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SULFUR HEXAFLUORIDE CLATHRATE OF DIANIN’S COMPOUND
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have estimated the value of PB a t about A.,38,39 p = 213, and p = -2.66 e.v. for benzene as tor, et d r 7 mentioned above. The results are shown in the 0.15 from the observed BN bond distance. Howlast column of Table 111. On the other hand, the ever, since no reliable data are available a t present observed ratio of the diamagnetic anisotropies of for the single bond distance as well as the double the two compounds is 36/54 = 0.67. Interpola- bond distance of BN bonds, the value thus obtained tion by means of Table I11 gives d = 1.06, q~ = is open to question. On the other hand, K ~ b a y a s h i ~ ~ 0.24, PBX = 0.45 and PBN = -2.31 e.v. for the has carried out SCF m.0. treatment on borazole and found q B = 0.52. molecular parameters of a borazole ring. The value of d is in excellent agreement with that The evaluation of the dependence of bond lengths given by Roothaan and Mulliken,8 1.0. The upon the bond order of bonds between different resulting value of (YN - O!B = -4.7 e.v. compares atoms presents considerable difficulties owing to The 9-electron favorably with ax - O!C = -(1.8-2.4) ~ . v . ~ O The the lack of sufficient value of B thus obtained gives the ratio, Bboraz ‘Pbenz bond order ~ B N= 0.45 for a BK bond distance = 2.3112.66 = 0.87 in good agreement with the Y B S = 1.44 A. for borazole is consistent with the ratio of overlap integrals, Sboraz/Sbenz = 0.219/0.25 = curve of CC bond lengths plotted against the bond 0.88. I t is known31 that (or the resonance inte- order and suggests the adequacy of thg values for gral) of CC bonds varies with the interatomic dis- the single bond distance (Y, = 1.$6 A.) and the tance in proportion to the overlap integral s. The double bond distance ( ~ d= 1.35 A,) proposed by present results confirm that the same relation is valid Coffin and Bauerj and those by Cartmell and F ~ w l e s ’ ~ (Y, = 1.54, Yd = 1.36 A,). On the other hand, the also for bonds involving heteroatom^.^' The extent of contribution of the donor-acceptor values of BN distancss given by Rector, et al.,7 double bond structure, i e . , the .rr-electron distribu- (Y, = 1.48, r d = 1.30 A.) and by Hedberg and Stotion q~ on boron atoms in a borazole molecule has (Y, = 1.49 K . ) deviate appreciably from the been a subject of considerable dispute. Although curve of CC bond lengths mentioned above. the marked similarity of a borazole ring to a benAcknowledgment.--\Ye wish to express our corzene ring suggests a fairly high value of q B , the dial thanks to Dr. R. Schaeffer of Indiana Univerpresent analysis gives 0.24 in agreement with the sity for providing us with some of the materials conclusion derived by Pease42s43 from observed in- used id the present investigation. teratomic distances that q B is not very great. Rec(44) H . Kobayashi, private communication. (38) B . P. Stoicheff, C a m J . Chem., 32, 339 (1954). (39) K. Kimura and RI. Kubo, J . Chem. P h y s . , t o be published. (40) F. A. Matsen. THISJ O U R N A L , 72, 5243 (1950). (41) G. W. Wheland, ibid., 64, 900 (1942). (42) R. S. Pease, i b i d . , 74, 4219 (1952). (43) K . S. Pease, Acla C y y s l . , 6 . 336 (1953).
[CONTRIBUTION FROM THE \VESTINGHOUSE
(45) E. G. Cox and G. B. Jeffries, PYOC. R o y . SOC.( L o i i d o n ) , 8 2 0 7 , 110 (1951). (46) C. A. Coulson, J . Phys. Chem., 66, 311 (1952). (47) E. Cartmell and G. W. A. Fowles, “Valency and Molecular Structure,” Butterworths, London, 1956. (48) K. Hedberg and A . J. Stosick, THISJ O U R X A L , 74, 954 (1952).
RESEARCH LABORATORIES, PITTSBURGH 35,
PENNSYLVANIA]
The Sulfur Hexafluoride Clathrate of Dianin’s Compound (4-p-Hydroxyphenyl-Z,2,4trimethylchroman) : Preparation, Characterization and Thermal Decomposition BY L. ~ I A N D E L CN.ON. RN GOLDBERG , AND R . E. HOFF RECEIVED OCTOBER14, 1989 T h e sulfur hexafluoride clathrate of Dianin’s compound is obtained by recrystallization a t a high prcisurc of sulfur Iiexxfluoride. T h e amount of sulfur hexafluoride contained in the clathrate so prepared is about 13y0by w i g h t , which on the basis of volume of containing solid, is equivalent t o a pressure of 25 atmospheres of gas. .-lt temperatures below its melting point, this clathrate decomposes b y sublimation of Dianin’s compound. T h e decomposition r a t e is limited by the ratio of sample volume t o exposed area and b y t h e magnitude of external gas pressure. i l n examination of infrared spectra reveals t h a t chemical interactions between t h e sulfur hexafluoride and its enclosing cages are very slight Evidence t h a t the guestfree form of Dianin’s compound also possesses the clathrate structure is derived from density measurements.
Introduction -1review of the subject of clathrates’ mentioned that these substances afford a convenient means for storage and for controlled release of inert gases. Generally, in clathrate systems, gases are retained under ordinary conditions and may be released easily by simple processes such as heating, dissolving or grinding. Sulfur hexafluoride is a gas that has found considerable use in electrical devices. It was felt that its range of practical applicability would be considerably enhanced if it were associated with a solid. A clathrate of sulfur hexafluoride appeared to fulfill this requirement. (1) I,. Mandelcorn, Chem. R e v s , 69, 827 (1959).
Dianin’s compound was selected as the host component for a clathrate of sulfur hexafluoride as a result of preliminary reports by Baker and LTcOmie2 and by Powell and Wetters3on an extensive investigation of the properties of this solid. They showed that three series of clathrates of Dianin’s compound are possible; their maximum-composition formulas being B C I ~ H Z ~3M1, O Z . 6ClaHzoOz .2hG and 6C18H2002.M3 where MI, M2 and h93 are molecules of the size of methanol, ethanol and hexachloroethane, respectively. Since the size of a sulfur (2) W. Baker and J. F. W. h l c o m i e , C h c r i i . &Y l i d . ( L o n d m i ) , 256 (1955). (3) H. A l , Powell and B. U. 1’. Wctters, cbid,,2,?(i (1955).
L. MANDELCORN, N. N. GOLDBERG AND R. E. HOFF
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Vol. 82
TABLE I SOME PROPERTIES OF DIANIN’SCOXPOUND AND Dianin’s comp. Ethanol clathrate
Two
OF
ITS CLATHRATES Sulfur hexafluoride clathrate
Composition C1sH2002 6Ci8Hzo02‘2C2HbOH -6CisHzcOn*l.7SFe Aleking point, “C. 158-159 165-166 163-16.5 Density, g./cc. 1.15 1.19 1 . 3 0 (6CisH~oO~~l.79SFs) Infrared spectra Similar t o C18HZ002 but added absorption band at 938 c111.-~ Thermal stability After 3 yr.
