. 5 g at a constant heating rate of 1°C/mm up to 225°C. Previously heated and dried nitrogen was flowed through the tube and exhausted through a one-way valve to prevent atmospheric oxygen from reaching 5theThe sample two and creating anhydrous decomposition samples showed conditions. the same M~ssbauer characteristics. Some anhydrous salt was also allowed to absorb water by exposure to air for 30 days.
Type! site is at the center of an octahedron formed by six oxygen atoms belonging to six different formate groups, whereas type!! site is at the center of an octahedron formed by four water dipoles and two oxygens. Thus, the ligand point group symmetries are °h and D4h for type I and type I! sites respectively. The type I site, belonging to a higher symmetry group, exhibits the smaller quadrupole splitting, It could be expected that in the anhydrous Fe~ formate the iron ions occupy a single environmental site formed by the formate groups. We prepared the a modification anhydrous ferrous formate as follows: Fe(HCO 2)2. 2H20 *In partial fulfilment of the M.Sc. degree of Pipman.
The Mössbauer absorber thickness of all 2 natural iron. The samples was about 10mg/cm MBssbauer experiments were performed with a constant velocity spectrometer described
J.
241
242
MOSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE
40L I
Vol.9, No.3
I.S. remains virtually the same. Infrared results.4 show that in going from the dihydrate to the anhydrous formate, apart from disappearance of
~.
3~
the H 32H
1
L0~-
1 b
20 band most of the doublet lines became singlets, indicating the existence of only one type site.
Table 1. M’ôssbauer parameters of the anhvdrous
:
formaie at various temperatures.*
56~
Tmeas. (°K) 298
I.S.t 1.22
1.86
0.39
56~
180
1.31
2.36
0.47
52~
101 1.34 2.57 77 1.34 2.63 All values are given in mm/sec with an
I I
Lot
-~
‘,~,
* -~ 2
0
02
04
06
VELOC~TYftn~~ci
ferrous FIG. 1. formate: Room temperature (a) anhydrous, Mössbauer (b) partially spectra of rehydrated, (c) dihydrate. elsewhere.6 The source used was 20 mC Co~’ in Pd matrix. The low temperature measurements were taken with the absorber in a transmission type cryostat and a moving source. The room temperature Mössbauer spectrum of the anhydrous ferrous formate is shown in Fig. la. The isomer shift relative to a-iron was measured to be (1.22 ±0.03) mm/sec, the quadrupole splitting [~e2
qQ(1
+
!
~2)
t’2]
equal to (1.86 ±0.03) mm/sec, and the line width f = (0.39 ±0.02) mm/sec. The spectrum may be interpreted as a single phase one, in accordance with the prediction of the existence of only one iron site, as concerns the local environment. The quadrupole splitting has an intermediate value in comparison with the two splitting values E 1 = O.6lmm~sec and E2 = 3.00 mm/sec of the parent salt, while the
Q.S.~
________________________________________________________________
0.48 0.47
accuracy of 10.03mm ‘sec relative 2 qQ [1to +a—iron ~ ~2] ¶/2 § absorption ~e full width at half height. t
The values of the quadrupole splitting isomer shifts and line widths of the anhvdrous salt measured at various temperatures between 80°K and 300°Kare given in Table 1. The line width increase of more than 20 per cent in going from 300°K to 180°Ksuggests the possibility that cooperative effects may occur at lower temperatures, as is known for other Fe~salts.7 The spectrum of the partially hydrated sample is shown in Fig. lb together with the spectrum of the dihydrate, Fig. ic for comparison. It can be seen that after 30 das the dehydrate was only partially hydrated, showing its relatively stability. The quadrupole interaction parameters and their interpretation in terms of crystal field theory from their temperature dependence are being determined.
lcknowledgement — We wish to thanic Mr. PA. Montano for useful comments.
Vol.9. No.3
MOSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE
243
REFERENCES 1.
HOY G.R., BARROS S. de S., BARROS F. de S. and FRIEDBERG S.A., J. App). Phys. 36, 936 (1965).
2.
HOY G.R., BARROS F. de S., Phys. Rev. 139, A929 (1965).
3.
RHODA N., FRAIOLI A.V., Inorganic Syntheses 4, 159, McGraw-Hill, New York (1953).
4.
MALARD C., C.R. hebd. séanc. Acad. Sci. Paris
5.
DOREMIEUX J.L. et BOULLE A., C.R. hebd sêanc Acad. Sd. Paris 250, 3184 (1960).
6.
Elscint, Electronic Industry Haifa, see also: LIPKIN TREVES D., Rev. scient Instrum 35, 1336 (1966).
7.
BARROS F. de S., ZORY P. and CAMPBELL L.E,, Phys. Leit. 7, 135 (1963).
Le sel a-Fe(HCO
263C, 480 (1966).
J.,
SHECHTER B., SHTRIKMAN S. and
2)2 obtenu par deshydratation de Fe(HCO2)2.2H20 a été etudie par spectroscopie Mössbauer. Comme prevu on a trouv~ pour le fer un environnement unique, présentant une decomposition quadrupolaire de (1.86 ±0.03) mm/sec, intermediaire entre les deux types de decompositions du fer dans Fe(HCO2)2.2H20, tandis que le deplacement isomére reste presque irichangé. Des mesures faites entre 300 et 77°K montrent un accroissement de largeur de raie de 20%.
Vol. 9, pp. 241—243, 1971. Pergamon Press.
Printed in Great Britain
MöSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE*
J.
Pipman~’and M. Ron
Department of Physics, Technion
—
Israel Institute of Technology, Haifa, Israel
(Received 10 November 1970 by C.W. McCombie)
a-Fe(HCO 2)2~ obtained by dehydration of Fe(HCO 2) 2 ~ 20 was studied by M6ssbauer spectroscopy. As expected, a single environmental iron site was found, displaying a Q.S. of (1.86 ±0.03) mm/sec, midway between the two iron splittings in Fe(HCO 2) 2~2H20, whereas the !.S. remained almost unchanged. Measurements between 300 and 77°K show a line width increase of 20%.
IT WAS shown by X-ray studies 1 that Fe ++ formate dihydrate crystallizes in a monoclinic structure in which the iron ions are located at four inequivalent sites, differing in their local surrounding and spatial orientation. However, 1’2 have led to the further Mössbauer studies conclusion that there are only two inequivalent local environments of the metal ion sites — type I and II — with two electric field gradients, displaying two different quadrupole splittings,
was synthetized according to a known method ~ and identified by means of X-rays and Mössbauer spectroscopy. A 5 g sample of powdered ferrous formate dihydrate, placed in a glass tube, was introduced a furnace 245°C,resulting fast heatinginto of the sample,atand was held therein for 15 mm. The water vapor released during the dehydration was evacuated with a rotation pump. A poor vacuum was recorded during the dehydration process. The product was a brownish powder. It was identified by its X-rays diffraction pattern as a-Fe(HCO 2)2, in accordance with reference 4. The anhydrous salt was also prepared from the Fe(HCO2)2.2H20 by heating a sample of Ca. 5 g at a constant heating rate of 1°C/mm up to 225°C. Previously heated and dried nitrogen was flowed through the tube and exhausted through a one-way valve to prevent atmospheric oxygen from reaching 5theThe sample two and creating anhydrous decomposition samples showed conditions. the same M~ssbauer characteristics. Some anhydrous salt was also allowed to absorb water by exposure to air for 30 days.
Type! site is at the center of an octahedron formed by six oxygen atoms belonging to six different formate groups, whereas type!! site is at the center of an octahedron formed by four water dipoles and two oxygens. Thus, the ligand point group symmetries are °h and D4h for type I and type I! sites respectively. The type I site, belonging to a higher symmetry group, exhibits the smaller quadrupole splitting, It could be expected that in the anhydrous Fe~ formate the iron ions occupy a single environmental site formed by the formate groups. We prepared the a modification anhydrous ferrous formate as follows: Fe(HCO 2)2. 2H20 *In partial fulfilment of the M.Sc. degree of Pipman.
The Mössbauer absorber thickness of all 2 natural iron. The samples was about 10mg/cm MBssbauer experiments were performed with a constant velocity spectrometer described
J.
241
242
MOSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE
40L I
Vol.9, No.3
I.S. remains virtually the same. Infrared results.4 show that in going from the dihydrate to the anhydrous formate, apart from disappearance of
~.
3~
the H 32H
1
L0~-
1 b
20 band most of the doublet lines became singlets, indicating the existence of only one type site.
Table 1. M’ôssbauer parameters of the anhvdrous
:
formaie at various temperatures.*
56~
Tmeas. (°K) 298
I.S.t 1.22
1.86
0.39
56~
180
1.31
2.36
0.47
52~
101 1.34 2.57 77 1.34 2.63 All values are given in mm/sec with an
I I
Lot
-~
‘,~,
* -~ 2
0
02
04
06
VELOC~TYftn~~ci
ferrous FIG. 1. formate: Room temperature (a) anhydrous, Mössbauer (b) partially spectra of rehydrated, (c) dihydrate. elsewhere.6 The source used was 20 mC Co~’ in Pd matrix. The low temperature measurements were taken with the absorber in a transmission type cryostat and a moving source. The room temperature Mössbauer spectrum of the anhydrous ferrous formate is shown in Fig. la. The isomer shift relative to a-iron was measured to be (1.22 ±0.03) mm/sec, the quadrupole splitting [~e2
qQ(1
+
!
~2)
t’2]
equal to (1.86 ±0.03) mm/sec, and the line width f = (0.39 ±0.02) mm/sec. The spectrum may be interpreted as a single phase one, in accordance with the prediction of the existence of only one iron site, as concerns the local environment. The quadrupole splitting has an intermediate value in comparison with the two splitting values E 1 = O.6lmm~sec and E2 = 3.00 mm/sec of the parent salt, while the
Q.S.~
________________________________________________________________
0.48 0.47
accuracy of 10.03mm ‘sec relative 2 qQ [1to +a—iron ~ ~2] ¶/2 § absorption ~e full width at half height. t
The values of the quadrupole splitting isomer shifts and line widths of the anhvdrous salt measured at various temperatures between 80°K and 300°Kare given in Table 1. The line width increase of more than 20 per cent in going from 300°K to 180°Ksuggests the possibility that cooperative effects may occur at lower temperatures, as is known for other Fe~salts.7 The spectrum of the partially hydrated sample is shown in Fig. lb together with the spectrum of the dihydrate, Fig. ic for comparison. It can be seen that after 30 das the dehydrate was only partially hydrated, showing its relatively stability. The quadrupole interaction parameters and their interpretation in terms of crystal field theory from their temperature dependence are being determined.
lcknowledgement — We wish to thanic Mr. PA. Montano for useful comments.
Vol.9. No.3
MOSSBAUER STUDY OF ANHYDROUS FERROUS FORMATE
243
REFERENCES 1.
HOY G.R., BARROS S. de S., BARROS F. de S. and FRIEDBERG S.A., J. App). Phys. 36, 936 (1965).
2.
HOY G.R., BARROS F. de S., Phys. Rev. 139, A929 (1965).
3.
RHODA N., FRAIOLI A.V., Inorganic Syntheses 4, 159, McGraw-Hill, New York (1953).
4.
MALARD C., C.R. hebd. séanc. Acad. Sci. Paris
5.
DOREMIEUX J.L. et BOULLE A., C.R. hebd sêanc Acad. Sd. Paris 250, 3184 (1960).
6.
Elscint, Electronic Industry Haifa, see also: LIPKIN TREVES D., Rev. scient Instrum 35, 1336 (1966).
7.
BARROS F. de S., ZORY P. and CAMPBELL L.E,, Phys. Leit. 7, 135 (1963).
Le sel a-Fe(HCO
263C, 480 (1966).
J.,
SHECHTER B., SHTRIKMAN S. and
2)2 obtenu par deshydratation de Fe(HCO2)2.2H20 a été etudie par spectroscopie Mössbauer. Comme prevu on a trouv~ pour le fer un environnement unique, présentant une decomposition quadrupolaire de (1.86 ±0.03) mm/sec, intermediaire entre les deux types de decompositions du fer dans Fe(HCO2)2.2H20, tandis que le deplacement isomére reste presque irichangé. Des mesures faites entre 300 et 77°K montrent un accroissement de largeur de raie de 20%.