1836 NOTES
Inorganic Chemistry
+
sented (eq. 3). The tv-0-term denominator, K [I-], suggests the operation of a two-step-mechanism, either step of which may become rate-determining, depending upon the relative magnitudes of K and [I-]; i t also suggests that solvent and iodide ion compete for an intermediate present a t its steady-state concentration. The rate law reveals the compositions of the activated complex in each step; these are (Cr13") and (Cr12"), respectively. A mechanism consistent with the observed kinetics of the reaction is given by the following reaction sequence (in which coordinated solvent molecules have been omitted) CrI2+
+ I~
kl
k2
k3
12
+ I--
18-
(kl
Io atoms in these strings results in triangular tight groupings of molybdenum atoms.
(e) A. Magneli, Arkiv Kenii, Jfiirci,ol. (;POL.,
24A, No. 2, 1 (lU47).
NOTES 1839
Vol. 4, No. 12, December 1965 Acknowledgments.-We wish t o thank Dr. Carl Moeller for making the magnetic measurements; Dr. F. R . Ahmed of the National Research Council, Ottawa, Canada, for his structure factor program; Drs. W. R. Busing, K. 0. Martin, and H. A. Levy for their leastsquares program; and Mr. Norman Morrow of our own laboratory for adapting the program for powder work. The computational part of this work was carried out in the Computer Center of the University of Connecticut, which is supported in part by grant GP-1819 of the National Science Foundation. The support of the National Science Foundation under grant GP-1396 is gratefully acknowledged.
-5.2
,."., ,'e
Figure l.--"B n.m.r. spectra of (CH3)4NBsCzHllI- (arid BgCzH121 (--) a t 19.3 Mc./sec.
- - -)
CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, tuted anions were prepared in an identical manner. ReplaceOF CALIFORNIA, RIVERSIDE, CALIFORNIA ment of Iz by Brz gave an analogous monobrominated material. UNIVERSITY Relevant analytical data are presented in Table I. X representative l1B n.m.r. spectrum is shown in Figure 1. B&H121.-A solution of ( C H I ) ~ N + B ~ C ~ HinI Iaqueous IacetoHalodicarbaundecaborate( 11) Ions nitrile was passed through an acidic ion-exchange column and the resulting solution concentrated to dryness. The product was BY FREDERIC P. OLSENAND M. FREDERICK HAWTHORNE~ purified by sublimation at 40 -50" under high vacuum. Like its unhalogenated analog,2 the product was both extremely hygroReceived August 23, 1965 scopic and thermally~nstable.~The yield of purified product of p. 70-71" was about 100jo.s Anal. Calcd. for B&gHlzI: m Ions of composition B&zHloRIRz- have been reC, 9.23; H , 4.62; B, 37.4; I, 48.8; equiv. wt.,260. Found: C, ported2 as the product of alcoholic base on the BUG9.26; H, 5.11; B, 36.8; I , 48.8; equiv. wt., 262.
HloRlRz carboranes. These ions are precursors t o a variety of other compounds including carboranes3 and organometallic analogs. A route to monohalogenated derivatives of the BgC2HloR1R2- ions has now been found.
Experimental BgC?HJ-.--A solution of 5.9 g. of iodine (24 mmoles) in 25 ml. of absolute ethanol was slowly added to a stirred solution of 4.0 g. (24 mmoles) of KB9C2Hl2 in 25 ml. of absolute ethanol.
Results and Discussion Addition of 1 2 to an aqueous ethanol solution of M+B9C2H12-precipitated MI and left the H30+ salt of B9CzHl1I- in solution. After the addition of 1 mole of 12, the reaction was complete and any additional 1 2 was not decolorized. The structure shown in Figure 2 is favored for the product. Evidence in support thereof comes from the
TABLE I ANALYTICAL DATAFOR ( C H I ) ~ N + B ~ H & ~ R I R ~ X Yield, Ri
H H H
Ra
X
H I CH3 I CsH6 I
CHI CH3 CHI CHI
I Br
%
Xmax
E
75 78 83
229 231 226 255 231 225
3880 4600 6140 6230 550 4100
76 71
-Equiv. w t . 7 Calcd. Found
r -
C
H
Calcd, yo---N R
r
X
C
--Found, %-------H N B
X
333 347 409
340 348 411
21.6 24.2 35.2
6.9 7.2 6.6
4.2 4.0 3.4
29.1 27.9 23.7
38.2 36.6 31.1
21.7 24.4 34.8
7.4 7.3 7.0
3.8 4.0 3.1
29.0 28.1 23.4
38.0 36.9 30.9
361 314
371 314
26.6 30.6
7.5 8.6
3.9 4.5
26.9 30.9
35.2 25.5
26.5 30.6
7.5 8.8
4.0 4.7
26.8 30.7
35.3 25.7
The color of the Iz was rapidly discharged and KI precipitated during the addition. After filtration the ethanolic solution was diluted t o 250 ml. with water and excess aqueous tetramethylammonium chloride was added. The solution was cooled t o 0' and the tetramethylammonium salt of the monohalogenated ion was separated by filtration. Recrystallization of the crude tetramethylammonium salt from hot aqueous ethanol gave the product as plates in 75% yield. Iodinated derivatives of C-substi(1) Alfred P. Sloan Research Fellow. (2) R. A. Wiesboeck and M. F. Hawthorne, J . AWZ.Chem. SOC., 86, 1642 (1964). (3) F. N. Tebbe, P. M. Garrett, and M. F. Hawthorne, ibid., 86, 4222 (1964). ' (4) M. F. Hawthorne, D. C. Young, a n d P. A. Wegner, ibid., 87, 1818 (1965); M. F. Hawthorne and T. D. Andrews, ibid., 87, 2496 (1965): M. F. Hawthorne and R. L. Pilling, ibid., in press.
IlB n.m.r. spectrum of B9C2H121formed by protonation of B 9 ~ z ~ l l ~ - Electrophilic . substitution is expected to occur a t the open face of the B9C2HI2-ion. Since C,C'-dimethyl derivatives were Obtained, attack a t carbon is ruled out. Halogenation of the two types of boron atoms present in the open face would lead to products which may be differentiated on the basis of llB n.m.r. spectra. Halogenation of the boron atom which lies upon the plane Of molecular symmetry would yield a product ion which contained only one doublet of relative intensity 1. Attack a t the boron atoms which lie off the plane would make all ( 5 ) The bulk of the material consisted of nonvolatile yellow solids.
