Terpyridine Zn(II), Ru(III), and Ir(III) complexes: The relevant role of the nature of the metal ion and of the ancillary ligands on the second-order nonlinear response of terpyridines carrying electron donor or electron acceptor groups

Article abstract of DOI:10.1021/ic050975q

Coordination of 4′-(C₆H₄-p-X)-2,2′: 6′,2″-terpyridines [X = NO₂, NBu₂, (E)-CH=CH-C₆H₄-p-NBu₂, (E,E)=(CH=CH) ₂-C₆H₄-p-NMe₂] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning of the ancillary ligands.

Full text of DOI:10.1021/ic050975q

Inorg. Chem. 2005, 44, 8967−8978
Terpyridine Zn(II), Ru(III), and Ir(III) Complexes: The Relevant Role of
the Nature of the Metal Ion and of the Ancillary Ligands on the
Second-Order Nonlinear Response of Terpyridines Carrying Electron
Donor or Electron Acceptor Groups
Francesca Tessore,* Dominique Roberto, Renato Ugo, and Maddalena Pizzotti
Dipartimento di Chimica Inorganica, Metallorganica e Analitica dell’UniVersita` di Milano, Centro
di Eccellenza CIMAINA, Unita` di Ricerca di Milano dell’INSTM e Istituto di Scienze e Tecnologie
Molecolari del CNR, Via G. Venezian, 21-20133 Milano, Italy
Silvio Quici and Marco Cavazzini
Istituto di Scienze e Tecnologie Molecolari del CNR, Via C. Golgi, 19-20133 Milano, Italy
Silvia Bruni
Dipartimento di Chimica Inorganica, Metallorganica e Analitica dell’UniVersita` di Milano, Via G.
Venezian, 21-20133 Milano, Italy
Filippo De Angelis
Istituto di Scienze e Tecnologie Molecolari del CNR, c/o Dipartimento di Chimica, UniVersita` di
Perugia, Via Elce di Sotto 8-06123 Perugia, Italy
Received June 15, 2005
Coordination of 4′-(C6H4-p-X)-2,2′:6′,2′′-terpyridines [X ) NO2, NBu2, (E)-CHdCH−C6H4-p-NBu2, (E,E)-(CHdCH)2−
C6H4-p-NMe2] to Zn(II), Ru(III), and Ir(III) metal centers induces a significant enhancement of the absolute value of
the second-order nonlinear optical (NLO) response of the terpyridine, measured by means of both electric field
induced second harmonic generation and solvatochromic methods. By varying the nature of the metal center, the
enhanced second-order NLO response shifts from positive to negative. Such a shift is controlled by electronic
charge-transfer transitions, such as metal-to-ligand or ligand-to-metal transitions, in addition to the intraligand charge
transfer. The enhancement generated by coordination is also controlled by the chelation effect and by fine-tuning
of the ancillary ligands.
Introduction
have been extensively studied for a series of metal com-
plexes. For instance when these push-pull ligands bear a
NR2 electron donor substituent, a significant increase was
usually reported upon coordination of âλ, which is the
projection of the vectorial component of the quadratic hyper-
polarizability tensor along the dipole moment direction,
In recent years organometallic and coordination com-
pounds have attracted increasing attention as new chro-
mophores for second-order nonlinear optical (NLO) re-
sponses. In particular, they may offer additional flexibility
by introducing new electronic charge-transfer transitions
between the metal and the ligand, and a response, tunable
by virtue of the nature, oxidation state, and coordination
sphere of the metal center.1,2 In particular, the effects of
coordination of various push-pull ligands, such as substi-
tuted pyridines,3a-e,g bipyridines,4 and phenanthrolines,3b,f
(1) (a) Coe, B. J. ComprehensiVe Coordination Chemistry II; McCleverty,
J. A., Meyer, T. J., Eds.; Elsevier Pergamon: Oxford, UK, 2004; Vol.
9, pp 621-687. (b) Roundhill, D. M.; Fackler, J. P. Optoelectronic
Properties of Inorganic Compounds; Plenum Press: New York, 1999.
(c) Heck, J.; Dabek, S.; Meyer-Friedrichsen, T.; Wong, H. Coord.
Chem. ReV. 1999, 190-192, 1217-1254.
(2) (a) Le Bozec, H.; Renouard, T. Eur. J. Inorg. Chem. 2000, 229-239.
(b) Di Bella, S. Chem. Soc. ReV. 2001, 30, 355-366.
* E-mail: francesca.tessore@unimi.it.
10.1021/ic050975q CCC: $30.25
Published on Web 10/22/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 24, 2005 8967

Tessore et al.
measured by the solution-phase dc electric field induced
second harmonic (EFISH) generation method, working at
an incident wavelength λ.5 As suggested by solvatochromic
investigations,3d,e,6 this enhancement is mainly due to a
bathochromic shift of the intraligand charge-transfer (ILCT)
transition, the major origin of the second-order NLO response
of these kinds of push-pull ligands. This shift is often
strongly dependent upon the Lewis acceptor properties of
the metal center.3e,f An important role is also played by chela-
tion, which imposes a rather planar arrangement of π-delo-
calized chelating ligands, such as bipyridines. Such planar
arrangements lead to a strong enhancement of the second-
order NLO response, by stabilization of the π* levels, in-
volved in the ILCT transition,3f,4b through a higher conjuga-
tion of the π system. The second-order NLO response of
complexes carrying stilbazoles or phenanthrolines with elec-
tron acceptor substituents is, on the contrary, mainly con-
trolled by metal-to-ligand charge-transfer (MLCT) processes.3b,e
The aim of this work is to show how the electronic nature
of the metal ion can influence by coordination, the value,
and sign of the second-order NLO response of a chelating
nitrogen donor push-pull ligand, as, for example, a terpy-
ridine substituted with an electron donor or electron acceptor
group, acting either through a perturbation toward lower
energy of the ILCT transition or by introducing new metal-
to-ligand (MLCT) or ligand-to-metal (LMCT) charge-transfer
transitions, which can control the overall second-order NLO
response.
Figure 1. Terpyridinic ligands under investigation.
2,2′:6′,2′′-terpyridine (T0) (see Figure 1) to Zn(II), Ru(III),
and Ir(III) ions indicated a relevant role of the nature of the
metal ion and of the ancillary ligands on the value and sign
of the quadratic hyperpolarizability of T0. The value of the
quadratic hyperpolarizability of T0,8a upon coordination to a
“ZnY2” center (Y ) Cl, CF3CO2), increases and remains
positive as occurs in other Zn(II) complexes with chelated
π-delocalized nitrogen donor ligands.3f,4 On the other hand,
upon coordination of T0 to “IrCl3” or “Ru(CF3CO2)3” centers,
â1.34 not only increases significantly in absolute value, but
it becomes negative. A careful solvatochromic investigation
has shown that only in Zn(II) complexes is the increase due
to the usual red-shift3f of the ILCT transition of T0. With
coordination to an Ir(III) center, the second-order NLO
response is dominated by the significant negative contribution
of a band at lower energy, tentatively assigned to a metal-
to-ligand charge-transfer (MLCT) transition.7f,g On the other
hand, by coordination to a Ru(III) center, the negative sign
of â1.34 originates from the high contribution of a relatively
weak absorption band at very low energy, tentatively
assigned to a ligand-to-metal charge-transfer (LMCT) transi-
tion.9,10
Metal complexes of terpyridines have been extensively
studied for their photochemical and photophysical properties,7
but they have never been investigated from a NLO point of
view before our preliminary work8a and a few other examples
concerning second-order8b or third-order8c NLO properties.
Our work on the effect of coordination of 4′-(C6H4-p-NBu2)-
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8968 Inorganic Chemistry, Vol. 44, No. 24, 2005

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes
γ (-2ω; ω, ω, 0), a third-order term at frequency ω of the incident
light, is the electronic contribution to γEFISH, which is negligible
for the kind of molecules investigated here.3d,e,14 âλ is the vectorial
projection along the dipole moment axis of the vectorial component
of the tensor of the quadratic hyperpolarizability, âVEC, working
with an incident wavelength λ. We usually worked with a
nonresonant 1.34 µm wavelength, but in the case of some Ir(III)
complexes, measurements were performed with an incident wave-
length of 1.907 µm.
EFISH measurements at 1.34 µm were carried out at the EÄ cole
Normale Supe´rieure de Cachan in CHCl3 solutions, while those at
1.907 µm were performed at the Dipartimento di Chimica Inor-
ganica Metallorganica e Analitica dell’Universita` di Milano, using
a Q-switched, mode-locked Nd3+:YAG laser. All experimental
EFISH âλ values are defined according to the “phenomenological”
convention.15
To confirm these preliminary observations, we have
extended our investigation to include two new terpyridines,
T1 and T2 (see Figure 1), which should show a higher second-
order NLO response with respect to T0, due to the greater
π-delocalization of the push-pull system, and to terpyridine
T3 (see Figure 1), which bears a strong electron acceptor
group such as NO2. In this latter case, our major objective
was to confirm not only the correct assignment of the ILCT
transitions but in particular the assignment as a MLCT to
the band dominating with its negative contribution the sign
of the second-order NLO response of [IrCl3T0] and as a
LMCT, the band at very low energy which generates the
negative and dominating contribution to the second-order
NLO response of [Ru(CF3CO2)3T0]. In the following we
report the results of this investigation.
(ii) Solvatochromic Measurements. The quadratic hyperpolar-
izability along the charge-transfer direction (âCT) of terpyridines
and their corresponding Zn(II), Ru(III), and Ir(III) complexes was
evaluated by the solvatochromic method, using UV-visible absorp-
tion spectra recorded in a series of solvents such as cyclohexane,
carbon tetrachloride, toluene, chloroform, anisole, dichloromethane,
ethyl acetate, 1,2-dichloroethane, acetone, and acetonitrile. The
radius a of the cavity (which can be supposed to be pseudo-spherical
taking into account the size and coordination sphere of the metal
complexes investigated) occupied by the solute molecule in the
solvent was evaluated from the molecular weight of the compound
using eq 2:6
Experimental Section
General Comments. ZnCl2‚xH2O, Zn(CF3CO2)2‚2H2O, Ag(CF3-
CO2), 4-ethylbenzoic acid, 2-acetylpyridine, 4-(dibutylamino)-
benzaldehyde, 4-(dimethylamino)cinnamaldehyde, 4-nitrobenzal-
dehyde, p-tolualdehyde, and triphenylphosphine were purchased
from Sigma-Aldrich and RuCl3‚xH2O and IrCl3‚xH2O were pur-
chased from Engelhard. All reagents and solvents were used without
further purification. The terpyridine ligands were prepared under
nitrogen atmosphere using flasks that were previously dried over
flame and cooled under nitrogen flow. Ligands11 and complexes,
N-[2-(pyrid-2′-yl)-2-oxoethyl]pyridinium iodide11a and 4-EtC6H4-
CO2Ag,12 were prepared using modified literature methods as
1/3
3M
4πNd
1
R )
(2)
described below. Products were characterized by H NMR (with
(
)
the exception of some paramagnetic Ru(III) complexes) (Bruker
AC-200 and Bruker DRX-300 spectrometers) and UV-visible
(Jasco V-530 spectrophotometer) spectroscopy, mass spectrometry
(Varian VG9090 spectrometer), and elemental analysis. Dipole
moments, µ, were measured in CHCl3 by using a WTW-DM01
dipole meter (dielectric constant) coupled with an RX-5000
ATAGO digital refractometer (refractive index) according to the
Guggenheim method.13 Elemental analyses were carried out at the
Dipartimento di Chimica Inorganica, Metallorganica e Analitica
of the Universita` di Milano.
The quadratic hyperpolarizability tensor âCT along the charge-
transfer direction was calculated for each absorption band of the
visible spectrum according to the Oudar two-level equation, eq 3:16
2
νa reg2∆µeg
3
âCT
)
(3)
2h2c2 (νa2 - νL )(νa2 - 4νL )
2
2
where reg is the transition dipole moment related to the integrated
intensity f of the absorption band, νa is the frequency of the charge-
transfer absorption band, νL is the frequency of the incident
radiation, and ∆µeg is the variation of the dipole moment upon
excitation.
For the numbering used in the attribution of the 1H NMR signals,
see Figure 1 and Scheme 3.
Determination of the Second-Order NLO Response. (i)
EFISH Measurements. The molecular quadratic hyperpolariz-
abilities of terpyridines and their complexes (Table 1) were
measured in CHCl3 solution by the solution-phase dc electric field
induced second harmonic (EFISH) generation method,5 which can
provide direct information on the intrinsic molecular NLO properties
through eq 1:
The total value of âCT was determined by adding the contributions
of the various absorption bands (see Table 1).
Computational Details. Calculations, based on density func-
tional theory and time-dependent DFT (TDDFT), were carried out
for the 4′-(C6H4-p-NMe2)-2,2′:6′,2′′-terpyridine, analogous to T0,
but with a shorter aliphatic chain on the NR2 donor group, to
evaluate its optimized geometry, dipole moment, absorption
spectrum, and EFISH quadratic hyperpolarizability. Geometry
optimizations were performed in vacuo. The B3LYP exchange-
correlation functional,17 as implemented in the Gaussian03 program
package,18 was used together with a 3-21g* basis set.19
γEFISH ) (µâλ/5kT) + γ (-2ω; ω, ω, 0)
(1)
where µâλ/5kT represents the dipolar orientational contribution and
(11) (a) Kro¨hnke, F. Synthesis 1976, 1-24. (b) Spahni, W.; Calzaferri, G.
HelV. Chim. Acta 1984, 67, 450-454. (c) Mukkala, V. M.; Helenius,
M.; Hemmila, I.; Kanare, J.; Taralo, H. HelV. Chim. Acta 1993, 76,
1361-1378. (d) Constable, E. C.; Smith, D. R. Supramol. Chem. 1994,
4, 5-7.
(12) Imuda, J.; Saito, J.; Ueda, J. Jpn. Kokai Tokkyo Koho, Patent No. JP
05213854; CAN 119: 270800 AN 1993: 670800, 1993.
(13) (a) Guggenheim, E. A. Trans. Faraday Soc. 1949, 45, 714-720. (b)
Smith, W. Electric Dipole Moments; Butterworth Scientific Publica-
tions: London, 1965. (c) Thompson, B. H. J. Chem. Educ. 1966, 43,
66-73.
(14) Lesley, M. J. G.; Woodward, A.; Taylor, N. J.; Marder, T. B.;
Cazenobe, I.; Ledoux, I.; Zyss, J.; Thornton, A.; Bruce, D. W.; Kakkar,
A. K. Chem. Mater. 1998, 10, 1355-1365.
(15) Willetts, A.; Rice, J. E.; Burland, D. M.; Shelton, D. P. J. Chem. Phys.
1992, 97, 7590-7599.
(16) (a) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664-2668.
(b) Oudar, J. L. J. Chem. Phys. 1977, 67, 446-457. (c) Oudar, J. L.;
Le Person, H. Opt. Commun. 1975, 15, 258-262.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8969

Tessore et al.
Table 1. Electronic Spectra, Dipole Moments, and EFISH â1.34 and âCT,1.34 of Terpyridine Ligands T0, T1, T2, and T3 and Their Complexes with
Zn(II), Ru(III), and Ir(III), Measured in CHCl3 Solution
a,h
l
â1.34
âCT,134
molecule
λmax abs.a (nm)
µ
a,f (D)
µEFg
(×10-30 esu)
â
1.34EFi
∆µegj (D)
fa,k
(×10-30 esu)
T0
T1
T2
T3
360b
395b
399b
280c
425b
427b
454b
444b
2.1
3.6
3.9
1.7
8.0
10
8.3
8.9
22
52
95
-12
67
88
181
137
8.0
8.3
8.7
nd
10.8
8.2
5.3
7.2
0.40
0.26
0.49
nd
0.33
0.34
0.32
0.17
43
43
60
nd
98
79
64
42
[ZnCl2T0]
3.8
4.8
2.3
2.3
3.0
4.0
3.5
1.4
[Zn(CF3CO2)2T0]
[Zn(CF3CO2)2T1]
[Zn(CF3CO2)2T2]
[Ru(CF3CO2)3T0]p
416b
508d
911d
9.2
4.4
-70
3.2
12.7
5.4
15.8
0.15
0.20
0.04
48
75
-208
-85
[RuCl3T1]
469b
866d
2.9
2.4
1.2
0.42
0.01
59
-6
53
10.3
nd
nd
nd
[Ru(CF3CO2)3T3]
[IrCl3T0]
496m
465b,e
533e
8.1n
7.9
4.8n
3.8
nd
10.2
0.05
2.6
-109
-84o
5.0
-0.1
-2.9
0.81
0.31
-4
-79
-83
[Ir(4-EtPhCO2)3T0]
[IrCl3T1]
463b,e
531e
8.8
10.9
9.1
4.2
3.0
5.3
-64o
nd
0.6
19
-0.4
0.20
0.05
-2
-38
-40o
-15.9
476b,e
538e
-30
-2.9
-10.2
0.18
0.01
-22
-11
-33
[Ir(4-EtPhCO2)3T3]
413e
521e
-230
-21.4
-27.2
0.05
0.03
-27
-63
-90
-126o
a In CHCl3. b Assigned to the ILCT of the ligand. c Assigned to a π-π* transition centered on the ligand (LC). d Assigned to LMCT, according to refs
9, 10. e Assigned to MLCT, according to ref 7f,g. f Measured by the Guggenheim method, according to ref 13. g Dipole moment enhancement factor, given
i
by µcomplex/µfree
.
h Measured by the EFISH technique. â1.34 enhancement factor, given by â1.34 complex/â1.34
.
j ∆µeg is the difference between
free ligand
ligand
excited- and ground-state molecular dipole moments, obtained from solvatochromic data; see ref 6. k f is the oscillator strength, obtained from the integrated
absorption coefficient; see ref 6. l Quadratic hyperpolarizability tensor along the charge-transfer direction. m In CH2Cl2. n µ value obtained by DFT calculations
according to the methodology reported in ref 20. o â measured in CHCl3 with an incident wavelength of 1.907 µm. p The complex [RuCl3T0], not soluble
enough for dipole moment and EFISH measurements, shows three absorption bands at 416, 476, and 795 nm.
Calculations of the absorption spectrum were performed, within
TDDFT, in chloroform solution by means of the nonequilibrium
implementation20a of the polarizable continuum model (PCM) of
solvation.20b Hyperpolarizability calculations were performed by
numerical differentiation of analytic polarizabilities, obtained by a
coupled-perturbed procedure and calculated at finite electric field
values. The zzz component of the static first-order hyperpolariz-
ability tensor is the only relevant component (all the other
components are at least 2 orders of magnitude smaller), so that it
can be directly related to the EFISH quadratic hyperpolarizability.
Geometry optimizations in vacuo were also performed at the
B3LYP/3-21G* level on the [Ru(CF3CO2)3T3] complex, followed
by a single point calculation in chloroform solution to evaluate its
dipole moment.
Synthesis. (i) Synthesis of 4′-(C6H4-p-X)-2,2′:6′,2′′-terpy-
ridines. 4′-(Phenyl-p-dibutylamino)-2,2′:6′,2′′-terpyridine (T0).
2-Acetylpyridine (1.88 g, 15.4 mmol) was added to a stirred solution
(17) Becke, A. D. J. Chem. Phys. 1993, 98, 5642-5652.
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M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(19) Binkley, J. S.; Pople, A. J.; Herhe, W. J. J. Am. Chem. Soc. 1980,
102, 939-947.
t
of BuOK (2.6 g, 23.1 mmol) in anhydrous THF (40 mL). After
the mixture was stirred at room temperature in an inert atmosphere
for 2 h, a solution of 4-(dibutylamino)benzaldehyde (1.63 g, 7
mmol) in anhydrous THF (40 mL) was added. The reaction mixture
was stirred overnight at room temperature. During this time a dark
red color developed. NH4OAc (18.5 g, 238 mmol) and EtOH (80
mL) were added sequentially and the mixture was heated at reflux
for 4 h. Removal of the solvent in vacuo afforded a thick residue
which solidified upon addition of a small amount of EtOH. This
solid was washed with H2O, EtOH, and Et2O, affording 1.85 g of
T0 (60%) as a yellow solid.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.72 (d,
2H, J6,5 ) 4.7 Hz, H6, H6′′), 8.69 (s, 2H, H3′, H5′), 8.65 (d, 2H, J3,4
) 7.9 Hz, H3, H3′′), 7.86 (ddd, 2H, J4,3 ) J4,5 ) 7.6 Hz, J ) 1.8
Hz, H4, H4′′), 7.85 (d, 2H, Jortho ) 8.9 Hz, H7, H7′), 7.32 (ddd, 2H,
J5,4 ) 7.4 Hz, J5,6 ) 4.8 Hz, J ) 1.7 Hz, H5, H5′′), 6.73 (d, 2H,
(20) (a) Cossi, M.; Barone, V. J. Chem. Phys. 2001, 115, 4708-4717. (b)
Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003,
24, 669-681.
8970 Inorganic Chemistry, Vol. 44, No. 24, 2005

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes
Jortho ) 8.9 Hz, H8, H8′), 3.33 (t, 4H, J ) 7.6 Hz, N-CH2-CH2-
CH2-CH3), 1.61 (m, 4H, N-CH2-CH2-CH2-CH3), 1.39 (m, 4H,
N-CH2-CH2-CH2-CH3), 0.97 (t, 6H, J ) 7.3 Hz, N-CH2-
CH2-CH2-CH3); MS-EI: m/z 436 (calcd for C29H32N4 ) 436).
Anal. Calcd (found): C, 79.78 (79.96); H, 7.39 (7.24); N, 12.83
(13.20).
give a brown oily residue. This product was stirred with MeOH (5
mL) overnight to afford 0.38 g of T1 (53%) as a bright yellow
solid.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.79 (s,
2H, H3′, H5′), 8.77 (d, 2H, J6,5 ) 4.7 Hz, H6, H6′′), 8.70 (d, 2H, J3,4
) 7.9 Hz, H3, H3′′), 7.97 (d, 2H, Jortho ) 8.2 Hz, H7, H7′), 7.90
(ddd, 2H, J4,3 ) 7.8 Hz, J4,5 ) 5.8 Hz, J ) 1.6 Hz, H4, H4′′), 7.62
(d, 2H, Jortho ) 8.2 Hz, H8, H8′), 7.44 (d, 2H, Jortho ) 8.5 Hz, H13,
4′-(p-Tolyl)-2,2′:6′,2′′-terpyridine (1). 2-acetylpyridine (2.42 g,
t
20 mmol) was added to a stirred solution of BuOK (3.37 g, 30
mmol) in anhydrous THF (70 mL). After the mixture was stirred
at room temperature in an inert atmosphere for 2 h, a solution of
p-tolualdehyde (1.20 g, 10 mmol) in anhydrous THF (40 mL) was
added. The reaction mixture was stirred overnight at room tem-
perature. During this time a dark red color developed. NH4OAc
(35.9 g, 466 mmol) and MeOH (140 mL) were added sequentially
and the mixture was heated at reflux for 4 h. Removal of the solvent
in vacuo afforded a thick residue which solidified upon addition
of a small amount of MeOH. This solid was recrystallized from
MeOH, affording 1.29 g of 1 (40%) as crystalline needles.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.73 (s,
2H, H3′, H5′), 8.73 (d, 2H, J6,5 ) 5.1 Hz, H6, H6′′), 8.66 (d, 2H, J3,4
) 7.9 Hz, H3, H3′′), 7.87 (ddd, 2H, J4,3 ) J4,5 ) 7.7 Hz, J ) 1.8
Hz, H4, H4′′), 7.81 (d, 2H, Jortho ) 8.1 Hz, H7, H7′), 7.35 (ddd, 2H,
J5,4 ) 7.7 Hz, J5,6 ) 4.8 Hz, H5, H5′′), 7.31 (d, 2H, Jortho ) 7.8 Hz,
H8, H8′), 1.62 (s, 3H, CH3). MS-EI: m/e 323 (calcd for C22H17N3
m/e 323). Anal. Calcd (found): C, 81.70 (81.51); H, 5.23 (5.31);
N, 12.91 (12.80).
4′-(Phenyl-p-bromomethyl)-2,2′:6′,2′′-terpyridine (2). N-Bro-
mosuccinimide (0.66 g, 3.71 mmol) and a catalytic amount of
dibenzoylperoxide were added to a suspension of 1 (1.20 g, 3.71
mmol) in CCl4 (20 mL). The mixture was stirred at reflux for 4 h,
irradiating with a 100 W lamp. The floating succinimide was then
separated by filtration and the liquid phase evaporated to dryness
to afford a thick residue, which solidified by adding a small amount
of EtOH to give 0.977 g of 2 (65%) as a white solid.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.73 (s,
2H, H3′, H5′), 8.71 (d, 2H, J6,5 ) 5.1 Hz, H6, H6′′), 8.66 (d, 2H, J3,4
) 8.07 Hz, H3, H3′′), 7.88 (d, 2H, Jortho ) 7.7 Hz, H7, H7′), 7.87
(m, 2H, H4, H4′′), 7.53 (d, 2H, Jortho ) 8.4 Hz, H8, H8′), 7.35 (ddd,
2H, J5,4 ) 7.3 Hz, J5,6 ) 4.8 Hz, H5, H5′′), 4.56 (s, 2H, CH2Br).
MS-EI: m/e 401, 322 (M - Br) (calcd for C22H16N3Br m/e 401).
Anal. Calcd (found): C, 65.68 (65.72); H, 4.01 (3.70); N, 10.44
(10.29).
4-(2,2′:6′,2′′-Terpyridyl-4′)-benzyl Triphenyl Phosponium
Bromide (3). A solution of triphenylphosphine (0.89 g, 3.43 mmol)
and 2 (1.378 g, 3.43 mmol) in toluene (16 mL) was refluxed for 3
h under magnetic stirring. During this time a white solid precipitate
formed. The reaction mixture was cooled with an ice bath and the
solid was collected by filtration, affording 1.90 g of 3 (83%) as a
white solid.
H13′), 7.37 (dd, 2H, J5,6 ) 4.8 Hz, J5,4 ) 5.1 Hz, H5, H5′′), 7.16 (d,
1H, Jtrans ) 16.2 Hz, H10 or H11), 6.95 (d, 1H, Jtrans ) 16.2 Hz, H10
o H11), 6.67 (d, 2H, Jortho ) 8.5 Hz, H14, H14′), 3.32 (t, 4H, J ) 7.4
Hz, N-CH2), 1.61 (m, 4H, N-CH2-CH2-CH2-CH3), 1.39 (m,
4H, N-CH2-CH2-CH2-CH3), 0.99 (t, 6H, J ) 7.3 Hz, CH3).
1H NMR (300 MHz, CD3COCD3, 25 °C, TMS): δ (ppm) 8.87
(s, 2H, H3′, H5′), 8.77 (m, 4H, H6, H6′′, H3, H3′′), 8.02 (ddd, 2H, J4,3
) 7.6 Hz, J4,5 ) 5.8 Hz, J ) 1.8 Hz, H4, H4′′), 7.96(d, 2H, Jortho
)
8.3 Hz, H7, H7′), 7.78 (d, 2H, Jortho ) 8.3 Hz, H8, H8′), 7.50 (m,
4H, H5, H5′′, H13, H13′), 7.30 (d, 1H, Jtrans ) 16.3 Hz, H10 or H11),
7.08 (d, 1H, Jtrans ) 16.3 Hz, H10 o H11), 6.73 (d, 2H, Jortho ) 8.8
Hz, H14, H14′), 3.39 (t, 4H, J ) 7.4 Hz, N-CH2), 1.63 (m, 4H,
N-CH2-CH2-CH2-CH3), 1.42 (m, 4H, N-CH2-CH2-CH2-
CH3), 0.98 (t, 6H, J ) 7.3 Hz, CH3). MS-EI: m/e 538 (calcd for
C37H38N4 m/e 538). Anal. Calcd (found): C, 82.50 (82.35); H, 7.10
(7.30); N, 10.40 (10.35).
4′-(4-{(E,E)-4-[4-(N,N-Dimethylamino)phenyl]-buta-1,3-dienyl}-
phenyl)-2,2′:6′,2′′-terpyridine (T2). tBuOK (0.336 g, 3 mmol) was
added to a solution of 3 (1.0 g, 1.50 mmol) in anhydrous DMF (20
mL). The black solution was stirred at room temperature for 30
min, after which 4-(dimethylamino)cinnamaldehyde (0.289 g, 1.65
mmol) was added. The reaction mixture was heated at 80 °C for 4
h, then cooled at room temperature. A yellow solid was collected
and washed with a small amount of cold DMF. It was then dissolved
in CH2Cl2 (200 mL) and washed with water (3 × 50 mL). The
organic layer was dried over Na2SO4 and evaporated, to obtain 0.46
g of T2 (64%) as a yellow powder.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.78 (s,
2H, H3′, H5′), 8.77 (d, 2H, J6,5 ) 6.0 Hz, H6, H6′′), 8.70 (d, 2H, J3,4
) 7.9 Hz, H3, H3′′), 7.91 (d, 2H, Jortho ) 8.1 Hz, H7, H7′), 7.90 (m,
2H, H4, H4′′), 7.57 (d, 2H, Jortho ) 8.3 Hz, H8, H8′), 7.38 (d, 2H,
Jortho ) 8.5 Hz, H15, H15′), 7.37 (m, 2H, H5, H5′′), 7.07 (dd, 1H,
Jtrans ) 15.4 Hz, J12,11 ) 10.2 Hz, H12), 6.86 (d, 1H, Jtrans ) 15.3
Hz, H10), 6.72 (d, 2H, Jortho ) 8.5 Hz, H16, H16′), 6.67 (m, 2H, H11,
H13), 3.01 (s, 6H, N(CH3)2).
1H NMR (300 MHz, CD3COCD3, 25 °C, TMS): δ (ppm) 8.86
(s, 2H, H3′, H5′), 8.77 (m, 4H, H6, H6′′, H3, H3′′), 8.01 (ddd, 2H, J4,3
) 7.5 Hz, J4,5 ) 5.8 Hz, J ) 1.7 Hz, H4, H4′′), 7.96 (d, 2H, Jortho
) 8.3 Hz, H7, H7′), 7.74 (d, 2H, Jortho ) 8.3 Hz, H8, H8′), 7.50 (m,
2H, H5, H5′′), 7.41 (d, 2H, Jortho ) 8.8 Hz, H15, H15′), 7.23 (dd, 1H,
Jtrans ) 15.6 Hz, J12,11 ) 10.4 Hz, H12), 6.94 (dd, 1H, Jtrans ) 15.2
Hz, J11,12 ) 10.4 Hz, H11), 6.74 (m, 4H, H16, H16′, H10, H13), 3.01
(s, 6H, N(CH3)2). MS-EI: m/e 480 (calcd for C33H28N4 m/e 480).
Anal. Calcd (found): C, 82.47 (82.51); H, 5.87 (5.69); N, 11.66
(11.80).
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.69 (d,
2H, J6,5 ) 6.6 Hz, H6, H6′′), 8.65 (d, 2H, J3,4 ) 7.8 Hz, H3, H3′′),
8.58 (s, 2H, H3′, H5′), 7.92-7.62 (m, 9H, H4, H4′′, H7, H7′, C6H5P),
7.39-7.15 (m, 4H, H5, H5′′, H8, H8′), 5.61 (d, 2H, CH2P). Anal.
Calcd (found): C, 72.29 (72.51); H, 4.70 (4.56); N, 6.32 (6.44).
4′-(4-{2-[4-(N,N-Dibutylamino)phenyl]ethenyl}phenyl)-2,2′:
6′,2′′-terpyridine (T1). A sample of 3 (0.884 g, 1.33 mmol) was
(E)-3-(4′′-Nitrophenyl)-1-(pyrid-2′-yl)prop-2-enone (4). A 10%
aqueous NaOH solution (0.5 mL) was added to a suspension of
4-nitrobenzaldehyde (1.26 g, 8.34 mmol) in EtOH (10 mL). To
the resulting mixture, cooled at 0 °C, 2-acetylpyridine (0.93 mL,
8.30 mmol) was added dropwise in 2.5 h. The solution was stirred
at 0 °C for 2 h, allowing the formation of a precipitate, which was
collected by filtration and washed with a small amount of EtOH,
affording 1.43 g of 4 (67%) as a yellow solid.
t
added to a solution of BuOK (0.603 g, 5.38 mmol) in anhydrous
DMF (30 mL). The black solution was stirred at room temperature
for 10 min, after which 4-(dibutylamino)benzaldehyde (0.32 mL,
1.33 mmol) was added. The reaction mixture was heated at 80 °C
for 4 h. Removal of the solvent in vacuo afforded a thick residue
which was taken up with H2O and extracted with CH2Cl2 (3 × 30
mL). The organic layer was dried over Na2SO4 and evaporated, to
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.78 (d,
2H, J6,5 ) 4.7 Hz, H6), 8.46 (d, 2H, Jtrans ) 16.0 Hz, H7), 8.30 (d,
Inorganic Chemistry, Vol. 44, No. 24, 2005 8971

Tessore et al.
2H, Jortho ) 8.7 Hz, H10, H10′), 8.23 (d, 2H, J3,4 ) 7.9 Hz, H3),
7.94 (m, 1H, H4), 7.94 (d, 2H, Jtrans ) 16.1 Hz, H8), 7.89 (d, 2H,
Jortho ) 8.6 Hz, H9, H9′), 7.55 (m, 1H, H5). Anal. Calcd (found):
C, 66.14 (66.54); H, 3.96 (3.67); N, 11.02 (11.09).
4′-(Phenyl-p-nitro)-2,2′:6′,2′′-terpyridine (T3). A solution of
5 (0.633 g, 1.94 mmol) in MeOH (10 mL) was added to a solution
of 4 (0.491 g, 1.94 mmol) in MeOH (10 mL) and the resulting
mixture was refluxed for 24 h. The brown solid formed was
collected by filtration, washed with a small amount of cold MeOH,
and finally crystallized from EtOH, affording 0.531 g of T3 (78%)
as a pale violet solid.
H8, H8′), 3.28 (t, 4H, J ) 7.2 Hz, NCH2CH2CH2CH3), 1.56 (m,
4H, NCH2CH2CH2CH3), 1.41 (m, 4H, NCH2CH2CH2CH3), 1.02
(t, 6H, J ) 7.2 Hz, NCH2CH2CH2CH3). MS-FAB+: m/e 613 (M
- CF3CO2)+ (calcd for C33H32N4O4F6Zn m/e 726). Anal. Calcd
(found): C, 54.44 (54.70); H, 4.43 (4.43); N, 7.69 (7.51).
[Zn(CF3CO2)2T1]. A solution of T1 (0.539 g, 0.216 mmol) in
EtOH (50 mL) was added to a solution of Zn(CF3CO2)2‚xH2O
(0.291 g, 0.216 mmol) in EtOH (25 mL). The reaction mixture
was stirred at room temperature in the dark (aluminum foil) for 2
h. Removal of the solvent under vacuum afforded a red powder,
which was dissolved in CH2Cl2 and precipitated by addition of
n-pentane at room temperature, giving 0.145 g of [Zn(CF3CO2)2T1]
(81%) as a yellow powder.
1H NMR (300 MHz, CD3COCD3, 25 °C, TMS): δ (ppm) 8.96
(d, 2H, J6,5 ) 4.2 Hz, H6, H6′′), 8.90 (s, 2H, H3′, H5′), 8.71 (m, 2H,
H3, H3′′), 8.21 (m, 2H, H4, H4′′), 8.10 (d, 2H, Jortho ) 8.0 Hz, H7,
H7′), 7.85 (m, 2H, H5, H5′′), 7.65 (d, 2H, Jortho ) 7.8 Hz, H8, H8′),
7.50 (d, 2H, Jortho ) 8.8 Hz, H13, H13′), 7.29 (d, 1H, Jtrans ) 16.4
Hz, H10 or H11), 7.02 (d, 1H, Jtrans ) 16.0 Hz, H10 o H11), 6.75 (d,
2H, Jortho ) 8.8 Hz, H14, H14′). MS-FAB+: m/e 715 (M - CF3-
CO2)+ (calcd for C41H38N4O4F6Zn m/e 828). Anal. Calcd (found):
C, 59.32 (59.71); H, 4.61 (4.59); N, 6.74 (6.43).
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 8.77 (s,
2H, H3′, H5′), 8.75 (d, 2H, J6,5 ) 4.1 Hz, H6, H6′′), 8.70 (d, 2H, J3,4
) 8.0 Hz, H3, H3′′), 8.38 (d, 2H, Jortho ) 8.6 Hz, H8, H8′), 8.06 (d,
2H, Jortho ) 8.6 Hz, H7, H7′), 7.91 (ddd, 2H, J4,3 ) 8.0 Hz, J4,5
6.3 Hz, J ) 1.7 Hz, H4, H4′′), 7.39 (dd, 2H, J5,4 ) 6.3 Hz, J5,6
4.6 Hz, H5, H5′′).
)
)
1H NMR (300 MHz, CD3CN, 25 °C, TMS): δ (ppm) 8.79 (s,
2H, H3′, H5′), 8.73 (d, 2H, J6,5 ) 4.1 Hz, H6, H6′′), 8.71 (d, 2H, J3,4
) 8.0 Hz, H3, H3′′), 8.39 (d, 2H, Jortho ) 9.0 Hz, H8, H8′), 8.01 (d,
2H, Jortho ) 9.0 Hz, H7, H7′), 7.98 (ddd, 2H, J4,3 ) 8.0 Hz, J4,5
6.3 Hz, J ) 1.7 Hz, H4, H4′′), 7.46 (dd, 2H, J5,4 ) 6.3 Hz, J5,6
)
)
4.6 Hz, H5, H5′′). MS-EI: m/e 354 (calcd for C21H14N4O2 m/e 354).
Anal. Calcd (found): C, 71.18 (71.32); H, 3.98 (4.16); N, 15.81
(15.56).
[Zn(CF3CO2)2T2]. A solution of T2 (66 mg, 0.138 mmol) in
EtOH (65 mL) was added to a solution of Zn(CF3CO2)2‚xH2O (40
mg, 0.138 mmol) in EtOH (5 mL). The reaction mixture was
refluxed in the dark (aluminum foil) for 3 h. Removal of the solvent
in vacuo afforded a red powder, which was dissolved in CH2Cl2
and precipitated by n-hexane at room temperature, giving 72 mg
of [Zn(CF3CO2)2T2] (68%) as a dark orange powder.
1H NMR (300 MHz, CD3COCD3, 25 °C, TMS): δ (ppm) 9.01
(m, 4H, H3′, H5′, H6, H6′′), 8.86 (m, 2H, H3, H3′′), 8.32 (m, 2H, H4,
H4′), 8.19 (d, 2H, J ) 7.5 Hz, H7, H7′), 7.88 (m, 2H, H5, H5′′), 7.73
(d, 2H, H8, H8′), 7.41 (d, 2H, Jortho ) 8.6 Hz, H15, H15′), 7.26 (dd,
Silver 4-Ethylbenzoate. A solution of 4-ethylbenzoic acid (0.312
g, 2.08 mmol) in CH3CN (20 mL) was added dropwise to a
suspension of Ag2CO3 (0.287 g, 1.04 mmol) in CH3CN (20 mL) at
room temperature and under vigorous stirring. The reaction mixture
was refluxed for 7 h, and then after it cooled at room temperature,
a light brown precipitate was collected by filtration. This solid was
suspended in H2O (100 mL) and the suspension was refluxed until
the major part of the solid was dissolved. After hot filtration and
evaporation to dryness, 0.120 g of 4-EtC6H4CO2Ag (45%) was
obtained as a pale yellow powder.
1H NMR (300 MHz, CD3OD, 25 °C, TMS): δ (ppm) 7.93 (d,
2H, Jortho ) 7.7 Hz, H2, H2′), 7.28 (d, 2H, Jortho ) 7.7 Hz, H3, H3′),
2.70 (q, 2H, Jvic. ) 7.8 Hz, -CH2-), 1.26 (t, 3H, Jvic. ) 7.6 Hz,
-CH3). MS-EI m/e 149 (M - Ag) (calcd for C9H9O2Ag m/e 256).
Anal. Calcd (found): C, 42.05 (42.06); H, 3.53 (3.51).
1H, Jtrans ) 15.2 Hz, J12,11 ) 10.4 Hz, H12), 6.94 (dd, 1H, Jtrans
)
15.6 Hz, J11,12 ) 10.6 Hz, H11), 6.76 (d, 2H, Jortho ) 8.8 Hz, H16,
H
16′), 6.76 (m, 2H, H10, H13), 3.01 (s, 6H, N(CH3)2). MS-FAB+:
m/e 657 (M - CF3CO2)+ (calcd for C37H28N4O4F6Zn m/e 770).
Anal. Calcd (found): C, 57.56 (57.47); H, 3.63 (3.86); N, 7.26
(6.99).
[RuCl3T0]. A solution of T0 (0.317 g, 0.726 mmol) in EtOH
(50 mL) was added to a solution of RuCl3‚xH2O (% Ru ) 42.68%)
(0.172 g, 0.726 mmol) in EtOH (30 mL). The dark brown reaction
mixture was refluxed under vigorous stirring for 6 h, then left at
room temperature overnight, affording a brown precipitate which
was collected by filtration. It was then dissolved in CH2Cl2 (50
mL) and the small insoluble residue was filtered off. The filtrate
was evaporated to dryness, leading to 0.281 g of [RuCl3T0] (60%)
as a dark brown powder.
(i) Synthesis of the Complexes. [ZnCl2T0] and [Zn(CF3CO2)2T0].
A solution of T0 (0.200 g, 0.46 mmol) in EtOH (20 mL) was added
to a solution of the Zn(II) salt (0.46 mmol) in EtOH (10 mL). The
reaction mixture was vigorously stirred at room temperature for 1
h. Removal of the solvent under vacuum afforded an orange-yellow
solid, which was dissolved in CH2Cl2 and precipitated by the
addition of n-pentane at room temperature, giving the desired
product as a bright yellow powder (80%).
[ZnCl2T0]. 1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm)
8.87 (d, 2H, J6,5 ) 4.1 Hz, H6, H6′′), 7.78 (d, 2H, J3,4 ) 8.0 Hz, H3,
H3′′), 7.74 (s, 2H, H3′, H5′), 7.49 (dt, 2H, J4,3 ) J4,5 ) 7.7 Hz, H4,
H4′′), 7.47 (d, 2H, Jortho ) 8.9 Hz, H7, H7′), 7.27 (dd, 2H, J5,4 ) 7.4
Hz, J5,6 ) 4.1 Hz, H5, H5′′), 6.73 (d, 2H, Jortho ) 8.9 Hz, H8, H8′),
3.22 (t, 4H, J ) 7.3 Hz, NCH2CH2CH2CH3), 1.56 (m, 4H,
NCH2CH2CH2CH3), 1.40 (m, 4H, NCH2CH2CH2CH3), 1.03 (t, 6H,
J ) 7.2 Hz, NCH2CH2CH2CH3). MS-FAB+ m/e 535 (M - Cl)+
(calcd for C29H32N4Cl2Zn m/e 570). Anal. Calcd (found): C, 60.80
(60.51); H, 5.63 (5.81); N, 9.78 (9.88).
MS-FAB+: m/e 608 (M - Cl)+ (calcd for C29H32N4RuCl3 m/e
643). Anal. Calcd (found): C, 54.08 (54.25); H, 5.01 (5.11); N,
8.69 (8.44).
[Ru(CF3CO2)3T0]. Ag(CF3CO2) (63.4 mg, 0.287 mmol) was
added at room temperature to a solution of [RuCl3T0] (51.7 mg,
0.0803 mmol) in CH3CN (7 mL). The dark red mixture was
vigorously stirred at room temperature for 24 h, then the solvent
was evaporated to dryness. The residue was dissolved in CH2Cl2
(100 mL) and the insoluble part filtered off. The filtrate was
evaporated to dryness, affording 41.7 mg of [Ru(CF3CO2)3T0] (59%)
as a dark red solid.
1
[Zn(CF3CO2)2T0]. H NMR (300 MHz, CDCl3, 25 °C, TMS):
δ (ppm) 8.89 (d, 2H, J6,5 ) 5.1 Hz, H6, H6′′), 8.06 (s, 2H, H3′, H5′),
7.94 (d, 2H, J3,4 ) 8.0 Hz, H3, H3′′), 7.75 (t, 2H, J4,3 ) J4,5 ) 7.5
Hz, H4, H4′′), 7.52 (d, 2H, Jortho ) 8.9 Hz, H7, H7′), 7.47 (dd, 2H,
J5,4 ) 7.5 Hz, J5,6 ) 5.2 Hz, H5, H5′′), 6.48 (d, 2H, Jortho ) 8.8 Hz,
MS-FAB+: m/e 764 (M - CF3CO2)+ (calcd for C35H32N4O6F9-
Ru m/e 877). Anal. Calcd (found): C, 47.95 (47.74); H, 3.68 (3.59);
N, 6.39 (6.16).
8972 Inorganic Chemistry, Vol. 44, No. 24, 2005

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes
[RuCl3T1]. A solution of T1 (46.2 mg, 0.0858 mmol) in EtOH
(3 mL) was added to a solution of RuCl3‚xH2O (%Ru ) 39.95%)
(22 mg, 0.0866 mmol) in EtOH (2 mL). The dark red solution was
refluxed for 4 h, then stirred at room temperature overnight, leading
to 43.2 mg of [RuCl3T1] (67%) as a a dark red powder.
MS-FAB+: m/e 710 (M - Cl)+ (calcd for C37H38N4RuCl3 m/e
745). Anal. Calcd (found): C, 59.56 (59.35); H, 5.13 (5.59); N,
7.15 (7.26).
(4-EtC6H4CO2)2)+ (calcd for C56H59N4O6Ir m/e 1075). Anal. Calcd
(found): C, 62.49 (62.30); H, 5.52 (5.67); N, 5.20 (5.13).
[IrCl3T1]. A solution of T1 (0.101 g, 0.188 mmol) in EtOH (100
mL) was added to a solution of IrCl3‚xH2O (%Ir ) 52.15%) (0.069
g, 0.188 mmol) in EtOH (100 mL). The resulting mixture was
refluxed for 6 h and the red precipitate formed was collected and
dissolved in CH2Cl2 (100 mL). The insoluble residue was filtered
off and the filtrate evaporated to dryness, affording 35.5 mg of
[IrCl3T1] (22.6%) as a dark red powder.
1H NMR (300 MHz, CD3COCD3, 25 °C, TMS): δ (ppm) 9.42
(d, 2H, J6,5 ) 5.04 Hz, H6, H6′′), 8.95 (s, 2H, H3′, H5′), 8.78 (d, 2H,
J3,4 ) 8.1 Hz, H3, H3′′), 8.26 (t, 2H, J4,3 ) J4,5 ) 7.6 Hz, H4, H4′′),
8.15 (d, 2H, Jortho ) 8.3 Hz, H7, H7′), 7.94 (dd, 2H, J5,6 ) 5.2 Hz,
J5,4 ) 7.4 Hz, H5, H5′′), 7.79 (d, 2H, Jortho ) 7.7 Hz, H8, H8′), 7.50
(m, 2H, H13, H13′), 7.34 (d, 1H, Jtrans ) 16.5 Hz, H10 or H11), 7.10
(d, 1H, Jtrans ) 15.9 Hz, H10 or H11), 6.78 (m, 2H, H14, H14′). MS-
FAB+: m/e 800 (M - Cl)+ (calcd for C37H38N4IrCl3 m/e 835). Anal.
Calcd (found): C, 53.07 (53.55); H, 4.57 (4.35); N, 6.69 (6.49).
[Ru(CF3CO2)3‚2CH3CN‚H2O]. Ag(CF3CO2) (0.252 g, 1.14
mmol) was added at room temperature to a solution of RuCl3‚xH2O
(%Ru ) 39.95%) (0.096 mg, 0.38 mmol) in CH3CN (15 mL). The
dark green reaction mixture was vigorously stirred for 1 h, then
AgCl was filtered off and the filtrate evaporated to dryness. The
dark brown residue was triturated several times with small amounts
of n-hexane, affording in almost quantitative yield [Ru(CF3-
CO2)3‚2CH3CN‚H2O] as a dark brown powder.
Anal. Calcd (found): C, 22.20 (22.10); H, 1.49 (1.60); N, 5.18
(5.18).
[IrCl3‚3CH3CN]. A solution of IrCl3‚xH2O (%Ir ) 52.15%)
(0.252 g, 0.684 mmol) in CH3CN (40 mL) was refluxed under
nitrogen atmosphere for 6 h. The solvent was then removed,
affording in almost quantitative yield [IrCl3‚3CH3CN] as a yellow
powder, stored under nitrogen and in the dark (aluminum foil).
MS-FAB+: m/e 421 (M + H)+, 386 (M - Cl)+, 380 (M -
CH3CN)+ (calcd for C6H9N3IrCl3 m/e 420). Anal. Calcd (found):
C, 17.07 (17.26); H, 2.13 (2.26); N, 9.96 (9.93).
[Ru(CF3CO2)3T3]. A suspension of [Ru(CF3CO2)3‚2CH3CN‚
H2O] (0.103 g, 0.191 mmol) in EtOH (25 mL) was added to a
suspension of T3 (0.074 g, 0.210 mmol) in EtOH (25 mL). The
dark brown reaction mixture was refluxed for 7 h. Removal of the
solvent under vacuum afforded a thick oily residue, which was
triturated with a small amount of n-hexane, giving 0.090 g of [Ru-
(CF3CO2)3 T3] (59%) as a dark brown powder.
1H NMR (300 MHz, CD3CN, 25 °C, TMS): δ (ppm) 9.09 (s,
2H, H3′, H5′), 8.69 (d, 2H, J3,4 ) 7.6 Hz, H3, H3′′), 8.59 (d, 2H,
Jortho ) 8.8 Hz, H8, H8′), 8.42 (d, 2H, Jortho ) 8.8 Hz, H7, H7′), 7.97
(dt, 2H, J4,3 ) J4,5 ) 8.0 Hz, J ) 1.7 Hz, H4, H4′′), 7.43 (d, 2H, J6,5
) 4.8 Hz, H6, H6′′), 7.19 (ddd, 2H, J5,4 ) 7.6 Hz, J5,6 ) 4.02 Hz,
J ) 1.6 Hz, H5, H5′′). MS-EI: m/e 795 (calcd for C27H14N4O8F9Ru
m/e 795). Anal. Calcd (found): C, 41.70 (41.71); H, 2.98 (2.81);
N, 8.15 (8.38).
[IrCl3T3]. A solution of [IrCl3‚3CH3CN] (0.146 g, 0.347 mmol)
in N,N-dimethylacetamide (20 mL) was added to a solution of T3
(0.123 g, 0.347 mmol) in N,N-dimethylacetamide (5 mL). The
reaction mixture was stirred at 100 °C in the dark (aluminum foil)
for 4 h. The resulting suspension was filtered and the filtrate
evaporated to dryness. The resulting oily product was triturated
with a small amount of n-pentane, affording 0.080 mg of [IrCl3T3]
(35.3%) as a dark brown powder.
1H NMR (300 MHz, DMSO-d6, 25 °C, TMS): δ (ppm) 9.23
(m, 4H, H3′, H5′, H6, H6′′), 8.93 (d, 2H, J3,4 ) 8.1 Hz, H3, H3′′),
8.52 (m, 4H, H7, H7′, H8, H8′), 8.34 (t, 2H, J4,3 ) 8.0 Hz, H4, H4′′),
8.01 (m, 2H, H5, H5′′). MS-FAB+: m/e 617 (M - Cl)+ (calcd for
C21H14N4O2IrCl3 m/e 652). Anal. Calcd (found): C, 38.62 (38.97);
H, 2.16 (2.27); N, 8.58 (8.42).
[IrCl3T0]. A solution of T0 (0.357 g, 0.818 mmol) in EtOH (50
mL) was added to a solution of IrCl3‚xH2O (% Ir ) 53.57%) (0.293
g, 0.818 mmol) in EtOH (50 mL). The dark brown reaction mixture
was refluxed under vigorous stirring for 6 h, then stirred at room
temperature overnight, affording a brown precipitate. It was then
dissolved in CH2Cl2 (100 mL) and the small insoluble residue was
filtered off. The filtrate was evaporated to dryness, leading to 212
mg of [IrCl3T0] (35%) as a red powder.
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 9.58 (d,
2H, J6,5 ) 4.3 Hz, H6, H6′′), 8.12 (s, 2H, H3′, H5′), 8.06 (d, 2H, J3,4
) 7.5 Hz, H3, H3′′), 7.86 (t, 2H, J4,3 ) J4,5 ) 7.6 Hz, H4, H4′′), 7.63
(m, 4H, H7, H7′, H5, H5′′), 6.73 (d, 2H, Jortho ) 7.9 Hz, H8, H8′),
3.39 (t, broad, NCH2), 1.43 (m, 8H, CH2), 1.03 (t, 6H, J ) 7.3 Hz,
CH3). MS-FAB+: m/e 699 (M - Cl)+ (calcd for C29H32N4IrCl3
m/e 734). Anal. Calcd (found): C, 47.38 (47.32); H, 4.39 (4.44);
N, 7.62 (7.52).
[Ir(4-EtC6H4CO2)3T3]. [IrCl3T3] (80 mg, 0.122 mmol) was
added to a solution of 4-EtC6H4CO2Ag (94.5 mg, 0.366 mmol) in
N,N-dimethylacetamide (100 mL). The resulting mixture was stirred
in the dark and under nitrogen atmosphere at 120 °C for 4 days.
The suspension was filtered and the red filtrate evaporated to
dryness, affording an oily product, which was triturated with a small
amount of n-pentane, giving an orange powder. This powder was
dissolved in CHCl3 (50 mL). After filtration of the insoluble residue
and evaporation of the filtrate, 43.3 mg of [Ir(4-EtC6H4CO2)3T3]
(35.7%) was obtained as a dark orange powder.
[Ir(4-EtC6H4CO2)3T0]. 4-EtC6H4CO2Ag (52.9 mg, 0.206 mmol)
was added to a solution of [IrCl3T0] (50.4 mg, 0.0686 mmol) in
CHCl3 (80 mL). The red reaction mixture was stirred at room
temperature for 24 h. AgCl was filtered off and the filtrate
evaporated to dryness, affording 62 mg of [Ir(4-EtC6H4CO2)3T0]
(84%) as a red powder.
MS-FAB+: m/e 844 (M - (4-EtC6H4CO2))+ (calcd for
C48H41N4O8Ir m/e 993). Anal. Calcd (found): C, 57.99 (58.43); H,
4.16 (4.20); N, 5.63 (5.64).
Results and Discussion
1H NMR (300 MHz, CDCl3, 25 °C, TMS): δ (ppm) 9.59 (d,
broad, 2H, H6, H6′′), 8.13 (s, 2H, H3′, H5′), 8.05 (m, 8H, H3, H3′′,
CH benzoate), 7.94 (t, 2H, J4,3 ) J4,5 ) 7.3 Hz, H4, H4′′), 7.67 (m,
4H, H7, H7′, H5, H5′′), 7.29 (d, 6H, CH benzoate), 6.76 (d, 2H, Jortho
) 8.5 Hz, H8, H8′), 3.40 (t, broad, 4H, NCH2), 2.75 (q, broad, 6H,
CH3CH2C6H4), 1.43 (m, 8H, CH2), 1.03 (t, 6H, J ) 7.3 Hz, CH3),
0.87 (t, 9H, J ) 7.5 Hz, CH3CH2Ph). MS-FAB+: m/e 926 (M -
1. Synthesis of Ligands and Complexes. A series of 4′-
(C6H4-p-X)-2,2′:6′,2′′-terpyridines (X ) NBu2 (T0), (E)-CHd
CH-C6H4-p-NBu2 (T1), (E,E)-(CHdCH)2-C6H4-p-NMe2
(T2), NO2 (T3)) (see Figure 1) and their complexes with Zn-
(II), Ru(III), and Ir(III) ions carrying various ancillary ligands
were synthesized and characterized.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8973

Tessore et al.
Scheme 1
Scheme 3
Terpyridine 1, used as starting material for the synthesis
of T1 and T2, was synthesized by the Kro¨hnke methodology
(see Scheme 1),11a the most convenient way to prepare
aromatic substituted terpyridines, by condensation of p-
tolualdehyde with 2 equiv of 2-acetylpyridine, in the presence
of potassium tert-butoxide as a base and in anhydrous THF.
The corresponding 1,5-diketone, not isolated, was then
reacted with NH4OAc to afford 1 (40% yield). This procedure
was followed, as previously reported,8a for the synthesis of
T0 (60% yield). Terpyridine 1 was then brominated, follow-
ing a methodology described in the literature,11b with
N-bromosuccinimide in CCl4 and a catalytic amount of
dibenzoylperoxide as radical starter. Quaternization of
compound 2 with triphenylphosphine in refluxing toluene
afforded the salt 3 (over 80% yield). Wittig condensation of
3 was carried out with p-(dibutylamino)benzaldehyde in
anhydrous N,N-dimethylformamide, using potassium tert-
butoxide as a base, and afforded terpyridine T1 (53% yield),
while the reaction carried out under the same conditions
between 3 and p-(dimethylamino)cinnamaldehyde afforded
terpyridine T2 (64% yield) (see Scheme 2).Terpyridine T3,
with the strong electron-withdrawing nitro group, was
obtained by a convergent synthesis (see Scheme 3), as
reported in the literature,11c starting from p-nitrobenzalde-
hyde, which was condensed with 1 equiv of 2-acetylpyridine,
in the presence of a 10% aqueous solution of NaOH,
affording the corresponding enone 4 in good yields. By
reaction of 2-acetylpyridine with pyridine and iodine, the
pyridinium salt 5 was obtained.11a Finally, stoichiometric
amounts of compounds 4 and 5 were condensed with
ammonium acetate to obtain T3 (78% yield). To study the
role of the ancillary ligand on the second-order NLO
response, Zn(II) complexes of terpyridine T0 with chlorine
and trifluoroacetate ancillary ligands were prepared in good
yield (80%) by reaction of stoichiometric amounts of the
Zn(II) salt and of the ligand T0 with terpyridines T1 and T2;
only Zn(II) complexes with the trifluoroacetate as ancillary
ligand were prepared, following the procedure above. Ac-
cording to the known structure of [ZnCl2(2,2′:6′,2′′-terpyri-
dine)],21 in these Zn(II) complexes the terpyridines T0, T1,
and T2, which, when free, are in transoid geometry, as
confirmed by experimental and theoretical dipole moments
(see later), assume the cis-like configuration expected for a
metal chelated terdentate ligand, while the Zn(II) ion assumes
a trigonal bipyramidal geometry of the coordination sphere.
Ru(III) and Ir(III) complexes of T0 and T1 with chlorine
as an ancillary ligand were synthesized by mixing terpyridine
and stoichiometric amounts of RuCl3‚xH2O or IrCl3‚xH2O
respectively, followed by refluxing in absolute ethanol.
However, the complex [RuCl3T0] is not soluble enough in
CHCl3 for dipole moments and EFISH measurements, so that
in its reaction with silver trifluoroacetate in CH3CN, the more
soluble complex [Ru(CF3CO2)3T0] was synthesized.
The complex [Ru(CF3CO2)3T3] was prepared by reacting
RuCl3‚xH2O with the stoichiometric amount of silver tri-
fluoroacetate in refluxing acetonitrile. This afforded, in
almost quantitative yield, the compound [Ru(CF3CO2)3‚2CH3-
CN‚H2O], which was then reacted with the stoichiometric
amount of terpyridine T3 under refluxing ethanol (59% yield).
Scheme 2
Finally, we prepared the complex [Ir(4-EtC6H4CO2)3T3],
which is soluble enough for dipole moments and EFISH
measurements since both [IrCl3T3] and [Ir(CF3CO2)3T3] are
not sufficiently soluble. Its synthesis first required the
preparation of [IrCl3‚3CH3CN], by reaction of IrCl3‚xH2O
with excess CH3CN, followed by an exchange reaction with
terpyridine T3 in N,N-dimethylacetamide to give [IrCl3T3]
(35.3% yield). The ancillary ligand exchange was made by
(21) (a) Einstein, F. W. B.; Penfold, B. R. Acta Crystallogr. 1966, 20, 924-
926. (b) Douglas, J. E.; Wilkins, C. J. Inorg. Chim. Acta 1969, 635-
638.
8974 Inorganic Chemistry, Vol. 44, No. 24, 2005

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes
Scheme 4
the reaction of this latter complex with 4-EtC6H4CO2Ag. In
the same way, a reaction of [IrCl3T0] with 4-EtC6H4CO2Ag
in CHCl3 afforded [Ir(4-EtC6H4CO2)3T0] (35.7% yield), a
reference compound to be compared with [Ir(4-EtC6H4-
CO2)3T3].
2. Characterization of Some Electronic Properties of
terpyridines and Their Zn(II), Ir(III), and Ru(III) Com-
1
1
plexes. H NMR Spectra. In the H NMR spectra (see
Experimental Section) of terpyridines T0, T1, and T2 coor-
dinated to Zn(II) and Ir(III) metal centers, the signals of
hydrogens in R position to the terpyridine nitrogen atoms
are shifted to lower fields with respect to those of the ligand,
as already observed for other Zn(II) complexes with similar
nitrogen donor ligands such as phenanthrolines and stilbazoles3f
(for example, ∆δ in CDCl3 0.15-0.17 ppm for [ZnCl2T0]
and [Zn(CF3CO2)2T0] respectively; ∆δ in CD3COCD3 0.09-
0.15 ppm for [Zn(CF3CO2)2T1] and [Zn(CF3CO2)2T2] re-
spectively; and ∆δ in CD3COCD3 0.55 ppm for [IrCl3T1]).
This shift is related to the electron transfer from the nitrogen
donor atoms to the metal center, which appears to be, in
agreement with the Lewis acidity of the metal center, more
relevant for the Ir(III) ion than the Zn(II) ion. The coupling
constant between the trans olefinic hydrogens in terpyridines
T1 (Jtrans ) 16.2 Hz) and T2 (Jtrans ) 15.4 Hz) is maintained
in their metal complexes (see Experimental Section).
The molecular geometry of the model 4′-(C6H4-p-NMe2)-
2,2′:6′,2′′-terpyridine of T0 was optimized taking into account
two isomers, labeled as “up” (or transoid) and “down” (or
cisoid), which differ for the orientation of the terpyridyl
nitrogen atoms (see Scheme 4). For the up isomer the three
terpyridine aromatic rings are essentially planar, while the
substituted phenyl ring bearing the donor group is twisted
with respect to the terpyridine plane by 30.4°. The NMe2
group is essentially coplanar with the phenyl ring to which
it is bound. The down isomer is instead characterized by a
twisting of the terminal terpyridine rings with respect to the
central one of ca. 30° to minimize the repulsion between
the two nitrogen lone pairs.
We calculate the up isomer to be more stable than the
corresponding down isomer by 14.5 kcal/mol when including
solvation effects. Therefore, the very low experimental dipole
moment of all the terpyridines investigated is obviously
related to the presence in solution of only the up isomer,
with a transoid configuration about the interannular carbon-
carbon bonds, as it occurs for 2,2′:6′,2′′-terpyridines.23 As a
matter of fact, we obtained a fairly good agreement between
the calculated dipole moment (1.69 D) of the reduced model
of T0 with two methyl groups at the nitrogen atom and the
experimental dipole moment of T0 (2.1 D).
The Ru(III) ion is a d5 low-spin (5t2g) paramagnetic metal
center, but in the case of the [Ru(CF3CO2)3T3] complex, a
1
well-defined H NMR spectrum in CD3CN was obtained,
which showed the expected “Fermi contact shift” of the
hydrogen atoms of the terpyridine ligand closer to the
paramagnetic metal center.22a,b The spectrum of [Ru(CF3-
CO2)3T3], when compared, for example, to that of [IrCl3T3],
shows that the signals of the hydrogens in R position of the
central pyridinic ring are shifted, not to lower fields with
respect to those of the free terpyridine (δ ) 8.43 ppm in
CD3CN), but to higher fields, with a significant shielding
effect (δ ) 7.43 ppm in CD3CN). This observation would
suggest that, in the Ru(III) complex, the electron spin density
is shifted from the metal to the terpyridine ligand.
The shift of the terpyridine geometry from transoid to
cisoid configuration upon coordination also justifies the
unusually strong increase of the dipole moment (Table 1)
occurring upon coordination (µ enhancement factor )
µ
complex/µterpyridine), an increase much stronger than that of other
chelating nitrogen donor π-delocalized ligands, such as
phenanthrolines and bypyridines.3f,4b However, the enhance-
ment factor is slightly higher for terpyridine T0 (µ enhance-
ment factor 3.8-4.8) than for the more delocalized terpy-
ridines T1 and T2 (µ enhancement factor 2.3-3), which is
in agreement with what was reported for some Zn(II) and
Cd(II) complexes with substituted phenanthrolines.3f For Zn-
(II) complexes of T0, the dipole moment increased with the
increased electron-withdrawing strength of the ancillary
ligand (see Table 1; µ enhancement factor ) 3.8 for
[ZnCl2T0] and 4.7 for [Zn(CF3CO2)2T0]).
Given its very low dipole moment, coordination of
terpyridine T3 to Ir(III) leads to a very high enhancement
factor (5.3). In the case of [Ru(CF3CO2)3T3], which was not
soluble enough in CHCl3 to obtain reproducible dipole
moment measurements, the dipole moment calculated by
DFT in CHCl3 solution (see Table 1) confirms a significant
enhancement factor (4.8).
Dipole Moments. Dipole moments of terpyridines and
complexes, when sufficiently soluble, were measured in
CHCl3 by the Guggenheim method (see Table 1).13
Dipole moments of terpyridines T1 and T2 are low,
comparable to each other, and only slightly higher than that
of the less π-delocalized ligand T0. In addition, dipole
moments of T0 and T3 are similar, although they bear a strong
donor and a strong acceptor substituent respectively (Table
1). This result would suggest, as confirmed by DFT geometry
optimizations (see below), that the phenyl group in position
4 of the central pyridine ring of these terpyridines is not
coplanar with the pyridine ring itself, thus reducing the π
interactions between the two rings and therefore the signifi-
cant electronic transitions.
(22) (a) Bertini, I.; Luchinat, C. NMR of Paramagnetic Molecules in
Biological Systems; Benjamin-Cummings: Menlo Park, CA, 1986. (b)
Banci, L.; Piccioli, M.; Scozzafava, A. Coord. Chem. ReV. 1992, 120,
1-28.
(23) Fallahpour, R. A. Synthesis 2003, 2, 155-184.
Inorganic Chemistry, Vol. 44, No. 24, 2005 8975

Tessore et al.
UV-Visible Spectra. The UV-visible spectra in CHCl3
of terpyridines carrying a NR2 electron donor substituent
show one strong absorption band around 360-399 nm,
attributed to the n f π* ILCT transition, which emanates
from the donor group.3d,e,6 As in chelating nitrogen donor
ligands, such as phenanthrolines,3f the absorption band of
the ILCT transition is located at lower energy by increasing
the length of the π-delocalized spacer between the electron
donor group and the chelating system (see Table 1). For the
reduced model of T0, the calculated TDDFT absorption
maximum in solution for the ILCT transition (368 nm) is in
excellent agreement with the experimental value of 360 nm
and confirms the assignment of the main spectral feature as
a ILCT single transition involving the HOMO and LUMO
as starting and arriving orbitals, respectively.
Upon coordination of T0, T1, and T2 to Zn(II), Ru(III), or
Ir(III) metal centers, this ILCT transition is red-shifted with
respect to the free terpyridine (0.46-0.77 eV for T0; 0.41-
0.54 eV for T1; 0.31 eV for T2; see Table 1), according to
the increased acceptor properties of the π* orbitals of the
terpyridine due to coordination.3d-f In the case of T0 and T1,
the shift of the ILCT transition is higher by coordination to
Ir(III) and Ru(III) centers than to Zn(II) centers, in agreement
with the increased Lewis acidity.3e In addition to the ILCT
transition, terpyridines T0, T1, and T2 show absorption bands
at higher energy, which can be attributed mainly to π f π*
transitions, involving their π core only, much less solvato-
chromic, as expected for transitions centered on the ligand
(LC) of low charge-transfer character.
transition (red-shifted, as expected, by 105, 103, and 81 nm
respectively, with respect to the ILCT transition of the free
ligands), but also to another charge-transfer contribution
located under the ILCT, probably a MLCT transition.7f,g This
latter hypothesis is evidenced by both the high intensity of
the band and the slightly negative value of ∆µeg obtained
by a solvatocromic investigation, which would suggest the
presence of a MLCT transition under the ILCT transition,
which, if alone, should produce a positive ∆µeg contribution.
This hypothesis is also supported by the larger negative
value of ∆µeg for [IrCl3T1] than for [IrCl3T0] and by the very
large negative value of ∆µeg of the absorption band at 413
nm for the complex [Ir(4-EtC6H4CO2)3T3], with a terpyridine
that bears an electron acceptor NO2 instead of an electron
donor NR2 group. Therefore, the ILCT transition is lacking,
being originated by the NR2 group, and the absorption band
is related only to a MLCT transition, in agreement with the
large negative value of ∆µeg favored by the presence of the
electron-withdrawing NO2 group (see Table 1).
All Ir(III) complexes show a second weaker band at 520-
540 nm, which can be tentatively assigned to another MLCT
transition according to the literature7f,g and is in agreement
with its significant negative ∆µeg value (obtained by a
solvatocromic investigation), which increases by going from
the T0 and T1 complexes to [Ir(4-EtC6H4CO2)3T3], as
expected for a MLCT transition (see Table 1).
3. EFISH and Solvatochromic Investigation of Second-
Order NLO Properties. The EFISH technique5 was used
to investigate the effect of the different metal centers studied
in this work on the quadratic hyperpolarizability âλ of
terpyridines T0, T1, T2, and T3. Measurements were per-
formed in CHCl3, working mainly with a fundamental
incident wavelength of 1.34 µm, chosen to have a second
harmonic (at 670 nm) far enough from the absorption bands
of all the complexes investigated. In this way the quadratic
hyperpolarizability is not overestimated due to resonance
effects, as it could occur, for instance, in the case of Ru(III)
complexes if working with a fundamental incident wave-
length of 1.907 µm, which is usually considered off
resonance, but which in these complexes could produce a
second harmonic resonant with the weak absorption around
795-911 nm (see Table 1).
However, for Ir(III) complexes, EFISH measurements
were carried out working with both 1.34 and 1.907 µm
incident wavelengths, with the exception of [Ir(4-EtC6H4-
CO2)3T0]. In this case, the quadratic hyperpolarizability was
measured only with an incident wavelength of 1.907 µm.
The investigation on the second-order NLO properties was
also supported by a solvatocromic investigation, carried out
to define the contributions of the various absorption bands
to the second-order NLO response.6,8a
In accordance with the absence of ILCT transitions, the
UV-visible spectrum of terpyridine T3, bearing an electron-
withdrawing NO2 group instead of an electron-donating NR2
group, shows only one absorption band at higher energy (λ
) 280 nm), as expected for a π f π* transition centered on
the ligand (LC).
In addition to the red-shifted ILCT absorption band, in
the spectra of [Ru(CF3CO2)3T0], [RuCl3T0], and [RuCl3T1]
one relatively weak absorption band appears at 911, 795,
and 866 nm respectively. The latter can be tentatively
assigned to a LMCT transition,8a on the basis of the positive
value of ∆µeg (difference between excited- and ground-state
dipole moments) obtained by a solvatochromic investigation
(see Table 1) and according to the literature.9,10 In addition
this assignment is in agreement with the sensitivity of the
energy of the transition to the nature of the anionic ancillary
ligand and in particular with the absence of such a band in
the spectrum of the complex [Ru(CF3CO2)3T3] (see Table
1), where the terpyridine is lacking the donor group, which
is involved in the LMCT transition. A recent, theoretical
time-dependent DFT investigation on the electronic transi-
tions of [Ru(CF3CO2)3T0] has confimed our assignment.24
The electronic spectra of Ir(III) complexes show two major
absorption bands (see Table 1). For the complexes with T0
and T1 ligands, the band at higher energy (465, 463, and
476 nm respectively) cannot be due only to an ILCT
The static hyperpolarizability value calculated for the
reduced model of T0, essentially due to the zzz component,
is in good agreement with the experimental frequency-
dependent values (19 × 10-30 and 22 × 10-30 esu respec-
tively). Clearly, the calculated value is smaller due to the
effect of frequency dispersion.
(24) De Angelis, F.; Fantacci, S.; Sgamelotti, A.; Cariati, F.; Roberto, D.;
Tessore, F.; Ugo, R. manuscript submitted to Dalton Transactions.
8976 Inorganic Chemistry, Vol. 44, No. 24, 2005

Terpyridine Zn(II), Ru(III), and Ir(III) Complexes
The latter result is more evidence that, in the terpyridines
investigated in this work carrying a NR2 donor group, the
quadratic hyperpolarizability value is dominated by the ILCT
transition, as confirmed by solvatochromic investigation
(Table 1).
We have shown that, for terpyridines carrying a NR2 group
(T0, T1, T2), increasing the length of the π-conjugated spacer
between the NR2 group and the chelated system of the
terpyridine, a significant increase of â1.34 occurs (from 22
× 10-30 esu for T0 to 52 × 10-30 esu for T1 and finally to
95 × 10-30 esu for T2). A similar enhancement was reported
for planar ligands such as stilbazoles,3e or 5-X-1,10-phenan-
throlines (X ) NMe2, X ) trans-CHdCHC6H4-4′-NMe2, X
) trans,trans-(CHdCH)2C6H4-4′-NMe2).3f As in the case of
pyridines para substituted with an electron-withdrawing
group,3e the â1.34 value of T3, carrying an electron-withdraw-
ing NO2 group, is small and negative (see Table 1).
In agreement with the significant red shift of the ILCT
(see Table 1), upon coordination of terpyridines T0, T1, and
T2 to Zn(II), the quadratic hyperpolarizability value shows
a relevant enhancement and has still a positive sign. The
enhancement factor EF (given by â1.34,complex/â1.34,terpyridine), a
useful parameter to evaluate the coordination effectiveness,3e,f
increases with the increasing electron-withdrawing character
of the ancillary ligand (EF ) 3.0 for [ZnCl2T0]; EF ) 4.0
for [Zn(CF3CO2)2T0]). Some of us3e,f have already shown
that, given the same metal center and the same ancillary
ligands, the EF decreases when the length of the π-conju-
gated system of the linker connecting the donor NR2 group
is increased. (EF ) 4.0 for [Zn(CF3CO2)2T0]; EF ) 3.5 for
[Zn(CF3CO2)2T1]; EF ) 1.4 for [Zn(CF3CO2)2T2]).
the band at 533 nm, attributed to a MLCT transition (see
Table 1). Interestingly, in this complex, the positive contribu-
tion of the red-shifted ligand ILCT transition is not so
relevant, due to the negative contribution of a MLCT
transition. Both transitions are probably under the absorption
band of 465 nm, as discussed in the section devoted to UV-
visible spectra, so that the contribution of this band is finally
slightly negative.
The negative value of the quadratic hyperpolarizability of
this kind of terpyridinic complexes of Ir(III) was confirmed
by the second-order NLO response of [IrCl3T1] and [Ir(4-
EtC6H4CO2)3T0] (Table 1).
In agreement with the significant role of the MLCT
transition at about 520-540 nm in Ir(III) complexes, the â1.34
value for the complex [Ir(4-EtC6H4CO2)3T3] is relevant and
negative (see Table 1). In this latter case the â1.34 enhance-
ment factor is very high (EF ) 19), and, as confimed by the
solvatochromic investigation, is mainly due to the strong
negative contribution of the MLCT transition at 521 nm,
enhanced by the presence of the electron-withdrawing NO2
substituent and of the negative contribution of the absorption
band at 413 nm, which becomes significant due to the lack
of the positive contribution of the ILCT transition (Table
1).
The comparison of â1.907 of [Ir(4-EtC6H4CO2)3T0] (-70
× 10-30 esu) and [Ir(4-EtC6H4CO2)3T3] (-126 × 10-30 esu)
is in support of the aforementioned statement.
In this work the solvatochromic investigation has con-
firmed its useful role for the study at least qualitatively of
the electronic origin of the second-order NLO response.
For terpyridines T0, T1, and T2 and their Zn(II) complexes
we have shown that the major contribution to âCT is given
by the absorption band due to an ILCT transition at about
360-399 nm for the ligands and at about 425-454 nm for
the complexes (see Table 1). EFISH â1.34 and âCT at 1.34
µm incident wavelength are comparable for the three
terpyridines and for the Zn(II) complex with T0, while âCT
is definitively lower than EFISH â1.34 in the case of Zn(II)
complexes with the more π delocalized terpyridines T1 and
T2 (see Table 1).
However, such relevant enhancement factors cannot be
attributed only to the red-shift of the ligand ILCT transition,
but also to the stabilization of the cisoid conformation of
the terpyridine due to chelation. The significant role of
chelation in increasing the quadratic hyperpolarizability of
chelating ligands was already discussed by some of us for
bypyridines carrying NR2 strong electron donor groups.4b
The negative value of â1.34 of [Ru(CF3CO2)3T0], as shown
by the solvatochromic investigation (Table 1), is due to the
significant contribution to the second-order NLO response
of the band at 911 nm. This band must produce a negative
contribution since it is located at a wavelength higher than
the second harmonic. The ILCT transition of the ligand, red-
shifted as expected, gives a significant positive contribution
to â1.34 as it occurs in Zn(II) complexes. Also, the absorption
band at 508 nm, which we attributed to a LMCT transition,
gives a positive contribution to â1.34, but, in this case, â1.34
remains dominated by the negative contribution of the band
at 911 nm (Table 1). In fact, the negative contribution of
this LMCT band becomes much less relevant in the specific
case of the related complex [RuCl3T1], thus giving rise to a
Interestingly, there is good agreement, in sign and absolute
value, between EFISH â1.34 and âCT , working with a 1.34
µm incident wavelength for the Ru(III) complex of T0 and
for the Ir(III) complexes of T0 and T1 (Table 1). The
agreement is less satisfactory for the Ir(III) complex of T3,
although the sign is negative and the absolute value quite
high in both cases. Such an excellent agreement would
suggest that many charge-transfer transitions, which con-
tribute to the overall second-order NLO response in Ir(III)
and Ru(III), are located along the dipole moment axis. In
fact, âCT can be compared to EFISH âλ only when the charge-
transfer processes controlling the second-order NLO response
are located close in direction to the dipole moment axis. This
location was proved by a theoretical investigation carried
out on the complex [Ru(CF3CO2)3T0].24
positive value of â1.34
.
The complex [IrCl3T0] shows a significant enhancement
of the absolute value of the quadratic hyperpolarizability (EF
) 5.0) which, however, becomes negative. As suggested in
our preliminary communication,8a this is due to the large and
negative contribution to the quadratic hyperpolarizability of
The solvatochromic investigation has proved to be helpful
in getting the necessary information to explain the positive
Inorganic Chemistry, Vol. 44, No. 24, 2005 8977

Tessore et al.
sign of EFISH â1.34 and âCT of [RuCl3T1] when compared
to the negative sign of EFISH â1.34 and âCT of [Ru(CF3-
CO2)3T0].
change of sign was reported for low oxidation state metal
complexes only when the push-pull π-delocalized nitrogen
donor ligand carries an electron withdrawing group, due to
the significant role of the MLCT transition.3b,d,e We have
shown that this effect is strongly enhanced in an Ir(III)
complex with a terpyridine carrying an electron withdrawing
NO2 group. We have also confirmed that an important role
is also played by chelation and by ancillary ligands; the
ligands can tune the acceptor properties of the metal center,
acting on the contribution of various transitions, to the overall
second-order NLO response, either by perturbation of the
π* level of the push-pull π delocalized nitrogen donor
ligand (ILCT) or by controlling the energy of LMCT or
MLCT processes.
In [RuCl3T1] the positive value of âCT is due to a very
weak absorption band at higher wavelengths (866 nm), thus
giving only a small negative contribution to the overall âCT,
and is then dominated by the positive contribution of the
band at 469 nm, which is probably the sum of a ILCT and
an LMCT transition.24 This latter observation confirms the
important role played by ancillary ligands in tuning the
second-order NLO response of these terpyridinic complexes,
as shown when comparing the values of the quadratic
hyperpolarizabilities of [ZnCl2T0] and [Zn(CF3CO2)2T0] and
of [IrCl3T0] and [Ir(4-EtC6H4CO2)3T0] (see Table 1).
It is also noteworthy that the terpyridines investigated in
this work, which can be considered as 4-substituted pyridines
but with the phenyl ring twisted about the interannular
bond,24,26 show a much higher second-order NLO response
when free or coordinated to a metal center with respect to
simple 4-substituted pyridines, for example 4-NMe2C5H4N
(â1.34 ) 0.06 × 10-30 esu)3e or 4-CNC5H4N (â1.06 computed
value ) 0.33 × 10-30 esu).3e It seems that the nonplanarity
of the two fused rings and therefore their poor π-conjugation
do not decrease the quadratic hyperpolarizability, but, on the
contrary, introduce a significant enhancement. This is an
observation which deserves further investigation.
Conclusions
In this work we have confirmed our preliminary findings8a
about the relevant role of the nature of the metal ion in tuning
the absolute value and sign of the second-order NLO
response of Zn(II), Ru(III), and Ir(III) complexes with
terdentate chelating push-pull π delocalized nitrogen donor
ligands such as 4′-(1-C6H4-p-X)-2,2′:6′,2′′-terpyridines (X )
NBu2, trans-CHdCH-C6H4-p-NBu2, trans,trans-(CHd
CH)2-C6H4-p-NMe2, NO2).
While the second-order NLO response of other π-delo-
calized nitrogen donor ligand complexes (stilbazoles, phenan-
throlines, etc.), carrying a NR2 donor group with low
oxidation state soft metal centers such as Rh(I) (4d8), Ir(I)
(5d8), Os(II) (5d6), W(0) (5d6),3c-e or “Os3(CO)11” cluster
core25 or relatively hard Zn(II) (3d10) centers,3f,4 is dictated
mainly by the red-shift of the ligand ILCT transition, we
have shown that coordination of π-delocalized nitrogen donor
ligands, such as terpyridines, to higher oxidation d open metal
centers such as Ir(III) (5d6) or Ru(III) (4d5) produces a
second-order NLO response strongly influenced also by
LMCT or MLCT transitions, in such a way that they can
even change the sign of the quadratic hyperpolarizability. A
Acknowledgment. We thank Dr. Isabelle Rak-Ledoux
and the EÄ cole Normale Supe´rieure de Chachan (France) for
their kindness to allow Dr. Francesca Tessore to carry out
some EFISH measurements. This work was supported by
the Ministero dell’Istruzione, dell’Universita` e della Ricerca
(Programma di ricerca FIRB, year 2001, Research Title:
Nano-organization of hybrid organo-inorganic molecules
with magnetic and non linear optical properties).
IC050975Q
(25) Lucenti, E.; Cariati, E.; Dragonetti, C.; Manassero., L.; Tessore, F.
(26) Constable, E. C.; Lewis, J.; Liptrot, M. C.; Raithby, P. Inorg. Chim.
Acta 1990, 178, 47-54.
Organometallics 2004, 23, 687-692.
8978 Inorganic Chemistry, Vol. 44, No. 24, 2005