Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1963 Preparation and reactions of some lower tungsten halides and halide complexes Theodore Martin Brown Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Inorganic Chemistry Commons Recommended Citation Brown, Theodore Martin, "Preparation and reactions of some lower tungsten halides and halide complexes " (1963). Retrospective Theses and Dissertations. 2522. https://lib.dr.iastate.edu/rtd/2522 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. This dissertation has been 64—3858 microfilmed exactly as received BROWN, Theodore Martin, 1934- PREPARATION AND REACTIONS OF SOME LOWER TUNGSTEN HALIDES AND HALIDE COMPLEXES. Iowa State University of Science and Technology Ph.D., 1963 Chemistry, inorganic University Microfilms, Inc., Ann Arbor, Michigan PREPARATION AND REACTIONS OF SOME LOWER TUNGSTEN HALIDES AND HALIDE COMPLEXES by Theodore Martin Brown A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Inorganic Chemistry Approved: Signature was redacted for privacy. Signature was redacted for privacy. Signature was redacted for privacy. Dean^ Gr^^uat^ Co] Iowa State University Of Science and Technology Ames, Iowa 1963 ii TABLE OF CONTENTS Page INTRODUCTION 1 PART I. PREPARATION AND REACTIONS OF SOME 3 TUNGSTEN HALIDES REVIEW OF PREVIOUS WORK 4 EXPERIMENTAL 12 RESULTS AND DISCUSSION 36 SUMMARY 67 SUGGESTIONS FOR FUTURE WORK 69 PART II. SPECTROPHOTOMETRIC AND SUSCEPTIBILITY 72 STUDIES OF SOME TUNGSTEN(IV) COMPLEXES REVIEW OF PREVIOUS WORK 73 EXPERIMENTAL 75 RESULTS AND DISCUSSION 82 SUMMARY 115 SUGGESTIONS FOR FUTURE WORK 116 BIBLIOGRAPHY 118 ACKNOWLEDGEMENTS 123 1 INTRODUCTION Tungsten derives its name from the Swedish tungsten - heavy stone. Another common name, Wolfram (Wolfrahm = Wolf's foam), resulted from the interference of the tungsten mineral in tin ores in the smelting of tin by slagging or eating up the tin. The metal was discovered by Scheele (1) in 1781. At present, the chief ores are wolframite (iron, manganese tungstate), scheelite (calcium tungstate), and stolzite (lead tungstate). The purification of tungsten from its ores is relatively simple. The wolframite is first converted to alkaline tungstate which is then changed into tungsten(VI) oxide. The oxide is reduced with hydrogen to give the pure metal. Among its more valuable commercial uses are the preparation of high-speed tool steels and incandescent-lamp filaments. Due to their ease of preparation, the halides containing tungsten in its higher oxidation states such as plus five and plus six have received considerable attention. These compounds, especially tungsten hexachloride, have found commercial uses as catalysts in the polymerization of olefins (2), the alkyla- tion of parafins with olefins to motor fuels (3), fluorocarbon manufacture (4), dehydrochlorination of polychloroethanes (5), 2 and organic synthesis (6). On the other hand, only little interest has been shown in the lower halides of tungsten. This is apparently due to the difficulty with which these materials are obtained and their increased inertness as the oxidation state of tungsten in these compounds is decreased. While the tungsten(IV) halides are unstable with regard to hydrolysis in the presence of moist air and undergo dispro- portionation on heating, the tetrahalodi(pyridine)tungsten(IV) compounds show exceptional stability in this respect. Thus the question arises as to whether these complexes retain the initial structure of the parent halide or have a unique struc­ ture of their own giving rise to this increased stability. To enlarge the chemistry of tungsten in its lower oxidation states, it seemed desirable to undertake a study of some of the lower halides of tungsten and their corresponding compounds. This dissertation is divided into two parts. Part I is concerned with the preparation and reactions of some tungsten halides while Part II is devoted to spectrophotometric and magnetic susceptibility studies of some tungsten(IV) complexes. Since this investigation was carried out on the chlorides and bro­ mides of tungsten, only these halides will be discussed. 3 PART I. PREPARATION AND REACTIONS OF SOME TUNGSTEN HALIDES 4 REVIEW OF PREVIOUS WORK The Preparation and Properties of Some Tungsten Halides Tungsten(VI) halides Direct chlorination of tungsten metal at temperatures greater than 600°C. results in the formation of the hexachlor- ide as illustrated in Equation 1. If oxygen is present, W + 3C12 = WC16 (1) oxychlorides of tungsten are also formed. Oxygen and traces of moisture may be removed by first heating the metal in a stream of hydrogen at 700 to 1000°C. The resulting hexachlor- ide is further purified by repeated sublimations (7, 8, 9, 10, 11). Michael and Murphy (12) prepared tungsten(VI) chloride by heating carbon tetrachloride and tungsten(VI) oxide in a sealed tube. The reaction which takes place is illustrated in Equation 2. The necessary conditions to prevent the formation W03 + 3CC14 = WClfc + 3COC12 (2) of oxychlorides are: (1) excess carbon tetrachloride; (2) no oxygen or moisture present; and (3) sufficiently high tempera­ ture . Other methods available for the preparation of tungsten(VI) chloride include the chlorination of tungsten(II) sulfide and 5 the action of phosphorus(V) chloride on tungsten(VI) oxide (13, 14, 15). However, in these cases the resulting product is difficult to purify. Tungsten(VI) chloride is a dark violet or steel blue crystalline material, easily fused and volatilized. It has a melting point of 284°C. and a boiling point of 336.5°C. (16). The following transformations have been observed (16). solid o (152° - 226.93°) : log Pmm=10,732 - ^582 (3) solid B (226.93°- 284°) : log Pmm=9,255 - (4) liquid (284° - 362°) : log Pmm=8.352 - (5) The heat of vaporization of the hexachloride has also been determined. a vapor: 20.94 kcal/mole 0 vapor: 17.54 kcal/mole liquid vapor: 15.24 kcal/mole The electrical conductivity of liquid tungsten(VI) chloride was found to be very low and varied with temperature. Electron diffraction shows that the WCl^ molecule is a regular octahedron having a W-Cl distance of 2.26% (17). The same form has been observed in the solid by crystal structure measurements (18). The hexachloride undergoes hydrolysis in the presence of 6 moist air but is relatively stable if very pure. In the presence of moisture the compound slowly transforms to the oxychloride, WOCI4, and the hydrate, WO3•2H2O. Tungsten(VI) bromide was first prepared by Schaffer and Smith (19) by passing a stream of nitrogen saturated with bromine vapor over warmed tungsten. The hexabromide sublimes readily and is deposited as blue-black needles. Due to the instability of this compound at elevated temperatures (it decomposes at temperatures greater than 200°C.) it is diff­ icult to obtain free from lower bromides. More recently, Shchukarev, Novikov, and Kokovin (20) prepared this substance by reacting bromine with tungsten hexacarbonyl at 0°C. as illustrated by Equation 6. W(C0)6 + 3Br2 - WBr6(s) + 6C0(g) (6) In structure and properties tungsten(VI) bromide closely resembles the hexachloride. Tungsten(V) halides Reduction of tungsten(VI) chloride with hydrogen at 200°C., according to Equation 7, results in the formation of the penta- 2WC16 + H2 = 2WCI5 + 2HC1 (7) chloride (7, 8, 21). The resulting product is separated from the other chlorides by sublimation in a stream of nitrogen. 7 This material is also one of the products resulting from the disproportionation of tungsten(IV^ chloride. The penta- chloride prepared by this method is relatively pure. Tungsten(V) chloride is a deep purple-black solid which melts at 248°C. and boils at 276°C. Like the hexachloride, liquid tungsten(V) chloride has a relatively low electrical conductivity. The material is hygroscopic and sensitive to oxidation by the air. In this respect it is less stable than the hexachloride. Direct combination of the elements at 800°C. results in tungsten(V) bromide (9, 21, 22). Generally some hexabromide is also formed if an excess of bromine is present. The pure pentabromide is obtained by subliming the product at temper­ atures greater than 200°C. with adequate provision for removing the bromine. Reduction of the hexachloride with hydrogen bromide at 250 to 300°C. yields the pentabromide (13). The pentabromide is a crystalline brown-black solid melt­ ing at 286°C. and boiling at 392°C. with slight decomposition (20). The substance is unstable in air, undergoing hydrolysis and partially decomposing at elevated temperatures to give lower bromides. In the presence of oxygen, the oxybromide, W02Br2, is formed (13, 23). It is also possible to replace 8 the bromine to give chlorides, sulfides, and phosphides using hydrogen chloride, hydrogen sulfide, and phosphine, respec­ tively. Tungsten(IV) halides The first synthesis of tungsten(IV) chloride involved the hydrogen reduction of tungsten hexachloride (7, 8, 21). Other methods of preparation include the chlorination of tungsten(IV) oxide with carbon tetrachloride in a sealed tube at 280°C. (12) and the reduction of tungsten(VI) chloride with red phosphorus (24). Knecht and Hilbert (25) prepared tungsten(IV) chloride by the reduction of the hydrate, WOg'ZHgO, with zinc in concen­ trated hydrochloric acid. However, the anhydrous tetrachloride can not be isolated by this method. The tetrachloride of tungsten is a crystalline, nonvola­ tile material which hydrolyzes readily. The compound dispro- portionates when heated above 300°C.to give the di- and penta- chlorides of tungsten. The mechanism for this reaction is not known. Tungsten(IV) bromide has been prepared by McCarley and Brown (26).