X-ray structures and spectral characterization of simple ruthenium(II) nitrosyl complexes involving the [RuCl4(NO)(DMSO)]- or [RuCl4(NO)(H2O)]- complex anions

Article abstract of DOI:10.1016/j.molstruc.2010.05.033

Three simple ruthenium nitrosyl complexes of the compositions [Et ₄N][RuCl₄(NO)(DMSO)] (1), [Bu₄N][RuCl ₄(NO)(DMSO)] (2), and [Ph₄P][RuCl₄(NO)(H ₂O)]·DMSO (3); where DMSO = dimethyl sulfoxide, Et = ethyl, Bu = butyl and Ph = phenyl, have been synthesized in the single crystal form and their molecular and crystal structures have been determined. The Ru(II) centre is six-coordinated by four chlorido ligands in the equatorial plane and by the N (from NO⁺) and O (from DMSO in 1 and 2, H₂O in 3) atoms in the axial positions forming an RuCl₄NO donor set. The complexes have been also characterized by infrared and electronic spectroscopies, conductivity measurements, and thermogravimetric (TG) and differential thermal (DTA) analyses. The spectroscopic investigation is consistent with the {Ru(NO)}⁶ formulation with NO⁺ coordinated to the diamagnetic Ru(II) centre. The geometries of the complex anions as well as spectroscopic properties were calculated at the B3LYP/LANL2DZ/cc-pVTZ level of theory. These results were compared with those experimentally determined.

Full text of DOI:10.1016/j.molstruc.2010.05.033

Journal of Molecular Structure 977 (2010) 203–209
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Journal of Molecular Structure
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X-ray structures and spectral characterization of simple ruthenium(II) nitrosyl
complexes involving the [RuCl4(NO)(DMSO)]ꢀ or [RuCl4(NO)(H2O)]ꢀ complex
anions
ˇ
*
ˇ
ˇ
Miroslava Matiková-Malarová, Radka Novotná, Zdenek Trávnícek
ˇ
Department of Inorganic Chemistry, Faculty of Science, Palacky´ University, Trída 17. listopadu 12, CZ-771 46 Olomouc, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Three simple ruthenium nitrosyl complexes of the compositions [Et4N][RuCl4(NO)(DMSO)] (1), [Bu4N]
[RuCl4(NO)(DMSO)] (2), and [Ph4P][RuCl4(NO)(H2O)]ꢁDMSO (3); where DMSO = dimethyl sulfoxide, Et =
ethyl, Bu = butyl and Ph = phenyl, have been synthesized in the single crystal form and their molecular
and crystal structures have been determined. The Ru(II) centre is six-coordinated by four chlorido ligands
in the equatorial plane and by the N (from NO+) and O (from DMSO in 1 and 2, H2O in 3) atoms in the axial
positions forming an RuCl4NO donor set. The complexes have been also characterized by infrared and
electronic spectroscopies, conductivity measurements, and thermogravimetric (TG) and differential ther-
mal (DTA) analyses. The spectroscopic investigation is consistent with the {Ru(NO)}6 formulation with
NO+ coordinated to the diamagnetic Ru(II) centre. The geometries of the complex anions as well as spec-
troscopic properties were calculated at the B3LYP/LANL2DZ/cc-pVTZ level of theory. These results were
compared with those experimentally determined.
Received 3 March 2010
Received in revised form 21 May 2010
Accepted 21 May 2010
Available online 1 June 2010
Keywords:
Ruthenium(II) complexes
Crystal structures
Nitrosyl
Infrared spectroscopy
Thermal analysis
DFT calculations
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
lation of {Ru(NO)}6 is now the generalized description of the
RuANO bond in octahedral ruthenium nitrosyl complexes, where
Nitric oxide (NO) is a typical non-innocent ligand, which can
coordinate to a transition metal centre resulting in a linear or bent
MANAO geometry. It can assume three possible oxidation states
NO+, NO0 and NO depending on the nature of the central atom
and the coordination environment [1,2]. NO has become recog-
nized as an important molecule in a diverse array of physiological
processes. It is known to play critical roles in different cells and tis-
sues, in which it exhibits several functions, including cardiovascu-
lar control, neuronal signalling, inhibition of platelet aggregation
and immunological responses [3–6]. Recently, it has been demon-
strated that NO is involved as a mediator in one tumour induced
angiogenic process, which is a key step in the formation of metas-
tasis [7]. Nitric oxide is a radical molecule produced by many cells
in the human body. Due to high affinity of ruthenium for NO, a
number of ruthenium complexes are currently being investigated
as potential therapeutic NO scavengers, e.g. for the treatment of
septic shock [8–10]. On the other hand, ruthenium nitrosyl com-
plexes are being studied as controlled NO-releasing agents with
pharmaceutical applications ranging from treatment of high blood
pressure to their potential use as antitumour agents capable of
releasing cytotoxic NO within tumour cells [9,11–14]. The formu-
NO+ is bound to the diamagnetic Ru(II) centre [15]. The release of
NO for delivery to biological targets can be induced either by pho-
tochemical activation or by a one electron reduction at NO+ to yield
coordinated NO0, which is subsequently released [12–14,16]. The
presence of NO in cells may result in DNA cleavage and cell apop-
tosis, as has been observed for pancreatic, leukaemia, and neuronal
cells [17–19]. The possibility to act as NO-donors and thus as novel
antitumour agents was suggested e.g. for the complexes mer,cis-
[RuCl3(NO)(DMSO)2] and cis,mer-[RuCl2(NO)(py)3](BF4) (py = pyri-
dine) [20,21].
NAMI-A, i.e. [ImH][RuCl4(DMSO)(Im)], where Im = imidazole,
which has been recently introduced into phase I clinical trials, is
very effective in selectively inhibiting the formation and growth
of spontaneous metastases. The low cytotoxicity of NAMI-A and re-
lated Ru–DMSO complexes of the type (HL)[RuCl4(DMSO)(L)]
(L = e.g. indazole, 1,2,4-triazole, 4-amino-1,2,4-triazole, 1-methyl-
1,2,4-triazole) shows that their primary mechanism of action is dif-
ferent from that of cytostatic cisplatin-derived drugs. It has been
suggested that the activity of NAMI-A against disseminated tu-
mours might be related with NO metabolism in vivo [20–22].
In this paper, we describe the synthesis, spectroscopic, thermal
and structural characterizations of three simple ruthenium nitrosyl
complexes [Et4N][RuCl4(NO)(DMSO)] (1) [Bu4N][RuCl4(NO)(DMSO)]
(2) and [Ph4P][RuCl4(NO)(H2O)]ꢁDMSO (3). Although the synthesis
* Corresponding author. Tel.: +420 585 634 352; fax: +420 585 634 954.
ˇ
E-mail address: zdenek.travnicek@upol.cz (Z. Trávnícek).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.05.033

ˇ
M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
204
of complex 2 has already been described in the literature [20], its
crystal structure is reported for the first time in this paper. Many
coordination compounds involving the above-mentioned complex
anions have often been successfully used as precursors for the
preparation of other chemically and structurally more complicated
ruthenium nitrosyl complexes, which may be bearers of various
types of biological activity. It has already been reported that
complexes of the composition [X][RuCl4(NO)(DMSO)], where X =
(DMSO)2H+, Bu4N+ and ImH+, can be convenient for the preparation
of new ruthenium nitrosyl complexes, as the OAbonded DMSO can
be relatively easily replaced by a suitable NAdonor ligand [20,23].
For example, [(Im)2H][RuCl4(Im)(NO)] was prepared from [ImH]
[RuCl4(NO)(DMSO)] and is a proven NO-releasing agent [20]. Aqua
ligands can be also substituted, as was shown e.g. by the use of
[RuCl3(NO)(H2O)2] for the preparation of cis-[RuCl2(NO)(terpy)]Cl
(terpy = terpyridine), which was shown to posses significant cyto-
toxicity on A2780 (human ovarian carcinoma) cell lines with an
2.2. X-ray crystallography
X-ray data of 1–3 were collected on a four-circle j-axis diffrac-
tometer Xcalibur2 (Oxford Diffraction Ltd.) equipped with a Sa-
phire2 CCD detector with Mo K radiation (monochromator
a
Enhance, Oxford Diffraction Ltd.) at 120 K. The CRYSALIS software
package [30] was used for data collection and reduction. A multi-
scan absorption correction integrated in the CRYSALIS software
was applied on the data of all three complexes. All three structures
were determined by direct methods using SHELXS-97 and refined
anisotropically on F2 using a full-matrix least-squares procedure
by SHELXL-97 [31]. All H-atoms were found in the difference Fou-
rier maps, and they were refined using a riding model, except for
those of the water molecule, which were refined freely with the
fixed Ueq. Crystal data and structure refinements of 1–3 are given
in Table 1. The selected geometric parameters are displayed in Ta-
bles 2 and 3. Non-bonding interactions present within the crystal
structures of the complexes were interpreted as well as the figures
were drawn using Diamond 3.1e [32].
IC50 value of 0.49 lM [24].
2. Experimental
2.3. Synthesis of the complexes
2.1. General consideration
2.3.1. Synthesis of [Et4N][RuCl4(NO)(DMSO)] (1)
0.5 g (1 mmol) of [(DMSO)2H][RuCl4(NO)(DMSO)] was partly
dissolved in 10 ml of ethanol. Then, 0.17 g (1 mmol) of solid tet-
ra-n-ethylammonium chloride [Et4N]Cl was added. The resulting
suspension was stirred at room temperature. After 30 min, the
undissolved solid was filtered off and the solution was left aside
for crystallization. After 3 days of standing at room temperature,
violet prismatic crystals suitable for single-crystal X-ray analysis
formed. The crystals were collected by filtration, washed with ace-
tone and dried under vacuum. Yield 35%. [Et4N][RuCl4(NO)(DMSO)]
(1): Anal. Calcd. for C10H26N2Cl4O2Ru1S1 (481.26): C, 25.0; H, 5.4; N,
5.8%; Found: C, 24.7; H, 5.2; N 5.3%. kM = 72.2 S cm2 molꢀ1. IR
Ruthenium(III) chloride hydrate (Aldrich), sodium nitrite (Fish-
er), sodium hydroxide (Fisher), tetra-n-butylammonium terafluo-
roborate (Aldrich), tetra-n-ethylammonium chloride (Aldrich),
tetra-n-phenylphosphonium chloride (Merck), dimethyl sulfoxide
(Lach-Ner), nitromethane (Lach-Ner), sulphuric acid (Lach-Ner)
and hydrochloric acid were obtained from commercial sources
and used without further purification. [(DMSO)2H][RuCl4(DMSO)2]
[25], and [(DMSO)2H][RuCl4(NO)(DMSO)] [20], the starting com-
pounds used for the syntheses of the title complexes, were pre-
pared according to previously published procedures.
Elemental analyses (C, H, N) were performed on a Flash EA-
1112 Elemental Analyser (Thermo Finnigan). Infrared spectra were
obtained on a Nexus 670 FT–IR spectrometer (Thermo Nicolet)
using KBr (4000–400 cmꢀ1) and Nujol (600–200 cmꢀ1) techniques.
Electronic absorption spectra in the solid state were recorded on a
Lambda40 spectrometer (Perkin–Elmer) in the 320–800 nm range.
Conductivity measurements of the complexes in N,N0-dimethyl-
formamide (DMF) solutions (10ꢀ3 M) were performed on a Con-
d340i/SET conductometer (WTW) at 25 °C. The room
temperature magnetic susceptibilities were measured using an
MSB-AUTO magnetic balance (Sherwood Scientific, Ltd.). Simulta-
neous thermogravimetric (TG) and differential thermal analyses
(DTA) were carried out using a thermal analyzer Exstar TG/DTA
6200 (Sieko Instruments, Inc.) with the sample weights of about
10 mg. TG/DTA studies were performed in ceramic pans in the
temperature range of 25–700 °C, with a 5 °C temperature gradient
in dynamic air atmosphere. X-ray powder diffraction patterns of
the thermal decomposition product of complex 1, as a representa-
tive example, were taken on an XRD-7 powder diffractometer
(Seifert) and interpreted using the ZDS system and PDF-2 database
(ICCD No. 43-1027) [26,27]. The geometry and IR spectral vibra-
tions of the complex anions [RuCl4(NO)(DMSO)]ꢀ (present in com-
plexes 1 and 2) and [RuCl4(NO)(H2O]ꢀ (in 3) were optimized at the
B3LYP/LANL2DZ/cc-pVTZ level of theory by means of a Spartan06
software package [28]. The results are presented in Tables S1 and
S2 in Appendix A. Supplementary data. The theoretical electronic
absorption spectra of the complex anions [RuCl4(NO)(DMSO)]ꢀ
and [RuCl4(NO)(H2O)]ꢀ in vacuum have been obtained by means
of time-dependent DFT method (TD-DFT; Gaussian03 program
[29]) at the above-mentioned level of theory and the calculated
transition energies (in nm) are reported in Table S3 in Appendix
A. Supplementary data.
(cmꢀ1): 3012w, 2987m, 2980w, 2939w, 2903w, 1857vs
1458m, 1396m, 1385m, 1308m, 1286w, 1017m, 981m, 922vs
as(S@O), 794m, 625w (RuAN), 605w d(RuANO); (far IR) 491s,
471s (RuAO), 346vs, 324vs (RuACl), 171vs. UV–Vis spectrum
(kmax = 501 nm).
mas(N@O),
m
m
m
m
2.3.2. Synthesis of [Bu4N][RuCl4(NO)(DMSO)](2)
A single crystal of complex 2 suitable for X-ray analysis was
prepared by a slightly modified procedure described by Serli et
al. [20]. 0.25 g (0.5 mmol) of [(DMSO)2H][RuCl4(NO)(DMSO)] was
dissolved in 2 ml of water. Then, 0.28 g (1 mmol) of tetra-n-ethy-
lammonium tetrafluoroborate [Bu4N](BF4) dissolved in 1.4 ml of
water was added. A violet precipitate formed immediately. The
resulting suspension was stirred for 15 min at room temperature.
The powder portion was removed by filtration. The filtrate was left
aside for crystallization and after 2 days, violet single crystals of 2
formed in the solution. The crystals were collected by filtration,
washed with acetone and dried under vacuum. Yield 20%. [Bu4N][-
RuCl4(NO)(DMSO)](2): Anal. Calcd. For C18H42N2Cl4O2Ru1S1
(593.48): C, 36.4; H, 7.1; N, 4.7%; Found: C, 36.0; H, 7.0; N 4.3%.
kM = 90.7 S cm2 molꢀ1. IR (cmꢀ1): 2961m, 2930m, 2873w, 1867
m
s(N@O), 1472 m, 1419w, 1406w, 1315w, 1160vw, 1030w, 980w,
937m s(S@O), 883w, 734w, 634w (RuAN), 596w d(RuANO);
(far IR) 492s s(RuAO), 328s s(RuACl), 162w. UV–Vis spectrum
(kmax = 506 nm).
m
m
m
m
2.3.3. Synthesis of [Ph4P][RuCl4(NO)(H2O)]ꢁDMSO (3)
The aqueous-ethanolic (80:20, v/v) solution containing
[(DMSO)2H][RuCl4(DMSO)2] (0.55 g, 1 mmol) and [Ph4P]Cl (0.56 g,
1.5 mmol) was bubbled with nitric oxide for over two hours. Nitric
oxide was generated by dripping concentrated sulphuric acid onto
NaNO2, passing it through a saturated aqueous solution of NaOH.

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M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
205
Table 1
Crystal data and structure refinements for 1–3.
1
2
3
Molecular formula
Formula weight
Crystal system
Space group
C
10H26Cl4N2O2RuS
C18H42Cl4N2O2RuS
593.47
Triclinic
C26H28Cl4NO3PRuS
708.39
Monoclinic
P21/c
481.26
Triclinic
P–1
P–1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
8.2581(2)
8.5397(2)
14.2219(3)
83.7808(18)
73.996(2)
84.576(2)
2
956.21(4)
1.671
115(2)
11.2853(3)
11.3484(3)
12.5056(3)
69.535(2)
67.504(2)
85.652(2)
2
1383.22(6)
1.425
120(2)
9.7923(3)
20.3750(6)
15.2676(5)
90.0
95.412(3)
90.0
a
(°)
b (°)
c
(°)
Z
4
V (Å3)
3032.59(15)
1.552
120(2)
Dcalc (Mg cmꢀ3
T (K)
)
l
(mmꢀ1
)
1.489
1.044
1.019
Data collection
Index ranges
ꢀ9 6 h 6 9
ꢀ10 6 k 6 9
ꢀ16 6 l 6 12
2.61–25.00
8074
ꢀ13 6 h 6 11
ꢀ12 6 k 6 13
ꢀ14 6 l 6 12
2.65–25.00
11,165
ꢀ11 6 h 6 11
ꢀ23 6 k 6 24
ꢀ13 6 l 6 18
3.10–24.99
21,175
h (° ranges)
Reflections collected
Independent reflections
Goodness-of-fit on F2
3343 [Rint = 0.0150]
1.276
4813 [Rint = 0.0209]
1.071
5328 [Rint = 0.0337]
1.179
R indices [I P 2
r
(I)]
R1 = 0.0174
wR2 = 0.0484
R1 = 0.0215
wR2 = 0.0619
0.459 and ꢀ0.383
R1 = 0.0239
wR2 = 0.0726
R1 = 0.0333
wR2 = 0.0879
0.725 and ꢀ0.477
R1 = 0.0463
wR2 = 0.1044
R1 = 0.0567
wR2 = 0.1076
0.911 and ꢀ0.789
R indices (all data)
Max./min. residual electron density (e Åꢀ3
)
Table 2
Selected bond lengths and angles for 1 and 2 (Å, °).
powder formed. The crystals were collected by filtration, washed
with acetone and dried under vacuum. Yield 45%. [Ph4P][RuCl4
(NO)(H2O)]ꢁDMSO (3): Anal. Calcd. for C26H28N1Cl4O3P1Ru1S1
(708.43): C, 44.1; H, 4.0; N, 2.0%; Found: C, 44.4; H, 3.9; N 1.6%.
kM = 57.1 S cm2 molꢀ1. IR (cmꢀ1): 3089w, 3062m, 3052m, 3022m,
1
2
Ru1–N2
Ru1–O1
Ru1–Cl2
Ru1–Cl3
Ru1–Cl1
Ru1–Cl4
S1–O1
N2–O2
1.7087(18)
2.0541(14)
2.3655(5)
2.3747(5)
2.3743(5)
2.3757(6)
1.5547(15)
1.159(2)
Ru1–N10
Ru1–O7
Ru1–Cl3
Ru1–Cl2
Ru1–Cl6
Ru1–Cl4
S1–O7
N1–O10
1.702(2)
2.0593(18)
2.3635(6)
2.3728(19)
2.3661(6)
2.3622(6)
1.5454(19)
1.159(3)
2906m, 1865vs
1384s, 1187w, 1164w, 1108s, 1002s, 950 m
(PAC4), 721s, 690s, 600w (RuANO), 527vs; (far IR) 462
343vs, 318vs (RuACl), 170vs. UV–Vis spectrum (kmax = 508 nm).
m
as(N@O), 1624bw d(H2O), 1485m, 1442s, 1400s,
s(S@O), 760m
(RuAO),
m
m
m
m
m
N2–Ru1–O1
Cl2–Ru1–Cl3
Cl1–Ru1–Cl4
O1–Ru1–Cl1
N2–Ru1–Cl4
S1–O1–Ru1
O2–N2–Ru1
176.67(7)
176.699(18)
172.178(19)
84.90(4)
96.02(6)
121.26(8)
175.66(18)
N10–Ru1–O7
Cl3–Ru1–Cl2
Cl4–Ru1–Cl6
O7–Ru1–Cl6
N10–Ru1–Cl4
S1–O7–Ru1
O1–N10–Ru1
178.94(9)
174.44(2)
173.30(3)
87.46(6)
93.17(8)
121.57(10)
175.3(2)
3. Results and discussion
3.1. Syntheses, general properties and spectral characterization
Three simple ruthenium nitrosyl complexes [Et4N][RuCl4
(NO)(DMSO)] (1), [Bu4N][RuCl4(NO)(DMSO)](2) and [Ph4P][RuCl4
(NO)(H2O)]ꢁDMSO (3) have been prepared (see Scheme 1) in the
forms of single crystals and their molecular and crystal structures
have been determined. Among the prepared complexes, the syn-
thesis of complex 2 has already been described in the literature
[20], however, its X-ray structure has not been elucidated yet. Sin-
gle crystals of 2 suitable for X-ray analysis were obtained based on
fact that we slightly modified the literature procedure. In addition,
it is interesting to note that the synthesis of complex 3 from
[(DMSO)2H][RuCl4(NO)(DMSO)] (the precursor for the preparation
of complexes 1 and 2) instead of [(DMSO)2H][RuCl4(DMSO)2] did
not lead to the formation of a product with a defined composition.
Table 3
Selected bond lengths and angles for 3 (Å, °).
3
Ru1–N2
Ru1–O2
1.706(4)
2.055(3)
2.3511(11)
2.3669(11)
2.3667(11)
2.3747(11)
1.522(3)
1.151(5)
1.791(4)
1.800(4)
107.5(2)
112.7(2)
178.3(4)
Ru1–Cl4
Ru1–Cl1
Ru1–Cl2
Ru1–Cl3
S1–O1
N2–O3
P1–C30
P1–C40
The obtained molar conductivity values (57.1–90.7 S cm2 molꢀ1
,
see Section 2.3) proved the ionic nature of all the three complexes
in DMF solutions (1:1 electrolyte type). The results of the room
temperature magnetochemical measurements confirmed the dia-
magnetic nature of the complexes.
C30–P1–C10
C30–P1–C40
O3–N2–Ru1
The infrared spectra of compounds 1, 2 and 3, besides a strong
stretching vibration in the region belonging to the linear-coordi-
nated nitrosyl (1867–1857 cmꢀ1), show also the S@O stretching
bands of OAbonded DMSO at 922 and 937 cmꢀ1 (for 1 and 2, respec-
The resulting solution was left standing at room temperature. After
several days, violet needle crystals and a small amount of orange

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M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
Scheme 1. A schematic representation of the preparation pathways of the ruthenium(II) complexes 1–3.
tively) and for the solvent molecule of DMSO at 950 cmꢀ1 (for 3). The
The solid state electronic spectra of 1–3 are characterizedbybroad
absorption peaks at about 505 nm (Fig. 1). These spectra were found
to be completely different from the spectrum of the precursor
[(DMSO)2H][RuCl4(DMSO)2], which is dominated by typical strong
charge-transfer bands from the chlorides to the ruthenium(III) atom.
On the other hand, the spectra of 1–3 are very similar to that of
[(DMSO)2H][RuCl4(NO)(DMSO)], in which the absorptionpeak is cen-
tred at about 500 nm [20,25]. The differences between the spectrum
of [(DMSO)2H][RuCl4(DMSO)2] and those of prepared complexes are
consistent with the change in the oxidation state of ruthenium upon
binding of NO+ [20]. The theoretical electronic absorption spectra of
the complex anions [RuCl4(NO)(DMSO)]ꢀ and [RuCl4(NO)(H2O)]ꢀ in
vacuum have been obtained by means of time-dependent DFT meth-
od (TD-DFT) and the calculated transition energies (in nm) are re-
ported in Table S3 in Appendix A. Supplementary data. The
transition energies to the singlet excited states have been calculated
for the electronic ground state DFT (the B3LYP/LANL2DZ/cc-pVTZ
level of theory) optimized structures. The calculations presented
were focused on the singlet states between 800 nm and 440 nm
where the experimental transitions were detected (at ca 500 nm).
Just for comparison, TD-DFT calculations were performed in the
position of the m(N„O) bands at relatively high values is consistent
with the {Ru(NO)}6 formulation with NO+ coordinated to the dia-
magnetic Ru(II) centre [15]. The stretching vibration of RuAN and
the deformation vibration of RuANO are often coupled, as their fre-
quencies are close to each other. In the cases of complexes 1 and 2,
the bands are well resolved, contrary to complex 3, where the ‘‘pure”
m(RuAN) vibration was not observed probably in connection with its
overlapwith the d(Ru–NO)one. Theabsorptionbandscorresponding
to m
(RuAN) were observed at 625 cmꢀ1 (for 1) and 634 cmꢀ1 (for 2),
and d(RuANO) at 605 or 596 cmꢀ1. For complex 3, only the RuANO
deformation vibration was observed at 600 cmꢀ1. The presence of
the tetra-n-alkylammonium cations as well as DMSO in 1 and 2
was confirmed by characteristic absorption peaks, which are
assignable to
(2951–2929 cmꢀ1);
(1498–1472 cmꢀ1) and ds(CAH) (1141–1384 cmꢀ1). The tetraphen-
ylphosphonium cation is represented in the spectrum of 3 by (C4P)
m
as(CAH) in CH3 (2987–2960 cmꢀ1);
(CAH) in CH2 (2910–2872 cmꢀ1); das(CAH)
ms(CAH) in CH3
m
m
at 760 cmꢀ1 and by the strong sharp absorption peaks at 721 and
527 cmꢀ1 corresponding to d(CAC)ar. The assignments of absorption
bands were made according to the literature [33–35]. The geome-
tries of the complex anions [RuCl4(NO)(DMSO)]ꢀ (present in com-
plexes 1 and 2) and [RuCl4(NO)(H2O)]ꢀ (in 3) as well as IR spectral
vibrations of the complex anions were optimized and calculated at
the B3LYP/LANL2DZ/cc-pVTZ level of theory and compared with
those experimentally determined (see Tables S1 and S2 in Appendix
A. Supplementary data). The calculated values of vibrations were
not scaled. Therefore, in most cases, they tend to be higher than
cases of the octahedral Ru(II) complex cations [Ru(phen)2(dppz)]2+
,
[Ru(tap)2(dppz)]2+ and [Ru(trpy)(tmp)(NO)]3+ (phen = 1,10-phenan-
throline, tap = 1,4,5,8-tetra-azaphenanthrene, dppz = dipyridophen
azine, trpy = 2,20:60,200-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-
phenanthroline) [37].
3.2. Thermal behaviour
the corresponding experimental ones, e.g. mas(N@O) was found at
1865 cmꢀ1 in the spectrum of 3, while the calculated value is equal
The complexes 1, 2 and 3 were also studied by means of ther-
mogravimetric (TG) and differential thermal (DTA) analyses. The
to 1994.0 cmꢀ1 for the [RuCl4(NO)(H2O)]ꢀ complex anion. On the
other hand, the calculated m(RuAN) and d(RuANO) vibrations were
found at lowerfrequencies thanthe experimentalones. For example,
in the complex anion [RuCl4(NO)(DMSO)]ꢀ, the frequency values for
m
(RuAN) were found to be 625 and 634 cmꢀ1 (in spectra of 1 and 2,
respectively) and 533.3 cmꢀ1 (calcd), and for d(RuANO) 605 and
596 cmꢀ1 (in 1 and 2, respectively) and 540.4 cmꢀ1 (calcd). In accord
with the experimental findings, the calculated
m(RuAN) and
d(RuANO) vibrations were well resolved in [RuCl4(NO)(DMSO)]ꢀ.
On the contrary, in the [RuCl4(NO)(H2O)]ꢀ complex anion, the
stretching vibration
m(RuAN) is clearly coupled with
m(RuANO) in
the calculated spectrum. Therefore, only the calculated
m
(RuANO)
was interpreted at 569.9 cmꢀ1. The comparison of the IR vibrations
is presented in Table S2 in Appendix A. Supplementary data in great-
er details. The interpretation of the calculated maxima has been re-
lated to the literature data of the following Ru-containing complexes
or complex ions: [RuCl5(NO)]2ꢀ, [Ru(NH3)4Cl(NO)]2+, [Ru(NH3)5
(NO)]3+, [RuCl3(NO)(H2O)2], [RuCl(mqn)2NO] and [RuCl(cqn)2(NO)]
[(2-methyl-8-quinolinol (Hmqn) or 2-chloro-8-quinolinol (Hcqn)]
[36].
Fig. 1. Electronic absorption spectra of 1–3 in the solid state.

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M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
207
TG and DTA curves for 1, 2 and 3 are presented in Figs. S1, S2, and
S3, respectively, in Appendix A. Supplementary data.
The courses of the TG curves proved that the complexes 1 and 2
are non-solvated, because the named compounds have been found
to be thermally stable up to 99 °C, and 108 °C, respectively. Fur-
ther, the decompositions of both 1 and 2 continued without forma-
tion of any thermally stable products. This part of the degradation
of 1 was accompanied by weak exothermic effects with the max-
ima at 123, 276 and 380 °C and endothermic effects with the min-
ima at 193 and 224 °C. The strongest exo-effect was observed at
437 °C. In the case of 2, the progress of the degradation was analog-
ical to 1. The weak exo-effect with the maximum at 249 °C was de-
tected, while the sharp exothermic effect had the maximum at
363 °C. Only one weak endo-effect accompanying the thermal
decomposition of 2 was found at 112 °C. The courses of thermal
degradations of both compounds were finished at 471 °C for 1
and 435 °C for 2. The final product of thermal decomposition of 1
was determined to be RuO2 (ICCD No. 43-1027) [26,27] using an
X-ray powder diffraction measurement.
The thermal decomposition of complex 3 was found to be dif-
ferent from those of 1 and 2. It started at a very low temperature
of 33 °C, which could be connected with a gradual release of the
DMSO molecule of crystallization present in the structure of com-
plex 3. However, no plateau was observed on the TG curve, there-
fore the non-solvated complex is not a stable intermediate of the
degradation. Most likely, the process of desolvation gradually
passes onto the release of the coordinated water molecule and to
further decomposition of the complex. The whole process of
decomposition was accompanied by weak endo-effects with the
minima at 50 °C and 247 °C, and by two weak and one subsequent
strong exo-effect at 216, 242, and 388 °C, respectively. The course
of thermal degradation of 3 proceeded without formation of any
thermally stable intermediates up to 443 °C. RuO2 was calculated
as the final product of the decomposition.
Fig. 3. The molecular structure of 2. The non-hydrogen atoms are drawn as
displacement ellipsoids at the 50% probability level.
tures, [(DMSO)2H][RuCl4(NO)(DMSO)] [20], [2Cl-BapH][RuCl4(NO)
(DMSO)] [2Cl-Bap = 6-(2-chlorobenzylamino)purine] [38] and [AcyH]
[RuCl4(NO)(DMSO)] (Acy = acyclovir) [39] with the same complex
anion have been structurally characterized up to now.
Ruthenium displays the expected octahedral coordination geom-
etry with the linear nitrosyl group, which is in the trans position to
the DMSO molecule, coordinated to ruthenium though the oxygen
atom. Ru(II)isdisplaced by0.114(2) Å in1 and by 0.124(2) Å in2 from
the equatorial mean plane formed by four chlorido ligands. The
RuANAO angles in the structures of 1 and 2 were determined to be
175.66(18)°, and 175.3(2)°, respectively. The RuAN bond distances
were found to be quite short, which is consistent with the strong
The differences between the overall weight losses determined
by the thermal analyses and calculated to RuO2 did not differ by
more than 0.8% for all three complexes.
d
p
?
pꢂ back-bonding. The RuAN bond lengths were found to be
1.7087(18) in 1 and 1.702(2) Å in 2 and are in good agreement with
those found in [(DMSO)2H][RuCl4(NO)(DMSO)] [1.712(5) Å] and
[Bu4N][RuCl4(NO)(pyz)] [1.705(6) Å, pyz = pyrazine] [20,40]. The
NAO bond lengths were detected to be 1.159(2) Å in both complexes
and are a bit longer than in other ruthenium nitrosyl complexes, e.g.
[(DMSO)2H][RuCl4(NO)(DMSO)] [1.134(5) Å], [Bu4N][RuCl4(NO)(pyz)]
[1.152(8) Å] and [RuCl3(NO)dppf] [1.149(6) Å, dppf = 1,10-bis-
(diphenylphosphine)ferrocene] [20,40,41]. The Ru–O distance trans
to NO+ was found to be 2.0541(14) and 2.0539(18) Å in 1, and 2,
respectively, which is quite comparable with the average Ru–O dis-
tance (2.049 Å), as found from ten X-ray structures involving trans-
(DMSOARuANO) moiety and deposited in Cambridge Structural
Database [42]. However, these bond lengths are significantly shorter
than the average Ru–O distance (2.126 Å) as found in nine Ru–DMSO
compounds deposited in the Cambridge Structural Database [42] in
which CO is the opposite ligand. This is a manifestation of the trans
3.3. X-ray structural description of 1 and 2
The molecular structures of 1 and 2 were determined by single-
crystal X-ray analysis and are depicted in Figs. 2 and 3, respec-
tively. The crystal data and structure refinements are given in Table
1, the selected bond lengths and angles are listed in Table 2.
The molecular structures of both 1 and 2 are ionic and consist of
the [RuCl4(NO)(DMSO)]ꢀ anion and the tetra-n-alkylammonium
cation [Et4N]+ in 1 and [Bu4N]+ in compound 2. Only three struc-
shortening effect induced by the strong
p-accepting nitrosyl ligand
to a -donor ligand [43,44]. In the equatorial positions of complexes
r
1 and 2, there are four chlorido ligands. The Ru–Cl distances
[2.3622(6)–2.3757(6) Å] (Table 2) fall into the range [2.320–
2.419 Å] reported for the twelve ruthenium(II) complexes involving
the [RuCl4(NO)X] species (X = any chemical element) deposited in
the Cambridge Structural Database [42].
In both compounds 1 and 2, the secondary structures are stabi-
lized by intermolecular weak interactions of the CAHꢁ ꢁ ꢁCl type in
the range of 2.810(5)–2.943(6) Å in 1 and 2.733(6)–2.945(8) Å) in
compound 2. There is only one CAHꢁ ꢁ ꢁO interaction in the struc-
ture of 1 [H2Aꢁ ꢁ ꢁO1iii = 2.595(2) Å; symmetry code: (iii) 1 ꢀ x,
1 ꢀ y, ꢀz]. The CAHꢁ ꢁ ꢁO type interactions [2.372(2)–2.711(3) Å]
Fig. 2. The molecular structure of 1. The non-hydrogen atoms are drawn as
displacement ellipsoids at the 50% probability level.

ˇ
208
M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
Table 4
are also present in the structure of 2. Figs. S4 and S5, showing the
non-bonding interactions in complexes 1 and 2, respectively, are
presented in Appendix A. Supplementary data.
Possible hydrogen bonds for 3 (Å, °).
DAHꢁ ꢁ ꢁA
d(D–H)
d(Hꢁ ꢁ ꢁA)
1.764(6)
2.912(6)
1.842(7)
d(Dꢁ ꢁ ꢁA)
2.642(4)
3.771(3)
2.659(4)
<(DHA)
O2AH2Vꢁ ꢁ ꢁO1i
O2AH2Vꢁ ꢁ ꢁS1i
O2AH2Wꢁ ꢁ ꢁO1
0.90(6)
0.90(6)
0.85(6)
162.90(6)
159.17(5)
161.43(7)
3.4. X-ray structural description of 3
The molecular structure of 3 is depicted in Fig. 4. The crystal
data and structure refinements are listed in Table 1, the selected
geometric parameters are given in Table 3, while the hydrogen
bond parameters are summarized in Table 4.
The molecular structure of 3 is similarly as in 1 and 2 ionic, but
consists of the [RuCl4(NO)(H2O)]ꢀ anion, [Ph4P]+ cation and one
solvent dimethyl sulfoxide molecule (Fig. 4). The same complex
anion has been structurally characterized in two complexes, i.e.
[(Bu4N)2][RuCl4(NO)(H2O)][RuCl5(NO)]0.5?H2O [45] and [RuCl(NO)
(dppe)2][RuCl4(NO)(H2O)][RuCl6]0.5?nH2O [46], where dppe stands
for bis(trans-bis(1,2-bis(diphenylphosphino)ethane.
Symmetry transformation used to generate equivalent atoms: (i) 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
The geometries of the complex anions [RuCl4(NO)(DMSO)]ꢀ and
[RuCl4(NO)(H2O)]ꢀ as well as their vibrations maxima were calcu-
lated at the B3LYP/LANL2DZ/cc-pVTZ level of theory and the ob-
tained results were compared with those determined by X-ray
analysis. The calculated RuACl bond lengths were found to be in
good agreement within both the theoretically calculated structures
of [RuCl4(NO)(DMSO)]ꢀ and [RuCl4(NO)(H2O)]ꢀ, however, they dif-
fer significantly from the experimental ones. The experimental and
calculated values of NAO differ only slightly, since they equal
1.159(3) Å and 1.147 Å for [RuCl4(NO)(DMSO)]ꢀ, and 1.151(5) Å
and 1.1427 Å for [RuCl4(NO)(H2O)]ꢀ, respectively. The complete
agreement was found for RuAO in [RuCl4(NO)(H2O)]ꢀ [exp.
2.055(3) Å; calcd. 2.055 Å]. The calculated RuAN and SAO bond
lengths are in all cases significantly longer than the experimental
ones. Similarly, high differences between the experimental and cal-
culated values of angles were found both in [RuCl4(NO)(DMSO)]ꢀ
and [RuCl4(NO)(H2O)]ꢀ. The values of the calculated bond lengths
and angles have also been compared with the literature data of
the following ruthenium complexes: [RuCl5(NO)]2ꢀ, [Ru(NH3)4Cl
The ruthenium ion displays the compressed octahedral geome-
try with the linear nitrosyl group in trans position to the coordi-
nated molecule of water. Ru(II) is also displaced by 0.14(3) Å
from the equatorial mean plane formed by four chlorido ligands to-
wards the nitrosyl group. The angle RuANAO equals 178.3(4)° and
is comparable with those in complexes 1 and 2. Due to the strong
d
p
?
pꢂ back-bonding of the nitrosyl ligand, the Ru–N distance is
short [1.706(4) Å], similarly as in 1 and 2. The NAO bond length
is equal to 1.151(5) Å, which is a typical value for a triple bond.
The Ru–O distance [2.055(3) Å] is quite comparable to those in 1
and 2, where in the trans position to the NO group, there is not
the water molecule as in 3 but OAbonded DMSO. The Ru–Cl dis-
tances range from 2.3511(11) to 2.3747(11) Å and do not differ
from the bond lengths found in other similar ruthenium nitrosyl
complexes [20,41]. The [PhP4]+ cation is tetrahedral with the PAC
bond lengths ranging from 1.791(4) to 1.800(4) Å, which are com-
parable with the average bond length of 1.795 Å, as found in 72
ruthenium compounds containing the [Ph4P]+ cation, which are
deposited in the Cambridge Structural Database [42].
The OAHꢁ ꢁ ꢁO and OAHꢁ ꢁ ꢁS hydrogen bonds (Table 4) connect
the solvent DMSO molecule with complex anions forming a square
arrangement of the oxygen atoms. The secondary structure is fur-
ther stabilized by the CAHꢁ ꢁ ꢁCl intermolecular interactions
[2.673(2)–2.854(2) Å] and CAHꢁ ꢁ ꢁC type interactions [2.649(5)–
2.887(5) Å]. Fig. S6, displaying the hydrogen bonds in complex 3,
is presented in Appendix A. Supplementary data.
(NO)]2+
,
[RuCl3(NO)(PPh3)(pyrazole)], [Ru(NH3)5(NO)]3+ and
[RuCl3(NO)(H2O)2] [36]. The results are given in Tables S1 and S2
in Appendix A. Supplementary data.
4. Conclusions
We have prepared and characterized three simple ruthenium(II)
nitrosyl complexes of the compositions [Et4N][RuCl4(NO)(DMSO)]
(1), [Bu4N][RuCl4(NO)(DMSO)](2) and [Ph4P][RuCl4(NO)(H2O)]ꢁ
DMSO (3). Complexes 1 and 2 have been synthesized by the reaction
of [(DMSO)2H][RuCl4(NO)(DMSO)] with the corresponding tetra-n-
alkylammonium salt. Complex 3 has been prepared by bubbling of
nitric oxide through the system containing [(DMSO)2H][RuCl4(DM-
SO)2] and [Ph4P]Cl. The spectroscopic results indicate the presence
Fig. 4. The molecular structure of 3. The non-hydrogen atoms are drawn as displacement ellipsoids at the 50% probability level.

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M. Matiková-Malarová et al. / Journal of Molecular Structure 977 (2010) 203–209
209
of the NO+ group bound to the Ru(II) ion, which corresponds to the
{Ru(NO)}6 formulation. Complexes 1–3 have been prepared in the
single crystal form and their molecular and crystal structures have
been determinedby single-crystalX-ray analysis. All the three struc-
turally characterized compoundsare ionic representing the 1:1 elec-
trolyte type. The central Ru(II) ion is octahedrally coordinated by
four chlorido ligands in the equatorial plane and by the N (from
NO+) and O (from DMSO in 1 and 2, H2O in 3) atoms in the axial posi-
tions forming an RuCl4NO chromophore. The geometries of the com-
plex anions and infrared spectral vibrations were calculated at the
B3LYP/LANL2DZ/cc-pVTZ level of theory. These results were com-
pared with the experimentally determined data. The prepared com-
plexes may find an application as synthetic precursors for the
preparation of other ruthenium nitrosyl complexes bearing various
types of biological activities.
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ˇ
gratefully acknowledged. The authors also wish to thank Ms.
ˇ
Kamila Štepánková and Ms. Pavla Chlubná for synthetic assistance
and Mr. Pavel Štarha for carrying out the thermal analyses.
Appendix A. Supplementary material
CCDC 767775, 767776 and 767777 contain the supplementary
crystallographic data for the complexes 1, 2, and 3, respectively.
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