A THESIS Topics in the Chemistry of Niobium and Tantalum Pentafluorides and other Higher Halides Submitted to the University of .Glasgow by J. C. Fuggle B.A. in part fulfillment of the reopj.ireme.nts for the degree of Doctor of Philosophy in the Faculty of Science Work presented in this thesis is the result of research carried out by the author, in the Chemistry Department of the University of Glasgow, between October 1968 and Kay -1971 except where specific reference is made to other publication ftLAS<30W 1 v/iivERsmn LIBRARY:_J ProQuest Number: 11012000 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 11012000 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 This thesis is dedicated to all those who have played a part in my education and in particular to my parents, whose share in the work involved was greatest, and probably most arduous. ”Ad apris ki bien conuist ahan" Song of Roland nThe converse is also true." - Ph.D student GLASGOW 1971 I gratefully record my obligation to my supervisors, Professor P. W. A. Sharp and Dr. J. M. Winfield for their encouragement, advice, tolerance, and patience during the course of my work. To my colleagues in the Chemistry Department, in particular to Dr. A. P. Lane, J. Dunsmuir, and I.Forrest I would like to express my gratitude for many helpful and stimulating discussions during the last three years. I am also grateful to the University of Strathclyde, and Dr. D. Adams of the University of Leicester for allovring me use of their Raman Spectrometers, to the technical staff of the University of Glasgow Chemistry Department who built some of my apparatus, and to Miss M. McCartney who proof­ read- most of this thesis. - I - Summary Research presented in this thesis falls into four- areas* 1) Vibrational spectra of pentafluorides. 2) Preparation and spectra of NbF^~ and TaF,_ complexed with Lewis- bases. 3) Preparation and some properties of some Kb, and Ta (V) fluoride-halides and pseudohalides. j \ Q h Nb n.q.r. spectra of some compounds derived from NbF.-. 3 93 Kb n.c.r. srectra of dbF-.L-, and vibrational soectraX of NbF,- and TaF- are inter ere ted in terms of a very small deviation from symmetry in the tetrameric molecules of the solid state. I.P. spectra suggest that WbF^, and TaF^ are polymeric in the liquid state up to at least 130°C, but that the Lev/is acid-base complexes formed by reaction of NbFc, y or TaFc with a scries of oxygen, and nitrogen donor molecules r contain no bridging fluorine atoms. Assignment of vibrational frequencies associated with the coordinated Lewis bases is Q3 almost complete. Vibrational and I-Tb n.q.r. soectral data of 1:2 complexes of NbF,-, and rj?aFc prove neither the absence y t/ or -•nreser.ee of NbF-- or fal’V” anions. o c Substitutions for P atoms in pentaflucrides by I-IICt9, Cl, Br, Cm, IIJ3, hCO (0) and (id'e) grcuios using the reacticj 1 /2 1 /2 The products of substitution reactions wore investigated by I.P., and Raman spectroscopy and x-ray powder photography. Evidence obtained suggests that the fluoride-diaDkylanides are weaker Lewis acids than the parent pentafluorides and consist of fluorine-bridged polymers. Evidence obtained from other mixedhalide materials is not sufficient to prove the Id s 0 nee of mixtures of compounds... 93 An investigation of the use of '^Nb n.q.r. spectroscopy as an aid to study of some niobium compounds is reported. Resonances observed for NbF.-, Nbf' .2Py, NbF_.CH CION, 5 5 5 2 NbFc.Meo0, RbF-.XeF-, and. (NbF-.)- XeF are assigned to the 5 2 ’ 5 2 ’ 5 2 2 ° °3 possible quadrupole transitions of the 9/2 Nb spin syste: and some conclusions relevant to the structures of the c o mp o und s a.r e p res e n t e d. - Ill - Contents section page I Introduction I References II Chapter 1; 'Pentafluorides and their Complexes with Lewis Bases. 1:1 Introduction 13 1:2 Results 21 1:3 Vibrational Spectra and Stereochemistry of Metal Pentafluorides 22 1:4 Stereochemistry of 1:1 and 1:2 Comr>lexes of Metal Pentahalides in the Solid State 37 1:3 Stereochemistry of Pentafluoride Adducts in the Vapour and Liquid State 48 1:6 Some Chemical Aspects-of Reactions of Pentahalides with Bases and Vibrational Spectra of Complex©d Bases 31 1:7 Reactions between Niobium and Tantalum Pentafluorides and Dialkyl Sulphides and Selenides. 84 1:8 Reactions of Pentafluorides with Dialky- 1 amines 84 1:9 Experimental 8? References 1C 4 - IV ~ section Chapter 2; Substitution Reactions of Pentafluorides. 2:1 Introduction 118 2:2 General Considerations 125 2:3 Nitrogen-Ketal Fluorine Compounds 133 Fluoride-Chlorides and Fluoride-Bromides 1*f2 2:3 Other Substitution Reactions 1^8 2:6 Experimental 151 93 ✓ Chapter 3j Nb n.q.r. Investigations of some Niobium Compounds. 3:1 Introduction 167 3:2 Results 185 3:3 Discussion 19^ 3:^ Experimental 205 References 207 Appendices Al Experimental Methods 210 All Activity of I.R. & Raman. Modes in Pentafluoride Oligomers 217 AlII Observed Vibrational Spectra, X-ray Powder Photograph, Data 221 AIV Ratios of Energies of n.o.r. Transitions 93 for the rib 9/2 Spin System 2d1 A' V Suggestions for Further VJork 2-i2 introduction The history of investigations of halogens and halides is long and eventful. There can be little doubt that the corrosive suffocating, greenish-yellow fumes of chlorine must have been known from the thirteenth century by those who made, and used, (1 ) aqua regia. The recognition of chlorine as an elementnt MBSwas bound up with the evolution of the concept of "elements1 and with bromine, and iodine (established as elements in 182 ^ and 1813 ^ ^ respectively) it has been recognised as an element from the period at the beginning of the ninteenth century when "chemistry" may be said to have pvolved from alchemy. Chlorine, bromine, and iodine may all be isolated by treatment of halides with oxidising agents, but no satis­ factory ’chemical’ method for isolation of fluorine has been found and only electrolytic methods are extensively used. Although the existence of an element "fluorine" was postulated (6) in 1810 experimental difficulties, largely attributable to the extreme reactivity of fluorine, delayed its isolation until i88'f.(7) Many of the binary fluorides were known and recognised before the isolation of fluorine itself and by the end of the first third of the twentieth century fluorides of most of the non-metallic, and main-group metallic elements, .nc. a number of those of transition metals, were knew-n. however, during, and after the Second 7/orld 'far a ronmwd interest in - 2 - fluorine chmoistry rev;:; rded by the discovery of many new binary fluorides, culminating in the spectacular discovery of noble-gas fluorides in 1962^*'^. It should not be inferred from the differences in the history of these halogens that either fluorine, or fluorides, are fundamentally different from the other halogens, or halides. The chemistry of the halides is more dependent on the metal, or non-metal, combined with halogen, and its oxidation state, than the halogen present (e.g. NbF;- shows more similarity to NbCl^ than PF_). 1 ) ■' 7 > . ’ ’ Fluorine atoms bond more strongly to other atoms and are more electronegative than other halogens and the P-F bond strength is weaker th~n the corresponding bond strength of the other halogens. This leads to higher reactivity of fluorine, with respect to other halogens, and a greater thermodynamic stability of fluorides with respect to ether halides. It is no coincidence that modern chemistry evolved from alchemy at about the same time that modern methods of scientific glassblowing were developed Use of silicate-based glasses has become .almost fundamental in modern experimental chemistry. Fluorine, and ...any fluorides, react with silicate glasses, either alone, or in the presence of minute amounts of vat or -which act as catalysts i • o • ::f_+i-i?o-* i-:of__ 0 +2HF SiO^-r^iF ** 5iF,+2E 0 Phosphate glasses are not attacked by fluorides, but arc not suitable for glass blowing. Although many fluorides, s.;. (11) v I F ^ . do not react wrtn drv ...lass very snail amounts of b 7 water, or hydrogen fluoride, catalyse the reaction -with glass which itself contains water, both in its surface layers and in the bulk, which can never be entirely removed by (12) degassing. Free hydrogen fluoride may also be produced by reaction of fluorides with hydrocarbon, and rubber-based greases. Many higher halides are air, and/or moisture sensitive and dry-bo;; techniques have been developed to handle air- sensitive materials. However no dry-boxes are perfect (come are worse than others) and whenever a moisture-sensitive fluor is used in a dry-box it will inevitably pick up some moisture. The above r...marks suggest bhat experimental work with higher halides will always be done in conditions the t are less than perfect, but that great care should ’be taken to ensure that water levels are acceptable.