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UNFAMILIAR OXIDATION STATES AND THEIR STABILIZATION JACOB KLEINBERG University of Kansas, Lawrence, Kansas
TEEdemands of the past decade have stimulated research into the chemistry of practically every element. One outstanding phase of recent investigations has been the preparation and characterization of unfamiliar, i . e., little-known, oxidation states of well-known elements. These investigations have shed much light on the very important problem of the stabilization of oxidation states. An attempt has been made in this paper to summarize in a qualitative fashion those aspects of the chemistry of unfamiliar oxidation states of well-known elements which are mentioned above. The approach utilized is suggestive rather than exhaustive. The survey is limited t o cases where the groups bonded to the element in question have definite, generally accepted oxidation numbers in the compounds; the carbonyls and nitrosyls are, therefore, excluded from consideration. Also, material concerning oxidation states existing only at high temperatures is not included. The concept of oxidation state or oxidation number is frequently, particularly for covalent compounds, a purely arbitrary one. For simple ions the oxidation state, it is true, does correspond to the number of unit electrical charges on the ion; in this instance, therefore, the terms oxidation state and valence are synonymous. The concept, however, frequently loses its objectivity in the case of covalent compounds. For example, in the extreme instance of the compounds of carbon, in which this element exhibits a constant covalence of four, application of the oxidation state idea often leads to values for carbon which might be said to be almost entirely devoid of structural significance. With metals, however, where, in many cases a t least, changes in oxidation state can be related t o loss or gain of electrons in experimentally realizable half-reactions, discussion of oxidation states is of more obvious chemical significance. -
emphasizes the fact that important periodic relationships have not yet been realized, perhaps because most of t,he work with these elements has been performed either in the dry state or in water as solvent. Uniand tripositive states of thallium are well known and there is excellent evidence for unipositive gallium and indium ( I ) , while the existence of the dipositive state for these elements is open to question ( 2 ) . The data from a few scattered experiments on the anodic oxidation of aluminum in various solvents (3') may best be explained on the assumption that some of the metal goes into solution in an oxidation state lower than three. Striking proof that aluminum, gallium, and indium, when anodically oxidized in anhydrous acetic acid, enter solution in lower oxidation states is offered by some recent work (4). In the cases of the two first named, there is no doubt that a t least some of the metal is oxidized t o the unipositive state. Much remains to be done with this group of elements, particularly in nonaqueous solvents. Research on the unfamiliar oxidation states of the copper group has brought into much clearer focus the great similarity of these elements, particularly of copper and silver, in their higher states. For example, t.here have been prepared a series of remarkably similar complexes containing copper and silver in their tripositive states bound to the periodate or tellurate group (6). Compounds of the elements of the copper group in each oxidation state from +1 to +3, with the exception of +2 gold, are now well known. Most of the compounds of dipositive silver and of tripositive copper and silver are complex in nature. The preparation of element 85, astatine, by the bombardment of bismuth of mass 209 with 32-m. e. v. alpha particles, and the subsequent observations on its rhemical ~ r o ~ e r t i e(6). s have brought t o light some interesting relationship$ within the halogen family. The behavior of astatine, in many of its reactions, is that of a typical metal; for example, hydrogen sulfide ~ r e c i ~ i t a t eelement s 85 auantitativelv as sulfide in hydrochloric acid solutionup to 6 normal. At first glance, this is extremely surprising, but it appears less so when it is realized that iodine, the element above 85 in the family, also possesses some metallic characteristics. Indeed, compounds in which iodine exists as a unipositive ion stabilized by coordination with organic amines have been prepared (7). The behavior of astatine is also in line with the increased metallic character of the elements in a given group with increas-
THE IMPORTANCE OF THE STUDY OF OXIDATION STATES
In addition to sugaestina numerous moblems w o r t h of research, acquaritanceuwith the chemistry of unfamiliar oxidation states clarifies and extends many periodic relationships, and also, as has already been mentioned, adds greatly t o our knowledge of factors ~ ~ h i c in h , general, influence the stabilization of oxidation states. These points are expanded in some detail below. An examination of the chemistry of the aluminum group (i.e., aluminum, gallium, indium, and thallium) 32
JANUARY, 1950
ing atomic numher from carbon to lead, nitrogen to bismuth, and oxygen to polonium. Investigations in the field of unfamiliar oxidation numbers have considerably increased our information concerning the general problem of the stabilization of oxidation or valence states. The term, stabilization o j valence states, is used in the chemical literature in two ways: first, stabilization with respect to oxidation or reduction or both, an effect which may he expressed in terms of changes in oxidation-reduction potentials (8) ; and second, the preparation of the desired state of the element under conditions which permit either its isolation and study, or its examination in solution. The following pertinent observations on this subject may he niade: (1) Higher oxidation states are frequently formed and stabilized in alkaline solution. This is not surprising in view of the increasing acid character of oxides with increasing oxidation state of the central atom. Numerous investigators have shown that the anodic oxidation of iron in concentrated alkali converts iron to the +6 ferrate, FeOr, state (9),and that increasing akali concentration favors ferrate formation. Oxidation of cupric hydroxide of alkaline solution with sodium hydroperoxide, NaOOH, apparently gives copper(II1) oxide (10). Determination of the voltagecurrent curve for a silver anode in sodium hydroxide solution gives breaks corresponding to the formation of AgzO and Ago (11). (2) Negative groups containing a central atom of high oxidation numher have been found to stabilize high oxidation states. Heteropolymolyhdates of cobalt(1V) and nickel(1V) of the formulas 3Kz0.Cooz. 9MoOa. 6'/&0 and 3Ba0. NiOz. 9MoOs 12H,O have been characterized (12). The periodate and tellurate groups have frequently been used for this purpose. Reference has already been made to complexes of tripositive copper and silver containing these groups as stabilizers (6). It is interesting in this connection that all of these compounds are obtained in alkaline medium. Evidence has been presented which indicates that the dipositive silver formed when silver nitrate in nitric acid solution is treated with ozone, exists in the form of nitrate complexes (IS). (3) Lower oxidation states have been stabilized by means of groups, or in solvents, which possess reducing properties. Complexes of dipositive chromium with hydrazine are extremely stable in air; in fact, some of the compounds are not oxidized even when suspended in water and stirred with air. The stahility of these complex compounds has been attributed to the reducing properties of hydrazine (14). Undoubtedly, however the stahility of these hydrazine complexes is in part accounted for by their insolubility in water. The importance of the role of the solvent is clearly demonstrated by the fact that it is possible to isolate and study complex cyanides of nickel(O), nickel(1) (15) and palladium(0) (16) by the reduction in liquid ammonia of cyanides containing the metals in higher oxidation number. Aqueous solutions of the complex
33
cyanide of nickel(1) have been ohtained also, but they are rather unstable, partly because of the oxidizing action of water. No evidence, however, has been ohtained in aqueous solution for the more powerfully reducing nickel(0) or for palladium(0). (4) The suggestion has been made that the complex cyanide ions, N~(CN)A'and Ni(CN)8-, containing zeroand unipositive nickel, respectively, resonate between double- and single-bonded structures (17). Such resonance would contribute to the stahility of these ions. (5) Actual or near attainment of certain electronic configurations enhances the stability of many oxidation states. With regard to comparatively littleknown states this is exemplified in the case of the "anomalous" valences of the rare earths. It has been proposed, on the basis of quantum mechanical considerations, as well as chemical observations, that an j subshell is most stable when it has 0, 7, or 14 electrons (18). This explains the stability of the CeC4, Eu+', Tb+4, and Yb+z ions. Tetrapositive cerium possesses no 4f electrons. Dipositive europium and tetrapositive terbium have a half-completed 4 j shell, whereas +2 ytterbium has this suhshell filled. The same hypothesis also provides a reasonable explanation for the existence of Sm+l (4fa) and its lesser stability as compared to dipos~tiveeuropium. Similar considerations are pertinent to a discussion of +4 and +5 praseodymium. They account also for the transition in preferred oxidation state from +6 for uranium to +3 for americium and curium (19). Apparently there is an increase in the stahility of the 5f subshell as it approaches a halffilled condition. Curium, which probably has seven 5 j electrons, appears to exhibit an oxidation state of +3 only. Presumably, the half-completed subshell does not participate in chemical combination. (6) The solubility of the substance of desired oxidation state frequently is a factor in its stabilization. The probability that the stahility of the hydrazine complexes of dipositive chromium may he attributed in part to their insolubility has been mentioned. There are numerous other examples of the contribution of insolubility to stabilization, of which only a few will he mentioned. The preparation of copper(II1) oxide by oxidation of cupric hydroxide in strongly alkaline solution (10) is undoubtedly favored by the insolubility of the product. The relationship of structure to the stahility of dipositive europium has been discussed, hut there is no question that the stability of europium (11) sulfate is further enhanced by its insolubility in water, the medium in which it is prepared. (7) Both crystal structure and oxidation state in one compound may play important roles in promoting the formation of a certain oxidation state in a second compound. Although this phenomenon appears to he rather general, only two instances will he cited here. Cerium(1V) oxide markedly catalyzes the formation of Proz when praseodymium oxide is heated in high concentrations of pure oxygen (20). In fact, it has been claimed that the ratalytic effect of small amounts
34
of ceria has been responsible for the contradictory results obtained in the study of the higher oxides of praseodymium. Attempts to precipitate low concentrations of manganese dioxide on y-alumina, by heating a solution of manganese(I1) nitrate on the latter, result in the conversion of the manganese to the sesquioxide only. I n order to obtain conversion to manganese dioxide it is necessary to support the manganese on a high area rutile, TiOz. This phenomenon has been named valenee inductivity ( d l ) . (8) Specific instances of stabilization of unfamiliar states by coordination have already been cited. There is, however, one phase of stabilization by coordination which is worthy of special emphasis. Molecules or ions capable of chelation, i. e., of occupying two or more coordinat,ing positions and forming rings (preferably five- or six-membered rings), in general yield more stable compounds than coordination groups occupying single positions. Numerous examples of the great stabilizing effect of chelation are available in the literature. Of particular interest to this discussion is a report of recent work ($2) which has implications which may be of general utility in stabilizing low (and perhaps high) oxidation states. It was demonstrated that the oxidation state of cobalt in complexes with azo and azomethine dyes depends upon the nature of the dye molecule. The critical factors determining the oxidation state of the cobalt are the number of replaceable hydrogen atoms in the positions ortho t o the azo or azomethine group and also the total number of positions available for coordination.
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molecules within the coordination sphere bringing the cobalt to its appropriate coordination number. It would be of extreme interest t o determine how generally applicable are these ideas which have been so successfully applied to cobalt. M m O D S FOR CHARACTERIZING UNFAMILIAR STATES
Unfamiliar oxidation states have been characterized principally by four types of evidence: (I), analytical data and chemical properties; (2), isomorphism with compounds containing atoms of known oxidation state; (3), magnetic susceptibility measurements; and (4), X-ray studies. I n some instances a combination of two or more of these has been necessary for the complete characterization of the oxidation state in question. Analytical data, in conjunction with a study of the chemical properties of the substance, frequently give sufficient information for the determination of oxidation state. The necessity of a knowledge of the chemical properties of the substance in question is made apparent by the following illustration: a compound containing silver and oxygen in equal atomic proportions may be made by the oxidation of unipositive silver wit,h persulfate in alkaline medium ($3). Analysis obviously indicates the formation of either silver(I1) oxide or silver peroxide. The latter possibility, however, is eliminated by the fact that acidification of the compound gives no hydrogen peroxide. Occasionally, it may be demonstrated that an atom possesses a specific oxidation state by proving that the compound in which it occurs is isomorphous with a known substance. Oxidation of a mixture of silver HO and cadmium salts with persulfate in the presence of \ pyridine yields mixed crystals of complexes with ~ x = s ~ pyridine, proving that the silver and cadmium comA pounds are isomorphous and, hence, that the silver is dipositive ($4). A particularly interesting illustration concerns the formation of ammonium cobaltic alum by the electrolytic oxidation of cobalt(I1) sulfate in the presence of ammonium sulfate (85). Identification was made both by analysis and by the alum-like crystal structure of the material. In the absence of ammonium sulfate, no cobalt(II1) compound is found.' The formation of this alum apparently involves t,hestabilization of an unusual valence state by the attainment of a stable crystal lattice. Magnetic susceptibility measurements very often For example, the metal is found to be in the $3 give definite information concerning oxidation states state in the complex with dye A which contains one and the nature of their chemical binding. Two inreplaceable hydrogen; since there are only two coordi- stances in which such data have been utilized to prove nation positions available for binding, three dye residues structure are described below. A series of salts in are necessary t o give the cobalt a coordination number which ethylenedibiguanide is coordinated to tripositive of six. On the other hand, dye B, which also possesses silver has been prepared. Tripositive silver and one replaceable hydrogen, fills three coordination dipositive palladium have the same electronic configurapositions and only two molecules of dye are necessary tion and the complexes of the former would be expected for attainment of coordination number six; thus, to be diamagnetic, as are those of the latter, provided +2 cobalt is stabilized. Dye C, with two replaceable ' SWANN,S., JR., AND T. S. XANTHAKOB (J. Am. Chen. Soc., 53, hydrogens, also stabilizes the +2 state. I n this case, 400 (1931))have been able t o obtain cobalt(II1) sulfate hy the the complex contains only one dye residue, water anodic oxidation of cohalt(I1) sulfate in 10 N sulfuric acid.
JANUARY, 1950
35
in 10 N sulfuric acid (38). A reaction which has been extensively investigated involves the electrolysis of a solution of silver nitrate in nitric acid. This reaction yields a t an inert anode a black material to which several investigators have assigned the formula AgrNOll This substance unquestionably contains some silver in the tripositive form (33). The potentialities of ozone and fluorine as oxidizing agents for the study of higher states have scarcely been tested. Ozone acts on a cold solution of a nickel(I1) salt dissolved in sodium bicarbonate to give a red solution from which, it is claimed, nickel(1V) oxide may be obtained (34). This claim, which is not supported with quantitative data, deserves further study. The action of ozone on silver nitrate in concentrated nitric acid has been exhaustively studied, and it has been demonstrated that dipositive silver is formed in this reaction (35). Evidence is available which indicates that dry ozone may react with powdered silver t o form silver(II1) oxide (36). Very few reactions involving direct oxidation by fluorine to give higher states have been described. When fluorine reacts with cobalt(I1) chloride, a t 150°C. in a quartz vessel, the tripositive fluoride is formed (37). The difluoride of silver is formed by the action of fluorine on silver and silver halides (38). Low oxidation states have been obtained either by the reduction of higher states or by the anodic oxidation GENERAL METHODS I'OR THE PREPARATION OF of free metals in various solvents. The latter method UNFAMILIAR OXIDATION STATES OF THE METALS has already heen referred to in connection with the Four general methods have been successfully used anodic disiolution of aluminum, gallium, and indium for the production of high oxidation states of well- in oxidation states lower than three (3, 4). I n this known metals. They involve oxidation of lower states respect it is noteworthy that no compounds containing with persulfate, with ozone, with fluorine, or anodically. these elements in low oxidation states have actually The persulfate ion, frequently in alkaline solution, is been isolated in this manner. The reduction of higher oxidation states has been one of the most, widely used oxidizing agents. A few examples are cited. Treatment of cohalt(I1) sulfate accomplished by means of hydrogen at elevated temin ammoniacal solution with hydrogen peroxide and peratures, cathodically, by means of active metals ammonium persulfate gives rise to a complex ion of the in aqueous and nonaqueous media, and by thermal formula [(NH&COO~CO(NH&]+~ (31). This ion pre- decomposition. Examples are given below. The reaction of hydrogen with chromium(111) sumably contains both tri- and tetrapositive cobalt. Oxidation of nickel(I1) and cobalt(I1) sulfates with chloride a t elevated temperatures gives the correammonium persulfate in the presence of ammonium sponding dipositive salt (30). Similarly, reduction molybdate yields the previously mentioned hetero- of the trihalides of samarium, europium, and ytterbium polymolybdates of the corresponding tetrapositive ions yields the dipositive compounds (40). Electrolytic (12). The use of the periodate and tellurate radicals reduction of tripositive europium and ytterbium is also for the stabilization of tripositive copper and silver effective for the formation of the dipositive materials has already been mentioned (11). Oxidation to the (41). The use of active metals as agents for reduction tripositive state in compounds containing these groups may be accomplished, in each case, by means of potas- appears to be of rather general applicability. A few interesting examples are described. The cyano comsium persulfate in alkaline solution. Thc anodic oxidation, under appropriate conditions, plexes of nickel(O), nickel(I), and palladium(0) either of free metals or of ions in lower states, has have been mentioned (15, 16). These compounds are served for the preparation of higher oxidation states. obtained by the reduction, with potassium in liquid Reference has already been made to the formation of ammonia, of complex cyanides containing the respecthe ferrate ion, FeOa=, and of Ago, by the electrolytic tive elements in their dipositive states. Used in a Jones oxidation of the respective metals in concentrated reductor, zinc has found some application in the proalkali (9, 11). A method has been described for the duction of low valence states; particularly intriguing preparation and isolation of cobalt(II1) sulfate a t the is the reduction of the perrhenate ion to uninegative anode in an electrolyte consisting of the dipositive salt rhenium (48). the coordination bonds are of the planar, hybrid dspZ type. Magnetic measurements prove that this is the case (26). Such measurements have also proved that dipositive europium and tripositive gadolinium are isoelectronic, the magnetic susceptibilities of the two ions being nearly equal, and any other possibility being excluded by the low value obtained for A, the molecular field constant in the Curie-Weiss law, x, = C/T A (27). The results of X-ray studies are often of prime importance for the positive characterization of compounds containing atoms in unfamiliar oxidation states. The problem of the determination of the correct stmcture of the superoxide ion is a case in point. Magnetic measurements on superoxides give values corresponding to the presence of one unpaired electron in the superoxide ion, and thereby indicating the structure :0::.0:(28). Povder photographs of potassium superoxide show that this substance possesses a face-centered lattice of the calcium carbide type. The structure is analogous to that of strontium and barium peroxides, thus confirming the existence of the Oa- structure ($0). Moreover, the value of 1.28 1 0.07 i. for the distance between adjacent oxygen nuclei is in satisfactory agreement with that expected for a single bond plus a threeelectron bond (SO).
+
JOURNAL O F CHEMICAL EDUCATION
The t h e r m a l decomposition of certain tripositive rare e a r t h halides serves as a means of preparing t h e dihalides. The products of the t h e r m a l decomposition of the triiodide and bromide of s a m a r i u m at 800 t o 900°C. i n a high v a c u u m are the dihalides and t h e corresponding free halogens (45). Halides of dipositive y t t e r b i u m a r e prepared i n a similar manner (44). ACKNOWLEDGMENT
The a u t h o r is indebted to Professors J o h n C. Bailar, Jr., a n d A r t h u r W. Davidson for their valuahle rontributions to t h i s manuscript,.
(21) SELWOOD, P. W., Abstracts of Papers, Division of Physical and Inorganic Chemistry, American Chemical Society, Chicago, April 1948, p. 20 Sect. 0. (22) BAILAR, J. C., JR., AND C. F. CALLIS,paper presented before the Physical and Inorganic Division of the American Chemical Society a t the San Francisco meeting, March 27-April 1, 1949. (23) DEBOER, J . H., AND J. VAN ORUIONDT, British patent 579,817 (1946); Chem. Abstracts, 41, 1401 (1947). (24) BARBIERI, G. A., Atli acead. n u . Lincei, 13, 882 (1931). (25) MARSHALL, H., Proc. Roy. Snr. Rdinbu~gh,14, 203 (188G
-. ,. 27)
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(26) R ~ YP., , AND K. CHAKRAVARTY. J. Indian Chem. Soe.., 21. 47 (1944). (27) SELWOOD, P. W., J. Am. Chem. Sac., 55,4869 (1933). E. W., J. Chem. Phys., 2, 31 (1934); HELMS,A,, (28) NEUMAN, LITERATURE CITED AND W. KLEMM, Z. aw7g. U .allgem. Chem., 241,97 (1939). (1) BRUKL,A., AND G. ORTNER, Z. cZn0Tg. U allgem. cham,, 203, (29) KASSATOCEKIN, W., AND W. K o ~ o v ,J . Chem. Phys., 4, 23 (1931); KLEMM,W., AND I. SCHNICK, ibid., 226, 353 458 (1936). (1936); BRUKL,A., AND G. ORTNER,Monatsh., 56, 358 (30) PAULING, L., "The Nature of the Chemical Bond," 2nd od., 1930; NILSON, L. F., AND 0 . PETTERSON, Z. phwik. Chem., Cornell University Press, Ithaca, 1945, p. 272. 2, 657 (1888); THIEL, A,, A N D H. KOEI.SCH, Z. anorg. (31) GLEU,K., AND K. REHM,Z. anwg. u. allgem. Chem., 237, Chem., 66, 288 (1910). 79 (1938). . . (2) EMEL~US, H. J., AND J. S. ANDERSON, "Modern Aspects of (32) SVANN,A., JR., AND T. S. XANTHAKOS, J. Am. Chem. Soe., Inorganic Chemistry," D. Van Nostrand Company, Inc., 53,400 (1931). New York, 1939, pp. 144-5. O., Z. anorg. Chem., 12, 89 (1896); WATSON, E. R., F., AND H. Bum, Ann., 103,218 (1857); TURREN- (33) &.c, (3) WOHLER, J. Chem. Soe., 89, 578 (1906); BARBIERI,G. A., Atti. TINE, J. W., J . Ph,g8. Chem., 12, 448 (1908); SBORGI, U., accad. Lincei, 151, 16, II,72 (1907); BABOROYSRY, G., AND AND P. MARCHETTI, Numo cimento, 22, 151 (1921); DEL G. K U ~ M Z. A ,physik. Chem., 67,48 (1909); NOYES,A. A,, BOCA,M. C., He6. Chim. Acta, 16,565 (1933). D. DEVAULT,C. D. CORYELL, AND T. J. DEAHL, J. Am. A. W., AND F. E. JIRIK,J . Am. Chem. Soc. (in (4) DAYIDSON, Chem. Soe., 59, 1326 (1937). press). C., A N D W. RIEDEL,Z. anorg. Chem., 72, 219 (34) TUBANDT, (5) MALATESTA, L., Gu:. chim. ital., 71, 467, 580 (1941). (1911). AND E. SEGRO,P h g ~ . (6) con so^, D. R., K. R. MACKENZIE, Rev., 57, 459 (1940); 58, 672 (1940); S E G R ~ E., , K. R. (35) NOYES,'A.A., ET AL., .I. Am. Chem. Soc., 57, 1221, 1229, - 1316 1238. i1997). ~ - ~,.. . - - ~ A N D D. R. CORSON, ibid., 57, 1087 (1940); MACKENZIE, %. anorg, u. allgem. Chem., 158, LEININGER, R. F., AND E. SEGRB,paper delivered at a (36) JIRSA,F., AND J. JELINEK, 61 (1926). symposium of the Division of Physical and Inorganic ibid., 183, 193 (1929). Chemistry of the American Chemical Societ,~at Syracuse, (37) RUFF,O., AND E. ASCHBR, E. L. RODOWSKAS, AND J. C. W. FRAZER, New York, June 28-30, 1948, as reported in Chem. Eng. (38) EBERT, J. Am. Chem. Soc., 55, 3056 (1933); RUFF, O., AND M. News, 26, 2052 (1948). GIEBE,Angau. Chem., 47, 480 (1934). J., THISJOURNAL, 23, 559 (1946). (7) KLEINBERG, A., J. prakt. Chem., [I], 29, 175 (1843); PELIGOT, M. J., I,. S. F-STER,AND J. C. BAILAR,JR., Chem. (39) MOBERG, (8) COPLEY, E., Ann. ehim. phgs., [3], 12, 528 (1944). Revs., 30,227 (1942). C., AND E. CAZES,Compt. rend., 142,83 (1906); (9)POGGENDORFF, J. C., Pogg. Ann., 54,161 (1841); HABER, F., (40) MATIGNON, Z . Elektrorhem., 7, 215 (1900); PICK,W., ibid., 7, 713 PRANDTL, W., AND H. KOGL,Z. anorg. u . allgem. Chem., 172, 265 (1928); KLEMM, W., AND J. ROCKSTROH, ibid., (19W); G ~ u m G., , A N D H. GMELIN,ibid., 26, 153, 459 (1920). 176, 181 (1928); URBAIN, G., AND F. BOURION, Compt. , , rend., 153, 1155 (1911); JANTSCH, G., H. ALBER,AND H. (10) BUNTIN,A,, AND B. VLASOV, A d a Uniu. Vomnegiensis, 8, GRUBITSCH, Monatsh., 53-54, 305 (1929); BECK,G., h ~ ) No. 4, 6 (1935). W. Nomnc~r, Naturwissenschajten, 26, 495 (1938); %. anwg. Chem., 57, 290 (11) LUTHER,R., AND F. POKORNY, KLEMM, W., AND W. SCHUTH, Z. anorg. u. allgem. Chern., (1908). (12) HALL,R.. D., J . Am. Chem. Soc., 29, 692 (1907). 184, 352 (1929); SENFF,H., AND W. KLEMM, ibid., 242, 92 (1939). (13) NOYES,A. A,, D. DEVAULT,C. D. CORYELL, AND T. J. DEAHL,J . Am. Chem. Soe., 59, 1326 (1937). (41) YNTEMA,L. F., J . Am. Chem. Soe., 52,2782 (1930); MARSH, W., AND W. PASSARGE, Ber., 46, 1505 (1913). (14) TRAUBE, J . K., J. Chem. Sac., 1972 (1934); McCoy, H. N., J. Am. J. Am. Chem. Soe., 64, (15) EASTES,J . W., AND W. M. BURGESS, Chem. Soc., 58, 1577 (1936); BALL,R. W., AND L. F. 2715 (1942). ~ ~,~ J . Am. Chem. Sm., 52, 4264 (1930); PEARCE, YNTEMA, (16) BITREAGE, J. T., A N D W. C. FERNELLITS, ibid., 65, 1484 D. W., C. R. NAESAR,AND B. S. HOPKINS,Trans. Elee(1949) \.".-,. trochem. Sac., 69,557 (1936); MARsn, J . K., J . Chem. Soe., (17) DEASY,C. L., ibid., 67, 152 (1945). 1367 (1937). "The (18) YOST,D. M., H. RUSSELL,JR., AND C. S. GARNER. J . Research Nat. (42) LUNDELL, C . E . F., AND H. B. KNOWLES, Rare Earth Elements and Their Compounds," John Bur. Standards, 18, 629 (1937). Wiley and Sons, Inc., New York, 1947, pp:4-6. (43) JANTSCH, G., AND N. SKALLA, Z. anmg. u. allgem. Chem., (19) MEGGERS, W. F., Seiace, 105, 514 (1947). 193, 391 (1930). J . Am. Chem. Soc., (44) JANTSCH, (20) PAGEL,H. A., AND P. H. M. P. BRINTON, G., N. SKALLA, A N D H. MAWUREK, ihid., 201,207 51, 42 (1929). (1931). ~
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