New series of ruthenium(II) and osmium(II) complexes showing solid-state phosphorescence in far-visible and near-infrared

Article abstract of DOI:10.1021/ic900586e

A new Ruii complex, [Ru(fpbpymH)2]Cl₂ (1), in which fpbpymH = [5-(trifluoromethyl)pyrazol-3-yl](2,2'-bipyrid-6-yl)methane, was prepared by the treatment of [Ru(DMSO)₄Cl₂] with 2 equiv of the terdentate chelate fpbpymH in refluxing ethanol. A single-crystal X-ray diffraction study of 1 revealed a distorted octahedral Ruii framework, showing strong N-H- ... Cl hydrogen bonding between the fpbpymH ligand and Cl anions. In the presence of Na₂CO₃, the methylene linkers of chelates in 1 underwent stepwise oxygenation, forming the charge-neutral complexes [Ru(fpbpym)(fpbpyk)] (2) and [Ru(fpbpyk)₂] (3) [fpbpykH = [5-(trtfluoromethyl)pyrazol-3-yG(2,2'-bipyrid-6-yl) ketone] in sequence. The respective charge-neutral Osii complex [Os(fpbpyk)₂] (4) was also isolated by the treatment of OsCl₃ -3H₂O with 2 equiv of the terdentate chelate fpbpymH. Electrochemical analysis indicated that the introduction of the electron-withdrawing ketone group in 2-4 increased the metal-based oxidation potential in sequence. For the photophysical properties, complexes 1-4 are essentially nonluminescent in solution (e.g., CH ₂Cl₂ or MeOH) at room temperature, but all exhibit 600-1100 nm phosphorescence with moderate intensity for the powdery, solid sample at room temperature. The trend in terms of the emission peak wavelength of 1 (666 nm) < 3 (795 nm) < 2 (810 nm) < 4 (994 nm) among titled complexes is in agreement with the corresponding onset of absorption spectra as well as the time-dependent density functional theory calculation of 1 < 3 < 2 < 4.

Full text of DOI:10.1021/ic900586e

Inorg. Chem. 2010, 49, 823–832 823
DOI: 10.1021/ic900586e
New Series of Ruthenium(II) and Osmium(II) Complexes Showing Solid-State
Phosphorescence in Far-Visible and Near-Infrared
†
Jing-Lin Chen, Yun Chi,* and Kellen Chen
†
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan. Present address: School of
Material and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou,
Jiangxi 341000, China.
Yi-Ming Cheng, Min-Wen Chung, Ya-Chien Yu, Gene-Hsiang Lee, and Pi-Tai Chou*
Department of Chemistry and Instrumentation Center, National Taiwan University, Taipei 106, Taiwan
Ching-Fong Shu
Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan
Received March 26, 2009
II
A new Ru complex, [Ru(fpbpymH) ]Cl (1), in which fpbpymH = [5-(trifluoromethyl)pyrazol-3-yl](2,2 -bipyrid-6-yl)methane,
0
2
2
was prepared by the treatment of [Ru(DMSO) Cl ] with 2 equiv of the terdentate chelate fpbpymH in refluxing ethanol.
2
4
II
A single-crystal X-ray diffraction study of 1 revealed a distorted octahedral Ru framework, showing strong N-H Cl
3 3
3
hydrogen bonding between the fpbpymH ligand and Cl anions. In the presence of Na CO , the methylene linkers of chelates
in 1 underwent stepwise oxygenation, forming the charge-neutral complexes [Ru(fpbpym)(fpbpyk)] (2) and [Ru(fpbpyk) ]
2
3
2
0
(
3) [fpbpykH = [5-(trifluoromethyl)pyrazol-3-yl](2,2 -bipyrid-6-yl) ketone] in sequence. The respective charge-neutral
Os complex [Os(fpbpyk) ] (4) was also isolated by the treatment of OsCl 3H O with 2 equiv of the terdentate chelate
fpbpymH. Electrochemical analysis indicated that the introduction of the electron-withdrawing ketone group in 2-4 increased
the metal-based oxidation potential in sequence. For the photophysical properties, complexes 1-4 are essentially
nonluminescent in solution (e.g., CH Cl or MeOH) at room temperature, but all exhibit 600-1100 nm phosphorescence
II
2
3
3
2
2
2
with moderate intensity for the powdery, solid sample at room temperature. The trend in terms of the emission peak
wavelength of 1 (666 nm) < 3 (795 nm) < 2 (810 nm) < 4 (994 nm) among titled complexes is in agreement
with the corresponding onset of absorption spectra as well as the time-dependent density functional theory calculation of
1
< 3 < 2 < 4.
1
. Introduction
Since the first preparation of the 2,2 :6 ,2 -terpyridine
and good absorptivity and luminescence in visible and near-
infrared (NIR) regions. Recently, the fast development of
3
0
0
00
1
transition-metal-based supramolecular chemistry has also re-
(
tpy) chelate was reported over 75 years ago, the chem-
II
II
vitalized relevant research on bis-terdentate Ru and Os
complexes. This is mainly attributed to the fact that, upon
insertion of conjugated π bridges between these complexes,
the resulting rodlike donor-sensitizer-acceptor molecular
assemblies are capable of executing directional electron
istry of tpy-based, transition-metal complexes has been
2
the target of extensive investigation. In particular,
II
II
the respective Ru and Os complexes have exhibited
excellent chemical stability, reversible redox processes,
4
and/or energy transfers with high efficiencies.
*
To whom correspondence should be addressed. E-mail: ychi@mx.nthu.
edu.tw (Y.C.), chop@ntu.edu.tw (P.-T.C.). Fax: þ886 3 572 0864 (Y.C.),
(
4) (a) Sauvage, J. P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.;
þ886 2 2369 5208 (P.-T.C.).
Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem.
Rev. 1994, 94, 993. (b) Zeng, F.; Zimmerman, S. C. Chem. Rev. 1997, 97, 1681.
(c) Flamigni, L.; Barigelletti, F.; Armaroli, N.; Collin, J.-P.; Dixon, I. M.; Sauvage,
J.-P.; Williams, J. A. G. Coord. Chem. Rev. 1999, 190, 671. (d) Collin, J.-P.;
Dietrich-Buchecker, C.; Gavina, P.; Jimenez-Molero, M. C.; Sauvage, J.-P. Acc.
Chem. Res. 2001, 34, 477.
(1) Morgan, G. T.; Burstall, F. H. J. Chem. Soc. 1932, 20.
(2) (a) Constable, E. C. Prog. Inorg. Chem. 1994, 42, 67. (b) Cargill
Thompson, A. M. W. Coord. Chem. Rev. 1997, 160, 1.
(
3) (a) Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergamini, G.; Balzani,
V. Top. Curr. Chem. 2007, 280, 117. (b) Kumaresan, D.; Shankar, K.; Vaidya, S.;
Schmehl, R. H. Top. Curr. Chem. 2007, 281, 101.
r 2009 American Chemical Society
Published on Web 12/23/2009
pubs.acs.org/IC

8
24 Inorganic Chemistry, Vol. 49, No. 3, 2010
Chen et al.
Chart 1
Chart 2
Accordingly, much effort has been made in the design and
Chart 3
synthesis of terdentate polypyridine ligands to improve the
II
II
photophysical properties of the corresponding Ru and Os
5
complexes. The typical approach takes advantage of the
3
substituent effects for tuning the energy gap of MLCT and
3
6
MC states, which involves the insertion of judiciously
7
selected heterocyclic substituents to the tpy chelate. Also,
an increase of the ligand bite angle was attempted by making
8
the complex adopt a less distorted octahedral arrangement
and hence increased the ligand field strength and reduced the
nonradiative decay. For instance, as shown in Chart 1, when
one methylene group is introduced between the pyridyl units
of terpyridine, the ligand bite angle of the corresponding
Alternatively, being ascribedto a class of terdentate chelate
6-(5-trifluoromethyl-pyrazol-3-yl)-2,2 -bipyridine (fpbpyH;
0
2þ
0
complex [Ru(bppm)2] (bppm = [6-(2,2 -bipyridyl)(2-pyri-
dyl)methane]) is increased, affording a longer excited-state
lifetime (17-18 ns) relative to its parent complex [Ru-
Chart 2) has latent potential for the preparation of various
luminescent metal complexes for organic light emitting
11
diodes (OLEDs) as well as dye-sensitized solar cell
2þ
9
12
(
tpy) ] (0.25 ns), for which the shortened lifetime is most
(DSSC) applications. Particularly, the related bidentate
2
probably due to the distortion of metal-ligand bonding
away from the perfect octahedral arrangement. This leads
to a decrease of the ligand field strength and a stabilization of
the nonemissive d-d excited states relative to the desired
azolate chelates have been widely utilized in obtaining emis-
II
II
III
II
sive Ru , Os , Ir , and Pt metal complexes that are useful
for the fabrication of highly efficient phosphorescent
13,14
OLEDs.
Encouraged by these successful attempts, we
4a
metal-to-ligand charge-transfer (MLCT) excited state.
Furthermore, employing 2,6-bis(quinolin-8-yl)pyridine
bqp), because of its capability of forming double hexagonal
decided to shift our research endeavors to the [5-(trifluoro-
0
methyl)pyrazol-3-yl](2,2 -bipyrid-6-yl)methane (fpbpymH)
(
ligand, which is a modification of the respective terdentate
fpbpyH. Upon introduction of a saturated methylene linker,
fpbpymH would exhibit better skeletal flexibility in a manner
similar to that of the bppm and bqp chelates discussed earlier.
It is thus of great interest to know if such a modification has
any effect on the chemical and photophysical properties
versus those synthesized using its parent fpbpyH chelate as
well as the oxidized fbppykH analogue, [5-(trifluoromethyl)-
metallacycles, could, in turn, reduce the strain energy.
As a consequence, the as-prepared octahedral complex
2þ
[
Ru(bqp)2] shows a markedly enhanced excited-state life-
10
time of 3.0 μs at room temperature. It is thus feasible that
the enlargement of the ligand bite angle may gain positive
impact on the improvement of both the chemical stabilities
and photophysical properties of metal complexes.
0
pyrazol-3-yl](2,2 -bipyrid-6-yl) ketone (see Chart 2).
Herein, we describe the syntheses and structural and
photophysical studies of three Ru complexes 1-3 emanat-
ing from the reaction of the terdentate fpbpymH with a
(
5) (a) Hammarstr o€ m, L.; Barigelletti, F.; Flamigni, L.; Indelli, M. T.;
II
Armaroli, N.; Calogero, G.; Guardigli, M.; Sour, A.; Collin, J.-P.; Sauvage,
J. P. J. Phys. Chem. A 1997, 101, 9061. (b) Medlycott, E. A.; Hanan, G. S. Chem.
Soc. Rev. 2005, 34, 133. (c) Harriman, A.; Ziessel, R. Chem. Commun. 1996,
707. (d) Medlycott, E. A.; Hanan, G. S. Coord. Chem. Rev. 2006, 250, 1763.
6) (a) Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.;
[
Ru(DMSO) Cl ] reagent, among which 2 and 3 are obtained
4 2
1
from a ligand oxidation occurring on their predecessor 1 (see
(
Thompson, A. M. W. Inorg. Chem. 1995, 34, 2759. (b) Benniston, A. C.;
Harriman, A.; Grosshenny, V.; Ziessel, R. New J. Chem. 1997, 21, 405. (c)
Benniston, A. C.; Grosshenny, V.; Harriman, A.; Ziessel, R. Angew. Chem., Int.
Ed. 1994, 33, 1884. (d) Fang, Y.-Q.; Taylor, N. J.; Hanan, G. S.; Loiseau, F.;
Passalacqua, R.; Campagna, S.; Nierengarten, H.; van Dorsselaer, A. J. Am.
Chem. Soc. 2002, 124, 7912.
Chart 3). On the other hand, the reaction of fpbpymH with
OsCl failed to afford nonoxidized and partially oxidized
3
(11) (a) Chi, Y.; Chou, P.-T. Chem. Soc. Rev. 2007, 36, 1421. (b) Chen, K.;
Cheng, Y.-M.; Chi, Y.; Ho, M.-L.; Lai, C.-H.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H.
Chem. Asian J. 2007, 2, 155. (c) Song, Y.-H.; Chiu, Y.-C.; Chi, Y.; Chou, P.-T.;
Cheng, Y.-M.; Lin, C.-W.; Lee, G.-H.; Carty, A. J. Organometallics 2008, 27, 80.
(d) Chi, Y.; Chou, P.-T. Chem. Soc. Rev. 2010, DOI: 10.1039/b916237b.
(12) (a) Chen, K.-S.; Liu, W.-H.; Wang, Y.-H.; Lai, C.-H.; Chou, P.-T.;
Lee, G.-H.; Chen, K.; Chen, H.-Y.; Chi, Y.; Tung, F.-C. Adv. Funct. Mater.
2007, 17, 2964. (b) Chen, K.; Hong, Y.-H.; Chi, Y.; Liu, W.-H.; Chen, B.-S.; Chou,
P.-T. J. Mater. Chem. 2009, 19, 5329. (c) Chen, B.-S.; Chen, K.; Hong, Y.-H.;
Liu, W.-H.; Li, T.-H.; Lai, C.-H.; Chou, P.-T.; Chi, Y.; Lee, G.-H. Chem.
Commun. 2009, 5844.
(
7) (a) Beley, M.; Chodorowski, S.; Collin, J.-P.; Sauvage, J.-P.; Flamigni,
L.; Barigelletti, F. Inorg. Chem. 1994, 33, 2543. (b) Mano, A.; Stefio, I.; Poggi,
A.; Tringali, C.; Di Pietro, C.; Campagna, S. New J. Chem. 1997, 21, 1173. (c)
Duati, M.; Tasca, S.; Lynch, F. C.; Bohlen, H.; Vos, J. G.; Stagni, S.; Ward, M. D.
Inorg. Chem. 2003, 42, 8377.
(
8) (a) Abrahamsson, M.; Wolpher, H.; Johansson, O.; Larsson, J.;
˚
Kritikos, M.; Eriksson, L.; Norrby, P.-O.; Bergquist, J.; Sun, L.; Akermark,
B.; Hammarstr o€ m, L. Inorg. Chem. 2005, 44, 3215. (b) Abrahamsson, M.;
Becker, H.-C.; Hammarstr €o m, L.; Bonnefous, C.; Chamchoumis, C.; Thummel,
R. P. Inorg. Chem. 2007, 46, 10354.
(13) (a) Chou, P.-T.; Chi, Y. Eur. J. Inorg. Chem. 2006, 3319. (b) Chou,
P.-T.; Chi, Y. Chem.;Eur. J. 2007, 13, 380.
(
9) Wolpher, H.; Johansson, O.; Abrahamsson, M.; Kritikos, M.; Sun, L.;
˚
(14) (a) Yang, C.-H.; Cheng, Y.-M.; Chi, Y.; Hsu, C.-J.; Fang, F.-C.;
Wong, K.-T.; Chou, P.-T.; Chang, C.-H.; Tsai, M.-H.; Wu, C.-C. Angew.
Chem., Int. Ed. 2007, 46, 2418. (b) Niu, Y.-H.; Liu, M. S.; Ka, J.-W.; Bardeker, J.;
Zin, M. T.; Schofield, S.; Chi, Y.; Jen, A. K.-Y. Adv. Mater. 2007, 19, 300. (c)
Hwang, K.-C.; Chen, J.-L.; Chi, Y.; Lin, C.-W.; Cheng, Y.-M.; Lee, G.-H.; Chou,
P.-T.; Lin, S.-Y.; Shu, C.-F. Inorg. Chem. 2008, 47, 3307.
Akermark, B. Inorg. Chem. Commun. 2004, 7, 337.
(
€
10) (a) Abrahamsson, M.; J €a ger, M.; Osterman, T.; Eriksson, L.;
Persson, P.; Becker, H.-C.; Johansson, O.; Hammarstr o€ m, L. J. Am. Chem.
Soc. 2006, 128, 12616. (b) Abrahamsson, M.; Jaeger, M.; Kumar, R. J.;
Oesterman, T.; Persson, P.; Becker, H.-C.; Johansson, O.; Hammarstroem, L.
J. Am. Chem. Soc. 2008, 130, 15533.

Article
derivatives, namely, [Os(fpbpymH)2] and [Os(fpbpym)-
Inorganic Chemistry, Vol. 49, No. 3, 2010 825
2þ
CH
2
Cl
2
and ethyl acetate, giving the terdentate ligand fpbpymH
(
fpbpyk)], but only the doubly oxidized product [Os(fpb-
as a white solid. Yield: 1.3 g, 4.27 mmol, 36%.
Spectral data for fpbpymH: EI-MS m/z 304 (M ); H NMR
500 MHz, CDCl ) δ 11.80 (s, 1H), 8.71 (d, J = 5.0 Hz, 1H), 8.25
t, J = 9.0 Hz, 2H), 7.86 (td, J = 7.8 and 1.7 Hz, 1H), 7.79 (t, J =
þ
1
pyk) ] (4). The successful isolation of 2-4 demonstrates a
2
(
(
3
higher tendency to form the fpbpyk chelate, which could be
due to the synergism involving the greater π stabilization
induced by the carbonyl group and facile oxidation at the
8
1
.0 Hz, 1H), 7.37-7.33 (m, 1H), 7.24 (d, J = 7.0 Hz, 1H), 6.43 (s,
19
H), 4.26 (s, 2H); F NMR (470 MHz, CDCl
Preparation of [Ru(fpbpymH) ]Cl (1). A mixture of Ru-
DMSO) Cl (97 mg, 0.200 mmol) and fpbpymH (129 mg,
.424 mmol) in ethanol (30 mL) was refluxed for 12 h under a
3
) δ -62.13 (s, 3F).
II
activated position in the ligand framework of Ru -based
polypyridophenazine complexes. Moreover, the methy-
lene-to-carbonyl conversion discussed, which is similar to
15
2
2
(
4
2
0
1
6
what occurred in 2,6-bis(2-pyridylmethyl)pyridine, caused
the resulting fpbpyk ligand to afford a much reduced ligand-
centered energy gap, as evidenced by their photophysical and
electrochemical data elaborated in the following sections.
nitrogen atmosphere. After the mixture was cooled to room
temperature, the solvent was removed under vacuum. The
residue was recrystallized from a saturated CH
mixture (15:1) to give dark-brown crystals. Yield: 80 mg,
.102 mmol, 51%. Single crystals were obtained upon placement
of the supersaturated solution of 1 in a 1:20 mixture of methanol
and CH Cl
Spectral data for 1: H NMR (500 MHz, methanol-d
δ 8.65 (d, J = 8.5 Hz, 2H), 8.43 (d, J = 7.5 Hz, 2H), 8.33 (t, J =
2 2
Cl and ethanol
0
2
. Experimental Section
2
2
.
1
General Information and Materials. All reactions were perfor-
med under a nitrogen atmosphere using anhydrous solvents or
solvents treated with an appropriate drying reagent. Oxygen-
4
, 298 K)
8
7
4
.0 Hz, 2H), 8.08 (d, J = 7.5 Hz, 2H), 7.86 (t, J = 7.5 Hz, 2H),
.18 (t, J = 6.5 Hz, 2H), 7.03 (s, 2H), 6.93 (d, J = 5.5 Hz, 2H),
1
8
18
2
O , 97 atom % O, was purchased from ISOTEC. Mass
1
9
spectra were obtained on a JEOL SX-102A instrument operat-
ing in electron impact (EI) or fast atom bombardment (FAB)
.93 (d, J = 17 Hz, 2H), 4.42 (d, J = 17 Hz, 2H); F NMR (470
, 298 K) δ -62.12 (s, 6F, CF ). Anal. Calcd
for C H Cl F N Ru CH OH / CH Cl : C, 44.25; H, 3.18;
MHz, methanol-d
4
3
1
19
1
mode. H and F NMR spectra were recorded on a Varian
Mercury-400 or INOVA-500 instrument. Elemental analyses
were conducted at the NSC Regional Instrumentation Center at
National Chiao Tung University.
3
0
22
2
6
8
3
3
3
2
2
2
N, 13.11. Found: C, 44.26; H, 3.44; N, 13.35.
Preparation of [Ru(fpbpym)(fpbpyk)] (2). A mixture of [Ru-
(
mmol), and Na
DMSO)
4
Cl
2
] (77 mg, 0.159 mmol), fpbpymH (102 mg, 0.335
CO (36 mg, 0.340 mmol) in ethanol (25 mL)
The targeted fpbpymH chelate was prepared in three con-
0
2
3
secutive steps. First, 6-methyl-2,2 -bipyridine was obtained
0
was refluxed for 12 h under a nitrogen atmosphere. After the
mixture was cooled to room temperature, the solvent was
evaporated; the residue was then subjected to silica gel column
chromatography, and the product was eluted with a 2:1 mixture
from the reaction of 2,2 -bipyridine with methyllithium and
0
17
oxidative workup, while 6-acetonyl-2,2 -bipyridine was ob-
0
tained from lithiation of 6-methyl-2,2 -bipyridine with lithium
diisopropylamide at -78 °C and subsequent treatment with
dimethylacetamide. Finally, the fpbpymH ligand was synthe-
of CH Cl and acetonitrile. Complex 2 was further purified by
2
1
8
2
recrystallization from a 1:3 mixture of acetone and hexane at
room temperature. Yield: 40 mg, 0.0554 mmol, 35%. Single
crystals were obtained by the slow diffusion of an n-hexane
solvent into the acetone solution of 2.
0
sized by condensation of 6-acetonyl-2,2 -bipyridine and ethyl
trifluoroacetate, followed by cyclization with an excess of
1
7,19
hydrazine hydrate in refluxing ethanol.
Preparation of [5-(Trifluoromethyl)pyrazol-3-yl](2,2 -bipyrid-
-yl)methane (fpbpymH). To a stirred mixture of NaOEt (1.2 g,
0
101
þ
Spectral data for 2: MS (FAB, Ru) m/z 723 (M þ 1); IR
6
-1 1
(
8
7
KBr) ν(CO) 1628 cm ; H NMR (500 MHz, CD
3
CN, 298 K) δ
.84 (d, J = 8.5 Hz, 1H), 8.54 (d, J = 8.5 Hz, 1H), 8.39 (d, J =
.5 Hz, 1H), 8.25-8.17 (m, 3H), 8.12 (t, J = 8.0 Hz, 1H), 7.79 (d,
1
7.63 mmol) and THF (45 mL) at 0 °C was added a 30 mL
0
solution of 6-acetonyl-2,2 -bipyridine (2.5 g, 11.78 mmol) in
THF, followed by the addition of ethyl trifluoroacetate (2.1 mL,
J = 8.5 Hz, 1H), 7.65-7.61 (m, 3H), 7.37 (d, J = 5.5 Hz, 1H),
.14 (s, 1H), 7.00 (t, J = 6.5 Hz, 1H), 6.96 (t, J = 6.5 Hz, 1H),
.10 (s, 1H), 4.79 (d, J = 17 Hz, 1H), 4.54 (d, J = 17 Hz, 1H);
1
7.62 mmol). The mixture was allowed to heat for 12 h at 80 °C
and then was quenched with 2 M HCl until pH 5-6. The
resulting mixture was extracted with CH Cl
7
6
19
F
2
2
(3 ꢀ 80 mL). The
NMR (470 MHz, CD CN, 298 K) δ -60.03 (s, 3F, CF ), -61.31
3
3
combined extracts were washed with water, dried over anhy-
drous Na SO , and concentrated under vacuum to give the
(
s, 3F, CF
3
). Anal. Calcd for C30
H
18
F
N
6 8
ORu: C, 49.94; H,
2
4
2
.51; N, 15.53. Found: C, 49.75; H, 2.89; N, 15.30.
Preparation of [Ru(fpbpyk) ] (3). Method A. A mixture of
Ru(DMSO) Cl ] (83 mg, 0.171 mmol), fpbpymH (112 mg,
.368 mmol), and Na CO (57 mg, 0.538 mmol) in 25 mL
corresponding β-diketone compound (3.5 g).
Without further purification, hydrazine monohydrate (98%,
2
[
0
4
2
3
.0 mL, 62 mmol) was added into a solution of the β-diketone
reagent in EtOH (50 mL). After reflux for 12 h, the solvent was
evaporated. The residue was dissolved in CH Cl (100 mL), and
2
3
of diethylene glycol monoethyl ether (DGME) was heated at
70 °C for 24 h under a nitrogen atmosphere. After the mixture
2
2
1
the solution was washed with water, dried over anhydrous
Na SO , and concentrated. Finally, the product was purified
by silica gel column chromatography using a 7:3 mixture of
was cooled to room temperature, the solvent was removed under
vacuum, and the residue was subjected to alumina oxide column
2
4
2 2
chromatography, eluting with a 9:1 mixture of CH Cl and
acetonitrile. Complex 3 was further purified by recrystallization
from a 1:5 mixture of acetone and diethyl ether at room
temperature. Yield: 45 mg, 0.0612 mmol, 36%. Single crystals
were obtained by the slow diffusion of n-hexane into an acetone
solution of 3.
(
15) Rau, S.; Schwalbe, M.; Losse, S.; G o€ rls, H.; McAlister, C.;
MacDonnell, F. M.; Vos, J. G. Eur. J. Inorg. Chem. 2008, 1031.
16) (a) Abrahamsson, M.; Lundqvist, M. J.; Wolpher, H.; Johansson, O.;
(
Eriksson, L.; Bergquist, J.; Rasmussen, T.; Becker, H.-C.; Hammarstr o€ m,
˚
L.; Norrby, P.-O.; Akermark, B.; Persson, P. Inorg. Chem. 2008, 47, 3540. (b)
Method B. A mixture of 2 (10 mg, 0.0138 mmol) and Na
15 mg, 0.141 mmol) in ethanol (25 mL) was refluxed for 12 h
2 3
CO
Schramm, F.; Meded, V.; Fliegl, H.; Fink, K.; Fuhr, O.; Qu, Z.; Klopper, W.; Finn,
(
under an oxygen atmosphere. Application of similar workup
S.; Keyes, T. E.; Ruben, M. Inorg. Chem. 2009, 48, 5677.
(
17) Garber, T.; Van Wallendael, S.; Rillema, D. P.; Kirk, M.; Hatfield,
W. E.; Welch, J. H.; Singh, P. Inorg. Chem. 1990, 29, 2863.
18) (a) Wolfe, J. F.; Murray, T. P. J. Org. Chem. 1971, 36, 354. (b)
procedures gave isolation of 8.5 mg of 3 (0.0115 mmol, 83%).
] (36 mg, 0.0743
CO (31 mg,
0.292 mmol) in 10 mL of DGME was heated at 170 °C for 12 h
under an oxygen atmosphere. Application of similar workup
(
Method C. A mixture of [Ru(DMSO)
mmol), fpbpymH (49 mg, 0.161 mmol), and Na
4
Cl
2
Pasquinet, E.; Rocca, P.; Godard, A.; Marsais, F.; Qu ꢀe guiner, G. J. Chem. Soc.,
Perkin Trans. 1 1998, 3807. (c) Savage, S. A.; Smith, A. P.; Fraser, C. L. J. Org.
Chem. 1998, 63, 10048.
2
3
(
19) Constable, E. C.; Heirtzler, F.; Neuburger, M.; Zehnder, M. J. J. Am.
Chem. Soc. 1997, 119, 5606.
procedures gave isolation of 40 mg of 3 (0.054 mmol, 73%).

8
26 Inorganic Chemistry, Vol. 49, No. 3, 2010
Chen et al.
Table 1. Crystal Data and Structural Refinement Parameters for Complexes 1-4
3
/
1
3 2CH2
Cl
2
3 H2
O
4
CH OH
3
2 C
3
6
H
14
3
3 6
4 2C H O
3
3
empirical formula
fw
T (K)
C
992.43
150(2)
32.75
H
31Cl
6
F
6
N
8
O1.75Ru
C
764.68
293(2)
33
H
25
F
6
N
8
ORu
C
735.58
150(2)
30
H
16
F
6
N
8
O
2
Ru
36 28 6 8 4
C H F N O Os
940.86
150(2)
cryst syst
space group
monoclinic
P2 /c
16.6428(2)
27.0851(4)
19.3011(2)
104.4235(7)
8426.16(18), 8
1.565
0.819
monoclinic
C2/c
21.4805(3)
16.2765(3)
17.7118(2)
monoclinic
P2 /c
9.7564(4)
monoclinic
P2 /n
14.3862(2)
16.6975(2)
15.0748(2)
1
1
1
˚
a (A)
˚
b (A)
12.2193(5)
˚
c (A)
23.9532(10)
100.349(1)
2809.2(2), 4
1.739
0.644
1464
β (deg)
93.7405(10)
104.6891(7)
3
V (A ), Z
Fcalcd (g cm
abs coeff (mm
˚
6179.34(16), 8
1.644
0.587
3502.82(8), 4
1.784
3.726
-
3
)
-
1
)
F(000)
cryst size (mm )
reflns collcd
3980
0.35 ꢀ 0.16 ꢀ 0.13
3080
0.28 ꢀ 0.14 ꢀ 0.08
1848
0.30 ꢀ 0.25 ꢀ 0.17
3
0.20 ꢀ 0.15 ꢀ 0.15
36 024
18 749
21 264
6448 [0.0461]
22 328
8031 [0.0496]
indep reflns [R(int)]
max, min transm
data/restraints/param
14 841 [0.0372]
0.913, 0.781
14 841/15/998
1.048
7069 [0.0498]
0.951, 0.870
7069/2/428
0.9095, 0.8819
6448/0/424
1.114
0.553, 0.253
8031/6/487
1.017
2
GOF on F
1.029
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak
R1=0.0959, wR2=0.2875
R1=0.1338, wR2=0.3197
2.379 and -1.788
R1=0.0428, wR2=0.1051
R1=0.0987, wR2=0.1224
0.734 and -0.585
R1=0.0524, wR2=0.105
R1=0.0688, wR2=0.1127
1.077 and -0.619
R1=0.0400, wR2=0.1066
R1=0.0505, wR2=0.1137
2.043 and -2.024
-
3
˚
and hole (e A
)
1
01
þ
Spectral data for 3: MS (FAB,
Ru) m/z 736 (M ); IR
refinement and data reduction were performed with the SAINT
program. The structure was determined using the SHELXTL/
PC program and refined using full-matrix least squares. The
crystals of 1 are of relatively poor quality because of the
incorporation of three different kinds of solvates in the crystal
1 1
(
8
KBr) ν(CO) 1630 cm- ; H NMR (500 MHz, CD
.89 (dd, J = 8.25 and 1.25 Hz, 2H), 8.62 (dd, J = 8.25 and 1.25
Hz, 2H), 8.31 (t, J = 8.0 Hz, 4H), 7.70 (t, J = 7.4 Hz, 2H), 7.64
d, J = 6.0 Hz, 2H), 7.08 (s, 2H), 7.06 (t, J = 6.5 Hz, 2H);
NMR (470 MHz, CD CN, 298 K) δ -61.45 (s, 6F, CF ). Anal.
Calcd for C30 Ru: C, 48.99; H, 2.19; N, 15.23. Found:
C, 49.24; H, 2.46; N, 14.94.
3
CN, 298 K) δ
1
9
(
F
3
3
2 2
lattices, namely, CH Cl , water, and methanol; thus, its bond
H
16
F
N
6 8
O
2
distances and angles showed much larger standard deviations
and had to be handled with caution. The crystallographic
refinement parameters of complexes 1-4 are summarized in
Table 1.
18
Preparation of O-Enriched 3. To a nitrogen-filled Schlenk
flask was added [Ru(DMSO) Cl ] (50 mg, 0.103 mmol),
4
2
fpbpymH (68 mg, 0.223 mmol), Na
and degassed DGME (10 mL). The flask was evacuated, and
2
CO
3
(69 mg, 0.651 mmol),
Spectral Measurement. Steady-state absorption was recorded
with a Hitachi (U-3310) spectrophotometer. For measurement
of the NIR emission, a continuous-wave Ar-ion laser (514 nm,
Coherent Innova 90) was used as the excitation source and was
modulated at approximately 140 Hz by a mechanical chopper.
The NIR emission was then recorded at a direction perpendi-
cular to the pump beam and sent through a lock-in amplifier
(Stanford Research System SR830) before being detected by an
NIR-sensitive photomultiplier tube (Hamamatzu R5509-72)
operated at -80 °C.
1
8
18
O was admitted into the flask until the pressure of the O gas
2
2
reached 1 atm. The above mixture was heated at 150 °C for 24 h.
After the mixture was cooled to room temperature, the solvent
was removed under vacuum, and the residue was subjected to
alumina oxide column chromatography, eluting with a 9:1
mixture of CH
:5 mixture of acetone and diethyl ether gave 71 mg of 3
0.096 mmol, 93%).
Preparation of [Os(fpbpyk)
49 mg, 0.140 mmol) and fpbpymH (108 mg, 0.355 mmol) in
2 2
Cl and acetonitrile. Recrystallization from a
1
(
2
] (4). A mixture of OsCl
3
3H
2
O
Electrochemical Measurement. Cyclic voltammetry was car-
3
(
ried out in a three-compartment cell using a glassy carbon disk
working electrode, a platinum counter electrode, and a Ag/Ag
þ
2
0 mL of DGME was heated at 170 °C for 24 h. After the mix-
ture was cooled to room temperature, the solvent was removed
under vacuum, and the residue was subjected to silica gel column
chromatography, eluting with a 10:1 mixture of CH Cl and
3
(CH Instruments, 10 mM AgNO in MeCN) reference elec-
trode. All experiments were performed in dry acetonitrile with
0.1 M tertrabutylammonium hexafluorophosphate as the sup-
porting electrolyte. Potentials are quoted versus the ferrocene/
2
2
acetonitrile. The product was further recrystallized from a 1:6
mixture of acetone and diethyl ether at room temperature.
Yield: 37 mg, 0.045 mmol, 32%. Single crystals suitable for
X-ray diffraction study were obtained by the slow diffusion of
n-hexane into an acetone solution of 4.
þ
ferrocenium couple (Fc/Fc = 0.0 V).
Computational Methodology. Density functional theory
(DFT) calculations on the electronic singlet and triplet states
of complexes 1-4 were carried out using a hybrid Har-
tree-Fock/density functional model (PBE1PBE) based on the
1
92
þ
Spectral data for 4: MS (FAB, Os) m/z 826 (M ); IR (KBr)
-1
1
20
ν(CO) 1626 cm ; H NMR (500 MHz, CD CN, 298 K) δ 8.84
d, J = 8.5 Hz, 2H), 8.55 (d, J = 7.5 Hz, 2H), 8.23 (d, J = 8.0 Hz,
3
Perdew-Burke-Erzenrhof (PBE) functional. Restricted and
(
unrestricted formalisms were adopted in the singlet and triplet
geometry optimization calculations, respectively. A double-ζ
quality basis set consisting of Hay and Wadt’s effective core
potentials (LANL2DZ) was employed for the Ru and Os atoms
and a 6-31G* basis set for the H, C, N, O and F atoms, while a
relativistic effective core potential was applied to the inner core
2
J = 7.75 Hz, 2H), 6.97 (s, 2H), 6.93 (t, J = 6.25 Hz, 2H);
H), 7.86 (t, J = 8.0 Hz, 2H), 7.55 (d, J = 5.5 Hz, 2H), 7.41 (t,
F
1
9
NMR (470 MHz, CD
3
3
CN, 298 K) δ -61.56 (s, 6F, CF ). Anal.
2
Calcd for C H F N O Os: C, 43.69; H, 1.96; N, 13.59. Found:
16
30
6
8
C, 43.44; H, 2.26; N, 13.33.
X-ray Diffraction Studies. Single-crystal X-ray diffraction
data of 1-4 were measured on a Bruker SMART Apex CCD
(20) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77,
˚
diffractometer using Mo KR radiation (λ = 0.710 73 A). The
data collection was executed using the SMART program. Cell
3865. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78, 1396.
(c) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 827
2
1
electrons of those heavy transition metals. Time-dependent
DFT (TDDFT) calculations for the S f S and S f T
0
n
0
n
transitions using the PBE1PBE functional were then performed
based on the optimized geometries at ground state to probe the
2
2
emissive properties. Oscillator strengths were deduced from
the dipole transition matrix elements (for singlet states only). All
calculations were carried out using Gaussian 03.
2
3
3
3
Electronic configurations of MLCT and MC dd states were
calculated following the literature methodology.
1
6,24
The
3
MLCT state geometry was obtained by geometry optimization
along the triplet-state potential energy surface (PES) using the
X-ray crystal structure as the initial geometry. As for the MC
3
dd state, because the electron densities are mainly distributed on
the central metal atom, the metal-chelate bonding interaction
can be neglected for simplicity. We then performed geometry
3
optimization of the MC dd state following the methodology
1
6
illustrated in Persson’s work. The method starts with a dis-
torted geometry, for which the metal-ligand bonds are largely
elongated, so that its associated energy is expected to be far away
3
from the global minimum along the PES. The resulting MC dd
structure was then confirmed by the net spin values located on
the transition metal from the Mulliken population analysis. The
Figure 1. ORTEP diagram of 1 with thermal ellipsoids shown at 25%
˚
property level. Selective distances (A): Ru(1)-N(1) = 2.034(8), Ru-
3
(1)-N(2)= 2.049(7), Ru(1)-N(3) = 2.061(8), Ru(1)-N(5) = 2.046(7),
frontier orbitals of the MC dd states of complexes 1-4 are
Ru(1)-N(6) = 2.059(7), Ru(1)-N(7) = 2.061(7), Cl(1) H(4) = 2.190,
3
3 3
depicted in the Supporting Information (see Figures S1-S4).
The compositions of the molecular orbitals in terms of the
constituent chemical fragments were calculated using the AO-
Cl(2) H(8) = 2.202, N(8) H(11A) = 3.083, N(4) H(26B) =
.970. Bond angles (deg): N(1)-Ru(1)-N(3) = 170.7(3), N(5)-Ru-
3
3 3 3 3 3 3 3 3
2
(
1)-N(7) = 170.3(3), N(2)-Ru(1)-N(6) = 168.1(3).
25
Mix program. For characterization of the HOMO-x f
LUMOþy transitions as partial CT transitions, the following
definition of the CT character was used:
8.66-6.92. However, a unique NH signal was not detec-
ted, which is apparently because of its higher acidity
and, hence, a faster and reversible proton dissociation
upon dissolution in polar solvents. A similar pheno-
CTðMÞ ¼ %ðMÞHOMO-x - %ðMÞLUMOþy
II
menon has been documented in Pt complexes possessing
the related azolate chelates. Structural characterization
where %(M)HOMO-x and %(M)LUMOþy are electronic
densities on the metal in HOMO-x and LUMOþy. If the
excited state, e.g., S or T , is formed by more than one single-
26
of 1 further confirms the capability of fpbpymH to act as a
neutral chelate, despite of having such an acidic N-H
group.
1
1
electron excitation, then the metal CT character of this excited
state is expressed as a sum of the CT characters of each
participating excitation, i f j:
2
7
The single crystals of 1 were obtained by cooling of a
supersaturated solution prepared from a 1:20 mixture of
methanol and CH Cl at room temperature. As shown in
2 2
X
2
CTI ðMÞ ¼
½CI ðifjÞꢁ ½% ðMÞ -% ðMÞ ꢁ
i
j
Figure 1, the structure of 1 shows a much optimized
octahedral geometry compared to its parent complex
i,a
2
þ
where C
vector of the CI matrix.
I
(ifj) are the appropriate coefficients of the Ith eigen-
[Ru(tpy)2] , for which the transoidal N-Ru-N angles
are measured to be 170.7, 170.3, and 168.1° for 1 and 158,
2
þ
28
1
58, and 178° for the parent [Ru(tpy) ] complex.
2
3
. Results and Discussion
.1. Synthesis and Characterization. Synthesis of the
Moreover, both fpbpymH chelates appear as neutral
ligands. In addition, these N-H protons are linked to two
3
II
noncoordinated chlorides with distances Cl(1) H(4) =
homoleptic Ru complex 1 was performed using
Ru(DMSO) Cl ] and 2 equiv of fpbpymH in refluxing
ethanol. This complex is soluble in protic solvents such as
3 3 3
˚
.190 A and Cl(2) H(8) = 2.202 A, showing obvious
˚
2
[
3 3 3
hydrogen-bonding interaction. The Ru-N
tances span from 2.034 to 2.059 A, which are comparable
4
2
bond dis-
bpy
1
˚
methanol. The H NMR spectrum in CD OD exhibits
3
2
þ
to the average distance for Ru-N vectors in [Ru(bpy) ]
two methylene doublets at δ 4.93 and 4.42 with JHH = 17
Hz, consistent with their diastereotopic nature, together
with multiple aromatic proton signals in the region δ
3
2
9
˚
(
distances (1.974 and 1.981 A) of [Ru(tpy) ] , showing
∼2.056 A) but are longer than the middle Ru-N
2
þ
˚
2
relief of the internal strain energy. The averaged Ru-
˚
distance is ca. 2.061 A, which is also akin to
N
pyrazolate
(
21) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (b) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.; Wadt, W. R.
J. Chem. Phys. 1985, 82, 299.
(26) (a) Chang, S.-Y.; Chen, J.-L.; Chi, Y.; Cheng, Y.-M.; Lee, G.-H.;
Jiang, C.-M.; Chou, P.-T. Inorg. Chem. 2007, 46, 11202. (b) Chang, S.-Y.;
Kavitha, J.; Hung, J.-Y.; Chi, Y.; Cheng, Y.-M.; Li, E. Y.; Chou, P.-T.; Lee, G.-H.;
Carty, A. J. Inorg. Chem. 2007, 46, 7064.
(
22) (a) Jamorski, C.; Casida, M. E.; Salahub, D. R. J. Chem. Phys. 1996,
1
04, 5134. (b) Petersilka, M.; Grossmann, U. J.; Gross, E. K. U. Phys. Rev. Lett.
996, 76, 1212. (c) Bauernschmitt, R.; Ahlrichs, R.; Hennrich, F. H.; Kappes,
1
M. M. J. Am. Chem. Soc. 1998, 120, 5052. (d) Casida, M. E. J. Chem. Phys.
998, 108, 4439. (e) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem.
Phys. 1998, 109, 8218.
(27) (a) Vos, J. G.; Kelly, J. M. Dalton Trans. 2006, 4869. (b) Browne, W.
R.; O'Boyle, N. M.; McGarvey, J. J.; Vos, J. G. Chem. Soc. Rev. 2005, 34, 641. (c)
Koo, C. K.; Lam, B.; Leung, S. K.; Lam, M. H. W.; Wong, W. Y. J. Am. Chem.
Soc. 2006, 128, 16434.
(28) Lashgari, K.; Kritikos, M.; Norrestam, R.; Norrby, T. Acta Crystal-
logr., Sect. C 1999, C55, 64.
1
(
(
(
23) Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
24) Bark, T.; Thummel, R. P. Inorg. Chem. 2005, 44, 8733.
25) (a) Gorelsky, S. I. AOMix: Program for Molecular Orbital Analysis;
University of Ottawa: Ottawa, Ontario, Canada, 2007; http://www.sg-chem.net/.
b) Gorelsky, S. I.; Lever, A. B. P. J. Organomet. Chem. 2001, 635, 187.
(29) Rillema, D. P.; Jones, D. S.; Woods, C.; Levy, H. A. Inorg. Chem.
1992, 31, 2935.
(

8
28 Inorganic Chemistry, Vol. 49, No. 3, 2010
Chen et al.
Figure 3. ORTEP diagram of 3 with thermal ellipsoids shown at 25%
˚
propertylevel. Selective distances (A): Ru-N(1) = 2.053(3), Ru-N(2) =
Figure 2. ORTEP diagram of 2 with thermal ellipsoids shown at 25%
˚
2
2
1
.040(3), Ru-N(3) = 2.016(3), Ru-N(5) = 2.044(3), Ru-N(6) =
.045(3), Ru-N(7)=2.039(3), C(11)-O(1)=1.226(5), C(26)-O(2) =
.223(4). Bond angles (deg): N(1)-Ru-N(3) = 172.2(1), N(5)-Ru-
property level. Selective distances (A): Ru-N(1) = 2.051(3), Ru-N(2) =
2
.051(3), Ru-N(3) = 2.039(3), Ru-N(5) = 2.042(3), Ru-N(6) =
2
.039(3), Ru-N(7)=2.036(3), C(26)-O(1)=1.224(4), N(8) H(11A) =
3
3 3
N(7) = 170.9(1), N(2)-Ru-N(6) = 172.2(1).
2.817. Bond angles (deg): N(1)-Ru-N(3) = 172.2(1), N(5)-Ru-N-
(7) = 173.3(1), N(2)-Ru-N(6) = 174.2(1).
3
sp -hybridized nature of the methylene group. On the
II
those (2.063 and 2.065 A) observed in neutral Ru complex
˚
other hand, the newly formed fpbpyk chelate reveals a
planar arrangement, which is attributed to the sp -hybri-
12a
Ru(fpbpy)2].
2
[
Finally, one methylene proton of each
fpbpymH chelate displays a shortened nonbonding contact
to one pyrazolate N atom of the second fpbpymH chelate
dized carbonyl group. It is also noted that the methylene
group of the fpbpym chelate remains close to the uncoor-
˚
dinated pyrazolic N atom of the fpbpyk chelate, for which
˚
[
N(8) H(11A) = 3.083 and N(4) H(26B) = 2.970 A].
3 3 3 3 3
3
This intramolecular C-H N bonding interaction is ex-
the shorter C-H N contact of 2.817 A implicates
3
3 3
3 3 3
pected to increase its reactivity toward other reagents such
as dioxygen present in the reaction media.
We then made attempts to conduct a reaction of 1 with
nonnegligible bonding interaction, similar to those ob-
served in 1. For a fair comparison, the sum of the van der
3
1
˚
Waals radii of N and H atoms is calculated as ∼2.8 A.
Na CO for generation of the hypothetical neutral com-
2
Note that recent literature also reported the C-H
3 3 3
N
3
˚
plex [Ru(fpbpym) ]. Another alternative involves heating
2
hydrogen-bonding distances as ∼2.95 A in the 3D pack-
of the metal reagent [Ru(DMSO) Cl ] with 2 equiv of
4
ing of self-assembled organic materials, which provides
2
3
2
fpbpymH in basified ethanol. Both reactions, unfortu-
nately, failed to produce the designated [Ru(fpbpym)2]
but instead afforded a purple product in ∼35% yield,
the maximum distance for weaker C-H N bonding.
3
3 3
To assess the chemical stability of 2, we conducted
thermolysis in a DGME solvent at 170 °C for a period of
24 h. This harsh condition gave formation of a second
1
which is denoted as 2. The H NMR analysis of 2 showed
II
two doublets, which integrate for a total of two protons at
δ 4.79 and 4.54 with JHH = 17 Hz. These spectral data
unambiguously indicate one methylene-to-carbonyl
group conversion, as revealed by the simultaneous ap-
charge-neutral Ru complex 3 that possesses two fpbpyk
chelates. Again, the X-ray crystal structural study of 3
was examined, revealing two mutually orthogonal
fpbpyk chelates. Their bonding arrangement is similar
to that observed in 2 (Figure 3), except that the C-O
-
1
pearance of a νCO stretching band at 1628 cm in its IR
spectrum. Furthermore, the H NMR spectra of 2 ex-
1
˚
distances span 1.223 and 1.226 A, while both fpbpyk
II
chelates interact with the central Ru cation with typical
hibited a total of 16 aromatic resonances in the region δ
˚
8.84-6.10, expected for two nonequivalent bpy and two
pyrazolate fragments.
Ru-Nbpy distances of 2.044-2.053 A and Ru-Npyrazolate
distances of 2.016 and 2.039 A.
We further carried out the reaction of fpbpymH with
˚
As indicated in Figure 2, the structure of 2 consists of a
less distorted coordination geometry versus that observed
for 1, showing bond angles of N(1)-Ru-N(3) =
the third-row congener OsCl
3H
O in DGME at 170 °C,
giving the doubly oxidized Os complex 4 as the sole
3
3
2
II
1
72.2(1)°, N(5)-Ru-N(7) = 173.3(1)°, and N(2)-Ru-
product (Chart 3). As expected, this product showed no
discernible high-field H NMR signal attributed to the
1
N(6) = 174.2(1)° and the absence of counteranions. For
both terdentate chelates, Ru-N distances involving pyra-
methylene protons, showing its intimate correlation to
the Ru complex 3. The single-crystal structural analysis
II
˚
zolates (2.036-2.039 A) turned relatively shorter than
˚
of 4 was conducted. As shown in Figure 4, both of the
skeletal arrangement and metric parameters are identical
with those of 3.
those of the neutral bipyridine units (2.039-2.051 A); the
results can be rationalized by the increased Coulomb
II
interaction between the cationic Ru metal center
3
0
and anionic pyrazolates. On the one hand, the
fpbpym chelate shows a puckered geometry due to the
Hence, according to the chemistry established for both
Ru and Os systems, the instability of 1 is believed to be
II
II
(
30) (a) Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Chen, L.-S.; Shu, C.-F.; Wu,
F.-I.; Carty, A. J.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Adv. Mater. 2005, 17,
059. (b) Tung, Y.-L.; Chen, L.-S.; Chi, Y.; Chou, P.-T.; Cheng, Y.-M.; Li, E. Y.;
Lee, G.-H.; Shu, C.-F.; Wu, F.-I.; Carty, A. J. Adv. Funct. Mater. 2006, 16, 1615.
(31) (a) Batsanov, S. S. Inorg. Mater. 2001, 37, 871. (b) Taylor, R.; Kennard,
O. J. Am. Chem. Soc. 1982, 104, 5063.
(32) Moorthy, J. N.; Natarajan, R.; Savitha, G.; Venugopalan, P. Cryst.
Growth Des. 2006, 6, 919.
1

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 829
Chart 4
[
Os(fpbpy) ] exhibit one-electron reversible oxidation
2
peak potentials at þ0.16 and -0.11 V quoted versus a
þ
Fc/Fc standard and one-electron reversible reduction
peak potentials at -1.97 and -1.92 V, respectively. [Os-
(fpbpy) ] showed a notable cathodic shift in the potential
for oxidation versus that of the Ru counterpart, which is
2
II
II
attributed to the lowered intrinsic potential of the Os
metal element. In contrast, the nearly equal potential for
the reduction of both complexes shows electron addition
to the π* orbital of the fpbpy chelate, which is less
susceptible to the influence of the central metal atom.
On the other hand, complex 2 exhibits one-electron
reversible metal-centered oxidation at 0.03 V as well as
two-electron reversible waves at -1.79 and -2.19 V
because of the sequential reduction occurring at fpbpyk
and fpbpym chelates, respectively (see Figure S6 in the
Supporting Information). In addition, both the oxidation
and first reduction potentials of 2 are less and more
positive compared to those of the previously discussed
Figure 4. ORTEP diagram of 4 with thermal ellipsoids shown at 25%
properties level; selective distances: Os-N(1) = 2.047(4), Os-N(2)=
2
2
1
.043(4), Os-N(3) = 2.041(4), Os-N(5) = 2.044(4), Os-N(6) =
.047(4), Os-N(7) = 2.036(4), C(11)-O(1) = 1.227(6), C(26)-O(2) =
˚
.224(6) A and bond angles: N(1)-Os-N(3) = 171.4(2), N(5)-Os-
N(7) = 170.9(2), N(2)-Os-N(6) = 174.4(2)°.
due to the facile oxidation capability at the fpbpymH
sites. A similar increase of the chemical reactivity of
N-heterocyclic chelates was also reported in the litera-
1
4,33
ture,
which unambiguously demonstrated that tran-
sition-metal ions can exert considerable influence on the
metal-mediated or catalyzed oxygenation of alkane.
To further explore the origin of the incorporated O
atom(s) in complexes 2-4, a series of control and isotope-
labeling experiments were carried out, including com-
bis-terdentate complex [Ru(fpbpy) ], showing a reduced
2
HOMO/LUMO energy gap. This result is in good agree-
ment with the natural of the fpbpyk chelate, for which the
carbonyl group exerts an extended π conjugation versus
that of the parent fpbpy chelate. Because the carbonyl
group of fpbpyk is also more electronegative, further
1
8
parative reactions under regular and O-enriched dioxy-
gen atmospheres. Accordingly, refluxing of the ethanol
solution of 2 under a dioxygen atmosphere in the presence
of Na CO afforded 3 with an improved yield to 83%.
stabilization of the metal-centered d orbital is expected
π
for the fpbpyk chelate. As such, the oxidation wave for 3
2
3
Moreover, the reaction of [Ru(DMSO) Cl ] with 2 equiv
2
4
(
0.25 V) is more positive than that occurring for 2 (0.03
V), showing the consequence for the introduction of two
e.g., 3) and one (e.g., 2) fpbpyk chelates, respectively.
Moreover, two less positive reduction waves at -1.71 and
1.92 V of 3 are corresponding to the one-electron
of fpbpymH in DGME at 170 °C under a dioxygen
atmosphere also gave the doubly oxidized product 3 in
(
7
2% yield. Bearing this result in mind, we switched the
1
8
oxygen atmosphere of our control reaction to the O-
enriched dioxygen and then repeated the synthesis. To
our surprise, analyses of IR and FAB-MS spectral data
-
reduction at each of the fpbpyk chelates. It has been
reported that the anodic shifts are, in principle, exerted by
localization of an electron on the carbonyl group of each
1
8
showed no incorporation of the O oxygen label. There-
fore, the methylene-to-carbonyl conversion seems not to
originate from the direct attack of the dioxygen reagent
but is catalyzed by the dioxygen introduced. Unfortu-
nately, the detailed mechanism involving the possible
dioxygen participation and C-H abstraction remained
unclear at the current stage.
2
4
terdentate chelate.
Oxidation of the Os complex 4 occurs at -0.05 V,
which is again more negative than that of the Ru
II
II
analogue 3, consistent with the lower potential for the
third-row transition-metal elements. Likewise, the reduc-
tion waves at -1.67 and -1.93 V, which are essentially
identical with those of 3, show one-electron ligand-cen-
tered reduction occurring at each of the fpbpyk chelates.
Finally, as compared to the literature data of cationic
complexes [Ru(tpy)2] and [Os(tpy)2] (Table 2), all
redox potentials of 3 and 4 are found to be more negative
than those recorded for the tpy analogues, a result that is
attributed to the anionic charge associated with the fpbpy
chelates.
3.2. Electrochemical Properties. The redox properties
of reference complexes [Ru(fpbpy) ], [Os(fpbpy) ] (Chart
2
2
4
), and 2-4 were next investigated in acetonitrile and with
ferrocene as the internal standard, while a study of 1 was
skipped because of its poor solubility in acetonitrile and
greater sensitivity toward oxygen during electrochemical
measurement, making the data unreliable. As depicted in
2
þ
2þ
34
Table 2, the reference complexes [Ru(fpbpy) ] and
2
(
33) (a) Jitsukawa, K.; Oka, Y.; Yamaguchi, S.; Masuda, H. Inorg. Chem.
2
004, 43, 8119. (b) ten Hoedt, R. W. M.; Hulsbergen, F. B.; Verschoor, G. C.;
(34) Encinas, S.; Flamigni, L.; Barigelletti, F.; Constable, E. C.; Housecroft,
C. E.; Schofield, E. R.; Figgemeier, E.; Fenske, D.; Neuburger, M.; Vos, J. G.;
Zehnder, M. Chem.;Eur. J. 2002, 8, 137.
Reedijk, J. Inorg. Chem. 1982, 21, 2369. (c) Lee, D.-H.; Murthy, N. N.; Karlin,
K. D. Inorg. Chem. 1996, 35, 804.

8
30 Inorganic Chemistry, Vol. 49, No. 3, 2010
Chen et al.
II
II
Table 2. Photophysical and Electrochemical Data for Ru and Os Complexes 1-4 and Relevant Reference Samples in an Acetonitrile Solution
-3
-1
-1
a
ox
1/2
e
red
b
compound
abs λmax/nm (ε ꢀ 10 /[M cm ])
em λmax/nm
E
Φ
p
p
E1/2 /V [ΔE /mV]
[
[
Ru(fpbpy)
Os(fpbpy)
2
]
]
400 (9.1), 472 (6.4), 511 (7.7), 635 (1.4)
465 (9.9), 650 (2.8), 715 (2.9)
0.16 [53]
-0.11 [68]
-1.97 [53]
-1.92 [73]
d
2
(935)
1
2
3
4
246 (1.43), 294 (3.46), 467 (0.49)
255 (2.20), 299 (3.73), 518 (0.85)
271 (2.85), 310 (3.50), 507 (1.01), 629 (0.23)
273 (2.74), 312 (3.27), 508 (0.83), 775 (0.27)
269 (4.1), 307 (5.2), 475 (1.26)
666 (612)
810 (750)
795 (728)
994 (955)
(598)
0.082
0.012
0.020
0.007
0.03 [52]
0.25 [70]
-0.05 [57]
0.92
-1.79 [52], -2.19 [60]
-1.71 [60], -1.92 [59]
-1.67 [65], -1.93 [56]
-1.58, -1.82
2
þ
f
[
Ru(tpy)
2
]
]
0.48
2
þ
[
Os(tpy)
2
310 (7.4), 475 (1.5), 656 (0.42)
(689)
0.58
-1.63, -1.95
a
b
Emissions were measured using a solid-state (powder) sample at room temperature. Potentials were quoted versus the Fc/Fc reference; oxidation
þ
and reduction potentials were measured in acetonitrile; ΔE is defined as Eap (anodic peak potential) - Ecp (cathodic peak potential), and these data are
p
c
d e
quoted in millivolts. Data were measured in an alcohol solution. The numbers in parentheses were measured in the 77 K methanol glass. Data were
f
measured in the 77 K methanol glass. See ref
4a
.
result is intriguing. Because the emission is expected to be
in NIR, one may promptly mull that the emission is
subject to dominant quenching via certain potential non-
radiative pathways: (i) intersection with dd repulsive PES
3
5
and (ii) operation of the energy gap law, stating that the
electronic transition with a low energy gap may be
quenched by either high-frequency vibrational modes or
the low-frequency, high-density vibrational overlaps. The
latter path of ii may mainly be attributed to the hindered
vibration of the methylene or carbonyl group associated
with the fpbpym or fpbpyk ligands. However, except for
1
, pathway i is not quite possible because of the far
3
3
separation between MLCT and MC dd states (vide
infra). As for ii, the large amplitude, low-frequency
vibrations, in theory, may be subsided in the rigid solid
state. As a result, in the solid state, moderate emissions
appear for complexes 2-4 at room temperature (see
Figure 5). This viewpoint is also supported by the emis-
sion of 2-4 resolved in the 77 K MeOH glass, which
showed a slight blue-shifted emission (see Figure S5 in the
Supporting Information and Table 2). Moreover, the
emission quantum yields span the range from 0.012 to
Figure 5. Absorption spectra in an acetonitrile solution and normalized
solid-state (powder) emission spectra of complexes 1-4 recorded at room
temperature.
3
.3. Photophysical Properties. Pertinent photophysical
0
.007 (cf. 2 and 4), which are far less efficient than that for
data of all titled complexes 1-4 are also collected in
2
þ
4a
Ru(tpy)2 in 77 K methanol glass (Φ = 0.48). Because
moderate/weak emission was still observed, it is thus
confirmed that the nonradiative decay, in certain part,
is governed by the high-frequency vibrational modes, i.e.,
the operation of energy gap law, because of the low energy
gap. For 1, the emission yield in the 77 K methanol glass
was measured to be ∼0.08. In addition to pathway ii, we
demonstrate in the Computational Methodology section
Table 2, and the absorption spectra recorded in CH CN
are depicted in Figure 5. In general, complexes 1-4
possess allowed absorption bands in the UV region of
3
<
were measured to be >10 M cm and can thus be
375 nm, for which ε values at the absorption maxima
4
-1
-1
1
attributed to the ligand-centered ππ* transitions of the
chelates, i.e., fpbpymH, fpbpym, and fpbpyk. Next, the
lower-lying absorption band with peak wavelengths at
4
3
that the MC dd state may also play a role in emission
quenching.
00-600 nm can be reasonably assigned to a spin-allowed
MLCT transition in the singlet manifold. The carbonyl
functionality in the fpbpyk chelate, in part, elongates the
π conjugation and hence decreases the MLCT gap (vide
infra). Thus, complexes 2-4 containing the fpbpyk che-
The trend of the emission peak wavelength [666 nm (1)
795 nm (3) < 810 nm (2) < ∼1000 nm (4)] among titled
<
complexes in the solid state is in agreement with the
corresponding onset of absorption spectra of 1 < 3 < 2
< 4. To gain more insight into the photophysical proper-
ties of these NIR luminescent Ru and Os complexes,
the TDDFT method is applied on the basis of the
optimized ground-state structures for all four complexes
to calculate the properties of the low-energy electronic
transitions. Major frontier orbitals involved in the low-
lying transitions are depicted in Figure 6, while the
1
late showed the MLCT absorption being further red-
shifted from that of complex 1. The much longer wave-
length absorption band observed in 4 (cf. 1-3) is con-
II
II
II
sistent with the oxidation potential of Os being ∼0.3 V
II
more negative than that of the Ru analogue 3 (see
section 3.2).
As for the emission, the releasing of strained chelating
bite angles for 1-4 is thought to have significant effects
on improving the emission quantum yields. In contrast,
the emission for the titled complexes 1-4, i.e., the phos-
phorescence, is too weak to be resolved in either an
aerated or a degassed solution at room temperature. This
(35) (a) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722. (b) Treadway, J. A.; Loeb, B.; Lopez, R.; Anderson, P. A.;
Keene, F. R.; Meyer, T. J. Inorg. Chem. 1996, 35, 2242.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 831
3
Figure 7. Energy diagram of complexes 1-4. MLCT indicates the
lowest triplet electronic state obtained from unrestricted optimization,
3
starting from X-ray crystal structures. The MC dd state is also refined by
the same method, but the initial structure is from a largely distorted
geometry; see the text for a detailed description.
Figure 6. Frontier orbitals of complexes 1-4 that were involved in the
S f S and S f T transitions.
0 1 0 1
result of the lower oxidation potential in 4 (vide supra) and
hence the smallest energy gap for the phosphorescence.
Finally, upon elongation of the chelate π conjugation,
the proof of concept for tuning the relative energy gap
Table 3. Calculated Energy Levels and Orbital Transition Analyses of Complexes
-4
1
MLCT
(%)
3
3
between the MLCT emitting and MC dd states is
elaborated for all complexes. In this approach, the higher-
lying MC dd states were calculated following methodol-
complex states
λ
cal
f
assignment
3
1
2
T
1
517.3 0
490.5 0.0054 HOMO f LUMO (þ98%)
HOMO f LUMO (þ92%)
59.90
63.81
46.18
1
6
S
1
ogy illustrated by Persson. Details of the calculation are
described in the Experimental Section. The result shown
in Figure 7 clearly indicates that the replacement of
fpbpymH chelates in 1 with at least one fpbpyk chelate
in 2-4 renders better π conjugation on the coordination
sphere. The net result is to decrease the energy of the π*
T
1
732.4 0
HOMO f LUMO (þ90%)
HOMO f LUMOþ1 (þ8%)
S
1
689.6 0.0186 HOMO f LUMO (þ91%)
43.10
45.73
43.30
48.72
35.33
3
4
T
1
665.6 0
614.8 0.0252 HOMO f LUMO (þ89%)
807.5 0
HOMO f LUMO (þ98%)
699.1 0.0317 HOMO f LUMO (þ83%)
HOMO f LUMO (þ94%)
S
1
T
1
S
1
3
orbital and hence the reduction of the MLCT energy
3
level in 2-4, whereas the MC dd state is much less
affected. This leads to an increase of the energy gap
calculated properties, such as energy gaps in terms of
wavelength (λ), oscillator strengths (f), and correspond-
ing transition assignments, are listed in Table 3. For all
complexes, the calculated lower-lying transitions match
well with respect to the experimental results. For example,
3
3
between the MLCT and MC dd states for 2-4 than
that for 1, as shown in Figure 7. In fact, because of the
3
3
proximity in the energy level for 1, the MLCT f MC f
S0 radiationless deactivation process, in part, may ac-
count for its extremely weak emissive nature in solution at
room temperature. In contrast, this process is less ther-
mally accessible, as evidenced by the good emission yield
the S states of 1-4 are calculated to be around ∼490, 690,
1
615, and 700 nm, the values of which are all close to the
observed onsets of the absorption spectra recorded in an
acetonitrile solution. The calculated S -T gaps of 1-4
0
1
(
the fact that a larger gap is observed between the MLCT
∼0.08; Table 2) of 1 in the 77 K matrix. Finally, despite
(
1, 517 nm; 2, 730 nm; 3, 665 nm; 4, 807 nm) are also
3
qualitatively in agreement with the blue edge of their
emission spectra recorded in the solid state (powdery
samples) as well as in the 77 K methanol glass.
3
and MC dd states for 2 and likewise 3 and 4, emission
was only slightly improved for 2-4 in methanol at 77 K
simply because of their near-IR emission gap, which is
subject to vibrational quenching.
As listed in Table 3, the lowest singlet and triplet excited
states (S and T ) for all four complexes are primarily
1
1
attributed to the HOMO f LUMO transition, for which
the HOMO of 1-4 is mainly localized at the central metal
atom and, in part, the pyrazolate moiety, while the
LUMO is mainly located in the bipyridyl moiety, imply-
ing that the lowest-lying transition involves MLCT mixed
with an intraligand charge-transfer transition. Both
HOMO and LUMO energies of 1 are apparently lower
than those of other complexes due to the 2þ positive
charge associated with the metal center. Figure 6 also
4
. Conclusions
In conclusion, a new series of bipyridyl-pyrazolate che-
II
II
lates and the corresponding Ru and Os complexes 1-4
were designed and synthesized. The exact molecular struc-
tures of 1-4 have been well-established by a single-crystal
X-ray diffraction study. Complex 1 is readily oxygenated and
converted to 2, showing the formation of one fpbpyk chelate
bearing the carbonyl group, which is produced by methylene
oxidation on the terdentate fpbpymH chelate. Upon a further
increase in the temperature and extension of the reaction
time, the moderately stable 2 can be further oxidized to the
thermodynamic product 3 with two oxygenated fpbpyk
chelates. It is believed that the oxidation of the methylene
II
depicts the difference of the HOMO energy between Ru
(
ronment. Clearly, compared to the Ru metal atom, the
II
3) and Os (4) complexes under the same ligand envi-
II
II
lower oxidation state of the Os atom leads to a higher
HOMO energy for 4, consistent with the electrochemical

8
32 Inorganic Chemistry, Vol. 49, No. 3, 2010
Chen et al.
may originate from an intramolecular C-H N interaction
design of flexible terdentate bipyridyl pyrazolate ligands used
in the preparation of Ru and Os complexes with poten-
tially high luminescent efficiency in the NIR region.
3
3 3
II
II
between one methylene proton and the pyrazolate N atom of
the adjacent fpbpymH chelate, as well as the yet unexplored
catalytic effect associated with both a centered metal cation
and the dioxygen introduced. Thus, oxidative conversion
from fpbpymH to fpbpyk chelate caused significant altera-
tions on the inherent properties of the corresponding metal
complexes. Finally, all complexes exhibit >600-1100 nm
far-visible and NIR emission in the solid state at room
temperature, of which the spectral features can be well
rationalized by the associated electronic transition proper-
ties. Changes in the emission property, in part, are due to the
incorporation of a carbonyl group that increases π conjuga-
tion and releases the internal constraint between the metal
and terdentate ligand. We thus believe that the results
presented here might provide new insight into the further
Acknowledgment. This work was supported by the
National Science Council and Ministry of Economic
Affairs of Taiwan. We are also grateful to the National
Center for High-Performance Computing for computer
time and facilities.
Supporting Information Available: X-ray crystallographic
data files (CIF) of complexes 1-4, frontier orbital distributions
and net spin values from DFT calculation, emission spectra,
and electrochemical spectra of the relevant complexes. This
material is available free of charge via the Internet at http://
pubs.acs.org.