CHROMIUM TETRAFLUORIDE and RELATED COMPOUNDS By
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CHROMIUM TETRAFLUORIDE AND RELATED COMPOUNDS by IOGINDER NATH SADANA M.Sc., The University of Agra, 1953 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1963 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Chemistry The University of British Columbia, Vancouver 8, Canada. Date April. 1963 GRADUATE STUDIES The University of British Columbia, • FACULTY OF GRADUATE STUDIES Field of Study: Inorganic Chemistry Topics in Inorganic Chemistry H.C. Clark PROGRAMME OF THE . N. Bart lett W.R. Cullen FINAL ORAL EXAMINATION Topics in Organic Chemistry D.E. McGreer J.P. Kutney FOR THE DEGREE OF R. Bonnet Advanced Inorganic Chemistry N. Bartlett DOCTOR OF PHILOSOPHY H.C. Clark Seminar D.E. McGreer of Related Studies: Structure of Metals II E. Teghtsoonian YOGINDER N. SADANA Physical Metallurgy J.A.H. Lund Applied Chemical Metallurgy E. Peters Mrs. A.M. Armstrong B.Sc, University of Agra, 1951 M.Sc, University of Agra, 1953 SATURDAY, MAY 4th, 1963, at 9:30 A.M. IN ROOM 261, CHEMISTRY BUIDING COMMITTEE IN CHARGE Chairman:. F.H. Soward N. Bartlett K.B. Harvey H.C. Clark C.A. McDowell F. W. Dalby E. Teghtsoonian. G. Dutton . J, Trotter External Examiner:. A.G. Sharpe Department of Inorganic Chemistry University of Cambridge Cambridge, England CHROMIUM TETRAFLUORIDE AND RELATED COMPOUNDS ABSTRACT molecule of bromine trifluoride per molecule of the com• The present investigation was concerned with a study, plex, if the removal of excess bromine trifluoride, of the preparation and properties of chromium tetra- after the reaction, was carried out at 100°C-. How• fluoride and its complexes; magnetic properties and X- ever, if removal was carried out at 160°C, the pure . ray structures were also studied. Attempts to prepare complexes were obtained. the pentafluoride of chromium using fluorinating agents other than fluorine were unsuccessful. Complexes of the type A2CrF^, where A =;.K, or Cs, were prepared in bromine trifluoride solutions„ The Chromium tetraf luoride was prepared by the, action of presence of extra bromine trifluoride in the molecule fluorine on the heated metal, the.products being invola- of the complex compound affected the structure seriously tile chromium trifluoride, volatile chromium tetra- in potassium complexes but had no effect on cesium fluoride, and more volatile fluorides which were con• complexes. Thus K^CirF^O,, SErF^ was tetragonal and on densed at "78°C. The best yields of chromium tetra• heating at 160°C in vacuo yielded the cubic modification 00 5BrF atl< fluoride were obtained at 3.50°C and with a moderate flow of pure K2CrFg; Cs' 3 ' * Cs2CrF6 were, both rate of fluorine. cubic. Chromium tetrafluoride is a glassy solid which forms Reactions of chromium trioxide with bromine trifluor• blue vapours when heated. It does not dissolve in the ide, bromine pentafluoride, and chlorine trifluoride usual organic solvents and is hydrolysed readily in were also investi.gate.de With bromine, fluorides, the moist air. It is paramagnetic, the moment corresponding products obtained were the corresponding adducts of to two unpaired electrons, and has a Weiss Constant of CrOFg. These are very reactive and sensitive to moist -70°. air. The compounds are paramagnetic. Chemically, chromium tetrafluoride is surprisingly The reaction with chlorine trifluoride was very inter• inert and at room temperature does not react with esting because the appearance of the product depended on ammonia, pyridine, sulphur dioxide, sulphur trioxide, the experimental conditions. If the reaction was carried iodine pentafluoride,bromine trifluoride, bromine penta- out at ordinary temperature, the product was a buff- fluoride, chlorine trifluoride, or selenium tetra• coloured powdery mass, but if the reaction was performed fluoride. However, it reacts instantaneously with water by passing chlorine trifluoride vapour over heated giving Cr+3 and Cr04~2 ions in solution. When heated chromium trioxide (100--120°C), the product was a brick- with bromine trifluoride for longer periods, reaction red substance. Chemical analyses and magnetic measure• occurs to give CrFg'O.5BrF3> On heating with a mixture ments indicated that both these products were identical of bromine trifluoride and bromine pentafluoride, a and had the composition CrOFg'0.25C1F3.- The brick-red wine-coloured solution was obtained, and the residue product could be converted into the light buff-coloured after distillation of volatile materials was CrOF3'0.25 powdery mass by heating at 70°C in vacuo. BrF3. The reaction of selenium tetrafluoride with chromium tetrafluoride at 120°C yielded two compounds, Reactions of potassium dichromate with bromine tri• CrF3.SeF4 and CrF2.SeF4. fluoride, bromine pentafluoride, and chlorine tri• fluoride were also investigated. Potassium dichromate Complexes of the type ACrF^, where A = K, Rb, or Cs, reacted with these smoothly at room temperature and the were prepared for the first time, by heating the respec• product of reaction in each case was KCrOF^. tive alkali metal chloride and chromium tetrafluoride in a 1:1 molar ratio in bromine trifluoride. The resulting complex compounds contained half a ii ABSTRACT The present investigation was concerned with a study of the preparation and properties of chromium tetrafluoride and its complexes; magnetic properties and X-ray structures were also studied. Attempts to prepare the pentafluoride of chromium using fluorinating agents other than fluorine were unsuccessful. Chromium tetrafluoride was prepared by the action of fluorine on the heated metal, the products being involatile chromium trifluoride, volatile chromium tetrafluoride, and more volatile fluorides which were condensed at -7&°C. The best yields of chromium tetrafluoride were obtained at 350°C and with a moderate flow-rate of fluorine. Chromium tetrafluoride is a glassy solid which forms blue vapours when heated. It does not dissolve in the usual organic solvents and is hydrolysed readily in moist air. It is paramagnetic, the moment corresponding to two unpaired electrons, and has a Weiss Constant of -70°. Chemically, chromium tetrafluoride is surprisingly inert and at room temperature does not react with ammonia, pyridine, sulphur dioxide, sulphur trioxide, iodine penta- " fluoride, bromine trifluoride, bromine pentafluoride, chlorine trifluoride, or selenium tetrafluoride. However, it reacts instantaneously with water, giving Cr+^ and CrO^""^ ions in solution. When heated with bromine trifluoride for longer periods, reaction occurs to give CrF^•0.5BrF-D)• On iii heating with a mixture of bromine trifluoride and bromine pentafluoride, a wine-coloured solution was obtained, and the residue after distillation of volatile materials was CrOF^O^BrF^. The reaction of selenium tetraf luoride with chromium tetrafluoride at 120°C yielded two compounds, CrFySeF^ and CrF2»SeF/f. Complexes of the type ICrF^, where A = K, Rb, or Cs, were prepared for the first time, by heating the respective alkali metal chloride and chromium tetrafluoride in a 1:1 molar ratio in bromine trifluoride. The resulting complex compounds contained half a molecule of bromine trifluoride per molecule of the complex, if the removal of excess bromine trifluoride, after the reaction, was carried out at 100°C. However, if removal was carried out at 160°C, the pure complexes were obtained. Complexes of the type A2CrF6, where A = K or Cs, were prepared in bromine trifluoride solutions. The presence of extra bromine trifluoride in the molecule of the complex compound affected the structure seriously in potassium com• plexes but had no effect on cesium complexes. Thus K2CrF^'0.5BrF^ was tetragonal and on heating at 160°C in, vacuo yielded the cubic modification of pure KgCrF^; Cs2CrF6'0.5BrF2 and Cs2CrF£ were both cubic. Reactions of chromium trioxide with bromine tri• fluoride, bromine pentafluoride, and chlorine trifluoride were also investigated. With bromine fluorides, the iv products obtained were the corresponding adducts of CrOF^. These are very reactive and sensitive to moist air. The compounds are paramagnetic. The reaction with chlorine trifluoride was very- interesting because the appearance of the product depended on/ the experimental conditions. If the reaction was carried out at ordinary temperature, the product was a buff-coloured powdery mass, but if the reaction was performed by passing chlorine trifluoride vapour over heated chromium trioxide (100—120°C), the product was a brick-red substance. Chemical analyses and magnetic measurements indicated that both these products were identical and had the composition CrOF^'O^SClFo,. The brick-red product could be converted into the light buff- coloured powdery mass by heating at 70°C in vaqup. Reactions of potassium dichromate with bromine trifluoride, bromine pentafluoride, and chlorine trifluoride were also investigated. Potassium dichromate reacted with these smoothly at room temperature and