ClþCl
!Cl 2 
 ð 40 Þ

The Cl 2 
radicals are strong oxidation and chlorination agents.
For instance, they are able to oxidize phenol and its derivatives
topara-benzochinone and/or CO 2 ( 230 ).
The secondary reactions depend on many factors such as solu-
tion pH, oxygenation, DOM, but the Cu(II) photoreduction
(Eq. 38) may lead to photodegradation of the chelate ligands or
external electron donors.
Cu(II) complexes with carboxylate ligands (acetate, malonate,
oxalate) undergo photodecarboxylation during irradiation within
their LMCT bands, for example( 231 ):

½ŠCuOOCCH 3 þsolv
!

LMCT CuOOCCH

½Š 3

þ

solv!Cu

þ

solv

þCH 3 þCO 2 ð 41 Þ

The electron donor ability of several carboxylic acids to Cu(II)
reduction photoassisted by TiO 2 has been compared and formate
was found to be a better electron donor than oxalate.
Aminocarboxylate ligands, such as glycine (NH 2 CH 2 COOH), glu-
tamine (NH 2 CO(CH 2 ) 2 (NH 2 )COOH), alanine (CH 3 CHNH 2 COOH),
nta (N(CH 3 COOH) 3 ), ida (NH(CH 3 COOH) 2 ), and edta
(C 2 H 4 N 2 (CH 2 COOH) 4 ), are able to undergo photooxidation under
these conditions. Complete photooxidation of these ligands yields
among other products carbon dioxide and ammonia. For example,
Cu(II) nitrilotriacetate irradiated at 350 nm demonstrated a signif-
icant photodecomposition of the ligand to CH 2 O, iminodiacetic acid
(ida), and CO 2 (206,230), whereas Cu(II) iminodiacetate underwent
photodegradation to Cu(I) species, NH 4 þ, HCHO, and CO 2 ( 207 ).
Ethylenediamine and others polyamine Cu(II) complexes can
also be oxidatively photodegraded producing NH 3 and CO 2.
Phenanthroline (C 12 H 8 N 2 ) and related compounds in mixed
ligand Cu(II) complexes were reported to undergo copper photo-
reduction and generation of the different radicals that originated
from the co-ligands, such as OH, CH 3 O, and CH 3 OHþ. The
radicals are able to oxidize many organic compounds, such as pri-
mary and secondary aliphatic alcohols or aromatic hydrocarbons
(benzene, toluene) and phenol( 230 ).
UV-irradiation of Cu(II) diketonate complexes generate Cu(0),
which can originate from a disproportionation of Cu(I) produced
in photodegradation of b-diketonate of Cu(II). The quantum
yields of these reactions are relatively high for UV-irradiation,
and solar light is also active( 2 ).

METAL COMPLEXES AS SOLAR PHOTOCATALYSTS 323