1568
COMMUNICATIONS TO THE EDITOR
Vol. 67
THE MAGNETIC SUSCEPTIBILITY OF PROMETHIUM-147 OXIDE1 Sir: At 25" promethium-147 oxide, whose color resembles that of erbium oxide, was found by the Gouy technique c.g.s. unit. to have specific susceptibility of 15.5 X After making an allowance for the diamagnetic contribution in the compound Pm203,the molar susceptibility was calculated to be 2660 X c.9.s. unit. Assuming that the ground state of Pm3+is 514 and that the multiplet intervals are large compared to IcT, a c.g.s. unit was molar susceptibility of 2960 X calculated using the familiar equation.2 These values are in reasonable agreement. The promethium-147 used in these experiments was obtained from a Hanford-type waste solution. It was separated from the other fission products by a "displacement-chromatographic" technique3 in which the diamagnetic Y3+ ion was used as a barrier ion. The eluent used was 0.015 M ethylenediaminetetraacetic acid solution, adjusted to a p H of 8.7 with ammonium hydroxide. The elution sequence4 under these conditions is such that large separation factors are obtained from the strongly paramagnetic heavy rare earth elements and possible sources of ferromagnetic impurities such as Fe3+, Co2+, and Ni2+. The estimated separation factors for the latter are of the order of lo9. Since the initial Fe3+concentration of the feed solution was found by spectrographic analysis to be less than 30 p.p.m., the final concentration must be much lower. Spectrographic analysis of the eluate indicated the iron concentration to be considerably less than 10 p.p.m., the limit of this particular measurement. Another indication of the purity of this material is that Am-241 and Eu-l54,155 could not be detected, indicating separation factors greater than lo6. Promethium from a fraction in the middle of the promethium band was then precipitated as the oxalate. Under these conditions a further separation is obtained from possible sources of ferromagnetic impurities such as Fe3+ and Co2+. The oxalate then was ignited a t 800' to form the oxide, PmzO3. After the magnetic experiment the sample was dissolved in perchloric acid and ultraviolet, visible, and near-infrared spectra were taken. Only those peaks6 characteristic of Pm+3were observed. The Pyrex sample tube (3 mm. i.d. X 10 cm.) used in the experiment was calibrated using reagent grade c.g.s. ferrous ammonium sulfate (x, = 31.6 X unit a t 25 ") .G As a check on the calibration, the susceptibilities of HgCo(SCN)4 and CuSO,. 5Hz0 were determined, and and 6.08 X loF6c.g.s. respective values of 16.4 X unit a t 25' were obtained which are in agreement with those found by Figgis and n'yh01m.~ A further check (1) Work performed under Contract KO. AT(45-1)-1350 for the U. S. Atomic Energy Commission. (2) J. H. Van Vleck, "The Theory of Electric and Xagnetio Susceptibilities,'' Oxford University Press, Oxford, 1932, p. 233. (3) F. H. Spedding and J. E. Powell, Chem. Eng. Prog., Syrnp. Serzes, SO, 7 (19543. (4) D. €3. James, J. E. Ponell, and F. H. Spedding, J . Inorg. Suez. Chem , 19, 133 (1961). (6) J. B. Gruher and J. G. Conway, zbzd., 14, 303 (1960). (6) L. C. Jackson, Phd. Trans. Boy. Soe. (London), 8224, 1 (1923). (7) B. N. Figgis and R. 5. Nyholm, J . Chem. Soc., 331 ( 1959).
500
100
.g
50
3 rn
m
J
x 's,
$ , ,
I
]
I
I
]
,
I
,
,
I
Pr
Nd
Pm
Sm
EU
Gd
Tb
DY
Ho
Er
Tm
La
Ce
, . y+ Yb
Lu
Fig. 1.-The gram-magnetic susceptibilities of the rare earth oxides a t 25". The triangle is the susceptibility of promethium147 oxide. The solid circles are values taken form Selwood.8 The solid and open squares are, respectively, values in agreement with and low compared to those reported by Selwood.8
involved the determination of the susceptibilities of several other rare earth oxides. These resuIts are shown with that of promethium oxide and those reported by Selwoodsin Fig. 1. The sample tube was loaded with the promethium oxide using remote manipulators which were necessitated by the high radiation levels. The sample then was suspended between the poles (1-in. gap) of a Varian 4-in. electroniagnet from a semimicro balance by means of a fine copper wire. From the force exerted on a 0.1591-g. sample of promethium oxide at 1.0, 1.2, and 1.4 amp. of magnet current, and after a small correction (-0.7 mg.) for the paramagnetism associated with the sample tube, respective values of 16.9, 15.5, and 15.5 X c.g.s. unit were obtained a t 25'. The fact that the low field value is high compared to the other two measurements suggests the possibility that the sample contains a trace of ferromagnetic impurity, but this seems very unlikely in view of the separation scheme used. Since the two high field measurements are the same within the experimental error of this method, which is estimated to be about 2%, it is suggested that the low field value may be in error. Assuming that the low field susceptibility is in error, a best value of 15.5 X 10-6 c.g.s. unit is obtained using the two liigli field values. A mean value of 16.0 X c.g.s. unit is the result if all values determined are used. If the possibility of ferromagnetic contamination is accepted, an extrapolation to infinite field strength yields c.g.s. unit. a value of about 13 X Self-heating of the sample and development of a (8) P. W. Selwood, "blagnetochemistry," Interscience Publishers, Inc., New York, N. Y., 1966, p. 149.
July, 1963
CORIMUNICATIOW TO THE EDITOR
static charge on the sample tube due to the very intense radiation field (- 3 X l O I 4 disintegrations/min.), nonuniform packing, and, of course, possible ferromagnetic contamination of the sample are possible experimental errors. Since promethium oxide may not be magnetically dilute, there may be an appreciable TNeiss constant which makes the observed value lower than that calculated.
5 i=i
1569
Ei(ick,T) = constant (1 QAT)
+
and
HAXFORD LABORATORIES J. C. SHEPPARD The first equation specifies that the molar absorptivjGENERAL ELECTRIC COMFANY E. J. WHEELWRIGHT ties of all absorbing species in the solution must have F. P. ROBERTS RICHLAND, WASHINGTON the same temperature dependence as the volume of the RECE~VED MARCH4, 1963
solution a t all S isosbestic points. The probability of such an occurrence for n > 1and S > 1is nil.
ISOSBESTIC POINTS I N ABSORBANCE SPECTRA
Si?-: With reference to my recent article on the occurrence of isosbestic points1 It has been kindly drawn to my attention by Dr. K. Buijs that isosbestic points can conceivably occur in closed systems consisting of three variable absorbing species. It was argued in the paper that the occurrence of more than two absorbing species was highly unlikely sirice the equation
must hold a t each isogbestic point, requiring in general that all molar absorptivities be equal. Systems which provide constant values of dCi/dCj, or derivatives all of which show the same dependence on the variable j , were overlooked. Under these conditions closed systems containing not only three but several absorbing species may give rise to isosbestic points, providing the species can be grouped into not more than two groups wherein the ratios of concentrations of the species within the group are constant. Such systems fall into the category described by Cohen and Fischer2 wherein the deDonder-Van Rysselberghe parameter can be successfully defined as a system parameter (linearly related systems). My original conclusions that occurrence of isosbestic points in closed, temperature dependent systems indicates only one absorbing species are still valid, even for linearly related systems. This is directly shown by development of Cohen’s and Fischer’s equation in extended version with consideration of time, concentration of a j t h species, and temperature as independent variables. The equation is given as follows. The reader is referred to the papers cited for definition of symbols.
In a closed system with equilibrium a t each temperature, this equation is reduced to
For a system OS n absorbing species to produce spectra with S wave lengths (&) of temperature invariant absorbance. two conditions must be obeyed, namely (1) J. R. RIorrey, J . Phys. Chem., 66, 2169 (1962). ( 2 ) X D. Cohsn a n d E. Fischer, J . Chem. Soc., 3044 (1962).
LABORATORIES GEXERAL ELIBCTRIC COMPANY WASHIXGTON RICHLAND, RECEIVED MAY2, 1963 HANFORD
J. R. MORRI~Y
THE CRYSTAL STRUCTURE OF THE MOLECULBR ADDITION COMPOUND XENOJS DIFLUORIDE-XENON TETRAFLUORIDE
Sir: The existence of the crystalline phase whose structure is reported here was noted in the earliest examinations1f2 of the xenon fluorides. Because it could be crystallized from vapor having primarily the infrared spectrum of XeF4, the substance was reported3 to be a polymorph of XeF4. From this assumed composition and the b = 7.33 8.) c = crystallographic data,3 a = 6.64 8., 6.40 A., p = 92” 40’, 2 = 4, it was deduced that the density was 10% higher than that of the other form; hence it has been referred to in the literature as “the highdensity form of XeF4.” We have shown, by crystal structure analysis, that it is in reality a distinct compound with the composition XeFz.XeF4. The true X-ray density is 4.02 g. ~ m . - - ~ . The preparation of this compound from the elements was described previously,3 but it should be added that the results of the crystal structure analysis indicate that some XeF2must have been present in the predominantly XeF4 preparation, either by incomplete reaction4 or by decomposition of XeF4. Further work is being carried out to prepare 1arge.r quantities of XeFz.XeF4by combining the components. The diffraction intensities from a single crystal of XeFz* XeF4 were measured by use of ill0 K a X-rays, ab goniostat,, and a scintillation counter detector. A total of 574 independent reflections was recorded, which included virtually all having detectable intensity. The specimen grew in size during the data collection, and a normalizat’ion factor, derived from repeated measurements of a reference reflection, was applied. The approximate shape O F the crystal was determined, making it possible t.0 calculat,e an absorption correction for each reflection.6 The mean diameter of the crystal was about 0.015 cm. ; the value of the absorption coefficient used was 119.5 cm.-l. (1) C. L. Chernick, et al., Science, 188, 136 (19132). (2) 8. Siege1 and E. Gebert, J . A m . Chem. SOC.,85, 240 (1963). (3) J. H. Burns, J . Phys. Chenz., 67, 536 (1963). (4) D. F. Smith, J . Chem. Phys., 38, 270 (1963). ( 5 ) D. J. Wehe, W. R. Busing, and H. A. Levy, “ORABS, A Fortran Program for Calculating Single Crystal Absorption Corrections,” ORNL TX-229, 1962.
