SOTES TABLE I
VALUES OF KO FOR D.1'
AT VARIOUS TEMPERATURES AND WAVELENGTHSO (a) D = S(CZH&S( K OX lo2) t 19.5' 30.9' 40.9' 17,200 1.05 1.70 2.23 17,200 1.04 1.68 2.23 14,600 1.04 1.68 2.19 2.22 Av. 1 . 0 4 1.68
880
Results and Discussion Values for K, and for E for the five complexes a t
various temperatures and wave lengths are given in Table I, while thermodynamic constants for the dissociation of the complexes a t 25" are given in Umr) Table 11. The corresponding values for the 1 : l 300 dioxane-iodine complex12are included for compari310 son purposes. These have been recalculated to cor320 respond to the units employed in the present work. For greater convenience of comparison, the six ( b ) D = Se(C2H&Se ( K OX 103) complexes are arranged in four series of three each. e 18.7' 32.9' 43.0' Umr) A given complex thus appears twice in the table. 3,160 2.70 420 4.82 6.90 It is evident from this and previous studies that 3,440 2.75 430 4.88 6.90 the complexing tendencies toward iodine are in the 3,450 2.55 440 6.84 4.89 order Se > S > 0, other factors being equal. This 3,240 2.99 450 5.03 7.01 is in keeping with the order of the availability of 6.91 Av. 2.75 4.91 electrons on the respective atoms. It is accordingly assumed that where the iodine molecule has a (c) D = O(C2Ha)S (KO X 10') choice, the attachment will be a t Se rather than a t e 15.7' 27.30 39.2' Xhr) S or 0 and a t S rather than a t 0. The effects of 9,750 1.15 1.80 300 2.30 the Se, S or 0 atom across the ring on the stabilities 10 500 1.14 1.83 310 2.35 of the complexes, although interesting and impor9,000 1.14 1.80 320 2.31 tant, are secondary from the standpoint of stability. 2.32 Av. 1.14 1.81 In Series A, the atom of attachment changes from 0 to S to Se, keeping the atom across the ring (oxy(d) D = O(C2H4)2Se( K OX lo3) e 16.5' 25.89 39.6' Umr) gen) constant. If one makes allowance for the 44,900 4.72 7.91 12.5 310 large standard deviation for the A S values and for 320 51 200 12.7 4.78 7.96 the fact that approximations were made in con46,400 4.81 7.86 330 12.8 verting AS0, to ASo, for dioxane, the results are as expected. Comparisons in Series B are complicated 12.7 Av. 4.77 7.91 by the fact that both the atom of attachment and (e) D = S(CIH4)2Se(KOX 103) the atom across the ring change. However, if e 15.8' 23.0' 36.7' x(md comparisons are made separately between the first 30 100 3.37 4.22 310 8.81 two complexes, then between the last two, the re320 33,600 3.55 4.41 8.62 sults are seen to be reasonable. I n Series C, the 28,700 3.45 330 8.31 4.28 attachment is a t Se while the atom across the ring 3.48 4.24 21,500 340 8.15 changes. In this case there is a gradual but sigAv. 3.46 4.29 8.47 nificant increase in AF of dissociation while AH reThe s ectra of all of the complexes are quite similar with mains essentially constant (within the experia relative6 intense band in the 290-350 mp region and a less intense band in the 400-470 mp region. In most cases in the mental error) and A S decreases. The total decrease of some 3 cal./deg. in the latter is probably of present study it was more convenient t o use the 290-350 mp band. significance. Finally, in Series D, there are large changes in both AF and AH in the expected direction but A S remains essentially constant. TABLE I1 THERMODYNAMIC CONSTANTS FOR DISSOCIATION OF I2 Acknowledgments.-The authors gratefully acCOMPLEXES AT 25" IN CARBON TETRACHLORIDE SOLUTION knowledge the financial assistance of the NaAF%, AH% AS% tional Science Foundation under Research Grant lOaKo kcal. kcal.' oal./dkg. NSF-G5922 and the cooperation of the Western (moles/l.) f0.03 f0.3 fl.O Data Processing Center on the UCLA Campus for Series A free access to the IBM 709 computer. 1000 0.0 3.3 11.o (12) J. A. A. Ketelaar, C. van de Stolpe, A. Goudsmit and W. 17.2 2.42 5.2 9.5 0
7.25
2.91
7.6
15.6
Series B 17.2 2.42 13.0 2.59 5.04 3.13
5.2 6.2 7.4
9.5 12.1 14.2
7.6 7.4 7.0
15.6 14.2 12.3
3.3 6.2 7.0
11.o 12.1 12.3
Series C 7.25 2.91 5.04 3.13 3.55 3.36 Series D 1000 13.0 3.55
0.0
2.59 3.36
Dacubas, ibid., 71, 1104 (1952).
HIGH PRESSURE POLYMORPHISM OF MANGANOUS FLUORIDE BYL. M. AZZARIA AND FRANK DACHILL~ Contribution No. 60-38. Mineral Industry College, The Pennsylvania State University, University Park, Penna. Received October 19, 1960
Extensive work has been done in this Laboratory on phase transitions and reactions in the solid state at pressures t o 60,000 bars and temperatures as high as 650°, and more recently t o 150,000 bars at lower temperatures. Much of the emphasis
SO0 r
I
I
I
0
40-
I
0
0
q
0
0
0
0
1 2 0
0
Y
9
0
0
1
.
I
100
0
1
300 400 Degrees C.
xx)
I
502
I
603
I
703
Fig. 1.-Stability fields of MnF2-I and MnF2-II determined in anvil type high pressure apparatus. Open circles represent the lInF2-I1 phase and the filling the amount of the I phase. The association of I with I1 may be due to incomplete transformation a t the lower temperatures and to difficulty in quenching. crn?.
700
€03
503
I
15
400 I
I
1
20 Microns,
25
Fig. 2.-Infrared
absorption spectra of MnF2-I and MnFs-I1 using KBr optics and KBr pellet procedure.
has been on the simpler oxides, halides, sulfides. germanate-silicate ~ o l i d solutions and a fenalumino-qilicates and their Cr, Ga, Ge, I e analogs.'-3 One of the more interesting compounds to be studied is JInF2,stable as a rutile structure analog. Interest in AInF2 results from the following: (1) the ionic radius ratio criteria of V. 31.Goldschmidt place this compound close t o the theoretical upper limit of the rutile field and just short of the fluorite field; ( 2 ) this ratio is practically identical with that of another important rutile analog, Pb02, placing it in an ideal position as a weakened model; (1) F. Dachille and R. Roy. A m . J . Sci., 268, 224 (1960). (2) F. Dachille and R. Roy, Z. Krzsf., 111, 451 (1959). (3) A . Hoffer, F. Dachille and R Roy (in prep.).
(3) it happens to be one of only two halides found to date (the other is BeF2)2which can be quenched metastably in a high pressure polymorphic form. It may be accepted in a general way that, (1) crystal structures are determined to a varying degree by the packing of different sizes of ions, and (2) anions are relatively more compressible than cations. Given the proper conditions favoring polymorphic transitions, a new form might be expected t o be favored by new and higher 'cation/'anion ratios. The values for N n F 2 and Pb02,both being 20 close to the fluorite field, would suggest that differential compressibilities might bring about a reconstructive change from the six to eight coordination of the cations. Such polymorphic pairs would be invaluable in many crystal studies: for example, they would help elucidate empirical observations and assignments of nfrared absorption bands and contribute to the utility of molar refra~tivity.~ Experimental The experimental work was done in a modified Bridgman uniaxial high pressure apparatus described elsewhere.l.2 A t the end of a run (a few hours to several days) the sample was "quenched" or cooled rapidly by directing a Etrong air blast around it while still under pressure. Uniformity, calibration and the essentially hydrostatic quality of the pressure on the sample are discussed elsewhere.' In this manner over 60 runs m-ere made on MnF2, which had been spectroscopically found to contain only less than 0.1% Ni as an impurity. Exploratory runs over a wide range of conditions disclosed the formation of a new phase a t pressures above 20,000 bars. The univariant p-t line separating the fields of the l h F ? rutile analog I from the new high pressure form IT (Buerger's terminology) is shown in Fig. 1. X-Ray diffraction was used as the primary analytical tool. Characteristic lines of phase I1 were quite strong for those runs just above the transition, the estimated conversion being 20% and greater. The extent of conversion usually increased with excess pressure over that required for the transition, but even a t the highest pressures used (nearly 60,000 bars) X-ray patterns showed E1-107~of the I form. Runs were made dry and with the addition of mineralizers such as H 2 0 , H F , NH4F and NH4C1 but the results were essentially the eame. The reversibility of the transition was established by a number of runs made in the following manner in order to avoid unnecessary handling of the small (few mg.) samples: Samples were held for three days a t 300" a t txice the transition pressure. (Cnder these conditions, duplicate runs resulted in 90% conversion to 11.) Pressure was reduced slowly (over a period of 1/2 hour) until definitely in the I stability field and held for tR-0 days a t the lower pressure. .4fter quenching, X-raT- examination showed only 30-60% of the I1 phase. Table I lists the d-spacings and cell parameters of the I1 phase obtained with the use of KaC1 as an internal powder standard, scanning at one-quartrr degree 2O/min. using Fe Iia radiation. The indexing follo.ived that of PbO? II.5 Attempts to use X-ray single crystal techniques were unsuccessful due to the inability to grow stable single crystals large enough for this xvork. Grains grown under special conditions (established after numerous trials) displaying apparently uniform extinction under the crossed riicols of the petrographic microscope formed only powder lines on oscillation S-rav films. Optical determinations xere difficult because of the finegrained nature of both the starting material and the products of the runs, although the latter generally were more iisefiil in this w-ork. The CY and y indices of I are 1.479 and 1.485. The indices of I1 are 1.484, 1.490 and 1.492, but since even the best grains of I1 displayed aggregate interference figures with apparent 21' of 4-18', the values are subject to some small error (0.002,. The molar refmctivi(4) F. Dachille and R Roy Z Krzst., 111, 462 (1959) (5) A . I. Zaslavsky, Y. D. Kondrashov and S 5. Tolhachev. Dok. A k a d . S a u k S S S R 75, 759 (1930).
31ny, lY61 ties ( R m )of the two forms calculated from these optical indices and X-ray densities are given in Table I. Infrared absorption spectra in the 11-26 p region are shown for both forms in Fig. 2 . The sample of I1 was the best one made, but its X-ray pattern showed that about 5% of I was present. The KBr window techni ue was used, the sample concentration amounting to in KBr. The instrument used was a Perkin-Elmer Model 21 double beam spectrophotometer, with K B optics. ~ ~h~ spectraare markedly similar with the exception that I1 does not show the small low band in the 18 fi region.
operatioil with the attempts studies.
TABLE I MnF2-II I/Io
3 . 7708 4.5 3 0849 10.0 2 6840 0.5 2 5478 1.o 2 3593 1.5 2.2691 2.5 1.8817 0.5 1 8015 0.5 1 7781 2.0 1 6142 0.5 1 5220 1.5 a = 4.960 b = 5.800 p(X-ray) = 3 99 ( 3 96rutileform) R, = 6 72 (6 68 rutile form)
hkl
110 111 002 021 102 121 220 130 221 113 311 c = 5.359
Discussion
It appears from the optical and infrared data that the 11 phase is not of the fluorite structure in the cubic system; rather, it is anisotropic, and the essentially unchanged infrared absorption spectrum and molar refraction may be taken as some proof that there has been no integra] change of the cation coordination. However, more important is that the unit cell is analogous to the high pressure orthorhombic phase of Pb0.6s6 Hence, while many factors certainly complicate packing in different crysta1 structures, these factors apparently work in the same manner in the polymorphic transitions of the model pair MnFz and PbO2. The similarity for more than the Despite the charge differences and the imp1ied differences ill bond strengths, the phase fields for the two cornpounds practically overlap (as they do also at higher pressures for the quartx-coesiteanalogsz for FurOther model pair, BeFz and sioz). ther, the transitions are brought about easily a t room temperature under the grinding and pressure action of simple mechallical mortarsand even that Of vibrator-mixers (Wig-L-Bug) such as arc used in spectroscopic laboratories.' There is an interesting possibility that although JInF2-I, an anti-ferromagnetic material, does not undergo any change in ionic coFrdination in the transition to MnFz-11, it may have changes in Ordering Or domain strUcture leading to magnetic properties. Acknowledgment.-Thls work was done as part of the research under ONR Contract No. Nonr e3c;(20). We are indebted to ProfWi30r R*Roy for critical interest in the study and for reading the manuscript, and t o Dr. L. Dent Glasser for co( 6 ) W. B. White, F. Dachille and R. Roy, J . A n . Ceram. Soc., (in PRE.9)
(7) F. Dachille and R. Roy, Nature. 183, 1257 (1959).
011
sillglc crystal
EQUIVALENT CONDUCTANCE OF BOROHYDRIDE ION
14
d
891
XOI'ES
BY
W, H. STOCBxAYER, M. A. REID AND C IF-. C h R L A x D
Department of Chemtstrg, Massachusetts Instztutp of bridge, ,?fassachu.setts Received October 20, 1960
zwl?torogy,
Cam-
Borohydride ion should be similar to the halide ions in many physical properties, just as ammonium ion resembles the alkali ions or methane the noble gases. The thermodynamic properties of aqueous borohydride ioni!2 support this expectation. We have now approximately determined the limiting equivalent conductance of borohydride ion in water at 25", obtaining a value close to those of bromide and iodide ions, which have about the same crystal radii. Since borohydride is unstable in neutral or acid solutions, it was necessary to work with basic solutions. The rate of hydrolysis3 is slow enough in 0.01 N potassium hydroxide for conductance measurements to be made. The direct, interpretation of the conductance of such solutions (containing the three ionic species K+, BH4- and OH-) is quite complicated.4 These complications have been avoided by comparing the conductance data for solutions of KBH4 in 0.01 1V KOH with a parallel set of data for solutions of KBr in 0.01 AyI
