FLUOROSULFATE DERIVATIVES OF NIOBIUM AND TANTALUM AND THEIR BEHAVIOR AS COMPONENTS OF NOVEL SUPERACID SYSTEMS By WALTER VLADIMIR CICHA B.Sc, The University of British Columbia, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1989 © Walter Vladimir Cicha, 1989 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 or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) ii ABSTRACT The goal of this study was to develop new superacid systems based on fluorosulfuric acid, HSO3F, (the strongest monoprotonic BrOnsted acid) and metal fluorosulfates capable of acting as Lewis acids. The in situ oxidation of niobium and tantalum in HSO3F by bis(fluorosulfuryl) peroxide, S2O6F2. resulted in the formation of the highly solvated Lewis acids M(S03F)5 with M = Nb or Ta. Based on electrical conductivity measurements, both solutes were found to behave as moderately strong, monoprotonic acids in HSO3F, with Ta(SC>3F)5 the markedly stronger acid of the two. The Hammett Acidity Function, HQ, determined for the HS03F-Ta(S03F)s superacid system confirmed its high acidity, which clearly exceeds that of HSO3F-SDF5 ("Magic Acid"), the most frequently used superacid system. In addition, both the solubility and acidity in HSO3F of the two new Lewis acids are vastly greater than those of the analogous fluorides, NbFs and TaFs, in either HF or HSO3F. The high solubility of Nb(S03F)s and Ta(S03F)s allowed the study of their solution behavior, using *H, 19F and 93Nb NMR, as well as Raman spectroscopy. Evidence for the existence of M(SC>3F)5, with M = Nb or Ta, comes from the synthesis of the salts Mx'[M(S03F)5+x], with M' = Cs or Ba and x = 1 or 2, which were characterized by vibrational spectroscopy. Salts with anions of the types [M(S03F)6]" or [M(S03F)7]2- have previously not been isolated. In solution, multicomponent equilibria appeared to be present between the anions [M(S03F)6]" and [M(S03F)7]2- with M = Nb or Ta. Synthesis of TaF4(S03F) from a 4:1 mixture of TaFs and Ta(S03F)s in HSO3F as well as the formation of NbF2(S03F)3 from a concentrated solution of HSO3F- Nb(S03F)5 suggested the possibuity "of a new family of superacid systems of the type iii HS03F-MFx(S03F)5-x, with x = 1-4. Initial investigations are reported. In addition, preliminary work dealing with analogous trifluoromethyl sulfuric acid (HSO3CF3) systems is also discussed. During the course of this study, bis(fluorosulfuryl) peroxide (S2O6F2) was found to behave as a weak base soluble only in acids stronger than 100% sulfuric acid. Addition of potassium fluorosulfate, KSO3F, to reduce the acidity of HSO3F also lowered the acid's ability to dissolve S2O6F2. The HSO3F-S2O6F2 system was studied using Raman, IH and WF NMR, and ESR spectroscopy, which led to evidence for proton transfer, hydrogen-bridging and fluorosulfate exchange between the solvent (HSO3F) and solute (S2O6F2). iv TABLE OF CONTENTS Page Abstract ii Table of Contents iv List of Tables x List of Figures xii List of Abbreviations xv Acknowledgements xvii CHAPTER 1. INTRODUCTION 1 LA. General Overview 1 l.B. Properties of Fluorosulfuric Acid .6 l.C. Superacid Systems and Their Applications .10 l.C.l. Establishing the Hammett Acidity Function 10 l.C.2. Superacid Systems 12 l.C.3. Synopsis of Superacid Applications 21 ID. Some Properties of S2O6F2 27 IE. Preparation of Metal Fluorosulfates 30 1JB.1. Solvolysis in HSO3F 30 1B.2. The Use of S2O6F2 31 l.E.3. SO3 Insertion Reactions 35 I.F. Vibrational Characterization of the Fluorosulfate Group 36 IF.I. Symmetry Considerations 36 V 1 F.2. Effect of Various Ruorosulfate Coordination on Vibrational Frequencies 37 1. G. Multinuclear NMR Spectroscopy Studies in HSO3F 41 References 45 CHAPTER 2. GENERAL EXPERIMENTAL 53 2. A. Introduction 53 2.B. Apparatus 54 2.C. Instrumentation and Methods 60 2. D. Chemicals 67 References 75 CHAPTER 3. THE SYSTEM F1.UOROSULFURIC ACID (HSO3F) AND BISCrT.UOROSULFURYL) PEROXIDE (S2O6F2): A SOLUTION STUDY 76 3. A. Introduction .76 3.B. Experimental. 78 3.C. Results and Discussion 79 3.C.I. Raman Spectroscopy 79 3.C.2. Solubility Studies of S2O6F2 in Strong Protonic Acids 84 3.C.3.19F and IH NMR Spectroscopy Studies 86 3.C.3.a. Single Acid-Phase Systems 87 3.C.3.b. Dual Phase Systems .94 3.C.4. ESR Spectroscopy Study of the Solvated Ruorosulfate Radical. 91 3.D. Summary and Conclusions 100 References 102 vi CHAPTER 4. FLUOROSULFATE DERIVATIVES OF NIOBIUM(V) 105 4 A. Introduction 105 4.B. Experimental 107 4.B.I. In Situ Synthesis of Pentakis(fluorosulfato)niobium(V), Nb(S03F)5 107 4.B.2. In Vacuo Degradation of Nb(SC-3F)5 107 4.B.3. Derivatives of Nb(S03F)s 108 4.B.4. Attempted Syntheses of Additional Nb(S03F)s Derivatives ... 110 4.B.5. Synthesis of Difluorotris(fluorosulfato)niobium(V), NbF2(S03F)3 Ill 4.C. Results and Discussion 113 4.C.I. Synthesis and General Discussion 113 4.C.l.a. In Situ Synthesis of Nb(S03F)s 113 4.C.l.b. Alternative Attempts to Isolate Nb(S03F)s 114 4.C.1.C Derivatives of Nb(S03F)5 116 4.C.l.d. Attempted Syntheses of Other Nb(S03F)5 Salts. ... 118 4.C.l.e. Synthesis of NbF2(S03F)3 119 4.C.2. Vibrational Spectroscopy 120 4.C.2.a. Csx[Nb(S03F)5+x], with x = 1 or 2 120 4.C.2.b. Ba[Nb(SC>3F)7] and Other Derivatives 124 4.C.2.C NbF2(S03F)3 126 4.C.3. Powder X-ray Diffraction Studies 130 4T). Conclusion . 131 References . 132 vii CHAPTER 5. FLUOROSULFATE DERIVATIVES OF TANTALUM(V) 134 5 A. Introduction 134 5.B. Experimental 135 5.B.I. In Situ Synthesis of Pentakis(fluorosulfato)tantalum(V), Ta(S03F)s 135 5.B.2. Derivatives of Ta(S03F)5 136 5.B.3. Attempted Synthesis of Additional Ta(S03F)s Derivatives . .138 5.B.4. The Synthesis of Terj^fluoro(fluorosulfato)tantalum(V), TaF4(S03F) 140 5.C. Results and Discussion 140 5.C.I. Synthesis and General Discussion 140 5.C.l.a.m Sim Synthesis of Ta(S03F)5 140 5.C1.D. Additional Attempts to Obtain Ta(SC>3F)5 142 5.C.1.C Derivatives of Ta(S03F)5 143 5.C.l.d. Attempted Syntheses of Other Ta(S03F)s Derivatives .145 5.c.l.e. Synthesis of TaF4(S03F) 147 5.C.2. Vibrational Spectroscopy 148 5.C.2.a. CsxrTa(S03F)5+x], with x = 1 or 2 148 5.C.2.b. Other Ta(S03F)5 Derivatives . 153 5.C.2.C TaF4(S03F) 154 5. D. Conclusion 157 References 158 CHAPTER 6. SOLUTION STUDIES IN HSO3F 160 6. A. Introduction 160 6.B. Experimental 165 viii 6.B.I. Electrical Conductivity Studies 165 6.B .2. Hammett Acidity Studies 166 6.B.3. Multinuclear NMR and Raman Spectroscopy Studies 167 6.C. Results and Discussion 168 6.C.I. Electrical Conductivity Studies 168 6.C.l.a. Electrical Conductance Measurements 168 6.C.l.b. Interpretation of Electrical Conductivity Data 176 6.C.1.C The [M(S03F)7]2-[M(S03F)6r EquUibrium Systems (M = NborTa) 191 6.C.2. The Hammett Acidity Function of the HSO3F- Ta(S03F)s System 196 6.C.2.a. Determination of Ho values 196 6.C.2.b. The Acidity of HSO3F - Ta(S03F)5 198 6.C.3. Multinuclear NMR Studies 204 6.C.3.a. Mx'[M(SC>3F)5+x] Solutions, with M' = Cs or Ba and x=lor2 204 6.C.3.b. M(S03F)5, M(S03F)5-S206F2 and M(S03F)5-MF5 (M = Nb or Ta) Systems 216 6.C.4. Raman Spectroscopy Studies of M(S03F)5-MFs (M = Nb or Ta) Solutions 229 6. D. Conclusion 232 References 234 CHAPTER 7. TRIFLUOROMETHYL SULFATE DERIVATIVES OF NIOBIUM(V) AND TANTALUMfV) 237 7. A. Introduction 237 7.B. Experimental 238 ix 7.B.I. Synthesis of Ted^uoro(rrifluoromemylsulfato^ TaF4(S03CF3) 238 7.B.2. Attempted Synthesis of Cesium Hexakis(tjifluoromeftylsulfato) tantalate(V) 239 7.B.3. Attempted Synthesis of TerrafluoTo(ttifluoromethylsulfato) niobium(V) 239 7.B.4. Attempted Synthesis of Penr^s(rrifluoromethylsulfato) tantalum(V) 240 7.C. Results and Discussion 240 7.C.I. Syntheses and General Discussion 240 7.C.l.a. TaF4(S03CF3) 240 7.C.l.b. Attempted Syntheses of M(S03CF3>5 (M = Nb or Ta) and Cs[Ta(S03CF3)6] 242 7. C2. Vibrational Spectroscopy Studies 243 7.C2.a. TaF4(S03CF3) 243 7.C2.b. "Cs[Ta(S03CF3)6]" 244 7. D. Conclusion 247 References 248 CHAPTER 8. GENERAL CONCLUSIONS 249 8. A. Summary 249 8.B. Exploratory Investigations and Suggestions for Future Work. 251 8. B.I.