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
