organophosphorus pesticides ( 12 ), and irgarol 1051 (2-met-
hylthio-4-terbutylamino-6-cyclopropylamino-s-triazine) ( 13 ).
HS form thermally stable complexes with transition metals,
among others with iron and chromium. On irradiation the Fe
(III) complexes undergo photoreduction producing Fe(II) and
organic radicals(6,14).
B. INVOLVEMENT OFANTHROPOGENICAGENTS
Among anthropogenic chelating agents the most ubiquitous in
the environment are aminopolycarboxylates and phosphonates,
which, unfortunately, are not or only slowly biodegradable and
are therefore rather persistent in the environment. Strong che-
lating agents occur in natural waters predominantly in the form
of metal complexes; they have thus the potential to upset the
natural speciation of metals and to influence metal bioavailabil-
ity. High concentrations of chelating agents may lead to the
remobilization of metals from sediments and aquifers, conse-
quently posing a risk to ground and drinking water( 15 ).
Coordination to a metal affects not only the compound solubil-
ity but also changes most of the metal and ligand features.
Among others, coordination affects essentially the photochemical
behavior. Ethylenediaminetetraacetic acid (edta) for example,
which concentration in European surface water is higher
than any other identified anthropogenic organic compound, is
resistant to chemical, photochemical, and bio-degradation in
the environment. However, when edta^4 is coordinated to Fe(III)
or Cr(III) it undergoes efficient solar photodegradation( 16 – 18 ).
This case illustrates the role of complex formation in the
photochemical self-cleaning processes.
IV. Transition Metal Photochemistry in Conversion of
Some Atmospheric GasesThe atmosphere is a complex medium in which several phases
coexist: gas, aerosol particles, condensed water, liquid, and ice
particles. All of the interactions that may occur between these
various phases are included in the term“multiphase or heteroge-
neous chemistry.”Clouds favor the development of atmospheric
multiphase chemistry, as they are composed of all three atmo-
spheric phases (i.e., gas, liquid, and solid phases that stimulate
a full set of reactions). Moreover, clouds modify radiative pro-
perties by diffusion of short-wavelength radiation coming from
METAL COMPLEXES AS SOLAR PHOTOCATALYSTS 299