Luminescent piano-stool complexes incorporating 1-(4-cyanophenyl)imidazole: Synthesis, spectral, and structural studies

Article abstract of DOI:10.1021/ic049256m

Three novel luminescent piano-stool arene ruthenium complexes of general formula [(η⁶-arene)RuCl₂(CPI)] (η⁶- arene = benzene, 1, p-cymene, 2, and hexamethylbenzene, 3; CPI=1-(4-cyanophenyl) imidazole were prepared. The molecular structures of 2 and 3 were determined crystallographically. Reaction of 1-3 with EPh₃ (E = P, As, or Sb) and N-N donor bases such as 2,2′-bipyridine and 1,10-phenanthroline afforded cationic mononuclear complexes of general formula [(η⁶- arene)RuCl(CPI)(EPh₃)]⁺ (η⁶-arene = C ₆H₆, E = P (1a), E = As (1b), E = Sb (1c); η⁶-arene = C₁₀H₁₄, E = P (2a), E = As (2b), E = Sb (2c); η⁶-arene = C₆Me₆, E = P (3a), E = As (3b), E = Sb (3c)) and [(η⁶-arene)Ru(N-N)(CPI)] ²⁺ (η⁶-arene = C₆H₆, N-N = bipy (1d), N-N = phen (1e); η⁶-arene = C₁₀H₁₄, N-N = bipy (2d), N-N = phen (2e); η⁶-arene = C₆Me ₆, N-N = bipy (3d), N-N = phen (3e)). Molecular structures of 1a and 2a were also confirmed by X-ray crystallography. Structural studies of the complexes 2, 3, 1a, and 2a supported coordination of CPI through the imidazole nitrogen and the presence of a pendant nitrile group. Structural data also revealed stabilization of crystal packing in the complexes 2, 3, and 2a by C-H...X (X = Cl, F) type inter- and intramolecular interactions and in complex 1a by π-π stacking. Moreover, neutral homonuclear bimetallic complexes 2f,g were prepared by using complex 2 as a metallo-ligand, where CPI acts as a bridge between two metal centers. Emission spectra of the mononuclear complexes [(η⁶-arene)RuCl2(CPI)] and its derivatives exhibited intense luminescence when excited in the metal to ligand charge-transfer band.

Full text of DOI:10.1021/ic049256m

Inorg. Chem. 2004, 43, 8600−8608
Luminescent Piano-Stool Complexes Incorporating
1-(4-Cyanophenyl)imidazole: Synthesis, Spectral, and Structural Studies
Sanjay K. Singh, Manoj Trivedi, M. Chandra, Abhaya N. Sahay, and Daya Shankar Pandey*
Department of Chemistry, Awadhesh Pratap Singh UniVersity, Rewa-486 003 (M.P.), India
Received June 8, 2004
Three novel luminescent piano-stool arene ruthenium complexes of general formula [(
arene benzene, 1, p-cymene, 2, and hexamethylbenzene, 3; CPI 1-(4-cyanophenyl)imidazole were prepared.
The molecular structures of 2 and 3 were determined crystallographically. Reaction of 1 3 with EPh3 (E P, As,
or Sb) and N N donor bases such as 2,2 -bipyridine and 1,10-phenanthroline afforded cationic mononuclear
complexes of general formula [( C6H6, E P (1a), E As (1b), E Sb
6-arene)RuCl(CPI)(EPh3)]+ 6-arene
(1c); C10H14, E P (2a), E Sb (2c); C6Me6, E P (3a), E As (3b),
6-arene 6-arene
Sb (3c)) and [( C6H6, N bipy (1d), N phen (1e);
6-arene)Ru(N 6-arene
C10H14, N C6Me6, N bipy (3d), N phen (3e)).
6-arene
η -
6-arene)RuCl2(CPI)] (η6
)
)
−
)
−
′
η
(
η
)
)
)
)
η
)
)
)
As (2b), E
)
)
η
−
)
)
)
+
E
)
η
−
N)(CPI)]2
(
η
6-arene
N
)
−
N
)
η
)
−N
)
bipy (2d), N
−N
)
phen (2e);
η
)
−N
)
−N )
Molecular structures of 1a and 2a were also confirmed by X-ray crystallography. Structural studies of the complexes
2, 3, 1a, and 2a supported coordination of CPI through the imidazole nitrogen and the presence of a pendant nitrile
group. Structural data also revealed stabilization of crystal packing in the complexes 2, 3, and 2a by C
Cl, F) type inter- and intramolecular interactions and in complex 1a by π−π stacking. Moreover, neutral
homonuclear bimetallic complexes 2f,g were prepared by using complex 2 as a metallo-ligand, where CPI acts as
a bridge between two metal centers. Emission spectra of the mononuclear complexes [(
6-arene)RuCl2(CPI)] and
its derivatives exhibited intense luminescence when excited in the metal to ligand charge-transfer band.
−H‚‚‚X (X
)
η
Introduction
since there is an almost perfect orbital decoupling in the
twisted internal charge transfer state.3 It is expected that the
complexes in which redox sites are bridged by this type of
molecule could be a good model to test the possibility of
molecular switching. In this regard, 1-(4-cyanophenyl)-
imidazole (CPI) has drawn special attention due to occur-
rence of twisted internal charge transfer (TICT) and the
presence of two donor sites.4 Bridging ability coupled with
the twisted internal charge transfer (TICT) in CPI offers
Considerable recent attention has been paid toward design-
ing of new homo-/hetero-binuclear complexes, in which a
strong electronic interaction affords a stable mixed-valence
state, because of their possible use in the study of electron-
transfer reactions and in molecular scale electronic devices.1
In search of molecular switching devices based on binuclear
metal complexes, a number of systems have been developed.
However, none of them have shown the ability to completely
allow or block the transfer of electrons between two parts
of the molecule.2 It has been shown that certain acceptor-
donor molecules exhibit twisted internal charge transfer
(TICT) which appears attractive for molecular switching,
(2) (a) Joachim, C.; Launay, J.-P. Chem. Phys. 1986, 109, 93. (b) Lehn,
J.-M. Angew. Chem., Int. Ed. Engl. 1990, 29, 1304. (c) Bissell, R. A.;
de Silva, A. P.; Gunaratne, H. Q. N.; Lynch, P. L. M.; Maguire, G. E.
M.; Sandanayake, K. R. A. S. Chem. Soc. ReV. 1992, 21, 187. (d)
Feringa, B. L.; Jager, W. F.; de Lange, B. Tetrahedron 1993, 49, 8267.
(e) Gilat, S. L.; Kawai, S. H.; Lehn, J.-M. J. Chem. Soc., Chem.
Commun. 1993, 1439. (f) Oneil, M. P.; Niemczyk, M. P.; Svec, W.
A.; Gosztola, D.; Gaines, G. L.; Wasielewski, M. R. Science 1992,
257, 63. (g) Broo, A. Chem. Phys. 1993, 169, 135. (h) Bissell, R. A.;
Cordova, E.; Kaifer, A. E.; Stoddart, J. F. Nature 1994, 369, 133. (i)
Rettig, W. Angew. Chem., Int. Ed. Engl. 1986, 25, 971. (j) Lippert,
E.; Rettig, W.; Bonacickoutecky, V.; Heisel, F.; Miehe, J. A. AdV.
Chem. Phys. 1987, 68, 1.
* Author to whom correspondence should be addressed. E-mail:
dsprewa@yahoo.com.
(1) (a) Willett, R. D., Gatteschi, D., Kahn, O., Eds.; Magneto-Structural
Correlations in Exchange-Coupled Systems; Reidel: Dordrecht, Hol-
land, 1985. (b) Meyer, T. J. Pure Appl. Chem. 1986, 58, 1193. (c)
Lehn, J. M. Supramolecular Chemistry; VCH: Weinheim, Germany,
1995. (d) Damrauer, N. H.; Cerullo, G.; Yeh, A.; Boussie, T. R.; Shank,
C. V.; McCusker, J. K. Science 1997, 275, 54. (e) Beyeler, A.; Belser,
P. Coord. Chem. ReV. 2002, 230, 29.
(3) Sowinska, M.; Launay, J.-P.; Mugnier, J.; Pouget, J.; Valeur, B. J.
Photochem. 1987, 37, 69.
8600 Inorganic Chemistry, Vol. 43, No. 26, 2004
10.1021/ic049256m CCC: $27.50
© 2004 American Chemical Society
Published on Web 12/02/2004

Luminescent Piano-Stool Complexes
Synthesis and Characterization. The complexes 1-3 were
prepared by following the general procedure as described below
for the complex 1:
interesting perspectives for the study of intramolecular metal
to metal charge transfer as well as photoinduced geometrical
changes.5
Synthesis of [(η6-C6H6)RuCl2(CPI)] (1). A suspension of [{(η6-
C6H6)Ru(µ-Cl)Cl}2] (0.502 g, 1.0 mmol) in 25 mL of dichlo-
romethane was treated with CPI (0.338 g, 2.0 mmol) and stirred at
room temperature for 4 h. Slowly the suspension dissolved, and a
bright yellow solution was obtained. The resulting solution was
evaporated to dryness under reduced pressure, and the solid mass
thus obtained was extracted with dichloromethane. It was filtered
through Celite to remove any solid impurities, and light petroleum
ether was added to the filtrate with stirring until it became turbid.
A yellow-orange microcrystalline product separated which was
separated by filtration, washed several times with petroleum ether
(40-60 °C), and dried under vacuo. Yield: 0.334 g, 80%. Anal.
Calcd for C16Cl2H13N3Ru: C, 45.82; H, 3.10; N, 10.02. Found: C,
During the past few years, we have been interested in the
construction of metallo-ligands based on organometallic
systems and their possible application in the synthesis of
homo-/hetero-binuclear complexes.6 In this direction reactiv-
ity of CPI with the (arene)ruthenium complexes [{(η6-arene)-
Ru(µ-Cl)Cl}2] was examined under varying reaction condi-
tions. In this paper we report the synthetic aspects of a series
of neutral mononuclear complexes [(η6-arene)RuCl2(CPI)]
which could behave as metallo-ligands, their spectral proper-
ties and reactivity, and molecular structures of [(η6-C10H14)-
RuCl2(CPI)] (2), [(η6-C6Me6)RuCl2(CPI)] (3), [(η6-C6H6)-
RuCl(CPI)(PPh3)]PF6‚CH2Cl2 (1a), and [(η6-C10H14)RuCl-
(CPI)(PPh3)]BF4 (2a), along with interaction studies.
1
45.78; H, 3.08; N, 10.00. IR (Nujol): 2226 cm-1 ν(CtN). H
(CDCl3): δ 5.94 (s, η6-C6H6), 7.45 (d, 1H, 7.4 Hz), 7.76 (d, 1H, 6
Hz), 7.83 (d, 2H, 9 Hz), 8.02 (d, 2H, 9 Hz), 8.51 (s, 1H) ppm. 13
C
Experimental Section
(CDCl3): δ 81.51 (C6H6), 111.14 (CN), 117.01, 120, 118, 131,
133, 138, 140.
Materials. All the synthetic manipulations were performed under
oxygen-free nitrogen atmosphere. The solvents were dried and
distilled before use by following the standard procedures. R-Phel-
landrene (Fluka), triphenylphosphine, triphenylarsine, triphenyl-
stibine, 2,2′-bipyridine, 1,10-phenanthroline, hydrated ruthenium(III)
chloride, hexamethylbenzene, ammonium tetrafluoroborate, and
ammonium hexafluorophosphate (all Aldrich) were used as re-
ceived. The ligand 1-(4-cyanophenyl)imidazole and the precursor
complexes [{(η6-arene)Ru(µ-Cl)Cl}2] were prepared and purified
by following the literature procedures.5,7-9
Synthesis of [(η6-C10H14)RuCl2(CPI)] (2). This complex was
prepared by treatment of [{(η6-C10H14)Ru(µ-Cl)Cl}2] (0.612 g, 1.0
mmol) with CPI (0.338 g, 2.0 mmol) in dichloromethane (25 mL)
following the above procedure. It was separated as yellow-orange
crystals. Yield: 0.403 g, 85%. Anal. Calcd for C20Cl2H21N3Ru: C,
50.52; H, 4.42; N, 8.84. Found: C, 50.58; H, 4.52; N, 8.86. IR
(Nujol): 2225 cm-1 ν(CtN). H (CDCl3): δ 1.30 (d, CH(CH3)2,
1
6.9 Hz), 2.22 (s, C-CH3), 3.07 (sp, CH(CH3)2, 6.8 Hz), 5.30-
5.50 (dd, C6H4, 6 Hz), 7.34 (d, 2H,6.0 Hz), 7.43 (d, 1H, 8.7 Hz),
7.48 (d, 2H, 6.0 Hz), 7.75 (d, 1H, 8.4 Hz), 8.38 (s, 1H). 13C
(CDCl3): δ 22.2 (CHMe2), 30.6 (CHMe2), 81.4 (C6H4), 81.5 (C6H4),
97.5 (C-CH3), 102.8 (C.CHMe2), 111.8 (CN), 117.6, 118.3, 121,
133.8, 134.1, 138.1, 138.8. FAB+, m/z: 440 ([M]+), 271 ([M -
CPI]+), 235 ([M - CPI - Cl]+).
Synthesis of [(η6-C6Me6)RuCl2(CPI)] (3). This was prepared
by reacting [{(η6-C6Me6)Ru(µ-Cl)Cl}2] (0.668 g, 1.0 mmol) with
CPI (0.338 g, 2.0 mmol) in 25 mL of dichloromethane. The yellow
microcrystalline complex was filtered off and washed several times
with petroleum ether and dried under vacuo. Yield: 0.428 g, 85%.
Anal. Calcd for C22Cl2H25N3Ru: C, 52.49; H, 4.97; N, 8.35.
Found: C, 52.34; H, 4.86; N, 8.28. IR (Nujol): 2222 cm-1 ν(Ct
N). 1H (CDCl3): δ 2.07 (η6-C6Me6), 7.44 (d, 2H, 9.0 Hz), 7.73 (d,
2H, 9.0 Hz), 7.83 (d, 1H, 3 Hz), 8.14 (d, 1H, 8.7 Hz), 8.29 (s, 1H).
13C (CDCl3): δ 15.40 (C6Me6), 93.18 (C6Me6), 111.5 (CN), 117.64,
121.29, 132.58, 133.93, 133.03, 137, 139.54.
Instrumentation. Elemental analyses of the complexes were
performed at Sophisticated Analytical Instrument Facility, Central
Drug Research Institute, Lucknow, India. Infrared spectra were
recorded on a Perkin-Elmer-577 spectrophotometer. NMR spectra
were obtained on Bruker-DRX300 MHz spectrometer with tetra-
methylsilane as an internal standard. Electronic and emission spectra
of the complexes were obtained on a Shimadzu UV-1601 and
Perkin-Elmer-LS 55 luminescence spectrometer, respectively. The
FAB mass spectra were recorded on a JEOL SX 102/DA 6000 mass
spectrometer using xenon (6 kV, 10 mA) as the FAB gas. The
accelerating voltage was 10 kV, and the spectra were recorded at
room temperature with m-nitrobenzyl alcohol as the matrix.
Electrochemical data were acquired on a PAR model 273A
electrochemistry system at a scan rate of 50 mV s-1. The sample
solutions (10-4 M) were prepared in purified acetonitrile containing
-
NEt4+ClO4 (0.1 M) as a supporting electrolyte. Solution was
deoxygenated by bubbling nitrogen for about 20 min in each
experiment. Platinum wire working and auxiliary electrodes and
an aqueous saturated calomel reference electrode were used in a
three-electrode configuration. Caution! Care must be taken while
working with perchlorate salts.
The complexes 1a-e, 2a-e, and 3a-e were prepared by
following the general method described below for complex 1a:
Synthesis of [(η6-C6H6)RuCl(CPI)(PPh3)]PF6.CH2Cl2 (1a). To
a suspension of complex 1, [(η6-C6H6)RuCl2(CPI)] (0.419 g, 1.0
mmol), in 25 mL of methanol was added PPh3 (0.262 g, 1.0 mmol),
and contents of the flask were heated under reflux for 1 h. The
resulting pale yellow solution was cooled to room temperature and
filtered through Celite. Ammonium hexafluorophosphate dissolved
in 10 mL of methanol was added to the filtrate. Just after addition
of salt, a yellow crystalline solid separated. It was filtered out and
washed several times with methanol and diethyl ether. Yield: 0.718
g, 82%. Anal. Calcd for C35Cl3F6H30N3P2Ru: C, 47.94; H, 3.42;
N, 4.79. Found: C, 47.88; H, 3.44; N, 4.68. IR (Nujol): 2227 cm-1
ν(CtN). 1H (CDCl3): δ 5.97 (η6-C6H6), 7.30-7.45 (br m, aromatic
protons of PPh3), 7.99 (d, 1H, 6 Hz), 7.83 (d, 2H, 9.0 Hz), 7.72 (d,
2H, 9.0 Hz), 8.42 (s, 1H), 7.75 (d, 1H, 6 Hz), 6.85 (d, 1H, 6.7 Hz).
(4) Schenter, G. K.; Duke, C. B. Chem. Phys. Lett. 1991, 176, 563.
(5) Hatzidimitriou, A.; Gourdon, A.; Devillers, J.; Launay, J.-P.; Mena,
E.; Amouyal, E. Inorg. Chem. 1996, 35, 2212.
(6) (a) Gupta, D. K.; Sahay, A. N.; Pandey, D. S.; Jha, N. K.; Sharma,
P.; Espinosa, G.; Cabrera, A.; Puerta, M. C.; Valerga, P. J. Organomet.
Chem. 1998, 568, 13. (b) Sahay, A. N.; Pandey, D. S.; Walwalkar,
M. G. J. Organomet. Chem. 2000, 605, 74. (c) Singh, A.; Singh, N.;
Pandey, D. S. J. Organomet. Chem. 2002, 642, 48.
(7) Robertson, D. R.; Robertson, I. W.; Stephenson, T. A. J. Organomet.
Chem. 1980, 202, 309.
(8) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974, 233.
(9) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg.
Synth. 1982, 21, 74.
Inorganic Chemistry, Vol. 43, No. 26, 2004 8601

Singh et al.
31P (dmso-D6): δ 36.57 (s). FAB+, m/z: 646 ([M]+), 477 ([M -
CPI]+), 441 ([M - CPI - Cl]+).
Characterization Data for [(η6-C6Me6)RuCl(CPI)(SbPh3)]BF4
(3c). An orange crystalline solid was formed. Yield: 0.668 g,
73.5%. Anal. Calcd for BC40ClF4H40N3RuSb: C, 52.81; H, 4.40;
N, 4.62. Found: C, 52.59; H, 4.71; N, 4.68. IR (Nujol): 2231 cm-1
ν(CtN). 1H (CDCl3): δ 2.03 (η6-C6Me6), 7.26-7.45 (br m,
aromatic protons of SbPh3), 7.36 (d, 1H, 6.2 Hz), 7.81 (d, 1H, 4.9
Hz), 7.87 (d, 2H, 8.9 Hz), 8.10 (d, 2H, 6.1 Hz), 8.49 (s, 1H). FAB+,
m/z: 822 ([M]+), 653 ([M - CPI]+).
Characterization Data for [(η6-C10H14)RuCl(CPI)(PPh3)]BF4
(2a). Orange crystals were formed. Yield: 0.577 g, 73%. Anal.
Calcd for BC38ClF4H36N3PRu: C, 57.72; H, 4.56; N, 5.32. Found:
1
C, 57.78; H, 4.78; N, 5.49. IR (Nujol): 2228 cm-1 ν(CtN). H
(CDCl3): δ 1.30 (d, CH(CH3)2, 6.9 Hz), 2.22 (s, C-CH3), 3.07
(sp, CH(CH3)2, 6.8 Hz), 5.30-5.50 (dd, C6H4, 6 Hz), 7.28-7.48
(br m, aromatic protons of PPh3), 7.81 (s, 1H), 7.63 (d, 1H, 8.4
Hz), 8.06 (d, 1H, 8.1 Hz), 8.42 (s, 1H). 31P (dmso-D6): 36.56 (s).
FAB+, m/z: 703 ([M]+), 534 ([M - CPI]+), 498 ([M - CPI -
Cl]+).
Characterization Data for [(η6-C6H6)Ru(bipy)(CPI)][PF6]2
(1d). Dark red crystals were formed. Yield: 0.572 g, 72%. Anal.
Calcd for C26F12H21N5P2Ru: C, 39.29; H, 2.64; N, 8.82. Found:
1
C, 39.41; H, 2.48; N, 8.45. IR (Nujol): 2230 cm-1 ν(CtN). H
(CDCl3): δ 9.77 (d, 2H, 5.4 Hz), 9.60 (d, 2H, 5.7 Hz), 8.79 (dt,
2H, 7.7 Hz), 8.88 (s, 1H), 8.62 (d, 1H, 4.8 Hz), 7.74 (m, 2H), 7.90
(d, 2H, 6.4 Hz), 7.84 (d, 2H, 6.4 Hz), 6.09 (s, 6H), 7.75 (d, 1H,
6.6 Hz). FAB+, m/z: 504 ([M]+), 336 ([M - CPI]+).
Characterization Data for [(η6-C6Me6)RuCl(CPI)(PPh3)]PF6
(3a). Greenish crystals were formed. Yield: 0.631 g, 72%. Anal.
Calcd for C40ClF6H40N3P2Ru: C, 54.79; H, 4.56; N, 4.79. Found:
1
C, 54.92; H, 4.89; N, 4.92. IR (Nujol): 2230 cm-1 ν(CtN). H
Characterization Data for [(η6-C10H14)Ru(bipy)(CPI)][PF6]2
(2d). Pale yellow crystals were formed. Yield: 0.586 g, 69%. Anal.
Calcd for C30F12H29N5P2Ru: C, 42.35; H, 3.41; N, 8.23. Found:
(CDCl3): δ 1.83 (η6-C6Me6), 7.21-7.57 (br m, aromatic protons
of PPh3), 7.76 (d, 2H, 7.5 Hz), 7.57 (d, 2H, 8.1 Hz), 7.32 (d, 1H,
8.4 Hz), 7.24 (d, 1H, 6.0 Hz), 8.39 (s, 1H). 31P (dmso-D6): 35.98
(s). FAB+, m/z: 731 ([M]+), 562 ([M - CPI]+), 526 ([M - CPI -
Cl]+).
Characterization Data for [(η6-C6H6)RuCl(CPI)(AsPh3)]PF6
(1b). Red crystals were formed. Yield: 0.662 g, 79%. Anal. Calcd
for AsC34ClF6H28N3PRu: C, 48.69; H, 3.34; N, 5.01. Found: C,
48.94; H, 3.37; N, 5.12. IR (Nujol): 2227 cm-1 ν(CtN). 1H
(CDCl3): δ 5.94 (η6-C6H6), 7.25-7.61 (br m, aromatic protons of
AsPh3), 7.45 (s, 1H), 7.76 (s, 1H), 7.83 (d, 1H, 8.7 Hz), 8.02 (d,
1H, 5.9 Hz), 8.51 (s, 1H).
1
C, 42.45; H, 3.55; N, 7.99. IR (Nujol): 2235 cm-1 ν(CtN). H
(CDCl3): δ 1.30 (d, CH(CH3)2, 6.9 Hz), 2.22 (s, C-CH3), 3.07
(sp, CH(CH3)2, 6.8 Hz), 5.30-5.50 (dd, C6H4, 6 Hz), 9.67 (d, 2H,
5.6 Hz), 9.50 (d, 2H, 5.7 Hz), 8.69 (dt, 2H, 7.6 Hz), 8.78 (s, 1H),
8.52 (d, 1H, 4.9 Hz), 7.64 (m, 2H), 7.80 (d, 2H, 6.5 Hz), 7.74 (d,
2H, 6.6 Hz), 7.65 (d, 1H, 6.6 Hz). FAB+, m/z: 560 ([M]+), 391
([M - CPI]+).
Characterization Data for [(η6-C6Me6)Ru(bipy)(CPI)][BF4]2
(3d). Yellow crystals were formed. Yield: 0.564 g, 74%. Anal.
Calcd for B2C32F8H33N5Ru: C, 50.39; H, 4.33; N, 9.19. Found:
Characterization Data for [(η6-C10H14)RuCl(CPI)(AsPh3)]BF4
(2b). Yellow crystals were formed. Yield: 0.571 g, 68.5%. Anal.
Calcd for AsBC38ClF4H36N3Ru: C, 54.74; H, 4.32; N, 5.04. Found:
1
C, 50.66; H, 4.39; N, 8.96. IR (Nujol): 2234 cm-1 ν(CtN). H
(CDCl3): δ 2.03 (η6-C6Me6), 9.57 (d, 5.5 Hz, 2H), 9.40 (d, 2H,
5.6 Hz), 8.59 (dt, 2H, 7.8 Hz), 8.68 (s, 1H), 8.42 (d, 1H, 4.8 Hz),
7.54 (m, 2H), 7.70 (d, 2H, 6.4 Hz), 7.64 (d, 2H, 6.7 Hz), 7.75 (d,
1H, 6.6 Hz). FAB+, m/z: 588 ([M]+), 419 ([M - CPI]+).
Characterization Data for [(η6-C6H6)Ru(phen)(CPI)][PF6]2
(1e). Brown crystals were formed. Yield: 0.499 g, 61%. Anal. Calcd
for C28F12H21N5P2Ru: C, 41.08; H, 2.57; N, 8.56. Found: C, 41.22;
H, 2.68; N, 8.39. IR (Nujol): 2233 cm-1 ν(CtN). 1H (CDCl3): δ
9.48 (d, 2H, 5.3 Hz), 8.80 (d, 2H, 8.4 Hz), 8.28 (s, 2H), 8.10 (dd,
2H, 8.4 Hz), 9.83 (s, 1H), 7.42 (s, 6H, C6H6), 7.85 (d, 2H, 6 Hz),
7.79 (d, 2H, 9 Hz), 7.59 (d, 1H, 6 Hz), 7.41 (d, 1H, 6 Hz). FAB+,
m/z: 528 ([M]+), 359 ([M - CPI]+).
1
C, 54.68; H, 4.41; N, 5.06. IR (Nujol): 2230 cm-1 ν(CtN). H
(CDCl3): δ 1.30 (d, CH(CH3)2, 6.9 Hz), 2.22 (s, C-CH3), 3.07
(sp, CH(CH3)2, 6.8 Hz), 5.30-5.50 (dd,C6H4, 6 Hz), 7.27-7.58
(br m, aromatic protons of AsPh3), 7.43 (d, 1H, 6.5 Hz), 7.80 (d,
1H,6.3 Hz), 7.86 (d, 2H, 9.1 Hz), 8.09 (d, 2H, 5.8 Hz), 8.63 (s,
1H). FAB+, m/z: 746 ([M]+), 577 ([M - CPI]+), 541 ([M - CPI
- Cl]+).
Characterization Data for [(η6-C6Me6)RuCl(CPI)(AsPh3)]BF4
(3b). Orange crystals were formed. Yield: 0.577 g, 67%. Anal.
Calcd for AsBC40ClF4H40N3Ru: C, 55.75; H, 4.65; N, 4.88.
Found: C, 55.91; H, 4.84; N, 4.76. IR (Nujol): 2229 cm-1 ν(Ct
Characterization Data for [(η6-C10H14)Ru(phen)CPI][PF6]2
(2e). Yellow crystals were formed. Yield: 0.655 g, 75%. Anal.
Calcd for C32H29F12N5P2Ru: C, 43.93; H, 3.32; N, 8.01. Found:
1
N). H (CDCl3): δ 1.82 (η6-C6Me6), 7.03-7.23 (br m, aromatic
protons of AsPh3), 7.50 (d, 1H, 5.6 Hz), 7.79 (d, 1H, 5.1 Hz), 7.86
(d, 2H, 8.9 Hz), 8.13 (d, 2H, 6.1 Hz), 8.59 (s, 1H). FAB+, m/z:
774 ([M]+), 605 ([M - CPI]+), 569 ([M - CPI - Cl]+).
1
C, 43.70; H, 3.08; N, 8.12. IR (Nujol): 2232 cm-1 ν(CtN). H
(CDCl3): δ 1.30 (d, CH(CH3)2, 6.9 Hz), 2.22 (s, C-CH3), 3.07
(sp, CH(CH3)2, 6.8 Hz), 5.30-5.50 (dd, C6H4, 6 Hz), 9.28 (d, 2H,
5.3 Hz), 8.60 (d, 2H, 8.4 Hz), 8.08 (s, 2H), 8.00 (dd, 2H, 8.4 Hz),
9.63 (s, 1H), 7.22 (s, 6H), 7.65 (d, 2H, 6 Hz), 7.59 (d, 2H, 9 Hz),
7.39 (d, 1H, 6 Hz), 7.21 (d, 1H, 6 Hz). FAB+, m/z: 584 ([M]+),
415 ([M - CPI]+).
Characterization Data for [(η6-C6H6)RuCl(CPI)(SbPh3)]PF6
(1c). Dark red crystals were formed. Yield: 0.715 g, 81%. Anal.
Calcd for C34ClF6H28N3PruSb: C, 46.21; H, 3.17; N, 4.76. Found:
1
C, 46.28; H, 3.27; N, 4.72. IR (Nujol): 2228 cm-1 ν(CtN). H
(CDCl3): δ 6.03 (η6-C6H6), 7.20-7.43 (br m, aromatic protons of
SbPh3), 7.55 (d, 1H, 6.9 Hz), 7.79 (d, 1H, 7.3 Hz), 7.79 (d, 2H,
8.8 Hz), 7.98 (d, 2H, 5.9 Hz), 8.61 (s, 1H). FAB+, m/z: 738 ([M]+),
569 ([M - CPI]+).
Characterization Data for [(η6-C6Me6)Ru(phen)CPI][BF4]2
(3e). Pale yellow crystals were formed. Yield: 0.558 g, 71%. Anal.
Calcd for B2C34F8H33N5Ru: C, 51.91; H, 4.20; N, 8.91. Found:
1
C, 51.65; H, 4.30; N, 9.02. IR (Nujol): 2229 cm-1 ν(CtN). H
Characterization Data for [(η6-C10H14)RuCl(CPI)(SbPh3)]BF4
(2c). Brown orange crystals were formed. Yield: 0.625 g, 71%.
Anal. Calcd for BC38ClF4H36N3RuSb: C, 51.76; H, 4.09; N, 4.77.
Found: C, 51.46; H, 4.18; N, 4.47. IR (Nujol): 2227 cm-1 ν(Ct
(CDCl3): δ 2.03 (η6-C6Me6), 9.38 (d, 2H, 5.3 Hz), 8.70 (d, 2H,
8.4 Hz), 8.18 (s, 2H), 8.10 (dd, 2H, 8.4 Hz), 9.73 (s, 1H), 7.32 (s,
6H), 7.75 (d, 2H, 6 Hz), 7.69 (d, 2H, 9 Hz), 7.49 (d, 1H, 6 Hz),
7.31 (d, 1H, 6 Hz). FAB+, m/z: 612 ([M]+), 419 ([M - CPI]+).
1
N). H (CDCl3): δ 2.07 (η6-C10H14), 7.14-7.35 (br m, aromatic
6
6
protons of SbPh3), 7.56 (d, 1H, 6.6 Hz), 7.83 (d, 1H, 6.2 Hz), 7.91
(d, 2H, 8.9 Hz), 8.07 (d, 2H, 6.3 Hz), 8.53 (s, 1H). FAB+, m/z:
794 ([M]+), 625 ([M - CPI]+).
Characterization Data for [(η -C10H14)RuCl2(µ-CPI)Ru(η -
C6H6)Cl2] (2f). A solution of the complex 2, [(η6-C10H14)RuCl2-
(CPI)] (0.475 g, 1 mmol), in 25 mL of dichloromethane was treated
8602 Inorganic Chemistry, Vol. 43, No. 26, 2004

Luminescent Piano-Stool Complexes
with dimeric complex [(η6-C6H6)Ru(µ-Cl)Cl}2] (0.502 g, 1 mmol),
and the resulting solution was stirred at room temperature for about
6 h. Slowly it turned brown, and a clear solution was obtained. It
was filtered and concentrated under reduced pressure. The solid
mass thus obtained was extracted with dichloromethane and filtered,
and the filtrate was layered with light petroleum ether and left for
slow crystallization. After a couple of days a brown microcrystalline
product was obtained. It was filtered out, washed several times with
petroleum ether, and dried under vacuo. Yield: 0.500 g, 69%. Anal.
Calcd for C26Cl4H27N3Ru2: C, 43.03; H, 3.72; N, 5.79. Found: C,
42.98; H, 3.70; N, 5.81. IR (Nujol): 2208 cm-1 ν(CtN). 1H
(CDCl3): δ 1.30 (d, CH(CH3)2, 6.9 Hz) 2.22 (s, C-CH3), 3.07
(sp, CH(CH3)2, 6.8 Hz), 5.30-5.50 (dd, C6H4, 6 Hz), 7.42 (s, 6H,
C6H6), 7.34 (d, 1H, 6.7 Hz), 7.43 (d, 2H, 8.7 Hz), 7.48 (d, 1H, 8.4
Hz), 7.75 (d, 2H, 8.4 Hz), 8.38 (s, 1H).
Scheme 1
The complexes 1-3 reacted with EPh3 (E ) P, As or Sb)
and N-N donor bases such as 2,2′-bipyridine and 1,10-
phenanthroline afforded new cationic complexes [(η6-arene)-
RuCl(CPI)(EPh3)]+ (η6-arene ) C6H6, E ) P (1a), E ) As
(1b), E ) Sb (1c); η6-arene ) C10H14, E ) P (2a), E ) As
(2b), E ) Sb (2c); η6-arene ) C6Me6, E ) P (3a), E ) As
(3b), E ) Sb (3c)) and [(η6-arene)Ru(N-N)(CPI)]+ (η6-arene
) C6H6, N-N ) bipy (1d), N-N ) phen (1e); η6-arene )
C10H14, N-N ) bipy (2d), N-N ) phen (2e); η6-arene )
C6Me6, N-N ) bipy (3d), N-N ) phen (3e)), which were
isolated as tetrafluoroborate or hexafluorophosphate salts
(Scheme 2).
Instead of substitution of metal-bound CPI, a chloro group
is being substituted in these reactions, suggesting that the
metal to CPI bond in the complexes is quite strong which
has further been supported by FAB-MS and structural data.
This observation is contrary to our earlier findings on the
closely related 4-cyanopyridine complexes [Ru(η6-arene)-
Cl2(CNPy)] (η6-arene ) benzene, p-cymene, and hexameth-
ylbenzene; CNPy ) 4-cyanopyridine) and η3:η3-bis(allyl)
complex [Ru(η3:η3-C10H14)Cl2(CNPy)] (η3:η3-C10H14 ) 2,7-
dimethyloctdienedienyl) wherein the metal-bound 4-cyan-
opyridine was displaced by the respective bases, but not the
chloro ligand, leading to the formation of [Ru(η6-arene)Cl2-
(EPh3)] and [Ru(η3:η3-C10H14)Cl2(EPh3)], respectively.6 In
the reactions involving N-N donor bases both chloro groups
are displaced by the incoming ligand bipy or phen to form
[(η6-arene)Ru(CPI)(N-N)]2+.
6
6
Characterization Data for [(η -C10H14)RuCl2(µ-CPI)Ru(η -
C6Me6)Cl2] (2g). A red brown compound formed. Yield: 0.566 g,
70%. Anal. Calcd for C32Cl4H39N3Ru2: C, 47.47; H, 4.82; N, 5.19.
Found: C, 47.58; H, 4.80; N, 5.16. IR (Nujol): 2212 cm-1 ν(Ct
N). 1H (CDCl3): δ 1.26 (d, CH(CH3)2, 6.9 Hz), 2.31 (s, C-CH3),
3.10 (sp, CH(CH3)2, 6.9 Hz), 5.29-5.52 (dd, C6H4, 6.1 Hz), 2.06
(η6-C6Me6), 7.35 (d, 1H, 5.9 Hz), 7.47 (d, 2H, 8.8 Hz), 7.49 (d,
1H, 8.3 Hz), 7.71 (d, 2H, 8.3 Hz), 8.41 (s, 1H).
X-ray Structure Determinations. Crystals suitable for single-
crystal X-ray analyses for the complex [(η6-C10H14)Ru(CPI)Cl2] (2),
[(η6-C6Me6)Ru(CPI)Cl2] (3), [(η6-C6H6)RuCl(CPI)(PPh3)]PF6‚CH2Cl2
(1a), and [(η6-C10H14)RuCl(CPI)(PPh3)]BF4 (2a) were grown from
CH2Cl2/petroleum ether (40-60 °C) at room temperature. Prelimi-
nary data on the space group and unit cell dimensions as well as
intensity data were collected on Enraf-Nonius MACH3 diffracto-
meter using graphite-monochromatized Mo KR radiation. The
crystal orientation, cell refinement, and intensity measurements were
made using the program CAD-4 PC. The structure was solved by
direct methods and refined by using MAXUS (1999) and SHELX-
97.10 The non-hydrogen atoms were refined with anisotropic thermal
parameters. All the hydrogen atoms were geometrically fixed and
allowed to refine using a riding model. The computer program
PLATON was used for analyzing the interaction and stacking
distances.10
Results and Discussion
Furthermore, the complex 2 reacted with dimers [{(η6-
arene)Ru(µ-Cl)Cl}2] (η6-arene ) benzene or hexamethyl-
benzene) to give binuclear complexes [(η6-C10H14)Cl2Ru(µ-
CPI)Ru(η6-C6H6)Cl2] (2f) and [(η6-C10H14)Cl2Ru(µ-CPI)Ru(η6-
C6Me6)Cl2] (2g), wherein the CPI acts as a bridge between
two metal centers (Scheme 3).
Synthesis and Characterization of the Complexes. The
new series of piano-stool complexes [(η6-arene)RuCl2(CPI)]
was obtained in excellent yield in the usual manner by
reacting the chloro-bridged dimers [{(η6-arene)Ru(µ-Cl)Cl}2]
with an excess of CPI in dichloromethane at room temper-
ature (Scheme 1).
Analytical data of the complexes conformed well to their
respective formulations. Information about composition of
the complexes was also obtained from ESMS and FAB-MS
spectra of the complexes (recorded in the Experimental
Section). The position of various peaks and overall frag-
mentation pattern in the FAB-MS spectra of respective
complexes conformed well to respective formulations. More
information about the structure and bonding in the complexes
has been deduced from the spectral studies.
Complexes 1-3 are air-stable solids and soluble in water
and other common organic solvents and do not show any
signs of decomposition in solution upon exposure to air for
days. It was observed that in the reactions involving
formation of the complexes 1-3 no intermediates were
isolated, it is supposed that the reactions pass through chloro
bridge cleavage and coordination of the CPI through imi-
dazole nitrogen.
The IR spectra of mononuclear complexes 1-3 and
cationic complexes 1a-e, 2a-e, and 3a-e displayed sharp
and intense bands around 2226 cm-1 corresponding to
ν(CtN). The position of the ν(CtN) remained unaltered,
compared to that in the ligand itself; this suggested linkage
(10) (a) Mackay, S.; Dong, W.; Edwards, C.; Henderson, A.; Gilmox, C.;
Stewart, N.; Shankland, K.; Donald, A. University of Glasgow,
Scotland, 1999. (b) Sheldrick, G. M. SHELX-97: Programme for
refinement of crystal structures; University of Gottingen: Gottingen,
Germany, 1997. (c) PLATON, Spek, A. L. Acta Crystallogr. 1990,
A46, C31.
Inorganic Chemistry, Vol. 43, No. 26, 2004 8603

Singh et al.
Scheme 2
Scheme 3
Table 1. Electronic and Emission Spectral Data for the Complexes
absorbance
emission
complexes
λ
max/nm (ꢀ/Μ-1 cm-1
)
λ
max/nm
[(η6-C6H6)RuCl2(CPI)] (1)
400 (1008), 315 (20 246), 267 (31 292)
332 (4156), 264 (52 478)
328 (845), 260 (19 160)
450
408
443
448
[(η6-C6H6)RuCl(CPI)(PPh3)](PF6)CH2Cl2 (1a)
[(η6-C6H6)RuCl(CPI)(AsPh3)](PF6) (1b)
[(η6-C6H6)RuCl(CPI)(SbPh3)](PF6) (1c)
[(η6-C6H6)Ru(bipy)CPI](PF6)2 (1d)
386 (2396), 270 (72 246)
350 (20 218), 317 (31 042), 287 (52 256).
355 (21 234), 317 (36 454), 267 (79 998)
407 (1730), 335 (2055), 249 (36 123)
338 (2543), 254 (39 640)
[(η6-C6H6)Ru(phen)CPI](PF6)2 (1e)
[(η6-C10H14)RuCl2(CPI)] (2)
476
462a
434
417
418
460
437
422
427
475
444
427
411
466
472
[(η6-C10H14)RuCl(CPI)(PPh3)](BF4) (2a)
[(η6-C10H14)RuCl(CPI)(AsPh3)](BF4) (2b)
[(η6-C10H14)RuCl(CPI)(SbPh3)](BF4) (2c)
[(η6-C10H14)Ru(bipy)CPI](PF6)2 (2d)
[(η6-C10H14)Ru(phen)CPI](PF6)2 (2e)
[(η6-C10H14)RuCl2(µ-CPI)Ru(η6-C6H6)Cl2] (2f)
[(η6-C10H14)RuCl2(µ-CPI)Ru(η6-C6Me6)Cl2] (2g)
[(η6-C6Me6)RuCl2(CPI)] (3)
388 (2286), 324 (42 285), 263 (45 042)
389 (2691), 338 (3277), 260 (45 751)
348 (3181), 316 (15 612), 304 (14 594), 255 (34 388)
367 (2758), 322 (60 000), 275 (39 365)
391 (2363), 333 (2875), 268 (34 362)
397 (3365), 333 (7822), 268 (36 243)
412 (1536), 342 (22 567), 267 (31 123)
336 (54 285), 250 (71 428), 233 (82 000)
398 (2102), 334 (37 428), 252 (42 766)
381 (2385), 318 (40 325), 260 (42 041)
404 (2589), 369 (3155), 291 (19 822)
356 (6258), 293 (21 387), 270 (50 010)
[(η6-C6Me6)RuCl(CPI)(PPh3)](PF6) (3a)
[(η6-C6Me6)RuCl(CPI)(AsPh3)](BF4) (3b)
[(η6-C6Me6)RuCl(CPI)(SbPh3)](BF4) (3c)
[(η6-C6Me6)Ru(bipy)CPI](BF4)2 (3d)
[(η6-C6Me6)Ru(phen)CPI](BF4)2 (3e)
a Φ ) 0.027.
of CPI with the metal center in the respective complexes
through imidazole nitrogen.5 The binuclear complexes 2f,g
displayed a shift in the position of ν(CtN) to ∼2210 cm-1.
The shift in the position of the ν(CtN) in binuclear
complexes relative to that in the free ligand or mononuclear
complexes could be attributed to kinematic effects arising
from coordination of pendant nitrile group with another
ruthenium center.
nitrogen. The conjugative and electron-withdrawing abilities
of the -CN group pulls electron density away from the
imidazole nucleus toward itself, leading to a decrease of
electron density on the metal center which, in turn, may pull
more electron density away from the η6-arene, leading to
deshielding of η6-arene protons. The 1H NMR spectra of the
EPh3 containing complexes 1a-c, 2a-c, and 3a-c or those
of N-N donor bases 1d,e, 2d,e, and 3d,e displayed signals
associated with CPI, EPh3, and bipy or phen.8 The position
and integrated intensity of various resonance supported well
the presence of ligand CPI and formulation of the respective
complexes. The nitrile carbon of the CPI in the complexes
resonated in the range 106.6-111.8 ppm, while the other
carbons of CPI resonated in the range 117.6-144.2 ppm.11
Electronic Spectroscopy. UV/vis absorption and emission
data for the complexes are listed in Table 1. The low-spin
1
NMR Spectroscopy. The H NMR spectral data of the
complexes along with their assignments are recorded in the
Experimental Section. In the 1H NMR spectra of the neutral
mononuclear complex 1-3 arene protons displayed down-
field shift as compared to that in the respective precursor
complexes.9 Downfield shift in the position of the arene
protons might result from the change in electron density on
the metal center due to linkage of CPI through its imidazole
8604 Inorganic Chemistry, Vol. 43, No. 26, 2004

Luminescent Piano-Stool Complexes
Emission Spectroscopy. All the complexes are found to
be luminescent at room temperature in dichloromethane. The
relevant luminescence data for the complexes are listed in
Table 1 (Figure 2). Complexes upon excitation in their
respective lowest energy MLCT band maximum (340-410
nm) corresponding to the ruthenium-imidazole charge
transfer resulted in a moderately strong emission (408-476
nm). The emission spectra are found to be parallel with their
respective absorption bands so that these emission bands can
be attributed to a metal to CPI MLCT band [Ru(dπ)-CPI-
(π*)], as the free CPI ligand does not emit at this wave-
length.5 The CPI molecule is planar in the ground state, due
to the conjugation between imidazole and the benzonitrile.
The HOMO is mainly located on the imidazole part whereas
the LUMO is mainly localized on the phenyl ring containing
the nitrile that results in intramolecular electron transfer.5
The complexes 1-3 show much lower energy luminescence
than their respective substitution products containing EPh3
or N-N donor bases. This is consistent with the fact that
the negatively charged ligands result in destabilization of
Figure 1. Electronic spectrum of the complex 2 in different solvents.
d6 configuration of Ru(II) in the complexes [(η6-arene)RuCl2-
(CPI)] provides filled t2g orbital of proper symmetry for their
interaction with relatively low-energy unoccupied π* orbital
3
the ground state and hence a decrease in the MLCT-based
luminescence. The presence of methyl substituents on the
arene ring (benzene to hexamethylbenzene) shifts the emis-
sion band to lower energy side. This decrease in energy can
be explained by an additional destabilization of the ground
state (GS) with increasing effect of σ donor ligand.
Electrochemistry. A cyclic voltammogram of the repre-
sentative complex [(η6-C6Me6)RuCl2(CPI)] (3) was obtained
in CH2Cl2 containing 0.1 M TEAP at a sweep rate of 50
mV/s in the range -2.0 to +2.0 V as shown in Figure 3. It
displayed a well-defined quasi-reversible oxidation reduction
wave corresponding to a Ru(II)/Ru(III) redox couple with a
of CPI. One therefore expects for a MLCT transition t2g
f
π* in these complexes, whose energy varies with the nature
of the ligand acting as an acceptor. Electronic spectra of the
mononuclear complexes showed moderately intense bands
in the region 400-416, 350, and 290 nm (Table 1). The
bands present in the range 400-416 nm have been assigned
to MLCT transitions.3,12 Further, it was observed that the
position of λmax in the electronic spectra of the complexes is
sensitive to the nature of different solvents, showed positive
solvatochromism, and is strong evidence in support of
charge-transfer assignment (Figure 1). Since MLCT bands
lead to separation of charge in the excited state, the transition
energy of this band should be sensitive to the environment
of the complex ion. The band in the region 350 nm also
exhibited a small solvatochromic effect. This band has also
been tentatively assigned to MLCT [Ru(II) f π* arene].
The high-intensity absorption bands in the region 290 nm
can be ascribed to the ligand-centered transition.3,12a Elec-
tronic spectra of the binuclear complexes 2f,g displayed a
significant blue shift (∼10 nm) in the position of λmax. The
shift in the position of λmax could be attributed to asym-
metrical nature of the bridging ligand. The π back-bonding
from imidazole-bound ruthenium to the imidazole ring should
raise the energy of π* orbitals of the nitrile end, while the
π back-bonding from the ruthenium to the NC group should
also raise the energy of the imidazole π* orbitals. Since
energy of MLCT is related to that of LUMO of the ligand,
increase in the energy of π* by both the metal centers should
result in a shift of MLCT bands toward higher frequency
side with respect to that in the mononuclear complexes.13
half-wave potential E1/2 of 1.152 V versus SCE and Epa
-
Epc ) 0.508 V.14 The waves associated with the Ru(II)/Ru-
(III) redox couple in the complex 1 and 2 were observed at
1.32 and 1.18 V, respectively. One can see that as the methyl
substitution at arene ligand increases from benzene to
hexamethylbenzene, there is a shift in the position of Ru-
(II)/Ru(III) redox couple toward less positive side. With an
increase in methyl substitution on the coordinated arene ring,
there is an increase in the electron density on the metal center.
This results in a significant destabilization of the ground-
state energy leading to a lowering of the metal-based
oxidation potentials. As expected, there was not any wave
due to the ligand CPI.5
Crystal Structures. Details about the data collection,
solution, and refinement are presented in Table 2. Molecular
structure of the complexes 2 and 3 and the complex cations
of 1a and 2a with atomic numbering scheme is shown in
Figure 4, and selected geometrical parameters and important
bond parameters are presented in Table 3. Crystal packing
in the complexes 2, 3, 1a, and 2a is stabilized by C-H‚‚‚X
type (X ) Cl, F) inter- and intramolecular hydrogen bonding.
(11) Levy, G. C.; Nelson, G. L. Carbon-13 Nuclear Magnetic Resonance;
Wiley-Interscience: New York, 1972; p 129.
(12) (a) Clarke, R. E.; Ford, P. C.; Inorg. Chem. 1970, 9, 227. (b) Curtis,
J. C.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1983, 22, 224. (c)
Didier, P.; Ortmans, I.; Kirschdemesmaeker, A.; Watts, R. J. Inorg.
Chem. 1993, 32, 5239.
(13) (a) Sundberg, R. J.; Bryan, R. F.; Taylor; I. F.; Taube, H. J. Am. Chem.
Soc. 1974, 96, 381. (b) Berger, R. M.; Ellis, D. D. Inorg. Chim. Acta.
1996, 241, 1.
(14) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17,
5239.
Inorganic Chemistry, Vol. 43, No. 26, 2004 8605

Singh et al.
Figure 2. Normalized emission spectra of the complexes in CH2Cl2.
Table 2. Crystallographic Data for Complexes 2, 3, 1a, and 2a
2
3
1a‚CH2Cl2
2a
empirical formula
fw
C20H21Cl2N3Ru
475.37
C22Cl2H25N3Ru
503.42
C35Cl3H30F6N3P2Ru
875.98
C38H36BClF4N3PRu
789.00
cryst system
space group
a, Å
b, Å
c, Å
monoclinic
P21
monoclinic
P21/c
triclinic
P1h
monoclinic
P21/n
11.504(2)
13.7250(8)
13.2170(14)
90.000(7)
105.232(13)
90.000(10)
2013.6(5)
4
12.2560(11)
12.8320(13)
14.3610(2)
90.00(10)
102.173(6)
90.00(8)
2189.9(4)
4
11.1490(9)
11.5520(12)
15.0040(13)
99.373(8)
97.987(7)
106.853(8)
1788.9(3)
2
12.6480(9)
15.4830(8)
18.5280(17)
90.000(6)
102.173(6)
90.000(5)
3546.7(5)
4
R, deg
â, deg
γ, deg
V, Å3
Z
d
calc, g cm-3
1.568
1.052
293(2)
1.527
0.972
293(2)
1.626
0.814
293(2)
1.478
0.616
293(2)
µ, mm-1
T, K
R1 all
0.0299
0.0293
0.0597
0.0490
R1 [I > 2σ(I)]
wR2
0.0270
0.0717
0.0262
0.0723
0.0463
0.1083
0.0368
0.0977
wR2 [I > 2σ(I)]
0.0689
0.0695
0.1168
0.0898
Table 3. Selected Bond Lengths (Å), Bond Angles (deg), and Torsion Angles (deg) in the Complexes
complex 2 complex 3 complex 1a‚CH2Cl2
Ru(1)-N(1)
complex 2a
2.097(12)
2.427(4)
2.412(4)
1.671
Ru-N(1)
Ru-Cl(1)
Ru-Cl(2)
Ru-Ct
2.124(2)
2.4180(8 )
2.4236(7 )
1.666
Ru-N(1)
2.124(4)
2.3971(13)
1.726
Ru(1)-N(1)
Ru(1)-Cl(1)
Ru(1)-Ct
2.125(3)
2.4007(10)
1.719
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Ct
Ru-Cl(1)
Ru-Ct
Ru-Cav
2.200
Ru(1)-Cav
Ru-P(1)
2.224
Ru(1)-Cav
2.181
Ru-Cav
2.194
Ru-P(1)
2.3806(13)
1.394(6)
1.303(6)
1.374(7)
1.347(6)
1.430(6)
1.126(7)
2.3715(11)
1.323(4)
1.378(5)
1.347(5)
1.366(5)
1.438(5)
1.132(6)
N(1)-C(11)
N(1)-C(12)
N(2)-C(11)
N(2)-C(13)
N(2)-C(14)
N(3)-C(20)
1.385(16)
1.396(16)
1.352(15)
1.457(18)
1.335(17)
1.22(2)
N(1)-C(13)
N(1)-C(14)
N(2)-C(13)
N(2)-C(15)
N(2)-C(16)
N(3)-C(22)
1.319(3)
1.381(4)
1.355(3)
1.380(4)
1.429(3)
1.126(4)
N(1)-C(25)
N(1)-C(27)
N(2)-C(26)
N(2)-C(27)
N(2)-C(28)
N(3)-C(34)
N(1)-C(11)
N(1)-C(12)
N(2)-C(11)
N(2)-C(13)
N(2)-C(14)
N(3)-C(20)
Cl(1)-Ru(1)-Cl(2)
Cl(1)-Ru(1)-N(1)
N(1)-Ru(1)-Cl(2)
88.79(14)
84.5(3)
86.7(3)
Cl(1)-Ru-Cl(2)
Cl(1)-Ru-N(1)
N(1)-Ru-Cl(2)
87.98(3)
86.53(6)
85.14(6)
N(1)-Ru-P(1)
Cl(1)-Ru-N(1)
P(1)-Ru-Cl(1)
89.14(10)
86.08(11)
86.05(4)
N(1)-Ru-P(1)
N(1)-Ru-Cl(1)
P(1)-Ru-Cl(1)
89.33(9)
86.22(8)
86.31(4)
C(13)-N(2)-C(14)-C(15) -53.8(14) C(13)-N(2)-C(16)-C(17)
42.4(4) C(26)-N(2)-C(28)-C(32)
31.3(8) C(13)-N(2)-C(14)-C(15) -4.2(7)
C(11)-N(2)-C(14)-C(15) 31(2) C(13)-N(2)-C(16)-C(21) -37.1(3) C(26)-N(2)-C(28)-C(29) -149.0(6) C(13)-N(2)-C(14)-C(19) 177.1(5)
Relevant bond distances and bond angles (please see Sup-
porting Information) are corroborated well with the reported
values.15 Contact distances between C-H‚‚‚F and C-H‚‚‚
Cl are 2.47-2.52 and 2.73-2.82 Å, respectively. These
interactions may be called vdW interactions since the lengths
are significantly less than the sum of van der Waals radii
(2.8 and 3.1 Å, respectively). The C-H‚‚‚Cl and C-H‚‚‚N
interaction in complex 2 leads to a rectangular grid network
(Figure 5a). The crystal packing in the complex 3 also
exhibits π-π stacking interactions between hexamethylben-
zene rings (arene-arene ring distance ) 3.39 Å) (Figure
5b), and in complex 2a it leads to a hexagonal network
(Figure 5c).15e
The crystallographic asymmetric unit of the complex 2
contains two independent molecules, which are essentially
identical. The metal center ruthenium in the complex 2 and
3 is coordinated through imidazole nitrogen N(1) from CPI,
Cl(1), Cl(2), and arene ring in an η6 manner. Similarly in
complexes 1a and 2a ruthenium is coordinated by N(1) from
CPI, the chloro group Cl(1), P(1) from PPh3, and benzene
(15) (a) Braga, D.; Grepioni, F. Chem. Commun. 1996, 571. (b) Steiner,
T. Angew. Chem., Int. Ed. 2002, 41, 48. (c) Desiraju, G. R.; Steiner,
T. The weak hydrogen bond in structural chemistry and biology;
Oxford University Press: Oxford, U.K., 1999. (d) Braga, D.; Grepioni,
F.; Tedesco, E. Organometallics 1998, 17, 2669. (e) Scaccianoce, L.;
Braga, D.; Calhorda, M. J.; Grepioni, F.; Johnson, B. F. G. Organo-
metallics 2000, 19, 790.
8606 Inorganic Chemistry, Vol. 43, No. 26, 2004

Luminescent Piano-Stool Complexes
Figure 3. Cyclic voltammogram of the complex 3 in acetonitrile.
and p-cymene rings in an η6-manner. Considering the arene
rings as a single coordination site, overall coordination
geometry about the metal center in the complexes 2, 3, 1a,
and 2a might be described as typical “piano-stool” geometry.
The arene rings, p-cymene, hexamethylbenzene, or benzene
ring in the respective complexes are almost planar, and
ruthenium is displaced by 1.671, 1.666, 1.726, and 1.719 Å
from centroid of the attendant arene ring in the complexes
2, 3, 1a, and 2a.16 The Ru-Cl bond distances are normal
and comparable with those observed in other Ru(II) arene
complexes.17 The Cl-Ru-Cl angles in the complexes 2 and
3 are comparable to those observed in other related systems.18
The Ru to imidazole nitrogen distance are 2.097(12), 2.124-
(2), 2.124(4), and 2.125(3) Å, respectively, in complex 2, 3,
1a, and 2a and followed a typical bonding pattern observed
in other imidazole complexes.19 These are comparable to
Ru-N distances in closely related ligand 1-methyl-3-(4-
cyanophenyl)imidazolium hexafluorophosphate and the Ru-
(II) complexes [Ru(η6-C10H14)Cl2(CNPy)] and [Ru(η3:η3-
C10H14)Cl2(CNPy)].5,6 The Ru-P distance in complex 1a and
(16) (a) Campagna, S.; Denti, G.; Derosa, G.; Sabatino, L.; Ciano, M.;
Balzani, V. Inorg. Chem. 1989, 28, 2565. (b) Schmehl, R. H.;
Auerbach, R. A.; Wacholtz, W. F. J. Phys. Chem. 1988, 92, 6202. (c)
Fuchs, Y.; Lofters, S.; Dieter, T.; Shi, W.; Morgan, R.; Strekas, T.
C.; Gafney, H. D.; Baker, A. D. J. Am. Chem. Soc. 1987, 109, 2691.
(d) Murphy, W. R.; Brewer, K. J.; Gettliffe, G.; Petersen, J. D. Inorg.
Chem. 1989, 28, 81.
(17) (a) Watkins, S. F.; Fronczek, F. R. Acta Crystallogr., Sect. B 1982,
38, 270. (b) McCormick, F. B.; Cox, D. D.; Gleason, W. B.
Organometallics 1993, 12, 610. (c) DiMarco, G.; Bartolotta, A.;
Ricevuto, V.; Campagna, S.; Denti, G.; Sabatino, L.; Derosa, G. Inorg.
Chem. 1991, 30, 270. (d) Luginbuhl, W.; Zbinden, P.; Pittet, P. A.;
Armbruster, T.; Burgi, H.-B.; Merbach, A. E.; Ludi, A. Inorg. Chem.
1991, 30, 2350. (e) Davenport, A. J.; Davies, D. L.; Fawcett, J.; Garratt,
S. A.; Russell, D. R. J. Chem. Soc., Dalton Trans. 2000, 4432.
(18) (a) Bruce, M. I.; Wong, F. S.; Skelton, B. W.; White, A. H. J. Chem.
Soc., Dalton Trans. 1981, 1398. (b) Gould, R. O.; Jones, C. L.;
Robertson, D. R.; Tocher, D. A.; Stephenson, T. A. J. Organomet.
Chem. 1982, 226, 199. (c) Hayashida, T.; Nagashima, H. Organome-
tallics 2002, 21, 3884. (d) Rath, R. K.; Nethaji, M.; Chakravarty, A.
R. J. Organomet. Chem. 2001, 633, 79. (e) Nishiyama, H.; Konno,
M.; Aoki, K. Organometallics 2002, 21, 2536. (f) Allardyce, C. S.;
Dyson, P. J.; Ellis, D. J.; Heath, S. L. Chem. Commun. 2001, 1396.
(g) Frodl, A.; Herebian, D.; Sheldrick, W. S. J. Chem. Soc., Dalton
Trans. 2002, 3664. (h) Chen, H. M.; Parkinson, J. A.; Parsons, S.;
Coxall, R. A.; Gould, R. O.; Sadler, P. J. J. Am. Chem. Soc. 2002,
124, 3064.
Figure 4. Molecular structures for (a) 2, (b) 3, (c) 1a.CH2Cl2, and (d) 2a.
2a are normal and comparable with Ru-P distances in other
complexes.20
In the complexes 2, 3, and 1a the ligand CPI has lost
planarity upon coordination with metal center. The cy-
anophenyl group of the ligand is not coplanar with imidazole
ring and is tilted with respect to the imidazole ring plane at
an angle of 31° (2), 42.4° (3), and 31.3° (1a) while in
complex 2a it is almost coplanar. The inter annular bond
distance N(2)-C(14) is 1.335(17) Å in complex 2 which is
(20) (a) Kratochvil, B.; Ondracek, J.; Velisek, J.; Hasek, J. Acta Crystallogr.,
Sect. C 1988, 44, 1579. (b) Alcalde, E.; Dinares, I.; Frigola, J.; Jaime,
C.; Fayet, J.-P.; Vertut, M.-C.; Miravitlles, C.; Rius, J. J. Org. Chem.
1991, 56, 4223. (c) Johnson, C. R.; Jones, C. M.; Asher, S. A.; Abola,
J. E. Inorg. Chem. 1991, 30, 2120.
(19) (a) Bennett, M. A.; Robertson, G. B.; Smith, A. K. J. Organomet.
Chem. 1972, 43, C41. (b) Elsegood, M. R. J.; Tocher, D. A.
Polyhedron 1995, 14, 3147. (c) Menendez, C.; Morales, D.; Perez, J.;
Riera, V.; Miguel, D. Organometallics 2001, 20, 2775.
Inorganic Chemistry, Vol. 43, No. 26, 2004 8607

Singh et al.
complex 2a [N(2)-C(14) 1.438(5) Å]. These are slightly
shorter than a single C-N bond indicating a double-bond
character. The nitrile CtN bond lengths in the complexes
2, 3, 1a, and 2a are 1.22(2), 1.126(4), 1.126(7), and 1.132-
(6) Å, respectively. The CtN bond distances in complexes
1a and 2a are comparable to each other, and these are shorter
than that in the complex 2. These are consistent with other
reports.5,6
Conclusion. A series of new piano-stool complexes [Ru-
(η6-arene)Cl2(CPI)] (η6-arene ) benzene, p-cymene, and
hexamethylbenzene), [(η6-arene)RuCl(CPI)(EPh3)]+, and [(η6-
arene)Ru(N-N)(CPI)]2+ incorporating the ligand CPI have
been prepared, and linkage of CPI with the metal center
through its imidazole nitrogen has been verified crystallo-
graphically. Further, the representative mononuclear complex
[Ru(η6-C10H14)Cl2(CPI)] has been used as a metallo-ligand
in the synthesis of homonuclear bimetallic complexes.
Attempts to verify the molecular structure of the representa-
tive binuclear complex at our hands failed due to poor quality
of the crystals. In the binuclear complexes two metal centers
are bridged by a ligand exhibiting twisted internal charge
transfer (TICT). The work toward development of homo-/
hetero-binuclear mixed-valence binuclear complexes and
study of their photophysical and photochemical properties
is in progress in our laboratory.
Acknowledgment. Thanks are due to Department of
Science and Technology, New Delhi, India, for financial
assistance (SP/S1/F-04/2000). We also thank the Head, SAIF,
Central Drug Research Institute, Lucknow, India, for provid-
ing analytical and spectral facilities. Special thanks are due
to Prof. P. Mathur, Department of Chemistry, Indian Institute
of Technology, Mumbai, India, and National Single Crystal
X-ray Diffraction Facility, Indian Institute of Technology,
Mumbai, India, for providing single-crystal X-ray data and
Prof. T. K. Chandrasekhar, Department of Chemistry, Indian
Institute of Technology, Kanpur, India, for providing emis-
sion spectral data.
Supporting Information Available: Crystallographic data for
the complexes 2, 3, 1a, and 2a in CIF format and relevant bond
distances, bond angles, and symmetries summarized in Table S1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Figure 5. (a) Rectangular grid network in the crystal structure for complex
2. (b) Crystal packing diagram for complex 3 showing the π-π interaction.
(c) Hexagonal planar network for complex 2a.
slightly shorter than that in the complex 3 [N(2)-C(16)
1.429(3) Å], complex 1a [N(2)-C(28) 1.430(6) Å], and
IC049256M
8608 Inorganic Chemistry, Vol. 43, No. 26, 2004