Bimetallic neutral palladium (II) bis(dithiolene) complex: Unusual synthesis, structural and theoretical study

Article abstract of DOI:10.1016/j.crci.2012.03.007

The unusual synthesis of the dimeric dithiolene complex [(PPh ₃)Pd(ethylene-1,2-dithiolate)]₂ (1), containing the simplest dithiolene ligand, has been achieved through the reaction between tetrathiafulvalene (TTF) and Pd(PPh₃)₄. The complex shows a folded structure in the solid state, according to single crystal X-ray analysis performed on crystals grown from two different system solvents and conditions, with a central [Pd₂S₂] ring folded about the S···S hinge by 67.9°. The optimized geometry at the DFT level is in excellent agreement with the experimental structure. Moreover, TD-DFT calculations allowed the assignment of the low energy band arising at 576 nm to the HOMO→LUMO transition, between frontier orbitals having mixed metal and dithiolene character.

Full text of DOI:10.1016/j.crci.2012.03.007

C. R. Chimie 15 (2012) 904–910
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Full paper/Memoire
Bimetallic neutral palladium (II) bis(dithiolene) complex: Unusual
synthesis, structural and theoretical study
*
Flavia Pop, Diana G. Branzea, Thomas Cauchy, Narcis Avarvari
ˆ
UMR 6200, CNRS, laboratoire Moltech-Anjou, UFR Sciences, universite´ d’Angers, Batiment K, 2, boulevard Lavoisier, 49045 Angers, France
A R T I C L E I N F O
A B S T R A C T
Article history:
The unusual synthesis of the dimeric dithiolene complex [(PPh3)Pd(ethylene-1,2-
dithiolate)]2 (1), containing the simplest dithiolene ligand, has been achieved through
the reaction between tetrathiafulvalene (TTF) and Pd(PPh3)4. The complex shows a folded
structure in the solid state, according to single crystal X-ray analysis performed on crystals
grown from two different system solvents and conditions, with a central [Pd2S2] ring
folded about the SꢀꢀꢀS hinge by 67.98. The optimized geometry at the DFT level is in
excellent agreement with the experimental structure. Moreover, TD-DFT calculations
allowed the assignment of the low energy band arising at 576 nm to the HOMO!LUMO
transition, between frontier orbitals having mixed metal and dithiolene character.
ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Received 2 March 2012
Accepted after revision 20 March 2012
Available online 22 May 2012
Keywords:
S ligands
Tetrathiafulvalenes
Bimetallic complexes
Structure elucidation
Theoretical calculations
1. Introduction
initially formed dianionic compounds, these low energy
absorption bands, attributed to p-p* transitions of HOMO–
Metal-dithiolene complexes have been extensively
studied since many years for the elaboration of molecular
materials with conducting, magnetic and optical properties
[1], their peculiarity coming from the non-innocence of the
dithiolate ligands. Indeed, the frontier orbitals of such
complexes develop both on the ligands, especially the sulfur
atoms, and on the metal centers [2]. This feature, combined
with their propensity to engage in intermolecular SꢀꢀꢀS and
metalꢀꢀꢀS interactions, thus providing excellent stacking
properties in the solid state, makes them valuable building
blocks for conducting and magnetic materials [3]. In
addition, metal bis(dithiolene) complexes in different
oxidation states show strong absorption in the near infrared
SOMO and HOMO–LUMO types, respectively [6]. Accord-
ingly, such complexes have found applications as near
infrared photodetectors [7], optical switching devices [8],
organic dyes [9], and organic electronics [10].
In the case of the simplest 1,2-dithiolene ligand, e.g. 1,2-
ethylene-dithiolate (S2C2H2), also considered as the
‘‘parent dithiolene’’, the crystal structures of the neutral
bis(dithiolene) complexes [M(S2C2H2)2] (M = Ni, Pd, Pt)
show, interestingly, dimeric units formed through MꢀꢀꢀM
bonds for Pd and Pt, while the Ni complex consists of
isolated monomers [11]. The low energy absorption bands
for these ‘‘parent complexes’’, in which the oxidation from
the dianion to the neutral species affects mainly the ‘‘non-
innocent’’ ligands, appear at 720 nm (Ni) [5a], 785 nm (Pd)
[5b], and 680 nm (Pt) [5c]. Neutral metal mono(dithiolene)
complexes (M = Ni, Pd, Pt) can be obtained by formally
replacing one dithiolene ligand by two monodentate or
one bidentate neutral ligand, such as the phosphines.
However, in this case there is no ambiguity on the
oxidation state of the components, since the metal is 2+
and the dithiolene 2–. Accordingly, an extensive series of
neutral mono(dithiolene) complexes formulated as
region [4] from 700 nm (nickel) up to 1.6 mm (gold)
depending on the nature of the metal and the substitution
pattern of the dithiolene ligand [5]. The group 10 (Ni, Pd, Pt)
square planar complexes show in the monoanionic or
neutral species, very often obtained upon oxidation of the
* Corresponding author.
E-mail address: narcis.avarvari@univ-angers.fr (N. Avarvari).
1631-0748/$ – see front matter ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2012.03.007

F. Pop et al. / C. R. Chimie 15 (2012) 904–910
905
(P2)M(dithiolene) (M = Ni, Pd, Pt) have been synthesized,
where P2 stands generally for two PPh3 or one dppe ligands
(dppe = 1,2-bis(diphenylphosphino)ethane) [12]. The col-
ours of these complexes when the dithiolene is maleoni-
triledithiolate (mnt) vary from brown-red for Ni to orange
for Pd and, finally, yellow for Pt, yet large variations are
observed upon changing the substitution pattern on the
dithiolene ligand. For example, the Pd complex formulated
as (Ph3P)2Pd(S2C2(SMe)2), thus containing the bis(thio-
methyl)dithiolene ligand, for which the single crystal X-ray
structure was described, was obtained as red-violet crystals
[12c]. Note that in all the crystal structures described so far
the complexes appear as monomeric units. Generally, the
synthesis of these neutral mono(dithiolene) complexes
involves either the reaction between the (P2)MCl2 complex
with the dithiolate [12e], the displacement of a dithiolene
ligand from the neutral bis(dithiolene) complexes by
phosphines [12a,b], or the displacement of a cyclooctadiene
(COD) from (COD)Pt(dithiolene) by phosphines [12f,g].
However, other more specific methods have been also
employed, suchasthedirect reactionbetweenthePd(PPh3)4
complex and the dimethyltetrathiooxalate in the case of
(Ph3P)2Pd(S2C2(SMe)2) [12c]. To our knowledge, in all but
one case [12g], the dithiolene ligand was not the parent one.
Surprisingly indeed in this series, only the platinum
complex (Ph3P)2Pt(edt) (edt = 1,2-ethylene-dithiolate) was
described as a bright yellow solid, although without any
crystal structure analysis [12g].
Indeed, after refluxing during 48 h an equimolar
mixture of TTF and Pd(PPh3)4 in toluene, the only product
which has been isolated after chromatographic work-up
was the dimeric dithiolene complex 1. Clearly, the yield of
this reaction is low, yet the unreacted TTF is fully
recovered, while the excess of palladium complex affords
black colloidal palladium together with phosphine and
phosphine-oxide. The complex 1 was obtained as an air
stable dark violet crystalline solid which was first
characterized by spectroscopic methods. 31P NMR spec-
trum shows a sharp single peak at 30.26 ppm, indicative of
PPh3 ligands symmetrically coordinated to a Pd-dithiolate
fragment [14]. 1H NMR is in agreement with a 1:1 ratio
between an edt and a PPh3 ligand, although the chemical
shift of one of the vinylic protons is somewhat puzzling,
since it appears rather shielded, at 4.46 ppm, when
compared with the other proton at 6.28 ppm, the usual
value for this type of proton. The explanation for this
upfield shift lies very likely in the location of the
corresponding proton in the anisotropy cone of one phenyl
ring of the PPh3 ligand. This assumption is supported by
the crystal structure (vide infra) of the complex, showing
˚
clearly the short distance (2.63–2.65 A) between the
proton and the centroid of one phenyl ring. An important
result was the observation of the molecular peak of the
dimer in MALDI-TOF, indicating the presence and stability
of the species also in solution and not only in the crystal
structure.
We describe herein the unexpected synthesis of the
[(Ph3P)Pd(edt)]2 dimeric complex 1, together with its
spectroscopic and structural characterization. DFT and TD
DFT calculations have been performed in order to support
the experimental geometry and to explain the electronic
structureofthisunprecedenteddimericdithiolenecomplex.
At the present stage, the formation of 1 is hard to
explain through a reaction mechanism. One can speculate
that in an initial step the unsaturated Pd(PPh3)2 fragment,
generated by decoordination of two phosphines upon
heating, coordinates to the outer double bond of TTF, as it
was observed for the Pt(PPh3)2 fragment, for which h2
complexes [(PPh3)2Pt(h2-TTF)] and [(PPh3)2Pt(h2-o-
Me2TTF)] have been evidenced, including a single crystal
X-ray structure for the latter [15]. Interestingly, the
coordination of the Pt center took place exclusively to
the unsubstituted double bond, thus suggesting that the
steric hindrance of the Me groups very likely hampers the
h2 coordination. Accordingly, the initial occurrence in our
case of a h2 complex [(PPh3)2Pd(h2-TTF)] (or bis-h2
complex [(PPh3)2Pd(h2-TTF-h2)Pd(PPh3)2]) does not seem
unlikely, all the more since when we heated Me4-TTF
(TMTTF), with both double bonds substituted by methyl
groups, with Pd(PPh3)4 in toluene no dithiolene complex
was formed and only the precipitation of black colloidal Pd
was observed. The same result was obtained when TTF-
tetra(methylcarboxylate) (TTF(COOMe)4), an electron
poorer donor, was heated in the presence of Pd(PPh3)4.
In such hypothesized h2 complex, [(PPh3)2Pd(h2-TTF)], the
Pd center, perpendicular to the TTF mean plane, would be
in favorable situation to interact with the neighboring S
atoms and eventually to migrate on them, followed by the
insertion in one of the C–S bonds. Then a reductive
elimination of a carbene species would generate the
monomeric [(PPh3)2Pd(edt)] complex which further
dimerizes in the reaction conditions, upon loss of a
phosphine ligand, to afford the most stable species 1.
As already mentioned, the complex 1 was obtained as a
dark violet crystalline solid. Solutions of 1 in methylene
2. Results and discussion
2.1. Synthesis and characterization
We noticed initially the formation of the title com-
pound [(Ph3P)Pd(edt)]2 (1), identified after single crystal
X-ray analysis (vide infra), as traces of by-product during
our attempts of Stille type coupling between TTF-SnMe3
and various halogenated aromatic substrates in the
presence of the standard Pd(0) catalyst Pd(PPh3)4 [13].
Puzzled by this observation we decided to rationalize the
formation of 1 and assumed that the direct reaction
between TTF and Pd(PPh3)4 would afford 1, in the absence
of any other obvious reaction paths (Scheme 1).
Scheme 1. Synthesis of 1.

906
F. Pop et al. / C. R. Chimie 15 (2012) 904–910
complex crystallizes in the monoclinic system, space group
C2/c, with one independent half of molecule of complex in
the unit cell, the other half being generated through the
inversion center, and one molecule of solvent disordered
over the inversion center (Fig. 2). With the exception of the
solvent molecule (CH2Cl2 versus C7H8) the two structures
are identical, therefore only the structural parameters of
the CH2Cl2 solvate will be detailed hereafter.
Each Pd atom is surrounded by one P atom, one m1
S
atom (S2) and two bridging
m
2 S atoms (S1 and S10) within
a slightly distorted square planar geometry, as shown by
the bond angles around the metal center (Table 1). Pd–S
˚
bond lengths range between 2.30 and 2.36 A, the longest
one being that with the bridging S atom belonging to the
neighboring dithiolene ligand.
The central [Pd2S2] metallacycle is highly folded about
the S1ꢀꢀꢀS10 hinge, the corresponding torsion angle
amounting to 67.98 (Fig. 3), while the metalla-dithiolene
rings are practically planar. Note the values for the dihedral
angles between the two five-membered metallacycles
(83.58), and also between the least-squares plane 5 atoms
Pd1, S2, C2, C1, S1 and least-squares plane 3 atoms Pd1, S1,
Pd10 (57.38). An interesting feature lies on the very short
distance between one vinylic proton of each dithiolene
ligands (H1 and H7, respectively) and the centroid of a
phenyl ring (as highlighted in Fig. 2), very likely providing a
strong shielding of these protons in the 1H NMR spectrum
(vide supra).
Fig. 1. UV-Vis spectra of [(Ph3P)Pd(edt)]2 (1) (
Lꢀmolꢁ1ꢀcmꢁ1, c = 10ꢁ5 M).
lmax = 576 nm, e = 3270
chloride are stable to air and have an intense violet
greenish color. UV-Visible spectra of CH2Cl2 solutions of 1
(Fig. 1) clearly show a low energy absorption band at
l
= 576 nm (
e
= 3270 Lꢀmolꢁ1ꢀcmꢁ1) and a more intense
one at
l
= 408 nm (
e
= 10,470 Lꢀmolꢁ1ꢀcmꢁ1).
The lowest energy band thus appears at higher energy
when compared to the neutral bis(dithiolene) complex
[Pd(edt)2] (l = 785 nm [5b]), for which the nature of the
corresponding electronic transition has been well docu-
mented.
Cyclic voltammetry measurements on 1 show only an
irreversible oxidation peak at 0.80 V vs SCE.
This suggests, together with the single resonance
measured in 31P NMR spectroscopy, that the configuration
observed in the solid state is rigid and very likely preserved
also in solution at room temperature. On the contrary, in
the case of the saturated analogue [(Ph3P)Pd(ethane-
dithiolate)]2 (with dithiolate ligands instead of dithio-
lenes), described by Hong [16], two singlets were observed
in the 31P NMR spectrum in solution in spite of the
symmetrical coordination of the two phosphines, as shown
by single crystal X-ray analysis. The authors suggested that
this behaviour was likely due to an equilibrium between
two conformations in solution. Note that this saturated
2.2. Structural analysis of [(Ph3P)Pd(edt)]2 (1)
The final proof for the dimeric structure of 1 was
provided by a single crystal X-ray analysis. Suitable
crystals have been grown either by slow evaporation of
toluene from a solution of 1, or by slow diffusion of
methanol onto a solution of 1 in CH2Cl2. In both cases the
Fig. 2. Molecular structure of [(Ph3P)Pd(edt)]2ꢂCH2Cl2 (left) and [(Ph3P)Pd(edt)]2ꢂPhCH3 (right).

F. Pop et al. / C. R. Chimie 15 (2012) 904–910
907
Table 1
˚
Selected lengths (A) and angles (8) for compound 1.
˚
Distances (A)
Angles (8)
Dihedral angles (8)
67.9
Pd(1)ꢀꢀꢀPd(10)
Pd(1)-S(1)
Pd(1)-S(2)
Pd(1)-S(10)
Pd(1)-P(1)
C(1)-C(2)
2.9825(6)
2.3300(6)
2.3001(7)
2.3637(6)
2.2862(6)
1.317(4)
1.759(3)
1.741(3)
S(1)-Pd(1)-S(10)
79.99(3)
88.75(3)
90.15(2)
101.30(2)
Pd(1)-S(1)- S(10)-Pd(10)
S(1)-Pd(1)-S(2)
S(2)-Pd(1)-P(1)
P(1)-Pd(1)-S(10)
S(1)-C(1)
S(2)-C(2)
[(Ph3P)Pd(edt)]2ꢂCH2Cl2 . . .. . .. . .’ = ꢁx + 1, y, ꢁz + 1/2.
short perpendicular CHvinylꢀꢀꢀPh and CHPhꢀꢀꢀPh contacts
˚
(3.6–3.8 A).
2.3. Theoretical study on [(Ph3P)Pd(edt)]2 (1)
In order to investigate on the conformation of 1 in the
gas phase, hence in the absence of any intermolecular or
packing interactions occurring in the solid state, and also to
assign the electronic transitions observed in the UV-Visible
spectrum, theoretical calculations have been performed at
the DFT level, with the PBE0 functional [17] and LanL2dz
for Pd and D95 for the other elements as basis set [18]. The
optimized geometry is in excellent agreement with the
experimental one determined by X-ray analysis, especially
when considering the value of the folding angle about the
Fig. 3. The central motif in the structure of [(Ph3P)Pd(edt)]2ꢂCH2Cl2 with
an emphasis on the folding of the [Pd2S2] metallacycle. Phenyl rings have
been omitted for clarity.
central
m
Sꢀꢀꢀ
mS hinge (Table 2).
The analysis of the frontier orbitals of the complex 1
reveals that the occupied HOMO and HOMO-1 develop
mainly on the edt ligands (83% and 87%, respectively),
including the participation of the ethylene bridge, with a
bis(dithiolate) complex adopts in the solid state a similar
folded conformation to our complex 1, with comparable
bond lengths and angles around the Pd centers.
2
significant contribution of the metal centers (14% dz
The dimeric units in the structure of [(Ph3P)Pd
(edt)]2ꢂCH2Cl2 stack in a zipper motif (Fig. 4), with some
orbital and 10% dxz orbital, respectively), while in the
LUMO and LUMO+1 the contribution of the metal orbitals
Fig. 4. Zipper type stacking in the bc plane in the structure of [(Ph3P)Pd(edt)]2ꢂCH2Cl2.

908
F. Pop et al. / C. R. Chimie 15 (2012) 904–910
Table 2
In conclusion we have synthesized through an unusual
reaction between TTF and Pd(PPh3)4 the unprecedented
dimeric Pd-dithiolene complex [(Ph3P)Pd(edt)]2, having a
rigid folded structure of the central [Pd2S2] ring, as shown
by single crystal X-ray structure and NMR. In spite of the
fact that neither the metals nor the dithiolene ligands are
oxidized in this complex, it shows a rather low energy
absorption band. Theoretical calculations at the TD-DFT
level support the assignment of this band mainly to the
HOMO!LUMO transition, while the frontier orbitals are
clearly combinations of metal and dithiolene orbitals.
Experimental and calculated geometrical parameters for compound 1.
˚
˚
Parameter
d( S-Pd)
Exp. (A)
Calc. (A)
m
2.330
2.364
2.300
2.286
2.983
2.412
2.467
2.388
2.377
3.015
d(S-Pd)
d(P-Pd)
d(PdꢀꢀꢀPd)
mS-Pd-
m
S
80.08
67.98
79.68
73.08
Pd- S-
m
mS-Pd
Table 3
3. Experimental
Calculated energies of frontier orbitals and their composition according to
a Mulliken population analysis.
3.1. General
MO
eV
%Pd
%dt
%PPh3
LUMO+1
LUMO
ꢁ1.89
ꢁ2.37
36
34
48
48
17
18
Reactions were carried out under Argon and using
toluene HPLC. Nuclear magnetic resonance spectra were
recorded on a Bruker Avance DRX 500 spectrometer
(operating at 500.04 MHz for 1H, 125 MHz for 13C and
202.39 MHz for 31P). Chemical shifts are expressed in parts
per million (ppm) downfield from external TMS. The
following abbreviations are used: s; singlet and m;
multiplet. MALDI- TOF MS spectra were recorded on
Bruker Biflex-IIITM apparatus; equipped with a 337 nm N2
laser. Elemental analyses were recorded using Flash 2000
Fisher Scientific Thermo Electron analyzer. IR spectra were
recorded on Bruker FT-IR Vertex 70 spectrometer equipped
with a Platinum diamond ATR accessory.
HOMO
ꢁ5.23
ꢁ5.39
14
10
83
87
2
3
HOMO-1
2
(dx 2)is much more important (34% and 36%, respective-
ꢁy
ly), while that of the edt ligands still remains consistent
(48% in both orbitals) (Tables 3 and 4).
Moreover, TD-DFT, despite the relatively small basis set,
reproduces well the experimental UV-Visible spectrum
(Fig. 5) and allowed us to identify the orbitals involved in
the corresponding electronic transitions (Table 5).
Accordingly, the major component of the lowest energy
band is the HOMO!LUMO transition, while the HOMO-
1!LUMO+1 transition is mainly responsible for the next
band, in both cases mixed metal-dithiolene ligands being
involved.
3.2. Synthesis of [(Ph3P)Pd(edt)]2
1
To a degassed solution of tetrathialfulvalene (102 mg,
0.5 mmol) in 10 ml of toluene, Pd(PPh3)4 (600 mg,
Table 4
Representation of selected molecular orbitals with an isovalue of 0.05.
MO
MO
LUMO
LUMO+1
HOMO
HOMO-1

F. Pop et al. / C. R. Chimie 15 (2012) 904–910
909
Table 6
Crystallographic data, details of data collection and structure refinement
parameters.
[(Ph3P)Pd(edt)]2ꢂCH2Cl2 [(Ph3P)Pd(edt)]2ꢂPhCH3
Formula
M [gmolꢁ1
T [K]
C20.50 H18 Cl P Pd S2
501.29
C23.50 H17 P Pd S2
500.86
]
293 (2)
293 (2)
Crystal system
Monoclinic
C2/c
Monoclinic
C2/c
Space group
˚
a [A]
27.042 (5)
9.4680 (14)
16.2415 (9)
90.00
27.6952 (13)
9.6533 (9)
16.2542 (17)
90.00
˚
b [A]
˚
c [A]
a
b
g
[8]
[8]
[8]
94.757 (7)
90.00
95.387 (6)
90.00
3
˚
V [A ]
4144.0 (10)
8
4326.4 (6)
8
Z
rcalcd [gcmꢁ3
[mmꢁ1
]
1.607
1.538
m
]
1.305
1.131
Goodness-of-fit 1.065
on F2
1.090
Fig. 5. Experimental (black) and theoretical (red) absorption spectra.
Final R1/wR2
[I > 2 (I)]
R1/wR2
(all data)
0.0333/0.0762
0.0233/0.0485
0.0387/0.0554
s
0.0646/0.0903
0.5 mmol) was added and the mixture was stirred at reflux
for 48 h. After cooling the solution was filtered over a path
of silica and washed with dichloromethane. After the
removal of the solvents the crude was purified by
chromatography using as eluent a mixture of hexane/
dichloromethane 1/1 followed by dichloromethane. Black
rhombohedral crystals were obtained by slow diffusion of
methanol in a dichloromethane solution of the compound,
or by slow evaporation of toluene.
performed on a Bruker Kappa CCD diffractometer, operat-
˚
(l = 0.71073 A) X-ray tube with a graphite
a
ing with a MoK
monochromator. The structures were solved (SHELXS-97)
by direct methods and refined (SHELXL-97) by full matrix
least-square procedures on F2 [19]. All nonhydrogen atoms
were refined anisotropically. Hydrogen atoms were intro-
duced at calculated positions (riding model), included in
structure factor calculations but not refined. Crystallo-
graphic data for the two structures have been deposited
with the Cambridge Crystallographic Data Centre, deposi-
tion number CCDC 866362 ([(Ph3P)Pd(edt)]2ꢂPhCH3) and
CCDC 866363 ([(Ph3P)Pd(edt)]2ꢂCH2Cl2). These data can be
obtained free of charge from CCDC, 12 Union road,
Cambridge CB2 1EZ, UK (deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
Yield: 5%. 1H-NMR (500 MHz, CDCl3)
d/ppm: 4.46 (m,
2H), 5.30 (s, 0.7 H, CH2Cl2), 6.28 (m, 2H), 7.37 (m, 12H, HPh),
7.43 (m, 6H, HPh), 7.67 (m, 12H, HPh).
13C-NMR (125 MHz, CDCl3)
d/ppm: 53.43 (CH2Cl2),
112.62 (-S-CH-CH-S-), 128.25, 128.29, 128.33, 130.47,
130.85, 134.57 (CPh), 147.80 (-S-CH-CH-S-).
31P-NMR (202 MHz, CDCl3)
d/ppm: 30.26.
MS (MALDI-TOF): m/z: 917.60 (Mth = 917.75).
Elemental analysis calcd. (%) for C40H34P2Pd2S4: C,
52.35; H, 3.73; P, 6.75; Pd, 23.19; S, 13.98; found: C, 51.69;
H, 3.65; S, 13.99.
IR (ATR) cmꢁ1: 1516, 1479, 1433, 1094, 997, 802, 745,
687, 524, 505, 436.
3.4. Theoretical calculations
An optimized geometry, starting from the X-Ray data,
has been obtained with the Gaussian09 [20] package at the
DFT level of theory. The PBE0 functional [17] with the
LanL2dz for Pd and D95 for the other elements basis set has
been used [18]. Vibrations frequency calculations per-
formed on the optimized structures at the same level of
theory yielded only positive values. TD-DFT calculations
for the first 50 singlet excited states have been performed
at the same level of theory on the equilibrium geometry.
3.3. X-ray structure determinations
Details about data collection and solution refinement
are given in Table 6. X-ray diffraction measurements were
Table 5
TD-DFT calculated energies and assignment of the most pertinent
electronic excitations over 300 nm.
3.5. Cyclic voltammetry measurements
Excited Wavenumber
l
(nm)
Osc.
Transition
state
(cmꢁ1
)
Cyclic voltammetry measurements were carried out
with a Biologic SP-150 potentiostat under nitrogen by
using a three-electrode cell equipped with a platinum
millielectrode of 0.126 cm2 area, an Ag/Ag+ pseudo-
reference electrode and a platinum wire counter electrode.
The potential values were then re-adjusted with respect to
the saturated calomel electrode (SCE). The electrolytic
media involved a 0.1 mol/L solution of (nBu4N)PF6 in
1
6
14,660
21,933
682 0.017 HOMO!LUMO (82%)
456 0.084 HOMO-1!LUMO + 1 (68%),
HOMO-4!LUMO (14%),
HOMO!LUMO (10%)
10
11
26,810
28,966
373 0.075 HOMO-6!LUMO (64%),
HOMO-19!LUMO + 1 (6%). . .
345 0.040 HOMO-3!LUMO + 1 (21%),
HOMO-19!LUMO (18%). . .

910
F. Pop et al. / C. R. Chimie 15 (2012) 904–910
(b) T. Taguchi, H. Wada, T. Kambayashi, B. Noda, M. Goto, T. Mori, K.
Ishikawa, H. Takezoe, Chem. Phys. Lett. 421 (2006) 395.
[11] K.W. Browall, L.V. Interrante, J.S. Kasper, J. Am. Chem. Soc. 93 (1971)
6289.
dichloromethane/acetonitrile 4/1. All experiments were
performed at room temperature at 0.1 V/s.
[12] (a) V.P. Mayweg, G.N. Schrauzer, Chem. Commun. (1966) 640;
(b) G.A. Bowmaker, P.D.W. Boyd, G.K. Campbell, Inorg. Chem. 22
(1983) 1208;
Acknowledgements
(c) C. Kraffert, D. Walther, K. Peters, O. Lindqvist, V. Langer, J. Sieler, J.
Reinhold, E. Hoyer, Z. Anorg. Allg. Chem. 588 (1990) 167;
(d) M. Ebihara, M. Tsuchiya, T. Kawamura, Acta Cryst. C50 (1994) 1880;
(e) K.G. Landis, A.D. Hunter, T.R. Wagner, L.S. Curtin, F.L. Filler, S.A.
Jansen-Varnum, Inorg. Chim. Acta 282 (1998) 155;
Financial support from the National Agency for
Research (ANR, Project 09-BLAN-0045-01), the University
of Angers and the Re´gion Pays de la Loire (grant to D.B.),
and the CNRS is gratefully acknowledged.
(f) C.E. Keefer, S.T. Purrington, R.D. Bereman, B.W. Knight, D.R. Bedgood
Jr., P.D. Boyle, Inorg. Chim. Acta 282 (1998) 200;
(g) C.E. Keefer, R.D. Bereman, S.T. Purrington, B.W. Knight, P.D. Boyle,
Inorg. Chem. 38 (1999) 2294;
References
[1] (a) N. Robertson, L. Cronin, Coord. Chem. Rev. 227 (2002) 93;
(b) C.L. Beswick, J.M. Schulman, E.I. Stiefel, Prog. Inorg. Chem. 52 (2004) 55.
[2] R. Kato, Chem. Rev. 104 (2004) 5319.
[3] (a) M. Bousseau, L. Valade, J.-P. Legros, P. Cassoux, M. Garbauskas, L.V.
Interrante, J. Am. Chem. Soc. 108 (1986) 1908;
(b) A.M. Madalan, N. Avarvari, M. Fourmigue´, R. Cle´rac, L.F. Chibotaru,
S. Clima, M. Andruh, Inorg. Chem 47 (2008) 940.
[4] (a) U.T. Mueller-Westerhoff, D.I. Yoon, K. Plourde, Mol. Cryst. Liq. Cryst.
183 (1990) 291;
(h) E. Cerrada, A., Moreno, M., Laguna, Dalton Trans. (2009) 6825.
[13] F. Riobe´, N. Avarvari, P. Grosshans, H. Sidorenkova, T. Berclaz, M.
Geoffroy, Phys. Chem. Chem. Phys. 12 (2010) 9650.
[14] R. Cao, M. Hong, F. Jiang, B. Kang, X. Xie, H. Liu, Polyhedron 15 (1996)
2661.
[15] M.N. Jayaswal, H.N. Peindy, F. Guyon, M. Knorr, N. Avarvari, M. Four-
migue´, Eur. J. Inorg. Chem. (2004) 2646.
[16] R. Cao, M. Hong, F. Jiang, H. Liu, Acta Cryst. C 51 (1995) 1280.
[17] C. Adamo, V. Barone, J. Chem. Phys. 110 (1999) 6158.
[18] (a) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270;
(b) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 284;
(b) U.T. Mueller-Westerhoff, B. Vance, D.I. Yoon, Tetrahedron 47 (1991)
909.
[5] (a) G.N. Schrauzer, V.P. Mayweg, J. Am. Chem. Soc. 87 (1965) 3585;
(b) K.W. Browall, L.V. Interrante, J. Coord. Chem. 3 (1973) 27;
(c) F. Bigoli, P. Deplano, F.A. Devillanova, V. Lippolis, P.J. Lukes, M.L.
Mercuri, M.A. Pellinghelli, E.F. Trogu, J. Chem. Soc., Chem. Commun.
(1995) 371;
(d) F. Bigoli, P. Deplano, F.A. Devillanova, J.R. Ferraro, V. Lippolis, P.J. Lukes,
M.L. Mercuri, M.A. Pellinghelli, E.F. Trogu, Inorg. Chem. 36 (1997) 1218;
(e) M.C. Aragoni, M. Arca, F. Demartin, F.A. Devillanova, A. Garau, F. Isaia, F.
Lelj, V. Lippolis, G. Verani, J. Am. Chem. Soc. 121 (1999) 7098.
[6] C. Lauterbach, J. Fabian, Eur. J. Inorg. Chem. (1999) 1995.
[7] M.C. Aragoni, M. Arca, F.A. Devillanova, F. Isaia, V. Lippolis, A. Manchini,
L. Pala, G. Verani, T. Agostinelli, M. Caironi, D. Natali, M. Sampietro,
Inorg. Chem. Commun. 10 (2007) 191.
[8] (a) S. Olivier, C. Winter, Adv. Mater. 4 (1992) 119;
(b) C.S. Winter, S.N. Olivier, J.D. Rush, C.A.S. Hill, A.E. Underhill, Mol.
Cryst. Liq. Cryst. 235 (1993) 181.
[9] N. Kuramoto, K. Asao, Dyes Pigm. 12 (1990) 65.
[10] (a) T.D. Anthopoulos, S. Setayesh, E. Smits, M. Co¨lle, E. Cantatore, B. de
Boer, P.W.M. Blom, D.M. de Leeuw, Adv. Mater. 18 (2006) 1900;
(c) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299.
[19] G.M. Sheldrick, SHELXL91, Release 97-2, Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[20] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark,
J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox,
J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli,
J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
¨
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas,
J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision
A.2, Gaussian, Inc., Wallingford CT, 2009.