MOLECULAR FORMULA O F CESIUM TETRAIODIDE
(10) (11) (12) (13) (14)
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KILPATRICK, &I., AND MEARS,W . H.: J. Am. Chem. SOC.62, 3051 (1940). M.: J. Am. Chem. SOC.69,572 (1937). MASON,R . B., AND KILPATRICK, MINNICK,L. J., A N D KILPATRICK, M.: J. Phys. Chem. 43, 259 (1939). WOOTEN, L.A , , AKD HAMMETT, L. P.: J. .4m. Chem. SOC. 67, 2289 (1935). WYXNE-JONES, W.F. K . : Proc. Roy. Sot. (London) A140, 440 (1933).
POLYIODIDES OF CESIUM. I V
X KOTEON
THE
MOLECL-LAR FORMULA OF CESICMTETRAIODIDE 8. S HTJBhRD‘
Depai tment
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C h e m i s t r y , Cornell L‘nztersziy, Ithaca, Neui York Recezved J u l y Z8,1941
Although the existence of cesium tetraiodide has been definitely established (3), there has been considerable speculation about its molecular formula and structure, and the same can be said of “even” polyhalides in general. This paper presents some pertinent data on cesium tetraiodide; the conclusions can perhaps be applied also to cesium tetrabromide (8) and to the sodium tetraiodide recently reported (2, 4). The empirical formula of cesium tetraiodide is Cs14,but it is extremely doubtful that this is the true molecular formula, as will now be shown. If the tetraiodide group were actually I4-, the total number of valence electrons would be 29, the sum of the 28 (4 X 7) due to iodine plus the one captured from cesium. Thus an unpaired electron would be present. On the other hand, if the true formula were some even multiple of Cs14, there would be no unpaired electrons. The simplest and most probable of these formulas is CszIg, corresponding to 58 (2 X 29) valence electrons in the polyiodide group. Therefore, a measurement of the magnetic susceptibility of the compound seemed advisable and was obtained by Dr. h.hl. Saum, to whom we are very grateful. The tetraiodide proved to be diamagnetic, with a susceptibility of -220.5 X C.G.S. units per mole, which agrees well with the theoretical value of -227.8 X C.G.S units calculated on the basis of the additivity principle.? A formula weight of 640 (corresponding to CsIJ was assumed in obtaining both valuesa Present address: Tusculum College, Greeneville, Tennessee. This value was calculated from data for cesium iodide and iodine given by Klemm (6) and by Bhatnagar and Mathur (1). Since the available data are not entirely concordant, an average value is reported. The lowest and highest values calculated were, respectively, -219.7 X 10-0 and -236 X 10-ec G.S. units. If the true formula is CsJs, the observed and theoretical values become, respectively, -441.0 X lo+ and -455.6 X IO4 C.G s. units. 2
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S. S. HUBARD
If the tetraiodide contained an unpaired electron, it should either be paramagnetic or have a component of paramagnetism sufficient to produce a large discrepancy between the calculated and observed diamagnetic susceptibilities. It seems almost certain, therefore, that the correct formula is Cs&. If the true formula is Cs218,the most probable arrangement in the polyiodide group seems to be the sharing of an iodine molecule between two triiodide groups, i.e., Csf [-Is-12-13-]
cs+
Rae (9) found in studying the dehalogen curve for cesium tetraiodide at room temperature that the compound first loses iodine to form the triiodide (CsIJ before the final decomposition into cesium iodide and iodine. If the foregoing arrangement is assumed, this would occur with a minimum of disturbance of the constituent triiodide groups,-by a simple splitting out of the iodine molecule shared between them. There is further support of this view, although somewhat indirect, in some work of Wheat (lo), who found that a t very low temperatures chloroform and chlorine react to form the compound 2CClsH. C12; here it seems quite certain that the chlorine molecule is shared between two chloroform molecules. At ordinary temperatures the iodine of addition in cesium tetraiodide seems to be held quite strongly. The dissociation pressure (0.0479 mm. at 25OC.) calculated by Foote, Bradley, and Fleischer (5) is considerably below the vapor pressure of iodine (0.313 mm.), and the heat of dissociation calculated by them is 15,800 calories per mole. Similar data on cesium triiodide (5) indicate a n even greater stability of this compound. Merely as a suggestion, this stability may be ascribed in part to a system of resonating electronic configurations in the triiodide and tetraiodide groups. Such a concept has the further advantage of eliminating fixed decets of electrons around any of the iodine atoms by mobilizing the extraoctet pair on a given atom (cf. Pauling's configuration of the triiodide ion (7)). We hope eventually to clarify the structure of the tetraiodide group by x-ray cryst,al data. SUMMARY
Evidence that the molecular formula of cesium tetraiodide is Csn18 rather than Cs14 is presented. It is suggested that the marked stability of both of the cesium polyiodides may be traced in part to resonating configurations in the halogen groups. REFERENCES (1) BHATNAGAR AND MATHUR: Physical Principles and Applications of Magnetochemistry. The Macmillan Company, Ltd., London (1935). ( 2 ) BRIQGS, GEIQLE,AND EATON:J. Phys. Chem. 46,595 (1941).
SOLUBILITY DIAGRAMS
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(3) BRIGGS AND HUBARD: J . Phys. Chem. 46,806 (1941). (4) CHEESMAN, DUNCAN, AND HARRIS:J. Chem. SOC.1940,837.
(5) FOOTE,BRADLEY, AND FLEISCHER: J . Phys. Chem. 87, 21 (1933). (6) KLEMM:Magnetochemie. Akademische Verlagsgesellschaft, m.b.H., Leipzig (1936). (7) PAULING:The Nature of lhc Chemical Bond, 2nd edition, p . 111. Cornell University Preas, Ithaca, New York (1940). (8)RAE:J. Chem. SOC.lW1, 1578. (9) RAE: J. Phys. Chem. S6, 1800 (1931). (10) WHEAT: Thesis, Cornell University, 1939.
T H E SOLUBILITY DIAGRAMS FOR T H E SYSTEMS ETHYLI D E N E DIACETATE-ACETIC ACID-WATER AND VINYL ACETATE-ACETONE-WATER JULIAN C. SiMITH Plant Research Laboratories, Shawinigan Chemicals Lid.,Shawinigan Falls, Quebec, Canada Received July $8, f04f
Both vinyl acetate and ethylidene diacetate are produced commercially in large quantities by the reaction of acetylene with acetic acid, but the published data on both of these compounds are very incomplete. The solubility diagram for the system vinyl acetate-acetic acid-water has already appeared (2), and the diagrams in figures 1 and 2 are submitted in order to supplement the available information. The limiting solubility curve (see table 1) for the system ethylidene diacetate-acetic acid-water was determined by placing known mixtures of ethylidene diacetate and water in a set of small Erlenmeyer flasks and immersing them in a constant-temperature bath at 25°C. They were then titrated with pure glacial acetic acid until turbidity just disappeared. The tie lines were determined by making up a series of mixtures containing about equal quantities of ethylidene diacetate and water and varying amounts of acetic acid. After thorough shaking a t 25"C., each mixture was transferred to a separatory funnel and allowed to settle. About 1 cc. was then pipetted from the top layer and placed in a tared flask. A somewhat larger sample was withdrawn from the bottom layer. After weighing, each sample was analyzed for acetic acid by titration with standard 0.2 N sodium hydroxide. I n each case the tie line determined by the two analyses passed through the point representing the over-all composition; this served to check the accuracy of the work. The limiting solubility curve for the system vinyl acetate-acetone-water
