SOME SALTS of VERY STRONG ACIDS. by Kenneth Charles Moss. a Thesis Presented in Partial Fulfilment of the Requirements for the D
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SOME SALTS OF VERY STRONG ACIDS. By Kenneth Charles Moss. A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy of the University of London* AUGUST 1962. -1- ABSTRACT An investigation of monohydroxyfluoroborates was undertaken with reference to the sodium, potassium and tetraalkyl ammonium salts as the existence of these, compounds is in some doubt. Sodium and potassium monohydroxyfluoroborates were prepared and characterised, but the tetraalkylammonium salts could not be prepared. Several fluoroborate metal hydrates were prepared and their X-ray photographs indexed. They are found to be isomorphous with the corresponding perchlorates. It was found that silver(2) fluoride reacts with boron trifluoride to give silver(1) fluoroborate. A study oil the solubility of anhydrous first-row transition metal perchlorates, fluoroborates, trifluoroacetates, hexafluoro -phosphates, -vanadates, -silicates and -titanates in organic solvents such se benzene, toluene,ether and nitro- methane was carried out. The d-d spectra of the solutions of these salts in ether were obtained. The preparation of solid anhydrous fluoroborates, perchlorates and trifluoro- acetates from non-aqueous solvents was investigated and mum perchlorates and trifluoroacatates were obtained. Magnetic measurements were made on the solid trifluoroacetates and on solutions of the perchlorates in ether. -12- The stability of complexes of phosphorous penta- fluoride with Group V triaryls was investigated, and.it was found that only triphenylphosphine forms a stable complex. Phosphine-metal-fluorides of Pt, Pd and Ir were prepared from phosphlne-metal-hydrides and are the first complexes to be prepared with both phosphine and fluorine bonded to the same metal atom. The existence ofid4PLIPd(0) has been disproved and io shown to be iAPLIPdHs. The compound APhiPt[C0i2F2 has also been prepared. No correspondin; first-row transition meta/ complexes could be prepared. .,-3- ACKNOWLEDGEMENTQ.., ? The work in this thesis was carried out in the Inorganic Chemistry Laboratories of the Imperial College of Science and Technology, London, and in the Royal College of Science and Technology, Glaegow. I wish to express my sincere thanks to my supervisor, Dr. E. R. Roberts,and to Dr. D.W.A. Sharp for his continued .help and encouragement. Thanks are due also to Dr. L. Pratt for help with n.m.r. measurements and to the Microanalytical Departments in both London and Glasgow. I am'indebted to Imperial Chemical Industries Ltd., Fisons Ltd., and the United States Navy (European Research Programme, Contract No. N 62258-3061) for financial support. -4- CONTENTS. Page. Abstract 1. Acknowledgements. 3. Introduction. 5. Chapter I. Some Fluoroborates and Monohydroxyfluoroborates, 11. Chapter 2. The Preparation of Some 1st Row Transition Metal Salts of Strong Acids. 67. Chapter 3. Some Physical and Chemical Properties of lst Row Transition Metal Fluoreborates, Perchiorates and Trifluoroacetates. 104. Chapter 4. Some Phosphine Fluoride Complexes. 148. Chapter 5. Molybdenum and Tungsten Phthalocyanines, 179. References. 184. -5- INTROD. UCTIO N The study of, fluorine chemistry, intensified because of the nuclear programme developed during the last World Wary has received further stimulation from the preparation of fluorocarbons and from their interesting properties. These fluorOearbons have many uses such as inert plattice, aerosols, dielectrics, lubricants, solvents and pharmaceuticals. The study of fluorine derivatives of carbon opens up a vast new field of chemistry in the same way that the boron hydrides would seem to do. The importance of complex anions in. catalysis (F2iedel and Crafts type) is becoMing increasingly rare obvious0 Strong acids usually provide such anions. The strength of an acid depends - not only on the nature of the acid itself but also on the.medium in which it is dissolved. For example nitric acid acts as• an acid in water but as a base in hydrogen fluoride. HNO3 + nH20 [11,ni + ion r + NO3— HNO3 + nHF [H21105 if (FnIlmeir The complex fluoro acids are all extremely strong acids due to the nature of the very electronegative fluorine. -6- Fluoroboric acid, for example, can only exist in solution when it is protonated;. no evidence for a 1:1 complex between hydrogen fluoride and boron trifluoride has been found (McCauley and Lien 1951). Isolation by itself would involve divalent fluorine or pentavalent boron or a free proton; similar conditions prevail for other fluoro-anions e.g. PPG -. A few examples of fluorine bridges are known however; the antimony pentafluoride- arsenic trifluoride complex has been given the structura (Muetterties and Phillips 1957) and arsenic fluorosuiphonate the structure FN N 0 0 .2A\ As F SO 0 0/ 0S---F 1 1 0 0 0/ \F (Muetterties and Coffman 195a). The value of complex halogen anions as catnlysi- e in organic chemistry and the preparation of organo-met- allic compounds has been developed only comparatively recently. The discovery of the catalytic properties of anhydrous aluminium -7- chloride by Friedel and Crafts (1877) was the beginning of an intensive investigation into its properties and mechanism. Industrial use of hydrogen fluoride-boron trifluoride mixtures in the separation of aromatic isomers through formation of protonated systems is well established and has been thoroughly established by workers including Brown and Brady (/952). Complexes of the type ArH" BP4 have actually been isolated (Olah, Kuhn and Pavlath 1956) and have been extended to salts r- . such as F BFI (Olah, Noszaki and Pavlath \._-NO 2 I H 1957). The solubility or miscibility of aluminium chloride and the fluoride systems is the key to their importance. The solubility of silver perchlorate (Hill 1921) and fluoroborate in organic solvents is well known and the latter has been shown to have catalytic properties in difficult alkylation reactions. Silver fluoroborate and ethyl bromide catalyse the formation of 1,3 dioxo- lenium salts from 2-alkyl-19 3 dioxolanes (Meerwein, Hederich and Wunderlich 1958). The discovery of Ziegler catalysts has stimulated the study of the solubility of inorganic salts in organic 8m solvents. Sharp and Sharpe (1956 a) have shown the solubility of a number of silver fluoro salts in aromatic systems. The bonding in such systems is undoubtedly due to Tr -bonding from the aromatic system and back bonding through the full 3d orbitals of the silver ion to the anti-bonding 1- orbitals of the aromatic system as in silver-olefin complexes. The main part of this thesis is devoted to a study of the solubility and properties of let row transition metal salts of strong acids in organic solvents of low dielectric constant. All the anions studied, except for C104- and CF3CO2are complex fluoro anions. These solutions, particularly solutions of trivalent titanium, are potentially important as catalysts. It is expected that these solutions may also be valuable starting points for the preparation of organo-metallic compounds. The solutions in benzene and toluene could be very important in the formation of carbonylst for example,which are known to proceed, in some cases, through an intermediate benzene complex. There are many Tr bonded complexes known but comparatively few have a fluorine atom bonded to the same transition metal as the Tr bonding ligand. This type of complex with the other halogens are well characterised -9- and in these complexes there is the possibility of back bonding to the halide ions because of the availability of unfilled d orbitals which are of not too high an energy. This back-donation is unlikely in fluorine complexes due to the non-availability of d orbitals to receive electrons. However, it is believed that, providing the correct methods for preparation can be found, Trbonded ligand-metal-fluorine complexes are as stable as the corresponding chlorides although experimental evidence suggests that the form of these complexes may be different from the complexes of the other halides where there may be additional back-bonding to the halogen atom. Platinum and rhodium carbonyl fluorides (Sharp 1960) have been prepared and their properties indicate that they are indeed different from other metal carbonyl halides of platinum and rhodium where the foimal oxidation number is always low. The platinum dicaibOnyloctafluoride is considered as having a co-ordination number of ten whereas rhodium dicarbonyltrifluoride is considered as being dimeric with possibly fluorine bridges. This thesis describes the preparation of some phosphine-metal- fluoride complexes and some phosphine-metal-carbonyl- fluoride complexes which are found to be very stable. -11- CHAPT_ERI SWE FLUOROBORATES AND MONCHYDROXYFLUOROBOR:tT,Z. At the beginning of the nineteenth century intensive investigation into the properties of the alkali and alka- line-earth metals was sparked off by Sir Humphrey Davy's discovery of the electrolytic processes of their simple molten salts. At that time neither fluorine nor boron had been isolated. However Davy (1808a) did isolate a dark combustible solid from the electrolysis of boric acid and a few months later the same product was obtained by heating boric oxide with potassium (Davy 1808b)0 At the same time Gay-Lussac and Thgnard (1811) prepared boron trifluoride by a reaction involving fluate 'of lime and glacial boracic acid' but they confused this gas with hydrogen fluoride. In 'Reserches Physicochimiques' (Gay- Lussac and Thgnard 1811) there is a detailed description of the preparation and properties