2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-derived [RuII(tptz) (acac)(CH3CN)]+ and mixed-valent [(acac) 2RuIII{(μ-tptz-H+)-}Ru II(acac)(CH3CN)]+

Article abstract of DOI:10.1021/ic0514288

Mononuclear [Ru^II(tptz)(acac)(CH₃CN)]ClO₄ ([1]ClO₄) and mixed-valent dinuclear [(acac)₂Ru ^III{(μ-tptz-H⁺)^-}Ru^II(acac) (CH₃CN)]ClO₄ ([5]ClO₄; acac = acetylacetonate) complexes have been synthesized via the reactions of Ru^II(acac) ₂(CH₃CN)₂ and 2,4,6-tris(2-pyridyl)-1,3,5- triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO ₄, tptz binds with the Ru^II ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO₄, tptz bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the Ru^II center and cyclometalated N,C^- state with the Ru^III site (motif F). The activation of the coordinated nitrile function in [1]ClO ₄ and [5]ClO₄ in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO₄ and [7]ClO₄) and amidine ([4]ClO₄) derivatives, respectively. Crystal structure analysis of [2]ClO₄ reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H- - - - -O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the Ru^II state in both the mononuclear {[(acac)(tptz)Ru^II-N≡C-CH₃]ClO₄ ([1]ClO₄) ? [(acac)(tptz)Ru^II-NH=C(CH ₃)-OC₂H₅]ClO₄ ([2]ClO₄) > [(acac)(tptz)Ru^II-NH₂-C₆H ₄(CH₃)]ClO₄ ([3]ClO₄) > [(acac)(tptz)Ru^II-NH=C(CH₃)-NHC₂H ₅]ClO₄ ([4]ClO₄)} and dinuclear {[(acac) ₂Ru^III{(μ-tptz-H⁺)^-}Ru ^II(acac)(N≡C-CH₃)]ClO₄ ([5]ClO ₄), [(acac)₂Ru^III{(μ-tptz-H ⁺(N⁺-O^-)₂)^-}Ru ^II(acac)(N≡C-CH₃)]ClO₄ ([6]ClO ₄), [(acac)₂Ru^III{(μ-tptz-H ⁺)^-}Ru^II(acac)(NH=C(CH₃)-OC ₂H₅)]ClO₄ ([7]ClO₄), and [(acac)₂Ru^III{(μ-tptz-H⁺) ^-}Ru^II(acac)(NC₄H₄N)]ClO ₄ ([8]ClO₄)} complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the Ru^III center in the dinuclear complexes remain more or less invariant. The mixed-valent Ru^IIRu^III species ([5]ClO₄-[8]ClO₄) exhibits high comproportionation constant (K_c) values of 1.1 × 10¹²-2 × 10 ⁹, with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display Ru^II- and Ru ^III-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high K_c values for [5]ClO ₄-[8]ClO₄, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to 2000 nm. The paramagnetic Ru^IIRu^III species ([5]ClO₄-[8] ClO₄) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (〈g〉 ～ 2.15 and Δg ～ 0.5), typical of a low-spin Ru^III ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [Ru^II(tptz^?-) (acac)(CH₃CN)] (1) and [(acac)₂Ru^III{(μ- tptz-H⁺)^?2-}Ru^II(acac)(CH₃CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.

Full text of DOI:10.1021/ic0514288

Inorg. Chem. 2006, 45, 2413−2423
+
2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-Derived [RuII(tptz)(acac)(CH3CN)]
+ -
+†
and Mixed-Valent [(acac)2RuIII RuII(acac)(CH3CN)]
{(µ-tptz-H ) }
Sandeep Ghumaan,‡ Sanjib Kar,‡ Shaikh M. Mobin,‡ B. Harish,‡ Vedavati G. Puranik,§ and
Goutam Kumar Lahiri*,‡
Department of Chemistry, Indian Institute of TechnologysBombay, Powai, Mumbai 400076, India,
and Center for Materials Characterization, National Chemical Laboratory, Pune,
Maharashtra 411008, India
Received August 22, 2005
Mononuclear [RuII(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2RuIII
{(µ ) }-
-tptz-Η+ -
RuII(acac)(CH3CN)]ClO4 ([5]ClO4; acac
)
acetylacetonate) complexes have been synthesized via the reactions of
RuII(acac)2(CH3CN)2 and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In
[1]ClO4, tptz binds with the RuII ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz bridges the metal
ions unsymmetrically via the tridentate neutral N,N,N mode with the RuII center and cyclometalated N,C- state with
the RuIII site (motif F). The activation of the coordinated nitrile function in [1]ClO4 and [5]ClO4 in the presence of
ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives,
respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster
having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom
of the perchlorate ion, which, in turn, makes short (C
to a H-bonding network. The redox potentials corresponding to the RuII state in both the mononuclear
(tptz)RuII [(acac)(tptz)RuII OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)RuII
CH3]ClO4 ([1]ClO4) NH C(CH3)
NH2 NH C(CH3) NHC2H5]ClO4 ([4]ClO4) and dinuclear
C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)RuII [(acac)2RuIII-
-tptz-H+)- RuII(acac)(N CH3)]ClO4 ([5]ClO4), [(acac)2RuIII -tptz-H+(N+ O-)2)- RuII(acac)(N
CH3)]ClO4
([6]ClO4), [(acac)2RuIII OC2H5)]ClO4 ([7]ClO4), and [(acac)2RuIII -tptz-Η+ -
RuII(acac)(NC4H4N)]ClO4 ([8]ClO4)
complexes vary systematically depending on the electronic nature of the coor-
−H- - - - -O) contacts with the neighboring molecule, leading
{[(acac)-
−N
t
C
−
.
−
d
−
−
−
−
d
−
}
{
{
(
µ
}
t
C
−
{
(
µ
−
}
tC−
{(µ
-tptz-H+)-
}
}
RuII(acac)(NH
dC(CH3)
−
{(µ
) }-
dinated sixth ligands. However, potentials involving the RuIII center in the dinuclear complexes remain more or less
invariant. The mixed-valent RuIIRuIII species ([5]ClO4
of 1.1
1012 109, with substantial contribution from the donor center asymmetry at the two metal sites. Com-
plexes display RuII- and RuIII-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in
the visible region and ligand-based transitions in the UV region. In spite of reasonably high Kc values for [5]ClO4
[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to
2000 nm. The paramagnetic RuIIRuIII species ([5]ClO4
[8]ClO4) displays rhombic electron paramagnetic resonance
(EPR) spectra at 77 K ( g 2.15 and
0.5), typical of a low-spin RuIII ion in a distorted octahedral environment.
The one-electron-reduced tptz complexes [RuII(tptz•-)(acac)(C
RuII(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g
−[8]ClO4) exhibits high comproportionation constant (Kc) values
×
−2 ×
−
−
∼
∆g
∼
2
-
Η
3CN)] (1) and [(acac)2RuIII
{(µ ) }-
-tptz-Η+ •
)
2.0 with partial metal contribution.
Introduction
Ru chemistry of tptz has been confined to a limited number
of mononuclear and dinuclear complexes.3 In principle, tptz
can bind to the metal ions in a number of ways and the motifs
A, B and C, D (Chart 1) have indeed been reported for
mononuclear3a-o and dinuclear3p-r Ru complexes, respec-
tively. The trinucleating mode of tptz (motif E) though has
been mentioned in one report.4
Moreover, Ru-ion-mediated intramolecular hydroxylation
of the coordinated tptz unit3c and DNA binding3b,n properties
of Ru-tptz complexes have also been explored.
2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz) has long been
used as an analytical reagent1 and more recently for develop-
ing metal complexes with diverse perspectives.2 However,
† Dedicated to Professor Wolfgang Kaim, Institut fuer Anorganische
Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart,
Germany, on the occasion of his 55th birthday.
* To whom correspondence should be addressed. E-mail: lahiri@
chem.iitb.ac.in.
‡ Indian Institute of TechnologysBombay.
§ National Chemical Laboratory.
10.1021/ic0514288 CCC: $33.50
Published on Web 02/16/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 6, 2006 2413

Ghumaan et al.
Chart 1
{Ru(acac)2}, encompassing an electronically rich acetylace-
tonate (acac-) group. The choice of “acac-” as the ancillary
ligand for the present study originates from our recent
observations that the presence of the “acac-” unit with the
Ru ion instead of π-acidic bpy-like ligands makes significant
differences toward the overall energetics and subsequent
chemical behaviors of the complexes.5 Thus, the interaction
of Ru(acac)2(CH3CN)2 with tptz has led to the formations
of hitherto unprecedented mixed-valent RuIIRuIII species,
[5]ClO4 having motif F and the corresponding mononuclear
RuII complex [1]ClO4 (motif A). Further, the relatively
electrophilic nitrile function in both the mononuclear [1]ClO4
and dinuclear [5]ClO4 complexes has undergone direct
transformations to the coordinated iminoester ([2]ClO4 and
[7]ClO4) and amidine ([4]ClO4) derivatives in the presence
of protic nucleophiles, alcohol, and alkylamine, respectively.
In this paper, the detailed synthetic account of the
complexes [1]ClO4-[8]ClO4 (Scheme 1), crystal structures
of selective derivatives, spectroelectrochemical properties,
and the substitution/activation processes of the coordinated
nitrile function in [1]ClO4 and [5]ClO4 have been deliberated.
In the reported systems, the ancillary ligands associated
with the Ru-tptz unit were mostly π acceptor in nature,
either 2,2′:6′,2′′-terpyridine, 2,2′-bipyridine (bpy), 1,10-
phenanthroline, CO, or PPh3/AsPh3, etc.3 Therefore, the
present work deals with the perspective of further exploration
of the metalation aspects of tptz with the Ru precursor unit
(1) (a) Janmohamed, M. J.; Ayres, G. H. Anal. Chem. 1972, 44, 2263.
(b) Embry, W. A.; Ayres, G. H. Anal. Chem. 1968, 40, 1499. (c) Tsen,
C. C. Anal. Chem. 1961, 33, 849. (d) Diehl, H.; Buchanan, E. B., Jr.;
Smith, G. G. Anal. Chem. 1960, 33, 1117. (e) Collins, P. F.; Diehl,
H. Anal. Chim. Acta 1960, 22, 125. (f) Collins, P. F.; Diehl, H.; Smith,
G. F. Anal. Chem. 1959, 31, 1862.
Results and Discussion
Synthesis. The mononuclear [1]ClO4 (motif A) and
dinuclear [5]ClO4 (motif F) complexes were synthesized via
the reactions of precursor complex Ru(acac)2(CH3CN)2 with
tptz in molar ratios of 1:1 and 2:1, respectively, in refluxing
ethanol followed by chromatographic purifications using an
alumina column (Scheme 1). The formation of [1]ClO4 has
been authenticated by its single-crystal X-ray structure (see
later). The dinuclear complex [5]ClO4 could also be syn-
thesized in quantitative yield starting from the mononuclear
derivative [1]ClO4 in the presence of excess metal precursor
[Ru(acac)2(CH3CN)2]. All of our attempts to synthesize the
trinuclear derivative (motif E) using 3:1 or higher molar
ratios of the Ru precursor complex and tptz or from the
preformed [1]ClO4 as well as [5]ClO4 failed altogether. The
reaction always ended up yielding the dinuclear species,
[5]ClO4.
(2) (a) Paul, P.; Tyagi, B.; Bilakhiya, A. K.; Bhadbhade, M. M.; Suresh,
E.; Ramachandraiah, G. Inorg. Chem. 1998, 37, 5733. (b) Folgado,
J.-V.; Henke, W.; Allmann, R.; Stratemeier, H.; Beltra´n-Porter, D.;
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1981, 20, 3476. (f) Prasad, J.; Peterson. N. C. Inorg. Chem. 1971, 10,
88. (g) Fraser, F. H.; Epstein, P.; Macero, D. J. Inorg. Chem. 1972,
11, 2031. (h) Faus, J.; Julve, M.; Amigo, J. M.; Debaerdemaeker, T.
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Wietzke, R.; Mazzanti, M.; Latour, J.-M.; Pecaut, J. Inorg. Chem. 1999,
38, 3581. (k) Comba, P.; Zimmer, M. Inorg. Chem. 1994, 33, 5368.
(l) Arana, C.; Yan, S.; Keshavarz, K. M.; Potts, K. T.; Abrun˜a, H. D.
Inorg. Chem. 1992, 31, 3680. (m) Pagenkopf, G. K.; Margerum, D.
W. Inorg. Chem. 1968, 7, 2514. (n) Glaser, T.; Lu¨gger, T.; Fro¨hlich,
R. Eur. J. Inorg. Chem. 2004, 2, 394.
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Taylor, N. J.; Watanabe, M.; Tanaka, Y.; Loiseau, F.; Passalacqua,
R.; Campagna, S. Chem.sEur. J. 2004, 10, 3640. (b) Gupta, N.;
Grover, N.; Neyhart, G. A.; Singh, P.; Thorp, H. H. Inorg. Chem.
1993, 32, 310. (c) Paul, P.; Tyagi, B.; Bilakhiya, A. K.; Dastidar, P.;
Suresh, E. Inorg. Chem. 2000, 39, 14. (d) Metcalfe, C. M.; Spey, S.;
Adams, H.; Thomas, J. A. J. Chem. Soc., Dalton Trans. 2002, 4732.
(e) Saji, T.; Aoyagui, S. J. Electroanal. Chem. 1980, 110, 329. (f)
Tokel-Takvoryan, N. E.; Hemingway, R. E.; Bard, A. J. J. Am. Chem.
Soc. 1973, 95, 6582. (g) Paul, P.; Tyagi, B.; Bhadbhade, M. M.; Suresh,
E. J. Chem. Soc., Dalton Trans. 1997, 2273. (h) Thomas, N. C.; Foley,
B. L.; Rheingold, A. L. Inorg. Chem. 1988, 27, 3426. (i) Lin, C. T.;
Bottcher, W.; Chou, M.; Creutz, C.; Sutin, N. J. Am. Chem. Soc. 1976,
98, 6536. (j) Lalrempuia, R.; Govindaswamy, P.; Mozharivskyj, Y.
A.; Kollipara, M. R. Polyhedron 2004, 23, 1069. (k) Berger, R. M.;
Holcombe, J. R. Inorg. Chim. Acta 1995, 232, 217. (l) Sharma, S.;
Chandra, M.; Pandey, D. S. Eur. J. Inorg. Chem. 2004, 17, 3555. (m)
Chandra, M.; Sahay, A. N.; Pandey, D. S.; Tripathi, R. P.; Saxena, J.
K.; Reddy, V. J. M.; Puerta, M. C.; Valerga, P. J. Organomet. Chem.
2004, 689, 2256. (n) Chandra, M.; Sahay, A. N.; Pandey, D. S.; Puerta,
M. C.; Valerga, P. J. Organomet. Chem. 2002, 648, 39. (o) Singh,
A.; Singh, N.; Pandey, D. S. J. Organomet. Chem. 2002, 642, 48. (p)
Chirayil, S.; Hegde, V.; Jahng, Y.; Thumme, R. P. Inorg. Chem. 1991,
30, 2821. (q) Chandra, M.; Sahay, A. N.; Pandey, D. S. Indian J.
Chem. 2004, 43A, 323. (r) Berger, R. M.; Ellis, D. D. Inorg. Chim.
Acta 1996, 241, 1.
The effect of π-accepting tptz and electron-withdrawing
CH3CN ligands in the coordination sphere of [1]ClO4 has
been reflected in its reasonably high RuIII-RuII potential
(∼0.8 V vs SCE; see later). The mixed-valent RuIIRuIII
state in the dinuclear complex [5]ClO4 (motif F) develops
via the formation of a Ru-C- bond from the pendant
pyridine ring of tptz to the second metal ion in addition to
its linkage with the two electronically rich acac- units. It
may be noted that the Ru-ion-induced selective C-H bond
activation of the pyridazyl ring and subsequent stabiliza-
tion of the mixed-valent RuIIRuIII state in [RuII{N(pyri-
dyl), N(pyridazyl)O4(acac-)2}RuIII{N(pyridyl),C-(pyridazyl)-
O4(acac-)2}] has been reported recently.5e Similarly, cyclo-
metalation via the C-H bond activation of the pyridine ring
of diimine-based ligands is also known.6
(4) (a) Yenmez, I.; Specker, H. Fresenius’ Z. Anal. Chem. 1979, 296,
140. (b) The Scifinder search shows the structure of one trinuclear
Rh(3+) complex without any reference (registry no. 113006-61-4).
2414 Inorganic Chemistry, Vol. 45, No. 6, 2006

Mononuclear and Mixed-Valent Dinuclear Complexes
a
Scheme 1
a (i) 1:1 Ru(acac)2(CH3CN)2, EtOH, ∆; (ii) EtOH, ∆; (iii) (CH3)C6H4NH2, EtOH, ∆; (iv) C2H5NH2, EtOH, ∆; (v) 1:1 Ru(acac)2(CH3CN)2, EtOH, ∆; (v′)
1:2 Ru(acac)2(CH3CN)2, EtOH, ∆; (vi) m-ClC6H4CO3H, CH2Cl2, stir; (vii) EtOH, ∆; (viii) pyrazine, EtOH, ∆.
Chart 2
Alternatively, isomeric structure I or II (Chart 2) can also
be drawn as a possible formulation for the dinuclear complex
[5]ClO4. However, motif F has been considered favorably
as the metal-C bond because it originates from the available
(5) (a) Sarkar, B.; Patra, S.; Kaim, W.; Lahiri, G. K. Angew. Chem., Int.
Ed. 2005, 44, 5655. (b) 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. (c) Patra, S.; Sarkar, B.; Maji, S.; Fiedler,
J.; Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K.
Chem.sEur. J. 2006, 12, 489. (d) Kar, S.; Chanda, N.; Mobin, S.
M.; Urbanos, F. A.; Niemeyer, M.; Puranik, V. G.; Jimenez-Aparicio,
R.; Lahiri, G. K. Inorg. Chem. 2005, 44, 1571. (e) Ghumaan, S.;
Sarkar, B.; Patra, S.; Parimal, K.; van Slageren, J.; Fiedler, J.; Kaim,
pendant pyridine ring of tptz instead of utilizing the already
W.; Lahiri, G. K. Dalton Trans. 2005, 706. (f) Patra, S.; Sarkar,
coordinated pyridine ring as in I or II.
B.; Ghumaan, S.; Fiedler, J.; Kaim, W.; Lahiri, G. K. Dalton Trans.
2005, 754. (g) Patra, S.; Mondal, B.; Sarkar, B.; Niemeyer, M.;
Lahiri, G. K. Inorg. Chem. 2003, 42, 1322. (h) Patra, S.; Sarkar, B.;
Ghumaan, S.; Fiedler, J.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2004,
43, 6108. (i) Patra, S.; Miller, T. A.; Sarkar, B.; Niemeyer, M.; Ward,
M. D.; Lahiri, G. K. Inorg. Chem. 2003, 42, 4707. (j) Patra, S.; Sarkar,
B.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Inorg. Chem. 2003, 42,
6469.
The formation of an unprecedented cyclometalated N,C-
coordination mode of tptz with the second metal ion and
subsequent stabilization of the mixed-valent RuIIRuIII con-
figuration in [5]ClO4 (motif F) instead of the isovalent
RuIIRuII state via the usual N,N bonding mode with the
Inorganic Chemistry, Vol. 45, No. 6, 2006 2415

Ghumaan et al.
Scheme 2
Table 1. Mass Spectral Data in Acetonitrile for Complexes
[1]ClO4-[8]ClO4
compound
m/z, obsd
correspondence
m/z, calcd
[1]ClO4
554.09
513.06
600.45
513.34
620.23
513.14
599.29
513.19
854.16
812.13
887.19
854.17
900.23
854.18
813.16
893.04
813.01
[1]+
554.08
513.06
600.12
513.06
620.13
513.06
599.14
513.06
853.07
812.05
885.06
853.07
899.11
854.08
812.05
892.08
812.05
[1-CH3CN]+
[2]ClO4
[3]ClO4
[4]ClO4
[5]ClO4
[6]ClO4
[7]ClO4
[2]+
[2-NHC(CH3)(OEt)]+
[3]+
[3-(CH3)C6H4NH2]+
[4]+
[4-NHC(CH3)(NHEt)]+
[5]+
[5-CH3CN]+
[6]+
[6-2O]+
[7]+
[7-OEt]+
[7-NHC(CH3)(OEt)]+
[8]+
second metal (motif C) finds justification through its physical
parameters such as conductivity, magnetic moment, and
electron paramagnetic resonance (EPR) data (see below).
This has also been further evidenced via the facile trans-
formation of [5]ClO4 to the N+-O- dinuclear derivative
[6]ClO4, upon reaction with m-chloroperbenzoic acid in
CH2Cl2 (Scheme 1).7
The specific linkage of the π-accepting tptz unit with the
Ru ion makes the nitrile function in [1]ClO4 and [5]ClO4
sufficiently electrophilic such that upon reactions with EtOH
and ethylamine the corresponding iminoester ([2]ClO4 and
[7]ClO4) and amidine ([4]ClO4) derivatives, respectively
(Scheme 1), have been formed via the nucleophilic addition
routes, i and ii (Scheme 2).8,9 The formation of [2]ClO4 has
been authenticated by its single-crystal X-ray structure (see
later). However, the reaction of an aromatic primary amine,
p-toluidine, with [1]ClO4 resulted in a simple substituted
product, [3]ClO4 (Scheme 1), which has also been structurally
characterized (see later).
The key step toward the amidine formation in [4]ClO4
involves the nucleophilic attack of -NH-R on the carbonium
center of the coordinated nitrile function as shown in route
ii (Scheme 2). Thus, the electron-donating ethyl group as
“R” in the amine fragment instead of the electron-withdraw-
ing aryl group in p-toluidine facilitates the formation of active
nucleophile -NH-R, which, in turn, leads to the yield of
the amidine product [4]ClO4. Though [1]ClO4 can be easily
transformed to [4]ClO4, the reaction of ethyl- or methylamine
with the corresponding dinuclear species [5]ClO4 yielded
materials that are insoluble in common solvents such as
CH3CN, CH2Cl2, C6H6, dimethylformamide, dimethyl sul-
[8]ClO4
[8-pyrazine]+
foxide, and H2O. Thus, no attempt was made to further
characterize the product. Unlike [1]ClO4, the reaction of
p-toluidine with [5]ClO4 in a refluxing alcoholic medium
mostly generated the iminoester derivative [5]ClO4 along
with a slight amount of the corresponding amine-substituted
product (<5%).
It should be noted that under identical reaction condi-
tions (Scheme 1) the activation of the nitrile functions in
the precursor complex Ru(acac)2(CH3CN)2 did not take
place in the presence of alcohol or amine in an ethanolic
medium. The presence of electronically rich acac- ligands
in Ru(acac)2(CH3CN)2 fails to make the coordinated nitrile
functions electrophilic enough to participate in the acitivation
processes (Scheme 2).
Attempts to synthesize pyrazine-bridged tetranuclear spe-
cies from [5]ClO4 in ethanol failed; a simple pyrazine-
substituted product, [8]ClO4, resulted instead. However, the
same reaction of [1]ClO4 with pyrazine in an ethanolic
medium resulted in iminoester derivative [2]ClO4.
The formations of 1:1 conducting diamagnetic mono-
nuclear ([1]ClO4-[4]ClO4) and one-electron paramagnetic
dinuclear ([5]ClO4-[8]ClO4) complexes have been con-
firmed by their elemental analyses (see the Experimental
Section) and mass spectral data (Table 1 and Figures 1 and
S1 in the Supporting Information). The single-crystal X-ray
structures of [1]ClO4, [2]ClO4, and [3]ClO4 have also been
determined (see below).
Crystal Structures of [1]ClO4‚2H2O, [2]ClO4‚2H2O, and
[3]ClO4‚2H2O and the Formation of a Water Cluster in
[2]ClO4‚2H2O. The crystal structures of the cations of
[1]ClO4‚2H2O, [2]ClO4‚2H2O, and [3]ClO4‚2H2O are shown
in Figures 2-4. Selected crystallographic and structural
parameters are listed in Tables 2 and 3, respectively. In the
complexes, tptz is coordinated to the Ru ion in the expected
meridional fashion,10 with the acac ligand in a cis position.
The geometrical constraints due to the meridional binding
of the tridentate tptz are reflected by the intraligand trans
angles N1-Ru-N3 of 157.9(2), 157.76(16), and 158.2(2)°
in [1]ClO4, [2]ClO4, and [3]ClO4, respectively. The other
two interligand trans angles N2-Ru-O1 and N7-Ru-O2
remain close to 180° for all three complexes. As in other
(6) (a) Chen, J.-L.; Zhang, X.-D.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N.
Inorg. Chem. 2005, 44, 1037. (b) Minghetti, G.; Stoccoro, S.; Cinellu,
M. A.; Soro, B.; Zucca, A. Organometallics 2003, 22, 4770. (c) Ward,
M. D. J. Chem. Soc., Dalton Trans. 1994, 3095.
(7) Wenkert, D.; Woodward, R. B. J. Org. Chem. 1983, 48, 283.
(8) (a) Nagao, H.; Hirano, T.; Tsuboya, N.; Shiota, S.; Mukaida, M.; Oi,
T.; Yamasaki, M. Inorg. Chem. 2002, 41, 6267. (b) Bokach, N. A.;
Kukushkin, V. Y.; Kuznetsov, M. L.; Garnovskii, D. A.; Natile, G.;
Pombeiro, A. J. L. Inorg. Chem. 2002, 41, 2041.
(9) (a) Mondal, B.; Puranik, V. G.; Lahiri, G. K. Inorg. Chem. 2002, 41,
5831. (b) Chin, C. S.; Chong, D.; Lee, S.; Park, Y. J. Organometallics
2000, 19, 4043. (c) Chin, C. S.; Chong, D.; Lee, B.; Jeong, H.; Won,
G.; Do, Y.; Park, Y. J. Organometallics 2000, 19, 638. (d) Anderes,
B.; Lavallee, D. K. Inorg. Chem. 1983, 22, 3724. (e) Storhoff, B. N.;
Lewis, H. C., Jr. Coord. Chem. ReV. 1977, 23, 1. (f) Cotton, F. A.;
Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced Inorganic
Chemistry, 6th ed.; John Wiley and Sons: New York, 1999; pp 359-
360.
2416 Inorganic Chemistry, Vol. 45, No. 6, 2006

Mononuclear and Mixed-Valent Dinuclear Complexes
Figure 3. ORTEP diagram for the cation of [2]ClO4‚2H2O. Ellipsoids
are drawn at 50% probability.
Figure 1. Electrospray mass spectra of (a) [5]ClO4, (b) [6]ClO4, (c)
[7]ClO4, and (d) [8]ClO4 in CH3CN.
Figure 4. ORTEP diagram for the cation of [3]ClO4‚2H2O Ellipsoids are
drawn at 50% probability.
Table 2. Crystallographic Data for [1]ClO4, [2]ClO4, and [3]ClO4
C25H22ClN7O8Ru C27H32ClN7O9Ru C30H28N7O8Ru
mol formula
fw
[1]ClO4‚2H2O
685.02
[2]ClO4‚2H2O
735.12
[3]ClO4‚2H2O
751.11
radiation
cryst sym
space group
a (Å)
b (Å)
c (Å)
Mo KR
monoclinic
P21/n
8.7920(12)
13.0460(11)
24.771(3)
90
98.810(11)
90
2807.7(6)
4
Mo KR
monoclinic
P21/n
8.7430(11)
24.500(3)
15.570(2)
90
97.896(2)
90
3303.5(7)
4
Mo KR
triclinic
P1h
10.0010(7)
13.1560(11)
14.0430(8)
103.831(6)
106.312(5)
104.764(7)
1615.8(2)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
Figure 2. ORTEP diagram for the cation of [1]ClO4‚2H2O. Ellipsoids
are drawn at 50% probability.
µ (mm-1
T (K)
D
)
0.715
293(2)
1.621
0.615
293(2)
1.478
0.628
293(2)
1.544
Ru-tptz derivatives, the central Ru-N2(tptz) bond lengths
of 1.913(5), 1.909(4), and 1.885(6) Å in [1]ClO4, [2]ClO4,
and [3]ClO4, respectively, are significantly shorter than the
calcd (g cm-3
)
2θ range (deg)
3.32-49.82
4924 (0.0390)
0.0606
0.1666
1.036
3.12-50.00
5815 (0.0648)
0.0557
0.1610
1.056
3.40-49.9
5673 (0.0612)
0.0657
0.1644
1.008
E data (Rint
)
R1 [I > 2σ(I)]
wR2 (all data)
GOF
(10) (a) Patra, S.; Sarkar, B.; Ghumaan, S.; Patil, M. P.; Mobin, S. M.;
Sunoj, R. B.; Kaim, W.; Lahiri, G. K. Dalton Trans. 2005, 1188. (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) Chanda,
N.; Mobin, S. M.; Puranik, V. G.; Datta, A.; Niemeyer, M.; Lahiri,
G. K. Inorg. Chem. 2004, 43, 1056. (d) Sarkar, S.; Sarkar, B.; Chanda,
N.; Kar, S.; Mobin, S. M. Fiedler, J.; Kaim, W.; Lahiri, G. K. Inorg.
Chem. 2005, 44, 6092.
corresponding terminal Ru-N(tptz) distances, Ru-N1 [2.075-
(5), 2.081(4), and 2.064(6) Å] and Ru-N3 [2.088(5), 2.077-
(4), and 2.058(6) Å].3 The pendant pyridine ring of tptz is
Inorganic Chemistry, Vol. 45, No. 6, 2006 2417

Ghumaan et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
[1]ClO4‚2H2O, [2]ClO4‚2H2O, and [3]ClO4‚2H2O
of tptz and the oxygen atom (O2) of the coordinated acac of
a symmetry-related molecule have been observed. Moreover,
one of the methyl hydrogens (C19-H19A) of acac is
H-bonded to the oxygen atom (O5) of the ClO4 molecule
(Figure S2 and Table S1 in the Supporting Information).
The packing diagram of [2]ClO4 reveals the formation of
a beautiful eight-membered H2O cluster having a chair
conformation.13 The cluster is formed via O8, O9, O10, and
O11 of water molecules, and O8 of the water molecule is
disordered. Further, O10 of the cluster is H-bonded to N6
of the pendant pyridyl ring of tptz. O10 is also H-bonded
with O7 of the perchlorate ion, which, in turn, makes short
(C-H- - - - -O) contacts with the neighboring molecule,
leading to a H-bonding network with a water cluster of the
complex molecule. The H-bonding network is shown in
Figure 5, and the distances are listed in Table 4. All O- - -O
distances are below 3.0 Å (Table 4), confirming the stability
of the H-bonding network (Figure 5).
1H NMR Spectra. NMR spectral data of the diamagnetic
complexes [1]ClO4-[4]ClO4 are set in the Experimental
Section, and the representative spectra are shown in Figure
6. The calculated 12 and 16 aromatic protons for [1]ClO4/
[2]ClO4/[4]ClO4 and [3]ClO4, respectively, appear in the
range δ 7.0-9.0 as partially overlapping signals due to
similar chemical shifts of many protons. The singlets
corresponding to the C-H proton of acac and the CH3
protons of acac/acetonitrile are observed near δ 5.0 and δ
2.6-1.2, respectively. The ethyl signals of OEt and NHEt
for [2]ClO4 and [4]ClO4 appear at δ 3.4 (CH2, quartet)/0.6
(CH3, triplet) and δ 3.1 (CH2, quintet because of additional
coupling with the adjacent NH proton)/1.24 (CH3, triplet),
respectively. The coordinated NH proton of [2]ClO4 is
seen at δ 7.4 as a relatively broad singlet. However, the same
for [4]ClO4 displays a triplet profile at δ 7.6 because of the
N nuclear spin I ) 1.14 The uncoordinated NH proton of
[4]ClO4 is observed at δ 4.6 as a broad singlet. The NH2
protons of coordinated amine in [3]ClO4 appear as doublet
of doublets at δ 5.9 and 6.5.
bond length/angle
[1]ClO4‚2H2O
[2]ClO4‚2H2O
[3]ClO4‚2H2O
Ru-N2
1.913(5)
2.031(6)
2.066(5)
2.039(4)
2.088(5)
2.075(5)
1.115(9)
1.438(11)
1.909(4)
2.036(5)
2.061(3)
2.059(3)
2.077(4)
2.081(4)
1.165(8)
1.487(10)
1.456(10)
1.475(16)
1.53(2)
96.03(17)
178.65(15)
83.03(16)
89.83(14)
174.14(17)
91.10(14)
78.84(16)
91.49(18)
102.13(15)
89.83(15)
78.92(16)
90.37(17)
100.10(15)
90.57(14)
157.76(16)
146.6(6)
1.885(6)
2.145(6)
2.054(5)
2.043(5)
2.058(6)
2.064(6)
1.412(10)
1.384(11)
Ru-N7
Ru-O1
Ru-O2
Ru-N3
Ru-N1
N7-C25
C24-C25
C25-O3
O3-C26
C26-C27
N2-Ru-N7
N2-Ru-O1
N7-Ru-O1
N2-Ru-O2
N7-Ru-O2
O1-Ru-O2
N2-Ru-N3
N7-Ru-N3
O1-Ru-N3
O2-Ru-N3
N2-Ru-N1
N7-Ru-N1
O1-Ru-N1
O2-Ru-N1
N3-Ru-N1
Ru-N7-C25
94.3(2)
178.9(2)
86.6(2)
88.18(19)
177.5(2)
90.97(18)
79.0(2)
95.3(2)
178.9(3)
85.7(2)
87.4(2)
176.4(2)
91.6(2)
79.1(3)
89.1(3)
100.5(2)
89.0(2)
79.1(3)
92.7(2)
101.3(2)
90.1(2)
158.2(2)
118.5(5)
90.8(2)
101.7(2)
89.70(19)
78.8(2)
92.0(2)
100.4(2)
88.46(19)
157.9(2)
174.9(7)
slightly nonplanar with respect to the triazine ring, and the
dihedral angles are 5.25(0.46), 12.04(0.36), and 2.21(0.53)°
for [1]ClO4, [2]ClO4, and [3]ClO4, respectively. The much
larger dihedral angle in [2]ClO4 [12.04(0.36)°] compared to
the other two complexes ([1]ClO4 and [3]ClO4) might be
developed because of the H-bonding interaction between O10
of the eight-membered water cluster and N6 of the pendant
pyridine ring of tptz in [2]ClO4 (see later; Figure 5). The
Ru-O(acac) bond distances agree well with the reported
values.5,11 The coordinated acetonitrile molecule in [1]ClO4
is in its usual nearly linear mode with an N7-C25-C24
angle of 178.8(9)° and the N7-C25 triple-bond distance of
1.115(9) Å.10d,12 The Ru-N7 single-bond distances in
[1]ClO4, [2]ClO4, and [3]ClO4 are 2.031(6), 2.036(5), and
2.145(6) Å, respectively. The expected sp, sp2, and sp3
hybridizations of N7 in [1]ClO4, [2]ClO4, and [3]ClO4 are
reflected in Ru-N7-C25 angles of 174.9(7), 146.6(6),
and 118.5(5)°, respectively. However, the reasonable posi-
tive deviations of the Ru-N7-C25 angles from the ideal-
ized sp2 (120°) and sp3 (109.5°) angles in [2]ClO4 and
[3]ClO4, respectively, suggest the partial sp and sp2 charac-
teristics of N7 possibly due to the contributions from the
corresponding resonating forms. The RuN4O2 coordination
sphere in the complexes exhibits a distorted octahedral
geometry, as can be seen from the angles around the metal
ions (Table 3). The change in the triple-bond characteristics
of N7-C25 in [1]ClO4 [1.115(9) Å] to double bond in
[2]ClO4 [1.165(8) Å] along with the corresponding change
in the Ru-N7-C25 angle from linear to semibent geom-
etry establishes the formation of an iminoester derivative in
[2]ClO4 via the activation of the nitrile function of [1]ClO4
by ethanol, as shown in Scheme 2.
Redox Processes and EPR Spectra. The RuIII-RuII
couple for the mononuclear complexes [1]ClO4-[4]ClO4
appears in the range of 0.77-0.51 V vs SCE, and it follows
the order [1]ClO4 . [2]ClO4 > [3]ClO4 > [4]ClO4 (Table
5 and Figure 7a). The stability of the RuII state decreases
sharply upon moving from [1]ClO4 (0.77 V) to [2]ClO4 (0.59
V) based on the difference in the electron-withdrawing ability
between the nitrile (CH3CtN) and imine [NHdC(CH3)-
OC2H5] functions. The two triazine-based successive one-
(11) Chao, G. K. J.; Sime, R. L.; Sime, R. J. Acta Crystallogr. B 1973, 29,
2845.
(12) Rasmussen, S. C.; Ronco, S. E.; Mlsna, D. A.; Billadeau, M. A.;
Pennington, W. T.; Kolis, J. W.; Petersen, J. D. Inorg. Chem. 1995,
34, 821.
(13) (a) Ghosh, S. K.; Bharadwaj, P. K. Inorg. Chem. 2004, 43, 6887. (b)
Ghosh, S. K.; Bharadwaj, P. K. Angew. Chem., Int. Ed. 2004, 43,
3577. (c) Ludwig, R. Angew. Chem., Int. Ed. 2001, 40, 1808. (d) Kar,
S.; Sarkar, B.; Ghumaan, S.; Janardanan, D.; van Slageren, J.; Fiedler,
J.; Puranik, V. G.; Sunoj, R. B.; Kaim, W.; Lahiri, G. K. Chem.s
Eur. J. 2005, 11, 4901. (e) Head-Gordon, T.; Hura, G. Chem. ReV.
2002, 102, 2651. (f) Keutsch, F. N.; Cruzan, J. D.; Saykally, R. J.
Chem. ReV. 2003, 103, 2533.
In [1]ClO4, the intermolecular H-bonding interactions
between the C15-H of one of the coordinated pyridine rings
(14) Keerthi, K. D.; Santra, B. K.; Lahiri, G. K. Polyhedron 1998, 17, 1387.
2418 Inorganic Chemistry, Vol. 45, No. 6, 2006

Mononuclear and Mixed-Valent Dinuclear Complexes
Figure 5. (a) H-bonding network in [2]ClO4‚2H2O and (b) chair conformation of a water cluster in [2]ClO4‚2H2O down the b axis.
Table 4. Distances Relevant to H Bonds (Å) in [2]ClO4‚2H2O
atom 1 atom 2
symmetry 1
x, y, z
x, y, z
1 - x, -y, 1 - z 1 - x, -y, 1 - z
symmetry 2
x, y, z
1 - x, -y, 1 - z
1 + x, y, 1 + z
distance (Å)
O3
N6
O7
O7
O3
N6
O9
O9
O9
O8
O8′
O10
N2
2.929
2.880
2.871
2.871
2.929
2.880
2.817
2.099
2.913
2.747
2.210
3.015
O10
O10
O10
N2
O10
O10
O8
O8′
O11
O11
O11
1 + x, y, 1 + z
2 - x, -y, 2 - z 2 - x, -y, 2 - z
2 - x, -y, 2 - z 1 + x, y, 1 + z
x, y, z
x, y, z
x, y, z
x, y, z
x, y, z
1 - x, -y, 1 - z
x, y, z
x, y, z
1 + x, y, 1 + z
1 + x, y, 1 + z
1 - x, -y, 1 - z 1 - x, -y, 1 - z
electron reductions are observed in the range of -0.9 to -1.8
V (Table 5). However, in the complex [3]ClO4, the second
triazine-based reduction has surprisingly appeared at a much
lower potential, -1.27 V (Table 5). The ligand-centered
(tptz) reduction process has been supported by the free-
radical-type EPR signal at g ) 2.054, obtained from the
electrochemically generated one-electron-reduced species 1,
at 77 K (Figure 8a). The appearance of a slightly axial-type
EPR spectrum (∆g ) 0.08) suggests a partial metal contribu-
tion in the singly occupied lowest unoccupied molecular
orbital (LUMO). The expected N hyperfine splitting (I ) 1
for 14N) has not been resolved.15
The dinuclear complex [5]ClO4 exhibits two successive
RuIII-RuII couples at 0.20 (couple I) and 0.88 V (couple II)
vs SCE (Table 5 and Figure 7b). The first couple at 0.20 V
is associated with the reduction of the RuIII center encom-
passing an electronically rich two acac- and carbanion (C-)
Figure 6. 1H NMR spectra of (a) [1]ClO4 in CDCl3, (b) [2]ClO4, and (c)
[4]ClO4 in (CD3)2SO.
-
based {RuIII(O2 ,acac)2(N,C-,tptz)} chromophore, whereas
the couple at higher potential (couple II) originates from
the oxidation of the RuII center with a {RuIIO2(acac-)-
Inorganic Chemistry, Vol. 45, No. 6, 2006 2419

Ghumaan et al.
Table 5. Electrochemicala and EPRb Data
E°298 (V) (∆Ep (mV))
RuIII-RuII couple
RuIII f RuIV
Kc
ligand reduction
µB
g1
g2
g3
g
∆gf
d
e
compd
[1]ClO4
[2]ClO4
[3]ClO4
[4]ClO4
[5]ClO4
[6]ClO4
[7]ClO4
[8]ClO4
0.77 (90)
0.59 (90)
0.54 (120)
0.51 (80)
0.20 (80), 0.88 (80)
0.22 (90), 0.93 (90)
0.18 (120), 0.73 (60)
0.18 (90), 0.86 (90)
-0.99 (80), -1.72 (90)
-1.05 (90), -1.72 (90)
-0.91 (60), -1.27 (110)
-1.07 (100), -1.77 (120)
-0.97 (100)
1.57c
1.63c
1.57c
1.57c
3.4 × 1011
1.1 × 1012
2 × 109
2.2
1.9
1.9
2.0
2.35
2.34
2.36
2.38
2.23
2.18
2.24
2.21
1.85
1.84
1.86
1.81
2.15
2.13
2.16
2.15
0.5
0.5
0.5
0.56
-0.93 (110)
-0.94 (70)
-0.92 (70)
3.4 × 1011
e
2
2
2
a In CH3CN vs SCE. b In CHCl3 at 77 K. c Irreversible. d RT ln Kc ) nF(∆E). g ) [1/3(g1 + g2 + g3 )]1/2
.
f ∆g ) g1 - g3.
Figure 7. Cyclic voltammograms (s) and differential pulse voltammo-
grams (- - -) in CH3CN of (a) [1]ClO4 and (b) [5]ClO4.
N3(tptz)N(CH3CN)+} chromophore.5e The low RuIII-RuII
potential of couple I (0.20 V) facilitates the stabilization of
the mixed-valent state in [5]ClO4 under atmospheric condi-
tions. The corresponding irreversible RuIII f RuIV process
appears at 1.57 V (Table 5). However, the same correspond-
ing to couple II has not been detected until the solvent cutoff
point (2 V). The oxidation potential of the RuII center in
[5]ClO4 (couple II) is about 100 mV greater than that of the
corresponding mononuclear derivative, [1]ClO4. The pres-
ence of the second metal ion in the RuIII state via the
involvement of negatively charged tptz- and acac- ligands
in [5]ClO4 increases the stability of the adjacent RuII center
further compared to that in [1]ClO4. The 680 mV separation
in potential between the successive RuIII-RuII couples
(couple II-couple I) in [5]ClO4 is due to the consequences
of two simultaneously operating factors: (i) built-in donor
Figure 8. EPR spectra of (a) electrogenerated 1 in CH3CN/0.1 M
Et4NClO4 (inset shows the spectrum of electrogenerated 5 in CH3CN/0.1
M Et4NClO4) and (b) [7]ClO4 in CHCl3 at 77 K.
-
center asymmetry around the metal ions [{RuIII(O2 ,acac)2-
redox processes involving the RuIII center (RuIII-RuII,
couple I, and RuIII f RuIV) remain almost close to those of
[5]ClO4 (Table 5). However, relative to [5]ClO4, the stability
of the RuII center (couple II) in [7]ClO4 decreases reasonably
(0.88 V in [5]ClO4 vs 0.73 V in [7]ClO4), as has been
observed in the mononuclear systems, [1]ClO4 vs [2]ClO4.
On the other hand, the RuII-RuIII potential (couple II) for
the pyrazine derivative [8]ClO4 appears to be very close to
that of the parent acetonitrile complex [5]ClO4 (Table 5).
The Kc values for [7]ClO4 and [8]ClO4 are calculated as
2 × 109 and 3.4 × 1011, respectively. The variation in Kc
based on the electronic nature of the sixth ligands associ-
ated with the RuII center among similar dinuclear complexes,
Kc of [8]ClO4 (pyrazine) ) [5]ClO4 (CH3CN) . [7]ClO4
[NHdC(CH3)OC2H5] (Table 5), signifies that, in addition
(N,C-,tptz)} and {RuIIO2(acac-)N3(tptz)N(CH3CN)+}] and
(ii) bridging ligand (tptz) mediated intermetallic coupling
process.5e,16 The resulting comproportionation constant
(Kc) value of the mixed-valent RuIIIRuII state is 3.4 × 1011
[calculated using the relation RT ln Kc ) nF(∆E)17]. For
[7]ClO4 and [8]ClO4, the potentials corresponding to the
(15) (a) 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. (b) Chanda, N.; Laye, R. H.;
Chakraborty, S.; Paul, R. L.; Jeffery, J. C.; Ward, M. D.; Lahiri, G.
K. J. Chem. Soc., Dalton Trans. 2002, 3496. (c) Bock, H.; Jaculi, D.
Z.; Naturforsch, B. Anorg. Chem., Org. Chem. 1991, 46, 1091. (d)
Ward, M. D. Inorg. Chem. 1996, 35, 1712.
(16) Chakraborty, S.; Laye, R. H.; Munshi, P.; Paul, R. L.; Ward, M. D.;
Lahiri, G. K. J. Chem. Soc., Dalton Trans. 2002, 2348.
(17) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1.
2420 Inorganic Chemistry, Vol. 45, No. 6, 2006

Mononuclear and Mixed-Valent Dinuclear Complexes
Table 6. UV-Visible Spectral Data for Complexes [1]ClO4-[8]ClO4
in Acetonitrile
compd
λ
max (nm) (ꢀ (M-1 cm-1))
[1]ClO4
620 (4680),a 522 (11 340), 366 (11 000), 280 (38 280),
202 (41 890)
[2]ClO4
[3]ClO4
[4]ClO4
[5]ClO4
663 (3180),a 538 (11 900), 384 (9990), 280 (40 760),
208 (28 700)
668 (2530),a 542 (9310), 388 (7850), 278 (36 260),
202 (31 630)
694 (3620),a 554 (12 800), 398 (10 670), 279 (37 720),
248 (27 690), 206 (34 900)
624 (9380), 544 (6940), 384 (12 320), 276 (40 160),
200 (47 650)
[6]ClO4
[7]ClO4
560 (5970), 370 (5960), 280 (22 500), 202 (57 900)
624 (13 280), 562 (9200), 390 (14 260), 276 (47 650),
200 (49 600)
[8]ClO4
628 (11 820), 558 (7920), 392 (16 050), 278 (39 350),
198 (40 160)
a Shoulder.
to the tptz-mediated intermetallic coupling process, the factor
related to donor center asymmetry on the two Ru ions also
contributes significantly to the observed fairly large Kc
value.5e,16
One triazine-based reduction has also been detected for
all of the dinuclear complexes. However, the expected second
triazine-based reduction has not been observed within the
experimental potential range of -2.0 V, possibly because
of the effect of the additional negative charge associated with
the anionic tptz ligand in the dinuclear complexes. The
reduction potential is found to be slightly lower than that of
the corresponding mononuclear derivatives (Table 5) because
of the additional binding of tptz with the second Ru ion in
the RuIII state. The electrochemically generated tptz-reduced
species 5 exhibits a free-radical-type EPR spectrum at 77 K
( g ) 2.058 and ∆g ) 0.08) with a partial metal contribu-
tion, as has been observed earlier in the case of 1 (Figure
8a, inset).
Figure 9. UV-visible spectra in CH3CN of (a) [1]ClO4 (s), [2]ClO4
(- - -), [3]ClO4 (‚‚‚), and [4]ClO4 (-‚-) and (b) [5]ClO4 (-‚-),
[6]ClO4 (- - -), [7]ClO4 (‚‚‚), and [8]ClO4 (s).
been observed in their redox potentials (Table 5). The UV-
region strong transitions are believed to originate from the
intraligand π-π*/n-π* transitions.
The dinuclear complexes [5]ClO4, [7]ClO4, and [8]ClO4
exhibit two intense CT transitions in the visible region near
600 and 400 nm. The lowest-energy transition near 600 nm
is associated with an overlapping band near 550 nm (Figure
9b and Table 6). Though the position of the lowest-energy
band remains almost invariant, the next-higher-energy band
is seen to be red-shifted from 544 to 562 to 558 nm while
moving from [5]ClO4 f [7]ClO4 f [8]ClO4. Thus, the
lowest-energy bands near 600 nm may be considered as
ligand-to-metal CT (LMCT) transitions involving the RuIII
center having an identical RuO4NC chromophore in all three
complexes and tptz. The next-higher-energy bands near 550
nm may thus be assumed as MLCT transitions involving the
RuII center with varying sixth ligands and tptz similar to the
RuII-based MLCT transitions in the corresponding mono-
nuclear complexes [1]ClO4 and [2]ClO4, which also appear
near 550 nm. The intense band near 400 nm may be
considered as an acac-based MLCT or LMCT transition.
Ligand-based CT transitions are also observed in the UV
region. The same RuIII- and RuII-tptz-based LMCT and
MLCT transitions in [6]ClO4, however, appear as an
overlapping broad band at a relatively higher energy of 560
nm, and the acac-based transition is observed at 370 nm.
Therefore, the introduction of -N+-O- units in the tptz
framework of [6]ClO4 enhances the energy gap between the
donor and acceptor levels compared to that in the other
dinuclear complexes.
Mixed-valent RuIIRuIII dinuclear complexes [5]ClO4-
[8]ClO4 exhibit magnetic moments corresponding to those
of one unpaired electron and display rhombic EPR spectra
at 77 K (Table 5 and Figure 8b). The large g anisotropy
[∆g (g1 - g3) ∼ 0.5; Table 5] signifies a considerably
distorted octahedral arrangement around the metal ion, as
can be expected from the mixed {RuIIIO4NC} coordination
environment.18 The average g factor of g ∼ 2.15 is derived
2
2
2
from g ) [1/3(g1 + g2 + g3 )]1/2 (Table 5).5f
Electronic Spectra. Mononuclear complexes [1]ClO4-
[4]ClO4 exhibit multiple intense transitions in the UV-visible
region due to the presence of different acceptor levels (Table
6 and Figure 9a). The lowest-energy band near 500 nm is
associated with a broad shoulder at the further lower-energy
part. The visible-region bands near 500 and 400 nm can be
tentatively assigned as metal-to-ligand charge-transfer (MLCT)
transitions involving the RuII ion and the triazine- and acac-
based acceptor levels, respectively.3,5 The MLCT bands
expectedly blue-shifted with the increasing stability of the
RuII state, [1]ClO4 > [2]ClO4 > [3]ClO4 > [4]ClO4, as has
The mixed-valent RuIIRuIII complexes [5]ClO4-[8]ClO4
failed to show expected intervalence CT (IVCT) transitions
up to 2000 nm in spite of strong electrochemical coupling
(Kc ) 109-1012). A similar situation of high Kc but no IVCT
(18) (a) Poppe, J.; Moscherosch, M.; Kaim, W. Inorg. Chem. 1993, 32,
2640. (b) Bag, N.; Lahiri, G. K.; Basu, P.; Chakravorty, A. J. Chem.
Soc., Dalton Trans. 1992, 113.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2421

Ghumaan et al.
electrolyte was Et4NClO4, and the solute concentration was
∼10-3 M. The half-wave potential E°298 was set equal to 0.5(Epa
+ Epc), where Epa and Epc are anodic and cathodic cyclic vol-
tammetric peak potentials, respectively. A platinum wire-gauze
working electrode was used in coulometric experiments. All
experiments were carried out under a N2 atmosphere. The elemental
analysis was carried out with a Perkin-Elmer 240C elemental
analyzer. Positive ion electrospray mass spectra were recorded on
a Micromass Q-ToF mass spectrometer. The magnetic susceptibility
was measured with a Faraday balance (Cahn Instruments Inc., serial
no. 76240).
bands in the typically expected near-IR region in mixed-
valent states of Ru-acac-based dinuclear and trinuclear
complexes has also been reported recently.5c,f,h Mixed-valent
species with high Kc values but without any IVCT bands
are simply puzzling. Therefore, we prefer to assume that the
intensity of the IVCT band (ꢀ < 20) is too weak to be
detected under the present experimental conditions. Alter-
natively, it may also be considered that the expected IVCT
transition has been hidden in the intense CT band near 600
nm. The cyclic voltammetric and EPR results have already
indicated a strong interaction between the metals and the
negatively charged tptz-, raising the energies of Ru-tptz-
mixed occupied orbitals while that of the acceptor LUMO-
(tptz) remains constant.19
Synthesis of [1]ClO4. The precursor complex Ru(acac)2-
(CH3CN)2 (100 mg, 0.26 mmol) and the ligand tptz (81.9 mg, 0.26
mmol) in a 1:1 molar ratio were dissolved in 20 mL of ethanol,
and the mixture was heated to reflux for 10 h under a N2 atmos-
phere. The solid mass thus obtained upon evaporation of the solvent
was dissolved in a minimum volume of CH3CN. To this was added
an excess aqueous NaClO4 solution, and the mixture was kept in
deep freeze overnight. It was then filtered, and the solid mass was
washed with ice-cold water followed by cold ethanol and dried
under vacuum. It was then purified using a neutral alumina column.
Initially, a red compound corresponding to Ru(acac)3 was eluted
by CH2Cl2-CH3CN (20:1), followed by a violet compound corre-
sponding to [1]ClO4, which was eluted with CH2Cl2-CH3CN
(15:1). Evaporation of the solvent mixture yielded the pure com-
pound [1]ClO4. Yield: 70 mg (41%). Anal. Calcd (found) for
[1]ClO4 (RuC25H22N7O6Cl): C, 45.94 (45.64); H, 3.40 (3.60); N,
15.01 (14.80). Molar conductivity [ΛM (Ω-1 cm2 M-1)] in aceto-
Electrochemically oxidized mononuclear RuIII and di-
nuclear RuIIIRuII derivatives were found to be unstable at
the coulometric time scale at 298 K.
Conclusion
In summary, the Ru precursor complex Ru(acac)2-
(CH3CN)2 facilitates (i) the formation of an unprecedented
bridging motif of tptz (motif F) and (ii) the subsequent
stabilization of a mixed-valent RuIIRuIII configuration in
the native state of [5]ClO4-[8]ClO4. Moreover, the nitrile
function associated with the RuII center in the mononuclear
[1]ClO4 as well as dinuclear [5]ClO4 complexes has been
activated in the presence of protic nucleophiles such as
alcohol and alkylamine to yield the corresponding imino-
ester ([2]ClO4 and [7]ClO4) and amidine [4]ClO4 deriva-
tives, respectively. The mixed-valent dinuclear complexes
([5]ClO4-[8]ClO4) failed to show the expected IVCT
transitions in the typical near-IR region in spite of reasonably
high electrochemical coupling (Kc ) 109-1012).
nitrile at 298 K: 112. IR [ν(ClO4-)/cm-1]: 1097, 619. H NMR
1
[(CD3)2SO, δ (J, Hz)]: 9.0 (d, 7.2), 8.98 (multiplet, chemical shift
range 8.94-9.0 ppm), 8.72 (d, 4.8), 8.37 (t, 7.9, 7.6), 8.2 (t, 7.7,
7.9), 8.04 (t, 6.0, 6.8), 7.73 (t, 6.0, 7.5), 5.45 (s, CH(acac)), 2.13,
2.08 (s, CH3(acac)), 1.32 (s, CH3(CH3CN)).
Synthesis of [2]ClO4. [1]ClO4 (50 mg, 0.076 mmol) was refluxed
in ethanol for 36 h under a N2 atmosphere. The initial violet color
of the solution gradually changed to purple. The solvent was
removed under reduced pressure, and the residue was purified using
a neutral alumina column. A purple compound corresponding to
[2]ClO4 was eluted by CH2Cl2-CH3CN (5:1). Evaporation of the
solvent mixture yielded the pure compound [2]ClO4. Yield: 25 mg
(46%). Anal. Calcd (found) for [2]ClO4 (RuC27H28N7O7Cl): C,
46.35 (46.50); H, 4.04 (4.20); N, 14.02 (14.30). Molar conductivity
[ΛM (Ω-1 cm2 M-1)] in acetonitrile at 298 K: 102. IR [ν(ClO4-)/
Experimental Section
The starting complex Ru(acac)2(CH3CN)2 was prepared accord-
ing to the reported procedure.20 2,4,6-Tris(2-pyridyl)-1,3,5-triazine
(tptz) was purchased from Aldrich (Madison, WI). Other chemicals
and solvents were reagent grade and were used as received. For
spectroscopic and electrochemical studies, high-performance liquid
chromatography grade solvents were used.
1
cm-1]: 1121, 624. H NMR [CDCl3, δ (J, Hz)]: δ 9.04 (d, 7.8),
8.93 (multiplet), 8.69 (multiplet), 8.18 (t, 7.5, 7.8), 8.06 (multiplet),
7.82 (multiplet), 7.55 (multiplet), 7.44 (s, NH), 5.33 (s, CH(acac)),
3.38 (q, 7.2, 6.9, 7.2, CH2), 2.62, 1.96 (s, CH3(acac)), 1.30 (s,
CH3(CH3CN)), 0.60 (t, 6.9, 6.9, CH3).
UV-visible spectral studies were performed on a Jasco 570
spectrophotometer. A Perkin-Elmer Lambda-950 instrument was
used to check the possible near-IR transitions. Fourier transform
(FT) IR spectra were obtained on a Nicolet spectrophotometer with
samples prepared as KBr pellets. The solution electrical conductivity
Synthesis of [3]ClO4. [1]ClO4 (50 mg, 0.076 mmol) and
p-toluidine (8.21 mg, 0.076 mmol) were dissolved in 20 mL of
ethanol, and the mixture was heated to reflux for 8 h under a
N2 atmosphere. The solvent was removed under reduced pres-
sure, and the residue was purified using a neutral alumina column.
The complex [3]ClO4 was eluted by CH2Cl2-CH3CN (3:1).
Evaporation of the solvent mixture yielded the pure compound
[3]ClO4. Yield: 16 mg (30%). Anal. Calcd (found) for [3]ClO4
(RuC30H28N7O6Cl): C, 50.06 (50.34); H, 3.92 (4.12); N, 13.63
(13.84). Molar conductivity [ΛM (Ω-1 cm2 M-1)] in acetonitrile at
298 K: 130. IR [ν(ClO4-)/cm-1]: 1087, 619. 1H NMR [CDCl3, δ
(J, Hz)]: δ 8.95 (multiplet), 8.66 (d, 6.0), 8.46 (d, 7.5), 8.16 (t,
9.0, 6.0), 8.0 (multiplet), 7.82 (t, 6.0, 9.0), 7.75 (multiplet), 7.62
(multiplet), 7.54 (multiplet), 6.47 (d, 9.0, NH2), 5.95 (d, 9.0, NH2),
5.34 (s, CH(acac)), 2.62, 2.53 (s, CH3(acac)), 1.98 (s, CH3).
1
was checked using a Systronic 305 conductivity bridge. H NMR
spectra were obtained with a 300-MHz Varian FT spectrometer.
The EPR measurements were made with a Varian model 109C
E-line X-band spectrometer fitted with a quartz Dewar for 77 K.
Cyclic voltammetric, differential pulse voltammetric, and coulo-
metric measurements were carried out using a PAR model 273A
electrochemistry system. Platinum wire working and auxiliary
electrodes and an aqueous saturated calomel reference electrode
(SCE) were used in a three-electrode configuration. The supporting
(19) Chanda, N.; Sarkar, B.; Kar, S.; Fiedler, J.; Kaim, W.; Lahiri, G. K.
Inorg. Chem. 2004, 43, 5128.
(20) Kobayashi, T.; Nishina, Y.; Shimizu, K.; Satoˆ, G. P. Chem. Lett. 1988,
1137.
2422 Inorganic Chemistry, Vol. 45, No. 6, 2006

Mononuclear and Mixed-Valent Dinuclear Complexes
Synthesis of [4]ClO4. [1]ClO4 (50 mg, 0.076 mmol) and a 70%
aqueous solution of ethylamine in excess (1 mL) were refluxed in
ethanol for 4 h under a N2 atmosphere. The solvent was re-
moved under reduced pressure, and the residue was purified using
a neutral alumina column. A bluish-violet compound corresponding
to [4]ClO4 was eluted by CH2Cl2-CH3CN (4:1). Evaporation of
the solvent mixture yielded the pure compound [4]ClO4. Yield: 20
mg (37%). Anal. Calcd (found) for [4]ClO4 (RuC27H29N8O6Cl):
C, 46.41 (46.65); H, 4.19 (4.36); N, 16.05 (16.35). Molar
conductivity [ΛM (Ω-1 cm2 M-1)] in acetonitrile at 298 K: 130.
H, 4.14 (4.28); N, 9.82 (9.73). Molar conductivity [ΛM (Ω-1 cm2
M-1)] in acetonitrile at 298 K: 117. IR [ν(ClO4-)/cm-1]: 1128,
630.
Synthesis of [8]ClO4. The dinuclear complex [5]ClO4 (50 mg,
0.052 mmol) and pyrazine (4.2 mg, 0.052 mmol) were dissolved
in 20 mL of ethanol, and the mixture was heated to reflux for
8 h under a N2 atmosphere. The initial blue color of the solu-
tion gradually changed to greenish-blue. The solvent was re-
moved under reduced pressure, and the residue was purified using
a neutral alumina column. A bluish-green compound corresponding
to [8]ClO4 was eluted by CH2Cl2-CH3CN (3:1). Evaporation of
the solvent mixture yielded the pure compound [8]ClO4. Yield: 16
mg (31%). Anal. Calcd (found) for [8]ClO4 (Ru2C37H36N8O10Cl):
C, 44.80 (44.39); H, 3.66 (3.85); N, 11.30 (11.50). Molar
conductivity [ΛM (Ω-1 cm2 M-1)] in acetonitrile at 298 K: 112.
IR [ν(ClO4-)/cm-1]: 1107, 634.
1
IR [ν(ClO4-)/cm-1]: 1107, 629. H NMR [(CD3)2SO, δ (J, Hz)]:
δ 8.94 (multiplet), 8.79 (d, 5.0), 8.60 (t, 5.2, 5.6), 8.25 (t, 9.2, 8.0),
8.16 (t, 8.0, 6.4), 7.94 (t, 8.0, 8.0), 7.67 (t, coordinated NH), 5.51
(s, CH(acac)), 4.78 (s, uncoordinated NH), 3.12 (quintet, 7.2, 6.0,
8.0, 8.0, CH2), 2.57, 2.07 (s, CH3(acac)), 1.32 (s, CH3), 1.24 (t,
7.2, 7.2, CH3).
Synthesis of [5]ClO4. The precursor complex Ru(acac)2-
(CH3CN)2 (100 mg, 0.26 mmol) and tptz (40 mg, 0.13 mmol) in a
2:1 molar ratio were dissolved in 20 mL of ethanol, and the mix-
ture was heated to reflux for 10 h. The initial orange color of
the solution gradually changed to bluish-green. The bluish-green
mass thus obtained upon evaporation of the solvent was dis-
solved in a minimum volume of CH3CN. To this was added an
excess aqueous NaClO4 solution, and the mixture was kept in
deep freeze overnight. It was then filtered, and the solid mass
was washed with ice-cold water followed by cold ethanol and
diethyl ether and dried under vacuum. It was then purified using a
neutral alumina column. Initially, a red compound corresponding
to Ru(acac)3 was eluted by CH2Cl2-CH3CN (20:1), followed by a
blue compound corresponding to [5]ClO4, which was eluted with
CH2Cl2-CH3CN (20:3). Evaporation of the solvent mixture yielded
the pure [5]ClO4. Yield: 58 mg (46%). Anal. Calcd (found) for
[5]ClO4 (Ru2C35H35N7O10Cl): C, 44.12 (44.27); H, 3.71 (3.65); N,
10.30 (10.48). Molar conductivity [ΛM (Ω-1 cm2 M-1)] in aceto-
nitrile at 298 K: 126. IR [ν(ClO4-)/cm-1]: 1107, 629.
Crystal Structure Determination. Single crystals of [1]ClO4,
[2]ClO4, and [3]ClO4 were grown by slow evaporation of a 1:1
dichloromethane-hexane solution. The crystals of [1]ClO4, [2]ClO4,
and [3]ClO4 contain 2H2O as the solvent of crystallization. X-ray
data of [1]ClO4/[3]ClO4 and [2]ClO4 were collected using Enraf-
Nonius CAD-4 (MACH-3) and Bruker SMART APEX CCD single-
crystal X-ray diffractometers, respectively. The structures of
[1]ClO4/[3]ClO4 and [2]ClO4 were solved and refined by full-matrix
least-squares techniques on F 2 using the SHELX-97 and SHELX-
97 (SHELXTL program package), respectively.21 The absorption
corrections for [1]ClO4/[3]ClO4 and [2]ClO4 were done by ψ scan
and SADABS, respectively, and all of the data were corrected for
Lorentz and polarization effects. H atoms were included in the
refinement process as per the riding model.
The -CH2-CH3 group of [2]ClO4 is disordered, with C26 and
C27 atoms having two different positions with equal occupancy
and having large thermal vibrations; the corresponding constraints
have been used during refinement, and H atoms for C26 and C27
are not fixed.
Synthesis of [6]ClO4. The dinuclear complex [5]ClO4 (50 mg,
0.052 mmol) and excess m-chloroperbenzoic acid (18 mg, 0.11
mmol) were dissolved in 20 mL of dichloromethane, and the
mixture was stirred for 4 h under a N2 atmosphere. The initial blue
color of the solution gradually changed to violet. The solvent was
removed under reduced pressure, and the residue was purified using
a neutral alumina column. A purple-red compound corresponding
to [6]ClO4 was eluted by CH2Cl2-CH3CN (5:1). Evaporation of
the solvent mixture yielded the pure compound [6]ClO4. Yield: 16
mg (31%). Anal. Calcd (found) for [6]ClO4 (Ru2C35H35N7O12Cl):
C, 42.68 (42.82); H, 3.58 (3.50); N, 9.96 (9.75). Molar conductivity
[ΛM (Ω-1 cm2 M-1)] in acetonitrile at 298 K: 140. IR [ν(ClO4-)/
cm-1]: 1107, 629.
Synthesis of [7]ClO4. The dinuclear complex [5]ClO4 (50 mg,
0.052 mmol) was dissolved in 20 mL of ethanol and refluxed for
16 h under a N2 atmosphere. The initial blue color of the solution
gradually changed to bluish-green. The solvent was removed under
reduced pressure, and the residue was purified using a neutral
alumina column. A green compound corresponding to [7]ClO4 was
eluted by CH2Cl2-CH3CN (4:1). Evaporation of the solvent mixture
yielded the pure compound [7]ClO4. Yield: 24 mg (46%). Anal.
Calcd (found) for [7]ClO4 (Ru2C37H41N7O11Cl): C, 44.49 (44.62);
Acknowledgment. Financial support received from the
Department of Science and Technology and Council of
Scientific and Industrial Research, New Delhi, India, is
gratefully acknowledged. X-ray structural studies for [1]ClO4
and [3]ClO4 were carried out at the National Single Crystal
Diffractometer Facility, Indian Institute of Technologys
Bombay. Special acknowledgment is made to the Sophisti-
cated Analytical Instrument Facility (SAIF), Indian Institute
of TechnologysBombay, for providing the NMR and EPR
facilities.
Supporting Information Available: X-ray crystallographic data
in CIF format, electrospray mass spectra of [1]ClO4-[4]ClO4 in
CH3CN (Figure S1), H bonding in [1]ClO4‚2H2O (Figure S2), and
H-bonding parameters in [1]ClO4‚2H2O (Table S1). This material
is available free of charge via the Internet at http://pubs.acs.org.
IC0514288
(21) Sheldrick, G. M. SHELX-97, program for crystal structure solution
and refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2423