inorganic chemistry

This reaction proceeds also photochemically as indicated by the
concomitant spectral changes that are identical in both cases.
When the irradiation is carried out in acidic solution (L¼H 2 O)
comparable spectral variations are observed. Since the photolysis
products are apparently stable under these conditions and inter-
fering inner-filter effects are absent the photolysis can be per-
formed to completion. The Os(III) dimer disappears with
f¼ 8  10
^3 at lirr¼436 nm. Disproportionations of this kind
that take place as a consequence of the photochemical splitting
of a metal–metal bond are an important reaction type in organo-
metallic chemistry(17,18).
The stoichiometry ofEq. (17) has been confirmed experimen-
tally. Osmocene was extracted from the acidic solution with hex-
ane and spectroscopically identified ( 19 ) as well as quantitatively
determined. The comparison of the spectra of the extracted sol-
utions of the photolyzed samples and those kept in the dark
yielded a molar ratio of nearly 1:1.
When the photolysis of [Cp 2 OsIVH]þis performed with white
light instead of UV light the spectral variations do not follow a
simple pattern because the primary photolysis of the hydride
complex and the secondary photolysis of the Os(III) dimer are
superimposed. The combined photolysis with white light proceed
then according to the equation

Cp 2 OsIIþ2HþþH 2 O!H 2 þ Cp 2 OsIVðÞH 2 O

hi 2 þ

ð 18 Þ

The aqua complex (L¼H 2 O) is apparently light stable and does
not undergo any further photolysis. Various salts with the cation
[Cp 2 OsIVL]nþ (L¼halide or coordinating solvent) have been
prepared and characterized by Taube and coworkers( 14 ). The
reddish brown hydroxo complex [Cp 2 OsIV(OH)]PF 6 described by
Fischer and Gruber ( 20 ) is also a compound of this type. Aqueous
solutions of this salt are acidic and light sensitive. They are
bleached upon irradiation with visible light. As photoproducts
only osmocene and oxygen could be detected. From the spectral
changes it can be deduced that the hydroxo complex is converted
to osmocene nearly quantitatively. In addition, osmocene and
oxygen are formed in the molar ratio 1:0.5. These observations
are consistent with the equation:

Cp 2 OsIVðÞOH

hiþ

!

hn

Cp 2 OsIIþ

1

2

O 2 þHþ ð 19 Þ

The quantum yield for the disappearance of [Cp 2 OsIV(OH)]þ
amounts tof¼ 2  10
^3 (lirr¼405 nm). In the solid state, this
complex apparently undergoes this decomposition also ther-
mally, but only at 185C( 20 ). In the photolysis, oxygen is

PHOTOCHEMICAL ACTIVATION AND SPLITTING OF H 2 O 351