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Standard substances for magnetic susceptibility measurements
Notes
127
The high value at the high concentration suggests either non-ideality of the uranium species or formation of a higher complex. '
I
005
_•004 >.-
o tla
003
.J 0
002
@/Q
-•/
0,01,~ 0.0
, , , ,
I , , , , I ,
0.5
4.0
~ J,
l
L5
TTA CONCENTRATION ,moles/liter
FIG. l . - - S o l u b i l i t y o f u r a n y l T T A chelate in benzene s o l u t i o n s o f T T A .
It can be concluded from this analysis that the uranyl-TTA chelate forms an addition compound with TTA in benzene solution, with a formation constant of about 3.2. Solutions containing this complex are not ideal. The existence of this complex is not surprising in view of the many known examples of addition compounds of uranyl chelates.
Chemical Technoloffy Division Oak Ridge National Laboratory Oak Ridffe, Tennessee
SIGFREDPE'I'BRSON
Standard substances for magnetic susceptibility measurements (Received 26 November 1959) VERY often FeSO4"(NH4)2SO4"6H20, " M o h r ' s salt", is used as a standard substance for the calibration of magnetic susceptibility balances. This salt, recommended in SELWOOD'S~1~well-known book, has a gram susceptibility 9500 Zg = T ÷----~ " 10-~ erg/gaussZ' according to absolute measurements made by JACKSON. 12) (1~ P.W. SELWOOD, 5la~netochemistry p. 26. Interscience, New York (1956). (2~ L. C. JACKSON,Phil. Trans. Roy. Soc. A 224, 1 (1924).
128
Notes
A n u m b e r o f difficulties were encountered, however, in using this substance for calibration purposes. First o f all, appreciable variations were f o u n d in the balance c o n s t a n t s when calibrations were carried o u t at different temperatures. Secondly differences were f o u n d w h e n . s a m p l e s of different origin were used. This led to a c o m p a r a t i v e investigation o f the three T u t t o n salts MSO4"(NH0~SO1'6H.aO where M -- Fe "-+, Co 2+ and Ni 2+ respectively. In addition a calibration was carried out with f e r r i c - a m m o n i u m a l u m Fe,.(SO03(NH02SO4"24H20. As a result of this investigation NiSOa-(NH0~SO4.6H20 was chosen as s t a n d a r d substance for magnetic susceptibility m e a s u r e m e n t s bctween 80 a n d 300 K. It further appeared o f importance to have a suitable standard substance in the high-temperature region in order to be able to m a k e very accurate susceptibility m e a s u r e m e n t s between 300 a n d 1200 K. ~ ~. F o r several reasons Gd.,Oa was chosen for this purpose. Experhnental All susceptibility m e a s u r e m e n t s were carried out with a F a r a d a y torsion balance* in a v a c u u m case as described in the a u t h o r ' s thesis ~"~ where m o r e complete data m a y be found. The results of the m e a s u r e m e n t s were represented in t e r m s o f the balance c o n s t a n t s C as a function o f field strength using the k n o w n susceptibility-temperature relationships for the various compounds/-",:~ T h e balance c o n s t a n t s obtained with calibrations at different temperatures or with different substances are c o m p a r e d in Table 1. All results are given as differences in balance constant (AC)
TABLE 1 Origin o f sample
Substance
NiSOa.(NH 0,.SO4"6H20 NiSO~-(NH4)2SO~'6H20 NiSO~.(NH02SO~'6HzO NiSO~.(NH02SO~-6H20 NiSOa-(NH02SO4"6HzO NiSO4-(NH02SO c 6 H z O
Own Own Own Own
preparation preparation preparation preparation Merck Merck
Fe2(SO4)3"(NH0,.,SO ¢ 2 4 H 2 0 FeSO4-(NH~)2SO4-6H20 FeSO~.(NHa)2SOt'6H~O FeSO4-(NH02SOa'6H20 FeSO4"(NH0.,SOa'6H.20 FeSO~'(NH4)~SO4"6H20 CoSO4.(NH ~)2SO4.6H..O CoSO4.(NH.,) 2SO4"6H20
O w n preparation p.a. Merck p.a. Merck Merck p.a. recrystallized Merck p.a. recrystallized AnalaR A.R. O w n preparation O w n preparation
recrystallized recrystallized p.a. p.a.
Temperature (°C)
Ac(%)
20 --193 20 --193 20 --193
0 ~l -- 1 ~ 2 2 l
-- 193 20 --193 20 193 20 20 --193
0 -}-4 8 -~6 --12 --4 --8 --24
The susceptibility-temperature relationships for the Fe 2+, Co 2+ and Ni~+-salts have been given by JACKSON,~2~that for the ferric-ammonium alum by KLEMMJ71 In the last column: AC = (C--Co)/Co X 100% where Co -- balance constant found by calibration at room temperature with a sample of NiSO4"(NH4)2SO4"6H20 prepared by ourselves. The balance constant C is defined by U.C = zg.G with: U = reading of the torsion balance G -- weight of the sample Zg -- gram susceptibility of the sample. relative to the c o n s t a n t obtained by calibration at r o o m t e m p e r a t u r e with an arbitrary reference sample 6 f NiSO4-(NH4)2SO,'6H20, prepared in the laboratory. T h e origin o f the other samples is indicated in the table. * Balance and magnet were placed at our disposal by the management of Philips Research Laboratories, Eindhoven. ta) p. COSSEE,J. Inorg. Nucl. Chem. 8, 483 (1958). 14J p. COSSEE, Mol. Phys. To be published. 15~ p. COSSEEand A. E. VAN ARKEL, J. Phys. Chem. Solids To be published. (e~ p. COSSEE,Thesis, Leiden (1956). ~7' W. KLEMM, Magnetochemie p. 223. Akad. Verl. Ges., Leipzig (1936).
Notes
129
In the calibration with Gd2Oa (New Metals and Chemicals), the balance constants obtained with NiSO4"(NH02SO4-6H20 were used. When the reciprocals o f the resulting z-values were plotted as a function o f temperature, a perfectly linear relationship was obtained up to 1070°K. The deviation o f each individual point from an ideal Curie-Weiss behaviour did not exceed 0.5 ~ .
Discussion It is seen from Table 1 that consistent results were obtained for NiSO.a'(NH4)2SO4-6H20 regardless o f the temperature o f calibration or o f the origin o f the sample. The remaining fluctuations could be reduced to less than 1.0)~o by using small uniformly sized crystals.* Moreover, the calibrations with Fe2(SO4)3"(NH4)~SO4"24HzO at liquid-air temperature fit remarkably well into those made with NiSO4"(NH4)eSO4"6H20. It is quite obvious from the table that both the Fe ~ + - and Co 2 + - Tutton salts are very unsatisfactory as standard substances. It may be theoretically explained why the salts containing Ni - 2 + or Fe - 3 + ions are so much better as standard substances than the salts containing Fe - 2 + or Co - 2 + ions. Small variations in the composition o f the compounds may have an influence on the environment o f an appreciable percentage o f the magnetic ions. For instance, when FeSO4"(NH~)eSOa'6HeO contains 5.9 molecules o f water instead o f 6.0, the error in the chemical analysis is 0-5 ~ only. It may be, however, that 1 0 ~ o f the Fe e+ are now surrounded by 5 molecules o f water instead of by 6. It is further known from crystal-field considerations that in sixfold co-ordination Ni e+ and Fe 3+ have a singlet ground level, while Fe ~'* and Co s+ both have three low-lying levels, which makes the magnetic properties of the latter two strongly dependent on the environment. This possibly explains the sensitivity o f the susceptibility o f the Fe z+-- and Co s + - Tutton salts to recrystallization or to the origin o f the sample. Regarding the choice o f Gd203 as a secondary standard for the calibration at elevated temperatures, the following may be noted: A standard substance for the high temperature region must be non-volatile and stable against decomposition; valency changes o f the magnetic ions and strong ferro- or anti-ferro-magnetic coupling between them are not allowed. Moreover, many magnetic ions show a complicated behaviour at elevated temperatures owing to van Vleck paramagnetism or to the fact that the magnetic m o m e n t is no longer constant. F r o m theoretical considerations it can be concluded that only S-state ions like Mn 2+, Fe e+ or G d a+ guarantee that Curie's law will be obeyed up to very high temperatures. As Mn ~+ and Fe 3+ in oxide lattices may rather easily change their valency and furthermore show strong coupling effects, we have introduced GdaOa as a standard.
Acknowledgement--The author is much indebted to Dr. P. F. BONGERS for many discussions and helpful~uggestions.
Laboratorium voor Anor~anische en Physisehe Chemic Rijks Unicersiteit, Leiden
P. COSSEE~"
* A convenient recipe for the preparation of standard N iSOa'(NH0~SOa.6H20 is given below: NiSO4"(NH4)2SO4.6H20 (Merck) is recrystallized; the crystals are crushed in a mortar and small crystals of uniform size (0.3-0.5 mm diameter) are selected by sieving. They must be stored in a desiccator which in its lower part contains solid NiSO4.(NH02SOa.6H20 in equilibrium with the saturated solution in order to maintain the proper vapour-pressure, independently of temperature. The gram susceptibility is then given by ~'-'~ ( 3174 _ ~ erg Zo == \ Y + 2"5 0-30 ] I0 -~ gauss e Present address: Koninklijke/Shell-Laboratorium, Amsterdam.
The preparation of 9-tungstoberyllic acid (Received 9 September 1959; in revisedform 31 December 1959) BERYLLIUM complexes readily with many oxygenated molecules or anions. Thus it is to be expected that beryllium, which can exist fn an oxygenated anion, could complex with the simple tungstate ion 9
127
The high value at the high concentration suggests either non-ideality of the uranium species or formation of a higher complex. '
I
005
_•004 >.-
o tla
003
.J 0
002
@/Q
-•/
0,01,~ 0.0
, , , ,
I , , , , I ,
0.5
4.0
~ J,
l
L5
TTA CONCENTRATION ,moles/liter
FIG. l . - - S o l u b i l i t y o f u r a n y l T T A chelate in benzene s o l u t i o n s o f T T A .
It can be concluded from this analysis that the uranyl-TTA chelate forms an addition compound with TTA in benzene solution, with a formation constant of about 3.2. Solutions containing this complex are not ideal. The existence of this complex is not surprising in view of the many known examples of addition compounds of uranyl chelates.
Chemical Technoloffy Division Oak Ridge National Laboratory Oak Ridffe, Tennessee
SIGFREDPE'I'BRSON
Standard substances for magnetic susceptibility measurements (Received 26 November 1959) VERY often FeSO4"(NH4)2SO4"6H20, " M o h r ' s salt", is used as a standard substance for the calibration of magnetic susceptibility balances. This salt, recommended in SELWOOD'S~1~well-known book, has a gram susceptibility 9500 Zg = T ÷----~ " 10-~ erg/gaussZ' according to absolute measurements made by JACKSON. 12) (1~ P.W. SELWOOD, 5la~netochemistry p. 26. Interscience, New York (1956). (2~ L. C. JACKSON,Phil. Trans. Roy. Soc. A 224, 1 (1924).
128
Notes
A n u m b e r o f difficulties were encountered, however, in using this substance for calibration purposes. First o f all, appreciable variations were f o u n d in the balance c o n s t a n t s when calibrations were carried o u t at different temperatures. Secondly differences were f o u n d w h e n . s a m p l e s of different origin were used. This led to a c o m p a r a t i v e investigation o f the three T u t t o n salts MSO4"(NH0~SO1'6H.aO where M -- Fe "-+, Co 2+ and Ni 2+ respectively. In addition a calibration was carried out with f e r r i c - a m m o n i u m a l u m Fe,.(SO03(NH02SO4"24H20. As a result of this investigation NiSOa-(NH0~SO4.6H20 was chosen as s t a n d a r d substance for magnetic susceptibility m e a s u r e m e n t s bctween 80 a n d 300 K. It further appeared o f importance to have a suitable standard substance in the high-temperature region in order to be able to m a k e very accurate susceptibility m e a s u r e m e n t s between 300 a n d 1200 K. ~ ~. F o r several reasons Gd.,Oa was chosen for this purpose. Experhnental All susceptibility m e a s u r e m e n t s were carried out with a F a r a d a y torsion balance* in a v a c u u m case as described in the a u t h o r ' s thesis ~"~ where m o r e complete data m a y be found. The results of the m e a s u r e m e n t s were represented in t e r m s o f the balance c o n s t a n t s C as a function o f field strength using the k n o w n susceptibility-temperature relationships for the various compounds/-",:~ T h e balance c o n s t a n t s obtained with calibrations at different temperatures or with different substances are c o m p a r e d in Table 1. All results are given as differences in balance constant (AC)
TABLE 1 Origin o f sample
Substance
NiSOa.(NH 0,.SO4"6H20 NiSO~-(NH4)2SO~'6H20 NiSO~.(NH02SO~'6HzO NiSO~.(NH02SO~-6H20 NiSOa-(NH02SO4"6HzO NiSO4-(NH02SO c 6 H z O
Own Own Own Own
preparation preparation preparation preparation Merck Merck
Fe2(SO4)3"(NH0,.,SO ¢ 2 4 H 2 0 FeSO4-(NH~)2SO4-6H20 FeSO~.(NHa)2SOt'6H~O FeSO4-(NH02SOa'6H20 FeSO4"(NH0.,SOa'6H.20 FeSO~'(NH4)~SO4"6H20 CoSO4.(NH ~)2SO4.6H..O CoSO4.(NH.,) 2SO4"6H20
O w n preparation p.a. Merck p.a. Merck Merck p.a. recrystallized Merck p.a. recrystallized AnalaR A.R. O w n preparation O w n preparation
recrystallized recrystallized p.a. p.a.
Temperature (°C)
Ac(%)
20 --193 20 --193 20 --193
0 ~l -- 1 ~ 2 2 l
-- 193 20 --193 20 193 20 20 --193
0 -}-4 8 -~6 --12 --4 --8 --24
The susceptibility-temperature relationships for the Fe 2+, Co 2+ and Ni~+-salts have been given by JACKSON,~2~that for the ferric-ammonium alum by KLEMMJ71 In the last column: AC = (C--Co)/Co X 100% where Co -- balance constant found by calibration at room temperature with a sample of NiSO4"(NH4)2SO4"6H20 prepared by ourselves. The balance constant C is defined by U.C = zg.G with: U = reading of the torsion balance G -- weight of the sample Zg -- gram susceptibility of the sample. relative to the c o n s t a n t obtained by calibration at r o o m t e m p e r a t u r e with an arbitrary reference sample 6 f NiSO4-(NH4)2SO,'6H20, prepared in the laboratory. T h e origin o f the other samples is indicated in the table. * Balance and magnet were placed at our disposal by the management of Philips Research Laboratories, Eindhoven. ta) p. COSSEE,J. Inorg. Nucl. Chem. 8, 483 (1958). 14J p. COSSEE, Mol. Phys. To be published. 15~ p. COSSEEand A. E. VAN ARKEL, J. Phys. Chem. Solids To be published. (e~ p. COSSEE,Thesis, Leiden (1956). ~7' W. KLEMM, Magnetochemie p. 223. Akad. Verl. Ges., Leipzig (1936).
Notes
129
In the calibration with Gd2Oa (New Metals and Chemicals), the balance constants obtained with NiSO4"(NH02SO4-6H20 were used. When the reciprocals o f the resulting z-values were plotted as a function o f temperature, a perfectly linear relationship was obtained up to 1070°K. The deviation o f each individual point from an ideal Curie-Weiss behaviour did not exceed 0.5 ~ .
Discussion It is seen from Table 1 that consistent results were obtained for NiSO.a'(NH4)2SO4-6H20 regardless o f the temperature o f calibration or o f the origin o f the sample. The remaining fluctuations could be reduced to less than 1.0)~o by using small uniformly sized crystals.* Moreover, the calibrations with Fe2(SO4)3"(NH4)~SO4"24HzO at liquid-air temperature fit remarkably well into those made with NiSO4"(NH4)eSO4"6H20. It is quite obvious from the table that both the Fe ~ + - and Co 2 + - Tutton salts are very unsatisfactory as standard substances. It may be theoretically explained why the salts containing Ni - 2 + or Fe - 3 + ions are so much better as standard substances than the salts containing Fe - 2 + or Co - 2 + ions. Small variations in the composition o f the compounds may have an influence on the environment o f an appreciable percentage o f the magnetic ions. For instance, when FeSO4"(NH~)eSOa'6HeO contains 5.9 molecules o f water instead o f 6.0, the error in the chemical analysis is 0-5 ~ only. It may be, however, that 1 0 ~ o f the Fe e+ are now surrounded by 5 molecules o f water instead of by 6. It is further known from crystal-field considerations that in sixfold co-ordination Ni e+ and Fe 3+ have a singlet ground level, while Fe ~'* and Co s+ both have three low-lying levels, which makes the magnetic properties of the latter two strongly dependent on the environment. This possibly explains the sensitivity o f the susceptibility o f the Fe z+-- and Co s + - Tutton salts to recrystallization or to the origin o f the sample. Regarding the choice o f Gd203 as a secondary standard for the calibration at elevated temperatures, the following may be noted: A standard substance for the high temperature region must be non-volatile and stable against decomposition; valency changes o f the magnetic ions and strong ferro- or anti-ferro-magnetic coupling between them are not allowed. Moreover, many magnetic ions show a complicated behaviour at elevated temperatures owing to van Vleck paramagnetism or to the fact that the magnetic m o m e n t is no longer constant. F r o m theoretical considerations it can be concluded that only S-state ions like Mn 2+, Fe e+ or G d a+ guarantee that Curie's law will be obeyed up to very high temperatures. As Mn ~+ and Fe 3+ in oxide lattices may rather easily change their valency and furthermore show strong coupling effects, we have introduced GdaOa as a standard.
Acknowledgement--The author is much indebted to Dr. P. F. BONGERS for many discussions and helpful~uggestions.
Laboratorium voor Anor~anische en Physisehe Chemic Rijks Unicersiteit, Leiden
P. COSSEE~"
* A convenient recipe for the preparation of standard N iSOa'(NH0~SOa.6H20 is given below: NiSO4"(NH4)2SO4.6H20 (Merck) is recrystallized; the crystals are crushed in a mortar and small crystals of uniform size (0.3-0.5 mm diameter) are selected by sieving. They must be stored in a desiccator which in its lower part contains solid NiSO4.(NH02SOa.6H20 in equilibrium with the saturated solution in order to maintain the proper vapour-pressure, independently of temperature. The gram susceptibility is then given by ~'-'~ ( 3174 _ ~ erg Zo == \ Y + 2"5 0-30 ] I0 -~ gauss e Present address: Koninklijke/Shell-Laboratorium, Amsterdam.
The preparation of 9-tungstoberyllic acid (Received 9 September 1959; in revisedform 31 December 1959) BERYLLIUM complexes readily with many oxygenated molecules or anions. Thus it is to be expected that beryllium, which can exist fn an oxygenated anion, could complex with the simple tungstate ion 9