inorganic chemistry

with considerable electronic delocalization between both metal
centers, the triple bond of free N 2 is also present in the coordi-
nated state as indicated by vibrational spectroscopy. Finally,
the splitting of N 2 in the complex can be anticipated to proceed
by a simple intramolecular redox reaction that produces only
one excess electron that can lead to complications (Eq. 32):

ðNH 3 Þ 5 OsIIðÞm-N 2 OsIIIðNH 3

h

5

Š^5 þ!2 OsVIðNH 3 Þ 4 N

hi 3 þ

þ2NH 3 þ1e
 ð 32 Þ

The expected photoproduct [Os(NH 3 ) 4 N]^3 þis also quite stable
and well characterized ( 60 – 62 ). In this context, it should be
stressed that the reverse reaction has been observed as photo-
chemical (60,61) and thermal (63,64) process. It is obviously
much easier to couple two nitride complexes containing the
OsVIN| moiety to a binuclear N 2 complex owing to the extreme
stability of the NN triple bond.
The irradiation ofI(absorption spectrum( 5 ):lmax¼700 nm,
e¼4000 M
^1 cm
^1 ; lmax¼260 (sh), e¼21,000; and
lmax¼238 nm;e¼41,000) is associated with a bleaching of the
green color owing to the disappearance of the 700 nm absorption
(Fig. 1). WhileIis not luminescent, the photoproduct shows an
orange emission at lmax¼570 nm (Fig. 2) which grows with
increasing irradiation time. The emission is attributed to the for-
mation of [OsVI(NH 3 ) 4 N]^3 þ( 60 – 62 )II. This assignment is con-
firmed by the excitation spectrum of the photolyzed solution
(Fig. 2), which closely resembles the absorption spectrum
( 60 – 62,65)(lmax¼410 nm, e¼25; lmax¼325 (sh), e¼75;
lmax¼270 nm, e¼1350; and lmax¼236 nm, e¼3100), and the
excitation spectrum of an authentic sample ofII(Figs. 5 and 6).
The photolysis ofIdoes not take place upon irradiation of the
700 nm band but only upon shorter-wavelength irradiation
(lirr<450 nm). The quantum yield amounts to f¼0.002 at
lirr¼254 nm and f¼0.003 at lirr¼365 nm. Complex Iis not
completely converted toII. The molar ratio ofItoIIwas found

A

A

A

A

A OsII N N

A

A

A

A

OsIII

I 5+

A (A = NH 3 )

SCHEME3.

362 ARND VOGLER AND HORST KUNKELY