The
photochemical
behaviour
of
some
mixed
ligand
chromium(III)
complexes
with
amino
acids,
[Cr(C
2
O
4
)
2
(Aa)]
n
−
(where
Aa
=
alanine,
valine,
serine,
cysteine,
asparagine,
aspartic
acid)
was
studied.
The
attention
was
focused
on
the
photoredox
mode,
which
proceeded
via
inner-
or
intramolecular
path-
way
yielding
Cr(II)
species
and
hydrated
electrons,
respectively.
The
secondary
thermal
processes
were
dependent
on
the
O
2
presence
and
solution
pH:
(i)
in
oxygen-free
media
the
regeneration
of
substrate
and
photoaquation
induced
by
the
Cr(III)
→
Cr(II)
reduction
were
observed,
(ii)
in
the
presence
of
O
2
both
Cr(II)
and
ligands
were
oxidized
and
the
former
was
transformed
not
only
into
Cr(III)
but
also
to
Cr(VI)
(provided
that
pH
>
7).
Prolonged
irradiation
resulted
in
photoreduction
of
Cr(VI)
accompanied
by
pho-
todegradation
of
oxalate
and/or
amino-acid
ligands.
The
photoreaction
modes
were
independent
of
the
co-ligand
nature,
but
the
secondary
reaction
rates
and
efficiencies
were
sensitive
both
to
the
co-ligand
nature
and
its
side
substituent.
Environmental
consequences
of
the
chromium
photoreduction
are
dis-
cussed
in
the
paper:
the
parameters
affecting
production
and
consumption
of
Cr(VI)
are
analysed,
and
the
tools
of
controlling
the
photoredox
behaviour
of
the
Cr(III)
and
Cr(VI)
compounds
are
suggested.
keywords in English:
chromium(III) complexes, oxalate, chromate(VI), amino acid, photoinduced electron transfer, photoreduction