Experimental and theoretical characterization of Ru(II) complexes with polypyridine and phosphine ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.07.028

The synthesis and the experimental and theoretical characterization of ruthenium hydride complexes containing phosphorus and polypyridine ligands [RuH(CO)(N-N)(PPh₃)₂]⁺ with N-N = dppz 1, dppz-CH₃ 2 (2.1 isomer)

Full text of DOI:10.1016/j.jorganchem.2009.07.028

Journal of Organometallic Chemistry 694 (2009) 3781–3792
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Experimental and theoretical characterization of Ru(II) complexes
with polypyridine and phosphine ligands
e,
Mauricio Yáñez a, Juan Guerrero b, Pedro Aguirre c, Sergio A. Moya d, , Gloria Cárdenas-Jirón
*
*
a Laboratorio de Recursos Renovables, Centro de Biotecnología, Universidad de Concepción, Concepción, Casilla 160-C, Chile
b Laboratorio de Resonancia Magnética Nuclear, Facultad de Química y Biología, Universidad de Santiago de Chile, Chile
c Facultad de Ciencias Químicas y Farmacológicas, Universidad de Chile, Chile
d Laboratorio de Química Organometálica y Catálisis, Facultad de Química y Biología, Universidad de Santiago de Chile, Chile
e Laboratorio de Química Teórica, Facultad de Química y Biología, Universidad de Santiago de Chile (USACH), Casilla 40, Correo 33, Santiago, Chile
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and the experimental and theoretical characterization of ruthenium hydride complexes
containing phosphorus and polypyridine ligands [RuH(CO)(N-N)(PPh3)2]+ with N-N = dppz 1, dppz-CH3
2 (2.1 isomer), dppz-Cl 3 (3.1 isomer), ppl 4, and 2,20-biquinoline 5, (where dppz = dipyrido[3,2-a:20,30-
c]phenazine), are presented. 1H NMR, 31P NMR, 13C NMR, IR-FT, UV–Vis and elemental analysis are used
to characterize the complexes. Optimized molecular geometries in the gas phase at the B3LYP/LACVP(d,p)
level showed a distorted octahedral structure for ruthenium, the phosphine ligands are localized in a
trans position, while the polypyridine ligand, which in all the cases is planar except in 5, adopt a trans
position relative to the carbon monoxide and hydride ligands. The theoretical absorption spectra (one
hundred excited states) were calculated for the seven complexes by the time dependent density func-
tional theory (TD-DFT) in the gas phase. They predicted very well the UV–Vis spectra. It was possible
to identify the character of each electronic transition and the fragments of the complexes involved in
it. Theoretical evidence of the substituent effect in the polypyridine ligand and of the ligand effect
(dppz, biq, ppl) was found, displayed mainly in the longer wavelength band. The theoretical results
showed that the properties of these complexes can be tuned with changes localized in the polypyridine
ligand covalently bonded to ruthenium.
Received 26 January 2009
Received in revised form 13 July 2009
Accepted 14 July 2009
Available online 17 July 2009
Keywords:
Ruthenium
Polypyridine
Phosphine
Electronic absorption spectra
TD-DFT
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
N-N = 2,20-biquinoline
(biq),
dipyrido[3,2-a:20,30-c]phenazine
(dppz-R, with R = H, Me, Cl), and pyrazine[2,3-f][1,10]-phenanthro-
line (ppl). The quantum chemical study included a characterization
of the molecular and electronic structures of the complexes by anal-
ysis of optimized molecular geometries and electronic populations
by using the natural bond orbitals (NBO) scheme. The latter was
used to identify the nature of the interactions between the ligands
and the central metal atom. The quantum methodology called time
dependent density functional theory (TD-DFT) [12–14] was finally
used to calculate the electronic absorption spectra. Based on a
molecular orbital scheme, these results allowed the interpretation
of the UV–Vis spectra obtained at an experimental level.
Hydrides of the transition metals Fe, Co, Ni, Ru, Rh and Pd have
been applied as catalysts in numerous reactions presenting high
activity and selectivity [1]. Of these complexes, ruthenium hydride
containing carbonyl and triarylphosphine ligands have attracted
enough attention due to their reactivity and efficiency as catalysts
in hydrogenation reactions of unsaturated substrates, hydrogen
transfer, activation of C–H bonds, and isomerization reactions [2–9].
On the other hand, complexes of ruthenium containing
p-
acceptor nitrogen-bearing ligands such as polypyridines have been
widely studied as systems for the conversion of solar energy in
storable energy [10]. However, the study and application of ruthe-
nium hydride containing triphenylphospine and polypyridine li-
gands simultaneously in the coordination sphere has been
limited to a few specific examples [11].
2. Experimental
2.1. Materials
Here we report an experimental and quantum chemical study of
ruthenium complexes of the type [RuH(CO)(N-N)(PPh3)2]+, where
The chemicals used for the synthesis of the ligands, complexes,
and deuterated solvents were obtained from Sigma–Aldrich. The
phosphines used were purchased from Strem. All solvents used
were analytical grade from J.T. Baker. Solvents were dried accord-
* Corresponding author.
E-mail addresses: mayanez@udec.cl (M. Yáñez), sergio.moya@usach.cl (S.A.
Moya), gloria.cardenas@usach.cl (G. Cárdenas-Jirón).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.07.028

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M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
ing to published procedures [15a], and were distilled before use.
Complex polypyridine ligands were prepared following reported
procedure. Simple nitrogenous ligands such as 2,2-biquinoline
were purchased from Sigma–Aldrich. Dppz and replaced dppz
were prepared using reported procedures. [15b].
(vs); m (C–Cl) = 1091 (m). Yield 88%. Elem. Anal. Calc. for
C55H40ClF6N4OP3Ru: C, 59.17; H, 3.61; N, 5.01. Found: C, 58.99;
H, 3.49; N, 4.98%.
2.6. [RuH(CO)(ppl)(PPh3)2]PF6 (4)
1D 1H NMR, 31P{1H} NMR, 13C{1H} NMR, and 2D-ge 1H 1H COSY,
2D 1H 13C HSQC-ed, and 2D 1H 13C HMBC NMR spectra were re-
corded on a Bruker Avance 400 MHz spectrometer (400.133 MHz
for 1H, 100.624 MHz for 13C, 161.976 MHz for 31P) equipped with
a 5 mm broad band inverse probe head gradient enhanced. All
the measurements were made at 300 K and chemical shifts (d in
ppm) for 1H, 13C were reported relative to Me4S, and for 31P relative
to 85% H3PO4.
3
Colour: yellow. 1H NMR: d 9.63 (Ha, d, Jab = 7.68), 9.53 (Ha1, d,
3Ja1b1 = 8.23), (7.5–7.3) (overlapped by the protons of the triphen-
3
ylphosphine) (Hb), 8.16 (Hb1
,
q, Jb1a1 = 8.23), 9.92 (Hc, d,
3Jcb = 5.48), 8.6 (Hc1, d, Jc1b1 = 5.48), 9.42 (Hd + Hd1, m); ꢀ11.25
3
(hydride, t, JHP = 18.88). 31P NMR: 43.90. IR (KBr, cmꢀ1):
m (Ru–H) =
Not observed; m (CO) = 1948 (vs); m (C@C, C@N) = 1435–1481 (m); m
(PF6ꢀ) = 837 (vs). Yield 89%. Elem. Anal. Calc. for C51H39F6N4OP3Ru:
IR spectra were obtained on a Bruker IFS-66 V FT-IR spectropho-
tometer with solid samples in 0.22-mm thick KBr disks. Elemental
analysis was carried out using a CE Instruments EA 1108 model.
Electronic spectra were obtained on a UV–Vis SPECORD S 100
spectrophotometer. Melting points of the compounds was deter-
mined on an Electrothermal 9100 apparatus.
C, 59.36; H, 3.81; N, 5.93. Found: C, 58.90, H, 3.60; N, 5.45%.
2.7. [RuH(CO)(biq)(PPh3)2]PF6 (5)
Colour:yellow-orange. 1H NMR: d 9.06 (Ha, s), 8.24 (Ha1, d), 8.4
(Hb, m), 7.35 (Hb1, m), 7.59 (Hc, t), 7.35 (Hc1, m), 8.09 (Hd, d) 7.84
(Hd1, d), 8.4 (He, m), 7.35 (He1, m), 8.4 (Hf, m), 7.35 (Hf1, m);
2.2. Synthesis and characterization of ruthenium complexes of type
[RuH(CO)(NN)(PPh3)2]PF6]
ꢀ11.03 (hydride, t, JHP = 18.55). 31P NMR: 43.77. IR (KBr, cmꢀ1):
m
(Ru–H) = Not observed;
1509 (m);
m (CO) = 1940 (vs); m (C@C, C@N) = 1434–
m
(PF6ꢀ) = 839 (vs). Yield 86%. Elem. Anal. Calc. for
The compounds used in this study (Fig. 1) were prepared using
the following general experimental procedure, varying in each case
the corresponding NN ligand.
C55H43F6N2OP3Ru: C, 62.56; H, 4.10; N, 2.65. Found: C, 61.80; H,
3.95; N, 2.50%.
The precursor, RuHCl(CO)(PR3)3 and the ligand NN [N-
N:PR3 = (1) dppz:PPh3 (2) dppz-CH3:PPh3 (3) dppz-Cl:PPh3 (4)
ppl:PPh3 (5) 2,2-biq:PPh3 dissolved in ethanol were refluxed for
three hours. The solution was cooled to room temperature, the vol-
ume was reduced to one third, and ammonium hexafluorophos-
phate in ethanol was added to produce a precipitate. The solid
was separated by filtration, washed with two volumes of hexane,
recrystallized from diethylether, and dried under vacuum.
3. Computational methods
Molecular geometries of the singlet ground state of complexes
1–5 of the series [RuH(CO)(N-N)(PPh3)2]+ (Fig. 1) were fully opti-
mized in the gas phase at the B3LYP/LACVP(d,p) level of theory
using the Jaguar 6.0 package [16]. Jaguar is a high-performance
ab initio package used for both gas and solution phase simulations,
with particular strength in treating metal containing systems, like
those studied here. Jaguar is an extremely fast quantum mechanics
package, and because of the large size of the complexes studied
here, it was chosen for the molecular optimization stage.
2.3. [RuH(CO)(dppz)(PPh3)2]PF6 (1)
Colour: light brown. 1H NMR (CD3COCD3): d 9.57 (Ha, d,
3
3
3Jab = 8.9), 9.47 (Ha1, d, Ja1b1 = 8.9), 7.96 (Hb, dd, Jbc = 5.1), 7.2–
For each compound a frequency calculation was carried out,
verifying that the optimized molecular structure obtained corre-
sponds to an energy minimum, thus only positive frequencies were
expected. The exchange-correlation functional B3LYP is a hybrid
functional which includes three terms for the exchange: a Har-
tree-Fock exact exchange, a Slater local exchange, and a Becke
non-local exchange, and two terms for the correlation: a local cor-
relation provided by Vosko, Wilk, and Nusair (VWN) and a non-lo-
cal correlation given by Lee, Yang, and Parr (LYP) [17]. An effective
core potential LACVP was used to describe the ruthenium atom,
and the basis set used for the lighter atoms (C, N, O, P, H, Cl) was
6-31G with a set of ‘‘d” and ‘‘p” polarization functions [18].
The TD-DFT (time dependent density functional theory) method
[12–14] was employed to calculate the electronic absorption spec-
tra of the complexes in the gas phase, previously optimized, at the
B3LYP/LANL2DZ-6-31++G(d) level of calculation using GAUSSIAN03
Rev. E.01 [19]. LANL2DZ is an effective core potential used for
the ruthenium atom. The ++ sign represents s and p diffuse
functions.
7.4 (Hb1) (overlapping the triphenylphosphine signals), 9.70 (Hc,
3
3
d, Jcb = 5.1), 8.37(Hc1, d, Jc1b1 = 5.1), 8.46 (Hd + Hd1, m), 8.17
(He + He1, m); ꢀ10.99 (hydride, t, JHP = 19.83); 31P NMR: 46.50, IR
(KBr pellets, cmꢀ1):
m
m (Ru–H) = not observed; m (CO) = 1937 (vs);
(C@C, C@N) = 1436–1480 (m); m
(PF6ꢀ) = 839 (vs). Melting point
330 °C (d). Yield 70.4%. Elem. Anal. Calc. for C55H41F6N4OP3Ru: C,
61.05; H, 3.81; N, 5.17. Found: C, 61.7; H, 3.87; N, 5.43%.
2.4. [RuH(CO)(dppz-CH3)(PPh3)2]PF6 (2 and 2.1)
Colour: light brown. 1H NMR: (CD3COCD3), d 8.34 (Ha, m), 8.34
(Ha1, m), 7.98 (Hb, m), 7.98 (Hb1, m), 9.54 (Hc, d), 9.44 (Hc1,d), 8.23
(Hd, d), 9.69 (Hd1, s), 7.4–7.2 (He) (overlapping the triphenylphos-
phine signals), 2.8 (CH3), ꢀ10.99 (hydride, t, JHP = 19.21). 31P
NMR: 46.48. IR (KBr, cmꢀ1):
m
(Ru–H) = 2014 (m);
m (CO) = 1934
(vs);
m
(C@C, C@N) = 1435–1481 (m);
m
(PF6ꢀ) = 841 (vs). Yield:
85.5%. Elem. Anal. Calc. for C56H43F6N4OP3Ru: C, 61.37; H, 3.95;
N, 5.11. Found: C, 59.99; H, 3.92; N, 5.07%.
TD-DFT is a quantum mechanic method used in chemistry to
investigate the properties of a molecular system in an excited state.
The method is based on the knew Runge–Gross theorem [20],
which corresponds to the time-dependent analog of the Hohen-
berg–Kohn theorem [21]. Therefore, it is an extension of the DFT
theory where variable time is included as a perturbation. TD-DFT
has been successful in the calculation of excited states of isolated
chemical systems [22]. In this work 100 singlet excited states
was calculated as vertical transitions for all the complexes 1, 2,
2.5. [RuH(CO)(dppz-Cl)(PPh3)2]PF6 (3 and 3.1)
Colour: brown. 1H NMR: (CD3COCD3), d 8.49 (Ha, m), 8.49 (Ha1
m), 7.98 (Hb, m), 7.4–7.2 (Hb1) (overlapped by the triphenylphos-
,
3
3
phine signals), 9.53 (Hc, d, Jcb = 7.68), 9.44 (Hc1, d, Jc1b1 = 7.68),
8.37 (Hd, s), 9.74 (Hd1,s), 8.14 (He, d); ꢀ11.01 (hydride, t,
JHP = 19.21), 31P NMR: 46.44, IR (KBr, cmꢀ1):
m
(Ru–H) = 2009 (m);
m
(CO) = 1934 (vs); m (C@C, C@N) = 1433–1487 (m); m
(PF6ꢀ) = 839

M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
3783
Hb1
Hc1
Ha1
Hd1
P
Ph
Ph
PF6
P(2) Ph 3
(2)
3
PF6
N
N
N (1)
H
N
N
N (1)
H
He1
He
H3C
Ru
Ru
C
C1
1
N (2)
N(2)
O
O
P
P(1) Ph 3
Hd
(1)
3
Hc
Ha
1
2
Hb
P(2) Ph 3
PF6
P(2) Ph 3
PF6
N
N
N(1)
H
N
N
N(1)
H
Cl
Ru
Ru
H3C
C1
C1
N(2)
N(2)
O
O
P(1) Ph 3
P(1) Ph 3
3
2.1
Hb1
Hc1
Ha1
P(2) Ph 3
P(2) Ph 3
PF6
PF6
N
N
N(1)
H
N
N(1)
H
Hd1
Ru
Ru
C1
C1
Hd
N(2)
Cl
N
N(2)
O
O
P(1) Ph 3
P(1) Ph 3
Hc
Ha
3.1
4
Hb
Hc1
Hd1
Hb1
Ha1
He1
P(2) Ph 3
PF6
O
N(1)
H
Hf1
Hf
Ru
C1
N(2)
P(1) Ph 3
Ha
He
Hd
Hb
5
Hc
Fig. 1. Molecular structure of the [RuH(CO)(N-N)(PPh3)2]+ complexes with N-N = dppz (1), dppz-CH3 (2), dppz-Cl (3), ppl (4), biq (5); 2.1 and 3.1 are the isomers of the
corresponding complexes.
2.1, 3, 3.1, 4 and 5. Due to the size of the complexes, and in order to
determine the effect of the solvent on the absorption spectrum, the
latter was only calculated for complex 1 in the solution phase
(dichloromethane solvent).
All the complexes were considered in their cationic form, and
present a singlet spin multiplicity. The ruthenium atom presents
an oxidation state of +2.
A natural bond orbital (NBO) analysis was also made for all the
complexes using the NBO 5.0 package [23]. Natural bond orbitals
are orbitals localized on one or two atomic centers, that describe
molecular bonding in a manner similar to a Lewis electron pair
structure, and they correspond to an orthonormal set of localized
orbitals of maximum occupancy. NBO analysis provides the contri-
4. Results and discussion
4.1. Spectroscopic characterization of the complexes of the series
[RuH(CO)(dppz-R)(PPh3)2]PF6 with R = H, Cl, CH3
bution of atomic orbitals (s, p, d) to the NBO
r
and
p
hybrid orbi-
The 31P NMR spectrum of the [RuH(CO)(dppz)(PPh3)2]PF6 com-
plex shows a singlet at 46.5 ppm indicating that the triphenylphos-
phine ligands are located in a trans position in the structure of the
complex. The 2J 31P–1H couplings are weak, but sufficiently strong
to be seen. The signals of phosphorus at ꢀ132.4, ꢀ138.3, ꢀ144.1
tals for bonded atom pairs. In this scheme, three NBO hybrid
orbitals are defined, bonding orbital (BD), lone pair (LP), and core
(CR), which were analyzed on the atoms directly bonded to or pre-
senting some kind of interaction with the ruthenium atom.

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M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
and ꢀ150 ppm indicate the presence of the hexafluorophosphate
counterion.
the protons and the heteronucleus of 13C. Finally, using HMBC (het-
eronuclear multiple bond correlation) experiments, it was possible
to obtain the connectivity to two and three bonds, giving strong
support to the interpretation of the H–H and H–C correlations for
the complexes studied. The HMBC spectrum (Fig. S2) shows a
selection of signals which confirms the preliminary assignment
carried out for the 1H one-dimensional spectrum. It is clearly seen
that the signal for the C14–Hb1 coupling again confirms that the Hb1
proton is overlapped by the signals of the triphenylphosphine. Both
experiments provide enough information to have the complete sig-
nal assignment as can be seen in the 13C NMR spectrum (Fig. 4).
The 1H NMR spectrum of the [RuH(CO)(dppz-Cl)(PPh3)2]PF6
complex shows (see Section 2) that Hd is the most unshielded pro-
ton because of the presence of a neighbouring chlorine atom. This
proton appears as a singlet signal due the absence of coupling with
other neighbouring protons. The hydride signal appears at high
The 1H NMR spectrum of the [RuH(CO)(dppz)(PPh3)2]PF6 com-
plex (Fig. 2) shows clearly the presence of the aromatic protons
of the polypyridine ligand in addition to a set of signals corre-
sponding to the triphenylphosphine ligand. The protons adjacent
to the carbonyl group are the most deshielded due to the paramag-
netic effect provided by this group. Proton Hc is recorded at very
low field because it is also highly deshielded due to the anisotropic
effect provided by the nitrogen atom of the pyrazine ring,
The signal is a doublet due to the magnetic ortho coupling with
Hb (3Jcb = 5.1 Hz). Hb appears as a doublet of doublets by coupling
with Hc (3Jbc = 5.1 Hz). Ha and Ha1 are both recorded as doublets be-
cause of their orthocoupling with Hb and Hb1, respectively
(3Jab = 8.9 Hz), (3Ja1b1 = 8.9 Hz). The corresponding signals of
Hd + Hd1:He + He1 are multiplets. The signal of Hb1 overlaps the sig-
nals of the protons of the phenyl group, and this is supported by
bidimensional NMR (vide infra). The signal at high field
(ꢀ10.9 ppm) indicates the presence of the hydride coordinated
with the metal. The shift of the signal is due to the shielding effect
of the metal and to the negative charge of the hydrogen atom. The
signal is a triplet due to coupling with the two trans equivalent
phosphorus atoms (JHP = 20.4 Hz).
field (ꢀ11 ppm). The 31P NMR spectrum shows
a signal at
46.4 ppm, which confirm the trans position of the triphenylphos-
phine ligands. The 1H and 31P NMR spectra of the complexes con-
taining the dppz-CH3 (2) y ppl (4) ligands are similar to those of the
complex analyzed above.
The double pattern of signals seen in the 13C NMR spectra for
the complexes with R = CH3 (2) and Cl (3) suggest that two isomers
can be obtained (see Fig. 5), and this is supported by the 2D NMR
spectra.
The 31P NMR spectrum shows a singlet at 46.5 ppm indicating
that the triphenylphosphine ligands are located in a trans position
in the structure of the complex. The 2J 31P–1H couplings are weak
to be observed. The signals of phosphorus at ꢀ132.4, ꢀ138.3,
ꢀ144.1 and ꢀ150 ppm indicate the presence of the hexafluoro-
phosphate counterion.
4.2. FT-IR analysis of the complexes of type [RuH(CO)(N-N)(PR3)2]PF6
Complexes of type RuH(CO)(dppz-R)(PPh3)2]PF6 display stronꢀg
C@O bands between 1937 and 1934 cmꢀ1. The presence of PF6
is revealed by the intense bands registered between 838 and
840 cmꢀ1. Stretching vibrations for C@C and C@N are observed in
the 1435–1480 cmꢀ1 range. The bands for the Ru–H bond are dis-
played at 2014 and 2009 cmꢀ1, respectively, for the systems with
R = CH3 and R = Cl. For the complex with the dppz ligand this par-
ticular band is not seen as in others.
The inclusion of an electron-donor substituent such as a methyl
in the polypyridine ligand (dppz), produces a decrease of about
3 cmꢀ1 in the vibration frequency of the CO bond. This is the result
of the net effect of this substituent, which provides electron den-
The unequivocal proton NMR assignments were made by con-
certed analysis of 1D 1H, 1D 13C, 2D-ge 1H 1H COSY, 2D 1H 13C
HSQC-ed, and 2D 1H 13C HMBC spectra (vide infra), which also sup-
port the presence of two isomers.
The bidimensional H–H-COSY-NMR spectral analysis of the
[RuH(CO)(dppz)(PPh3)2]PF6 complex (see Fig. 3) gives strong sup-
port to the assignment made by 1H NMR.
In order to completely characterize the structure of the com-
plexes, a determination of the 13C–1H correlations by HSQC (heter-
onuclear single quantum correlation) was made (see Fig. S1). This
made it possible to know the scalar coupling to one bond between
Fig. 2. 1H NMR spectrum of the [RuH(CO)(dppz)(PPh3)2]PF6 complex.

M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
3785
Fig. 3. 2D-H–H COSY spectrum of the[RuH(CO)(dppz)(PPh3)2]PF6 complex in CDCl3.
Fig. 4. 13C NMR of the [RuH(CO)(dppz)(PPh3)2]PF6 complex in CDCl3.
sity to the metal and this in turn delivers electron density via back-
bonding to the anti-bonding orbitals of the CO. This decreases the
bond order of CO, thus decreasing the vibration energy of the CO
bond.
On the other hand, the inclusion of an electron-acceptor substi-
tuent such as chlorine in the dppz ligand should produce a reverse
effect, decreasing the electron density on the metal, and therefore
increasing the bond order of the CO bond and increasing the vibra-
tion frequency. However, this expected behaviour is not seen since
the observed vibration frequency was 1934.3 cmꢀ1, which is rather
similar to that seen when the substituent is an electron-donor. This
anomalous behaviour may be the result of electron delocalization,
that is, a resonance effect involving a chlorine atom with the aro-
matic system of the dppz ligand. This interpretation is supported
by theoretically determined charge values. These values indicate
that there is no net negative charge on the chlorine atom. Actually,
calculations performed at the B3LYP/LACVP(d,p) level provided po-
sitive values on the chlorine atom (0.04) in compound 3.

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M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
Fig. 5. 13C NMR spectrum of the [RuH(CO)(dppz-R)(PPh3)2]PF6 complex (a) R = CH3 and (b) R = Cl in CDCl3.
Considering the same electronic effect shown before, the CO
phosphine to the metal has taken place, that is, the metal provides
back-donation of electron density mainly to the d orbitals of phos-
phorus and not to the orbitals of the Ru–CO bond. Consequently,
the bond order of CO increases and the vibration frequency in-
creases by 5 cmꢀ1 as observed in the IR spectrum. Vibration fre-
quency values are summarized in Table 1.
vibration frequencies in the complexes with the biq and ppl ligands
are 1944 cmꢀ1 and 1947 cmꢀ1, respectively, so it can be said that
these ligands behave as acceptors with respect to the dppz-R ser-
ies. In fact, by reducing the electron density on the metal the car-
bonyl ligand it will receive the electron density via dp ?
p*
interaction, which would increase the bond order, in turn increas-
ing the vibration frequency of the CO bond.
4.3. Optimized molecular structures
Besides, we can also see that inclusion in the structure of a
phosphine such as methydiphenylphosphine, which is more basic
than triphenylphosphine, causes an increase in the vibration fre-
quency of the carbonyl bond from 1937 cmꢀ1 to 1942 cmꢀ1, indi-
cating that further donation of sigma electron density from the
We studied five complexes of the [RuH(CO)(N-N)(PPh3)2]+ ser-
ies in their ground state and two diastereomers of the substituted
complexes, 2.1 and 3.1. The results obtained for the optimized
molecular structures are shown in Fig. 6 and the more representa-
Table 1
Absorption frequencies for the complexes [RuH(CO)(N-N)(PR3)2][PF6].
Complex
Absorption frequency IR (cmꢀ1) KBr
ꢀ
mRu–H
mC„O
mC@C,
m
mC–Cl
C@N
PF6
RuHCl(CO)(PPh3)3
RuHCl(CO)(PPh2Me)3
2013 (m)
No obs
No obs
2009 (m)
2014 (m)
No obs
1922 (vs)
1926 (vs)
1937 (vs)
1934 (vs)
1934 (vs)
1944 (vs)
1947 (vs)
1942 (vs)
[RuH(CO)(dppz)(PPh3)2)]PF6
[RuH(CO)(dppz-Cl)(PPh3)2]PF6
[RuH(CO)(dppz-CH3)(PPh3)2]PF6
[RuH(CO)(2,2-biqui)(PPh3)2]PF6
[RuHCO(ppl)(PPh3)2]PF6
1435–1480 (m)
1432–1486 (m)
1434–1481 (m)
1433–1509 (m)
1434–1481 (m)
1419–1490 (m)
838 (vs)
838 (vs)
840 (vs)
839 (vs)
836 (vs)
838 (vs)
1091 (m)
No obs
No obs
[RuH(CO)(dppz)(PPh2Me)2]PF6
m: medium; vs: very strong.

M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
3787
Table 2
Bond lengths (Å) and bond angles (°) more relevants for the complexes [RuH(CO)(N-N)(PPh3)2]+ with N-N = dppz (1), dppz-CH3 (2), dppz-Cl (3), ppl (4), biq (5) calculated at the
B3LYP/LACVP(d,p) level. 2.1 and 3.1 corresponds to the isomers of the respective complexes.
Bond lengtha
1
2
2.1
3
3.1
4
5
Ru-C1
Ru–H
Ru–P1
Ru–P2
Ru–N1
Ru–N2
C1–O
1.864
1.601
2.463
2.428
2.177
2.235
1.157
1.866
1.601
2.429
2.465
2.184
2.243
1.159
1.865
1.588
2.445
2.452
2.181
2.251
1.159
1.864
1.598
2.456
2.441
2.169
2.264
1.161
1.864
1.604
2.445
2.443
2.173
2.242
1.161
1.866
1.597
2.460
2.424
2.184
2.241
1.159
1.858
1.577
2.453
2.466
2.244
2.319
1.161
Bond anglea
1a
2
2.1
3
3.1
4
5
<P1RuP2
<N1RuN2
<HRuC1
<N1RuC1
<N2RuH
<N1RuH
<N2RuC1
172.73
75.66
88.82
177.03
169.76
94.13
170.33
75.57
89.50
175.38
170.64
95.09
99.82
169.42
75.58
86.86
178.77
169.63
94.08
174.19
75.45
87.16
178.18
166.64
91.18
171.16
75.80
89.66
177.92
168.21
92.40
167.21
75.51
89.84
175.31
170.26
94.76
99.86
166.41
74.27
84.43
179.43
169.27
95.11
101.36
103.45
106.19
102.12
106.16
a
For atom numeration see Fig. 1.
Fig. 6. Optimized molecular structures of the [RuH(CO)(N-N)(PPh3)2]+ complexes with N-N = dppz (1), dppz-CH3 (2), dppz-Cl (3), ppl (4), biq (5); 2.1 and 3.1 are the isomers
of the corresponding complexes, calculated in the gas phase at the B3LYP/LACVP(d,p) level.

3788
M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
Fig. 6 (continued)
tive bond lengths and bond angles of the compounds are presented
in Table 2.
ing that the effect of a change in the polypyridine ligand produces a
modification in the interaction between the metal and the nitro-
p
The optimized structure of 1 shows a point group C1 distorted
octahedral structure with respect to the ligands. It is seen that
the triphenylphosphine ligands (PPh3) are located in a trans posi-
tion, while the polypyridine ligand adopts a trans position relative
to the carbon monoxide and hydride ligands. In complexes 2 and 3,
the polypyridine ligands dppz-Cl and dppz-CH3 present the same
planarity as the isolated ligands before coordinating with Ru,
retaining their aromatic character. The same planarity trend is
found with the ppl ligand in 4, however, in 5 the 2,20-biquinoline
ligand is distorted out of the plane at an angle of 17°. The presence
of a single bond connecting both quinolines facilitates rotation
around this bond, and it is responsible for the distortion. Optimized
geometries show that the Ru–N1 and Ru–N2 bonds are different
and therefore the structure of the polypyridine ligand is not sym-
metric. A similar behaviour is seen for the Ru–P1 and Ru–P2 bonds.
Optimized bond lenghts of the complexes with substitution on the
polypyridine ligand (1–3) does not represent an important change.
The larger change with respect to the unsubstituted complex 1 oc-
curs for the Ru–P1 and Ru–P2 bonds of complex 2, with values of
gen atoms, which can be explained by the size and aromatic char-
acter of this ligand.
Table 2 shows that the Ru–C(CO) and C–O (C„O) bond lengths
do not undergo important changes due to the kind of the polypyr-
idine ligand, and only a slight decrease of ꢁ0.01 Å is seen for biq. In
relation to the bond angles associated with the metal atom, the cal-
culations show that these parameters present slight changes. In
particular, a reduction of 1° is seen in the chelation angle
(N1RuN2) of the polypyridine ligand 2,20-biquinoline, an effect that
can be attributed to the presence of a single bond between the two
quinolines, favouring rotation around this bond.
4.4. Hybrid orbital and molecular orbital description
Results corresponding to the hybrid orbitals obtained from the
NBO analysis of all the compounds of the [RuH(CO)(N-
N)(PPh3)2]+ set are shown in terms of atomic composition in Table
S1. For all the complexes we found that the nitrogen atoms N1 and
N2 belonging to the polypyridine ligand do not show covalent
bonding with ruthenium. However, the optimized structures (Sec-
tion 4.3) gave an atomic distance for both Ru–N1 (2.17–2.18 Å) and
Ru–N2 (2.23–2.32 Å) close to the standard value for a Ru–N bond
length [24–27]. This fact can be explained by the donor acceptor
energies E(2) calculated with the NBO 5.0 package [23]. E(2) values
account for the degree of delocalization of the electronic density
0
0
0.034 ÅA and 0.037 ÅA, respectively.
On the other hand, a change in the dppz ligand by ppl produces
a slight change in the bond lengths of the ligands coordinated to
ruthenium. However, the change from dppz to biq generates devi-
ations of the bond lengths of 0.038 Å for Ru–P2 and 0.023 Å for Ru–
H. The Ru–N1 and Ru–N2 bonds show the largest changes with re-
spect to 1, increasing by 0.067 Å and 0.076 Å, respectively, indicat-

M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
3789
produced between one NBO orbital acting as a donor fragment, and
another NBO orbital acting as an acceptor fragment.
Based on the E(2) values, for all the complexes interactions of
the lone pair N2 ? r* Ru–H type (47–58 kcal/mol) and lone pair
N1 ? r* Ru–C1 type (75–83 kcal/mol), where r* represents the
anti-bonding orbital, were found, indicating that a charge transfer
occurs. As it can be seen in Fig. 6, the Ru–H bond is colinear with
N2, and the Ru–C1 bond is colinear with N1, and this would account
for the existence of such interactions. These results suggest a de-
crease in the strength of the interaction between N1 and N2 and
Ru, leading to noncovalent bonding.
Table S1 shows that the interactions between the phosphorous
atoms (P1, P2) of the triphenylphosphines and the ruthenium atom
does not follow the same behaviour for all the complexes. For 1, 2.1
and 4, a covalent bonding is found for the Ru–P2 interaction, but a
charge transfer of the lone pair P1 ?
r
* Ru–P2 type (120–141 kcal/
mol) was obtained. An opposite behaviour is found for complexes
2, 3, 3.1 and 5, the covalent bonding is found for Ru–P1 and the do-
nor acceptor interaction is associated with the lone pair P2 ? r*
Ru–P1 (118–144 kcal/mol). Table S1 shows that all the complexes
present the phosphorus atom in the covalent bonding with a nearly
sp3 hybridization, which can account for the tetrahedral environ-
ment around the atom in the tetraphenylphosphine ligand. NBO
analysis allowed knowing the nature of the coordination between
ruthenium and the atoms of the ligands directly interacting with it.
This methodology also gave a better understanding of the opti-
mized molecular structures.
Analysis of the frontier molecular orbitals, HOMO (highest
occupied molecular orbital), and LUMO (lowest unoccupied molec-
ular orbital) in organometallic compounds like those studied here
is useful for understanding the charge transfer that they undergo.
HOMO and LUMO surfaces are shown in Fig. 7, and the compo-
sition of these molecular orbitals in terms of the more relevant
atomic fragments are given in Table S2. Fig. 7a shows that HOMOs
are mainly localized on the ruthenium atom (44–51%), with a con-
tribution of dxy and dyz atomic orbitals. These molecular orbitals
also have an important contribution from the triphenylphosphine
ligands of 21–26% each. On the other hand, LUMOs (Fig. 7b) are
basically located in the polypyridine ligand (93–98%) in atomic
orbitals py.
Our results suggest that an electron oxidation can occur on
ruthenium and on PPh3, and that an electron reduction can occur
on the polypyridine ligand. It means that the complexes studied
can present a charge transfer at the intramolecular level from the
oxidation sites (Ru, PPh3) to the reduction sites (dppz, ppl, biq).
4.5. Experimental and theoretical electronic absorption spectra
UV–Vis electronic absorption spectra of all the complexes were
measured in dichloromethane. Fig. 8 shows the electronic spectra
of complexes 1, 2 and 3, which present a change of substitution
in the polypyridine ligand. It is seen that these complexes present
three absorption bands, one of them of higher intensity and lower
Fig. 7. Molecular surfaces of the (a) HOMO and (b) LUMO frontier molecular
orbitals for the set of [RuH(CO)(N-N)(PPh3)2]+ complexes calculated at the B3LYP/
LANL2DZ-6-31++G(d) level.
wavelength occurs at 232 nm with a value of
e
= 2.5 ꢂ 104–
4.0 ꢂ 104 cmꢀ1 Mꢀ1 (Table S3), depending on the complex, which
can be associated with electronic transitions of the
p
?
p* type.
in the polypyridine ligand. It suggests that the –CH3 and –Cl sub-
stituents have an effect on the outermost electrons of the com-
pounds able to produce red shifted absorption bands. Therefore,
this kind of substituents can tune the absorption properties of
these complexes.
Fig. 9 shows a comparison of the electronic spectra of the com-
pounds that have different polypyridine ligands, 1, 4 and 5. A red
shift is seen of the lower wavelength band when the polypyridine
A second band of similar
e
value appearing at ꢁ280 nm, and a third
band of much lower intensity in the 360–380 nm region. The pres-
ence of an electron-donor substituent in the polypyridine ligand,
such as methyl group (–CH3) 2, produces a bathocromic shift of this
band with respect to the unsubstituted form 1 (360 nm) in an
amount of 12 nm (372 nm). The substituent (–Cl) in 3 also pro-
duces a similar bathocromic shift, but a somewhat greater red shift
of 24 nm (384 nm) with respect to the unsubstituted compound 1.
Therefore, of the three bands seen, the absorption band of higher
wavelength presents a greater change with respect to substitution
ligand, which is planar in
1 (360 nm), is replaced by the
2,20-biquinoline ligand 5 (371 nm). This ligand presents a slight
distortion when coordinated with the ruthenium atom because it

3790
M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
R=Cl
R=CH3
R=H
200
250
300
350
400
450
500
550
600
Wavenumber (nm)
Fig. 8. UV–Vis spectra of the [RuH(CO)(dppz-R)(PPh3)2]PF6 complexes in CH2Cl2; R = H 1 blue line, R = CH3 2 red line, R = Cl 3 green line. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
1.4
1.2
dppz
1.0
0.8
0.6
biq
0.4
0.2
ppl
0.0
200
250
300
350
400
450
500
550
600
650
700
Wavenumber (nm)
Fig. 9. UV–Vis spectra of the [RuH(CO)(N-N)(PPh3)2]PF6 complexes in CH2Cl2 N-N = dppz 1 blue line, N-N = 2,2-biqui 4 green line, N-N = ppl 5 red line. (For interpretation of
the references to colour in this figure legend, the reader is referred to the web version of this article.)
presents a single bond between two isoquinolines. A greater red
shift is seen for 4, where the structure of the polypyridine ligand
(Fig. 1) suggests a higher electron delocalization.
The full theoretical absorption spectra were obtained from the
calculation of the singlet excited states with TD-DFT at the
B3LYP/LANL2DZ/6-31++G(d) level in the gas phase. Computation
of 100 excited states of all the complexes allowed the interpreta-
tion of the experimental spectra in the 230–420 nm range. The ex-
cited states assigned to the absorption bands are shown in Table 3
and the full spectra are displayed in Fig. S3.
Previously, we compared for the complex 1 the excited states
computed in the gas phase and in the solution phase with dichlo-
romethane as the solvent. The results are included in Supplemen-
tary material (Fig. S3). We found that the position of the bands
remained constant but their intensity changed. An increased inten-
sity is seen for the theoretical spectrum computed in the solution
phase. These results gave theoretical evidence that calculation of
the electronic spectra in the gas phase constitutes a very good
approximation for these kind of complexes. Therefore, we only
computed the spectra of the other complexes in the gas phase.
For the complexes with the dppz ligand (1, 2, 2.1, 3, 3.1), the
calculated excited states predict very well the experimental values
of the two bands of longer wavelength. In complex 1 the error for
the observed band at 360 nm is zero. The maximum error of the
theoretical longest wavelength band compared to the experimen-
tal one is found for 2, with 19 nm, and for the second longest wave-
length band for 3.1 (9 nm). Anyway, the errors found are negligible.
However, for the shortest wavelength band found for all the
complexes at 232 nm, the theoretical calculations predicted it in
the range of 263–267 nm. For the assignment of the observed
bands to the calculated excited states, both the position and the
relative intensity of the former were considered.

M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
3791
Table 3
Experimental (Exp.) and theoretical (Calc.) excitation energies and oscillator strengths (f) calculated at the B3LYP/LANL2DZ-6-31++G(d) level for the complexes of the series
[RuH(CO)(N-N)(PPh3)2]+ with N-N = dppz (1), dppz-CH3 (2, 2.1), dppz-Cl (3, 3.1), ppl (4), biq (5).
Excited state
Exp.
Calc.
f
Electronic transition
Characterc
1
8
48
65
3.44a (360)b
4.40 (282)
5.34 (232)
3.44 (360)
4.32 (287)
4.72 (263)
0.0458
0.5294
0.1908
dH-5 ? L (ꢀ0.27),H-1 ? L + 1 (0.38)
H-8 ? L + 2 (ꢀ0.30),H-3 ? L + 2 (ꢀ0.32)
H-1 ? L + 3 (0.40), H ? L + 7 (0.27)
MLLCT,MLLCT
MLLCT,MLLCT
MLMLCT, MLMLCT
2
8
44
66
3.33 (372)
4.32 (287)
5.34 (232)
3.51 (353)
4.23 (293)
4.71 (263)
0.0662
0.5664
0.2214
H-6 ? L (0.32), H-2 ? L + 1 (0.22)
H-1 ? L + 2 (0.29), H-2 ? L + 2 (ꢀ0.24)
H-2 ? L + 3 (0.35), H-1 ? L + 3 (0.24)
MLLCT,MLLCT
MLLCT, MLLCT
MLMLCT,MLMLCT
2.1
4
42
63
3.33 (372)
4.32 (287)
5.34 (232)
3.28 (378)
4.19 (296)
4.64 (267)
0.0505
0.5151
0.1616
H-2 ? L (0.38), H-1 ? L (0.49)
LLCT, MLLCT
LLCT,LLCT
MLMLCT, MLLCT
H-2 ? L + 2 (0.37), H-8 ? L (ꢀ0.30)
H-1 ? L + 3 (0.41), H-19 ? L + 1 (0.30)
3
4
43
64
3.23 (384)
4.40 (282)
5.34 (232)
3.25 (381)
4.23 (293)
4.70 (264)
0.0827
0.2116
0.2124
H-5 ? L (0.24), H-2 ? L (0.57)
MLLCT, MLLCT
LLCT, MLLCT
MLMLCT, MLMLCT
H-8 ? L + 2 (0.41), H-7 ? L + 2 (ꢀ0.26)
H-1 ? L + 3 (0.41), H ? L + 3 (ꢀ0.31)
3.1
4
44
62
3.23 (384)
4.40 (282)
5.34 (232)
3.28 (378)
4.23 (293)
4.65 (266)
0.0753
0.5609
0.2297
H-3 ? L (-0.22), H-2 ? L (0.60)
H-1 ? L + 2 (0.34), H-7 ? L + 2 (0.27)
H-1 ? L + 3 (0.47), H ? L + 3 (ꢀ0.31)
MLLCT,LLCT
MLLCT, MLLCT
MLMLCT, MLMLCT
4
1
2.94 (422)
4.35 (285)
4.81 (258)
5.37 (231)
2.79 (445)
4.35 (285)
4.89 (254)
5.26 (236)
0.0333
0.0544
0.3124
0.0247
H ? L (0.66), H ? L + 1 (ꢀ0.19)
MLLCT,MLLCT
MLMLCT,MLMLCT
LLCT, MLLCT
50
70
89
H-6 ? L + 3 (0.21), H-3 ? L + 3 (0.43)
H-17 ? L + 2 (0.32), H-16 ? L + 2 (0.29)
H-3 ? L + 4 (0.29), H-1 ? L + 6 (ꢀ0.18)
MLMLCT,MLMLCT
5
13
24
40
3.34 (371)
4.59 (270)
5.37 (231)
3.64 (341)
4.19 (297)
4.65 (267)
0.0710
0.1301
0.0729
H-1 ? L + 3 (-0.21), H ? L + 3 (0.49)
H-1 ? L + 3 (0.37), H ? L + 4 (ꢀ0.22)
H ? L + 5 (0.26), H ? L + 7 (ꢀ0.21)
MLMLCT,MLMLCT
MLMLCT, LMLCT
MLLCT, MLMLCT
a
eV.
nm.
b
c
MLLCT: metal-ligand to ligand charge transfer; LMLCT: ligand to metal-ligand CT; MLMLCT: metal-ligand to metal-ligand CT; LLCT: ligand to ligand CT.
H: HOMO; L: LUMO.
d
In the case of the diastereomers, considering only the first ob-
attributed to MLLCT and MLMLCT (metal-ligand to metal-ligand
charge transfer), respectively.
served band where the major change is due to the position of the
substituent, complex 2.1 (378 nm) and complex 3 (381 nm) repro-
duce well the experimental results of 372 nm and 384 nm, respec-
tively. The other observed bands of these complexes present
similar values for the diastereomers (2, 2.1 and 3, 3.1). These re-
sults indicate that the position of the substituent, that is cis or trans
to the ligand CO, is more important in excited states localized in
the region near 400 nm, and shows the needed to consider all
the isomeric structures.
For a better understanding of the observed bands, the corre-
sponding calculated excited states can be interpreted in terms of
electronic transitions between occupied and unoccupied molecular
orbitals. Table 3 shows the two electronic transitions of largest
contribution to the corresponding excited states.
For complexes 2.1 and 3 we found for the red shifted band that
the major contribution corresponds to a charge transfer of the
MLLCT type, with the H-1 ? L and H-2 ? L electronic transitions,
respectively. However, the charge transfer in both complexes is
different. In 2.1 the charge transfer goes from the region of ruthe-
nium (45%) and both phosphine ligands toward the dppz-CH3 li-
gand. In 3 the H-2 molecular orbital is located in ruthenium
(13%), dppz-Cl, and both phosphine ligands, and the charge trans-
fer occurs completely toward the dppz-Cl ligand (Table S2).
It is seen that the main differences found due to the presence of
a substituent on the dppz ligand are in the initial molecular orbital
participating in the charge transfer. In complex 1 it corresponds to
38% in Ru and 58% in phosphine ligands, in 2.1 the values are 45%
Ru and 49% PPh3, and in 3 the values are 13% Ru and 24% PPh3.
These results indicate an effect of the properties of the substituents
(–CH3) and (–Cl).
In contrast to complex 1, the second band of 2.1 and 3 predicted
as the excited states 42 and 43, respectively, is associated with the
ligand to ligand charge transfer (LLCT), in the region of the dppz li-
gand. The observed bands at 232 nm for 2.1 and 3 are predicted by
the excited states 63 (267 nm) and 64 (264 nm), respectively, and
attributed to a charge transfer MLMLCT.
We also studied what happens by changing the polypyridine li-
gand in the complex: dppz (1), ppl (4) and biq (5). Again, we found
a major change in the excited state associated to the higher wave-
length band, as expected. The other excited states of these complexes
does not present dramatic changes due to the polypyridine ligand.
In complex 1, excited state 8, which reproduces the observed
360 nm band, predicts electronic transitions of the H-5 ? L and
H-1 ? L + 1 type. We found that H-1 is preferentially located on
ruthenium (38%) and on the two PPh3 ligands (58%), and L + 1 is lo-
cated on the phenanthroline fragment (89%) of the polypiridine li-
gand (Table S2). The H-5 molecular orbital has
a smaller
contribution of Ru (2%) and a larger contribution of one PPh3 ligand
(87%), and L is found preferentially on the dppz ligand (98%) (Table
S2). These results suggest that the absorption band at 360 nm cor-
responds to a charge transfer occurring from the metal and the
phosphine ligand regions toward the polypyridine ligand, and
therefore it can be assigned to a metal-ligand to ligand charge
transfer (MLLCT) character. The bands at 282 nm and 232 nm are
predicted by the excited states 48 and 65, respectively, and are

3792
M. Yáñez et al. / Journal of Organometallic Chemistry 694 (2009) 3781–3792
Table 3 shows that the band in complex 4 at 422 nm is pre-
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unsubstituted form (1) can be attributed to the more extended
p
current of the molecular structure (Fig. 1).
In complex 5, the observed band at 371 nm is blue shifted in the
calculation to 341 nm (excited state 13), with an error of 30 nm.
The excited states for complexes 1 and 4 indicated that the charge
transfer is MLLCT. In both cases the main contribution in the arrival
molecular orbital of the electronic transition is located on the poly-
pyridine ligand (89% on dppz for 1, 94% on ppl for 4). In contrast, in
complex 5 the arrival molecular orbital of the transition is centered
on ruthenium (31%) and both phosphine ligands (62%), so the
charge transfer is MLMLCT.
The results discussed in this section showed the same trend as
the experimental data, showing that the TD-DFT methodology and
the B3LYP functional were appropriate.
5. Summary
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The authors acknowledge the financial support of FONDECYT
under Project 1085135, and the computational time provided by
the DICYT-USACH Complementary Support Project. M.Y. thanks
CONICYT for a doctoral fellowship and terminal thesis fellowship.
Appendix A. Supplementary material
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.07.028.