Rj. Shaver et al., STRUCTURE, PHYSICAL AND PHOTOPHYSICAL PROPERTIES, AND CHARGE SEPARATION STUDIES OF RE(BPM)(CO)(3)L(N-PTZ)() COMPLEXES (L=CH3CN, PY, MEQ(+),PY), Inorganic chemistry, 34(22), 1995, pp. 5446-5454
The synthesis, structure, and physical and/or photophysical properties
of Re(bpm)(CO)(3)L(n+), where bpm is 2,2'-bipyrimidine and L = CH3CN,
py (pyridine), MeQ(+) (N-methyl-4,4'-bipyridinium ion), and py-PTZ (1
0-(4-picolyl)phenothiazine), are described. The structure of [Re(bpm)(
CO)(3)(CH3CN)]PF6 . 1/2CH(3)CN was determined by single-crystal X-ray
diffraction. It crystallized in the space group P ($) over bar 1 with
cell dimensions a = 10.089(11) Angstrom, b = 11.855(6) Angstrom, c = 1
8.990(6) Angstrom, alpha = 89.71(3)degrees, beta = 77.65(6)degrees, ga
mma = 65.83(6)degrees, Z = 4, and D-calcd = 2.082 g/cm(3). Of the 5565
reflections (Mo K alpha, 3.5 degrees less than or equal to 2 theta le
ss than or equal to 45 degrees), 4721 reflections with F-0 > 3.0 sigma
(F-0) were used in full-matrix least-squares refinement. Final residua
ls were R(F) = 0.0692 and R(w)(F) = 0.1026. The asymmetric unit contai
ned two independent cations. The Re-N(bpm) bond distances were 2.171(9
) and 2.198(10) Angstrom for one cation and 2.161(12) and 2.187(12) An
gstrom for the other; the two Re-N(CH3CN) bond distances were 2.094(14
) and 2.177(13) Angstrom, and the Re-C(CO) bond distances were 1.908(1
5), 1.938(17), and 1.912(12) Angstrom for the first cation and 1.897(1
5), 1.896(19), and 1.919(15) W for the second. The complexes exhibited
three CO infrared-active bands in the 1900-2100 cm(-1) region and und
erwent optical transitions in the 300-350 nm region assigned to d pi(R
e) --> pi(bpm) transitions and in the 200-300 nm region assigned to i
ntraligand pi --> pi transitions. The complexes underwent multiple re
ductions attributed to reduction of coordinated bpm and MeQ(+). The fi
rst reduction of Re(bpm)(CO)(3)-py(+) was located at E(1/2) = -0.84 v
VS SSCE, whereas the first reduction of Re(bpm)(CO)(3)MeQ(2+) was obse
rved at E(1/2) = -0.70 V vs SSCE and was attributed to reduction of th
e MeQ(+) ligand. The only oxidations observed were for Re(bpm)(CO)(3)p
y-PTZ(+). These were located at E(1/2) values of 0.82 and 1.53 V vs SS
CE and were attributed to oxidation of the py-PTZ ligand. Emission was
observed from all the complexes in acetonitrile at room temperature e
xcept from Re(bpm)(CO)(3)py-PTZ(+). The emission quantum yields were l
ow (Phi(em) = (0.5-2) x 10(-3)) and the emission lifetimes were short
(tau similar to 2 ns). Transient absorption spectra revealed that char
ge separation occurred for both Re(bpm)(CO)(3)MeQ(2+) and Re(bpm)(CO)(
3)py-PTZ(+) and involved transfer of an electron from Re(I) to MeQ(+)
generating Re(II) and the MeQ(.) radical in the former and from py-PTZ
to Re(II) forming the py-PTZ(+) radical cation and Re(I) in the latte
r. Intramolecular back electron transfer in [(bpm(-))Re-I(CO)(3)(py-PT
Z(+))](+) occurred at a rate of 1.6 x 10(8) s(-1) and in [(bpm)Re-II(C
O)(3)(MeQ(.))](2+) at a rate of 5.5 x 10(7) s(-1).