Synthesis, crystal structure, spectroscopic, and photoreactive properties of a ruthenium(II)-mononitrosyl complex

Article abstract of DOI:10.1016/j.poly.2016.09.010

A compound of formula [Ru^IICl(NO)(Cl-py)₄](PF₆)₂, in which Cl-py is the 4-chloropyridine, has been synthesized in four steps and fully characterized. It crystallizes in the P1ˉ triclinic space group as [Ru^IICl(NO)(Cl-py)₄](PF₆)₂·1.25H₂O. Upon irradiation at λ?=?473?nm in the solid state, the N-bounded nitrosyl ligand (ground state GS: [Ru^II(NO)]) turns into O-bounded nitrosyl metastable state 1 (MS1: [Ru^II(ON)]). The population of the long-lived metastable Ru^II(ON) isomer is equal to 27% on powder samples, therefore 3 times less than that of the parent [Ru^IICl(NO)(py)₄](PF₆)₂derivative. Spectroscopy and TD-DFT studies are proposed to find a rational for this difference at the molecular level, which is tentatively related to different UV–visible spectra in the metastable Ru^II(ON) isomer. Surprisingly, and while the switching efficiency of [Ru^IICl(NO)(Cl-py)₄](PF₆)₂appears relatively modest, its capability for releasing the biologically active nitric oxide (NO^[rad]) radical under irradiation in solution is find to be about 100 times that of the [Ru^IICl(NO)(py)₄](PF₆)₂derivative.

Full text of DOI:10.1016/j.poly.2016.09.010

Polyhedron 119 (2016) 350–358
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, crystal structure, spectroscopic, and photoreactive properties
of a ruthenium(II)-mononitrosyl complex
⇑
Marine Tassé, Hasan S. Mohammed, Chloé Sabourdy, Sonia Mallet-Ladeira, Pascal G. Lacroix ,
Isabelle Malfant
⇑
Laboratoire de Chimie de Coordination du CNRS, UPR 8241, 205 route de Narbonne, F-31077 Toulouse, France
a r t i c l e i n f o
a b s t r a c t
A compound of formula [RuIICl(NO)(Cl-py)4](PF6)2, in which Cl-py is the 4-chloropyridine, has been syn-
Article history:
Received 16 June 2016
Accepted 4 September 2016
Available online 15 September 2016
II
ꢀ
thesized in four steps and fully characterized. It crystallizes in the P1 triclinic space group as [Ru Cl(NO)
(Cl-py)4](PF6)2ꢀ1.25H2O. Upon irradiation at k = 473 nm in the solid state, the N-bounded nitrosyl ligand
(ground state GS: [RuII(NO)]) turns into O-bounded nitrosyl metastable state 1 (MS1: [RuII(ON)]). The
population of the long-lived metastable RuII(ON) isomer is equal to 27% on powder samples, therefore
3 times less than that of the parent [RuIICl(NO)(py)4](PF6)2 derivative. Spectroscopy and TD-DFT studies
are proposed to find a rational for this difference at the molecular level, which is tentatively related to
different UV–visible spectra in the metastable RuII(ON) isomer. Surprisingly, and while the switching effi-
ciency of [RuIICl(NO)(Cl-py)4](PF6)2 appears relatively modest, its capability for releasing the biologically
active nitric oxide (NOÅ) radical under irradiation in solution is find to be about 100 times that of the
[RuIICl(NO)(py)4](PF6)2 derivative.
Keywords:
Ruthenium complexes
Nitric oxide
Molecular switch
NO release
Computational chemistry
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
population of metastable states limited to a few percent [15],
and in metal-(nitrosyl) complexes (N-bounded nitrosyl, ground
Photochromism, in which a molecule is reversibly photo-trans-
formed between two isomers having different absorption spectra,
has been a promising research topic in modern molecular science
[1], in relation to the intriguing concepts of molecular switches
and memories [2], and molecular machines [3]. Various classes of
molecules have been reported to possess photo-switching capabil-
ities, such as diarylethenes [4], spiropyrans [5], or azobenzenes [6].
A particular interest is devoted to solid state photo-isomerization
which could lead to applications for data storage, and ultrafast
photonic devices [7–10]. Although it may occasionally be observed
in few classes of photochromic species like spiropyrans [11,12], it
is usually hampered by the effect of the crystal rigidity which pre-
vents any significant intramolecular motion involved in the iso-
merization process. Therefore, solid state isomerization is mainly
observed in systems in which the atomic rearrangements are
restricted to the minimum. This requirement is fulfilled in N-sali-
cylidene anilines derivatives which undergo a tautomeric (proton
transfer supported by the solid state environment) equilibrium
between ketonic and enolic forms, if we [13,14], with typical
state GS), which are reversibly isomerized to a metal-(iso-nitrosyl)
(O-bounded nitrosyl, metastable state MS1), as follows:
½M ꢁ ðNOÞꢂ
ꢀ
½M ꢁ ðONÞꢂ
GS
MS1
Indeed, since the discovery of long-lived metastable states in
sodium nitroprusside (Na2[Fe(CN)5(NO)]ꢀ2H2O) [16], the NO/ON
isomerization has been observed in various metal-nitrosyl deriva-
tives (e.g. iron, ruthenium, osmium, manganese, iron, nickel and
platinum) in solid state [17–21]. Few years ago, we have observed
a remarkably large population (P92%) of the metastable state MS1,
in [RuIICl(NO)(py)4]2+ (12+, in Scheme 1) after irradiation of a crys-
tal of [RuIICl(NO)(py)4](PF6)2 ꢀ 0.5H2O at k = 473 nm [22], while the
previous highest populations reported was that of Hauser, in 1977,
with only 50% of MS1 in a single crystal of sodium nitroprusside
[16]. In a previous investigation [23], we have targeted the role
devoted to the solid state environment to account for this effect.
Indeed, we have observed that the population of the metastable
[RuIICl(ON)(py)4]2+ units strongly depends on the nature of the
counterions, present in the vicinity of the nitrosyl ligand. In this
second investigation, we wish to target the influence of the
intramolecular electronic properties to the rate of isomerization.
[RuIICl(NO)(Cl-py)4](PF6)2, an alternative system closely related to
⇑
Corresponding author. Fax: +33 5 61 55 30 03.
E-mail addresses: pascal.lacroix@lcc-toulouse.fr (P.G. Lacroix), isabelle.malfant@
lcc-toulouse.fr (I. Malfant).
http://dx.doi.org/10.1016/j.poly.2016.09.010
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

M. Tassé et al. / Polyhedron 119 (2016) 350–358
351
2+
2+
O
N
O
Cl
N
N
N
N
N
N
N
RuII
Cl
N
N
RuII
Cl
Cl
Cl
Cl
12+
22+
Scheme 1. Ruthenium(II)-nitrosyl based cations.
[RuIICl(NO)(py)4](PF6)2 will be described and fully characterized.
Then, the solid-state photochromic properties of both [RuIICl(NO)
(Cl-py)4](PF6)2, and [RuIICl(NO)(py)4](PF6)2 will be compared. The
observed differences will be tentatively rationalized from a com-
putational investigation of the spectroscopic properties of the
switchable cations conducted within the framework of the time-
dependent density functional theory (TD-DFT) method [24]. The
molecular structure of the two cations involved in this study is
shown in Scheme 1 (22+ for [RuIICl(NO)(Cl-py)4]2+).
[RuIICl(NO)(Cl-py)4](PF6)2.
[RuIICl2(4-NH2py)4]
(271 mg,
0.494 mmol) was dissolved in a mixture of 20 mL of ethanol and
5 mL of distillated water. Sodium nitrite (204 mg, 2.96 mmol) in
solution in water (5 mL) was added to the complex. The resulting
solution was refluxed for 4 h. 4 mL of hydrochloric acid (37%)
was then added and the solution was refluxed for additional
45 min. The solution was left to cool down to room temperature,
then NH4PF6 (260 mg, 1.6 mmol in 3 mL of water) was added to
precipitate the complex as an orange powder. The solution was
filtered, washed with water and dried under vacuum. Yield
(204 mg, 45%. Elemental analysis found: C, 25.95; H, 1.78; N,
8.01%. C20H16Cl5F12N5OP2Ru requires C, 26.38; H, 1,77; N, 7.69%.
2. Experimental
1H NMR((CD3)2SO, 300 MHz, 298 K): d 8.54 (8H , d, 3J 5.2), 7.92
a
2.1. General procedures
(8Hb, d, 3J 5.4). IR (KBr) mmax cmꢁ1: 3044 (C–Haromatic), 1910
(NAO), 1614 (C@N), 1424 (C@C), 825 (P-F).
[RuIICl(NO)(py)4](PF6)2 was synthesized following the previ-
ously reported procedure [22]. 4-Chloropyridine hydrochloric, 4-
aminopyridine and the Griess reagent used for the NO detection
were obtained from Sigma. Ruthenium trichloride hydrate
RuIIICl3ꢀxH2O was obtained from Strem Chemicals. The solvents
were analytical grade and used without further purification.
Elemental analyses were performed at LCC with a Perkin Elmer
2400 serie II Instrument. 1H NMR spectra were obtained at 298 K
in D2O, or (CD3)2SO as internal reference and were recorded on a
Bruker Avance 400. Chemical shifts (d) are reported in ppm and
coupling constants (J) in Hz. Infrared spectra were recorded on a
Perkin Elmer Spectrum 100 FT-IR Spectrometer, using a diamond
ATR. Ultraviolet–visible spectra were recorded on Jasco V-670
spectrophotometer.
2.3. X-ray crystallography
Single crystals suitable for X-ray diffraction were obtained
as yellow plates by slow evaporation of
a
solution of
[RuIICl(NO)(Cl-py)4](PF6)2 in an acetonitrile/water mixture. Data
were collected at low temperature (100(2) K) on a Bruker Kappa
Apex II diffractometer equipped with a 30 W air-cooled microfo-
cus, using MoKa radiation (k = 0.71073 Å), and an Oxford Cryosys-
tems Cryostream cooler device. Phi- and omega- scans were used
for data collection. The structure was solved by direct methods
with SHELXS-97 [25]. All non-hydrogen atoms were refined
anisotropically by means of least-squares procedures on F2 with
the aid of the program SHELXL-97 [25]. All the hydrogen atoms were
refined isotropically at calculated positions using a riding model
except those of water molecules which were not found in differ-
ence Fourier maps and therefore they were not included into the
model. The oxygen atom of one water molecule is disordered over
two positions (O2 and O20) in a 43:57 ratio and the water molecule
O3 has an occupancy of 0,25. In the solvent region some residual
electron density were difficult to model, therefore the SQUEEZE func-
tion of PLATON [26] was used to eliminate the contribution of this
electron density from the intensity data for the final refinement.
The crystal structure of [RuIICl(NO)(Cl-py)4](PF6)2 has been depos-
ited with the Cambridge Crystallographic Data Center.
2.2. Synthesis of [RuIICl(NO)(Cl-py)4](PF6)2
‘‘Ruthenium (II) blue” solution. RuCl3ꢀxH2O (500 mg, 2.4 mmol)
was dissolved in 25 mL of hydrochloric acid (3 mol Lꢁ1) and stirred
for 20 min. The solution was then heated to 100 °C under vacuum
until dryness (black product). The dry RuCl3 residue was dissolved
in a mixture of ethanol (30 mL) and distilled water (25 mL) and
was heated to 100 °C for 4 h to give ‘‘Ruthenium (II) blue” (inter-
mediate). CAUTION: the solution of ‘‘ruthenium blue” is unstable
and has to be readily used for the synthesis of the desired
complexes.
[RuIICl2(4-NH2py)4]. 4-Aminopyridine (1.534 g, 16.32 mmol)
was dissolved in 15 mL (1/3 H2O–2/3 ethanol) and was added to
‘‘Ruthenium (II) blue” (500 mg, 2.4 mmol RuCl3ꢀxH2O). The solu-
tion was refluxed for 1.5 h, and then concentrated to the half of
its initial volume. 50 mL of acetone was added to precipitate the
complex. Yield (325 mg, 25%), black powder. Elemental analysis
found: C, 43.89; H, 4.48; N, 20.50%. C20H24Cl2N8Ru requires C,
43.80; H, 4.41; N, 20.43%. 1H NMR, (D2O, 400 MHz, 298 K): d 7.90
2.4. Computational methods
The molecular geometries of 12+ and 22+ were computed using
the GAUSSIAN-09 program package [27] within the framework of
the DFT at the B3LYP/6-31G⁄ level [28–30], the LANL2DZ pseudo-
potential being used to account for relativistic effects on the ruthe-
nium atom [31]. The widely applied B3LYP functional was selected
for a better consistency with our previous investigation of 12+ [23].
The computations were performed in the presence of acetonitrile
with the SCRF method implemented in Gaussian, using the
(8H
(NH2), 3180 (NH2), 1611 (NH2), 1508 (C@N).
a
, d, J 7.17), 6.76 (8Hb, d, J 7.12). IR (KBr) mmax (cmꢁ1): 3304

352
M. Tassé et al. / Polyhedron 119 (2016) 350–358
polarizable continuum model (PCM) [32]. Vibrational analysis was
performed at the same level in order to establish the presence of a
minimum on the potential energy surfaces. In a first step of com-
putation, no symmetry was imposed. However, the C4 symmetry
was observed in the final geometries within a tolerance of
0.002 Å for both cations. Therefore, the actual geometries were
assumed to be C4 in the final computations.
In a second step, the UV–visible spectra were computed at the
PBE0/6-31G⁄ level. The choice for this functional was motivated
by the fact that it reproduced fairly well the experimental spectra
by comparison with B3LYP, TPSSh, and B3PW91, previously used in
the investigation of ruthenium(II) complexes with polypyridines
and chlorides ligands [23,33,34] (Supplementary Materials:
Fig. S1).
2.5. Photochemistry
Photoswitch in the solid state. IR spectra were recorded on a
Perkin Elmer GX2000 spectrophotometer. [RuIICl(NO)(Cl-py)4]
(PF6)2 (1 mg) was mixed with KBr (99 mg), grinded and pressed
to a pellet (1 ton, 2 min). The sample was cooled down to 100 K,
in a SPECAC (P/N 20600) cryostat, and irradiated during 180 min
with monochromatic light (diode laser: k = 473 nm). The experi-
ment was performed in the same pelletizing and temperature con-
ditions on [RuIICl(NO)(py)4](PF6)2 to ensure a reliable comparison.
NO release. The UV–visible spectra were recorded on 2 mL of
non-deoxygenated solutions of the nitrosyl complexes
(0.93 mmol/L) in acetonitrile, under irradiation realized with a
Muller reactor device equipped with a cooling water filter and a
mercury arc lamp equipped with appropriate interference filter
to isolate the desired irradiation wavelength (kmax = 436 nm, inten-
sity 9 mW). The sample solutions were placed in a quartz cuvette
of 1 cm pathlength, and stirred continuously. The temperature
was maintained at 27 °C during the whole experiment. Details on
kinetic studies with the use of the Griess reagent are reported in
Supplementary Materials.
Fig. 1. Asymmetric unit for [RuIICl(NO)(Cl-py)4](PF6)2 ꢀ 1.25H2O. Displacement
ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for
clarity.
one [RuIICl(NO)(Cl-py)4](PF6)2 entity and molecules of water. One
molecule of water is disordered between two sites, with occupa-
tion rate of 0.43 and 0.57, for O(2) and O(20), respectively. A second
molecule labeled as O(3) is present without disorder, with an occu-
pation rate of 0.25. Each [RuIICl(NO)(Cl-py)4]2+ unit is linked to four
neighboring cationic species through short contacts observed
between the chlorine atoms of adjacent complexes (Clꢀ ꢀ ꢀCl dis-
tance around 2.25 Å) as illustrated in Fig. 2, so the overall packing
3. Results and discussion
3.1. Synthesis and characterization of [RuIICl(NO)(Cl-py)4](PF6)2
Following the general route previously described for [RuIICl(NO)
(py)4](PF6)2 [22], [RuIICl(NO)(Cl-py)4](PF6)2 was synthesized from
RuIIICl3 and 4-chloropyridine by a four-steps procedure with slight
variations. While [RuIICl(NO)(py)4](PF6)2 was obtained in pyridine
acting both as ligand and solvent, [RuIICl(NO)(Cl-py)4](PF6)2 was
synthesized in ethanol in which 4-chloropyridine (Cl-py) was
dissolved. However, this route implies a tedious purification
process, which brings down the overall yield. By contrast,
[RuIICl(NO)(Cl-py)4](PF6)2 was also unexpectedly obtained from
the 4-aminopyridine with
a better yield (see Section 2).
[Ru(4-NH2py)4Cl2] in presence of an excess of sodium nitrite and
hydrochloric acid leads to the diazonium salt that finally forms
the 4-chloropyridine as described in Scheme 2.
3.2. Crystal structure description
[RuIICl(NO)(Cl-py)4](PF6)2 crystallizes in the P1 triclinic space
ꢀ
group. The asymmetric unit cell, shown in Fig. 1, is built up from
HCl
+
N
Cl
N
NH2
N
N2
Fig. 2. ClꢀꢀCl Van der Waals contacts shown by dashed lines, between adjacent
[RuIICl(NO)(Cl-py)4]2+ cations. Displacement ellipsoids are drawn at the 50%
probability level. Hydrogen atoms, water molecules and counter-anions are omitted
for clarity.
NaNO2
Scheme 2. Synthetic route towards 4-chloropyridine.

M. Tassé et al. / Polyhedron 119 (2016) 350–358
353
results from slabs of cations, with PFꢁ6 anions and water molecules
Table 1
Crystal data and structure refinement parameters for [RuCl(NO)(Cl-py)4](PF6)2.
inserted in between (Fig. 3).
The main bond lengths and angles in the coordination sphere of
Chemical formula
C20H16Cl5N5ORu, 2(F6P), 1.25(H2O)
the 22+ cation are gathered in Table 2 and compared with those of
1
2
Formula weight
Crystal system
Space group
T (K)
Wavelength (Mo K
a (Å)
933.14
2+, previously reported [22](a). In the solid state, the symmetry of
triclinic
2+ is C4, within a tolerance of 0.2 Å. At first glance, the C4 symme-
P1
ꢀ
try can be assumed for the solid state geometry of 12+ as well, but
within a tolerance enlarged to 0.6 Å and 0.8 Å, for the two cations
present in the asymmetric unit cell, 12+ (A) and 12+ (B), respec-
tively. The first thing to check on the molecular structure is the
conformation of the Ru–NO linkage. With a Ru–N–O angle of
179.6(4)° supported by an experimental mNO vibrational mode at
1910 cmꢁ1, the electron configuration in the {Ru–NO}6 corre-
sponds to RuII–(NO)+. Indeed, it has clearly be established that,
for mononitrosyl {M–NO}6 photochromic complexes such as
[FeII(CN)5(NO)]2ꢁ or [RuIICl(NO)(py)4]2+, the M–NO group is linear
in the ground state and the mNO vibrational mode is ranging in
the 1900 cmꢁ1 region [35].
100(2)
a
) (Å)
0.71073
11.846(2)
11.9150(18)
12.379(2)
89.918(5)
73.153(5)
89.858(5)
1672.2(5)
2
1.848
1.062
23,990
6082
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc. (g cmꢁ3
)
Absorption coefficient (mmꢁ1
)
Reflections collected
Uniques
Rint
0.0588
0.0742
0.1080
1.003
a
The data gathered in Table 2, suggest that the introduction of
chloro substituents, while located at the periphery of the molecule,
may introduce significant changes in the internal conformations
around the metal atom. The largest difference observed in the first
coordination spheres of RuII for 12+ and 22+ is 0.03 Å at the Ru-Cl
bond length, which corresponds to a decrease of 1.25% of the value
on passing from 12+ to 22+. The other averaged metal distances dif-
ferences fall in the range of esds uncertainty. Something interest-
ing to point out is the surprisingly short NO bond length of 1.125
(5) Å observed in 22+, which corresponds to a shortening of 1.87%
of the averaged value find in 12+ (1.146(2) Å and 1.147(2) Å, for
(A) and (B), respectively). Nevertheless, this value is in the
range of magnitude of 1.117(4)–1.126(5) Å found in related
[RuIICl(NO)(py)4]2+ based crystal structures, and is therefore fully
acceptable [23].
In order to understand if these differences arise from
intramolecular electronic effects rather than from crystal packing
effects, the DFT computed conformations are provided in Table 2.
The data clearly indicate that both 12+ and 22+ cations exhibit
grossly the same molecular geometries. Concerning the first coor-
dination sphere, the computation confirms that the largest differ-
ence is expected in the Ru-Cl bond length, but it is reduced from
0.029 Å (X-ray) to 0.006 Å (DFT). Similarly, the shortening of the
NO bond length is modest in the computed 22+ species (0.002 Å)
R1
b
wR2 [I > 2
r
(I)]
Goodness-of-fit (GOF) on F2
P
P
jjF0j ꢁ jFC jj= jF0j.
a
R1
¼
1=2
2
P
P
2
½
½
wR2 ¼ ½ wðF20 ꢁ FC2 Þ ꢂ= ðwF20Þ ꢂꢂ
.
b
compared to the X-ray data. These experimental differences may
tentatively be related to different solid state environments around
the cations. Indeed, few short contacts involving the NO ligands are
evidenced as follows: in 12+ (A), two short O–F distances of 2.908
(2) Å and 2.912(2) Å are present between NO and different PF6-
anions; in 12+ (B), one O–F distance of 2.932(2) Å is present
between NO and a first PF-6 anion, two O–F distances of 2.801
(2) Å and 2.898(2) Å are present between NO and a second PF6-
anion, and one O–H distance of 2.616(2) Å is present between NO
and an hydrogen atom of a pyridine of a neighboring cation; in
2
2+, one O–F distances of 2.952(5) Å is present between NO and a
PF-6 anion, and one O–O distance of 2.930 Å is present between
NO and a molecule of water. To summarize, two short contacts
are observed involving the NO ligand of 12+ (A), and 22+, and four
short contacts are observed in the case of 12+ (B).
In the next section, spectroscopic investigations are reported to
further characterize the effect of the chloro substituents on the
Fig. 3. Crystal packing for [RuIICl(NO)(Cl-py)4](PF6)2 ꢀ 1.25 H2O projected in the (110) plane, showing the cationic slabs, maintained by Clꢀ ꢀ ꢀCl short contacts.

354
M. Tassé et al. / Polyhedron 119 (2016) 350–358
Table 2
Comparison of crystallographic and computed bond lengths (in Å) and angles (in °) for 12+, and 22+
.
X-ray
DFT
12+
22+
1
2+(C4)
2
2+(C4)
Molecule A1
Molecule B1
Ru(1)–N(1)NO
Ru(1)–N(2)py
Ru(1)–N(3)py
Ru(1)–N(4)py
Ru(1)–N(5)py
Ru(1)–Cl(1)
N(1)–O(1)
Cl(1)–Ru(1)–Npy
N(1)NO–Ru(1)-Npy
Ru(1)–N(1)–O(1)
1.7550(17)
2.1044(17)
2.1041(17)
2.1069(18)
2.1142(17)
2.3206(6)
1.146(2)
88.4
1.7537(16)
2.1036(16)
2.1015(17)
2.1050(17)
2.1213(16)
2.3231(5)
1.147(2)
88.0
1.767(4)
2.103(4)
2.100(4)
2.098(3)
2.114(4)
2.2927(13)
1.125(5)
88.2
1.771
2.150
2.150
2.150
2.150
2.367
1.143
88.0
1.775
2.148
2.148
2.148
2.148
2.361
1.141
88.0
2
2
91.6
178.30(16)
92.1
172.42(16)
91.8
179.6(4)
92.0
180.0
92.0
180.0
1
2
Reference [22a].
Averaged value.
electronic properties and switching capabilities, at the molecular
level.
ruthenium atom and the nitrogen of the nitrosyl ligand at the
LUMO and LUMO + 1 level in both cases supports the resulting
photo-lability of the NO fragment.
3.3. Spectroscopic properties
3.4. Photochromic properties
The experimental UV–visible spectra of [RuIICl(NO)(Cl-py)4]
(PF6)2 (2(PF6)2) and [RuIICl(NO)(py)4](PF6)2 (1(PF6)2) are shown in
Fig. 4. In both cases, the overall spectra exhibit the same qualitative
shape, with a low lying band having absorption maxima located at
We have previously reported a remarkably large population
(P92%) of metastable state in [RuIICl(NO)(py)4](PF6)2 [22]. In this
first report, the measurements were carried out on small-sized sin-
gle crystals. By contrast, the present investigation is based on pow-
dered samples diluted in diffusing KBr pellets. Infrared
spectroscopy upon irradiation at 100 K on ruthenium nitrosyl can
evidence the reversible structural change associated with the for-
mation of metastable state MS1 from the ground state GS (Fig. 6).
457 nm (e e
= 665 molꢁ1 L cmꢁ1) and 448 nm ( = 151 molꢁ1 L cmꢁ1),
for 2(PF6)2, and 1(PF6)2, respectively, and very intense bands below
300 nm. What immediately strikes in the observation of the figure
is the large difference in the intensity of the spectra, for so closely
related species. Indeed, the absorbance appears at least 4 times
more intense in 2(PF6)2 than in 1(PF6)2. The theoretical spectra
were therefore computed to try to rationalize these differences
(Fig. S1). The results are gathered in Table 3. Experiment and com-
putation indicate a tendency for red shift and higher intensity in
GS/GM1 conversion is easily observable by the shift of mNO vibration
frequency to lower frequencies. In [RuIICl(NO)(Cl-py)4](PF6)2, the
vNO frequency is observed at 1910 cmꢁ1 for GS and a band occurs
at 1762 cmꢁ1 for MS1. The peak area ratio before and after irradia-
tion at 1910 cmꢁ1, in the absorbance spectra allows evaluating the
population of the metastable state MS1. In previous work [22,23] on
powder sample of [RuIICl(NO)(py)4](PF6)2, the population was
found to be 76%. In [RuIICl(NO)(Cl-py)4](PF6)2, this ratio was
decreasing down to 27%.
2
2+, although the full extent of the enhancement of the extinction
coefficient (e22þ ꢃ 4 ꢄ ꢀ12þ ) is not fully explained by the computa-
tion (f22þ ꢃ 2 ꢄ f12þ ). At the orbital level, the low-lying bands arise
from two transitions degenerated for symmetry reason in the C4
point group. They involve contributions of the HOMO ꢁ 3 ? LUMO
and LUMO + 1, and the HOMO ? LUMO and LUMO + 1 excitations,
for 12+ and 22+, respectively, in which an important charge transfer
towards the nitrosyl ligand is observed in any cases. The involved
orbitals are shown in Fig. 5. Except for a weak contribution of a p
orbital of the chlorine atoms at the HOMO level of 22+, the elec-
tronic properties appear closely related in both species. In particu-
lar, the strong antibonding character observed between the
A time of irradiation of 180 min led to no more apparent evolu-
tion of the m(NO) IR spectra, however the completeness of the switch
may not have been strictly achieved, according to previous obser-
vations which indicate that the population of metastable state may
be surpassed in single crystal experiments [36]. Indeed, the yield of
photoconversion of [RuIICl(NO)(py)4]2+ to [RuIICl(ON)(py)4]2+ is
reduced from 92% to 76%. Interestingly, and under the same
experimental conditions, the population of metastable state of
[RuIICl(NO)(4Cl-py)4](PF6)2, is only 27%, about three times less than
that of the parent [RuIICl(NO)(py)4](PF6)2.
In the previous sections, we have pointed out that the solid
state environments and the presence of chloro substituents could
modulate the overall electronic responses of 12+, and 22+, although
it is difficult to estimate the real magnitude of both effects, pre-
cisely. In an attempt to get more insights at the intramolecular
level on the comparison of the switching capabilities, the Gibbs
free energies have been computed for the following equilibriums:
4000
3500
3000
2500
2000
1500
2(PF6)2
1000
500
0
½RuIIClðNOÞðpyÞ4ꢂ2þ
ꢀ
½RuIIClðONÞðpyÞ4ꢂ2þ
1(PF6)2
ð1Þ
ð2Þ
12þ
102þ
300
400
500
600
700
800
λ (nm)
½RuIIClðNOÞðCl-pyÞ4ꢂ2þ
ꢀ
½RuIIClðONÞðCl-pyÞ4ꢂ2þ
Fig. 4. Experimental UV–visible spectra of [RuII(Cl-py)4ClNO](PF6)2 (2(PF6)2) com-
pared to that of the parent [RuII(py)4ClNO](PF6)2 (1(PF6)2), in acetonitrile.
22þ
202þ

M. Tassé et al. / Polyhedron 119 (2016) 350–358
355
Table 3
Comparison of experimental and TD-DFT data for 12+ and 22+: absorption maxima (kmax in nm), extinction coefficients (
e
in molꢁ1 L cmꢁ1), oscillator strengths (f), main
component and character of the configuration interaction (CI) expansion.
Compound
UV–vis spectra
TD-DFT computations
Dominant composition of the CI expansion1
Character
kmax
e
Transition
kmax
f
12+
22+
448
150
1 ? 3
1 ? 4
1 ? 2
1 ? 3
419
419
429
429
0.0020
0.0020
0.0041
0.0041
0.672 v104 ? 108
d
d
xy ? dxz
xy ? dyz
–
–
p
p
x(NO)⁄
y(NO)⁄
ꢁ0.672 v104 ? 109
457
665
0.537
0.537
v
139 ? 141 + 0.321 v139 ? 140
dxy + 4
dxy + 4
e
e
(pCl) ? dxz–x(NO)⁄
v139 ? 140–0.321 v139 ? 141
(pCl) ? dyz–p
y(NO)⁄
Orbitals 139, 140, and 141 are the HOMO, LUMO, and LUMO + 1, respectively, for 22+
.
1
Orbitals 104, 108, and 109 are the HOMO ꢁ 3, LUMO, and LUMO + 1, respectively, for 12+
.
ruthenium-iso-nitrosyl [RuII(ON)] (10 and 202+) MS1 isomers have
been investigated computationally, in the same conditions that
those of the starting [RuII(NO)] (12+ and 22+) GS isomers. The com-
puted UV–visible spectra are shown in Fig. 7, and the correspond-
ing transitions of interest are shown in Table 4. All of them lead to
a significant charge transfer to the iso-nitrosyl (ON) ligand, and
hence to a possible back isomerization towards the stable 12+
and 22+ starting isomers.
2+
109
108
-4.5
140
14
1
E (e.V)
-5
Something important to point out is that, within the conditions
of our experimental setup, the irradiation of the starting [RuII(NO)]
species could not be conducted in a continuous range of frequen-
cies. Instead, the set of optical filters available imposed the selec-
tion of k = 473 nm, as the only wavelength compatible with the
experimental 440–460 nm range of absorption maxima for the
[RuII(NO)] species (Fig. 4). Doing so, the irradiations were per-
formed at slightly lower energies, than those required from the
spectra. In order to transpose these experimental conditions to
the computational analysis, one has to keep in mind that the the-
oretical electronic transitions were found to be slightly blue shifted
by about 1 500 cmꢁ1 (30 nm) with respect to the experimental
data (Table 3). This leads us to consider the effect of a theoretical
irradiation at 441 nm (instead of 473 nm). Doing so, the
-5.5
-7.5
106
107
139
105
104
-8
X
Z
-8.5
12+
22+
Fig. 5. Dominant orbitals involved in the low-lying transitions of 12+ and 22+
.
Fig. 6. Infrared spectra of 2(PF6)2 without irradiation (blue) and after irradiation
(red). (Color online.)
The results lead to
D ,
G° = 38.1 kcal molꢁ1 and 37.8 kcal molꢁ1
for Eqs. (1) and (2), respectively. Therefore, there is no thermody-
namic reason to infer that the process described in (1) should far be
more efficient than that in (2).
A second approach implies the analysis of the effect of the light
on the metastable state. Indeed, the irradiation has to be conducted
at a wavelength in which the metastable state does not absorb in
order to avoid a possible back isomerization and hence a poorly
efficient isomerization process. The optical properties of both
Fig. 7. Computed UV–visible spectra (oscillator strengths f against wavelengths k)
2+
2+
for 10 (top) and 20 (bottom). The arrows indicate the wavelength of theoretical
irradiation (k = 441 nm).

356
M. Tassé et al. / Polyhedron 119 (2016) 350–358
Table 4
2+
Comparison of relevant TD-DFT data for 10 and 202+: absorption maxima (kmax in nm), oscillator strengths (f), main component and character of the configuration interaction (CI)
expansion.
Compound
Transition
kmax
f
Composition of the CI expansion1
0.346 107 ? 108 + 0.346 v106 ? 109
103 ? 108 + 0.321 v102 ? 109
Dominant character
10
1 ? 9
469
0.0021
v
pCl
+
p(py) ? dxz + dyz
ꢁ
ꢁ
p⁄x(NO) ꢁ p⁄y(NO)
p⁄x(NO) ꢁ p⁄y(NO)
2+
ꢁ0.341
v
1 ? 18
1 ? 9
1 ? 12
1 ? 13
1 ? 14
369
450
444
422
422
0.0165
0.0012
0.0016
0.0073
0.0073
0.468
0.416
0.419
v
v
v
99 ? 109 + 0.468 v100 ? 108
135 ? 140 + 0.416 v134 ? 141
134 ? 140 + 0.419 v135 ? 141
pCl
pCl
pCl
+
+
+
p
(py) ? dxz + dyz
(Cl-py) ? dxz + dyz
2+
20
v
ꢁ
ꢁ v⁄x(NO) ꢁ p⁄y(NO)
p
(Cl-py) ? dxz + dyz p⁄x(NO) ꢁ vy⁄(NO)
0.699 v133 ? 140
0.699 v133 ? 141
p(Cl-py) ? dyz
ꢁ
ꢁ
p⁄y(NO)
p⁄x(NO)
p(Cl-py) ? dxz
Orbitals 133, 135, 140, and 141 are the HOMO ꢁ 6, HOMO ꢁ 4, LUMO, and LUMO + 1, respectively, for 22+
.
1
Orbitals 107, 108, and 109 are the HOMO, LUMO, and LUMO + 1, respectively, for 12+
.
experimental conditions can be approached for the 12+ and 22+
2+
2+
ground states and, more importantly, for the 10 and 20 meta-
stable states, as well. The effects of such irradiations are shown
in Fig. 7 (blue arrows). In the case of 102+, the irradiation falls in
the vicinity of transition 1 ? 9, but it corresponds to a weak effec-
tive oscillator strength (f) of 0.0012 (top of Fig. 7). By contrast, the
irradiation conducted on the metastable 202+ species involves a set
of four (1 ? 9, 1 ? 12, 1 ? 13, and 1 ? 14) transitions, and leads
to an effective f of 0.0140 (bottom of Fig. 7). This higher intensity
computed for 202+ suggests a yield of back RuII(ON) ? RuII(NO) iso-
LUMO
LUMO(+1)
-5
E (e.V.)
-6
2+
merization much larger in 20 than in 102+, in agreement with the
experimental data, and the theoretical work previously reported
on 12+ [33].
1
13
1
14
-7
-8
Finally, a last issue has to be addressed in this computational
investigation, regarding the understanding of the origin of such dif-
2+
2+
ferent spectra for the metastable 10 and 20 isomers, while the
stable 12+ than 22+ species exhibit rather similar spectra (Table 3
and Fig. 5). More precisely, the orbitals of the chlorine atoms pre-
sent in 22+ appear not to contribute significantly to the main tran-
sitions of the starting [RuII(NO)] species, thus leading to charge
transfer transition nearly identical, with a tendency for enhanced
intensities in 22+, as the only noticeable difference. By contrast,
X
2+
the UV–visible spectrum of 20 exhibits two very intense (1 ? 13,
Z
HOMO(-6)
and 1 ? 14) degenerated transitions centered at 422 nm, in which
the dominant involved orbitals are shown in Fig. 8. Interestingly,
the only occupied orbital involved in these transitions is the
#133 (HOMO ꢁ 6) in which the contribution of the chlorine atoms
is dominant. It is therefore not surprising that these intense transi-
tions do not find their counterpart in 102+, where no chlorine is pre-
sent, thus leading to so different UV–visible spectra between both
species.
Fig. 8. Dominant orbitals involved in the intense 1 ? 13 and 1 ? 14 degenerated
2+
transitions of 20
.
experiments, the rapid photo-release is followed by the formation
of a solvent bound ruthenium(III) photoproduct, according to the
following equation:
3.5. NO release in [RuIICl(NO)(Cl-py)4](PF6)2
Photoactive cations deriving from [RuIICl(NO)(py)4]2+ have
recently witnessed an increasing interest in relation to their capa-
bility for providing solid state photo-switches with high yields.
Alternatively, there is an additional photoreaction which leads to
the release of the biologically active NOÅ radical. Clearly, there is
no obvious correlation between the NOꢀ release, which is basically
a molecular process, and the photo-switch, which implies various
molecular and solid state parameters. Nevertheless, and although
the purpose of the present study is dedicated to NOÅ/ONÅ switches,
the issue of achieving a NOÅ release with these species arises
naturally.
h
v
½RuIIðNOÞꢂ þ solvent !½RuIIIðsolventÞꢂ þ NOꢅ
ð3Þ
This reaction can be followed spectroscopically either by (i) the
appearance of a broad and low-lying electronic transition ascrib-
able to a ligand ? RuIII(solvent) charge transfer, largely red shifted
with respect to the related ligand ? RuII(NO) charge transfer, or (ii)
the appearance of a specific transition involving the use of a NO-
sensitive sensor. Alternatively, the appearance of a paramagnetic
RuIII ion, instead of the close-shell (d6) RuII ion, can be checked
magnetically.
The changes in the electronic absorption spectra of [RuIICl(NO)
(Cl-py)4](PF6)2 exposed to 436 nm light in acetonitrile are shown in
Fig. S2. The presence of isosbestic points at 314, 450, and 484 nm
indicates a clean conversion of the RuII(NO) complexes to related
photolyzed species. It is important to note that no back-reaction
is observed when the light is turned off. The quantum yield
observed for NO release at 436 nm light irradiation is 0.29. To con-
firm that the photoreaction corresponds to the release of nitric
Previous investigations conducted on [RuIICl(NO)(py)4](PF6)2
have revealed a very modest quantum yield (# NOÅ released/# pho-
tons absorbed) of 1.6 ꢄ 10ꢁ3, thus prohibiting any use of 12+ as a
NOÅ donor [37]. Nevertheless, the NOÅ release from ruthenium-
nitrosyls species has been known for over 40 years, and was sum-
marized by Mascharak [38]. Therefore, it is worth checking the NOÅ
release capabilities of any new Ru(NO) complexes. In these

M. Tassé et al. / Polyhedron 119 (2016) 350–358
357
oxide (Eq. (3)), the Griess test has been applied, in which an in situ
oxidation of the released NOÅ to NOꢁ2 takes place in aqueous med-
ium, under aerobic condition, followed by a reaction with sulfanil-
amide and naphtylethylenediamine dihydrochloride, thus
providing a diazonium cation, and finally the formation of a pink
azo dye (kmax = 540 nm in CH3CN/H2O) [39,40]. The. changes
observed in the optical spectrum of [RuIICl(NO)(Cl-py)4](PF6)2 irra-
diated at 436 nm in the presence of the Griess reagent are shown in
Fig. S3. The gradual appearance of a pink color is clearly evidenced
from the experimental data, and undoubtedly proves that NO
release takes place under irradiation. It is important to point out
that, without irradiation, no color change is evidenced, which indi-
cates the chemical stability of the RuII(NO) complex.
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.poly.2016.09.010.
References
[1] Photochromism: Memories and Switches, special issue of Chem. Rev. 2000,
100(5). Photochromism: Molecules and Systems, H. Dürr, H. Bouas-Laurent
eds. Elsevier, 2003.
[2] B.L. Feringa (Ed.), Molecular Switches, Wiley-VCH Verlag, 2001.
[3] V. Balzani, A. Credi, M. Venturi, Molecular Devices and Machines: Concepts and
Perspectives for the Nanoworld, second ed., Wiley-VCH Verlag, 2008,
Copyright Ó 2008.
[4] M. Irie, T. Fukaminato, K. Matsuda, S. Kobatake, Chem. Rev. 114 (2014)
12174.
[5] G. Berkovic, V. Krongauz, V. Weiss, Chem. Rev. 100 (2000) 1741.
[6] H.M.D. Bandara, S.C. Burdette, Chem. Soc. Rev. 41 (2012) 1809.
[7] P. Günter, J.P. Huignard, Photorefractive Materials and their Application,
Springer, Berlin, 1988.
[8] J. Ashley, M.P. Bernal, G.W. Burr, H. Coufal, H. Guenther, J.A. Hoffnagle, C.M.
Jefferson, B. Marcus, R.M. Macfarlane, R.M. Shelby, G.T. Sincerbox, IBM J. Res.
Develop. 44 (2000) 341.
[9] S. Kawata, Y. Kawata, Chem. Rev. 100 (2000) 1777.
[10] N. Tamai, H. Miyasaka, Chem. Rev. 100 (2000) 1876.
[11] S. Bénard, Y. Pei, Adv. Mater. 12 (2000) 48.
Importantly, this quantum yield of 0.29 is in the range of quite
high NO quantum yields values for ruthenium nitrosyl complexes
and indeed much higher than the value of 1.6 ꢄ 10ꢁ3, reported
on the parent compound [RuIICl(NO)(py)4](PF6)2 [37]. However,
our attempts to confirm this low value were unsuccessful, the
low extinction coefficient (e
= 151 molꢁ1 L cmꢁ1), leading to an
insufficient photo-release process, and hence to unreliable experi-
mental data. This limitation must be pointed out to emphasize the
fact that any practical biological applications of such ruthenium-
polypyridinic species would imply higher extinction coefficients
[12] J. Harada, Y. Kawazoe, K. Ogawa, Chem. Commun. 46 (2010) 2593.
[13] For a review on solid state switches in N-salicylidene derivatives, see: E.
Hadjoudis, I. Mavridis Chem. Soc. Rev. 33 (2004) 579.
[14] (a) For representative reports on solid state switch in N-salicylidene
derivatives, see: D.A. Safin, M. Bolte, Y. Garcia Cryst. Eng. Comm. 16 (2014)
8786;
(e
> 103 molꢁ1 L cmꢁ1), and lead to the examination of more
(b) M. Avadanei, V. Cozan, S. Shova, J.A. Paixao, Chem. Phys. 444 (2014) 43;
(c) M. Sliwa, S. Létard, I. Malfant, M. Nierlich, P.G. Lacroix, T. Asahi, H.
Masuhara, P. Yu, K. Nakatani, Chem. Mater. 17 (2005) 4727.
[15] (a) A. Patra, R. Métivier, J. Piard, K. Nakatani, Chem. Commun. 46 (2010) 6385;
(b) M. Sliwa, S. Létard, I. Malfabnt, M. Nierlich, P.G. Lacroix, T. Asahi, H.
Masuhara, P. Yu, K. Nakatani, Chem. Mater. 17 (2005) 4727.
[16] (a) U. Hauser, V. Oestriech, H.D. Rohrweck, Z. Physik. A 280 (1977) 17–25;
(b) U. Hauser, V. Oestriech, H.D. Rohrweck, Z. Physik A 280 (1977) 125.
[17] (a) T. Woike, H. Zöllner, W. Krasser, S. Haussühl, Solid State Commun. 73
(1990) 149;
sophisticated pyridine-based ligands. Nevertheless, although the
importance of our result should not be overestimated, as the stabil-
ity of pyridine and chloride based complexes is far from being
insured in biological medium, it confirms that the present species
could also be regarded as promising NO sources [34].
4. Conclusion
(b) T. Woike, S. Haussühl, Solid State Commun. 86 (1993) 333;
(c) D. Schaniel, T. Woike, C. Boskovic, H.U. Gudel, Chem. Phys. Lett. 390 (2004)
347;
(d) D. Schaniel, T. Woike, D. Biner, K. Kraemer, H.U. Guedel, Phys. Chem. Chem.
Phys. 9 (2007) 5149;
[RuIICl(NO)(py)4](PF6)2 and [RuIICl(NO)(Cl-py)4](PF6)2 are two
related photo-reactive compounds, however with surprisingly dif-
ferent optical features. While the starting 12+ and 22+ ruthenium-
nitrosyl cations exhibit nearly similar electronic spectra, leading to
a first expectation of similar intrinsic NO/ON switching capabilities,
(e) D. Schaniel, T. Woike, N.R. Behrnd, J. Hauser, K. Kraemer, T. Todorova, B.
Delley, Inorg. Chem. 48 (2009) 11399.
[18] J.A. Guida, O.E. Piro, P.J. Aymonino, Inorg. Chem. 43 (1995) 4113.
[19] D.V. Fomitchev, P. Coppens, T. Li, K.A. Bagley, L. Chen, G.B. Richter-Addo, Chem.
Commun. 19 (1999) 2013.
[20] S.C. Da Silva, D.W. Franco, Spectrochim. Acta, Part A 55A (1999) 1515.
[21] T.E. Bitterwolf, Inorg. Chem. Commun. 11 (2008) 772.
[22] (a) B. Cormary, I. Malfant, M. Buron-Le Cointe, L. Toupet, B. Delley, D. Schaniel,
N. Mockus, T. Woike, K. Fejfarova, V. Petricek, M. Dusek, Acta Crystallogr. Sect.
B 65 (2009) 612;
(b) D. Schaniel, B. Cormary, I. Malfant, L. Valade, T. Woike, B. Delley, K.W.
Kraemer, H.U. Guedel, Phys. Chem. Chem. Phys. 9 (2007) 3717.
[23] B. Cormary, S. Ladeira, K. Jacob, P.G. Lacroix, T. Woike, D. Schaniel, I. Malfant,
Inorg. Chem. 51 (2012) 7492.
[24] G. Scalmani, M.J. Frisch, B. Mennucci, J. Tomasi, R. Cammi, V. Barone, J. Chem.
Phys. 124 (094107) (2006) 1.
2+
2+
significant differences are predicted in their related 10 and 20
iso-nitrosyl photoisomers, by DFT. In the case of the chloropy-
ridine-based species (22+), a significant overlap is found between
the UV-spectra of both RuII(NO) and RuII(ON) isomers, which
prohibits the photo-isomerization from being conducted until
completion, by contrast to [RuIICl(NO)(py)4](PF6)2 in which the
RuII(NO) ? RuII(ON) and RuII(ON) ? RuII(NO) transitions are fairly
well separated in energy. Alternatively,
a surprisingly fast
and efficient capability for NOÅ release has been found in
[RuIICl(NO)(Cl-py)4](PF6)2, with could attract more interest in the
future.
[25] G.M. Sheldrick, Acta Cryst. A 64 (2008) 112.
[26] P.V.D. Sluis, A.L. Spek, Acta Crystallogr. Sect. A 46 (1990) 194–201.
[27] 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, Ö. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision E.01, Gaussian, Inc.,
Wallingford, CT, 2009.
Acknowledgements
The authors thank B. Cormary for fruitful discussions. Hasan
Shamran Mohammed thanks the Iraqi/French Institution for a
Grant, and Campus France – (France) (Moyen-Orient, 776290J)
for financial support.
Appendix A. Supplementary data
[28] A.D. Becke, J. Chem. Phys. 98 (1993) 564.
[29] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[30] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270.
[31] A.W. Ehlers, M. Böhme, S. Dapprich, A. Gobbi, A. Höllwarth, V. Jonas, K.L.
Köhler, R. Stegmann, A. Vedkamp, G. Frenking, Chem. Phys. Lett. 208 (1993)
111.
[32] J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 105 (2005) 2999.
[33] J.S. García, F. Alary, M. Boggio-Pasqua, I.M. Dixon, I. Malfant, J.L. Heully, Inorg.
Chem. 54 (2015) 8310.
CCDC 1484591 contains the supplementary crystallographic
data for [RuIICl(NO)(Cl-py)4](PF6)2. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this

358
M. Tassé et al. / Polyhedron 119 (2016) 350–358
[34] J. Akl, I. Sasaki, P.G. Lacroix, I. Malfant, S. Mallet-Ladeira, P. Vicendo, N. Farfán,
R. Santillan, Dalton Trans. 45 (2014) 12721.
[37] A.G. De Candia, J.P. Marcolongo, R. Etchenique, L.D. Slep, Inorg. Chem. 49
(2010) 6925.
[35] G.K. Lahiri, W. Kaim, Dalton Trans. 39 (2010) 4471.
[36] Th. Woike, W. Krasser, H. Zöllner, W. Kirchner, S. Haussühl, Z. Phys. D 25
(1993) 351–356.
[38] N.L. Fry, P.K. Mascharak, Acc. Chem. Res. 44 (2011) 289.
[39] J.P. Griess, Ber. Deutsch Chem. Ges. 12 (1879) 426.
[40] D. Tsikas, J. Chromatogr. B 851 (2007) 51.