Studies of Some Co-Ordination Compounds of Iron and Cobalt

Abstract

Part 1 of this thesis is the study of the behaviour of tris 2-2' bipyridyl iron II cation in strongly acidic media. It is shown that the tris 2-2' bipyridyl iron II perchlorate is completely dissociated in concentrated hydrochloric acid to monoprotonated bipyridyl and chloro-ferrate. The pale blue solutions given by the tris bipyridyl iron II perchlorate in concentrated nitric, sulphuric and perchloric acids are attributed to the formation of iron III species including possibly a bis 2-2' bipyridyl complex. A solid of composition [Fe (bipy)2(NO3)2)C10] has been isolated from the nitric acid solution. Magnetic and Mossbauer data have shown that this complex contains low spin iron III, This species generates the familiar red coloured tris bipyridyl iron II rapidly when dissolved in water in the presence of light, but is very stable in solutions of concentrated acids. Part II is a study of some aspects of the iron and cobalt complexes of dipyridylamine and tripyridylamine, The low temperature infra red spectra of the bis complexes of cobalt II with 4-methyl and 5-methyl substituted tripyridylamines have been studied and compared with that of the isomorphous nickel II and iron II species, The similarity of the spectra of the iron II complexes with those of the cobalt II species was further confirmed, The ease with which the substituted tripyridylamines form the yellow spin paired bis Co III species has been demonstrated, A green solid containing both Co II and Co III has been isolated from an acetone medium. The tris dipyridylamine Co II perchlorate is shown to react with hydrogen peroxide forming a spin-paired bis dipyridylamine diperoxy bridged Co III species, This complex on treatment with concentrated hydrochloric and hydrobromic acids formed the corresponding bis dipy am dichloro and dibromo cobalt III complexes which are believed to contain trans halogeno ligands, All attempts towards the direct synthesis and the oxidation of spin free tris dipyridylamine and spin paired bis tripyridylamine iron II complexes to produce the corresponding iron JII species were unsuccessful, Thereby, an effort to place bidentate dipyridylamine and bi- or terdentate tripyridyl amine with respect to iron III in the spectrochemical series proved futile. However, iron III as its chloride or bromide has been shown to form an oxybridged complex with dipyridylamine which Mossbauer data has confirmed to be unsymmetrically bridged species, Room temperature magnetic measurements gave a spin paired value of 2,2 B.M, however, Mossbauer data showed that the isomershifts corresponded to spin free iron III, thereby indicating that the low moment is due to antiferromagnetic interaction across the Fe - O - Fe bond. A yellow complex possibly a precursor of this oxybridged species has been isolated, Iron III as the thiocyanate formed a spin-free violet black complex of stoichiometry Fel 1.5 (SCN)3. Ion exchange studies excluded the presence of [ Fe(SCN)6]3- species and Mossbauer data showed the presence of two definite iron sites, Tripyridylamine reacted with iron III as its chloride to form bright yellow 1:1 complex of stoichiometry FeLc13. The thiocyanate formed a spin free compound with bidentate tripyridylamine. Stoichiometry Fe L1.5(SCN)3. Once again ion exchange studies excluded the presence of hexathiocyanato ferrate III species. Mossbauer data show that iron III was in an unsymmetrical environment, Iron II as the thiocyanate formed a brick-red complex of stoichiometry FeL (SCN)2 with terdentate tripyridylamine, Room temperature magnetic measurements gave a moment of 3,74 B.M per iron atom. Mossbauer data showed a singlet with isomer shift corresponding spin paired iron II, Low temperature measurements will reveal the presence of a spin free species too. The reactions of 4 methyl and 5 methyl substituted tripyridylamines with iron III and iron II were found to be similar to those of tripyridylamine itself,