Fcb., 1048
ss 1
COMMUNICATIONS TO THE EDITOR
order OT a t different rates. However, the induced exchange was reproducible when conditions were held constant so we were able to correct for it using the equation % exchange == % exchange (measured) - % exchange (induced) (100) 100 - yo exchange (induced) The corrected values (always three or more excluding the value a t zero time) obeyed the exponential exchange law.',' The half-times for the exchange rates are summarized in Table I. As expected the exchange rate is not dependent on the method of separation when proper account is taken of the induced exchange.
Hg' are each bound to two boron atoms. Each boron atom has three boron neighbors at 1.74 f 0.04 kX and one hydrogen neighbor a t 1.34 * 0.04 kx. In addition, B4, B4', B4" and B4"' each has a boron neighbor a t 1.96 * 0.04 kx and another hydrogen neighbor a t 1.54 * 0.04 kX; B1, B:, Bz, Bz', each has two boron neighbors a t 1.96 * 0.04 kx: BI and Ba', each has another hydrogen neighbor a t 1.34 * 0.04 kX. 45'
TABLB I TI(1)-TI(II1)EXCHANGE RATES 0.0244 f . Tl(I), 0.0244 f . Tl(II1) Acid
Temperature
Method of separation
Exchange half-tim; hr.
1.0 f. "01 1 . 5 f. HNOr 1 . 5 f . "0% 1 . 5 f . HClO, 1 . 5 f . HClO' 1 . 5 f . HClO, 2 . 5 f . HClO, 3 . 5 f . HClO,
25°C. 24.8 * 0.2" 24.8 * 0 . 2 " 24.8 * 0.2" 24.8 =t0.2" 24.8 * 0.2" 24.8 * 0.2" 24.8 f 0.2"
Bromide Bromide Hydroxide Hydroxide Bromide Bromide Bromide Brornitlc
2.5 * 0.2 1.8 * 0. 1.6 * 0 . 2 36 * 4 35 * 4 33 * 4 45 * 4 67 * 5
M.
O=BORON I 0 :HYDROGEN
Fig. 1.
We are extending this work to determine the effect of temperature, ionic strength, and concentrations of the reactants on the exchange rate.
Each boron atom is bound to five or six other atoms, but the bonds are not all equivalent. In(3) H. A. C. McKay, Nalurc, 119, 997 (1938). asmuch as a bond distance of 1.96 k X has about (4) R. B. Duffield and M. Calvin, TaIs JOURNAL, 68, 557 (1946). half the "bond number"2 of a bond distance of DEPARTMENT OF CHEMISTRY 1.74 kX, one can say that each boron forms five WASZINGTON UNIVERSITY REN&J. PRESTWOODbonds of bond number 0.60. The corresponding Sr. LOUIS,M i s s o m ARTHURC. WAHL radius, R(0.60) = 0.87 kx. Consequently, R(l) RECEMX DECEMBER I 10, 1947 = 0.80 kX in agreement with Pauling.2 This structure for BloHlr gives excellent agreement with the observed X-ray diffraction intensiTHE STRUCTURE OF THE DECABORANE MOLECULE ties and also with the electron diffraction observasir: tions of S. Bauer.a A detailed discussion of the determination of the We axe studying the structure of crystalline decaborane, BIOHl,,by single crystal X-ray dif- structure of crystalline decaborane will be pubfraction methods. We have established the ap- lished soon. (2) L.PaUbg, THIS JOURNAL, 69, 542 (1947). proximate positions of the ten boron atoms and (3) S. Bauet, ibid., TO, 116 (1948). four of the hydrogen atoms, and have assigned probable positions to the remaining ten hydrogen RESEARCH LAFIBORATORY JOHNS. KASPER ELECTRICCOMPANY C. M. LUCHT atoms. (Hydrogen atoms are well resolved in GENERAL NEW YORK. DAVIDHARKER SCHENECTADY, fourier sections.) RECEIVED JANUARY 21,1948 The BlOHI4 molecule has the symmetry &mm2. The bond distances are as follows (see figure): B1-Bl', Bl-BI, B2-Bs, Bn-B,, BrB4, are HETEROGENEITY OF CRYSTALLINE BETA-LACTOGLOBULIN all 1.74 t0.04kX; Bl-Bz and B4-B4' are 1.96 f 0.04 m; B4-H4 is 1.34 f 0.04 kX,l and all other Sir : B-H distances axe assumed the same, except B4That crystalline &lactoglobulin is not a homoHs which is assumed to be 1.54 0.04 kx. (B4- geneous protein was indicated by the solubility B4'" and BI'-B~' are 2.76 * 0.04 k X and are not measurements of Gronwall' and by the electrobond distances.) Each hydrogen atom, except HII phoretic results of Li.% Our experiments with and He' is bound to a single boron atom; HIIand (1) Grbnmll, Compt. mend. haw. lab. Carlsbw;. S4, no. 6-11. 188 f
and H P ' werelocated on an electron density map; (1) Hd, Ed', the position. of the other hydrogen atom are aasumed.
(1042). (2) Li,
JOUZlNAb,
68, 2746 (1946).
