inorganic chemistry

In the following, we discuss our results on the characterization
and photocatalytic properties of titania–halogenometal
complexes of Pt(IV) and Rh(III). Considering that the surface of
titania contains about 3–6 OH groups per nm^2 andunder-coordi-
nated titanium atoms it may act both as a mono- and bidentate
ligand (Fig. 1 a–c) and as a coordination centre (Fig. 1 d–f).
Research on the latter topic was recently summarized ( 14 ).

II. Titania–Chloroplatinum(IV) Complexes

In the very first investigations, we have found that simple
metal chloride complexes like Na 2 [PtCl 6 ], AuCl 3 , and RhCl 3
introduced into the bulk of amorphous microporous titania
( 15 – 17 ) by sol-gel methods induce a photomineralization of the
water pollutant 4-chlorophenol (4-CP) by visible light. Surpris-
ingly, in the platinum doped material isolated PtCl 4 units are
present in an amorphous titania matrix exhibiting no bonding
interactions with the lattice components. Thus, the visible light
absorption is located at the PtCl 4 units. It is noted that a physi-
cal mixture of PtCl 4 and silica does not afford a visible light
active photocatalyst. Recalling that photocatalysis is a surface
phenomenon we replaced the sol-gel method by a simple surface
modification procedure in order to introduce chemical bonding
between titania and the metal halide complex. The aim of this
work was to investigate how the photoredox properties of titania
are changed by the covalent attachment to chloroplatinate or
chlororhodate and how the primary photoprocesses of charge

FIG. 1. The dual role of the titania surface in coordination chemistry.

378 HORST KISCH