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,

Date of Award	1972
Original language	English