Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)]n+ (trpy = 2,2′:6′,2″-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline)

Article abstract of DOI:10.1021/ic702160w

Nitrosyl complexes with {Ru-NO}⁶ and {Ru-NO}⁷ configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] ⁿ⁺ [trpy = 2,2′:6′,2″-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline] as the perchlorate salts [4](ClO ₄)₃ and [4](ClO₄)₂, respectively. Single crystals of protonated material [4-H⁺](ClO₄) ₄·2H₂O reveal a Ru-N-O bond angle of 176.1(7)° and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of [4]³⁺ in the form of [Ru(trpy)(L)(Cl)](ClO₄)·4.5H₂O and [Ru(trpy)-(L-H)(CH₃CN)](ClO₄)₃·H ₂O. In agreement with largely NO centered reduction, a sizable shift in ν(NO) frequency was observed on moving from [4]³⁺ (1953 cm ^-1) to [4]²⁺ (1654 cm^-1). The Ru ^II-NO^? in isolated or electrogenerated [4] ²⁺ exhibits an EPR spectrum with g₁ = 2.020, g₂ = 1.995, and g₃ = 1.884 in CH₃CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); ¹⁴N (NO) hyperfine splitting (A₂ = 30 G) was also observed. The plot of ν(NO) versus E°({RuNO}⁶ → {RuNO}⁷) for 12 analogous complexes [Ru(trpy)(L′)(NO)] ⁿ⁺ exhibits a linear trend. The electrophilic Ru-NO⁺ species [4]³⁺ is transformed to the corresponding Ru-NO ₂^- system in the presence of OH^- with k = 2.02 × 10^-4 s^-1 at 303 K. In the presence of a steady flow of dioxygen gas, the Ru^II-NO^? state in [4] ²⁺ oxidizes to [4]³⁺ through an associatively activated pathway {ΔS^? = -190.4 J K^-1 M^-1) with a rate constant (k[s^-1]) of 5.33 × 10^-3. On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)]²⁺ ([4]²⁺) undergoes facile photorelease of NO (k_NO = 2.0 × 10^-1 min^-1 and t _1/2 ≈ 3.5 min) with the concomitant formation of the solvate [Ru^II(trpy)(L)(CH₃CN)]²⁺ [2′] ²⁺. The photoreleased NO can be trapped as an Mb-NO adduct.

Full text of DOI:10.1021/ic702160w

Inorg. Chem. 2008, 47, 3218-3227
Formation, Reactivity, and Photorelease of Metal Bound Nitrosyl in
[Ru(trpy)(L)(NO)]n+ (trpy ) 2,2′:6′,2′′-Terpyridine,
L ) 2-Phenylimidazo[4,5-f]1,10-phenanthroline)
Somnath Maji,† Biprajit Sarkar,‡ Malay Patra,† Atanu Kumar Das,‡ Shaikh M. Mobin,†
Wolfgang Kaim,*,‡ and Goutam Kumar Lahiri*,†
Department of Chemistry, Indian Institute of TechnologysBombay, Powai, Mumbai 400076, India,
and Institut für Anorganische Chemie, UniVersität Stuttgart, Pfaffenwaldring 55,
D-70550 Stuttgart, Germany
Received November 2, 2007
Nitrosyl complexes with {Ru-NO}6 and {Ru-NO}7 configurations have been isolated in the framework of
[Ru(trpy)(L)(NO)]n+ [trpy ) 2,2′:6′,2′′-terpyridine, L ) 2-phenylimidazo[4,5-f]1,10-phenanthroline] as the perchlorate
salts [4](ClO4)3 and [4](ClO4)2, respectively. Single crystals of protonated material [4-H+](ClO4)4 ·2H2O reveal a
Ru-N-O bond angle of 176.1(7)° and triply bonded N-O with a 1.127(9) Å bond length. Structures were also
determined for precursor compounds of [4]3+ in the form of [Ru(trpy)(L)(Cl)](ClO4) · 4.5H2O and [Ru(trpy)-
(L-H)(CH3CN)](ClO4)3 ·H2O. In agreement with largely NO centered reduction, a sizable shift in ν(NO) frequency
was observed on moving from [4]3+ (1953 cm-1) to [4]2+ (1654 cm-1). The RuII-NO• in isolated or electrogenerated
[4]2+ exhibits an EPR spectrum with g1 ) 2.020, g2 ) 1.995, and g3 ) 1.884 in CH3CN at 110 K, reflecting partial
metal contribution to the singly occupied molecular orbital (SOMO); 14N (NO) hyperfine splitting (A2 ) 30 G) was
also observed. The plot of ν(NO) versus E°({RuNO}6 f {RuNO}7) for 12 analogous complexes [Ru(trpy)(L′)(NO)]n+
exhibits a linear trend. The electrophilic Ru-NO+ species [4]3+ is transformed to the corresponding Ru-NO2–
system in the presence of OH- with k ) 2.02 × 10-4 s-1 at 303 K. In the presence of a steady flow of dioxygen
gas, the RuII-NO• state in [4]2+ oxidizes to [4]3+ through an associatively activated pathway (∆Sq ) -190.4 J
K-1 M-1) with a rate constant (k [s-1]) of 5.33 × 10-3. On irradiation with light (Xe lamp), the acetonitrile solution
of paramagnetic [Ru(trpy)(L)(NO)]2+ ([4]2+) undergoes facile photorelease of NO (kNO ) 2.0 × 10-1 min-1 and t1/2
≈ 3.5 min) with the concomitant formation of the solvate [RuII(trpy)(L)(CH3CN)]2+ [2′]2+. The photoreleased NO
can be trapped as an Mb-NO adduct.
Introduction
with suitable nucleophiles;2 (iii) mechanistic studies of the
M-NO•/O2 interaction in order to understand the biological
autoxidation of free NO•;3 and (iv) the exploration of
selective photolytic cleavage of M-NO and the eventual
transfer of photoreleased “NO” to biologically relevant target
molecules in order to develop alternative molecular devices
capable of functioning as efficient “NO” donors under
biological conditions.4
The research activities in the area of metal-nitrosyl
chemistry have grown extensively over the recent years with
the following primary perspectives: (i) understanding the
bonding features of the noninnocent “NO” molecule on
metalation as it can occur either as cationic NO+, as radical
NO•, or as anionic NO-, depending on the electronic nature
of the ancillary ligands associated with the M-NO frag-
ment;1 (ii) variation of the extent of electrophilicity of the
M-NO+ moiety and resulting reactivity profiles of M-NO+
(1) (a) Videla, M.; Jacinto, J. S.; Baggio, R.; Garland, M. T.; Singh, P.;
Kaim, W.; Slep, L. D.; Olabe, J. A. Inorg. Chem. 2006, 45, 8608. (b)
Singh, P.; Sarkar, B.; Sieger, M.; Niemeyer, M.; Fiedler, J.; Zalis, S.;
Kaim, W. Inorg. Chem. 2006, 45, 4602. (c) Sieger, M.; Sarkar, B.;
Zalis, S.; Fiedler, J.; Escola, N.; Doctorovich, F.; Olabe, J. A.; Kaim,
W. Dalton Trans. 2004, 1797. (d) Roncaroli, F.; Baraldo, L. M.; Slep,
L. D.; Olabe, J. A. Inorg. Chem. 2002, 41, 1930. (e) Slep, L. D.; Pollak,
S.; Olabe, J. A. Inorg. Chem. 1999, 38, 4369.
* To whom correspondence should be addressed. E-mail: kaim@
iac.uni-stuttgart.de (W.K.), lahiri@chem.iitb.ac.in (G.K.L.).
†
Indian Institute of TechnologysBombay.
Universität Stuttgart.
‡
3218 Inorganic Chemistry, Vol. 47, No. 8, 2008
10.1021/ic702160w CCC: $40.75  2008 American Chemical Society
Published on Web 03/01/2008

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+
Scheme 1
The present work originates from the outlook of the
aforesaid objectives using newly synthesized nitrosyl ruthe-
nium derivatives [RuII(trpy)(L)(NO+)](ClO4)3 ) [4](ClO4)3
and [RuII(trpy)(L)(NO•)](ClO4)2 ) [4](ClO4)2 (trpy ) 2,2′:
6′,2′′-terpyridine, L ) 2-phenylimidazo[4,5-f]1,10-phenan-
throline). Although L has been of interest in the field of
coordination chemistry for a number of years,5 only few
ruthenium complexes of L and its derivatives have been
reported so far from different perspectives, mainly directed
at studies of interaction with DNA.6
Results and Discussion
Synthesis and Characterization. The nitrosyl complex
[RuII(trpy)(L)(NO)](ClO4)3 ) [4](ClO4)3 has been synthe-
sized from the precursor [RuII(trpy)(L)Cl](ClO4) ) [1](ClO4)
via the aqua form [RuII(trpy)(L)(H2O)](ClO4)2 ) [2](ClO4)2
or the acetonitrile solvate [RuII(trpy)(L)(CH3CN)](ClO4)2 )
[2′](ClO4)2 and the nitro complex [RuII(trpy)(L)(NO2)](ClO4)
) [3](ClO4) (Scheme 1). Attempts of direct synthesis of pure
[4](ClO4)3 either from [1](ClO4), [2](ClO4)2 or [2′](ClO4)2
using NO gas or (NO)(BF4) have failed, thus, the stepwise
synthetic route via the nitro complex as shown in Scheme 1
was followed. The isolated nitrosyl radical species [RuII-
(2) (a) Roncaroli, F.; Videla, M.; Slep, L. D.; Olabe, J. A. Coord. Chem.
ReV. 2007, 251, 1903. (b) McCleverty, J. A. Chem. ReV. 1979, 79,
53. (c) Thiemens, M. H.; Trogler, W. C. Science 1991, 251, 932. (d)
Feelisch, M., Stamler, J. S., Eds. Methods in Nitric Oxide Research;
Wiley: Chichester, England, 1996. (e) Enemark, J. H.; Feltham, R. D.
Coord. Chem. ReV. 1974, 13, 339. (f) Bottomley, F. In Reactions of
Coordinated Ligands; Braterman, P. S., Ed.; Plenum: New York, 1985;
Vol. 2, p 115. (g) Bottomley, F. Acc. Chem. Res. 1978, 11, 158. (h)
Ford, P. C.; Bourassa, J.; Lee, B.; Lorkovic, I.; Miranda, K.; Laverman,
L. Coord. Chem. ReV. 1998, 171, 185. (i) Roncaroli, F.; Olabe, J. A.
Inorg. Chem. 2005, 44, 4719. (j) Roncaroli, F.; Ruggiero, M. E.;
Franco, D. W.; Estiu, G. L.; Olabe, J. A. Inorg. Chem. 2002, 41, 5760.
(k) Forlano, P.; Parise, A. R.; Olabe, J. A. Inorg. Chem. 1998, 37,
6406. (l) Bottomley, F. Coord. Chem. ReV. 1978, 26, 7.
(trpy)(L)(NO·)](ClO4)2 ) [4](ClO4)2 has been prepared by
reducing [4](ClO4)3 chemically using hydrazine hydrate.
Electrochemical reduction of [4]3+ leads to the quantitative
formation of [4]2+ which can then be reversibly oxidized to
[4]3+.
The diamagnetic compounds [1](ClO4), [2](ClO4)2, [2′]-
(ClO4)2, [3](ClO4), and [4](ClO4)3 and the doublet species
[4](ClO4)2 exhibit 1:1, 1:2, 1:2, 1:1, 1:3, and 1:2 conductivi-
ties, respectively, and give satisfactory microanalytical data
(see the Experimental Section). The electrospray mass spectra
of [1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), [4](ClO4)3,
and [4](ClO4)2 in CH3CN show molecular ion peaks centered
at m/z ) 665.94, 730.05, 729.93, 677.08, 730.72, and 730.42,
respectively, corresponding to {[1](ClO4) - ClO4}+ (calcu-
lated molecular mass: 666.07), {[2](ClO4)2 - ClO4 - H2O}+
(calculated molecular mass: 730.05), {[2′](ClO4)2 - ClO4
- CH3CN}+ (calculated molecular mass: 730.05), {[3](ClO4)
- ClO4}+ (calculated molecular mass: 677.09), {[4](ClO4)3
- 2ClO4 - NO}+ (calculated molecular mass: 730.05), and
{[4](ClO4)2 - ClO4 - NO}+ (calculated molecular mass:
730.05), respectively (Figure 1).
The molecular structures of the cationic, partially proto-
nated complexes in crystals of [1](ClO4) · 4.5H2O, [2′-H+]-
(ClO4)3 ·H2O and [4-H+](ClO4)4 ·2H2O are shown in Figures
2-4. Crystallographic parameters and selected bond dis-
tances and angles are listed in Tables S1 and S2 (see the
Supporting Information). In spite of numerous attempts, the
quality of the crystals remained low; however, the bond
distances and angles match reasonably with similar com-
plexes reported earlier.7 The lattice of [1](ClO4) · 4.5H2O
(3) Videla, M.; Roncaroli, F.; Slep, L. D.; Olabe, J. A. J. Am. Chem. Soc.
2007, 129, 278.
(4) (a) Halpenny, G. M.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
2007, 46, 6601. (b) Rose, M. J.; Olmstead, M. M.; Mascharak, P. K.
J. Am. Chem. Soc. 2007, 129, 5342. (c) Rose, M. J.; Patra, A. K.;
Alcid, E. A.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem. 2007,
46, 2328. (d) Patra, A. K.; Rose, M. J.; Murphy, K. A.; Olmstead,
M. M.; Mascharak, P. K. Inorg. Chem. 2004, 43, 4487. (e) Videla,
M.; Braslavsky, S. E.; Olabe, J. A. Photochem. Photobiol. Sci. 2005,
4, 75. (f) Zanichelli, P. G.; Miotto, A. M.; Estrela, H. F. G.; Soares,
F. R.; Grassi-Kassisse, D. M.; Spadari-Bratfisch, R. C.; Castellano,
E. E.; Roncaroli, F.; Parise, A. R.; Olabe, J. A.; de Brito, Alba Regina,
M. S.; Franco, D. W. J. Inorg. Biochem 2004, 98, 1921. (g) Sauaia,
M. G.; de.Lima, R. G.; Tedesco, A. C.; da Silva, R. S. Inorg. Chem.
2005, 44, 9946. (h) Karidi, K.; Garoufis, A.; Tsipis, A.; Hadjiliadis,
N.; den Dulk, H.; Reedijk, J. Dalton Trans. 2005, 1176.
(5) (a) Shavaleev, N. M.; Adams, H. A.; Weinstein, J. A. Inorg. Chim.
Acta 2007, 360, 700. (b) Wei, Y.-Q.; Zhuang, B.-T.; Zhou, Z.-F.;
Zhang, F. J. Mol. Struct. 2005, 751, 133.
(6) (a) Jiang, C.-W.; Chao, H. Polyhedron, 2001, 20, 2187. (b) Xiong,
Y.; He, X.-F.; Zou, X.-H.; Wu, J.-Z.; Chen, X.-M.; Ji, L.-N.; Li, R.-
H.; Zhou, J.-Y.; Yu, K.-B. J. Chem. Soc., Dalton Trans. 1999, 19. (c)
Wu, J.-Z.; Ye, B.-H.; Wang, L.; Ji, L.-N.; Zhou, J.-Y.; Li, R.-H.; Zhou,
Z.-Y. J. Chem. Soc., Dalton Trans. 1997, 1395. (d) Wu, J.-Z.; Li, L.;
Zeng, T.-X.; Ji, L.-N.; Zhou, J.-Y.; Luo, T.; Li, R.-H. Polyhedron
1997, 16, 103. (e) Uma Maheswari, P.; Palaniandavar, M. J. Inorg.
Biochem. 2004, 98, 219. (f) Jiang, C.-W.; Chao, H.; Li, R.-H.; Li, H.;
Ji, L.-N. J. Coord. Chem. 2003, 56, 147. (g) Chao, H.; Li, R.-H.; Jiang,
C.-W.; Li, H.; Ji, L.-N.; Li, X.-Y. J. Chem. Soc., Dalton Trans. 2001,
1920. (h) Zheng, K. C.; Deng, H.; Liu, X. W.; Li, H.; Chao, H.; Ji,
L. N. J. Mol. Struct. 2004, 682, 225. (i) Li, J.; Xu, L.-C.; Chen, J.-C.;
Zheng, K. C.; Ji, L.-N. J. Phys. Chem. A 2006, 110, 8174. (j) Tan,
L.-F.; Chao, H.; Zhou, Y.-F.; Ji, L.-N. Polyhedron 2007, 26, 3029.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3219

Maji et al.
Figure 1. ESI mass spectra of (a) [1](ClO4), (b) [2](ClO4)2, (c) [2′](ClO4)2, (d) [3](ClO4), (e) [4](ClO4)3, and (f) [4](ClO4)2 in CH3CN.
mixture over a period of 1 month (Figure 3). The linearity of
the RuII-N(8)-O(1) bond (176.1(7)°) and the triple bond
feature of N(8)-O(1) (1.127(9) Å) support the electrophilic
NO+ character in [RuII(trpy)(L-H+)(NO)](ClO4)4 ·2H2O; ad-
ditional evidence from the νNO stretching frequency and
E°(RuII-NO+/RuII-NO•) will be described later.7 In all cases,
the ligand L forms a five-membered chelate ring with the metal
ion via the nitrogen donor centers of the phenanthroline unit.6b
1
Spectral Aspects. The H NMR spectra of diamagnetic
[1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), and [4](ClO4)3
in (CD3)2SO (Figure S1, Supporting Information, and Ex-
perimental Section) display severe overlap of the expected
22 signals in the aromatic region between 7.0 and 10.5 ppm,
11 resonances each from the trpy and the L ligand. The
chemical shift of the resonances varies slightly depending
on the monodentate ligands, Cl-, H2O, CH3CN, NO2 , or
-
NO+. The N-H proton of the imidazole ring of coordinated
L has only been observed for [1](ClO4) at 14.4 ppm.8 The
absence of the N-H signal of the coordinated L in the other
complexes can be attributed to rapid exchange.6j The signal
due to the CH3 group of coordinated acetonitrile in
[2′](ClO4)2 appears at 2.38 ppm. While single crystals for
X-ray diffraction were obtained in an imidazole-protonated
form for the complexes with the electrophilic CH3CN and
NO+ monodentate ligands (see above), the dissolved species
are identified as the imidazole forms with neutral L
Figure 2. Molecular structure of the nonequivalent cations [Ru(trpy)(L)
(Cl)]+ in the asymmetric unit of the crystal of [1](ClO4)·4.5H2O.
consists of two crystallographically independent molecules
(Figure 2) which differ conspicuously in the relative orientation
of the imidazole of L and the Ru-Cl bond. The acetonitrile
complex has become protonated at the basic imine N of the
imidazole ring to [RuII(trpy)(L-H+)(CH3CN)](ClO4)3 during
the crystallization process from a CH3CN-benzene (1:1)
3220 Inorganic Chemistry, Vol. 47, No. 8, 2008

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+
Figure 3. Molecular structure of the trication [Ru(trpy)(L-H+)(CH3CN)]3+
in the crystal of [2′-H+](ClO4)3 ·H2O.
Figure 4. Molecular structure of the tetracation [Ru(trpy)(L-H+)(NO)]4+
in the crystal of [4-H+](ClO4)4 ·2H2O.
according to elemental analysis, molar conductivity, and
1H NMR data.
The complexes exhibit ruthenium(II) based metal to ligand
charge transfer (MLCT) transitions to π*(trpy) and π*(L)
orbitals near 500 nm and ligand based multiple transitions
in the UV region (Figure 6, Table 2). The MLCT band
energy in acetonitrile solution follows the order [1]+ (509
nm) < [4]2+ (486 nm) < [3]+ (478 nm) < [2]2+ (462 nm) ≈
[2′]2+ (461 nm) < [4]3+ (370 nm), depending on the relative
stabilization of the dπ(Ru) level.7 The high energy shift of
the MLCT band in [4]3+ implies a strong dπ(RuII) f
π*(NO+) back-bonding interaction. This has further been
evidenced in the observed short Ru-N8(NO) bond distance
of 1.766(7) Å (Table S2) and the relatively high νNO
frequency of 1948 cm-1. Electronic spectra of [2]2+ in
solvents of different polarity show moderate variation (Table
2, Figure 6).10
The complexes are found to be luminescent in frozen
solution, the nitro derivative [3]+ displaying the strongest
emission. The excitation of [1]+, [2]2+, [2′]2+, [3]+, or [4]3+
at the respective MLCT bands in EtOH:MeOH (4:1) glass
at 77 K shows emission at λemis ) 705 nm (Φ ) 0.022) (Φ
corresponds to the quantum yield at 77 K with reference to
[Ru(bpy)3](PF6)2, Φ ) 0.3411), 675 nm (Φ ) 0.038), 597 nm
(Φ ) 0.025), 623 nm (Φ ) 0.20), and 580 nm (Φ ) 0.11),
respectively (Figure 6). The observed emissions are thought to
-
The ν(ClO4 ) vibrations are observed at 1096/623, 1089/
625, 1088/625, 1097/623, 1087/626, and 1091/628 cm-1 for
[1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), [4](ClO4)3, and
[4](ClO4)2, respectively. The typical Ru-NO2 frequencies
of [3](ClO4) appear at 1338 cm-1(asymmetric) and 1272
cm-1 (symmetric). The νNO stretching frequency of [4](ClO4)3
at 1948 cm-1 is lower than that reported for analogous
complexes {RuII(trpy)(L′)(NO+)} with L′ ) strongly π-acidic
L3 ) 1952 cm-1, L2 ) 1957 cm-1, L1 ) 1960 cm-1 (Table
1). However, it is much higher than that observed with
strongly σ-donating L10 ) 1858 cm-1 and L9 ) 1914 cm-1
and close to that found for moderately π-acidic L5 ) 1949
cm-1 (Table 1). The observed νNO value of [4](ClO4)3 is thus
suggestive of a moderately strong electrophilic character of
NO. On reduction of [4]3+ to [4]2+ the νNO frequency is
substantially reduced from 1948 (solid)/1953 (acetonitrile
solution) cm-1 to 1634 (solid)/1654 (acetonitrile solution)
cm-1 (Figure 5). The large shift in νNO frequency, ∆ν )
314(solid)/300(solution) cm-1, on moving from [4]3+ to [4]2+
agrees with a transformation of linear RuII-NO+, {RuNO},6
to most likely bent RuII-NO•, {RuNO}.7,1c,2b,9
(7) (a) Mondal, B.; Paul, H.; Puranik, V. G.; Lahiri, G. K. J. Chem. Soc.,
Dalton Trans. 2001, 481. (b) Chanda, N.; Paul, D.; Kar, S.; Mobin,
S. M.; Datta, A.; Puranik, V. G.; Rao, K. K.; Lahiri, G. K. Inorg.
Chem. 2005, 44, 3499. (c) Pipes, D. W.; Meyer, T. J. Inorg. Chem.
1984, 23, 2466. (d) Maji, S.; Chatterjee, C.; Mobin, S. M.; Lahiri,
G. K. Eur. J. Inorg. Chem. 2007, 3425. (e) Sarkar, S.; Sarkar, B.;
Chanda, N.; Kar, S.; Mobin, S. M.; Feidler, J.; Kaim, W.; Lahiri, G. K.
Inorg. Chem. 2005, 44, 6092. (f) Chanda, N.; Mobin, S. M.; Puranik,
V. G.; Datta, A.; Niemeyer, M.; Lahiri, G. K. Inorg. Chem. 2004, 43,
1056. (g) Dovletoglou, A.; Adeyemi, S. A.; Meyer, T. J. Inorg. Chem.
1996, 35, 4120. (h) Hadadzadeh, H.; DeRosa, M. C.; Yap, G. P. A.;
Rezvani, A. R.; Crutchley, R. J. Inorg. Chem. 2002, 41, 6521. (i) Singh,
P.; Fiedler, J.; Záliš, S.; Duboc, C.; Niemeyer, M.; Lissner, F.; Schleid,
T.; Kaim, W. Inorg. Chem. 2007, 46, 9254.
(8) (a) Maji, S.; Patra, S.; Chakraborty, S.; Mobin, S. M.; Janardanan,
D.; Sunoj, R. B.; Lahiri, G. K. Eur. J. Inorg. Chem. 2007, 314. (b)
Chakraborty, S.; Walawalkar, M. G.; Lahiri, G. K. J. Chem. Soc.,
Dalton. Trans. 2000, 2875. (c) Hirsch-Kuchma, M.; Nicholson, T.;
Davison, A.; Davis, W. M.; Jones, A. G. Inorg. Chem. 1997, 36, 3237.
(9) (a) Wanner, M.; Scheiring, T.; Kaim, W.; Slep, L. D.; Baraldo, L. M.;
Olabe, J. A.; Zalis, S.; Baerends, E. J. Inorg. Chem. 2001, 40, 5704.
(b) Haymore, B. L.; Ibers, J. A. Inorg. Chem. 1975, 14, 3060. (c)
Gaughan, A. P.; Haymore, B. L.; Ibers, J. A.; Myers, W. H.; Nappier,
T. F.; Meek, D. W. J. Am. Chem. Soc. 1973, 95, 6859. (d) Pandey,
K. K. Coord. Chem. ReV. 1992, 121, 1.
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Trans. 2000, 4209.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3221

Maji et al.
Table 1. Reduction Potentials of the {Ru(NO+)}f {Ru(NO•)} Process
and νNO Values for {RuII(trpy)(L′)(NO)}3+
Figure 6. (a) Electronic spectra in acetonitrile of [1]+, [2]2+, [2′]2+, [3]+,
[4]3+, and [4]2+. (b) Electronic spectra of [2]2+ in different solvents. (c) Emission
spectrum of [3](ClO4) in 4:1 EtOH-MeOH at 77 K.
b
L′
L1
L
E298° [V]a
ν(NO) (cm-1
)
refs
0.72
0.49
0.45
0.45
0.40
0.36
0.34
0.33
0.31
0.02
-0.28
0.40
1960
1948
1957
1952
1944
1949
1945
1940
1932
1914
1858
1957
7a
present work
L2
L3
L4
L5
L6
L7
L8
L9
L10
L11
7b
7c
7d
7e
7f
7b
7b
7g
7h
7i
Table 2. Electronic Spectral Data of Complexes
compound
solvent
λ [nm] (ε [M-1 cm-1])
[1](ClO4) acetonitrile
[2](ClO4)2 acetonitrile
methanol
509(18611), 314(56016), 294(59038),
276(82142), 236(53332)
462(25718), 303(71232), 293(75163),
282(97862), 276(100079), 222(60149)
479(13587), 310(57673), 277(81613),
203(69519)
water
477(22789), 310(90825), 222(82525),
310(90825)
a CH3CN/0.1 M Et4NClO4/SCE. b In KBr disk.
acetone
477(22949), 323(53235), 312(18958),
272(16284)
tetrahydrofuran
dichloromethane
481(11975), 312(46252), 292(50562),
281(58223), 235(33107)
485(11975), 310(49245), 294(52556),
280(65885), 225(39588)
dimethylformamide 497(15606), 316(66204), 296(70873),
281(69875), 246(23627), 236(36276)
[2′](ClO4)2 acetonitrile
461(24924), 305(60845), 292(64340),
281(67292), 244(37325), 221(55015)
478(26062), 308(94246), 293(93837),
279(100509), 220(74543)
370(17921), 305(52234), 279(63725),
276(67140), 222(55998)
[3](ClO4) acetonitrile
[4](ClO4)3 acetonitrile
[4](ClO4)2 acetonitrile
488(22696), 329(51801), 313(95981),
303(102867), 293(108636),
278(128496)
Figure 5. IR spectral changes for the conversion [4]3+f [4]2+ from
optically transparent thin layer electrode (OTTLE) spectroelectrochemistry
in CH3CN/0.1 M Bu4NPF6 with stepwise variation of the potential. Bands
below 1650 cm-1 arise from ring vibrations.
oxidized solutions has been established only for the
complex [2′]3+ via its typical rhombic EPR spectrum (g1
) 2.444, g2 ) 2.201, g3 ) 1.851; Figure S2 in the
Supporting Information). The potentials are in general
comparable to those of the analogous [RuII(trpy)(L′)(X)]n+
complexes (X ) Cl-, NO2-, H2O, or CH3CN) and vary
originate from the triplet (3MLCT) excited states as observed
in numerous ruthenium-polypyridine complexes.12
Redox Properties. The RuIII/RuII potentials of [1]+,
[2′]2+, and [3]+ in CH3CN and of [2]2+ in H2O (Table 3)
vary in the order of Cl- < H2O < NO2 < CH3CN for
-
(12) (a) Kar, S.; Chanda, N.; Mobin, S. M.; Datta, A.; Urbanos, F. A.;
Puranik, V. G.; Jimenez-Aparicio, R.; Lahiri, G. K. Inorg. Chem. 2004,
43, 4911. (b) Sarkar, B.; Laye, R. H.; Mondal, B.; Chakraborty, S.;
Paul, R. L.; Jeffery, J. C.; Puranik, V. G.; Ward, M. D.; Lahiri, G. K.
J. Chem. Soc., Dalton Trans. 2002, 2097. (c) Juris, A.; Balzani, V.;
Barigelletti, F.; Campagna, S.; Belser, P.; von Zelewsky, A. Coord.
Chem. ReV. 1988, 84, 85.
the monodentate ligand.7 The presence of RuIII in the
(11) (a) Alsfasser, R.; Van Eldik, R. Inorg. Chem. 1996, 35, 628. (b) Chen,
P.; Duesing, R.; Graff, D. K.; Meyer, T. J. J. Phys. Chem. 1991, 95,
5850.
3222 Inorganic Chemistry, Vol. 47, No. 8, 2008

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+
Table 3. Redox Potentials of Complexesa b
,
couple
NO+
f
NO• f
II
compound RuIII/Ru
NO•
NO-
trpy reduction
[1](ClO4) 0.69(66)
-1.53(54) -1.80(60)
-1.59(53) -1.93(67)
-1.58(66) -1.99(62)
-1.44(94) -1.97(58)
c
[2](ClO4)2 0.84(84)
[2′](ClO4)2 1.22(95)
[3](ClO4)
[4](ClO4)3
1.03(90)
0.49(110) -0.26(154)d -1.17(72) -1.43(51)
a Potentials E298° [V] (∆E [mV]) versus SCE. b In CH3CN/0.1 M
Et4NClO4. c In H2O/0.1 M NaClO4. d Quasi-reversible.
Figure 8. Experimental (top) and computer simulated (bottom) EPR
spectrum at 110 K of the radical complex [4]2+ generated by reduction of
[4](ClO4)3 in CH3CN/0.1 M Bu4NPF6.
and g3 ) 1.884 with an NO hyperfine splitting A2(14N) of
30 G in CH3CN at 110 K (Figure 8). The pronounced
anisotropic profile of the spectrum arises from close lying
π*(NO) orbitals (gav < 2) and from the partial contribution
of the metal ion to the singly occupied molecular orbital
(SOMO).1c,2b,9a,15 The similarity of the EPR parameters with
those observed and interpreted previously9a,15a is compatible
with contributions of about 1/3 from the metal ion and 2/3from
the NO group to the SOMO, implying a mixed resonance
formulation {RuI(NO+)} T {RuII(NO•)}.9a The stepwise reduc-
tion of coordinated trpy is observed at -1.17 and -1.43 V
(couples III and IV, Figure 7a, Table 3). The RuII-NO+ f
RuII-NO• reduction potentials for analogous complexes with
different ligands L′ (L1-L11, L) and the corresponding ν(NO)
values (Table 1) follow a linear trend (Figure 7b).7
Reaction of [RuII(trpy)(L)(NO+)]3+ ([4]3+) with OH-.
In spite of the relatively high ν(NO) stretching frequency of
1948 cm-1 for [4]3+, suggesting facile nucleophilic attack,
this complex ion is found to be persistent both in the solid
and in CH3CN solution; it is only sparingly soluble in water.
However, it undergoes facile transformation to the corre-
sponding nitro derivative [3]+ under alkaline conditions in
CH3CN. Due to the poor solubility of [4]3+ and the virtually
insoluble nature of the nitro derivative [3]+ in water (cf. its
preparation) the conversion had to be performed in CH3CN.
The conversion process (eq 1)
Figure 7. (a) Cyclic voltammogram of [4](ClO4)3 in CH3CN/0.1 M
Et4NClO4. (b) Least-squares plot of E° [V] {Ru(NO+)/Ru(NO•)} versus
ν(NO)/cm-1 of twelve related complexes as listed in Table 1; ν(NO) [cm-1
) 1903 cm-1 + 107 cm-1/VE° [V], R ) 0.943.
]
according to the electronic aspects of L′.7 The trpy ligand-
based reductions are observed in the range between -1.44
and -1.99 V (Table 3).13
The nitrosyl based reductions involving the NO+ f NO•
and NO• f NO- conversion in [4]n+ appear at +0.49 and
-0.26 V versus standard calomel electrode (SCE) (couples
I and II, Figure 7a, Table 3).7 The tricationic charge of [4]3+
facilitates the reversible reduction of the coordinated NO+
to NO• to occur at a rather high potential, and that effect is
even extended to the second one-electron reduction (NO• f
NO-). The 0.75 V potential difference between the succes-
sive NO centered reductions (couples I and II) gives rise to
a comproportionation constant (Kc) of 1012.7 (RT ln Kc )
∆E/0.059 (see ref 14) where ∆E ) 0.75 V) for the
intermediate (radical) species [4]2+. This large Kc value
reflects the chemical stability of the intermediate which
facilitated its isolation in the solid state. The EPR spectrum
of [4]2+ exhibits g components at g1 ) 2.020, g2 ) 1.995,
II
Ru (trpy)(L)(NO) 3+ + 2OH- f [RuII(trpy)(L)(NO2)]+ +
[
]
[4]3+
[3]+
H2O (1)
was monitored spectrophotometrically in the temperature
range 303–323 K in CH3CN in the presence of aqueous
NaOH solution ([4]3+, 0.22 × 10-4 M, and NaOH, 0.2 ×
10-2 M; pseudo pH ∼ 10). The well-defined isosbestic points
(Figure 9) are indicative of a clean conversion (1). The
pseudo-first-order rate constants (k [s-1]) at three different
temperatures are: 2.02 × 10-4 (303 K), 3.97 × 10-4 (313
K), 6.37 × 10-4 (323 K). The activation parameters (∆Hq/
(13) (a) Mondal, B.; Puranik, V. G.; Lahiri, G. K. Inorg. Chem. 2002, 41,
5831. (b) Chanda, N.; Mondal, B.; Puranik, V. G.; Lahiri, G. K.
Polyhedron 2002, 21, 2033. (c) Catalano, V. J.; Heck, R. A.; Ohman,
A.; Hill, M. G. Polyhedron 2000, 19, 1049. (d) Catalano, V. J.; Heck,
R. A.; Immoos, C. E.; Ohman, A.; Hill, M. G. Inorg. Chem. 1998,
37, 2150. (e) Patra, S.; Sarkar, B.; Ghumaan, S.; Patil, M. P.; Mobin,
S. M.; Sunoj, R. B.; Kaim, W.; Lahiri, G. K. Dalton Trans. 2005,
1188. (f) Hedda, T. B.; Bozec, H. L. Inorg. Chim. Acta 1993, 204,
103. (g) Deacon, G. B.; Patrick, J. M.; Skelton, B. W.; Thomas, N. C.;
White, A. H. Aust. J. Chem. 1984, 37, 929.
(15) (a) Frantz, S.; Sarkar, B.; Sieger, M.; Kaim, W.; Roncaroli, F.; Olabe,
J. A.; Zalis, S. Eur. J. Inorg. Chem. 2004, 14, 2902. (b) de Souza,
V. R.; da Costa Ferreira, A. M.; Toma, H. E. Dalton Trans. 2003,
458. (c) McGarvey, B. R.; Ferro, A. A.; Tfouni, E.; Bezerra, C. W. D.;
Bagatin, I. A.; Franco, D. W. Inorg. Chem. 2000, 39, 3577. (d)
Callahan, R. W.; Meyer, T. J. Inorg. Chem. 1977, 16, 574. (e) Diversi,
P.; Fontani, M.; Fuligni, M.; Laschi, F.; Marchetti, F.; Matteoni, S.;
Pinzino, C.; Zanello, P. J. Organomet. Chem. 2003, 675, 21.
(14) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3223

Maji et al.
{MNO}7 has been studied since long in the light of
understanding the biological NO autoxidation process.3
Mechanistic studies with a variety of transition metal-NO
species suggest the formation of nitrato or nitrito complexes
which proceeds via the intermediacy of an O-bound or
N-bound peroxynitrite complex.16 Therefore, the reaction of
O2 with the nitrosyl species [RuII(trpy)(L)(NO•)]2+ ([4]2+)
was followed spectrophotometrically at three different tem-
peratures (298, 308, 318 K) in acetonitrile in the presence
of 0.1 M HClO4 (acetonitrile was used due to the poor
solubility of [4]2+ in water). Though [4]2+ is stable in
acetonitrile under atmospheric conditions, in the presence
of a steady flow of dioxygen gas it slowly transforms to the
corresponding NO+ species [4]3+ (Figure 10) which can be
represented by eq 2.1a
Figure 9. Time evolution of the electronic spectrum (5 min time intervals)
of a solution of [Ru(trpy)(L)(NO)]3+ ([4]3+, 0.22 × 10-4 M) in the presence
of OH- (0.2 × 10-2 M; pseudo pH ∼ 10) in CH3CN at 313 K.
2[RuII(trpy)(L)(NO•)]2+ + O2 + 2H+ f
[4]2+
2[RuII(trpy)(L)(NO+)]3+ + H2O2 (2)
[4]3+
The isosbestic points in Figure 10 reveal the exclusive
involvement of two primary components ([4]2+/[4]3+) during
the transformation process at the spectrophotometric time
scale. The pseudo first order rate constants (k [s-1]) at three
different temperatures are the following: 5.33 × 10-3 (298
K), 7.82 × 10-3 (308 K), and 11.96 × 10-3 (318 K). The
activation parameters ∆Hq and ∆Sq are calculated as +29.3
kJ M-1 and -190.4 J K-1 M-1, respectively. On the basis
of the thermodynamic parameters, particularly the large
negative ∆Sq value, it may be proposed that the reaction
proceeds through an associatively activated pathway involv-
ing the initial binding of O2 with the M-NO fragment. The
same reaction (eq 2) has also been tested using air instead
of oxygen gas under similar experimental conditions at 298
K, and the estimated pseudo-first-order rate constant value
is found to be decreased significantly to 2.416 × 10-3 s-1.
Photocleavage of the RuII-NO Bond in [RuII(trpy)(L)
(NO•)]2+ [4]2+ and Binding of Photoreleased NO with
Myoglobin (Mb). The nitrosyl complex [RuII(trpy)(L)
(NO+)]3+ [4]3+ was found to be stable in acetonitrile solution
under ambient light conditions as well as under irradiation
with a Xenon 350 W lamp. However, on exposure to such
light the deoxygenated acetonitrile solution of the one-
electron reduced species, [RuII(trpy)(L)(NO•)]2+ [4]2+ un-
dergoes facile photorelease of NO over a period of ∼30 min
via the selective cleavage of the Ru-NO bond and with
concomitant formation of the solvate species [RuII-
(trpy)(L)(CH3CN)]2+ [2′]2+. The progression of the photo-
cleavage of the RuII-NO• bond in [4]2+ was monitored
spectrophotometrically in CH3CN (Figure 11), and the
presence of isosbestic points suggests the direct transformation
of [RuII(trpy)(L)(NO•)]2+ [4]2+ to [RuII(trpy)(L)(CH3CN)]2+
Figure 10. (a) Time evolution of the electronic spectrum (2 min time
intervals) of a solution of [Ru(trpy)(L)(NO)]2+ ([4]2+, 0.12 × 10-4 M) in
CH3CN/0.1 M HClO4 under a steady flow of O2. The inset shows a steady
decrease of 488 nm absorption corresponding to [4]2+
.
∆Sq) and equilibrium constant (K) values are calculated as
44.24 kJ M-1/-169.54 J K-1 M-1, and 88, respectively. The
large negative ∆Sq value implies that the nucleophilic attack
of OH- to the electrophilic NO+ center in [4]3+ takes place
through an associatively activated process.7 The equilibrium
constant of 88 suggests that the nitro species [RuII(trpy)(L)
(NO2)]+ ([3]+) exists as the main component.
The slope of the plot of pseudo-first-order rate constant
values (k [s-1]), 2.02 × 10-4, 3.88 × 10-4, 9.97 × 10-4 in
CH3CN ([4]3+, 0.22 × 10-4 M) at three different concentra-
tions of OH- of 0.2 × 10-2, 0.4 × 10-2, and 1.0 × 10-2 M,
respectively, yields the second order rate constant value of
9.9 × 10-2 M-1 s-1. The estimated low rate constant value
of 9.9 × 10-2 M-1 s-1 for reaction 1 in CH3CN as compared
to the second-order rate constant (k [M-1 s-1]) values
obtained for the analogous reported complexes [RuII-
(trpy)(L′)(NO)]3+ (Table 1) in H2O L1, 6.94 × 105; L2, 4.7
× 103; L5, 2.46 × 103; L6, 1.7 × 103; L8, 1.1 × 103 (assuming
that the concentration of OH- in H2O medium is 10-7 M)
can be considered primarily due to the effect of the
nonaqueous CH3CN medium. A similar effect of the non-
aqueous CH3CN solvent on the rate constant value of reaction
1 has also been observed in the case of [RuII(trpy)(L4)(NO)]3+
(k, 0.4 × 10-2 M-1 s-1).7d
[2′]2+. The rate of the first-order photolytic release of NO (kNO
)
has been determined at 2.0 × 10-1 min-1 (t1/2 ≈ 3.5 min). The
rate of photorelease of “NO” from the analogous complex
[RuII(trpy)(L4)(NO•)]2+ (kNO [min-1] ) 4.4 × 10-3 and t1/2
≈
157 min7d) is 45 times slower than that estimated for [4]2+.
Reaction of [RuII(trpy)(L)(NO•)]2+ ([4]2+) with O2. The
reaction of dioxygen with the metal bound nitrosyl group
(16) Ford, P. C.; Lorkovic, I. M. Chem. ReV. 2002, 102, 993.
3224 Inorganic Chemistry, Vol. 47, No. 8, 2008

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+
corresponding nitro species [3]+ in the presence of OH-.
The oxidation of the radical species [4]2+ to [4]3+ in the
presence of a steady flow of dioxygen proceeds through an
associatively activated pathway with a pseudo-first-order rate
constant of 5.33 × 10-3 s-1 at 298 K. In acetonitrile solution
the Ru-NO bond in [4]2+ is susceptible to undergo photo-
cleavage on exposure to light, forming the solvated species
[2′]2+. The liberated NO can be scavenged by myoglobin.
Experimental Section
19
Figure 11. Time evolution of the electronic spectrum (2 min time intervals)
of a solution of [Ru(trpy)(L)(NO)]2+ ([4]2+, 0.41 × 10-4 M) in CH3CN
under the exposure of light (Xe lamp, 350 W). The inset shows absorbance
Materials. The precursor complex Ru(trpy)Cl3 and 2-phe-
nylimidazo[4,5-f]1,10-phenanthroline (L)20 were prepared as re-
ported. 2,2′:6′,2′′-Terpyridine and silver nitrate were purchased from
Aldrich. Other chemicals and solvents were reagent grade and used
as received. For spectroscopic studies HPLC grade solvents were
used.
versus time plot at 488 nm corresponding to [4]2+
.
Instrumentation. Solution electrical conductivity was checked
using a Systronic conductivity bridge 305. Infrared spectra were
taken on a Nicolet spectrophotometer with samples prepared as KBr
1
pellets. H NMR spectra were recorded using a 300 MHz Varian
FT spectrometer with (CD3)2SO used as solvent. Cyclic voltam-
metric and coulometric measurements were carried out using a PAR
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 50 mV s-1. A platinum
gauze working electrode was used in the coulometric experiments.
All electrochemical experiments were carried out under dinitrogen
atmosphere. IR spectroelectrochemical studies were performed in
CH3CN/0.1 M Bu4NPF6 at 298 K using an optically transparent
thin layer electrode (OTTLE) cell21 mounted in the sample
compartment of a Perkin-Elmer 1760X FTIR instrument. The EPR
measurements were made in a two-electrode capillary tube22 with
a X-band Bruker system ESP300. UV–vis spectral studies were
performed on a Perkin-Elmer Lambda 950 spectrophotometer. The
elemental analyses were carried out with a Perkin-Elmer 240C
elemental analyzer. Electrospray mass spectra were recorded on a
Micromass Q-ToF mass spectrometer. Magnetic susceptibility was
measured with a CAHN electrobalance 7550. Emission experiments
were performed using a Perkin-Elmer LS55 luminescence spec-
trometer fitted with a cryostat.
Figure 12. Absorption spectra of met-Mb, reduced Mb, and the Mb-NO
adduct in water.
This sort of photolytic cleavage of an M-NO bond maintaining
the overall integrity of the remaining part of the molecule is
known to have biological significance.4 Therefore, the feasibility
of binding the liberated “NO” to a biological target molecule
such as myoglobin was explored.
When liberated “NO” from photolyzed [4]2+ in acetonitrile
was passed through the aqueous solution of reduced Mb
under deoxygenated condition the Mb-NO adduct was
spontaneously formed. This has been evidenced via the
development of a characteristic intense band of Mb-NO at
λmax ) 419 nm (Figure 12).17,18 The small absorption at 462
nm in the spectrum of Mb-NO arises from the presence of
the solvated species [RuII(trpy)(L)(CH3CN)]2+ [2′]2+ in the
photolyzed solution.
Kinetic Experiment. For the determination of k in the conversion
process of [RuII(trpy)(L)(NO+)]3+ ([4]3+) f [RuII(trpy)(L)(NO2)]+
([3]+) in acetonitrile in the presence of aqueous sodium hydroxide
solution (pH ∼ 10) the increase in absorbance (At) at 478 nm
corresponding to λmax of the nitro complex [3]+ was monitored as
a function of time (t). AR was measured when the intensity changes
leveled off. Values of pseudo first order rate constants, k, were
obtained from the slopes of linear least-squares plots of -ln(AR -
At) against t. The activation parameters ∆Hqand ∆Sq were deter-
mined from the Eyring plot.23
Conclusion
The present work demonstrates that the combination of
trpy and L coligands in the complex framework of {Ru-
(trpy)(L)(NO)} facilitates the stabilization of the nitrosyl
group in both the NO+ and NO• redox states which are
reversibly interconvertible via one-electron transfer. The
changes in {RuNO}6,7 bonding for [4]3+ and [4]2+ are evident
from the ca. 300 cm-1 shift in the ν(NO) stretching fre-
quency. The analysis of the EPR spectrum of [4]2+ suggests
significant metal contributions to the NO-based SOMO. The
NO+ center in [4]3+ is sufficiently electrophilic to form the
(19) Indelli, M. T.; Bignozzi, C. A.; Scandola, F.; Collin, J.-P. Inorg. Chem.
1998, 37, 6084.
(20) Liu, J. H.; Ren, X. Z.; Xu, H.; Huang, Y.; Liu, J. Z.; Ji, L. N.; Zhang,
Q. L. J. Inorg. Biochem. 2003, 95, 194.
(17) (a) Fernandez, B. O.; Lorkovic, I. M.; Ford, P. C. Inorg. Chem. 2004,
43, 5393. (b) Patra, A. K.; Mascharak, P. K. Inorg. Chem. 2003, 42,
7363.
(21) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. 1991, 317,
179.
(22) Kaim, W.; Ernst, S.; Kasack, V. J. Am. Chem. Soc. 1990, 112, 173.
(23) Wilkins, R. G. The study of kinetics and mechanism of reaction of
Transition Metal Complexes; Allyn and Bacon: Boston, MA, 1974.
(18) SenGupta, N.; Basu, S.; Payra, P.; Mathur, P.; Lahiri, G. K.; Bhaduri,
S. Dalton Trans. 2007, 2594.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3225

Maji et al.
The pseudo-first-order rate constant for the conversion of
[RuII(trpy)(L)(NO•)]2+ ([4]2+) f [RuII(trpy)(L)(NO+)]3+ ([4]3+) in
CH3CN/0.1 M HClO4 solution in presence of steady flow of
dioxygen was determined from the single-exponential fitting of the
plot of change in absorbance against time at λmax ) 488 nm. The
activation parameters ∆Hq and ∆Sq were determined from the
Eyring plot.23
The first-order rate constant for the photorelease of NO from
[RuII(trpy)(L)(NO•)]2+ [4]2+ was determined from a single-
exponential fitting of the plot of change in absorbance against time
under photolysis condition at λmax ) 488 nm in acetonitrile.
Photoreleased NO Trapping by Myoglobin. A solution of
[4](ClO4)2 (3.0 mL) in acetonitrile was prepared in a quartz cuvette
with an optical path length of 1 cm and sealed with a rubber septum.
The solution was deoxygenated by purging with nitrogen gas and
photolyzed for 30 min using a Xe 350 W lamp. The photoreleased
free NO was allowed to pass through a solution of reduced myoglobin
in water by a canula and the UV–vis spectrum was recorded.
Caution! Special precautions should be taken when handling
perchloric acid and organic perchlorates.
(2.98); N, 12.88 (12.56%). Molar conductivity [ΛM (Ω-1 cm2 M-1)]
in acetonitrile: 236. H NMR (CD3)2SO: δ ) 9.96 (d, 4.8 Hz, 1
H), 9.4 (d, 8.4 Hz, 1 H), 8.96 (d, 8.4 Hz, 2 H), 8.88 (d, 7.8 Hz, 1
H), 8.78 (d, 8.4 Hz, 2 H), 8.5 (t, 8.4 Hz, 7.8 Hz, 2 H), 8.32 (d, 7.2
Hz, 2 H), 8.08 (t, 6.9 Hz, 7.5 Hz, 2 H), 7.69 (m, 7 H), 7.34 (t, 6.3
Hz, 6.3 Hz, 2 H) ppm.
Synthesis of [Ru(trpy)(L)(NO2)](ClO4) [3](ClO4). The aqua
complex [2](ClO4)2 (100 mg, 0.118 mmol) was dissolved in 25
mL of hot water and an excess of NaNO2 (194 mg, 2.81 mmol)
was added. The mixture was heated at reflux for 1.5 h. The deep
red solution of the aqua species changed to deep orange during the
course of reaction. The pure crystalline nitro complex precipitated
during cooling to room temperature. The solid [3](ClO4) thus
obtained was filtered off, washed with ice-cold water and dried in
vacuo over P4O10. Yield: 76.91 mg (84%). Anal. Calcd for
C34H23ClN8O6Ru (776.04) (found): C, 52.57 (53.17); H, 2.99 (2.99);
N, 14.44 (14.44%). Molar conductivity [ΛM (Ω-1 cm2 M-1)] in
acetonitrile: 127. 1H NMR (CD3)2SO: δ ) 10.01 (d, 5.1 Hz, 1 H),
9.32 (d, 8.1 Hz, 1 H), 8.85 (t, 8.4 Hz, 6.9 Hz, 3 H), 8.71 (d, 8.1
Hz, 2 H), 8.40 (m, 4 H), 8.01 (t, 8.1 Hz, 7.8 Hz, 2 H), 7.59 (m, 7
H), 7.28 (t, 6.6 Hz, 6.0 Hz, 2 H) ppm.
1
Synthesis of [Ru(trpy)(L)(Cl)](ClO4) [1](ClO4). The starting
complex [Ru(trpy)Cl3] (100 mg, 0.23 mmol), 2-phenylimidazo[4,5-
f]1,10-phenanthroline (L) (67.19 mg, 0.227 mmol), excess LiCl (54
mg, 1.3 mmol), and NEt3 (0.4 mL) were taken in 25 mL of ethanol,
and the mixture was heated at reflux for 8 h under a dinitrogen
atmosphere. The initial greenish solution gradually changed to deep
purple. The solvent was then removed under reduced pressure. The
dry mass thus obtained was dissolved in a minimum volume of
acetonitrile, and an excess of a saturated aqueous solution of NaClO4
was added. The solid precipitate thus obtained was filtered off and
washed thoroughly with ice-cold water. The product was dried in
vacuo over P4O10. It was then purified by using a silica gel column.
The complex [1](ClO4) was eluted by 2:1 CH2Cl2-CH3CN.
Evaporation of the solvent under reduced pressure afforded pure
[1](ClO4). Yield: 118.28 mg (68%). Anal. Calcd for C34H23-
Cl2N7O4Ru (765.02) (found): C, 53.33 (53.01); H, 3.03 (2.96); N,
12.81 (12.79%). Molar conductivity [ΛM (Ω-1 cm2 M-1)] in
[Ru(trpy)(L)(NO)](ClO4)3 [4](ClO4)3. Concentrated HNO3 (2
mL) was added dropwise at 273 K on the solid nitro complex
[3](ClO4) (100 mg, 0.129 mmol) under stirring condition. To the
pasty mass thus obtained was added an ice-cold concentrated HClO4
solution (6 mL) with constant stirring. Addition of a saturated
aqueous NaClO4 solution resulted in a yellow precipitate which
was filtered and washed with about 4 mL of ice-cold water and
then dried in vacuo over P4O10. Yield: 101.22 mg (82%). Anal.
Calcd for C34H23Cl3N8O13Ru (957.94) (found): C, 42.59 (41.39);
H, 2.42 (2.42); N, 11.69 (10.99%). Molar conductivity [ΛM (Ω-1
1
cm2 M-1)] in acetonitrile: 314. H NMR (CD3)2SO: 9.83 (d, 5.4
Hz, 1 H), 9.66 (d, 9.0 Hz, 1 H), 9.28 (m, 3 H), 9.16 (t, 6.9 Hz, 9.3
Hz, 1 H), 9.04 (d, 8.1 Hz, 2 H), 8.70 (t, 8.1 Hz, 5.1 Hz, 1 H), 8.49
(t, 7.8 Hz, 8.1 Hz, 2 H), 8.33 (d, 7.2 Hz, 2 H), 7.89 (m, 3 H),
7.63(m, 6 H) ppm.
Synthesis of [Ru(trpy)(L)(NO)](ClO4)2 [4](ClO4)2. The nitroso
complex [4](ClO4)3 (100 mg, 0.116 mmol) was dissolved in 5 mL
of CH3CN, and excess hydrazine hydrate was added under stirring
over a period of 5 min under a dinitrogen atmosphere. The stirring
was continued at room temperature for further 0.5 h. The initially
yellow solution of [4](ClO4)3 changed to red-brown. The solvent
was then removed under reduced pressure and the solid mass thus
obtained was washed with little ice-cold water and then dried in
vacuo over P4O10. Yield: 65.4 mg (73%). Anal. Calcd for
C34H23Cl2N8O9Ru (859.00) (found): C, 47.51 (47.42); H, 2.70
(2.81); N, 13.04 (12.93%). Molar conductivity [ΛM (Ω-1 cm2 M-1)]
in acetonitrile: 215. Magnetic moment, µ(B.M.) at 298 K ) 1.83.
For other physical characterizations, see main text.
Crystallography. Single crystals of [1](ClO4)·4.5H2O, [2′-H+]-
(ClO4)3 ·H2O and [4-H+](ClO4)4 ·2H2O were grown by slow
evaporation of the respective 1:1 acetonitrile-benzene solutions
at 298 K in air. X-ray data were collected using an OXFORD
XCALIBUR-S CCD single crystal X-ray diffractometer. The
structures were solved and refined by full-matrix least-squares
techniques on F2 using the SHELX-97 program.24 The absorption
corrections were done by the multiscan technique. All data were
corrected for Lorentz and polarization effects, and the nonhydrogen
atoms were refined anisotropically. Hydrogen atoms were included
in the refinement process as per the riding model.
1
acetonitrile: 147. H NMR (CD3)2SO: δ )10.29 (d, 7.8 Hz, 1 H),
9.30 (d, 8.1 Hz, 1 H), 8.85 (d, 8.1 Hz, 2 H), 8.72 (t, 5.1 Hz, 2.7
Hz, 3 H), 8.59 (s, 1 H), 8.23 (m, 3 H), 7.94 (t, 7.2 Hz, 7.5 Hz, 2
H), 7.64 (m, 4 H), 7.51 (m, 3 H), 7.23 (t, 6.6 Hz, 6.6 Hz, 2 H)
ppm.
Synthesis of [Ru(trpy)(L)(H2O)](ClO4)2 [2](ClO4)2. The chloro
complex [1](ClO4) (100 mg, 0.130 mmol) was taken in 25 mL of
water and heated at reflux for 10 min. An excess of AgNO3 (221
mg, 1.3 mmol) was added to the hot solution and the heating was
continued for 1.5 h. It was then cooled and the precipitated AgCl
was separated by filtration through a sintered glass crucible (G-4).
The volume of the filtrate was reduced to 10 mL and an excess of
a saturated aqueous solution of NaClO4 was added. The solid aqua
complex [2](ClO4)2 thus obtained was filtered off, washed with ice-
cold water and dried in vacuo over P4O10. Yield: 86.24 mg (78%).
Anal. Calcd for C34H25Cl2N7O9Ru (847.01) (found): C, 48.18
(47.97); H, 2.97 (3.11); N, 11.57 (11.27%). Molar conductivity [ΛM
(Ω-1 cm2 M-1)] in acetonitrile: 240. 1H NMR (CD3)2SO: δ ) 9.37
(m, 1 H), 8.95 (m, 3 H), 8.76 (q, 6.3 Hz, 9.3 Hz, 8.7 Hz, 3 H),
8.45 (m, 1 H), 8.32 (m, 3 H), 8.03 (m, 2 H), 7.64 (m, 7 H), 7.36
(m, 2 H) ppm.
Synthesis of [Ru(trpy)(L)(CH3CN)](ClO4)2 [2′](ClO4)2. The
complex [2′](ClO4)2 was prepared following the same procedure
as stated above for [2](ClO4)2, except using CH3CN as solvent
instead of water. Yield: 84.03 mg (74%). Anal. Calcd for
C36H26Cl2N8O8Ru (870.02) (found): C, 49.65 (49.77); H, 3.01
Acknowledgment. Financial support received from the
Department of Science and Technology (DST) and Council of
3226 Inorganic Chemistry, Vol. 47, No. 8, 2008

Metal Bound Nitrosyl in [Ru(trpy)(L)(NO)]n+
Supporting Information Available: Crystallographic parameters
of [1](ClO4)·4.5H2O, [2′-H+](ClO4)3 ·H2O, and [4-H+](ClO4)4 ·
2H2O (Table S1); selected bond distances and angles of [1](ClO4)·
4.5H2O, [2′-H+](ClO4)3 ·H2O, and [4-H+](ClO4)4 ·2H2O (Table S2);
1H NMR spectra of [1](ClO4), [2](ClO4)2, [2′](ClO4)2, [3](ClO4), and
[4](ClO4)3 in (CD3)2SO (Figure S1); EPR spectrum of [2′]3+ in CH3CN
(Figure S2). This material is available free of charge via the Internet
at http://pubs.acs.org.
Scientific and Industrial Research (CSIR), New Delhi (India),
the DAAD, the DFG, and the FCI (Germany) is gratefully
acknowledged. Special acknowledgement is made to the
Sophisticated Analytical Instrument Facility (SAIF), Indian
Institute of Technology, Bombay, for providing the NMR
facility.
(24) Sheldrick, G. M. Program for Crystal Structure Solution and Refine-
ment; Universität Göttingen: Göttingen, Germany, 1997.
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