Synthesis and characterization of ionic Ru(III) complexes containing dimethylsulfoxide and dinitrogen heterocyclic ligands

Article abstract of DOI:10.1016/j.poly.2007.03.041

Several new Ru(III) DMSO compounds including [PPh₄]trans-[Ru(DMSO)₂Cl₄], [PPh₄]trans-[Ru(DMSO)(pyrazine)Cl₄] (2), [PPh₄]trans-[Ru(DMSO)(4,4′-bipyridine)Cl₄] and [PPh₄]trans-[Ru(DMSO)(pyrimidine)Cl₄] were reported and characterized. The crystal structure of 2 and its Na⁺ analogue were determined by X-ray diffraction methods. The PPh₄⁺ complex 2 is a discrete ionic compound, while the compound [Na]trans-[Ru(DMSO)(pyrazine)Cl₄] · DMSO (3) crystallized with a molecule of DMSO. The environment around the Na atom is a distorted octahedron with short contacts with three chloro ligands, two O atoms from the bonded and unbonded DMSO molecules, and the unbonded N atom of the pyrazine ligand. The Na atoms form bridges between the complexed anions in 3 resulting in the formation of infinite chains or ribbons parallel to the b axis. The chains are held together by van der Waals interactions.

Full text of DOI:10.1016/j.poly.2007.03.041

Polyhedron 26 (2007) 3661–3668
www.elsevier.com/locate/poly
Synthesis and characterization of ionic Ru(III) complexes
containing dimethylsulfoxide and dinitrogen heterocyclic ligands
a,
a
b
Craig M. Anderson *, Amnon Herman , Fernande D. Rochon
a
Department of Chemistry, Bard College, P.O. Box 5000, Annandale-on-Hudson, NY 12504-5000, United States
´
b
`
´ ´
De´partement de chimie, Universite´ du Que´bec a Montreal, CP 8888, Succ. Centre-Ville, Montreal, Quebec, Canada H3C 3P8
Received 6 March 2007; accepted 30 March 2007
Available online 10 April 2007
Abstract
Several new Ru(III) DMSO compounds including [PPh4]trans-[Ru(DMSO)2Cl4], [PPh4]trans-[Ru(DMSO)(pyrazine)Cl4] (2),
[PPh4]trans-[Ru(DMSO)(4,40-bipyridine)Cl4] and [PPh4]trans-[Ru(DMSO)(pyrimidine)Cl4] weþre reported and characterized. The crystal
structure of 2 and its Na+ analogue were determined by X-ray diffraction methods. The PPh4 complex 2 is a discrete ionic compound,
while the compound [Na]trans-[Ru(DMSO)(pyrazine)Cl4] Æ DMSO (3) crystallized with a molecule of DMSO. The environment around
the Na atom is a distorted octahedron with short contacts with three chloro ligands, two O atoms from the bonded and unbonded
DMSO molecules, and the unbonded N atom of the pyrazine ligand. The Na atoms form bridges between the complexed anions in 3
resulting in the formation of infinite chains or ribbons parallel to the b axis. The chains are held together by van der Waals interactions.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Ruthenium; DMSO; Pyrazine; Pyrimidine; 4,4-Bipyridine; Crystal structures; NMR; IR
1. Introduction
son for this can be attributed to the reduced side effects of
these complexes, due to their lower systemic toxicity. Com-
plexes with ruthenium(III) centers have been synthesized
and have demonstrated antitumor activity, as well as
remarkable antimetastatic behavior [10,11]. It is speculated
that ruthenium(III) complexes are reduced in vivo to the
more labile ruthenium(II) and this is a major reason for
its biological activity [9–11]. Due to lower oxygen and
lower pH at tumor sites, ruthenium’s ‘‘activation by reduc-
tion’’ process makes it very selective as the metal complex
may accumulate in these hypoxic environments [12]. Only a
small number of ruthenium(III) complexes have been
found to be effective, with the best examples being:
[Na]trans-[RuCl4(DMSO)(Im)] [13], NAMI, its imidazo-
lium analogue [ImH]trans-RuCl4(DMSO)(Im)] [14],
NAMI-A and the indazole compound [IndH]trans-
[RuCl4(Ind)2] [15], KP1019. NAMI-A shows high selectiv-
ity for solid tumor metastases [16,17] and low toxicity at
pharmacologically active doses and was found to effectively
interfere with cell cycle regulation and angiogenesis
[18–20]. The above properties have made NAMI-A the first
The anticancer drug cisplatin, cis-Pt(NH3)2Cl2, and a
few other platinum agents are widely used in the clinical
treatment of testicular, ovarian, bladder, head and neck
tumors [1–3]. The clinical success of cisplatin has proved
to be limited due to significant side effects and resistance
that cause relapse [3]. Therefore, much interest has focused
on developing new chemotherapeutic metal complexes with
improved properties. Subsequent studies on many plati-
num-containing complexes have been performed [4–8].
However, most of these complexes have been proven to
have the same or only slightly better efficacy than cisplatin
[3].
For the past two decades, much work has focused on the
synthesis and pharmacological evaluation of new com-
pounds containing ruthenium centers [9–11]. A major rea-
*
Corresponding author. Tel.: +1 845 758 7293.
E-mail address: canderso@bard.edu (C.M. Anderson).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.03.041

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C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
ruthenium(III) compound to successfully complete phase I
clinical trials [21]. The main feature of the majority of these
complexes is the presence of four chlorides, one DMSO,
and one N-donor ligand in the coordination sphere. At
present, very few examples of such ruthenium(III) com-
plexes exist that have been structurally characterized by
X-ray diffraction methods. These include complexes, for
example, where the N-donor ligand is ammonia [22], thia-
zole [23], guaninium [24], imidazole [22], pyridine [25], tri-
azole [26] as well as symmetrical ruthenium dimers with
pyrazine, pyrimidine, and bipyridine [27], and the unsym-
metrical dimer with bridging pyrazine [28]. Here we report
the synthesis and characterization of several ruthenium(III)
complexes with dimethylsulfoxide and heterocyclic dinitro-
gen ligands as well as the crystal structures of the
[Ru(DMSO)(pz)Cl4]ꢀ (pz = pyrazine) monoanion with
two different cations, tetraphenylphosphonium (PPh4)
and Na. These cations are quite different and the architec-
tures of the crystal structures were expected to differ con-
siderably. These two compounds are the first two Ru(III)
species containing a terminal pyrazine ligand to be charac-
terized structurally.
0.16 g of pyrazine (pyz) (2.0 mmol) was dissolved in 1 mL
of acetone. The ruthenium solution was added slowly to
the pyrazine solution to form a clear orange mixture. After
several hours the product precipitated as orange crystals.
The crystals were collected by filtration, washed with cold
diethylether and vacuum dried. Yield: 73%. Alternatively,
complex 2 can be synthesized from complex 3 by the addi-
tion of [PPh4]Br or [PPh4]Cl in aqueous solution. IR
(cmꢀ1): 1588 (pz), 1108s (DMSO–S), 420m m(Ru–S), 342,
328s m(Ru–Cl). 1H NMR (CD3CN/ppm): ꢀ12.6 (br,
DMSO–S), ꢀ5.6 (vbr, pz H2,6), ꢀ1.6 (br, pz H3,5), 7.95,
7.74 (phenyl protons). Anal. Calc. for C30H30Cl4N2OPSRu:
C, 48.6; H, 4.05; N 3.78. Found: C, 48.4; H, 3.84; N, 3.87%.
[Na]trans-[Ru(DMSO)(pz)Cl4] Æ DMSO (3). The syn-
thesis of this compound was similar to that reported [27] with
some changes. Pyrazine (80.2 mg, 1.00 mmol) dissolved in
5 mL of acetone was added to a solution of 82.5 mg
(0.198 mmol) of [Na]trans-[Ru(DMSO)2Cl4] dissolved in
2 mL of DMSO. The resulting mixture was filtered and the
filtrate was stirred at room temperature for 1.5 h. A 50/50
acetone/diethylether solution (5.0 mL) was added to the
reaction mixture followed by an additional 5.0 mL of dieth-
ylether. The mixture was then placed at 4 ° C. Orange crys-
tals appeared within 48 h. The mother liquor was decanted
2. Experimental
1
and the crystals washed with diethylether. Yield: 67%. H
Ethanol (100%) was purchased from Pharmaco Prod-
ucts Inc. All other reagents and solvents were purchased
from Sigma Aldrich Inc. IR spectra were recorded in the
solid state on a Nicolet 4700 FTIR spectrometer between
NMR (D2O/ppm): ꢀ13.9 (br), (DMSO–S), ꢀ7.5 (vbr, H3,5
pyz), ꢀ2.1 (br, H2,6 pyz). This compound was reported,
but the solvate molecules appear different [27].
[NBu4]trans-[RuCl4(DMSO)(bpy)] (bpy = 4,40-bipyri-
dine) (4). 0.63 g of [NBu4]trans-[RuCl4(DMSO)2] (0.98
mmol) was dissolved in 15 mL of acetone and 0.60 g of 4,4-
bipyridine (3.8 mmol) was dissolved in 4 mL of acetone.
The ruthenium solution was added to the 4,4-bipyridine
solution to form a clear orange solution. After several hours
of stirring, the product was precipitated after the addition of
10 mL of cold diethylether. The yellow precipitate was col-
lected by filtration, washed with cold diethylether and vac-
uum dried. Yield: 86% (0.60 g). IR (cmꢀ1): 1595, 1612w
(bpy), 1109s (DMSO–S), 422m m(Ru–S), 349, 325s m(Ru–
1
4000 and 250 cmꢀ1. H NMR spectra were measured in
D2O, acetone-d6, CDCl3, and CD3CN on a Varian Gemini
300 MHz spectrometer. The solvent peaks at 4.80 ppm,
2.05 ppm, 7.26 ppm, and 1.94 ppm for D2O, CD3COCD3,
CDCl3, and CD3CN, respectively, were used as internal
1
standards for the H NMR spectra. Spectral abbreviations
used below: br (broad), vbr (very broad), s (strong), m
(medium), w (weak), sh (shoulder).
2.1. Synthesis
1
Cl). H NMR (acetone/ppm): ꢀ12.2 (br, DMSO–S), 7.5
0
0
0
0
[(DMSO)2H]trans-[Ru(DMSO)2Cl4],
[Na]trans-[Ru-
(br, bpy H2 ;6 ), 6.0 (br, bpy H3 ;5 ), ꢀ1.2 (br, bpy H3,5),
ꢀ6.0 (vbr, bpy H2,6).
(DMSO)2Cl4], and [NBu4]trans-[RuCl4(DMSO)2] (Bu =
n-butyl) were synthesized according to the literature meth-
ods [27,29].
[PPh4]trans-[RuCl4(DMSO)(bpy)] (5). 0.50 g of
[PPh4]trans-[RuCl4(DMSO)2] (0.68 mmol) was dissolved in
15 mL of CH2Cl2 and 0.40 g of 4,4-bipyridine (2.6 mmol)
was dissolved in 6 mL of CH2Cl2. The ruthenium solution
was added to the 4,4-bipyridine solution to form a clear
orange solution. After several hours of stirring, the product
was precipitated after the addition of 10 mL of cold diethyl-
ether. The yellow precipitate was collected by filtration,
washed with cold diethylether, and vacuum dried. Yield:
82% (0.45 g). IR (cmꢀ1): 1595, 1612w (bpy), 1107s
[PPh4]trans-[Ru(DMSO)2Cl4] (1). Tetraphenylphos-
phonium chloride (0.34 g, 0.92 mmol) dissolved in 6 mL
of H2O was added to a solution of [(DMSO)2H]trans-
[Ru(DMSO)2Cl4] (0.34 g, 0.61 mmol) dissolved in 3 mL
of H2O, while stirring. A yellow precipitate formed within
minutes. The precipitate was collected by filtration, washed
with diethylether and vacuum dried. Yield: 89%. IR
(cmꢀ1): 1107s m(DMSO–S), 416w m(Ru–S), 339, 319s
m(Ru–Cl). 1H NMR (CD3CN/ppm): ꢀ13.0 (DMSO–S),
7.95, 7.74 (phenyl protons).
1
(DMSO–S), 422m m(Ru–S), 331s,br m(Ru–Cl). H NMR
0
0
(CDCl3/ppm): ꢀ12.8 (br, DMSO–S), 7.5 (br, bpy H2 ;6 ),
0
0
[PPh4]trans-[Ru(DMSO)(pz)Cl4] (2). [PPh4]trans-
[Ru(DMSO)2Cl4] (1) (0.30 g, 0.40 mmol) was dissolved in
a mixture of 7 mL acetone and 4 mL acetonitrile, while
5.5 (br, bpy H3 ;5 ), ꢀ1.7 (br, bpy H3,5), 8.06 (br, phenyl pro-
tons). Anal. Calc. for C36H34Cl4N2OPSRu: C, 52.9; H, 4.17;
N 3.43. Found: C, 52.6; H, 3.94; N, 3.23%.

C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
3663
[PPh4]trans-[RuCl4(DMSO)(pym)] (pym = pyrimi-
dine) (6). 0.20 g of [PPh4]trans-[RuCl4(DMSO)2]
(0.27 mmol) was dissolved in 5 mL of CH2Cl2 and 0.15 g
of pyrimidine (0.98 mmol) was dissolved in 1 mL of ace-
tone. The ruthenium solution was added to the pyrimidine
solution to form a clear orange solution. After several
hours of stirring, the product was precipitated with the
addition of 10 mL of diethylether. The yellow precipitate
was collected by filtration, washed with diethylether, and
vacuum dried. Yield: 67% (0.133 g). IR (cmꢀ1): 1585,
1560 (pym), 1107s (DMSO–S), 421m m(Ru–S), 339, 324sh
The coordinates of the Pt atom were determined by direct
methods and all the other non-hydrogen atoms were found
by the usual Fourier methods. The refinement of the struc-
ture was done on F2 by full matrix least-squares analysis.
The hydrogen atom positions were fixed in their calculated
positions with Ueq = 1.2 Ueq (or 1.5 for methyl groups) of
the carbon to which they are bonded. Corrections were
made for absorption (semi-empirical from psi-scans for 2
and integration for 3), Lorentz and polarization effects.
The calculations were done using the Bruker SHELXTL sys-
tem [30]. The crystallographic data and details are shown
in Table 1.
1
m(Ru–Cl). H NMR (CD3CN/ppm): ꢀ13.0 (br, DMSO–
S), 6.34 (pym H4), ꢀ0.58 (br, pym H5), ꢀ1.7 (vbr, pym
H6), ꢀ6.5 (vbr, pym H2), 7.96, 7.78 (br, phenyl protons);
(CDCl3/ppm): ꢀ12.7 (br, DMSO–S), 6.32 (br, bpy H4),
ꢀ0.52 (br, H5), 8.16 (br, phenyl protons). Anal. Calc. for
C30H30Cl4N2OPSRu: C, 48.6; H, 4.05; N 3.78. Found: C,
48.4; H, 3.78; N, 3.77%.
3. Results and discussion
3.1. [PPh4]trans-[Ru(DMSO)2Cl4] (1)
This yellow compound was synthesized from the aque-
ous reaction of [(DMSO)2H]trans-[Ru(DMSO)2Cl4] with
tetraphenylphosphonium chloride.
2.2. Crystallographic measurements and structure resolution
½ðDMSOÞ2Hꢁtrans-½RuðDMSOÞ2Cl4ꢁ
The crystallographic measurements of crystals 2 and 3
þ ½PPh4ꢁCl ! ½PPh4ꢁtrans-½RuðDMSOÞ2Cl4ꢁ
were done on a Bruker P4 diffractometer using graphite-
monochromatized Mo Ka (k = 0.71073 A) radiation. The
H2O
˚
The synthesis and characterization of this ionic complex
has not been reported yet in the literature, therefore we give
a brief description. The IR spectrum of the compound
shows a m(S–O) vibration at 1107 cmꢀ1. Absorption at
416 cmꢀ1 was assigned to the metal stretching vibration
m(Ru–S) while those at 339 and 319 cmꢀ1 were attributed
to m(Ru–Cl). The NMR spectrum of 1 and all of the com-
plexes reported here show peaks that are characteristic of
complexes containing paramagnetic ruthenium(III). Pro-
tons close to the paramagnetic center have large line-width
(often some peaks are too wide to be observable) and are
shifted greatly upfield [31–33]. The peak at ꢀ13.0 ppm is
assigned to the coordinated DMSO (through the S atom).
cell dimensions were determined at room temperature,
from a least-squares refinement of the angles 2h, x and v
obtained for well-centered reflections. The data collection
was made by the 2h/x scan technique using the XSCANS pro-
gram [30]. The background time to scan time ratio was 0.5.
Table 1
Crystallographic data and experimental details
Crystal
Name
2
3
PPh4[Ru(DMSO)(pz)Cl4]
Na[Ru(DMSO)(pz)Cl4] Æ
DMSO
Chemical
formula
Mw
C30H30Cl4N2OPRuS
C8H16Cl4N2NaO2RuS2
740.46
502.21
ꢀ
3.2. [PPh4][Ru(DMSO)(pyrazine)Cl4] (2)
Space group
a (A)
P21/n (No. 14)
13.161(3)
17.070(4)
14.826(4)
90.
104.65(2)
90.
3222.5(14)
4
P1 (No. 2)
˚
7.0972(7)
10.6838(15)
12.379(2)
91.164(14)
93.48(12)
105.83(11)
900.7(2)
2
˚
b (A)
This new ionic complex was synthesized from the reac-
tion of the bis-DMSO Ru(III) ionic complex 1 with pyra-
zine (pz) as shown in the following equation:
˚
c (A)
a (°)
b (°)
c (°)
½PPh ꢁtrans-½RuðDMSOÞ Cl ꢁ þ pz
½PPh ꢁ
ꢀꢀꢀꢀꢀꢀꢀꢀ!
3
˚
4
4
4
2
Volume (A )
acetone=acetonitrile
Z
qcalc (g cmꢀ3
l(Mo Ka)
)
1.526
0.959
1.852
1.718
trans-½RuðDMSOÞðpzÞCl4ꢁ
(mmꢀ1
)
Alternatively, compound 2 was also synthesized from the
aqueous reaction of compound 3 with tetraphenylphospho-
nium chloride or tetraphenylphosphonium bromide.
The IR spectrum of 2 shows a m(S–O) vibration at
1108 cmꢀ1, a m(Ru–S) band at 420 cmꢀ1 and m(Ru–Cl)
vibrations at 342 and 328 cmꢀ1. The NMR spectrum shows
a peak at ꢀ12.6 ppm integrating to six protons assigned to
the coordinated DMSO, while the peak at ꢀ1.6 ppm inte-
grating to two protons is assigned to the protons (H3 and
H5) on the pyrazine ring. The protons on the pyrazine ring
F(000)
Reflections
collected
Observed
Reflections
(I > 2r(I))
R1 (I > 2r(I))
wR2 (all data)
S
1500
12656
498
10499
4778
4284
0.0327
0.0748
1.049
P
0.0307
0.0770
1.023
P
P
P
R1 = (jFo ꢀ Fcj)/ jFoj, wR2 = [ (w(Fo ꢀ Fc2)2)/ (w(Fo2)2)]1/2
.
2

3664
C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
(H2 and H6) closest to the paramagnetic ruthenium center
are seen in a very broad peak at ꢀ5.6 ppm (for labeling see
Chart 1).
1.328(5) A), but the angles C–N–C are different. The inter-
nal ring angle at the metal-bonded N1 atom is larger
(116.3(3)°) than the angle of the non-bonded N4 atom
(114.7(3)°) as observed in Pt(II) compounds of the
type cis- and trans-Pt(R2SO)(pz)Cl2 where the bonded
angle C2–N1–C6 is slightly larger than the C3–N4–C5
angle [35].
˚
Compound 2 was recrystallized from acetone/diethyl-
ether and the crystals were studied by crystallographic
methods. The results have shown that the orange crystals
consist of discrete complexed anions, [Ru(DMSO)(pz)Cl4]ꢀ
(Fig. 1) and [PPh4]+ cations. The complexed anion is the
trans isomer and the coordination around the Ru(III) cen-
ter is octahedral. The bond distances and angles are shown
in Table 2. The cis angles around the metal vary between
87.73(7)° and 92.66(3)°, while the trans angles are between
177.32(3)° and 179.07(7)°. The Ru–Cl bond distances range
In order to minimize the interactions with the rest of the
molecule, the pyrazine ligand is at ꢂ45° to the different Ru
square planes. Here, the dihedral angle between the pyra-
zine and the RuN1S1Cl1Cl3 plane is 47.65(11)°, while it
is 42.36(10)° with the RuN1S1Cl2Cl4 plane. In the DMSO
ligand, the O atom of DMSO was found almost in the
RuS1N1Cl1Cl3 plane, which reduces steric hindrance in
the complexed ion, since the larger methyl groups are far
from the four cis chloro ligands. The torsion angles
Cl1–Ru–S–O and Cl3–Ru–S–O are ꢀ7.14(15)° and
172.94(15)°, respectively. In this conformation of the
DMSO and pyrazine ligands, the energy of the molecular
ion is close to a minimum.
˚
from 2.3425(9) to 2.3589(10) A, the Ru–S bond is
˚
˚
2.2941(9) A and the Ru–N distance is 2.118(2) A. These
values are in agreement with published values found in a
few related structures [22,24,27,28,34].
The environment around the S atom in the DMSO
ligand is approximately tetrahedral but there are small
deformations. The O–S–C angles are larger (ave.
107.18(17)°) than the C–S–C angle (98.77(18)°) as
expected. The Ru–S–O angle (117.98(10)°) is also larger
than the Ru–S–C angles (ave. 111.95(13)°). The average
angle Ru–N–C is 121.9(2)°. The N1–C bond lengths (ave.
The PPh4 cations are normal. The average P–C bond
distance is 1.800(3) A with an average C–P–C angle of
109.48(13)°. No H-bonds are expected in this crystal. The
ions are held together in the crystal by electrostatic forces
and by van der Waals interactions.
˚
˚
1.332(4) A) are not different from those of N4–C (ave.
O
O
Cl
Cl
Cl
H3C
H3C
CH3
(1)
S
Ru
S
P
Cl
CH3
O
2
3
Cl
P
(2)
(3)
Cl
1
N 4
H3C
H3C
N
S
Ru
Cl
Cl
6
5
.
Na
DMSO
(4)
(5)
N
P
O
2
3
5
Cl
2'
3'
Cl
1
N
1'
H3C
4'
4
N
S
Ru
H3C
Cl
6
5'
Cl
6'
O
2
3
N
Cl
Cl
Cl
1
H3C
H3C
4
N
(6)
S
Ru
P
Cl
5
6
Chart 1. Ruthenium(III) molecular structures.

C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
3665
Table 2
˚
Bond distances (A), bond and torsion angles (°)
2
3
Ru–Cl1
Ru–Cl2
Ru–Cl3
Ru–Cl4
Ru–N1
Ru–S1
S1–O1
S1–C (ave.)
S2–O2
2.3425(9)
2.3449(9)
2.3520(8)
2.3589(10)
2.118(2)
2.2941(9)
1.468(2)
1.787(3)
2.3754(7)
2.3458(7)
2.3395(8)
2.3684(7)
2.1257(19)
2.3027(7)
1.4705(19)
1.770(3)
1.496(2)
1.784(3)
1.343(3)
1.333(3)
S2–C (ave.)
N1–C (ave.)
N4–C (ave.)
P1–C (ave.)
N1–Ru–S1
N1–Ru–Cl1
N1–Ru–Cl2
N1–Ru–Cl3
N1–Ru–Cl4
S1–Ru–Cl1
S1–Ru–Cl2
S1–Ru–Cl3
S1–Ru–Cl4
Cl1–Ru–Cl2
Cl1–Ru–Cl3
Cl1–Ru–Cl4
Cl2–Ru–Cl3
Cl2–Ru–Cl4
Cl3–Ru–Cl4
Ru–N1–C (ave.)
Ru–S1–O1
Ru–S1–C (ave.)
O1–S1–C (ave.)
C–S1–C
1.332(4)
1.328(5)
1.800(3)
179.07(7)
177.68(6)
88.27(7)
90.08(7)
89.91(7)
87.73(7)
92.66(3)
90.02(4)
89.16(3)
92.15(4)
91.08(4)
178.18(3)
90.39(4)
89.00(4)
177.32(3)
89.46(4)
121.4(2)
88.35(6)
89.98(6)
89.29(6)
89.25(6)
93.96(3)
89.86(3)
88.40(3)
91.04(2)
87.95(3)
177.74(2)
88.55(2)
92.14(3)
176.43(2)
91.34(3)
121.64(16)
117.73(8)
112.15(12)
106.39(17)
100.4(2)
105.99(15)
98.49(17)
116.7(2)
115.2(2)
Fig. 1. ORTEP view of the [Ru(DMSO)(pz)Cl4]ꢀ anion in crystal 2.
Ellipsoids are shown at 40% probability level and the H atoms are of
arbitrary size.
3.3. [Na][Ru(DMSO)(pyrazine)Cl4] Æ DMSO (3)
This compound was synthesized from the reaction of
[Na][Ru(DMSO)2Cl4] with pyrazine in acetone and DMSO
similar to the procedure already reported.
½Naꢁ½RuðDMSOÞ Cl ꢁþpzacetone½Naꢁ½RuðDMSOÞðpzÞCl ꢁꢃDMSO
ꢀꢀ!
117.98(10)
111.95(13)
107.18(17)
98.77(18)
4
4
2
DMSO
The orange compound was crystallized in a mixture of ace-
tone and diethylether and the crystals were studied by X-
ray diffraction methods. The results have shown that the
compound crystallized with a molecule of solvent (DMSO).
The reported compound [27], which was not studied by
crystallographic methods, contained 1.5 molecule of
DMSO and 0.5 molecule of H2O, although it was crystal-
lized from the same solvents.
O1–S2–C (ave.)
C–S2–C
C2–N1–C6
C3–N4–C5
C–P–C (ave.)
Cl1–Ru–S1–O1
Cl3–Ru–S1–O1
Cl–Ru–N1–C (ave.)
116.3(3)
114.7(3)
109.48(13)
ꢀ7.14(15)
172.94(15)
ꢂ45
ꢀ161.74(11) (Cl2)
21.71(11) (Cl4)
ꢂ45
Fig. 2 shows the labeling scheme of the asymmetric unit
in crystal 3. The complexed anion is the trans isomer and
the coordination around the Ru(III) center is octahedral.
The bond distances and angles are shown in Table 2. The
cis angles around the metal vary between 87.95(3)° and
93.96(3)°, while the trans angles are between 176.43(2)°
and 177.74(2)°. The Ru–Cl bond distances range from
Distances and angles around the Na atom in 3
Na–O1
2.303(2)
2.519(2)
Na–O2
Na–Cl10
2.324(2)
2.7760(13)
2.8404(13)
86.13(8)
76.74(6)
92.89(8)
106.54(7)
92.00(6)
87.33(6)
Na–N40
Na–Cl4
2.9222(12)
92.97(9)
175.65(8)
104.86(7)
89.89(6)
162.13(7)
154.51(7)
104.10(4)
79.17(3)
135.34(13)
100.17(3)
111.28(3)
Na–Cl40
O1–Na–O2
O1–Na–Cl10
O1–Na–Cl40
O2–Na–Cl10
O2–Na–Cl40
N40–Na–Cl4
Cl10–Na–Cl4
Cl4–Na–Cl40
Na–O1–S1
Na0–Cl1–Ru
Na–Cl4–Ru
O1–Na–N40
O1–Na–Cl4
O2–Na–N40
O2–Na–Cl4
N40–Na–Cl10
N40–Na–Cl40
Cl10–Na–Cl40
Na–N4–C (ave.)
Na–O2–S2
Na0–Cl4–Ru
Na–Cl4–Na0
˚
˚
2.3395(8) to 2.3754(7) A, the Ru–S bond is 2.3027(7) A
˚
and the Ru–N distance is 2.1257(19) A. These values are
72.25(3)
very similar to those observed in crystal 2 described above
and they are in agreement with published values found in a
few related structures [22,24,27,28].
The environment around the bonded S atom in the
DMSO ligand is approximately tetrahedral but there are
small deformations. The O–S1–C angles are larger (ave.
106.39(17)°) than the C–S1–C angle (100.4(2)°) as
expected. The Ru–S–O angle (117.73(8)°) is also larger
than the Ru–S–C angles (ave. 112.15(17)°). The average
angle Ru–N–C is 121.64(16)°. The N1–C bonds (ave.
122.08(16)
124.79(12)
98.55(3)
100.83(3)
˚
1.343(3) A) are not very different from the N4–C bonds
˚
(ave. 1.333(3) A), but the angles C–N–C are slightly differ-
ent. The internal ring angle at the metal-bonded N1 atom is
slightly larger (116.7(2)°) than the angle of the non-bonded

3666
C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
21.71(11)°, respectively. The plane of pyrazine is located
at about ꢂ45° from the two different Ru(III) square planes.
The dihedral angle between the pyrazine and the
RuN1S1Cl2Cl4 plane is 41.56(6)°, while it is 48.18(7)°
with the RuN1S1Cl1Cl4 plane. This conformation of the
molecular ion is similar to the one observed in crystal
2 and corresponds approximately to the one of lowest
energy.
The environment around the Na atoms was closely
examined. There are six atoms in its close environment.
The distances and angles are shown in Table 2. The geom-
etry is a distorted octahedron. Three of the close contacts
are shown in Fig. 2. The Na–O1 (from bonded DMSO)
and Na–O2 (unbonded DMSO) distances are 2.303(2)
˚
and 2.324(2) A, respectively. The Na–Cl4 distance is
´
˚
2.9222(12) A. There are three other short contacts with
0
0
˚
˚
Fig. 2. ORTEP view of [Na][Ru(DMSO)(pz)Cl4] Æ DMSO (3) showing the
labelling scheme of the asymmetric unit. Ellipsoids are shown at 40%
probability level and the H atoms are of arbitrary size.
the 0following: N4 (2.519(2) A), Cl1 (2.7760(13) A), and
˚
Cl4 (2.8404(13) A). The chloro ligand Cl4 forms a bridge
between two Na atoms, while Cl1 forms a bridge between
a Na and a Ru atom. The two other Cl ligands are not
involved with the Na atoms. The DMSO ligand forms a
bridge between a Ru (through its S atom) atom and a Na
(through its O) atom, while the S atom of the second
DMSO molecule is free, but its O atom is in the close envi-
ronment of the Na atom. There are important distortions
from the octahedral structure around the Na atom. The
cis angles vary between 72.25(3)° (Cl0–Na–Cl40) and
106.54(7)° (O2–Na–Cl4), while the trans angles are between
154.51(7)° and 175.65(8)°.
The Na atom has a very important role in this structure.
It bridges the different complexed ions to form infinite poly-
meric chains or ribbons parallel to the b axis. One of these is
shown in Fig. 3. The two ligands Cl2 and Cl3, which are not
involved with the Na atoms point towards the outside of the
chain, along with S2 and the two C atoms of the free DMSO
molecule. Several cycles are formed, ranging from four
atoms (Ru, Cl1, Na, Cl4) to seven atoms (Ru, Cl1, Na,
Cl4, Na, O1, S1). These neutral ribbons are held together
by van der Waals forces. There may be weak p–p stacking
N4 atom (115.2(2)°), as observed in crystal 2, which also
contains a monodentate pyrazine ligand.
Complex 3 crystallized with a molecule of DMSO which
is not bonded to the Ru(III) atom. The S2–O2 bond is
˚
longer (1.496(2) A) than the S1–O1 bond distance in crys-
˚
tals 2 and 3 (ave. 1.469(2) A) as expected when the S atom
is not coordinated to a metal. When the binding site of
DMSO is the S atom, the order of the S–O bond increases
when compared to the free molecule, while it is reduced if
the molecule is bonded to the metal atom through its O
atom. The NMR and IR spectra are in agreement with
the published data. Only one m(S–O) band was observed
at 1104 cmꢀ1 [27].
The O atom of the bonded DMSO ligand was found close
to the RuS1N1Cl2Cl4 plane, which reduces steric hindrance
in the complexed anion, since the larger methyl groups are
far for the four cis chloro ligands. The torsion angles Cl2–
Ru–S1–O1 and Cl4–Ru–S1–O1 are ꢀ161.74(11)° and
Fig. 3. ORTEP view of a ribbon in compound 3 showing the octahedral environment around the Na atom (---), which bridges the anions
[Ru(DMSO)(pz)Cl4]ꢀ.

C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
3667
interactions of the pyrazine ligands, as the distance between
pyrazine pairs shown in Fig. 3 is 3.548(16) A [36].
3.5. [PPh4]trans-[Ru(DMSO)(pym)Cl4] (6)
˚
A few related structures were reported with the sodium
cation. In [Na][Ru(DMSO)(NH3)Cl4] Æ 2DMSO and
[Na][Ru(DMSO)(Im)Cl4] Æ H2O, CH3COCH3 [22], the
environment around the Na atom is tetrahedral with four
[PPh4]trans-[Ru(DMSO)(pym)Cl4] (6) was prepared
from [PPh4]trans-[Ru(DMSO)2Cl4] in methylene chloride
as shown in the following equation:
½PPh4ꢁtrans-½RuðDMSOÞ2Cl4ꢁ
˚
Na–O distances between 2.272(4) and 2.489(3) A. But the
þ pyrimidine
½PPh ꢁ½RuðDMSOÞðpymÞCl ꢁ
ꢀꢀꢀꢀꢀꢀꢀꢀ!
4
4
long-range arrangement in the crystal was not discussed.
A few other related structures containing Na ions were
published, but the environment around the Na atom was
not considered [27]. In these structures, the role of the
Na ions in the architecture, besides its counterion function,
was not studied.
In crystal 3, the unbonded DMSO molecule plays also a
very important role in the formation of the chains. In a few
reported structures containing the same cation, the chains
are not formed, but rather shorter oligomers [22] contain-
ing two Ru(III) and two Na atoms were produced. For
the latter structures, the tetrahedral environment around
the Na atoms is formed with four O atoms from DMSO
or H2O molecules.
methylene chloride
The NMR spectrum of compound 6 in acetonitrile solution
showed, along with signals for the tetraphenylphospho-
nium cation, five peaks for the protons of the coordinated
ligands. The signal at ꢀ13.0 ppm is assigned to the coordi-
nated DMSO as expected. There are four peaks seen for the
pyrimidine ligand as each proton is unique in this case due
to the loss of symmetry in the ligand once it has coordi-
nated. The peak at 6.34 ppm has the narrowest line-width
and is therefore assigned to the proton furthest from the
paramagnetic center, H4 [31]. The peak at ꢀ0.58 ppm is as-
signed to the H5 proton similar to complex 3. Two very
broad peaks are observed at ꢀ1.7 and ꢀ6.5 ppm and are
assigned to H6 and H2, respectively, those closest to the
paramagnetic ruthenium center. In chloroform solution
the peaks were observed at 6.32, ꢀ0.52, and ꢀ12.7 for
the H4, H5, and DMSO protons, respectively. The H2
and H6 protons were too broad to be seen. The IR spec-
trum of 6 shows a terminal pym mode at 1585 cmꢀ1 along
with a m(S–O) vibration at 1107 cmꢀ1, a m(Ru–S) band at
3.4. [NBu4]trans-[RuCl4(DMSO)(bpy)] (4) and
[PPh4]trans-[RuCl4(DMSO)(bpy)] (5)
[PPh4]trans-[Ru(DMSO)(bpy)Cl4]
(5)
(bpy = 4,40-
bipyridine) was prepared from [PPh4]trans-[Ru(DM-
SO)2Cl4] in methylene chloride as shown in the following
equation:
421 cmꢀ1, and m(Ru–Cl) vibrations at 339 and 324 cmꢀ1
.
½PPh4ꢁtrans-½RuðDMSOÞ2Cl4ꢁ
4. Conclusion
þ 4; 40-bpy
½PPh ꢁ½RuðDMSOÞðbpyÞCl ꢁ
ꢀꢀꢀꢀꢀꢀꢀꢀ!
4
4
methylene chloride
A library search in the Cambridge data file has revealed no
Ru complexes containing both a sulfoxide and a monoden-
tate pyrazine ligand. The two structures are also the first
examples of Ru(III) compounds containing a monodentate
pyrazine ligand. Three structures containing the pyrazine
ligand bridging two Ru(III) atoms were found. These are
the symmetric dimers Na[(DMSO)Cl4Ru(l-pz)RuCl4-
(DMSO)] Æ H2O Æ DMSO [27] and (TMSO)2 H[(TMSO)Cl4-
Ru(l-pz)RuCl4(TMSO)] Æ CH3COCH3 (where TMSO =
tetramethylenesulfoxide) [34], and the unsymmetrical NH4-
[(DMSO)Cl4Ru(l-pz)RuCl3(S–DMSO)(O–DMSO)] Æ CH3-
OH dimer [28]. It seems that pyrazine usually function as a
bridging ligand and it is more difficult to prepare complexes
containing monodentate pyrazine ligands. In the preparation
of these types of complexes, the potential bridging ligand was
added in a large excess, in order to reduce the formation of
pyrazine-bridged oligomeric species. The same is true for
the bipyridine and pyrimidine complexes.
The NMR spectrum of compound 5 showed, along with
signals for the tetraphenyl phosphonium cation, several
peaks for the protons of the coordinated ligands. The sig-
nal at ꢀ12.8 ppm is assigned to the coordinated DMSO
while the peak at ꢀ1.7 ppm is assigned to the protons
(H3 and H5) on the coordinated pyridine ring but furthest
from the paramagnetic ruthenium(III) center. The protons
closest to the ruthenium center (H2 and H6, Chart 1) are
not observed due to a line-width that is too broad for the
peak to be seen. The protons on 0the second pyridine ring
0
0
are observed at 5.5 (H3 and H5 ) and 7.5 ppm (H2 and
0
H6 ) for the two pairs closer and further from the ruthe-
nium atom, respectively. The IR spectrum of 5 shows a ter-
minal bpy mode at 1595 cmꢀ1 along with a m(S–O)
vibration at 1107 cmꢀ1, a m(Ru–S) band at 422 cmꢀ1, and
a m(Ru–Cl) vibration at 331 cmꢀ1
.
[NBu4]trans-[Ru(DMSO)(bpy)Cl4] (4) was prepared
similarly to complex 5, however the reaction was done in
acetone solution. The NMR and IR spectral characteriza-
tion and signal assignments were also similar, except in
the proton NMR, where all four sets of bpy proton pairs
were observed in this case. The protons closest to the ruthe-
nium atom (H2 and H6), unobservable for complex 5 are
seen as a very broad peak at ꢀ6.0 ppm.
+
þ
The use of cations like PPh4 or NR4 which do not
form H-bonds or other strong electrostatic attractions like
alkali metals should prevent the formation of infinite
chains or other materials with extended structures. In the
few published structures containing Na cations with a tet-
rahedral environment, small oligomers are formed [22].
In the case of crystal 3, the Na+ cations have an octahedral

3668
C.M. Anderson et al. / Polyhedron 26 (2007) 3661–3668
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environment and it can form bridges between the Ru(III)
complexed anions to form a ID extended structure. It
might be interesting to replace the Na atom by a larger
metal like Ba, which could accept a larger environment,
for example, a coordination number of 8 and form multidi-
mensional (2D or 3D) materials. The formation of such
species is an area of current interest in supramolecular
chemistry. The study of multidimensional compounds is
important in material science, especially for paramagnetic
species.
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15/00, A61K 31/28, WO 98/00431, 1998.
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Acknowledgements
The authors are grateful to the Natural Science and
Engineering Research Council of Canada for financial sup-
port. We also thank Orgometa, Skylar Ferrara, and Bard
College.
Appendix A. Supplementary material
CCDC 637826 and 637827 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic 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
article can be found, in the online version, at doi:10.
1016/j.poly.2007.03.041.
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