Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2′-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

Article abstract of DOI:10.1039/c1dt10761e

The present article describes ruthenium nitrosyl complexes with the {RuNO}⁶ and {RuNO}⁷ notations in the selective molecular frameworks of [Ru^II([9]aneS₃)(bpy)(NO⁺)] ³⁺ (4³⁺), [R

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PAPER
Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and
2,2¢-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic
structure and reactivity aspects†
Prinaka De,a Somnath Maji,a Abhishek Dutta Chowdhury,a Shaikh M. Mobin,a Tapan Kumar Mondal,b
Alexa Paretzkic and Goutam Kumar Lahiri*a
Received 26th April 2011, Accepted 31st August 2011
DOI: 10.1039/c1dt10761e
6
7
The present article describes ruthenium nitrosyl complexes with the {RuNO} and {RuNO} notations
in the selective molecular frameworks of [RuII([9]aneS3)(bpy)(NO+)]3+ (43+), [RuII([9]aneS3)(pap)
(NO+)]3+ (83+) and [RuII([9]aneS3)(bpy)(NO∑)]2+ (42+), [RuII([9]aneS3)(pap)(NO∑)]2+ (82+) ([9]aneS3 =
1,4,7-trithiacyclononane, bpy = 2,2¢-bipyridine, pap = 2-phenylazopyridine), respectively. The nitrosyl
complexes have been synthesized by following a stepwise synthetic procedure: {RuII–Cl} →
{RuII–CH3CN} → {RuII–NO2} → {RuII–NO+} → {RuII–NO∑}. The single-crystal X-ray structure of
43+ and DFT optimised structures of 43+, 83+ and 42+, 82+ establish the localised linear and bent
geometries for {Ru–NO+} and {Ru–NO∑} complexes, respectively. The crystal structures and 1H/13C
NMR suggest the [333] conformation of the coordinated macrocyclic ligand ([9]aneS3) in the
complexes. The difference in p-accepting strength of the co-ligands, bpy in 43+ and pap in 83+ (bpy <
pap) has been reflected in the n(NO) frequencies of 1945 cm-1 (DFT: 1943 cm-1) and 1964 cm-1 (DFT:
1966 cm-1) and E◦({RuII–NO+}/{RuII–NO∑}) of 0.49 and 0.67 V versus SCE, respectively. The n(NO)
frequency of the reduced {Ru–NO∑} state in 42+ or 82+ however decreases to 1632 cm-1 (DFT: 1637
cm-1) or 1634 cm-1 (DFT: 1632 cm-1), respectively, with the change of the linear {RuII–NO+} geometry
in 43+, 83+ to bent {RuII–NO∑} geometry in 42+, 82+. The preferential stabilisation of the eclipsed
conformation of the bent NO in 42+ and 82+ has been supported by the DFT calculations. The reduced
{RuII–NO∑} exhibits free-radical EPR with partial metal contribution revealing the resonance
formulation of {RuII–NO∑}(major)↔{RuI–NO+}(minor). The electronic transitions of the complexes
have been assigned based on the TD-DFT calculations on their DFT optimised structures. The
estimated second-order rate constant (k, M-1 s-1) of the reaction of the nucleophile, OH- with the
electrophilic {RuII–NO+} for the bpy derivative (43+) of 1.39 ¥ 10-1 is half of that determined for the pap
derivative (83+), 2.84 ¥ 10-1 in CH3CN at 298 K. The Ru–NO bond in 43+ or 83+ undergoes facile
photolytic cleavage to form the corresponding solvent species {RuII–CH3CN}, 22+ or 62+ with widely
varying rate constant values, (kNO, s-1) of 1.12 ¥ 10-1 (t1/2 = 6.2 s) and 7.67 ¥ 10-3 (t1/2 = 90.3 s),
respectively. The photo-released NO can bind to the reduced myoglobin to yield the Mb-NO adduct.
or in defence mechanisms against microorganisms and tumor
Introduction
cells3 makes it an attractive small molecule. At the cellular level,
NO is known to be produced from L-arginine catalysed by the
heme-containing enzyme NO synthase (NOS)4 and its deficiency
facilitates a wide range of physiological disorders.5 The interaction
of NO with the transition metal ions in biological fluids and
its redox non-innocent features as cationic NO+, radical NO∑,
or anionic NO- in the complex molecules have initiated an
intense renewed research interest from the broader perspective of
inorganic chemistry.6 This indeed has instigated the designing of
newer nitrosyl complexes, especially iron nitrosyls, as the natural
metal-binding centres.7 Though a large number of ruthenium
nitrosyl derivatives are known for a long time in the literature,8 it
has drawn considerable research interest in recent years primarily
The relevance of nitrogen monoxide (NO) in biological processes
including its role in neuro-signaling,1 cardiovascular control,2
aDepartment of Chemistry, Indian Institute of Technology Bombay, Powai,
Mumbai, 400076, India. E-mail: lahiri@chem.iitb.ac.in
bDepartment of Chemistry, Jadavpur University, Jadavpur, Kolkata, 700032,
India
cInstitut fu¨r Anorganische Chemie, Universita¨t Stuttgart, Pfaffenwaldring
55, D-70550, Stuttgart, Germany
† Electronic supplementary information (ESI) available: Crystallographic
materials, DFT data set and NMR, UV-vis. and EPR spectra (Tables
S1–S15 and Fig. S1–S10). CCDC reference numbers 823376–823380. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt10761e
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aneS3)(pap)(NO∑)]2+ (82+), respectively, ([9]aneS3
trithiacyclononane, bpy = 2,2¢-bipyridine, pap = 2-phenylazo-
pyridine, Scheme 1) have been synthesized.
due to their fascinating coordination chemistry,8a and potential
application as antitumor, and antiseptic agents,9 in catalysis10 and
in photochemical processes.11
=
1,4,7-
In this context ruthenium nitrosyl complexes with the selec-
∑
12
tive molecular frameworks of [RuII(trpy)(AL)(NO+¢ )]n
and
∑
13
[RuII(tpm)(AL)(NO+¢ )]n
incorporating meridionally and fa-
cially oriented tridentate ligands, 2,2¢:6¢,2¢¢-terpyridine (trpy) and
tris(1-pyrazolyl)methane (tpm), respectively, in combination with
other ancillary ligands (AL) with varying electronic properties
have been reported recently. The detailed studies reveal the
significant contribution of the ancillary ligands, trpy/AL or
tpm/AL in tuning the (i) electronic structural aspects, (ii) extent
of electrophilicity of the coordinated NO+, (iii) accessibility of
different redox states of NO (NO+, NO∑, NO-), (iv) photolability
∑
of the Ru–NO+¢ bond and (v) reactivities of {Ru–NO+} and {Ru–
NO∑} with OH- and O2.
This indeed has initiated the present programme of dealing with
the newer molecular frameworks of [RuII([9]aneS3)(bpy)(NO)]n
(4n) and [RuII([9]aneS3)(pap)(NO)]n (8n) involving facially co-
ordinated 1,4,7-trithiacyclononane ([9]aneS3) and moderately
p-accepting 2,2/-bipyridine (bpy) and strongly p-accepting 2-
phenylazopyridine (pap), respectively.
Scheme 1 Representation of complexes with their corresponding numer-
ical notations.
The nitrosyl complexes (43+/42+) and (83+/82+) are synthe-
sized by following the stepwise general synthetic procedure
[RuII([9]aneS3)(AL)(Cl)]+ → [RuII([9]aneS3)(AL)(CH3CN)]2+
→
[RuII([9]aneS3)(AL)(NO2)]+ → [RuII([9]aneS3)(AL)(NO+)]3+
→
[RuII([9]aneS3)(AL)(NO∑)]2+ (AL
=
bpy or pap, Scheme
1). The synthesis of the precursor bipyridine complex,
[RuII([9]aneS3)(bpy)(Cl)]+ (1+) has been performed by following
the reported procedure15m and its electronic and 1H NMR spectra
match fairly well with those reported in the literature. The
complexes have been isolated in the solid state as their perchlorate
salts. It may be noted that attempts to synthesize the nitrosyl
derivatives, 43+ and 83+ directly from the precursor chloro or solvate
by using either NO gas or [NO]BF4 proved unsuccessful.16b
The complexes have been characterized by their satisfactory
microanalytical, electrical conductivity and mass, IR, NMR
spectral data (see the Experimental section). The single-crystal X-
ray structures of selective derivatives have also been determined.
The crystal structures of the newly synthesized precursor com-
plexes, bpy derivative: [3](ClO4) (X = NO2) and pap derivatives:
[5](ClO4) (X = Cl), [6](ClO4)2 (X = CH3CN), [7](ClO4) (X = NO2) in
Scheme 1 are shown in Fig. S1–S4 in the Electronic Supplementary
Information (ESI†). Selected crystallographic parameters and
bond distances and angles are listed in Tables S1 and S2 in
the ESI,† respectively. The single-crystal X-ray structure of the
nitrosyl complex, [RuII([9]aneS3)(bpy)(NO+)](ClO4)3 ([4](ClO4)3)
has also been determined (Fig. 1 and Tables 1 and 2). In each
case the asymmetric unit consists of one independent molecule.
The endocyclic torsion angles, S–C–C–S, C–S–C–C and C–C–S–
C involving the coordinated macrocyclic [9]aneS3 (Table S3†) in the
complexes reveal the [333] conformation in the Dale nomenclature
in each case.15m
The present report describes the detailed synthetic and struc-
tural aspects of the nitrosyl derivatives, 4n and 8n including their
precursor complexes. The electronic structures and subsequent re-
activity aspects of 4n and 8n have been investigated by experimental
and DFT studies. The specific effect of [9]aneS3 in combination
with bpy (4n) or pap (8n) on the {Ru–NO} moiety has been
highlighted in relation with analogous reported systems.
It should be noted that the interaction of thiamacro-
cycle, 1,4,7-trithiacyclononane ([9]aneS3) with various transi-
tion metal ions14 including ruthenium15 has been well stud-
ied from various perspectives of coordination chemistry.
However, to the best of our knowledge there are only
16a
two reports till date, [Re([9]aneS3)(CO)2(NO)](OTf)2
and
[Ru(phpy)([9]aneS3)(L)]BF416b (phpy = phenylpyridine) which deal
with the metal-nitrosyl chemistry in combination with [9]aneS3.
Results and discussion
Synthesis, characterization and structural aspects
The nitrosyl complexes with the Enemark-Feltham notations17 of
6
7
{RuNO} and {RuNO} involving the selective molecular frame-
works of [RuII([9]aneS3)(bpy)(NO+)]3+ (43+), [RuII([9]aneS3)(pap)-
(NO+)]3+ (83+) and [RuII([9]aneS3)(bpy)(NO∑)]2+ (42+), [RuII([9]-
12528 | Dalton Trans., 2011, 40, 12527–12539
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Table 1 Crystallographic data for [RuII([9]aneS3)(bpy)(NO)](ClO4)3
[4](ClO4)3
Table 2 Selected bond distances (A) and bond angles (◦)
for RuII([9]aneS3)(bpy)(NO)] (ClO4)3 [4](ClO4)3 (X-ray) and
[RuII([9]aneS3)(bpy)(NO)]3+/2+ (43+/2+) (DFT)
˚
[4](ClO4)3.0.5 H2O
X-ray
DFT
Empirical formula
Mr
C16H20Cl3N3O13RuS3·0.5H2O
773.95
150(2)
Monoclinic
P21/n
16.7231(7)
10.3071(3)
17.4570(9)
90
116.828(6)
90
2685.13(19)
4
1.915
1.186
[4](ClO4)3
43+
42+
Temperature/K
Crystal symmetry
Space group
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–S(1)
Ru(1)–S(2)
Ru(1)–S(3)
Ru(1)–N(3)
N(3)–O(1)
S(1)–Ru(1)–S(2)
S(1)–Ru(1)–S(3)
S(2)–Ru(1)–S(3)
N(1)–Ru(1)–S(2)
N(1)–Ru(1)–S(1)
N(2)–Ru(1)–S(1)
N(1)–Ru(1)–S(3)
N(2)–Ru(1)–S(2)
N(2)–Ru(1)–S(3)
N(1)–Ru(1)–N(2)
N(1)–Ru(1)–N(3)
N(2)–Ru(1)–N(3)
S(1)–Ru(1)–N(3)
S(2)–Ru(1)–N(3)
S(3)–Ru(1)–N(3)
Ru(1)–N(3)–O(1)
2.083(4)
2.082(4)
2.3780(13)
2.3722(14)
2.3964(14)
1.766(4)
1.127(5)
87.12(5)
86.76(5)
86.70(5)
169.09(12)
97.63(11)
173.89(12)
83.78(12)
95.55(12)
87.91(12)
78.82(16)
94.88(18)
94.69(18)
90.55(14)
94.90(15)
176.79(14)
176.5(4)
2.118
2.119
2.461
2.455
2.466
1.789
1.135
85.25
85.10
85.07
170.1
97.86
171.9
85.83
97.55
87.64
78.15
94.14
93.15
94.09
95.00
179.2
179.5
2.123
2.124
2.408
2.409
2.459
1.939
1.168
85.94
86.45
86.29
174.0
98.13
175.5
89.60
98.10
91.77
77.67
91.37
89.68
92.13
92.82
178.4
140.4
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
Dc/g cm-3
m/mm-1
F(000)
1552
2q range (◦)
6.56 to 50
4730/0/361
1.037
0.0429, 0.1159
0.0596, 0.1202
1.261, -1.069
Data/restraints/parameters
GOF
R1, wR2 [I > 2s(I)]
R1, wR2 (all data)
Largest diff. Peak, hole/e A
-3
˚
˚
average Ru–N1(pyridine, pap) distance, 2.069(4) A in [5](ClO4),
[6](ClO4)2, [7](ClO4) due to (dp)RuII → p*(N N, pap) back-
bonding effect18 which has also been reflected in the longer N
N
˚
bond distances of 1.287(5), 1.287(6) and 1.284(5) A, respectively,
+
19
˚
as compared to the N N distance of free [Hpap] , 1.258(5) A.
The significantly shorter Ru –N3(NO) distance of 1.766(4) A and
II
˚
˚
the triple bond feature of N3–O1(NO) (1.127(5) A) along with an
almost linear Ru–N3–O1(NO) bond angle of 176.5(4)◦ reveal the
p-acceptor character of the coordinated nitrosonium (NO+) ion in
[4](ClO4)3.12b–d,g,j,k,13a,b Consequently, the Ru–S3 bond (2.3964(14)
˚
A) trans to the Ru–NO bond in [4](ClO4)3 is slightly longer than the
˚
other two Ru–S bonds (Ru–S1, 2.3780(13), Ru–S2, 2.3722(14) A).
The DFT optimised structures of [RuII([9]aneS3)(bpy)(NO+)]3+
(43+) (Fig. 2, Table 2) and [RuII([9]aneS3)(pap)(NO+)]3+ (83+) at the
B3LYP level with SDD basis set for Ru and 6-31G* for other
atoms (Fig. 3, Table S4†) also reveal the almost linear geometry
of the {Ru–NO+} group in 43+ and 83+ with Ru–N–O angles of
179.5 and 179.2◦, respectively, and the same N O distance of
Fig. 1 Molecular structure of the cation of [RuII([9]aneS3)(bpy)(NO)]-
(ClO4)3 in the crystal structure of [4](ClO4)3. Ellipsoids are drawn at 50%
probability. Hydrogen atoms and solvent of crystallisation are omitted for
clarity.
˚
The tridentate [9]aneS3 ligand binds to the ruthenium ion via the
three sulfur donors in tris-endodentate fashion with the expected
staggered conformation about the C–C bonds. The average RuII–
S bond distances and average S–Ru–S angles in the complexes
(Table S2† and Table 2) are close to those reported in analo-
gous ruthenium complexes.15 The reasonably shorter cis angles
involving the coordinated bidentate bpy and pap with respect
to the idealised 90◦ imply a distorted octahedral environment
around the ruthenium ion in the complexes. The interligand
trans angles, N1–Ru1–S2, N2–Ru1–S1, S3–Ru1–X (X = Cl or
CH3CN or NO2 or NO) are close to 180◦ except the appreciably
shorter N1–Ru1–S2 trans angle of 169.09(12)◦ in the nitrosyl
complex ([4](ClO4)3). Ru–N(pyridine or CH3CN or NO2) and Ru–
Cl distances match well with those of analogous complexes.12 The
1.135 A. On the other hand, the DFT optimised structures of the
reduced [RuII([9]aneS3)(bpy)(NO∑)}]2+ (42+) (Fig. 2, Table 2) and
[RuII([9]aneS3)(pap)(NO∑)}]2+ (82+) at the (U)B3LYP level (Fig.
3, Table S4†) predict the bent {Ru–N O∑} geometry: Ru–N–O,
140.4,139.4◦ and N O, 1.168, 1.165 A, respectively.
On
12l,13c,20
˚
moving from NO+ in 83+ to NO∑ in 82+ the DFT calculated Ru–
˚
N2(azo, pap) bond distance slightly decreases from 2.162 A to
+
˚
2.136 A due to the difference in p-accepting strength of the NO
and NO∑ states.
7
The bent geometry of {Ru–NO} in the distorted octahedral
environment introduces splitting in the degenerate e-level of {Ru–
6
7
NO} leading to a non-degenerate state in {Ru–NO} which in
effect yields eclipsed and staggered conformations with Strans–Ru–
N–O dihedral angles (q) of 0◦ and 45◦, respectively, at the two
extreme cases.6l,m,12m The geometry optimisation of 42+ or 82+ at
˚
average Ru–N2 (azo, pap) distance of 2.022(4) A is shorter than the
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Fig. 2 DFT-optimised structures of (a) [RuII([9]aneS3)(bpy)(NO)]3+ (43+
and (b) [RuII([9]aneS3)(bpy)(NO)]2+ (42+).
)
the G03/(U)B3LYP level reveals that eclipsed conformation is
favoured in both the cases. In the case of 42+, the optimised
geometry with the dihedral angle, q = 4.45◦ is calculated to be
energetically more favourable by 83.8 cm-1 (0.2396 kcal mol-1) and
260 cm-1 (0.7434 kcal mol-1) with respect to the idealised eclipsed
(q = 0◦) and staggered (q = 45◦) conformations in vacuo (Table
S5†). The slight deviation from the idealised q = 0◦ in the optimised
geometry (q = 4.45◦) could be attributed to the interaction between
the nearby sulfur (S(1) of [9]aneS3) and oxygen (O1) atoms.
Unlike the bpy complex 42+, for 82+ four different eclipsed as well
as staggered conformations are theoretically feasible due to the
unsymmetrical nature of the pap ligand. The optimised geometry
of 82+ reveals an almost eclipsed conformation (aligned parallel to
Ru–N(1) bond) with dihedral angle, q = 0.41◦ which is energetically
lowered by 266 cm-1 (0.7606 kcal mol-1) and 391 cm-1 (1.1179 kcal
mol-1), respectively, with regard to the idealised eclipsed form (q =
0◦) and staggered conformation with q = 45◦ in vacuo (Table S5†).
Though the eclipsed conformer is calculated to be more stable,
both eclipsed and staggered forms are energetically probable at
Fig. 3 DFT-optimised structures of (a) [RuII([9]aneS3)(pap)(NO)]3+ (83+
and (b) [RuII([9]aneS3)(pap)(NO)]2+ (82+).
)
room temperature due to their minor difference in energy (Table
S5†). The observed broad as well as slightly splitted profile of the
n(NO) band in the IR spectra of 42+ and 82+ (Fig. 4, see later) could
be rationalised on the basis of existence of both the conformers at
the IR time scale.
Spectral aspects
1H NMR spectra of the diamagnetic nitrosyl complexes, 43+ and
83+ in CD3CN are shown in Fig. S5† and chemical shift values
for all the complexes are set in Table S6.† In the aromatic region
bpy complexes, 22+, 3+, 43+ exhibit four distinct proton signals
(two doublets and two triplets) in the range of d, 7–9 ppm
corresponding to one pyridine ring of bpy due to the internal
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three, six aliphatic carbon signals, respectively, which essentially
justifies the single isomeric identity of the complexes in the solution
state.15g,m
The IR data involving n(ClO4), n(NO2) and n(NO) vibrations
of the respective complexes are given in the Experimental section.
The n(NO) stretching frequencies of [4](ClO4)3 and [8](ClO4)3 at
1945 cm-1 (DFT: 1943 cm-1) and 1964 cm-1 (DFT: 1966 cm-1),
respectively, (Fig. 4) suggest that the electrophilic character of the
coordinated NO+ group increases with the increase in p-accepting
character of the ancillary ligands, pap > bpy.21 A similar trend of
n(NO) frequency based on the difference in p-accepting nature
of bpy and pap has also been observed in analogous nitrosyl
complexes with meridionally oriented 2,2¢:6¢,2¢¢-terpyridine (trpy):
12a
bpy, 1952 cm-1;12h pap, 1960 cm-1
and facially oriented tris(1-
pyrazolyl)methane (tpm): bpy, 1959 cm-1;13a pap, 1962 cm-1.13c The
n(NO) band however shifts substantially (ª300 cm-1) to the lower
energy region on reduction of 43+ (1945 cm-1) to 42+ (1632 cm-1,
DFT: 1637 cm-1) or 83+ (1964 cm-1) to 82+ (1634 cm-1, DFT: 1632
cm-1) (Fig. 4). This implies predominantly NO centred reduction,
{RuII–NO+} in 43+/83+ to {RuII–NO∑} in 42+/82+ with the change
in localised geometry from sp-hybridised (N of NO+) linear {Ru–
NO+} to close to sp2-hybridised (N of NO∑) bent {RuII–NO∑} as
has also been revealed by the DFT optimised geometries (Fig. 2
and 3).
Ruthenium(II) based MLCT transition energy of the complexes
systematically varies with the change in ligand field strength
of the monodentate ligand (X) in [RuII([9]aneS3)(bpy)(X)]n or
[RuII([9]aneS3)(pap)(X)]n and it follows the order: X = Cl-< NO∑£
NO2< CH3CN (Fig. S8 and Fig. S9, Table S8†).12
Fig. 4 IR spectra (KBr disk) of (a) [RuII([9]aneS3)(bpy)(NO)](ClO4)3
([4](ClO4)3,---), [RuII([9]aneS3)(bpy)(NO)](ClO4)2 ([4](ClO4)2,—) and
(b) [RuII([9]aneS3)(pap)(NO)](ClO4)3 ([8](ClO4)3,---), [RuII([9]aneS3)-
(pap)(NO)](ClO4)2 ([8](ClO4)2, —) in the region of 2200–1500 cm-1.
symmetry and the chemical shift values vary slightly depending
on the electronic nature of the monodentate ligands, X = CH3CN,
NO2, NO+ (Scheme 1). The twelve methylene protons associated
with the three connecting (CH2)2 units of coordinated [9]aneS3 in
22+, 3+ and 43+ appear as multiplets in the chemical shift range
of d, 2–4 ppm due to geminal and vicinal couplings. On the
other hand the calculated number of nine aromatic protons of
the unsymmetrical pap ligand in 5+, 62+, 7+, 83+ appear as partially
overlapping signals in the chemical shift range of d, 7–9 ppm where
the d value differs slightly based on the monodentate ligands (X,
Scheme 1). The unsymmetrical nature of pap introduces more
complexities particularly in the CH2 proton signals where the
proton resonances are essentially distributed in the chemical shift
range of d, 1.3–4.2 ppm. The clearly resolved four or nine aromatic
proton resonances associated with the half of the symmetric bpy
or full molecule of unsymmetric pap, respectively, imply that
one conformation of the macrocyclic ligand, [9]aneS3 exists in
the solution state as well. Furthermore, 13C NMR spectra of the
representative nitro and nitroso derivatives, bpy (3+, 43+) and pap
(7+, 83+), Fig. S6, Fig. S7, Table S7†) exhibit five, nine aromatic and
The nitrosyl complexes with {RuII–NO+} configuration in 43+
and 83+ show one moderately intense absorption near 300 nm
with weak shoulders at the lower energy region around 400 nm
and multiple transitions in between 500–300 nm, respectively, in
CH3CN (Fig. S9†). The transitions are assigned based on the
TD-DFT calculations as ligand-to-ligand charge-transfer (LLCT)
and ligand-to-ligand/metal charge-transfer (LLMCT) transitions
(Table S9†). Ligand based higher energy HOMOs and the mixed
ligand and metal based lower energy LUMOs are primarily
involved in the observed transitions.
The charge-transfer transitions in the reduced nitrosyl com-
plexes with {RuII-NO∑} configuration in 42+ and 82+ appear
in the relatively lower energy region near 400 and 500 nm,
respectively (Fig. S9†). The TD-DFT calculations on the op-
timised 42+ and 82+ predict multiple near by transitions in the
above region which are essentially mixed metal/ligand-to-ligand
charge-transfer (MLLCT), ligand-to-ligand charge-transfer
(LLCT) and metal-to-ligand charge-transfer (MLCT) in nature
(Table S10†).
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Electron-transfer properties
reduced 42+ or 82+ signifies that the second reduction corresponds
to {RuII–NO∑}(major)/{RuI(NO+)}(minor) → {RuII–NO-}. The
subsequent reductions at the more negative potentials (Table
S11†) are associated with the ancillary ligands, bpy or [9]aneS3
or pap.
The RuII/RuIII potentials of the precursors in [RuII([9]-
aneS3)(bpy)(X)]n or [RuII([9]aneS3)(pap)(X)]n with X = Cl- (5+),
CH3CN (22+, 62+), NO2 (3+, 7+) vary systematically in each set: X =
Cl-< NO2 < CH3CN12 (Table S11†). The stronger p-accepting
feature of pap relative to bpy enhances the stability of the Ru(II)
state in 62+ (X = CH3CN) and 7+ (NO2) as compared to the
corresponding 22+ and 3+. Furthermore, successive two and three
ligand based reductions are observed for bpy and pap derivatives,
respectively, within -2.0 V versus SCE (Table S11†). The diimine
(N C–C N) and azo (N N) functions of coordinated bpy
and pap, respectively, are known to undergo successive two-step
one-electron reductions22 and [9]aneS3 also shows one irreversible
reduction at -1.09 V versus SCE in CH3CN.23
Besides ancillary ligand (bpy, [9]aneS3, pap) based reductions,
the nitrosyl complexes, 43+ and 83+ exhibit additional one quasi-
reversible reduction at 0.49 V and 0.67 V, followed by an
irreversible reduction at 0.07 V and 0.03 V versus SCE, respectively
(Fig. 5, Table S11†). These two reductions at relatively higher
positive potential region are assigned to the successive NO based
redox processes, NO+ → NO∑ (response I) and NO∑ → NO-
(response II). The DFT calculations on optimised 43+ and 83+
also predict that in both the cases LUMO and LUMO+1 are
dominated by NO+ based orbitals (~70%) (Tables S12 and S13†)
along with ~20% contribution from ruthenium due to (dp)Ru(II)
→ p*(NO+) back-bonding. The primarily nitrosyl based first
reduction of {RuII–NO+} → {RuII–NO∑} has also been revealed
by the NO dominated SOMO (~50%) in the MOs (a-spin) of
the reduced 42+ or 82+ (Tables S14 and S15†). The appreciable
contribution of Ru (30%) in the SOMO implies that the electronic
structure of 42+ or 82+ can be best represented as a mixed
situation of {RuII–NO∑}(major)/{RuI(NO+)}(minor). The dom-
inating contribution of NO in the LUMO (b-spin, >50%) for the
The stronger electrophilicity of the NO+ centre in 83+ has been
reflected in the100–200 mV positive shift of NO reductions relative
to those in 43+. The separation in potential of the two successive
NO based redox processes leads to the large comproportionation
constant (Kc) (RTlnKc = nF(DE))24 values of 107.1 and 1011.8 for the
intermediate 42+and 82+, respectively, which indeed has facilitated
the isolation of the radical {RuII–NO∑} derivatives.
The reduced {RuII–NO∑} displays a free radical EPR (g ~ 2.0)
(Fig. S10†) with slight metal based anisotropy as reported in
numerous analogous systems.25,26 The spin-density plots of 42+ and
8
2+ (Fig. 6) also predict that NO is the primary spin-bearing centre
with Mulliken spin densities of NO = 0.826, Ru = 0.100, [9]aneS3 =
0.057, bpy = 0.016 and NO = 0.820, Ru = 0.118, [9]aneS3 = 0.057,
pap = 0.005, respectively. The SOMO of 42+ or 82+ indicates s-
donation from the p* orbital of NO to the dz2(Ru) centre which
reveals {RuII–NO∑} as the predominant valence formulation along
with the considerable mixing of {RuI–NO+} configuration due
to the presence of ~30% metal contribution (Tables S14 and
S15†).12d Moreover, s-interaction between Ru and NO as revealed
by the SOMO and the spin density at the axial position result in
significant hyperfine splitting in the EPR spectrum due to 14NO (I =
1). The observed slight g anisotropy in the EPR spectrum develops
due to the bending mode of Ru–N–O (Fig. 2 and 3) and partial
mixing of ruthenium frontier orbitals with the close lying singly
occupied molecular orbital (SOMO) of NO∑. The anisotropy of the
g factor in the EPR of {Ru–NO∑} species including the modelling
aspects and spin Hamiltonian of metal bound NO∑ have been
discussed at length in earlier publications.8a,25
Fig.
5 Cyclic voltammograms (nitrosyl based reductions) of (a)
[RuII([9]aneS3)(bpy)(NO)]3+ (43+) and (b) [RuII([9]aneS3)(pap)(NO)]3+ (83+
)
in CH3CN/0.1 M Et4NClO4 versus SCE, scan rate: 100 mV s-1. Responses
I and II correspond to NO+ → NO∑ and NO∑ → NO- redox processes,
respectively.
Fig. 6 Spin density plots of (a) [RuII([9]aneS3)(bpy)(NO)]2+ (42+) and (b)
[RuII([9]aneS3)(pap)(NO)]2+ (82+).
12532 | Dalton Trans., 2011, 40, 12527–12539
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Unlike the precursor chloro (5+), solvate (22+, 62+) and nitro
(3+, 7+) derivatives, nitrosyl complexes, 43+ and 83+ do not exhibit
ruthenium(II) → ruthenium(III) oxidation (Table S11†) since
HOMOs are primarily composed of bpy and pap based orbitals,
respectively (Tables S12 and S13†). This can be attributed to the
effect of multiple strong p-acceptor ligands, bpy/pap, [9]aneS3
and NO+ in the molecular frameworks of 43+ and 83+. Appreciable
ruthenium contributions of 40% and 35% are predicted only in
the much lower HOMO-7 and HOMO-10 levels in 43+ and 83+,
respectively, revealing that the better p-accepting ability of pap
introduces greater stability of Ru(II) state in 83+ as has also been
reflected in the experimental results.
Fig. 7 Time evolution of the electronic spectra (time intervals: 5 min)
of (a) [RuII([9]aneS3)(bpy)(NO)]3+ (43+), (concentration: 0.59 ¥ 10-5 M in
CH3CN) in the presence of aqueous OH- (concentration of 2.44 ¥ 10-3 M)
at 298 K and (b) [RuII([9]aneS3)(pap)(NO)]3+ (83+), (concentration: 0.59 ¥
10-5 M in CH3CN) in the presence of aqueous OH- (concentration: 0.59 ¥
10-3 M) at 298 K. Insets show the plots of pseudo-first order rate constants
(k, s-1) at different OH- concentrations at 298 K.
Reactivity aspects
Reaction of {RuII–NO+} with the Nucleophile OH-. The ruthe-
nium nitrosyls 43+ and 83+ are stable in the solid state. However, 43+
and 83+ quickly transform to the corresponding nitro derivatives,
3+ and 7+, respectively, in H2O even with such a low concentration
of OH- of 10-7 M. This indeed had prevented us following the
reaction of 43+ or 83+ with the nucleophile OH- in aqueous medium
using the conventional spectrophotometric technique. However,
acetonitrile solutions of 43+ and 83+ are reasonably stable to follow
the reaction with 100 fold excess OH- under pseudo first-order
conditions (pseudo pH, 9.2) which leads to the formation of the
corresponding nitro complexes, 3+ and 7+, eqn (i) (AL = bpy or
pap). On the other hand, the reverse process
The negative DS‡ values of -136 and -144 J K-1 mol-1 (eqn(i))
for 43+ and 83+, respectively, (Table 3) reveal that the reaction of
{RuII–NO+} with OH- proceeds through an associatively activated
process involving the bound {RuII–NO2H} intermediate followed
by a rapid deprotonation step as shown by eqn (ii) and (iii) (AL =
bpy or pap).13a The estimated second-order rate constant value of
~10-1 M-1 s-1 for the present
[RuII ([9]aneS3(AL)(NO)]3+ +2OH− → [RuII ([9]aneS3(AL)(NO2 )+ +H2O
[RuII(aneS3)(AL)(NO+)]3+ + OH- →
(ii)
4
3+ or 83+
3+ or 7+
[RuII([9]aneS3)(AL)(NO2H)]2+
(i)
i.e. {RuII–NO2} → {RuIINO+} is triggered by the H+ ion as stated
before. The conversion of {RuII–NO+} to {RuII–NO2} proceeds
through distinct isosbestic points (Fig. 7) implying the presence
of only {RuII–NO2} and {RuII–NO+} species in the equilibriated
solution. The rate constant value for the reaction (eqn (i)) has been
determined by following the increase in absorbance of the product,
{RuII–NO2} with the progress of the reaction (Table 3). The pseudo
first-order rate constant values at different concentrations of OH-
exhibit a linear relationship (Fig. 7), therefore the second order
rate constant values are estimated simply by dividing the pseudo
first-order rate constant value with the used base concentration.
The second-order rate constant values at different experimental
temperatures for the bpy complex in 43+ are almost half to those
obtained for the pap complex, 83+ (Table 3) due to the difference
in the p-accepting features of bpy and pap.
[RuII(aneS3)(AL)(NO2H)]2+ → [RuII([9]aneS3)(AL)(NO2)]+ +
(iii)
H+
set of nitrosyl complexes (43+ and 83+) in CH3CN is much lower
than that reported for the analogous complex involving the facially
coordinated tris(1-pyrazolyl)methane (tpm) in combination with
bpy, [RuII(tpm)(bpy)(NO+)]3+ in H2O of ~106 M-1 s-1. The much
lower rate constant value for 43+ or 83+ can be attributed to
the effect of using non-aqueous CH3CN solvent instead of
water. Incidentally, the k, M-1 s-1 of 2.03 ¥ 10-1 at 298 K for
13c
[RuII(tpm)(pap)(NO+)]3+ in CH3CN
is close to 2.84 ¥ 10-1
determined for the analogous 83+ in acetonitrile and both the
complexes exhibit similar n(NO) frequencies of 1964 and 1962
cm-1, respectively.
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Table 3 Rate constant and activation parameters
Complex (concentration)
Temp./K
298
[OH-] M-1
k s-1
k M-1s-1
DH‡ kJ mol-1
DS‡ J K-1mol-1
K298
44.5
43+ (0.59 ¥ 10-5 M in CH3CN)
2.44 ¥ 10-3
4.88 ¥ 10-3
7.32 ¥ 10-3
9.76 ¥ 10-3
2.44 ¥ 10-3
2.44 ¥ 10-3
0.59 ¥ 10-3
1.18 ¥ 10-3
1.77 ¥ 10-3
2.36 ¥ 10-3
0.59 ¥ 10-3
0.59 ¥ 10-3
3.41 ¥ 10-4
6.67 ¥ 10-4
10.34 ¥ 10-4
13.56 ¥ 10-4
6.75 ¥ 10-4
13.67 ¥ 10-4
1.68 ¥ 10-4
3.35 ¥ 10-4
5.02 ¥ 10-4
6.67 ¥ 10-4
3.32 ¥ 10-4
6.63 ¥ 10-4
1.39 ¥ 10-1
52.11 0.03
-136.51 0.05
308
318
298
2.77 ¥ 10-1
5.60 ¥ 10-1
2.84 ¥ 10-1
83+ (0.59 ¥ 10-5 M in CH3CN)
51.49 0.02
-144.43 0.07
2.04
308
318
5.63 ¥ 10-1
11.24 ¥ 10-1
Photocleavage of the {RuII–NO} bond
primarily based on the difference in electronic nature of the
ancillary ligands, bpy and pap.
Under ambient light the nitrosyl complexes [RuII([9]-
aneS3)(bpy)(NO+)]3+ (43+) and [RuII([9]aneS3)(pap)(NO+)]3+ (83+)
are stable in CH3CN. However, on exposure to radiation from a
Xenon 350 W light source the deoxygenated acetonitrile solutions
of 43+ and 83+ spontaneously transform the corresponding
solvent species, [RuII([9]aneS3)(bpy)(CH3CN)]2+, 22+ and
[RuII([9]aneS3)(pap)(CH3CN)]2+, 62+ via the photocleavage of the
Ru–NO bond. The transformation of the nitrosyl complex, 43+
or 83+ to the corresponding solvate, 22+ or 62+ under photolytic
conditions occurs with the distinct change in colour as well as the
change in electronic spectral profile (Fig. 8).
The cleavage of the {RuII–NO+} bond in 43+ or 83+ via the photo-
irradiation process proceeds through the formation of the interme-
diate excited S = 1 state in {RuIII–NO∑}* as shown in eqn (iv).11a–c
The formation of {RuII–CH3CN} instead of {RuIII–CH3CN} as
the final metal-solvent fragment in the photolytic solution has
been established by comparing its electronic spectral feature with
the isolated solvent species, [RuII([9]aneS3)(bpy)(CH3CN)]2+, 22+
or [RuII([9]aneS3)(pap)(CH3CN)]2+, 62+ (Fig. 8).
Conclusion
The important features of the work are highlighted below:
– The nitrosyl function can be stabilised both in NO+ and
NO∑ redox states in the newly designed molecular frameworks
of [RuII([9]aneS3)(bpy)(NO)]n (4n) and [RuII([9]aneS3)(pap)(NOn)]n
(8n).
– The facially coordinated 1,4,7-trithiacyclononane ([9]aneS3) in
combination with the p-accepting bpy in 43+ and pap in 83+ develop
strongly electrophilic coordina◦ted NO+ centres as revealed by their
high n(NO) frequencies and E ({RuII–NO+}–{RuII–NO∑}) (Table
4). The difference in the p-accepting strength of bpy and pap has
been reflected in the electronic features of the molecules.
–
The reduced {Ru–NO∑} species in 42+ and 82+
can be best described by
a resonance formulation of
{RuII(NO∑)}(major)↔{RuI(NO+)}(minor).
– The electrophilic NO+ centres in 43+ and 83+ react with
the nucleophile OH- to yield the corresponding {RuII–NO2}
derivatives, 3+ and 7+, respectively. However, the rate of the
reaction (k, M-1 s-1) for 83+ is almost double that of 43+.
– On exposure to light both 43+ and 83+ undergo the photo-
cleavage reaction of the RuII–NO bond to form the corresponding
solvent species, 22+ and 62+, respectively, but the rate of photore-
lease of “NO” (kNO, s-1) is 700 times faster in the case of 43+ as
compared to 83+.
{RuII–NO+} + hn → {RuIII–NO∑}* → {RuII-solvent} + NO∑ (iv)
The electronic effect of p-accepting ancillary ligands (bpy or pap
and [9]aneS3) certainly facilitates the stabilisation of the {RuII–
CH3CN} species in the ground state.
It should be noted that the selective photolytic cleavage of the
M–NO bond, {(AL)MII–NO} → {(AL)MII(solvent)} maintaining
the integrity of the rest of the molecule is known to be biologically
significant.11
Experimental
The rate of first-order photorelease of NO (kNO) has been
determined to be 1.12 ¥ 10-1 s-1 (t1/2 = 6.2 s) or 7.67 ¥ 10-3 s-1
(t1/2 = 90.3 s) for 43+ or 83+, respectively. Thus, under identical
experimental conditions the rate of photocleavage of the {RuII–
NO+} bond (kNO, s-1) for the pap derivative (83+) is about 700 times
slower than that for the bpy complex (43+).
Materials
The ligand 2-phenylazopyridine (pap)12a and the start-
ing complexes [Ru([9]aneS3)(dmso)Cl2],28 [RuII([9]aneS3)(bpy)-
(Cl)](ClO4)15m were prepared as described in the literature. The
ligands 1,4,7-trithiacyclononane ([9]aneS3) and 2,2¢-bipyridyl were
purchased from Aldrich. Other chemicals and solvents were
reagent grade and used as received. For spectroscopic and
electrochemical studies HPLC grade solvents were used.
The liberated NO from the photolysed acetonitrile solution of
43+ or 83+ could easily be trapped as {Mb-NO} adduct as evident
from the emergence of a new band at lmax = 424 nm corresponding
to the standard absorption of {Mb-NO} (Fig. 8).27
Hence, the newly designed molecular frameworks of
[RuII([9]aneS3)(bpy)(NO+)]3+ (43+) and [RuII([9]aneS3)(pap)-
(NO+)]3+ (83+) extend a unique feature of photoreleasing “NO”
at quite different rates under identical experimental conditions
Physical measurements
Infrared spectra were taken on a Nicolet spectrophotometer with
samples prepared as KBr pellets. 1H NMR and 13C NMR spectra
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Table 4 IR vibrational frequencies and redox potentials
Complex
n(NO)cm-1a
E◦/V(RuII–NO+/RuII–NO∑)b
Epc/V(RuII–NO∑/RuII–NO-)b,c
Ref.
[RuII(trpy)(bpy)(NO+)]3+
1952
1960
1959
1962
1945
1964
0.45
0.72
0.55
0.60
0.49
0.67
-0.20
0.07
-0.24
-0.07
0.07
12h
12a
13a
13c
Present work
Present work
[RuII(trpy)(pap)(NO+)]3+
[RuII(tpm)(bpy)(NO+)]3+
[RuII(tpm)(pap)(NO+)]3+
[RuII([9]aneS3)(bpy)(NO+)]3+ (43+
[RuII([9]aneS3)(pap)(NO+)]3+ (83+
)
)
0.03
a As KBr disk. b In CH3CN versus SCE. c Epc value for the irreversible process.
model 273A electrochemistry system. A platinum wire working
electrode, a platinum wire auxiliary electrode and a saturated
calomel reference electrode (SCE) were used in a standard
three-electrode configuration. Tetraethylammoniumperchlorate
(TEAP) was used as the supporting electrolyte and the solution
concentration was ca. 10-3 M; the scan rate used was 100 mV s-1. A
platinum gauze working electrode was used in the coulometric ex-
periments. All electrochemical experiments were carried out under
dinitrogen atmosphere. UV-vis. spectral studies were performed
on a Perkin Elmer Lambda 950 spectrophotometer. The EPR
measurements were made with a Varian model 109 C E-line X-
band spectrometer fitted with a quartz Dewar for measurements
at 77 K. The elemental analyses were carried out with a Perkin-
Elmer 240 C elemental analyser. Electrospray mass spectra were
recorded on a Micromass Q-ToF mass spectrometer.
Synthesis
Synthesis of [RuII([9]aneS3)(bpy)(CH3CN)](ClO4)2 [2](ClO4)2.
The precursor chloro complex [RuII([9]aneS3)(bpy)(Cl)](ClO4)
(100 mg, 0.17 mmol) and an excess of AgNO3 (287 mg, 1.7
mmol) were taken in CH3CN (25 cm3) and heated at reflux for
2 h. The colour of the solution gradually changed from orange
to yellow. The solution was cooled to room temperature and the
precipitated AgCl was separated by filtration through a sintered
glass crucible (G-4). The volume of the filtrate was reduced to 5 cm3
and an excess saturated aqueous solution of NaClO4 was added.
The solid [2](ClO4)2 thus obtained was filtered off and washed
thoroughly with ice-cold water and dried in vacuo over P4O10.
Yield: 78 mg (66%). Anal. Calcd. for C18H23Cl2N3S3O8Ru (Mol.
wt. 676.91): C, 31.91; H, 3.42; N, 6.21. Found: C, 31.86; H, 3.48; N,
6.34%. Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 215.
ESI(+) Mass spectrum in CH3CN (m/z): 536.76 corresponding
Fig.
[RuII([9]aneS3)(bpy)(NO)]3+ (43+), (concentration: 0.63
CH3CN, time intervals:
s) and (b) [RuII([9]aneS3)(pap)(NO)]3+
8
Time evolution of the electronic spectra of (a)
+
to {[RuII([9]aneS3)(bpy)](ClO4)} (calcd. 536.93). IR (KBr, cm-1):
¥
10-5
M
in
n(ClO4 ), 1087, 623. l[nm] (e [M-1 cm-1]) in acetonitrile: 384(2280),
-
5
315(4080), 307(4680), 278(13010), 240(6400).
(83+), (concentration: 0.63 ¥ 10-5 M in CH3CN, time intervals: 2
s) under exposure to light (Xe lamp, 350 W). Insets show the (a)
absorbance versus time plot at 384 nm corresponding to the solvent
Synthesis of [RuII([9]aneS3)(bpy)(NO2)](ClO4) [3](ClO4).
RuII([9]aneS3)(bpy)(CH3CN)](ClO4)2 [2](ClO4)2 (100 mg, 0.15
mmol) and an excess of NaNO2 (103.5 mg, 1.5 mmol) were
taken in 25 cm3 water and the mixture was heated under reflux
for 5 h. The yellow colour of the solution darkened during
the course of the reaction. While cooling the solution to room
temperature pure crystalline nitro complex precipitated out. The
solid [3](ClO4) thus obtained was filtered off, washed several
times with ice-cold water and dried in vacuo over P4O10. Yield:
65 mg (76%). Anal. Calcd for C16H20ClN3S3O6Ru (Mol. wt.
582.92): C, 32.94; H, 3.46; N 7.21. Found: C, 32.87; H, 3.53; N,
species [RuII([9]aneS3)(bpy)(CH3CN)]2+ (22+
)
and (b) absorbance
versus time plot at 480 nm corresponding to the solvent species
[RuII([9]aneS3)(pap)(CH3CN)]2+ (62+). (c) Absorption spectra of met-Mb,
reduced Mb and Mb-NO adduct in water.
were recorded using a 300 MHz Varian FT NMR spectrometer
and a 400 MHz Bruker AV III FT NMR spectrometer with
CD3CN as solvent. Solution electrical conductivity was checked
using a Systronic conductivity bridge 305. Cyclic voltammetric
and coulometric measurements were carried out using a PAR
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7.45%. Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 129.
ESI(+) Mass spectrum in CH3CN (m/z): 482.92, corresponding
mg, 0.17 mmol) was taken in a 1 : 1(v/v) mixture of CH3CN–H2O
(25 cm3) and heated at reflux for 10 min. Excess AgNO3 (287 mg,
1.7 mmol) was added to the above hot solution and the heating
was continued for another 4 h. On cooling the solution to room
temperature the liberated AgCl precipitated out which was then
filtered off using a sintered glass crucible (G-4). The volume of
the filtrate was reduced to 5 cm3 under reduced pressure. The
solid mass of [6](ClO4)2 was obtained on addition of saturated
aqueous solution of NaClO4 to the above filtrate. The solid
thus obtained was filtered off and washed thoroughly with ice-
cold water. The product was dried in vacuo over P4O10. Yield:
96 mg (82%). Anal. Calcd for C19H24S3Cl2N4O8Ru (Mol. wt.
703.92): C, 32.39; H, 3.44; N, 7.96. Found: C, 32.32; H, 3.35; N,
8.14%. Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 198.
ESI(+) Mass spectrum in CH3CN (m/z): 563.92, corresponding
+
to {[RuII([9]aneS3)(bpy)(NO2)]} (calcd. 483.98). IR (KBr, cm-1):
n(ClO4 ), 1085, 622; n(NO2 ), 1343, 1297. l[nm] (e [M-1 cm-1]) in
-
-
acetonitrile: 408(1300), 316(2120), 283(12450), 241(7690).
Synthesis of [RuII([9]aneS3)(bpy)(NO)](ClO4)3 [4](ClO4)3. Ni-
tric acid (2 cm3) was added drop wise to the solid
[RuII([9]aneS3)(bpy)(NO2)](ClO4) [3](ClO4) (100 mg, 0.17 mmol)
under constant stirring at 273 K to form a pasty mass followed
by the addition of ice-cold HClO4 (3 cm3) under continuous
mechanical stirring using a glass rod. Then saturated aqueous
NaClO4 solution was added which resulted in a yellow solid
product. The precipitate was filtered off immediately, washed
with a little ice-cold water and then dried in vacuo over P4O10.
Yield: 92 mg (70%). Anal. Calcd for C16H20Cl3N3S3O13Ru (Mol.
wt. 764.83): C, 25.10; H, 2.64; N, 5.49. Found: C, 25.24; H, 2.45; N,
5.42%. Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 324.
ESI(+) Mass spectrum in CH3CN (m/z): 536.92, corresponding
+
to {[RuII([9]aneS3)(pap)](ClO4)} (calcd. 563.94). IR(KBr disk)
(cm-1): n(ClO4 ), 1084, 622. l [nm] (e [M-1 cm-1]) (CH3CN):
-
480(5450), 369(7260), 306(6700), 278(7940).
+
to {[RuII([9]aneS3)(bpy)](ClO4)} (calcd. 536.93). IR (KBr, cm-1):
Synthesis of [RuII([9]aneS3)(pap)(NO2)](ClO4) [7](ClO4). The
mixture of [RuII([9]aneS3)(pap)(CH3CN)](ClO4)2 [6](ClO4)2 (100
mg, 0.14 mmol) and an excess of NaNO2 (97 mg, 1.4 mmol) in
25 cm3 water was heated at reflux for 4 h. The pure crystalline
nitro complex [7](ClO4) precipitated out on cooling the solution
to room temperature. The solid [7](ClO4) was filtered off, washed
with ice-cold water and dried in vacuo over P4O10. Yield: 64 mg
(74%). Anal. Calcd for C17H21S3ClN4O6Ru (Mol. wt. 609.93). C,
33.45; H, 3.47; N, 9.18. Found: C, 33.38; H, 3.56; N, 9.26%.
Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 130.
ESI(+) Mass spectrum in CH3CN: 510.81 m/z, corresponding
n(ClO4 ), 1090, 624; n(RuII–NO+), 1945. l[nm] (e [M-1 cm-1]) in
-
acetonitrile: 306(6490), 226(17580).
Synthesis of [RuII([9]aneS3)(bpy)(NO)](ClO4)2 [4](ClO4)2. The
nitroso complex, [4](ClO4)3 (100 mg, 0.13 mmol) was taken in
5 cm3 acetonitrile and an excess of hydrazine hydrate was added
to it. The solution was stirred magnetically for 0.5 h under a
dinitrogen atmosphere. The solution of [4](ClO4)3 changed to
dark yellow. The solid mass thus obtained after removal of the
solvent under reduced pressure was washed with a little ice-
cold water and then dried in vacuo over P4O10. Yield: 73 mg
(84%). Anal. Calcd for C16H20Cl2N3S3O9Ru (Mol. wt. 665.88):
C, 28.83; H, 3.03; N, 6.31. Found: C, 28.71; H, 2.92; N, 6.22%.
Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 223.
ESI(+) Mass spectrum in CH3CN (m/z): 537.0, corresponding
+
to {[RuII([9]aneS3)(pap)(NO2)]} (calcd. 510.99) IR (KBr disk)
(cm-1): n(ClO4 ), 1084, 622; n(NO2 ), 1359, 1265. l [nm] (e [M-1
-
-
cm-1]) (CH3CN): 498(5190), 363(7160), 309(9330), 281(8360).
Synthesis of [RuII([9]aneS3)(pap)(NO)](ClO4)3 [8](ClO4)3.
Concentrated nitric acid (2 cm3) was added to the solid nitro
complex [RuII([9]aneS3)(pap)(NO2)](ClO4), [7](ClO4) (100 mg,
0.16 mmol) under constant stirring at 273 K. The slow addition
of ice-cold HClO4 (5 cm3) to the resulting paste under mechanical
stirring using a glass rod followed by the addition of saturated
aqueous NaClO4 solution resulted in a yellowish brown solid
product. The precipitate was filtered off immediately, washed with
a little ice-cold water and then dried in vacuo over P4O10. Yield:
102 mg (79%). Anal. Calcd for C17H21S3Cl3N4O13Ru (Mol. wt.
791.84): C, 25.76; H, 2.67; N, 7.07. Found: C, 25.67; H, 2.59; N,
7.08%. Molar conductivity [KM (X-1 cm2 M-1)] in acetonitrile: 315.
ESI(+) Mass spectrum in CH3CN: 563.97 m/z, corresponding
+
to {[RuII([9]aneS3)(bpy)](ClO4)} (calcd. 536.93). IR (KBr, cm-1):
∑
-
n(ClO4 ), 1087, 626; n(RuII–NO ), 1632. l[nm] (e [M-1 cm-1]) in
acetonitrile: 407(1790), 315(3400), 285(10760), 242(7260).
Synthesis of [RuII([9]aneS3)(pap)(Cl)](ClO4) [5](ClO4). The lig-
and 2-phenylazopyridine (42 mg, 0.23 mmol) was added to a
25 cm3 ethanolic solution of [RuII([9]aneS3)(dmso)Cl2] (100 mg,
0.23 mmol). The mixture was heated under reflux for 5 h under
dinitrogen atmosphere. The solid residue thus obtained on removal
of solvent under reduced pressure was redissolved in a minimum
volume of acetonitrile followed by the addition of excess saturated
aqueous solution of NaClO4 which resulted in a dark precipitate.
The precipitate was filtered off and washed several times with ice-
cold water and dried in vacuo over P4O10. The purification of the
dried precipitate using a silica gel column and CH2Cl2 : CH3CN
(5 : 1) mixture as eluant yielded the purple coloured complex
[RuII([9]aneS3)(pap)Cl](ClO4). Yield: 106 mg (76%). Anal. Calcd
for C17H21Cl2N3S3O4Ru (Mol. wt. 598.91): C, 34.06; H, 3.53; N,
7.01. Found: C, 34.16; H, 3.55; N, 7.13%. Molar conductivity
[KM(X-1 cm2 M-1)] in acetonitrile: 132. ESI(+) Mass spectrum in
+
to {[RuII([9]aneS3)(pap)](ClO4)} (calcd. 563.94) IR (KBr disk)
(cm-1): n(ClO4 ), 1089, 625; n(RuII–NO+), 1964. l [nm] (e [M-1
-
cm-1]) (CH3CN): 444(2750), 358(4370), 311(4190), 275(4370).
Synthesis of [RuII([9]aneS3)(pap)(NO)](ClO4)2 [8](ClO4)2. Ex-
cess hydrazine hydrate was added to a 5 cm3 acetonitrile solution
of the nitroso complex [8](ClO4)3 (100 mg, 0.13 mmol) and the
solution was stirred for 0.5 h under dinitrogen atmosphere. The
yellow solution of [8](ClO4)3 immediately changed to reddish
yellow. On removal of solvent under reduced pressure a dark solid
mass was obtained which was washed with little ice-cold water and
then dried in vacuo over P4O10. Yield: 59 mg (66%). Anal. Calcd for
C17H21S3Cl2N4O9Ru (Mol. wt. 692.89): C, 29.44; H, 3.05; N, 8.08.
+
CH3CN: 500.13 m/z, corresponding to {[RuII([9]aneS3)(pap)Cl]}
(calcd. 499.96) IR(KBr disk) (cm-1): n(ClO4 ), 1087, 623. l[nm] (e
-
[M-1 cm-1]) in acetonitrile: 534(4180), 367(4120), 316(8760).
Synthesis of [RuII([9]aneS3)(pap)(CH3CN)](ClO4)2 [6](ClO4)2.
The chloro complex [RuII([9]aneS3)(pap)(Cl)](ClO4) [5](ClO4) (100
12536 | Dalton Trans., 2011, 40, 12527–12539
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The Royal Society of Chemistry 2011
©

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Found: C, 29.34; H, 3.01; N, 8.13%. Molar conductivity [KM (X-1
Computational details
cm2 M-1)] in acetonitrile: 210. ESI(+) Mass spectrum in CH3CN
Full geometry optimisations of 43+, 42+ and 83+, 82+ were carried
out using the density functional theory method at the B3LYP
and (U)B3LYP level, respectively31 with Gaussian 03 program
package.32 All elements except ruthenium were assigned the 6-
31G(d) basis set. The SDD basis set with effective core poten-
tial was employed for the ruthenium atom.33 The vibrational
frequency calculations were performed to ensure that the opti-
mised geometries represent the local minima and there are only
positive eigenvalues. The frequencies calculated using the B3LYP
functional were scaled by a factor of 0.98. Vertical electronic ex-
citations based on B3LYP/(U)B3LYP optimised geometries were
computed for the time-dependent density functional theory (TD-
DFT) formalism34 in acetonitrile using conductor-like polarizable
continuum model (CPCM).35 GaussSum36 was used to calculate
the fractional contributions of various groups to each molecular
orbital.
+
(m/z): 563.93, corresponding to {[RuII([9]aneS3)(pap)](ClO4)}
(calcd. 563.94). IR (KBr disk) (cm-1): n(ClO4 ),1079, 624; n(RuII–
-
NO∑), 1634. l [nm] (e [M-1 cm-1]) (CH3CN): 500(3260), 343(5590),
315(5920), 282(5090).
CAUTION! Perchlorate salts of metal complexes are generally
explosive. Care needs to be taken while handling such complexes.
Kinetic experiments
The pseudo first-order rate constant values (k, s-1) for the
transformations of [RuII([9]aneS3)(bpy)(NO+)]3+ (43+) (0.59 ¥
10-5 M in CH3CN) → [RuII([9]aneS3)(bpy)(NO2)]+ (3+) and
[RuII([9]aneS3)(pap)(NO+)]3+ (83+) (0.59 ¥ 10-5 M in CH3CN)
→ [RuII([9]aneS3)(pap)(NO2)]+ (7+) in the presence of aqueous
sodium hydroxide solution of concentrations 2.44 ¥ 10-3 and 0.59
¥ 10-3 M, respectively, were determined by following the increase
in absorbance (At) at 408 nm and 498 nm corresponding to lmax
of the nitro complexes 3+ and 7+, respectively, as a function of
time (t) at three different temperatures, 298, 308, 318 K. Aa values
were measured when the intensity changes at 408 nm or 498 nm
completely leveled off. The pseudo first-order rate constant (k, s-1)
at each temperature was calculated from the slope of linear least-
squares plot of -ln(Aa - At) versus t. The activation parameters
DH‡ and DS‡ were determined from the Eyring plots.29
Acknowledgements
Financial support received from the Department of Science
and Technology, University Grant commission and Council of
Scientific and Industrial Research (New Delhi, India), is gratefully
acknowledged. X-ray structural studies were carried out at the
National Single Crystal Diffractometer Facility, Indian Institute
1
Technology Bombay. H NMR experiments were carried out at
The first order rate constant values (k, s-1) for the pho-
torelease of “NO” from [RuII([9]aneS3)(bpy)(NO+)]3+ (43+) and
[RuII([9]aneS3)(pap)(NO)]3+ (83+) in acetonitrile were determined
from the single-exponential fittings of the plots of change in
the Sophisticated Analytical Instrument Facility (SAIF), Indian
Institute of Technology Bombay.
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Single crystals of [3](ClO4), [4](ClO4)3, [5](ClO4), [6](ClO4)2 and
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