Influence of the 4-substituted pyridine ligand L′ on both the conformation and spectroscopic properties of the (2,2′-biquinoline- κN1,κN1′)

Article abstract of DOI:10.1002/hlca.200590227

A series of new rhenium(I) complexes of the type [Re^I(CO) ₃(L)(L′)]ⁿ⁺ (L = 2,2′-biquinoline (bqui) or 3,3′-(ethane-1,2-diyl)-2,2′-biquinoline (CH₂CN ₂)bqui); L′ = CF₃SO₃^-, pyridine (py), or 4-substituted pyridine (HOpy, Bzpy, or NCpy); n = 0 or 1) were prepared and characterized by FT-IR, ¹H-NMR, UV/VIS and emission spectroscopy, luminescence lifetimes, and cyclic voltammetry. The pseudo-octahedral facial configuration was established by X-ray single-crystal diffraction analysis of two complexes and by a FT-IR study of all complexes. The [Re(CO)₃(bqui)(Bzpy)](CF₃SO₃) complex crystallizes in the form of two mirror isomers arising from the conformational mobility of the biquinoline ligand. A correlation between the metal-to-ligand charge-transfer (MLCT) emission maxima and the σ+ Hammett parameter was established for the complexes of the bqui series, while such correlation was not observed for the complexes of the (CH₂CH₂)bqui series. No correlation between oxidation potentials and the Hammett parameters was established. The results were rationalized in function of the effect of the 4-substituted pyridine ligand on the octahedral distortion and conformational characteristic of the complexes. The ¹H-NMR data confirmed these results.

Full text of DOI:10.1002/hlca.200590227

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Influence of the 4-Substituted Pyridine Ligand L’ on both the Conformation
and Spectroscopic Properties of the (2,2’-Biquinoline-
kN1,kN1’)tricarbonyl(pyridine-kN1)rhenium(1+) Complex ([Re(CO)3-
(bqui)(py)]+) and Its Derivatives [Re(CO)3(L)(L’)]+ (L=2,2’-Biquinoline and
3,3’-(Ethane-1,2-diyl)-2,2’-biquinoline)
by Sergio A. Moya*a), Juan Guerreroa), Felipe J. Rodriguez-Nietob), Ezequiel Wolcanb), Mario R. Félizb),
Ricardo F. Baggioc) , and María T. Garlandd)
a) Departamento de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de
Chile, Casilla 40-33, Santiago, Chile
(fax: 56-2-6812108; e-mail: smoya@lauca.usach.cl or jguerrer@lauca.usach.cl)
b) Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA; CONICET-CICBA-UNLP),
Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Casilla de Correo
16 Suc. 4, La Plata (1900), Argentina (fax 54-21-254642; e-mail: mfeliz@isis.unlp.edu.ar)
c) Universidad de Argentina, Departamento de Física (Lab. TANDAR), Comisión Nacional de Energía Atómica,
Av. del Libertador 8250, 1429 Buenos Aires, Argentina (fax: 54-1-754-7121; e-mail: baggio@cnea.gov.ar)
d) Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago de Chile,
Chile
A series of new rhenium(I) complexes of the type [ReI(CO)3(L)(L’)]n+ (L=2,2’-biquinoline (bqui) or 3,3’-
(ethane-1,2-diyl)-2,2’-biquinoline (CH2CN2)bqui); L’=CF3SOꢀ3 , pyridine (py), or 4-substituted pyridine (HOpy,
Bzpy, or NCpy); n=0 or 1) were prepared and characterized by FT-IR, 1H-NMR, UV/VIS and emission spec-
troscopy, luminescence lifetimes, and cyclic voltammetry. The pseudo-octahedral facial configuration was estab-
lished by X-ray single-crystal diffraction analysis of two complexes and by a FT-IR study of all complexes. The
[Re(CO)3(bqui)(Bzpy)](CF3SO3) complex crystallizes in the form of two mirror isomers arising from the con-
formational mobility of the biquinoline ligand. A correlation between the metal-to-ligand charge-transfer
(MLCT) emission maxima and the s+ Hammett parameter was established for the complexes of the bqui series,
while such correlation was not observed for the complexes of the (CH2CH2)bqui series. No correlation between
oxidation potentials and the Hammett parameters was established. The results were rationalized in function of
the effect of the 4-substituted pyridine ligand on the octahedral distortion and conformational characteristic of
1
the complexes. The H-NMR data confirmed these results.
Introduction. – Luminescent transition-metal complexes have been utilized as photo-
sensitizers in areas such as solar-energy conversion, electron-transfer studies, chemilu-
minescent and electroluminescent systems, binding dynamics of heterogeneous media,
and probes of macromolecular structure [1]. In this regard, much attention has been
paid to ReI complexes in recent years [2]. Many of these compounds exhibit a wide
variety of energetically accessible metal-to-ligand charge transfer (MLCT), ligand-to-
ligand charge transfer (LLCT), and intraligand (IL) excited states [3].
Their chemical, photochemical, and photocatalytic properties have made rhe-
nium(I) complexes with polypyridine ligands potential thermal, photochemical, and
electrochemical catalyzers [1a][4]. Examples of these include the electroreduction
© 2005 Verlag Helvetica Chimica Acta AG, Zürich

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and photoreduction of CO2 which could be of interest in the conversion and storage of
solar energy [5].
The photophysical properties of the metal complexes are determined predomi-
nantly by the lowest-energy excited states [6]. However, the population of higher
excited states leads to photochemical pathways. Thus, the control or modulation of
the absorption and/or emission energy is a very important tool for the modification
of the catalytic behavior of these complexes.
To evaluate the effect of structural modifications in the polypyridine ligand on the
properties of the ground and excited states of these complexes, we have studied com-
plexes of the general structure [ReBr(CO)3(L)] with L=bidentate polypyridine ligand
[3h][7]. In previous studies of [ReBr(CO)3(R,R’bqui)], with R,R’bqui=3,3’-R,R’-2,2’-
biquinoline and R=R’=H or Me, or RꢀR’=CH2CH2 or CH2CH2CH2, we found that
the extended conjugation in the 2,2’-biquinoline (=bqui) ligand, as compared to 2,2’-
bipyridine (bpy) ligand, causes a shift towards lower energy both in the MLCT band
and in the reduction potential of the polypyridine ligand [7b,d]. Moreover, the confor-
mational characteristic of the complexes caused by the distortion degree from the pla-
narity in the bqui ligand induces a slight variation of these energies [7d]. We have asso-
ciated the emissions in these complexes with parallel relaxation processes from an IL
and a MLCT state [7e].
The substitution of the Br-ligand in the complexes [ReBr(CO)3(R,R’bqui)] by 4-
substituted pyridine ligands (L’) containing electron-donating or electron-attracting
groups represents a viable alternative to obtain both a new MLCT electronic state,
i.e., Re ! pyridine, and inductive effects upon the energy of the Re ! bqui MLCT
[6][7e]. The objective of the present work is to rationalize the inductive effect of the
4-substituted pyridine ligand on the properties of biquinolinerhenium complexes. For
this purpose, we report here the synthesis and spectroscopic studies of a new series
of complexes of the type [ReI(CO)3(L)(L’)]n+, with L=2,2’-biquinoline (bqui1) or
3,3’-(ethane-1,2-diyl)-2,2’-biquinoline (CH2CH2)bqui1); L’=CF3SO3þ, pyridine (py),
or 4-substituted pyridines Xpy, i.e., HOpy, Bzpy (Bz=benzyl), or NCpy, and n=0 or 1.
Results and Discussion. – The prepared complexes [ReI(CO)3(L)(L’)]n+ are stable
in air either as solids or in solution. They are soluble in several solvents of medium
polarity. The conductivity values are in accordance with the formulae of the corre-
sponding complexes.
The IR spectrum for the [Re(CO)3(L)(CF3SO3)] complexes (L=bqui or (CH2CH2)-
bqui) show three strong bands in the carbonyl stretching region that arise from a facial
configuration with a local Cs symmetry of the carbonyl groups around a hexacoordi-
nated Re-center. In case of complexes [Re(CO)3(L)(L’)] with L’=4-substituted pyri-
dine ligand=Xpy, the IR spectra exhibit two intense bands in the carbonyl stretching
region. This behavior results from a C3v local symmetry for the CO groups in a facial
configuration. The lowest-energy band is very broad, which can be attributed to a
1
)
Formerly, the following abbreviations were used instead of bqui and (CH2CH2)bqui; 2,2’-biquinoline=0,2N
and 3,3’-dimethylene-2,2’-biquinoline=3,3’-(ethane-1,2-diyl)-2,2’-biquinoline=2,2N, respectively. For sys-
tematic names, see Exper. Part.

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decrease of the octahedral symmetry in the complexes with 4-substituted pyridine
ligands [8].
Crystal structures were obtained by X-ray single-crystal diffraction analysis for
[Re(CO)3(bqui)(py)](CF3SO3) and [Re(CO)3(bqui)(Bzpy)](CF3SO3) (Table 1). The
compounds are mononuclear, with [Re(CO)3(bqui)(py)](CF3SO3) exhibiting just one
molecule in the asymmetric unit while two mirror isomers, hereafter represented by
A and B, are observed in the case of [Re(CO)3(bqui)(Bzpy)](CF3SO3). In both struc-
tures, the complex cations are electrically balanced by the triflate counteranions thus
giving rise to neutral entities (Fig. 1). In both species, the Re environment conforms
to a slightly distorted octahedron built up through the coordination of three carbonyl
groups, the bidentate bqui ligand, and the py or Bzpy ligand. The N(3) atom of the pyr-
idine ligand and the C(1) atom of one of the carbonyl units occupy the apical sites, and
the basal plane is defined by C(2) and C(3) (of the remaining carbonyl groups) and
N(1) and N(2) of the bqui ligand (arbitrary atom numbering, see Fig. 1). In all cases,
the metal atom is slightly displaced from the mean plane along the apical line toward
the py or Bzpy ligand (by 0.109(1)Å in [Re(CO)3(bqui)(py)](CF3SO3) and by 0.114(1)
and 0.108(1)Å in A and B, resp., of [Re(CO)3(bqui)(Bzpy)](CF3SO3)), suggesting a
base with the aspect of a depressed square pyramid. The apical axes are rather linear
(N(3)ꢀRe(1)ꢀC(1) 179.2(3)8 in [Re(CO)3(bqui)(py)](CF3SO3), and 178.0(5) and
179.3(5)8 in A and B, resp., of [Re(CO)3(bqui)(Bzpy)](CF3SO3)) with small departures
from the mean plane normals (4.3(2)8 in [Re(CO)3(bqui)(py)](CF3SO3), and 6.3(3) and
5.3(2)8 in A and B, resp., of bqui [Re(CO)3(bqui)(Bzpy)](CF3SO3)). The Re–carbonyl
interactions appear to be quite linear in [Re(CO)3(bqui)(py)](CF3SO3) (range of the
OꢀCꢀRe angle, 177.4–179.58) and show a slightly larger deviation in [Re(CO)3-
Table 1. Crystallographic Data
[Re(CO)3(bqui)(py)](CF3SO3)
[Re(CO)3(bqui)(Bzpy)](CF3SO3)
Formula
Mr
C27H17F3N3O6ReS
754.70
C34H23F3N3O6ReS
844.81
System
Space group
Crystal dimensions [mm]
Crystal color, shape
a [Å]
b [Å]
c [Å]
monoclinic
P 21/c (no.14)
0.30×0.24×0.16
orange, prisms
11.614(1)
12.597(1)
18.234(2)
98.31(1)
monoclinic
P 21/c (no.14)
0.25×0.18×0.16
orange, prisms
23.670(5)
10.755(2)
27.235(7)
111.84(2)
6436(2)
b [8]
Cell volume [Å3]
2639.8(4)
4
1.90
Z
8
1.74
Dx [gcmꢀ3
]
F(000)
1464
4.75
3312
3.91
m [mmꢀ1
]
Max, min absorpt. correct.
Unique refl., Rint, parameters
R1a), wR2b) (F2 >2s(F2))
0.39, 0.28
4644, 0.051, 384
0.044, 0.104
1.76, ꢀ1.68
0.52, 0.43
11317, 0.075, 880
0.064, 0.119
0.77, ꢀ0.87
Final D1 [eÅꢀ3
]
1
2
2
2
2
2 2
a) R1: S jjFojꢀjFcjj/SjFoj. b) wR2: [S[w(Fo ꢀFc ) ]/S[w(Fo) ]] .

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Fig. 1. Molecular diagrams a) for [Re(CO)3(bqui)(py)]+and b) for the isomers A and B of [Re(CO)3(bqui)-
(Bzpy)]+. Arbitrary atom numbering; displacement ellipsoids drawn at a 40% level.
(bqui)(Bzpy)](CF3SO3) (ranges of the OꢀCꢀRe angle, 174.9–177.28 in A and 171.9–
174.68 in B).
In the above complexes, the two independent moieties of the bqui ligand define a
substantial dihedral angle (17.78 in [Re(CO)3(bqui)(py)](CF3SO3), and 12.18 and
17.48 in A and B, resp., of [Re(CO)3(bqui)(Bzpy)](CF3SO3)), much larger than the cor-
responding N(1)ꢀC(13)ꢀC(14)ꢀN(2) torsion angle that would be a measure of any
eventual rotation around the C(13)ꢀC(14) bond (ꢀ4.68 in [Re(CO)3(bqui)(py)]-
(CF3SO3) and 3.68 and ꢀ1.48 in A and B, resp., of [Re(CO)3(bqui)(Bzpy)](CF3SO3)).
This conformational effect probably is responsible for the presence of two conforma-
tional isomers.
This important deformation arises when the bqui ligand is bi-coordinate to the Re-
center. The ligand is forced out of the octahedron’s equatorial plane in the way dis-
cussed previously, presumably to avoid as much as possible the steric hindrance
imposed by the eventual collision between the outermost H-atoms (HꢀC(8) and

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HꢀC(8’)) of bqui and equatorial carbonyl groups (see below Fig. 2 for bqui number-
ing). Due to the nonplanar character of the ligand, the effect is difficult to quantify
properly. However, its importance is suggested by the rather large dihedral angles
that the lateral wings subtend with the polyhedron equatorial plane N(1)ꢀN(2)ꢀ
C(2)ꢀC(3) (arbitrary numbering, see Fig. 1). In complexes with the same coordination
pattern but containing the smaller pyridine ligands, this angle usually amounts to only a
few degrees; but this dihedral angle is 35.3 and 37.78 in [Re(CO)3(bqui)(py)](CF3SO3),
and 32.9 and 35.18, and 35.6 and 36.58 in A and B, respectively, of [Re(CO)3
(bqui)(Bzpy)](CF3SO3). These observations reveal an additional effect on this angle
caused by the L’ ligands. In all cases, the bqui ligand is tilted towards the py or Bzpy
side of the coordination sphere.
1
The H-NMR spectra of the complexes are summarized in Tables 2 and 3. The
assignments of the chemical shifts were made by comparison with data from previously
reported studies of the free ligands and the precursor complexes[7d][9]. Generally, the
signals of the aromatic pyridine protons overlapped with those of the biquinoline pro-
tons. However, the characteristic AB pattern for the former protons are clearly distin-
guished in the spectra of the complexes with the Bzpy ligand.
The increase of deshielding of all the biquinoline protons observed in the new com-
plexes relative to the precursor complexes with a Br-ligand, notably of HꢀC(4,4’) local-
ized in the p-position of the coordinated N-atom, is a good indication that the pyridine
ligands induce a lower electron density on the Re-atom as compared to the Br and tri-
flate ligands. Similarly, an effect of the 4-substituted pyridine ligand Xpy on the d(H) of
the aromatic biquinoline protons is observed in both complex series (Tables 2 and 3).
The two m signals of the CH2CH2 protons of the (CH2CH2)bqui ligand in the
[Re(CO)3{(CH2CH2)bqui}(CF3SO3)] complex is characteristic for an A2B2 system
(Table 3 and Fig. 2). This pattern is due to the presence, in solution, of two conformers
in slow exchange. Both mirror-image isomers are generated by the distortion of the
(CH2CH2)bqui ligand in the complexes (Fig. 1,b). This A2B2 pattern is also observed
for the [ReBr(CO)3{(CH2CH2)bqui}] precursor complex [7b,d], but the chemical-shift
difference between the Ha and Hb protons decreases in the [Re(CO)3{(CH2-
CH2)bqui}(Xpy)]+ complexes. As shown in Table 3, these differences could be as
small as those observed for the [Re(CO)3{(CH2CH2)bqui}(py)]+ complex for which
the A2B2 signals collapse to a quasi-s (Fig. 2,b and c). This behavior is expected for iso-
mers in a fast exchange motion. The change in the shift difference between the Ha and
Hb signals along the L’ series of complexes indicates that the conformational-motion
rate depends on the pyridine ligands at the working temperature.
The UV/VIS data of the complexes [Re(CO)3(L)(CF3SO3)] (Table 4) reveal one
solvent-polarity-dependent band around 430 nm that has been assigned to a rhe-
nium-to-biquinoline (Re ! bqui) charge-transfer (MLCT) transition [3c] [7b,d]; for
the [Re(CO)3(L)(Xpy)]+ complexes, this band can be clearly observed as one or two
shoulders of low intensity above 400 nm. In the [Re(CO)3(L)(Xpy)]+ complexes,
these MLCT transitions are shifted to higher energies than those found in the com-
plexes with Br or triflate ligands, in agreement with a lower electron density on the
metal center induced by the pyridine ligand. However, it is not possible to evaluate
the inductive effect of the Xpy ligand on the MLCT band due to partial overlap with
the intraligand-transition bands (p ! p* biquinoline). The expected band below

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Fig. 2. a) 1H-NMR Spectrum of [Re(CO)3{(CH2CH2)bqui}(Bzpy)]+, b) CH2CH2 1H-NMR signals of the
ReBr(CO)3{(CH2CH2)bqui}] precursor, and c) CH2CH2 1H-NMR signals of [Re(CO)3{(CH2CH2)-
bqui}(Bzpy)]+. CDCl3 solutions at room temperature; for atom numbering see formula and Footnotes b and
c in Table 3.
400 nm for the Re-to-Xpy charge-transfer excited state [10][7d] was not observed
because it is overlapped by more intense bands corresponding to L intraligand transi-
tions.
Fig. 3,a shows the emission spectra for the bqui and (CH2CH2)bqui ligands and for
the corresponding perchlorate salts, i.e., bqui·2 HClO4 and (CH2CH2)bqui·2 HClO4,
when these compounds are excited with lexc 250 nm in MeCN. The inset in Fig. 3,a illus-
trates the protonation effect upon the UV/VIS spectra of bqui and (CH2CH2)bqui. It is
observed that both the absorption and emission maxima of (CH2CH2)bqui experience a
shift to lower energies after protonation. The emission spectrum of bqui experiences
minor changes towards lower energies after protonation; for bqui, the first excited sin-
glet state is of np* character, and its lowest triplet state is assigned as pp* [7i]. Inspec-
tion to Fig. 3,a suggests that, after protonation of (CH2CH2)bqui, fluorescence from the
1np* state (lem ca. 360 nm) diminishes, as expected, and the phosphorescence from the
3pp* state (lem ca. 430 nm) is increased, for the unprotonated (CH2CH2)bqui ligand,
there is a mixture of fluorescence and phosphorescence. Besides that, the emission
quantum yield fem increases by a factor of 5 after the protonation of (CH2CH2)bqui.
The bqui and (CH2CH2)bqui·2 HClO4 compounds, however, show mainly fluorescence
with a lower contribution from the 3pp* state to the total luminescence. Luminescence
quantum yields for bqui and bqui·2 HClO4 are nearly the same. The emission quantum
yield fem for (CH2CH2)bqui·2 HClO4, after excitation with lexc 250 nm, is nearly 10-fold
higher than that of bqui·2 HClO4. This can be explained by the hindrance to rotation

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Table 4. UV/VIS Data for Rhenium(I) Complexes at 258
Compound
Solvent
labs [nm] (10ꢀ3 e/dm3 molꢀ1 cmꢀ1
)
(t2g ! p*L)
(p ! p*)
[Re(CO)3(bqui)(CF3SO3)]
CH2Cl2
Me2O
MeCN
CH2Cl2
Me2O
MeCN
CH2Cl2
Me2O
MeCN
CH2Cl2
Me2O
MeCN
CH2Cl2
EtOH
MeCN
CH2Cl2
EtOH
MeCN
CH2Cl2
EtOH
MeCN
CH2Cl2
EtOH
MeCN
CH2Cl2
EtOH
MeCN
CH2Cl2
EtOH
MeCN
440 (1.5)
430 (sh)
424 (3.6)
430 (6.0)
420 (sh)
420 (sh)
425 (sh)
420 (sh)
418 (sh)
420 (sh)
414 (sh)
405 (sh)
416 (sh)
410 (sh)
400 (sh)
450 (sh)
430 (sh)
426 (0.4)
450 (sh)
438 (sh)
430 (sh)
451 (sh)
435 (sh)
425 (sh)
445 (sh)
430 (sh)
420 (sh)
451 (sh)
445 (sh)
435 (sh)
374 (8.1)
356 (5.2)
373 (17.1)
371 (12.4)
374 (296.0)
373 (285.5)
372 (254.4)
376 (234.0)
374 (262.2)
379 (sh)
374 (295.9)
373 (285.5)
372 (254.4)
379 (304.0)
378 (279.3)
377 (280.2)
395 (5.5)
265 (69.3)
354 (20.3)
262 (567.3)
357 (200.7)
350 (sh)
264 (411.9)
357 (226.4)
373 (366.0)
262 (567.3)
357 (200.7)
267 (568.6)
362 (208.0)
361 (197.2)
268 (532.0)
271 (17.7)
266 (9.1)
[Re(CO)3(bqui)(HOpy)]+
[Re(CO)3(bqui)(NCpy)]+
[Re(CO)3(bqui)(py)]+
[Re(CO)3(bqui)(Bzpy)]+
[Re(CO)3{(CH2CH2)bqui}(CF3SO3)]
[Re(CO)3{(CH2CH2)bqui}(HOpy)]+
[Re(CO)3{(CH2CH)bqui}(NCpy)]+
[Re(CO)3{(CH2CH2)bqui}(py)]+
[Re(CO)3{(CH2CH2)bqui}(Bzpy)]+
394 (3.1)
371 (12.4)
394 (251.1)
394 (165.1)
392 (250.5)
395 (199.3)
393 (187.7)
395 (254.8)
340 (250.0)
392 (81.6)
391 (169.9)
400 (350.6)
399 (215.1)
395 218.6)
354 (2.0)
378 (209.8)
378 (143.1)
268 (584.0)
379 (168.0)
377 (223.9)
268 (473.3)
268 (178.9)
267 (348.0)
268 (533.1)
269 (410.5)
269 (502.7)
imposed by the CH2CH2 group in (CH2CH2)bqui as compared to the ‘free’ bqui which
leads to a smaller nonradiative rate constant.
When solutions of the ReI complexes are optically excited with lex 250, 350, and 400
nm, three different emission spectra are obtained (Fig. 3,b) with lem near 370, 420, and
650 nm, respectively. The emission properties of the ReI complexes are shown in Table
5. The emission with lem near 370 nm (Fig. 3,b) exhibits some vibrational structure, and
it was observed for all the complexes under study. Moreover, this emission is very sim-
ilar to that obtained for bqui, (CH2CH2)bqui, and bqui·2 HClO4 (see Fig. 3,a). The
emission with lem near 370 nm could, therefore, be attributed to the fluorescence arising
from the bqui moiety. The emission with lem near 650 nm which shifts to the red (Fig. 4)
when the solvent polarity is increased, corresponds to a MLCT (Re ! bqui) excited
state [7e].
To analyze the effect of the 4-substituted pyridine ligands on the HOMO of the ReI
complex, the emission maxima (1/lem) were plotted against the s+Hammett parameters.
Emission and absorption energies augment with an increase in the electron-withdraw-

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Fig. 3. a) Room-temperature emission spectra of the ligands bqui (~) and (CH2CH2)bqui (*) and of the cor-
responding perchlorate salts bqui·2 HClO4 (5) and (CH2CH2)bqui·2 HClO4 (&) after irradiation with lexc
250 nm (the corresponding UV/VIS spectra are given in the inset). b) Room-temperature emission spectra of
[Re(CO)3(bqui)(Bzpy)]+ (*; lexc 250 nm) [Re(CO)3{(CH2CH2)bqui}(Bzpy)]+ (&; lexc 250 nm), [Re(CO)3-
(bqui)(py)]+ (~; lexc 350 nm) and [Re(CO)3{(CH2CH2)bqui}(NCpy)]+ (5; lexc 400 nm) in MeCN at different
excitation wavelengths.

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Fig. 4. Lippert Plot for the dependence of the emission energy of [Re(CO)3(bqui)(NCpy)]+ on solvent polar-
ity (top of x axis) and dependence of the emission energy of the bqui complexes on Hammett parameter s+
(bottom of x axis). For s+ values, see Exper. Part; for details see Table 6.
ing power of the pyridine substituents, with more positive s+’s providing more electron-
withdrawing power. It is known that s+ shows a better correlation with cationic species.
The formation of a MLCT excited state (Re ! bqui) makes the metal more positive
(ReII) with the resultant formation of positive charge on the pyridine ligand as the con-
sequence of partial withdrawal of electron density from the metal. Therefore, ligands
with more basic (more negative) s+ values, like OHꢀ will drive electron density into
the Re, making it more easily oxidized and lowering the MLCT energy; for the bqui
series, a linear correlation is observed between 1/lem and s+ (Fig. 4). However, the
(CH2CH2)bqui series did not show a good correlation (Table 5). This lack of correlation
in the (CH2CH2)bqui series could reflect the conformational effect of the pyridine
ligand on the whole complex that may modify both the LUMO and HOMO energies
[7d]. This conformational effect is better compensated in the series of the [Re(CO)3-
(bqui)L’]+ complexes than in that of the [Re(CO)3{(CH2CH2)bqui}L’]+ complexes
due to the major restriction of the conformational motion in this latter series.
Another emission, with lem near 420 nm, is illustrated in Fig. 3,b for the
[Re(CO)3{(CH2CH2)bqui}(py)]+ complex but was observed for all the complexes of
both the bqui and the (CH2CH2)bqui series after excitation with lexc 350 nm (Table
5). This emission is strongly dependent on the solvent, but no correlation could be
established between emission maxima and solvent polarity. However, the emission
near 420 nm is similar to that of (CH2CH2)bqui·2 HCl in Fig. 3,a. It could be assigned

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HELVETICA CHIMICA ACTA – Vol. 88 (2005)
to the 3pp* (3IL) excited states of the bqui and (CH2CH2)bqui ligands in the ReI com-
plexes. It is noteworthy that the emission quantum yield fem (lexc 350 nm) is higher by a
factor of 10 for the complexes of the (CH2CH2)bqui series than for those of the bqui
series (see the comment above concerning the difference of fm for (CH2CH2)bqui·2
HClO4 and bqui·2 HClO4)
After excitation with lexc 400 nm (MLCT (Re ! bqui) excited state) in both the
bqui and (CH2CH2)bqui series, the lowest emission quantum yields fem are obtained
for the complexes with the 4-substituted ligand HOpy, while the highest values are
obtained for those with the py and Bzpy ligands (Table 5). After excitation with lexc
350 nm, the fem are between two and ten-fold lower than the corresponding fem after
excitation with lexc 400 nm in both the bqui and (CH2CH2)bqui complex series. After
excitation with lexc 250 nm, the fem amount to 2–6·10ꢀ3 for all the bqui and
(CH2CH2)bqui complexes and are in general higher than the fem after excitation
with lexc 400 nm.
It is possible to account for the biexponential decay of the luminescence in the
[ReBr(CO)3{(CH2CH2CH2)bqui}] complex ((CH2CH2CH2)bqui=3,3’-(propane-1,3-
diyl)-2,2’-biquinoline) by considering the parallel relaxations of the lowest lying
3MLCTand 3IL states [7e]. Moreover, [Re(CO)3(bqui)L]+ complexes with L=pyrazine
(pz) and 4,4’-bipyridine (4,4’bpy) (see Table 5) showed a biexponential decay of the
luminescence with a longer lifetime, tem 58 ns for L=4,4’bpy and tem 114 ns for
3
L=pz, assigned to the radiative and nonradiative relaxations of the MLCT (Re !
bqui) excited state, and a shorter lifetime, tem ca. 6 ns, assigned to the decay of the
3IL states [3i]. In the present study (see Table 5), the luminescence lifetimes for the
ReI complexes were obtained after a curve fitting analysis of the oscillographic traces,
monitoring wavelengths between 400 and 650 nm. However, the longer lifetime was not
3
observed at monitoring wavelengths between 400 and 500 (where there is no MLCT
(Re ! bqui) emission). Only monitoring wavelengths between 550 and 650 showed
the longer luminescence lifetime. Therefore, it can be stated that the longer lumines-
cence lifetimes (ranging from 33 to 141 ns in Table 5) for [Re(CO)3(bqui)(NCpy)]+,
[Re(CO)3{(CH2Cl2)bqui}(NCpy)]+,
[Re(CO)3{(CH2CH2)bqui}(py)]+,
[Re(CO)3-
(bqui)(py)]+, [Re(CO)3{(CH2CH2)bqui}(Bzpy)]+, and [Re(CO)3(bqui)(Bzpy)]+ can
3
be ascribed to the luminescence decay of the MLCT (Re ! bqui) excited state. The
weak luminescence of [Re(CO)3{(CH2CH2)bqui}(OHpy)]+ and [Re(CO)3-
(bqui)(OHpy)]+ did not allow us to measure emission lifetimes with lexc 355 or 337
nm. The shorter lifetime, tem ca. 8–16 ns, which was mainly observed with monitoring
wavelengths between 400 and 500 nm, must be ascribed to the 3IL state.
The excitation spectra in Fig. 5, which are normalized to the emission-quantum-
yield values of Table 5, show that the highest fem are observed on irradiations at lex
420 nm when monitoring the emission at lem 650 nm, and at lex 340 nm when the emis-
sion is monitored at lem 420 nm. Nevertheless, the emission corresponding to the
3MLCT (Re ! bqui) is still significant when the excitation energy is near lex 340 nm.
Some contribution from the IL excited state to the emission with lem near 650 nm
can not be discarded when exciting with lex 350 nm since the biquinoline absorption
spectrum is still significant at that wavelength. In Fig. 5, the UV/VIS spectrum of the
[Re(CO)3{(CH2CH2)bqui}(NCpy)+ complex in MeCN is shown for comparison. The
lowest absorption band for this complex is placed between the two peaks of the two

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2855
excitation spectra. It was established in a previous work [7e] that a short-lived 3IL state
of the bqui ligand is placed between 15 and 20 kJ above the 3MLCT (Re ! bqui) state.
Intersystem crossing from the 3IL to the 3MLCT (Re ! bqui) state has been proposed
3
in [3i]. The shortening of the IL-state lifetime, tem ca. 8–16 ns, in both the bqui and
(CH2CH2)bqui complex series can be compared to the longer lifetimes (ca. 900 ns) of
3
the IL excited states in [ReCl(CO)3L2] complexes (L=quinoline or isoquinoline)
3
where the MLCT state is placed at higher energy than the IL excited state [7j]. The
shortening of the the 3IL-state lifetime in the [Re(CO)3(bqui)(L’)]+ and
[Re(CO)3{(CH2CH2)bqui}(L’)]+ complexes can be explained by a fast intersystem
crossing, i.e., on a time scale t<20 ns, between 3IL and 3MLCT excited states.
Redox potentials of the rhenium complexes are shown in Table 6. The complexes
may be divided into two groups based on their electrochemical properties. The first
group involves the py and Bzpy derivatives of the bqui and (CH2CH2)bqui series and
is characterized by two successive reversible reduction waves between 0.00 and
ꢀ2.00 V (vs. SCE) and only one reversible oxidation wave between 0.00 and +2.00
V (vs. SCE). The second group includes the OHpy and NCpy derivatives of both series,
where four reversible reduction waves are found between 0.00 and ꢀ2.00 V (vs. SCE)
and one irreversible oxidation wave between 0.00 and +2.00 V (vs. SCE).
According to previous studies [7b,d], the first reduction wave of the first group
could be attributed to a ligand-centered process that involves the addition of an elec-
tron to the p* orbital on the bqui moiety. Three possible processes could be assigned
to the second reduction wave, i) a metal-centered ReI/Re0 reduction, ii) a pyridine-
ligand reduction, and iii) a second reduction of the bqui moiety.
Fig. 5. Excitation spectra of [Re(CO)3{(CH2CH2)bqui}(NCpy)]+ in MeCN monitored at the emission wave-
length: lem 650 nm (—) and 420 nm (…) and absorption spectrum of [Re(CO)3{(CH2CH2)2bqui}(NCpy)]+
(– · – · –) in MeCN

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HELVETICA CHIMICA ACTA – Vol. 88 (2005)
Table 6. Electrochemical Data of the Complexesa)
Redox potential
Ered/V
Eox/V
[Re(CO)3(bqui)(HOpy)]+
[Re(CO)3(bqui)(Bzpy)]+
ꢀ0.79, ꢀ0.89
ꢀ0.71
ꢀ1.38, ꢀ1.57
+1.54b)
+1.71
ꢀ1.24
[Re(CO)3(bqui)(py)]+
ꢀ0.71
ꢀ1.24
+1.72
[Re(CO)3(bqui)(NPpy)]+
ꢀ0.71, ꢀ0.90
ꢀ0.75, ꢀ0.90
ꢀ0.71
ꢀ1.26, ꢀ1.47
ꢀ1.29, ꢀ1.40
ꢀ1.25
+1.41b)
+1.55b)
+1.70
[Re(CO)3(bqui)(HOpy)]+
[Re(CO)3{(CH2CH2)bqui}(Pzpy)]+
[Re(CO)3{(CH2CH2)bqui}(Py)]+
[Re(CO)3{(CH2CH2)bqui}(NCpy)]+
ꢀ0.71
ꢀ1.24
+1.72
+1.56b)
ꢀ0.77, ꢀ0.90
ꢀ1.23, ꢀ1.49
a) The experimental error in the potential measurements is ꢁ0.01 V. b) Irreversible wave.
The change in the pyridine-ligand basicity should affect the complex mainly by
destabilizing the eg orbitals. The lack of such an effect of the substituent at the pyridine
ligand on the second reduction potential values eliminates process i) as a possible
explanation. Process ii) may also be discarded considering that the reduction values
are the same for both the Bzpy and py complexes. Therefore, a second reduction of
the bqui moiety must be involved in the second reduction wave. Moreover, a difference
of ca. 500 mV between the first and the second reduction potential is consistent with
previous findings for similar complexes showing a similar electrochemical behavior
[11].
For the second group, the appearance of four reversible waves might be explained
by considering that the OHpy and NCpy ligands could generate a slow conformational
motion between both enantiomers (established by X-ray and NMR). Consequently,
two bqui moieties with different electrochemical behavior may be observed.
Each of the complexes displayed a reversible or irreversible oxidation between 1.00
and 2.00 V (vs. SCE) corresponding to a metal-centered process ReI/II. This process
involves the removal of an electron from the t2g orbitals of ReI [7d][12].
The effect of the basicity of the L’ ligand on the metal was analyzed considering the
correlation between the oxidation potentials and the Hammett parameter. The lack of
this correlation can be rationalized taking three aspects into account: first, the com-
plexes with the OHpy and NCpy ligands show irreversible oxidation waves; second,
the t2g orbitals should be, by symmetry, less affected by altering the pyridine basicities
rather than the eg ones; and finally, the substituent at the pyridine ligand provides a dif-
ferent influence on the planarity of the bqui moiety, which may affect sterically the t2g
energy. In accordance with the previous discussion, the importance of the latter effect is
notable and has been also observed in related complexes [7d][13].
Conclusion. – X-Rays studies of rhenium and manganese complexes containing the
same bqui and (CH2CH2)bqui ligands have revealed that the symmetry of the com-
pounds is departing by various degrees from a perfect octahedron [7d,g,h][13b]. This
deviation has a significant influence on the spectroscopic and electrochemical proper-
ties of the complexes [7]. Changes in the electronic repulsion between the d orbital of
the metal and the bqui orbitals as the consequence of biquinoline conformational dis-

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2857
tortions are responsible for these influences. Destabilization of the LUMO and stabili-
zation of the HOMO will usually result from an increase of this conformational distor-
tion.
The bqui complexes with L’ ligands show different correlations with the Hammett
parameter. The lack of a similar correlation for the corresponding (CH2CH2)bqui com-
plexes reveals an additional influence of the L’ ligand on both the conformational- and
exchange-motion rate of the complexes. This influence can presumably not be evalu-
ated. However, it constitutes a promising alternative to modulate the complex proper-
ties.
We thank DICYT-Usach, FONDECYT-Chile (Projects 1050168 and 29500074-95), CONICET-Argentina,
and CICBA-Argentina for financial support. Emission spectra were taken at INIBIOLP. The authors wish to
thank Dr. H. Garda for his assistance.
Experimental Part
General. The values of s+ in the Lippert plot (Fig. 4) are taken from [17]. All the operations were carried
out under purified N2 by standard Schlenk and vacuum-line techniques and by using freshly distilled, dried, and
degassed solvents. The solvents used in preparations, crystallizations, and spectroscopic analysis (Mallinckrodt,
grade HPLC) were distilled prior to use. For electrochemical studies, anh. MeCN was dried over CaH2 under N2
by refluxing for 2 h and then freshly distilled prior to use. Commercially available (Aldrich) 2,2’-biquinoline
(bqui)1) and pyridine ligands, AgCF3SO3, [ReBr(CO)5], and precursor compounds were used without further
purification. The synthesis of the 3,3’-(ethane-1,2-diyl)-2,2’-biquinoline ligand (=6,7-dihydrodibenzo[b,j][1,10]-
phenanthroline; (CH2CH2)bqui1) [9] and precursor complexes [ReBr(CO)3(L)] have been previously described
[7b,d]. Molar conductivities: Cole-Parmer-01481 conductivity meter; 10ꢀ3
M solns., in MeCN at 258. UV/VIS
Spectra: Shimadzu-UV-160 spectrophotometer; quartz cells; solns. in purified solvents of different polarity at
r.t. IR Spectra: Bruker-IFS-66-V FT-IR spectrophotometer; solid KBr disks; KBr cell (0.2 mm); scanned at
1
least 100 times; in cmꢀ1. H-NMR Spectra: 250-MHz-Bruker spectrometer. Microanalyses were performed at
the Facultad de Química y Farmacia, Universidad de Chile.
X-Ray Crystal-Structure Analyses. The X-ray single-crystal diffraction data were collected in a Siemens-
R3m four-circle diffractometer, with the w/2q scan mode and a variable scan speed of 4.2–29.38 minꢀ1. Struc-
tures were solved by direct methods [14] and refined by full-matrix least squares in F2 [15]. Anisotropic displace-
ment factors were used for non-H-atoms, while H-atoms (all of which were unambiguously defined by the con-
figuration) were included at their idealized positions and allowed to consider their presence onto their host
atoms. A check for higher symmetry present in [Re(CO)3(bqui)(Bzpy)](CF3SO3) was unsuccessful. The results
are given in Table 1 and Fig. 1 (see [16] for the drawn displacement ellipsoids). CCDC-169685 and -169686 con-
tains the supplementary crystallographic data for this paper. This data can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.can.ac.uk/data_request/cif.
Cyclic Voltammetry. The measurements were performed by standard techniques [7d]. A sweep rate of 200
mV sꢀ1 was used for all the scans. Potentials are reported as E =12 (Ep þ Ep ), where Ep and Ep are the anodic
1
2
a
c
a
c
and cathodic peak potentials, respectively.
Photophysical Measurements. The luminescence of the ReI complexes at r.t. was investigated with an SLM-
Aminco-4800 or a Perkin-Elmer-LS-50B spectrofluorimeter connected to a PC. The spectra were corrected for
differences in instrumental response and light scattering. Solns. were deoxygenated by bubbling N2 of high
purity in a gas-tight apparatus before recording the spectra. Emission quantum yields were measured relative
to rhodamine B in EtOH. Quantum yields were calculated according to Eqn. 1, where I is the integral of the
emission spectrum, A is the absorbance of the sample or standard at the excitation wavelength, and n is the sol-
vent refraction index. Luminescence lifetime measurements were performed by excitation with the third har-
monic of a Spectron-Nd-YAG laser (18 ns FWHM and 12 mJ/pulse at 355 nm) or with a Laseroptics nitrogen
laser (7 ns FWHM and 2mJ/pulse at 337 nm).
2
f
em =(Astandard/Asample)(Isample/Istandard)fem,standard(nsample/nstandard
)
(1)

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HELVETICA CHIMICA ACTA – Vol. 88 (2005)
Synthesis of Rhenium Complexes. The [Re(CO)3(L)(CF3SO3)] complexes [13b] were obtained by reaction
of the [ReBr(CO3)(L)] complex with silver trifluoromethanesulfonate in CH2Cl2 at 508 during 4 h, under an
inert atmosphere. AgBr was separated by passing the mixture through Celite. The filtrate was evaporated
and the obtained solid purified by column chromatography (alumina, CH2Cl2). The eluate was evaporated,
and pure crystals were isolated after crystallization.
The [Re(CO)3(L)(L’)](CF3SO3) complexes [13b] were obtained at 508 under an inert atmosphere by addi-
tion of the corresponding 4-substituted pyridine in stoichiometric amounts to the [Re(CO)3(L)(CF3SO3)] com-
plex dissolved in CH2Cl2. After 2 h, The resulting orange soln. was evaporated and the solid product purified by
column chromatography (alumina, CH2Cl2/MeOH 95 :5) The eluate was evaporated and a microcrystalline
orange product was obtained after dropwise addition of cool hexane. All the complexes were characterized
by elemental analysis, IR, molar conductivities, and melting points.
(2,2’-Biquinoline-kN1,kN1’)tricarbonyl(trifluoromethanesulfonato-kO)rhenium ([Re(CO)3(bqui)(CF3SO3)]:
Yield 84%. Molar conductivity: 21 Scm2molꢀ1. M.p. 3338 (dec.). IR 2029vs, 1935vs, 1914vs. Anal. calc. for
C22H12F3N2O6ReS: C 39.11, H 1.79, N 4.15; found: C 39.71, H 1.84, N 4.32.
(2,2’-Biquinoline-kN1,kN1’)tricarbonyl(pyridin-4-ol-kN1)rhenium(1+) Trifluoromethanesulfonate ([Re(CO)3-
(bqui)(HOpy)](CF3SO3)): Yield 79%. Molar conductivity: 110 S cm2 molꢀ1. M.p. 1548 (dec.). IR: 2015vs, 1901vs.
Anal. calc. for C27H17F3N3O7ReS: C 42.08, H 2.22, N 5.45; found: C 41.74, H 2.40, N 5.65.
(2,2’-Biquinoline-kN1,kN1’)tricarbonyl[4-(phenylmethyl)pyridine-kN1]rhenium(1+) Trifluoromethanesul-
fonate ([Re(CO)3(bqui)(Bzpy)](CF3SO3)): Yield 83%. Molar conductivity: 130 Scm2molꢀ1. M.p. 2138 (dec.).
IR: 2030vs, 1922vs. Anal. calc. for C34H23F3N3O6ReS: C 48.34, H 2.74, N, 4.97; found: C 48.13, H 2.76, N 5.15.
(2,2’-Biquinoline-kN1,kN1’)tricarbonyl(pyridine-kN1)rhenium(1+) Trifluoromethanesulfonate ([Re(CO)3-
(bqui)(py)](CF3SO3)): Yield 30%. Molar conductivity: 105 Scm2molꢀ1. M.p. 2138 (dec.). IR: 2015vs, 1898vs.
Anal. calc. for C27H17F3N3O6ReS: C 42.97, H 2.27, N 5.57; found: C 43.24, H 2.33, N 5.81.
(2,2’-Biquinoline-kN1,kN1’)tricarbonyl(pyridine-4-carbonitrile-kN1)rhenium(1+) Trifluoromethanesulfo-
nate ([Re(CO)3(bqui)(NCpy)](CF3SO3)): Yield 23%. Molar conductivity: 99 Scm2molꢀ1. M.p. 1038 (dec.). IR:
2020vs, 1904vs. Anal. calc. for C28H16F3N4O6ReS: C 43.13, H 2.07, N 7.19; found: C 43.49, H 2.26, N 7.47.
Tricarbonyl(6,7-dihydrodibenzo[b,j][1,10]phenanthroline-kN13,kN14)(trifluoromethanesulfonato-kO)rhe-
nium ([Re(CO)3{(CH2CH2)bqui}](CF3SO3)): Yield 87%. Molar conductivity: 18 Scm2molꢀ1. M.p. 3478 (dec.).
IR: 2031vs, 1927vs, 1903vs. Anal. calc. for C24H14F3N2O6ReS: C 41.09, H 2.01, N 3.99; found: C 41.41, H 2.31,
N 4.15.
Tricarbonyl(6,7-dihydrodibenzo[b,j][1,10]phenanthroline-kN13,kN14)(pyridin-4-ol-kN1)rhenium(1+) Trifluo-
romethanesulfonate [Re(CO)3{(CH2CH2)bqui}(HOpy)](CF3SO3)): Yield 63%. Molar conductivity: 109
Scm2molꢀ1. M.p. 1418 (dec.). IR: 2020vs, 1897vs. Anal. calc. for C29H19F3N3O7ReS: C 43.72, H 2.40, N 5.27;
found: C 44.08, H 2.51, N 5.01.
Tricarbonyl(6,7-dihydrodibenzo[b,j][1,10]phenanthroline-kN13,kN14)[4-(phenylmethyl)pyridine-kN1)rhe-
nium(1+) Trifluoromethanesulfonate ([Re(CO)3{(CH2CH2)bqui}(Bzpy)](CF3SO3)): Yield 83%. Molar conduc-
tivity: 120 Scm2molꢀ1(MeCN). M.p. 1158 (dec.). IR: 2029vs, 1911vs. Anal. calc. for C36H25F3N3O6ReS: C 49.65, H
2.89, N 4.83; found: C 48.80, H 2.78, N 5.04.
Tricarbonyl(6,7-dihydrodibenzo[b,j][1,10]phenanthroline-kN13,kN14)(pyridine-kN1)rhenium(1+) Trifluoro-
methanesulfonate [Re(CO)3{(CH2CH2)bqui}(py)](CF3SO3): Yield 22%. Molar conductivity: 100 Scm2molꢀ1
.
M.p. 3658 (dec.). IR: 2016vs, 1898vs. Anal. calc. for C29H19F3N3O6ReS: C 44.61, H 2.45, N 5.38; found: C
44.65, H 2.26, N 5.52.
Tricarbonyl(6,7-dihydrodibenzo[b,j][1,10]phenanthroline-kN13,kN14)(pyridine-4-carbonitrile-kN1)rhe-
nium(1+) Trilfuoromethanesulfonate ([Re(CO)3{(CH2CH2)bqui}(NCpy)](CF3SO3)): Yield 66%. Molar conduc-
tivity: 123 Scm2molꢀ1. M.p. 1448 (dec.). IR: 2024vs, 1899vs. Anal. calc. for C30H18F3N4O6ReS: C 44.72, H 2.25, N
6.95; found: C 45.01, H 2.57, N 6.55.
REFERENCES
[1] a) ‘Energy Resources Through Photochemistry and Catalysis’, Ed. M. Grätzel, Academic Press, New York,
1983; b) K. Kalyanasundaram, Coord. Chem. Rev. 1982, 46, 159; c) F. E. Lytle, D. M. Hercules, Photochem.
Photobiol. 1971, 13, 123; d) D. A. Buttry, F. A. Anson, J. Am. Chem. Soc. 1982, 104, 4824; e) H. S. White, A.
J. Bard, J. Am. Chem. Soc. 1982, 104, 6891; f) F. Bolleta, V. Balzani, J. Am. Chem. Soc. 1982, 104, 4250; g) A.
Vogler, L. El-Sayed, R. G. Jones, J. Namnath, A. W. Adamson, Inorg. Chim. Acta 1981, 53, L35; h) H.
Kunkely, A. Merz, A. Vogler, J. Am. Chem. Soc. 1983, 105, 7241; i) K. Kalyanasundaram, in ‘Photochem-
istry in Microheterogeneous System’, Academic Press, New York, 1987; j) C. V. Kumar, J. K. Barton, N. J.

H
ELVETICA
CHIMICA
ACTA – Vol. 88 (2005)
2859
Turro, J. Am. Chem. Soc. 1985, 107, 5518; k) J. K. Barton, E. Lolis, J. Am. Chem. Soc. 1985, 107, 708; l) J. K.
Barton, A. T. Danishefsky, J. M. Goldberg, J. Am. Chem. Soc. 1984, 106, 2172; m) R. M. Carlos, M. G. Neu-
mann, J. Photochem. Photobiol. A: Chem. 2000, 131, 67; n) S. Encinas, A. M. Barthram, M. D. Ward, F. Bar-
igelleti, S. Campagna, Chem. Commun. 2001, 277; o) J. Luo, K. B. Reddy, A. S. Salameh, J. F. Wishart, S. S.
Isied, Inorg. Chem. 2000, 39, 2321.
[2] S. S. Sun, A. J. Leas, Organometallics 2001, 20, 2353; S. Berger, A. Klein, W. Kaim, Inorg. Chem. 1998, 37,
5664; S. V. Wallendael, D. P. Shaver, D. P. Rillema, B. J. Yoblinski, M. Stathis, T. F. Guarr, Inorg. Chem.
1990, 29, 1761; G. Ferraudi, N. Nurakami, G. Ruiz, E. Wolcan, M. R. Feliz, Inorg. Chim. Acta 1994, 221,
161; J. A. Baiano, D. L. Carson, G. M. Wolosh, D. E. DeJesus, C. F. Knowles, E. G. Szabo, W. R. Murphy
Jr., Inorg. Chem. 1990, 29, 2327; V. W. W. Yam, Y. Yang, J. Zhang, B. W. K. Chu, N. Zhu, Organometallics
2001, 20, 4911; O. Ishifani, K. Kanai, Y. Yamada, K. Sakamoto, Chem. Commun. 2001, 1514; S. S. Sun, A. J.
Leas, Organometallics 2002, 21, 39; V. W. W. Yam, Chem. Commun. 2001, 789; R. Argazzi, E. Bertolasi, C.
Chiorboli, C. A. Bignozzi, M. K. Itokazu, N. Y. Murakami, Inorg. Chem. 2001, 40, 6885; T. Scheiring, J. Fie-
dler, W. Kaim, Organometallics 2001, 20, 1437; G. Ruiz, E. Wolcan, M. R. Feliz, J. Photochem. Photobiol.,
A 1996, 101, 119.
[3] a) L. Vallace, D. C. Jackman, D. P. Rillema, J. W. Merkert, Inorg. Chem. 1995, 34, 5210; b) R. M. Leasure,
L. A. Sacksteder, C. Nesselrodt, G. A. Reitz, J. N. Demas, B. A. DeGraff, Inorg. Chem. 1991, 3, 3722; c) M.
S. Wrighton, D. L. Morse, J. Am. Chem. Soc. 1974, 96, 998; d) P. L. Giordano, M. S. Wrighton, J. Am. Chem.
Soc. 1979, 101, 2888; e) P. L. Giordano, M. S. Wrighton, Inorg. Chem. 1977, 16, 160; f) G. J. Storr, D. J. Stuf-
kens, A. Oskan, Inorg. Chem. 1992, 31, 1318; g) K. S. Schanze, D. B. MacQueen, T. A. Perkins, L. A. Cab-
ana, Coord. Chem. Rev. 1993, 122, 63; h) M. R. Féliz, G. J. Ferraudi, J. Phys. Chem. 1992, 96, 3059; i) J.
Guerrero, O. E. Piro, E. Wolcan, M. R. Féliz, G. J. Ferraudi, S. A. Moya, Organometallics 2001, 20,
2842; j) R. Lopez, A. M. Leiva, F. Zuloaga, B. Loeb, E. Norambuena, K. M. Omberg, J. R. Schoonover,
D. Striplin, M. Devenney, T. J. Meyer, Inorg. Chem. 1999, 38, 2924.
[4] J. R. Shoonover, G. F. Strouse, R. B. Dyer, W. D. Bates, P. Chen, T. J. Meyer, Inorg. Chem. 1996, 35, 273; K.
Kalyanasundaram, in ‘Photosensitization and Photocatalysis Using Organometallic Compounds’, Ed. L.
Grätzel, Kluwer Academic Publishers, The Netherlands, 1993; J. A. Treadway, B. Loeb, R. Lopez, P.
Anderson, F. R. Keeneand, T. J. Meyer, Inorg. Chem. 1996, 35, 2242; B. D. Rossenaar, F. Hartl, D. J. Stufk-
ens, Inorg. Chem. 1996, 35, 6194; F. R. Keene, B. P. Sullivan, in ‘Mechanism of Electrochemical Reduction
of Carbon Dioxide Catalyzed by Transition Metal Complexes’, Elsevier, Amsterdam, 1993; C. A. Terraza,
J. Guerrero, S. A. Moya, F. M. Rabagliati, R. Quijada, Polym. Bull. 1998, 40, 27; C. A. Terraza, J. Guerrero,
S. A. Moya, F. M. Rabagliati, Polym. Bull. 1998, 41, 669.
[5] G. Ruiz, E. Wolcan, A. L. Capparelli, M. R. Feliz, Photochem. Photobiol. A, 1995, 89, 61; B. P. Sullivan, C.
M. Bolinger, D. Conrad, W. Vining, T. J. Meyer, J. Chem. Soc., Chem. Commun. 1985, 1414; J. Hawecker, J.
M. Lehn, R. J. Ziessel, J. Chem. Soc., Chem. Commun. 1983, 536; C. Pac, K. Ishii, S. Yanagida, Chem. Lett.
1989, 765; D. H. Gibson, H. He, Chem. Commun. 2001, 2082.
[6] M. R. Feliz, G. J. Ferraudi, H. J. Altmiller, J. Phys. Chem. 1992, 96, 257; C. Kutal, A. J. Corbin, G. J. Fer-
raudi, Organometallics, 1987, 6, 553; G. Ruiz, F. Rodriguez-Nieto, E. Wolcan, A. L. Capparelli, M. R.
Féliz, J. Photochem. Photobiol. A 1997, 107, 47.
[7] a) S. A. Moya, R Pastene, R. Schmidt, J. Guerrero, R. Sariego, R. Sartori, Bol. Soc. Chil. Quím. 1992, 37,
43; b) R. Sartori, J. Guerrero, R. Pastene, R. Schmidt, R. Sariego, S. A. Moya, Bol. Soc. Chil. Quím. 1992,
37, 311; c) S. A. Moya, R. Pastene, R. Schmidt, J. Guerrero, R. Sartori, Polyhedron 1992, 11, 1665; d) S. A.
Moya, J. Guerrero, R. Pastene, R. Schmidt, R. Sariego, R. Sartori, J. Sans-Aparicio, I. Fonseca, M. Marti-
nez-Ripoll, Inorg. Chem. 1994, 33, 2341; e) G. Ferraudi, M. R. Feliz, E. Wolcan, Y. Hsu, S. A. Moya, J.
Guerrero, J. Phys. Chem. 1995, 99, 4929; f) S. A. Moya, R. Pastene, A. J. Pardey, P. Baricelli, Bol. Soc.
Chil. Quím. 1996, 41, 251; g) J. Guerrero, S. A. Moya, R. Baggio, M. T. Garland, Acta Crystallogr. Sect.
C 1998, 54, 1592; h) J. Guerrero, S. A. Moya, M. T. Garland, R. Baggio, Acta Crystallogr. Sect. C 1999,
55, 932; i) R. H. Clarke, P. Mitra, K. Vinodgopal, J. Chem. Phys. 1982, 77, 5288; j) N. Murakami Iha, G.
Ferraudi, J. Chem. Soc., Dalton Trans. 1994, 2565.
[8] M. J. Bermejo, J. Y. Ruiz, X. Solans, J. Vinaixa, Inorg. Chem. 1988, 27, 4385.
[9] R. P. Thummel, F. Lefoulon, J. Org. Chem. 1985, 50, 666.
[10] J. C. Luong, L. Nadjo, M. S. Wrighton, J. Am. Chem. Soc. 1978, 100, 5790.
[11] R. Lin, Y. Fu, C. P. Brock, T. Guarr, Inorg. Chem. 1992, 31, 4336; M. K. De Armond, K. W. Hanck, D. W.
Wertz, Coord. Chem. Rev. 1985, 64, 65; J. B. Cooper, D. B. MacQueen, J. D. Petersen, D. W. Wertz, Inorg.
Chem. 1990, 29, 3701.

2860
HELVETICA CHIMICA ACTA – Vol. 88 (2005)
[12] L. A. World, R. Duesing, P. Cheng, L. Della-Ciana, T. J. Meyer, J. Chem. Soc., Dalton Trans. 1991, 849; W.
Yang, K. S. Schanze, Inorg. Chem. 1994, 33, 1354; S. A. Moya, R. Pastene, R. Sartori, P. Dixneuf, H. Le
Bozec, J. Braz. Chem. Soc. 1995, 6, 29.
[13] a) L. A. Sacksteder, A. P. Zipp, E. A. Brown, J. Streich, J. N. Demas, B. A. De Graff, Inorg. Chem. 1990, 29,
4335; b) S. A. Moya, J. Guerrero, R. Pastene, I. Azocar-Guzman, A. J. Pardey, Polyhedron 2002, 21, 439; c)
J. K. Hino, L. Della-Ciana, W. J. Dressick, B. P. Sullivan, Inorg. Chem. 1992, 31, 3701.
[14] G. M. Sheldrick, ‘SHELXS97. Program for Structure Resolution’, University of Göttingen, Germany,
1997.
[15] G. M. Sheldrick, ‘SHELXL97. Program for Structure Refinement’, University of Göttingen, Germany,
1997.
[16] G. M. Sheldrick, ‘XP in SHELXTL-PC’, Version 5.0, Siemens Analytical X-ray Instruments, Inc., Madison,
Wisconsin, USA, 1994.
[17] J. C. Scaiano, ‘Handbook of Organic Photochemistry’, Vol. II, CRC Press,1989; H. Eyring, ‘Physical
Chemistry. An Advanced Treatise’, Vol. VII, Academic Press, 1975.
Received June 28, 2005