Synthesis, characterization and photochemical properties of some ruthenium nitrosyl complexes

Article abstract of DOI:10.1016/j.poly.2012.07.032

Synthesis of new nitrosyl complexes [RuCl₃(CNPy) ₂(NO)] (1), [RuCl₃(AMPy)₂(NO)] (2), [RuCl ₃(CPI)₂(NO)] (3), [RuCl₃(NOPI)₂(NO)] (4), and [RuCl₃(HPI)₂

Full text of DOI:10.1016/j.poly.2012.07.032

Polyhedron 52 (2013) 837–843
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Synthesis, characterization and photochemical properties of some ruthenium
nitrosyl complexes
Amit Kumar a, Rampal Pandey a, Rakesh Kumar Gupta a, Kaushik Ghosh b, Daya Shankar Pandey a,
⇑
a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi – 221 005, India
b Department of Chemistry, Indian Institute of Technology, Roorkee – 247 667, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 20 July 2012
Synthesis of new nitrosyl complexes [RuCl3(CNPy)2(NO)] (1), [RuCl3(AMPy)2(NO)] (2), [RuCl3(CPI)2(NO)]
(3), [RuCl3(NOPI)2(NO)] (4), and [RuCl3(HPI)2(NO)] (5) [CNPy = 4-cyanopyridine; AMPy = 4-aminopyridine;
CPI = 1-(4-cyanophenyl)-imidazole; NOPI = 1-(4-nitrophenyl)-imidazole; HPI = 1-(4-hydroxyphenyl)-
imidazole] has been described. The complexes 1–5 have been characterized by satisfactory elemental anal-
yses, spectral (ESI-MS, FT-IR 1H, 13C NMR, UV–Vis) and electrochemical studies. Linear nitrosyl group and S0
state in these complexes have been supported by IR, 1H NMR spectral studies and X-ray single crystal anal-
yses on representaive complex 1. Photorelease of NO and its trapping by myoglobin have been monitored by
UV–Vis studies. Structure of the complexes under investigation has also been supported by theoretical
studies. The geometrical parameters of 1–5 are comparable to those obtained from single crystal X-ray dif-
fraction studies on 1.
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Ruthenium
Nitrosyl
Structures
Photolability
Myoglobin
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
characteristics of metal nitrosyl complexes make their electro-
chemical properties very attractive [32–34]. During past few years
Nitric oxide (NO) plays an essential role in many biological pro-
cesses including blood pressure control, neuro-transmission,
inflammatory response, antimicrobial applications, apoptosis, and
inhibition of tumor growth [1–15]. In this context nitrosyl com-
plexes capable of furnishing NO upon exposure to light have drawn
special attention because of their utility in photodynamic therapy
(PDT) and treatment of selected types of cancer [16,17]. The organic
NO donors such as nitrites (RONO), nitrates (RONO2), S-nitrosothiols
(RSNO) and diazenium-diolates (NONOates) release NO upon illu-
mination over the course of several hours (except specific NONO-
ates) therefore, these are not suitable for this purpose [18–22]. On
the other hand metal nitrosyls especially those based on ruthenium
are far more stable and yet exhibit significant degree of photolabil-
ity. These are of particular importance in photodynamic therapy be-
cause of their accumulation in tumor cells, stability of Ru-NO bond
at room temperature coupled with ability to survive under physio-
logical conditions [23–26]. Photolability of the NO arises from photo
we have been interested in metal nitrosyls and coordination chem-
istry of substituted pyridine and imidazole derivatives [35–40].
With an objective of developing photolabile ruthenium complexes
based on CNPy, AMPy, CPI, NOPI, and HPI the reactivity of aforesaid
ligands have been examined with precursor complex RuCl3
(NO)ꢀ2H2O. Inclusion of these ligands in nitrosyls may lead to sub-
stantial change in the properties of ensuing complexes. Through
this contribution we describe the synthesis, characterization and
photophysical properties of nitrosyl complexes [RuCl3(CNPy)2(NO)]
(1), [RuCl3(AMPy)2(NO)] (2), [RuCl3(CPI)2(NO)] (3), [RuCl3(NOPI)2
(NO)] (4) and [RuCl3(HPI)2(NO)] (5). We also present herein single
crystal X-ray structure of the representative complex 1 and photo-
release of coordinated NO in 1 and 5 and it’s trapping by
myoglobin.
2. Results and discussion
excitation of electrons from dp
(M) ? p⁄(NO) transitions [18,19,
2.1. Synthesis and characterization
27,28].
Nitrosyl group can exist in the complexes in cationic, anionic, as
well as radical forms (NO+, NOÅ, NO–) depending on electronic prop-
erties of the metal and co-ligands [29–31]. The redox non-innocent
The precursor complex RuCl3(NO)ꢀ2H2O reacted with 4-cyanopyr-
idine (CNPy), 4-aminopyridine (AMPy), 1-(4-cyanophenyl)-imidazole
(CPI), 1-(4-nitrophenyl)-imidazole (NOPI), and 1-(4-hydroxyphenyl)-
imidazole (HPI) in ethanol under refluxing conditions to afford nitrosyl
complexes [RuCl3(CNPy)2(NO)] (1), [RuCl3(AMPy)2(NO)] (2), [RuCl3(C-
PI)2(NO)] (3), [RuCl3(NOPI)2(NO)] (4), and [RuCl3(HPI)2(NO)] (5) in
⇑
Corresponding author. Tel.: +91 542 6702480; fax: +91 542 2368174.
E-mail addresses: dsprewa@yahoo.com, dspbhu@bhu.ac.in (D.S. Pandey).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.07.032

838
A. Kumar et al. / Polyhedron 52 (2013) 837–843
good yield (58–68%). Simple strategy adopted for the synthesis of 1–5
is shown in Scheme 1. Ensuing complexes (except 2, which is slightly
hygroscopic) are non-hygroscopic air-stable solids. These are soluble
in organic solvents like acetonitrile, dimethylformamide and dimeth-
ylsulphoxide, but insoluble in diethylether and hexane. Complex 1 is
sparingly soluble in dichloromethane, while 2 and 5 are soluble in
methanol, ethanol, and water. Their solution is stable for several days
under dark conditions, however 1 and 5 exhibit drastic changes in
presence of light due to the replacement of NO by solvent (vide-supra).
The complexes under investigation have been characterized by satis-
factory elemental analyses, ESI-MS, IR, NMR spectral UV–Vis and elec-
trochemical studies.
respective complexes. Sharp 1H NMR spectral features suggested S0
ground state for these complexes. The and b protons of coordinated
CNPy in 1 resonated at d 9.41 and 7.78 ppm with distinct downfield
shift relative to free ligand. It indicated coordination of the ligands
to metal centre through pyridyl nitrogen, which has further been
supoported by X-ray single crystal analyses (vide supra) [43,44]. Sim-
a
ilarly, the
a and b protons of AMPy in 2 resonated at 9.25 and
8.24 ppm, exhibiting a downfield shift. Distinct signal due to NH2
protons could not be observed in this complex, instead it appeared
in the region for solvent used for acquisition of the spectrum. The
CPI and NOPI protons in 3 and 4 appeared as broad signals [d 8.99
(1H), 8.09 (4H), 7.67 (2H), 3; 9.01 (1H), 8.44 (2H), 8.13 (2H), 7.69
(2H), 4]. In the same way, protons associated with HPI in 5 resonated
at 6.93 (2H), 7.53 (2H), 7.58 (2H), 7.87 (1H), 8.61 (1H) ppm along with
distinctive signals due to OH at 9.94 (1H) ppm. Notably, in 3–5 the
imidazolyl protons displayed a downfield shift and appeared at
ꢁ8.5–9.0 ppm relative to free ligands suggesting the coordination
of respective ligands through imidazolyl nitrogen [41,42]. 13C NMR
spectral data also supported formulation of the respective complexes.
The electronic absorption spectra of 1–5 were obtained in ace-
tonitrile (c, 1 ꢃ 10ꢂ4 M) at room temperature and resulting spectra
is shown in Fig. 2. In their absorption spectra, 1–5 displayed bands
at ꢁ325–330 and 250–290 nm. Complex 1 also exhibited a band at
ꢁ396 nm. The low energy bands have been ascribed to metal-to-li-
The formation of 1–5 has also been supported by electrospray
ionization mass spectral studies. In its ESI-MS, 1–5 displayed
molecular ion peaks at m/z 445.817 (M+), 1; 430.034 (M+ + 4), 2;
575.050 (M+), 3; 618.112 (M+ + 3), 4; and 557.926 (M+),
5
(Fig. S1–S5). In addition, spectra of all the complexes displayed a
prominent peak at m/z 169/170 and 147 assignable to {Ru(NO)Cl}
and RuNO moieties with one water molecule. A less abundant peak
at m/z 466.038 (M+ + 4 with 2H2O) in the mass spectra of 2 may be
due to hygroscopic nature of this compound. The presence of vari-
ous peaks and overall fragmentation pattern strongly supported
formation of respective complexes.
IR spectral data for 1–5 is summarized in the Section 5 and
their spectra depicted in Fig. S6–S10. An interesting feature of
the IR spectra of these complexs is presence of sharp bands at
ꢁ1850–1900 cmꢂ1 [1877 (vs), 1; 1845 (m), 2; 1864 (s), 3;
gand charge transfer (MLCT) transitions involving a d
p⁄(NO), while high energy bands to intra-ligand charge transfer
p⁄ transitions [45]. The low energy transition in these com-
p(Ru) ?
p
?
1884 (m), 4; 1872 (s), 5] assignable to
m
(NO). It strongly indi-
plexes have been proposed to be responsible for photolability of
cated the presence of linear NO group and positive charge resid-
ing on coordinated NO. Notably (NO) varies with the strength
of other ligands present in these complexes. An increase in the
acceptor ability of ligand leads to an increases in back dona-
tion from M ? L, in turn NO bond strength and (NO) increases.
On going from 1 to 2 (NO) decreases due to presence of –NH2
the {RuNO}6 moiety.
m
2.2. Electrochemical studies
p
m
Redox behavior of 1–5 has been followed by cyclic voltammetry
in acetonitrile (c, 1 ꢃ 10ꢂ4 M) at room temperature under inert at-
mosphere using tetrabutylammonium perchlorate as a suppport-
ing elctrolyte. Representative voltammogram for 1 is depicted in
Fig. 3 and S20. Potential of Fc/Fc+ couple under experimental con-
ditions was 0.10 V (100 mV) vs Ag/Ag+. The complexes 1–5 exhib-
ited reductions due to NO+{RuNO}6 ? NOÅ{RuNO}7 in the cathodic
potential window [46]. The redox active nitrosyl moiety exhibited
only one reduction wave (Epc = ꢂ1.08, 1; ꢂ1.31, 2; ꢂ1.14, 3; ꢂ1.13,
4; ꢂ1.15 V, 5.) On the basis of peak separation between anodic/
m
in place of a strong electron withdrawing group like –CN. Among
3–5 small variations has been observed due to relative electron
withdrawing ability of the substituents on phenyl rings. Complex
5 do not show any appreciable decrease in m(NO) realtive to 3 or
4. The band due to pyridyl ring vibrations in 1 and 2 appeared at
ꢁ1615 cmꢂ1
, while those for imidazolyl group appeared at
ꢁ1600 cmꢂ1 relative to free ligands (CPI, 1615; NOPI, 1610;
HPI, 1608 cmꢂ1) [41]. Shift in the position of
m(C=N) associated
with pyridyl/-imidazolyl moiety suggested coordination of
cathodic potential (DE) and current ratio (ipa/ipc) it may be viewed
respective ligands to the metal centre through pyridyl/-imidazo-
as a quasi-reversible process. The complexes 1–5 do not show any
redox wave in the potential range of +2 to ꢂ2 V (except for
NO+ ? NOÅ), which may be attributed to the formation of stable
complexes containing Ru(II) centres.
lyl nitrogen. Characteristic bands due to
m(CN), m(NH2), m(NO2)
and (OH) of the coordinated ligands CNPy, AMPy, CPI, NOPI
m
and HPI were displayed at their usual position in the spectra
of respective complexes (please See Section 5) [42].
1H and 13C NMR spectra were acquired in CDCl3/DMSO-d6. Result-
ing data is collected in the experimental section and spectra depicted
in Fig. 1 and through S11–S19. The position and integrated intensity
of various signals corroborated well with the formulation of
2.3. Crystal structure
Structure of 1 has been determined by X-ray single crystal anal-
yses. It crystallizes in monoclinic system with ‘P 21’ space group.
X
X
Cl
Cl
2
X
N
N
N
X
NO
N
2
N
NO
N
N
N
Ru
RuNOCl3.2H2O
Ru
Cl
Reflux
EtOH
Cl
Reflux
EtOH
N
Cl
Cl
X
X
X= CN,NO2,OH
X=CN,NH2
Scheme 1. Scheme showing the synthesis of 1–5.

A. Kumar et al. / Polyhedron 52 (2013) 837–843
839
Fig. 1. 1H NMR spectrum of 1.
Fig. 3. Cyclic voltammogram of 1.
Fig. 2. Electronic absorption spectra of 1–5.
covalency in this complex relative to other Ru–N and Ru–Cl bonds.
Further, Ru–N(1) bond distance of 1.747(4) Å and linear Ru–NO
moiety [Ru–N(1)–O: 177.8°] is consistent with E–F model [47,48].
Weak interaction studies on 1 revealed the creation of linear
motif with rectangular cavities [C(6)ꢀ ꢀ ꢀCl(3), 3.323(4); C(12)ꢀ ꢀ ꢀ
Cl(1), 3.427(5) Å] (Fig. S21) via Oꢀ ꢀ ꢀCl intermolecular interactions
(2.99 Å) between NO oxygen and Cl (-trans to NO). The intra- and
intermolecular ruthenium and nitrile carbon distances in rectangu-
lar cavities are 6.314(5)/ꢂ6.320(5) Å and 5.669(4)/5.771(5) Å,
respectively.
Details about crystallographic refinement data and selected geo-
metrical parameters are gathered in Tables 1 and 2 and molecular
structure is depicted in Fig. 4. Immediate coordination geometry
about ruthenium centre is distorted octhedral completed by three
chloro groups, nitrosyl nitrogen N(1) and N(2) and N(4) from CNPy
ligands. The ruthenium to nitrosyl nitrogen distance Ru–N(1) is
1.747(4) Å, which is shorter than ruthenium to pyridyl nitrogen
distances [Ru–N(2), 2.099(3); Ru–N(4) 2.102(3) Å]. These are
normal and comparable to Ru–N distances in other nitrosyl and
4-CNPy complexes [35–38]. The Ru–Cl(1) and Ru–Cl(3) bond dis-
tances are comparable [2.378(1) and 2.372(1) Å], while Ru–Cl(2),
the one trans to Ru–NO is significantly shorter [2.303(1) Å]. Short
Ru–N(1) and Ru–Cl(2) distances are indicative of higher degree of
2.4. Photochemical studies
Photochemical properties of 1–5 have been investigated in dry
MeCN (c, 1 ꢃ 10ꢂ4 M). Their solutions are stable under visible light,

840
A. Kumar et al. / Polyhedron 52 (2013) 837–843
Table 1
[Ru(III)] charge transfer [49]. The high energy bands in these com-
Crystallographic refinement parameters for 1.
plexes red shifted and appeared at 337 nm in 1 and 377 in 5. In
addition, new absorption bands appeared with isobestic points at
310 and 331 nm in 1 and 5. It is noteworthy to mention that pho-
toreactions are not reversible, i.e. new bands generated due to irra-
diation of 1 and 5 do not be disappear after light is turned off. On
the other hand, absorption spectra of 2–4 do not show any signif-
icant changes upon irradiation (Fig. S20). To have an insight into
the photoreactivity of these complexes electronic absorption spec-
tra were acquired after irradiation for longer durations (ꢁ24.0–
72.0 h). Notably, significant changes do not occur even after 72 h,
suggesting that 2–4 are not photoactive (Fig. S22). It is concluded
that following reaction takes place in the photochemical conver-
sion of nitrosyl complexes.
1
Empirical formula
Formula weight
Crystal color
Crystal size (mm3)
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
b (°)
C12H8Cl3N5ORu
445.65
red block
0.26 ꢃ 0.24 ꢃ 0.22
293
0.71073
monoclinic
‘P 21’
8.6885(17)
7.9753(15)
11.300(2)
90.00
93.861(3)
90.00
781.3(3)
2
1.894
1.523
1.079
(°)
c
(°)
V (Å3)
Photodissociation of 1 and 5 in acetonitrile solution
h
m
½RuðIIÞCl3ðNOÞðLÞ ꢄ þ MeCN ! ½RuðIIIÞCl3ðMeCNÞðLÞ ꢄ þ NOÅ
Z
ð1Þ
2
2
Dcalc (g/cm3)
l
(mmꢂ1
)
L ¼ CNPy ð1Þ and HPI ð5Þ
GOF a on F2
Final R indices[I > 2
r
(I)]
R1 = 0.0360
wR2 = 0.0705
R1 = 0.0322
wR2 = 0.0635
2.5. Trapping of NO to myoglobin
R indices(All data)
The possibility of NO releasing to biological targets has always
been the impetus for photochemical studies on metal nitrosyls.
The photolability of coordinated nitrosyl has been investigated
by trapping liberated NO with reduced Mb [18,19]. Electronic
absorption spectrum of myoglobin was recorded in phosphate buf-
fer (pH, 6.8). The UV–Vis spectrum of oxidized myoglobin (Mb) dis-
played an intense band at 409 nm (Soret band) and this band red
shifted to 434 nm upon reduction using excess of sodium dithio-
nite. When complex solution was treated with an aqueous solution
of reduced Mb (Fig. 6, dash-dot line) in the same cuvette, under or-
dinary light no reaction was observed (Fig. 6, dotted line). How-
ever, same mixture upon exposures to low-intensity UV light
(302 nm) displayed bands at 421 nm in 1 and 422 nm in 5 attribut-
able to the formation of Mb-NO adduct (Fig. 6) [35–37].
Table 2
Experimental and theoretical bond lengths (selected) for 1–5.
Selected bond lengths (Å)
Experimental
Theoretical
1
1
2
3
4
5
Ru–N1
Ru–N2
Ru–N4
Ru–Cl2
Ru–Cl3
Ru–Cl1
N1–O1
1.747(4)
2.099(3)
2.102(3)
2.303(13)
2.372(12)
2.378(11)
1.133(5)
1.775
2.147
2.147
2.353
2.450
2.472
1.151
1.767
2.144
2.144
2.364
2.456
2.478
1.154
1.770
2.120
2.126
2.363
2.470
2.474
1.152
1.771
2.117
2.117
2.361
2.466
2.472
1.152
1.760
2.113
2.114
2.387
2.461
2.481
1.153
3. Theoretical calculations
however 1 and 5 darkens upon exposure to UV light (302 nm) and
2–4 do not show any color change (Fig. 5; inset). It has been
ascribed to the photocleavage of coordinated NO and formation
of solvated complex. The clean conversion of NO-bound ruthenium
complexes to corresponding solvato species have been investi-
gated by UV–Vis spectral studies. Electronic absorption spectra of
the complexes were acquired after exposure to UV light for few
minutes (time interval 1 min.). Time dependent absorption
changes clearly indicated that photodissociation of NO under UV
light is rapid for 1 relative to 5 (10 min. 1; 12 min. 5; Fig. 5). The
photodissociation of NO is accompanied by formation of a solvent
bound photoproduct (Eq. (1)). It typically exhibits a low-energy
band (394, 1; 375 nm, 5) which may be acsribed to ligand to metal
3.1. Geometry optimisation
To establish the structure and verify geometrical parameters
(bond length and bond angles), geometrical optimizations were
performed on 1–5. The coordinates for 1 were taken from crystal
data and structure was optimized using GAUSSIAN 03 program with
hybrid B3LYP density functional method and structures are opti-
mized without any symmetry restrictions with standard 6-31G⁄⁄
basis sets [50,51] for C, H, N, O and Cl elements and LANL2DZ
[52–54], for ruthenium. The optimized structure of 1 is thermody-
namically stable and comparable to its crystal structure. Likewise,
coordinates of 2–5 were taken from chemcraft 1.6 and the struc-
tures of these are similar to 1. Optimized structure of 3 is shown
Fig. 4. Ortep diagram of 1 with atom numbering scheme.

A. Kumar et al. / Polyhedron 52 (2013) 837–843
841
Fig. 5. Photodissociation of 1 (a) and 5 (b). Inset showing the color change on photodissociation of 1 – 10 and 5 – 50.
Fig. 6. Red line, oxidized Mb (intense band at 409 nm); Green line, reduced Mb (at 433 nm, with excess of sodium dithionite); brown dotted line, reduced Mb + complex
solution (4.0 ꢃ 10–5 M) in dark; black line, Mb-NO adduct (a) at 421 nm obtained by reduced Mb and solution of 1 exposed to the light of UV lamp for 1 min. (b) at 422 nm
obtained by reduced Mb and solution of 5 exposed to the light of UV lamp for 2 min. (Color online.)
Fig. 7. Calculated structure of 3.
in Fig. 7 and minimized energy structures of other complexes are
given in Fig. S23. One can see that optimized bond lengths and
bond angles for 1 are in excellent agreement with the data from
X-ray diffraction analysis. The optimized Ru–NO bond lengths are
1.775 (1), 1.767 (2), 1.770 (3), 1.771 (4), 1.760 (5) Å are close to
the single crystal X-ray data for 1 (1.747 Å). All other important
bond length and bond angle are gathered in Table 2 and 3.
4. Conclusion
In summary through this work we have presented the synthesis
and characterization of some nitrosyl complexes [RuCl3(CNPy)2(-
NO)] (1), [RuCl3(AMPy)2(NO)] (2), [RuCl3(CPI)2(NO)] (3), [RuCl3(-
NOPI)2(NO)] (4), and [RuCl3(HPI)2(NO)] (5). Molecular structure
of 1 has been determined by crystallographically. The presence of

842
A. Kumar et al. / Polyhedron 52 (2013) 837–843
Table 3
under vacuo. Crystals suitable for X-ray diffraction analyses were
Experimental and theoretical bond angles (selected) for 1–5.
obtained by slow diffusion of hexane into dichloromethane solu-
tion of the complex. Yield: 138 mg (62%), Analytical data: Anal.
Calc. for C12H8Cl3N5ORu (Mol. Wt. 444.88): C, 32.34; H, 1.81; N,
15.71. Found: C, 32.18; H, 1.72; N, 15.56%. 1HNMR (CDCl3, dH
ppm): 9.41 (d, J = 6.6, 2H), 7.79 (d, J = 6.6, 2H), 13C NMR (DMSO-
d6, dC, ppm): 115.5, 123.4, 127.9, 155.3. FT-IR (KBr disk, cmꢂ1):
2237 (s), 1876 (vs), 1612 (s), 1421 (s), 1221 (s), 1059 (w). ESI-
MS. Calcd, found: m/z 444.884, 445.817 [M]+. UV–Vis (MeCN, kmax
Bond angle (°)
Experimental Theoretical
1
1
2
3
4
5
O1–N1–Ru
N1–Ru–N2
N1–Ru–N4
N2–Ru–Cl2
N4–Ru–Cl2
N1–Ru–Cl3
N2–Ru–Cl3
177.8(4)
90.10
175.46 175.39 178.54 178.36 179.63
93.26
93.22
86.78
86.74
93.57
89.71
90.13
89.74
87.23
90.20
90.23
89.06
93.11
93.11
86.89
86.89
93.63
89.74
90.03
89.73
87.02
90.23
90.22
89.05
93.68
93.74
86.46
86.47
91.10
89.43
90.05
89.47
89.43
90.59
89.81
89.42
93.17
93.81
86.40
86.61
91.07
89.66
89.92
90.21
89.41
90.40
89.66
89.58
93.03
93.34
87.73
85.91
90.95
88.47
90.50
91.01
90.16
89.50
90.89
88.41
92.85(17)
88.29(10)
88.77(13)
91.55(13)
89.65(10)
nm,
(10000).
e
Mꢂ1 cmꢂ1, c, 1 ꢃ 10ꢂ4 M): 397 (1048), 327 (6717), 270
Cl2–Ru–Cl3 88.82(5)
N4–Ru–Cl3
N1–Ru–Cl1
N2 Ru Cl1
N4 Ru Cl1
Cl2–Ru–Cl1 88.71(5)
N2–Ru–N4
N1–Ru–Cl2
90.02(10)
90.93(13)
90.96(10)
89.24(10)
5.3.2. [Ru(NO)Cl3(4-APy)2] (2)
It was prepared following the above procedure for 1 except that
4-AMPy (94 mg, 1.0 mmol, 2 equiv) was used in place of 4-CNPy.
The reaction mixture was evaporated to drynes under reduced
pressure, washed with diethylether and recrystallized from etha-
nol and diethylether. Yield: 123 mg (58%), Analytical data: Anal.
Calc. for C10H12Cl3N5ORu (Mol. Wt. 424.92): C, 28.22; H, 2.84; N,
16.45. Found: C, 28.14; H, 2.73; N, 16.32%. 1H NMR (DMSO-d6, dH,
ppm): 9.25 (4 H), 8.23 (4 H) 13C NMR (DMSO-d6 dC, ppm): 108.9,
139.9, 150.6. FT-IR (KBr disk, cmꢂ1): 3365 (br), 3203 (w), 2968
(w), 1845 (m), 1650 (s), 1527 (s), 1029 (m), 1026 (m). ESI-MS. Calc,
found: m/z 430.912, 430.034 [M+4]+. UV–Vis (MeCN, kmax nm,
177.05(18)
178.34(12)
173.50 173.76 172.57 173.01 173.61
176.29 176.02 178.84 178.91 178.38
179.19 179.34 179.13 179.50 173.74
Cl3–Ru–Cl1 177.44(6)
linear M–NO group in these complexes has been supported by IR,
NMR and structural studies. Further, by trapping released NO with
reduced myoglobin has been demonstrated that coordinated NO in
1 and 5 is photolabile.
e
Mꢂ1 cmꢂ1, c, 1 ꢃ 10ꢂ4 M): 321 (1330), 263 (19803).
5. Experimental
5.3.3. [Ru(NO)Cl3(CPI)2] (3)
It was prepared following the above procedure for 1 using CPI
(169 mg, 1.0 mmol, 2 equiv). Yield: 181 mg (63%), Analytical data:
Anal. Calc. For C20H14Cl3N7ORu (Mol. Wt. 574.94): C, 41.72; H, 2.47;
N, 17.03. Found: C, 41.58; H, 2.29; N, 16.92%. 1H NMR (DMSO-d6,
dH, ppm): 8.99 (s, 1H), 8.09 (s, 4H), 7.67 (2H). 13C NMR (DMSO-
d6, dC, ppm): 108.80, 116.89, 123.79, 134.25, 140.74, 155.78; FT-
IR (KBr disk, cmꢂ1): 3127 (m), 3448 (br), 2229 (m), 1864 (s),
1519 (s), 1309 (w), 1126 (w). ESI-MS. Calcd, found: m/z 574.937,
5.1. Materials
All the synthetic manipulations were performed under inert
atmosphere. The solvents were dried and distilled before their use
following standard procedures [55]. 4-Cyanopyridine, 4-aminopyr-
idine, 4-fluronitrobenzene, 4-imidazol-yl-phenol, imidazole, hy-
drated ruthenium(III) chloride (all Aldrich) and common reagents
were acquired from SD fine chem Mumbai, India. The ligands 1-
(4-cyanophenyl)imidazole [41], 1-(4-nitrophenyl)imidazole [42]
and precursor complex Ru(NO)Cl3.2H2O was prepared and purified
by the literature procedures [56,57].
575.050 [M]+. UV–Vis (MeCN, kmax nm,
1 ꢃ 10ꢂ4 M): 322 (1330), 257 (12878).
e
Mꢂ1 cmꢂ1
,
c,
5.3.4. [Ru(NO)Cl3(NOPI)2] (4)
5.2. Physical measurements
The complex 4 was prepared following the above procedure for 1
using NOPI (189 mg, 1.0 mmol). Yield: 178 mg (58%), Analytical
data: Anal. Calc. for C18H14Cl3N7O5Ru (Mol. Wt. 614.92): C, 35.11;
H, 2.29; N, 15.92. Found: C, 35.05; H, 2.13; N, 15.82%. 1H NMR
(DMSO-d6. dH, ppm): 9.03 (1H), 8.45 (2H), 8.13 (2H), 7.70 (2H);
13C NMR (DMSO-d6, dC, ppm): 117.8, 121.7, 125.0, 130.7, 131.5,
140.1, 146.5; FT-IR (KBr disk, cmꢂ1); 3424 (b), 3132 (w), 1884
(m), 1599 (m), 1520 (s), 1342 (s), 1063 (m). ESI-MS. Calc, found:
Elemental analyses for C, H and N were performed on a CE-440
analyser in the microanalytical laboratory of the Department of
Chemistry, Faculty of Science, Banaras Hindu University, Varanasi,
India. IR and electronic absorption spectra were acquired on a Per-
kin-Elmer 577 and Shimadzu UV-1701 spectrophotometers,
respectively. 1H (300 MHz) and 13C (75.45 MHz) NMR spectra were
obtained on a JEOL AL300 FT-NMR spectrometer using tetrameth-
ylsilane (TMS) as an internal reference. Electrochemical studies
were performed on a CHI 620c electrochemical analyser at room
temperature and scan rate of 100 mV sꢂ1. A glassy carbon working,
platinum wire auxiliary, and Ag/Ag+ reference electrodes were
used in a standard three-electrode configuration. Tetrabutylammo-
nium perchlorate (TBAP) was used as a supporting electrolyte and
the solution concentration was 1 ꢃ 10ꢂ4 M.
m/z 618.914, 618.113[M+2]+. UV–Vis (MeCN, kmax nm,
c, 1 ꢃ 10ꢂ4 M): 288 (14134).
e ,
Mꢂ1 cmꢂ1
5.3.5. [Ru(NO)Cl3(HPI)2] (5)
It was prepared using Ru(NO)Cl3ꢀ2H2O (136 mg, 0.5 mmol) and
HPI (160 mg, 1.0 mmol) following above procedure for 1. Yield:
189 mg (68%), Analytical data: Anal. Calc. For C18H16Cl3N5O3Ru
(Mol. Wt. 556.94): C, 38.76; H, 2.89; N, 12.56. Found: C, 38.67; H,
2.78; N, 12.42%. 1H NMR (DMSO-d6, 300 MHz, dH, ppm): 9.49 (s,
1H), 8.64 (s, 1H), 7.86 (s, 1H), 7.58 (s, 1H), 7.52 (d, J = 8.7, 2H),
6.93 (d, J = 8.7, 2H). 13C NMR (DMSO-d6, 75 MHz, dC, ppm):
108.13, 116.16, 127.75, 145.36, 163.74, 165.86; FT-IR (KBr disk,
cmꢂ1): 3441 (w), 1872 (s), 1633 (m), 1525 (s), 1453 (m), 1384
(w), 1269 (m), 1129 (m), 1067 (m), 872 (m). ESI-MS. Calc, found:
5.3. Syntheses
5.3.1. [Ru(NO)Cl3(4-CNPy)2] (1)
To a stirring solution of 4-CNPy (104 mg, 1.0 mmol, 2 equiv) in
ethanol (25 ml), Ru(NO)Cl3ꢀ2H2O (136 mg, 0.5 mmol, 1 equiv) was
added and contents of the flask heated under reflux for 12 h. After
cooling to room temperature a red solid separated which was iso-
lated by filtration, washed with ethanol, diethylether and dried
m/z 557.936, 557.926 [M+1]+. UV–Vis (MeCN, kmax nm,
c, 1 ꢃ 10ꢂ4 M): 325 (1335), 247 (11829).
e ,
Mꢂ1 cmꢂ1

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Thanks are due to the Council of Scientific and Industrial Re-
search (CSIR), New Delhi, India for financial assistance through
the scheme HRDG 01 (2361)/10/EMR-II. One of the authors (AK)
acknowledges CSIR for the award of a Junior Research Fellowship
(09/013(0330)/2010-EMR-I). We are also and also grateful to the
Head Department of Chemistry, Faculty of Science, Banaras Hindu
University, Varanasi, India for extending laboratory facilities and
Prof P.K. Bharadwaj, Indian Institute of Technology, Kanpur, India
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Appendix A. Supplementary data
The CCDC No- 854587 (1) contains the supplementary crystallo-
graphic 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 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
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2012.07.032.
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