A Diruthenium Complex of an N-Pyridyl-o-aminophenol Derivative: A Route to Mixed Valency

Article abstract of DOI:10.1002/chem.201903028

An N-pyridyl-o-aminophenol derivative that stabilises mixed-valence states of ruthenium ions is disclosed. A diruthenium complex, [(L_IQ⁰)Ru₂Cl₅]?MeOH (1?MeOH) is successfully isolated, in which L_IQ

Full text of DOI:10.1002/chem.201903028

A Journal of
Accepted Article
Title: A Di-ruthenium Complex of a N-Pyridyl-o-Aminophenol
Derivative: A Route to Mixed Valency
Authors: Prasanta Ghosh, Debarpan Dutta, and Suman Kundu
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A Di-ruthenium Complex of a N-Pyridyl-o-Aminophenol
Derivative: A Route to Mixed Valency
Debarpan Dutta,[a] Suman Kundu[a] and Prasanta Ghosh*[a]
Abstract:
A
N-pyridyl-o-aminophenol derivative that stabilizes
As the redox non innocence of the pz ligand was not established
so far, the Creutz and Taube ion has been defined here as a
Type A complex ion. Kaim and Lahiri reported several Types of
B complexes containing redox active bridging ligands.5 Lahiri
reported a mixed valence Type B complex, where LNI is
unsymmetrical.5i
mixed-valence states of ruthenium ion is disclosed. A diruthenium
complex, [(LIQ0)Ru2Cl5]•MeOH (1•MeOH) was successfully isolated,
where LIQ0 is the o-iminobenzoquinone form of 2-((3-nitropyridin-2-
yl)amino)phenol (LAPH2). In 1, LIQ0 towards one ruthenium centre is a
NO-donor redox noninnocent, while towards another ruthenium it is
a pyridine donor redox innocent ligand. 1 is a diruthenium (II, III)
[(LI)Ru-(LI)-Ru(LI)]n+
[(LI)Ru-(LNI)-Ru(LI)]n+
[(LNI)Ru-(LI)-Ru(LI)]n+
Type A
Type B
Type C
mixed valence complex, [RuII(LIQ0)(µ-Cl)2RuIII], with
a
minor
contribution of diruthenium (III, III) state, [RuIII(LISQ●-)(µ-Cl)2RuIII]
where LISQ●- is the o-iminobenzosemiquinonate anion radical form of
the ligand. 1- and 1+ are respectively diruthenium (II, II), [RuII(LIQ0)(µ-
Cl)2RuII], and diruthenium (III, III), [RuIII(LIQ0)(µ-Cl)2RuIII], complexes
of LIQ
.
12- is
a
diruthenium (II, II) complex of o-
0
Chart 1. Three types of diruthenium complexes containing redox innocent (LI)
and redox noninnocent (LNI) ligands.
iminobenzosemiquinonate anion radical (LISQ●-), [RuII(LISQ●-)(µ-
Cl)2RuII] with a minor contribution of diruthenium (III, II) form,
[RuIII(LAP2-)(µ-Cl)2RuII]. 12+ is a diruthenium (III, IV) mixed valance
complex of LIQ0, [RuIII(LIQ0)(µ-Cl)2RuIV]. 1 and 12+ exhibit inter valence
charge transfer transitions at 1300 and 1370 nm.
However, no Type C complex was documented so far. The
electronic environments of the two metal ions in Type C
complexes are not similar and elucidation of the electronic states
of the members of the redox series of the unsymmetrical Ru2-
core is a worthy investigation. Location of the electron transfer
centre in this multi-redox active unit and justification of it will
expand the knowledge that is momentous in exploring the metal
to metal electron transfer reaction.
Introduction
Bimetallic complex ion with Robin-Day Class-II and III states are
significant in analyzing the electron transfer reactions, inter
valance charge transfer (IVCT) transitions, electrically
conducting and magnetic properties.1 To expand this area,
ligand based mixed-valency has also been investigated
sincerely in several aspects.2 The mixed valence molecular
systems are equally important in material and chemical science
as well as metallo-protein chemistry.3 In this regard, the first
mixed valance ion, [(NH3)5Ru(pz)Ru(NH3)5]5+, where pz is a
bridging pyrazine ligand, reported by Creutz and Taube was
considered as the path-maker of this research area.4 In this
complex ion, the sum of the oxidation numbers of two metal ions
is an odd integer.
Chart 2. Three redox states of LAPH2, where L is a bridging ligand.
It is a calculated value based on the oxidation number of the
individual metal ions, as all the bridging and terminal co-ligands
of two ruthenium ions are redox innocent. However, introduction
of a redox non-innocent ligand to this unit will make a difference
and produce a bimetallic unit that involves a difference of
oxidation numbers of two metal ions of even less than unity.
Being emboldened by this idea, we envisage that the Type B
and C molecules as listed in Chart 1 are significant to be
modelled, where LI is a redox innocent ligand and LNI is a redox
noninnocent ligand.
In this effort, we have been successful to synthesize a N-
pyridyl-o-aminophenol
derivative,
2-((3-nitropyridin-2-
yl)amino)phenol (LAPH2) that can bridge producing Type C
complexes of transition metal ions as depicted in Chart 2. A
diruthenium complex of the type [(LIQ0)Ru2Cl5(PPh3)2] (1) was
0
successfully isolated, where LIQ is the o-iminobenzoquinone
form of LAPH2. In 1, LNI is the aminophenol compartment, LI are
the two (µ-Cl) and the pyridine compartment of the of LAPH2
ligand. The deprotonated LAPH2 exhibits three distinct redox
states as the dianionic o-amidophenolato (LAP2-), o-
0
iminobenzosemiquinonate anion radical (LISQ●-) and LIQ as
shown in Chart 2.6 In 1, the redox state of LAPH2 is LIQ0 with a
minor contribution of LISQ●- and 1 is defined as a mixed valence
diruthenium (II, III) complex of type [(PPh3)(Cl2)RuII(LIQ0)(µ-
______________________________________________________________
[a]
Department of Chemistry
R. K. Mission Residential College, Narendrapur
Kolkata 700103, West Bengal, India
E-mail: ghosh@pghosh.in
Cl)2RuIII(Cl)(PPh3)]
with
a
minor
contribution
of
[(PPh3)(Cl2)RuIII(LISQ●-)(µ-Cl)2RuIII(Cl)(PPh3)] as depicted in
Supporting Information: Crystallographic data of 1•MeOH, ESI mass
and 1H NMR spectra of LAPH2, ESI mass spectra of 1 (positive and
negative), EPR spectra and gas phase and solution optimized
coordinates.
Scheme 1.
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0
Scheme 1. Diruthenium (III, IV), diruthenium (III, III), diruthenium (II, III), diruthenium (II, II) states containing the LIQ form and a diruthenium (II, II) state
containing the LISQ●- form.
The redox behavior of 1 in which two ruthenium centres are not
equivalent, has been investigated by cyclic voltammetry. 1 is
electrochemically active and undergoes successive two
separate, reversible one-electron reductions due to formation of
diruthenium (II, II) complexes of types [(PPh3)(Cl)RuII(LIQ0)(µ-
Lambda 750 spectrophotometer of range 3300-190 nm.
Magnetic susceptibilities at 298 were measured on
K
a
Sherwood Magnetic Susceptibility Balance. The X-band EPR
spectra were measured on a Magnettech GmbH MiniScope
MS400 spectrometer (equipped with temperature controller TC
H03), where the microwave frequency was measured with an
FC400 frequency counter. The EPR spectra were simulated
using Easy Spin software. The electro analytical instrument,
BASi Epsilon-EC for cyclic voltammetric experiments in CH2Cl2
Cl)2RuII(Cl)2(PPh3)]-
(1-)
and
[(PPh3)(Cl)RuII(LISQ●-)(µ-
Cl)2RuII(Cl)2(PPh3)]2- (12-). One electron oxidation of 1 generates
a diruthenium (III, III) complex of the type [(PPh3)(Cl)RuIII(LIQ0)(µ-
Cl)2RuIII(Cl)2(PPh3)]+ (1+) and further oxidation affords
a
diruthenium
mixed
valence
(III,
IV)
complex,
as
solutions
containing
0.2
M
tetrabutylammonium
[(PPh3)(Cl)RuIII(LIQ0)(µ-Cl)2RuIV(Cl)2(PPh3)]2+
(12+)
hexafluorophosphate as a supporting electrolyte was used. The
BASi platinum working electrode, platinum auxiliary electrode,
Ag/AgCl reference electrode were used for the electrochemical
measurements. The redox potential data reported were
referenced to ferrocenium/ferrocene, Fc+/Fc, couple. 0.5
mm SEC-C thin layer quartz glass spectroelectrochemical cell kit
with platinum gauze working electrode (light path length of 1
mm) was used for spectroelectrochemistry measurements.
summarized in Scheme 1. 1-, 12-, 1+ and 12+ were not isolated,
but these were generated by constant potential bulk electrolysis
experiments. The molecular and electronic structures of 1 and
the related species were confirmed by single crystal X-ray
crystallography, EPR spectroscopy, spectroelectrochemical
measurements, inter valence charge transfer (IVCT) transitions
and broken symmetry (BS) density functional theory (DFT)
calculations.
Syntheses. 2-((3-Nitropyridin-2-yl)amino)phenol (LAPH2). To
2-chloro-3-nitropyridine (316 mg, 2.0 mmol) in N,N-di-
methylformamide (3 mL) in a 100 ml round-bottom flask were
added 2-aminophenol (218 mg, 2.0 mmol) followed by a pinch of
potassium carbonate (~300 mg). The reaction mixture was
refluxed at 363-365 K on an oil bath for 3 h. The reaction mixture
was cooled at room temperature and the reddish slurry was
poured into 200 ml ice-cold water in a beaker and stirred for 30
min. A reddish compound separated out, which was filtered
through a suction pump and the residue obtained was dried
under air. The collected mass was purified by column
chromatography using basic alumina and dichloromethane as an
eluent. The red product was finally re-crystallised from a
methanol solution. Yield: 322 mg. (70% with respect to 2-
aminophenol). Mass spectral data [electrospray ionization (ESI),
positive ion, CH2Cl2]: m/z 231.08 for [LAPH2]+. Anal. Calcd for
Experimental Section
Materials and Physical Measurements. Reagents or analytical
grade materials were obtained from Sigma-Aldrich and used
without further purification. Spectroscopic grade solvents were
used for spectroscopic and electrochemical measurements. The
C, H and N contents of the compounds were obtained from a
Perkin-Elmer 2400 Series II elemental analyzer. Infrared spectra
of the samples were measured from 4000 to 400 cm−1 with KBr
pellets at room temperature on a Perkin-Elmer Spectrum RX 1
FT-IR spectrophotometer. 1H NMR spectra were obtained at 295
K on a Bruker DPX 500 MHz spectrometer. ESI mass spectra
were recorded on a micro mass Q-TOF mass spectrometer.
Electronic absorption spectra were recorded on a Perkin-Elmer
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C11H9N3O3: C, 57.14; H, 3.92; N, 18.17. Found: C, 56.79; H,
3.78; N, 18.06. 1H NMR (CDCl3,500 MHz, 298 K): δ 8.63 (d, 1H,
J = 4.5 Hz), δ 8.53 (d, 1H, J = 8.0 Hz), δ 8.44 (d, 1H, J = 4.0 Hz),
δ 8.22 (d, 1H, J = 8.0 Hz), δ 7.46 (t, 1H, J = 6.5 Hz), δ 7.35 (d,
1H, J = 8.0 Hz), δ 7.14 (t, 1H, J = 7.5 Hz), δ 6.86 (t, 1H, J = 8.0
Hz), δ 6.79 (dd, 1H, J = 8.5; 4.5 Hz). IR/cm-1 (KBr): ν 3494 (m),
3313 (s), 3049 (s), 1611 (m), 1583 (s), 1538 (s), 1517 (s), 1459
(s), 1416 (m), 1354 (s), 1330 (m), 1277 (m), 1239 (m), 1191 (m),
1159 (m), 859 (m), 745 (m).
state, and those of 12+ and 12- were done with the doublet spin
state. Similarly the geometries of 1, 1+ and 1- were optimized in
CH2Cl2 using CPCM model. The BS calculations were performed
for 1+ and 12+ ions. Thus, the gas phase geometries of the 1+
and 12+ ions were also optimized with triplet and quartet spin
states. The BS MS = 0 state of 1+ was calculated by BS (1,1)
formalism, while the BS MS = ½ state of 12+ was calculated by
ORCA flip spin DFT method.10 For all calculations, the all-
electron valence double-zeta, def2-SVP,11 basis set with “new”
polarisation function developed by Karlsruhe group was used for
[(LIQ0)Ru2Cl5]•MeOH (1•MeOH). To LAPH2 (23 mg, 0.10 mmol)
in toluene (25 mL) in a round bottom flask was added
[RuII(PPh3)3Cl2] (190 mg, 0.20 mmol) and the mixture was stirred
for 3h in air at 298 K. A reddish solution was obtained and it was
allowed to evaporate slowly in air at room temperature. After 5 7
days, a dark-violet residue separated out, which was collected
upon filtration and dried. Diffusion of n-hexane to a CH2Cl2
solution of the residue containing a few drops of MeOH in air
afforded purple needles of 1•MeOH, which are collected upon
filtration and dried in air. Yield: 52 mg. (46% with respect to
LAPH2). Single crystals for X-ray diffraction analysis were
collected from this crop. Elemental analyses were performed
after evaporating the solvent of crystallization under high
vacuum. Mass spectral data [electrospray ionization (ESI),
positive ion, CH2Cl2]: m/z 579 for [(LIQ 0)Ru2Cl3(CH3CN)]+, 492
[(LAPH2)PPh3] and 333 [(LIQ0H)Ru]+; [electrospray ionization
(ESI), negative ion, CH2Cl2]: m/z 609 for [(LIQ0)Ru2Cl5]-, 490
[(LAPH)PPh3]-. Anal. Calcd for C47H37Cl5N3O3P2Ru2 (FW,
1133.16): C, 49.82; H, 3.29; N, 3.71. Found: C, 49.68; H, 3.14;
N, 3.57. IR/cm-1 (KBr): ν 3433 (broad), 3055 (s), 2923 (s), 2852
(m), 1631 (s), 1591 (s), 1536 (s), 1437 (s), 1180 (m), 1117 (s),
1090 (m), 746 (s), 722 (s), 693 (s), 542 (s).
P, N, Cl, O, C and H atoms. For Ru atom def2-TZVP,11
a
valence triple-zeta basis set with new polarisation function was
used. Resolution of Identity RIJCOSX12a approximation with
def2/J auxiliary basis set for Coulomb and HF exchange integral
for HF and hybrid DFT methods were employed for self-
consistent field (SCF) gradient calculations.12b The geometry
optimizations were carried out in redundant internal coordinates
without imposing symmetry constraints. The SCF calculations
were converged tightly (1 × 10-8 Eh in energy, 1 × 10-7 Eh in the
density change and 1 × 10-7 in maximum element of the DIIS
error vector). Time-dependent (TD) DFT13a-c calculation for
electronic absorption spectra was carried out on 1 using B3LYP
functional in CH2Cl2 with the application of the CPCM model13d-e
to screen the effects of solvent.
Results and Discussion
Syntheses and Characterization. Details of the syntheses of
LAPH2 and 1 and their characterization data are outlined in the
experimental section. LAPH2 was isolated in good yield from a
single step reaction of 2-chloro-3-nitropyridine and 2-
aminophenol (1:1) in N,N-dimethylformamide at 363-365 K.
Reaction of LAPH2 with [RuII(PPh3)3Cl2] in toluene at 298 K
affords a brownish solution, that on evaporation in air produces
a purple crystalline solid of 1. 1 is paramagnetic with one
unpaired spin, µeff = 1.81 BM at 298 K. Diffusion of n-hexane into
a dichloromethane-methanol (10:1) solution of 1 in air produces
Single Crystal X-ray Structure Determination. A single
crystal of 1•MeOH (CCDC No. 1890212) was picked up with a
nylon loop and was mounted on a Bruker APEX-II CCD and
Bruker AXS D8 QUEST ECO diffractometer equipped with a Mo-
target rotating-anode X-ray source and
a
graphite
1
monochromator (Mo-Kα, λ = 0.71073 Å). Final cell constants
were obtained from least-squares fits of all measured reflections.
Intensity data were corrected for absorption using intensities of
redundant reflections. The structures were readily solved by
direct methods and subsequent difference Fourier techniques.
The crystallographic data of 1 have been listed in Table S1. The
SHELXS-97 (Sheldrick 2008) software package was used for
solution and SHELXL-2014/6 (Sheldrick, 2014) was used for the
refinement.7 All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed at the calculated positions and
refined as riding atoms with isotropic displacement parameters.
single crystals of 1•MeOH in good yield. The ESI mass and H
NMR spectra of LAPH2 are illustrated in Figures S1 and S2
(Supporting information). The ESI mass spectrometry affirms
that the [Ru(µ-Cl)2Ru] moiety in 1 is stable in solution and the
m/z peaks due to the dinuclear core were detected both in ESI
positive and negative spectra as shown in Figures S3 and S4.
However the analysis infers that the coordinated PPh3 ligands
are labile and undergo dissociation in solution. The molecular
geometry of 1•MeOH in the crystal was confirmed by single
crystal X-ray crystallography and the redox activity was
investigated by cyclic voltammetry (vide infra).
Broken Symmetry (BS) Density Functional Theory (DFT)
Calculations. All DFT calculations were performed with the
ORCA program package.8 All calculations were done by the
hybrid PBE0 DFT method.9 The gas phase geometry of 1 was
optimized with a doublet spin state and the gas phase
geometries of 1- and 1+ were optimized with the singlet spin
X-ray Crystallography. 1•MeOH crystallizes in the P-1 space
group. The molecular geometry of 1•MeOH in crystals with the
atom-labelling scheme is illustrated in Figure 1. The significant
0
bond parameters are listed in Table 1. In 1, LIQ acts as a
bridging ligand and towards Ru(1) LIQ0 is a redox non-innocent
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Table 1. Selected Experimental Bond Lengths [Å] of 1•MeOH and the Corresponding Calculated Bond Lengths of 1 and 12- with Doublet Spin State, 1- with Singlet
Spin State, 1+ with Singlet and Broken Symmetry (BS) MS = 0 and 12+ with Doublet and BS (2,1) MS = ½ Spin States
calculated
1+
12+
Bond
experimental
1
1-
12-
(MS = ½)
(MS = 0)
(MS = ½)
BS (1,1)
(MS = 0)
BS (2,1)
(MS = ½)
MS = 0
MS = ½
Ru(1)-P(1)
Ru(1)-O(1)
Ru(1)-N(1)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Cl(3)
Ru(2)-Cl(2)
Ru(2)-Cl(3)
Ru(2)-Cl(4)
Ru(2)-Cl(5)
Ru(2)-P(2)
Ru(2)-N(2)
C(1)-O(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(1)
C(6)-N(1)
N(1)-C(7)
2.328(2)
1.994(3)
1.994(3)
2.347(2)
2.326(2)
2.497(2)
2.308(2)
2.418(2)
2.311(2)
2.329(2)
2.316(2)
2.289(3)
1.276(6)
1.429(7)
1.340(10)
1.423(11)
1.352(8)
1.429(7)
1.435(7)
1.357(6)
1.412(5)
2.309
1.991
2.034
2.333
2.384
2.534
2.440
2.441
2.313
2.322
2.334
2.238
1.283
1.416
1.375
1.421
1.374
1.417
1.444
1.350
1.387
2.304
1.987
1.990
2.387
2.382
2.460
2.399
2.489
2.389
2.393
2.295
2.189
1.286
1.415
1.378
1.416
1.379
1.415
1.439
1.359
1.385
2.279
1.996
2.046
2.415
2.411
2.496
2.407
2.520
2.424
2.425
2.255
2.201
1.307
1.406
1.392
1.399
1.393
1.403
1.425
1.385
1.355
2.322
1.976
1.986
2.316
2.374
2.559
2.361
2.459
2.243
2.245
2.377
2.261
1.277
1.420
1.371
1.427
1.372
1.419
1.450
1.348
1.397
2.375
2.015
2.019
2.266
2.326
2.517
2.447
2.472
2.286
2.302
2.343
2.239
1.265
1.424
1.367
1.436
1.367
1.425
1.459
1.332
1.409
2.367
2.005
2.030
2.249
2.346
2.651
2.357
2.480
2.236
2.237
2.408
2.315
1.265
1.423
1.366
1.439
1.368
1.424
1.465
1.333
1.407
2.367
2.004
2.030
2.252
2.350
2.667
2.474
2.358
2.255
2.240
2.423
2.323
1.264
1.423
2.366
1.439
1.367
1.424
1.465
1.333
1.408
N,O-chelating ligand,6 while towards Ru(2) it is a redox innocent
monodentate pyridine nitrogen donor ligand. Ru(2) binds two
terminal Cl ligands, while Ru(1) contains only one terminal Cl
ligand. Thus the distorted RuONPCl3 and RuNPCl4 octahedrons
are not equivalent. Notably the bond lengths of the two
coordination spheres are significantly different. All the Ru(2)-Cl
terminal bond lengths are relatively shorter than the
corresponding Ru(1)-Cl lengths. The Ru(1)-Cl(1) bond length is
2.347(2) Å, while the Ru(2)-Cl(4) and Ru(2)-Cl(5) bond lengths
are 2.311(2) and 2.329(2) Å that are consistent with a ruthenium
(III) state. For comparison, the terminal and bridging Ru-Cl bond
lengths of diruthenium (III, III), diruthenium (II, II), diruthenium (II,
III) and 1•MeOH are listed in Chart 3.14-16 The average Ru-Clb (b
= bridging) bond lengths are significantly different for [RuIII(µ-
Cl)3RuIII], [RuII(µ-Cl)3RuIII] and [RuII(µ-Cl)3RuII] units. The
calculated average Ru-Clb lengths for them respectively are
2.429(2), 2.446(2) and 2.485 Å. 1•MeOH contains a [Ru(µ-
Cl)2Ru] unit and notably, the bridging Ru(2)-Cl(2) and Ru(2)-
Cl(3) bond lengths in 1•MeOH, 2.308(2) and 2.418(2) Å are
relatively shorter than Ru(1)-Cl(2) and Ru(1)-Cl(3) bond lengths,
2.326(2) and 2.497(2) Å. Due to weaker trans influence, the Ru-
Clb bonds trans to terminal chlorides are shorter than the Ru-Clb
bonds trans to PPh3 ligands.16 Thus, the Ru(1)-Cl(3) bond trans
to the PPh3 ligand is relatively longer than all other Ru-C1
lengths. The average Ru(1)-Clb and Ru(2)-Clb bond lengths
respectively 2.411(2) and 2.363(2) Å, strongly suggest the
different oxidation states of the Ru(1) and Ru(2) ions of the two
asymmetrical octahedral units in 1•MeOH.
Considering the relatively shorter Ru(2)-Clb and Ru(2)-Clt (t =
terminal) bond lengths, a 3+ state has been assigned to Ru(2)
ion. In this respect, the oxidation level of LAPH2 that exists as
●-
0
LAP2-, LISQ and LIQ forms as given in Chart 2, is significant to
analyze. In 1 the C(1)-O(1) and C(6)-N(1) lengths are 1.276(6)
and 1.357(6) Å.
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(a)
(b)
Figure 1. Molecular geometry of (a) 1•MeOH in crystals (50% thermal ellipsoids, solvent molecules and hydrogen atoms are omitted for clarity) and (b) the gas
phase optimized geometry of 1 by hybrid PBE0 DFT method.
(a) [RuIII(µ-Cl)3RuIII]
Ru1-Cl1
2.398(2)
Ru2-Cl1
2.402(2)
Ru1-Cl2
Ru1-Cl3
Ru1-Cl4
Ru1-Cl5
2.484(2)
2.398(2)
2.321(2)
2.313(2)
2.426(2)
Ru2-Cl2
Ru2-Cl3
Ru2-Cl6
Ru2-Cl7
2.502(2)
2.392(2)
2.316(2)
2.313(2)
2.432(2)
Ru1-Clb (avg)
Ru2-Clb (avg)
(b) [RuII(µ-Cl)3RuII]
Ru1-Cl1
Ru1-Cl2
2.46
2.50
Ru2-Cl1
Ru2-Cl2
2.46
2.50
Ru1-Cl3
Ru1-Clb (avg)
2.49
2.48
Ru2-Cl3
Ru2-Clb (avg)
2.52
2.49
(c) [RuII(µ-Cl)3RuIII]
Ru1-Cl1
2.365(2)
Ru2-Cl1
2.351(2)
Ru1-Cl2
Ru1-Cl3
Ru1-Cl4
2.476(2)
2.527(2)
2.370(2)
Ru2-Cl2
Ru2-Cl3
Ru2-Cl5
2.477(2)
2.483(2)
2.357(2)
Ru1-Clb (avg)
2.456(2)
Ru2-Clb(avg)
2.437(2)
(d) [RuII(µ-Cl)2RuIII] in 1•MeOH
Ru1-Cl2
Ru1-Cl3
Ru1-Cl1
2.326(2)
2.497(2)
2.347(2)
Ru2-Cl2
Ru2-Cl3
Ru2-Cl4
2.308(2)
2.418(2)
2.311(2)
Ru2-Cl5
Ru2-Clb(avg)
2.329(2)
2.363(2)
Ru1-Clb(avg)
2.411(2)
Chart 3. Experimental bond lengths of (a) diruthenium (III, III) unit in [Ph3P=O
H
O=PPh3][Ru2Cl7(PPh3)2]•0.5(CH2Cl2)(H2O)14 (b) diruthenium (II, II) unit
in [Ru2C13(PMe2Ph)6]PF615 (c) diruthenium (II, III) unit in [Ru2C15(chiraphos)2] (chiraphos = 2(S),3(S)-bis(diphenylphosphino)butane)16 and (d) 1•MeOH.
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The C-O and C-N lengths of the o-iminoquinone forms of an bi-
dentate o-aminophenol ligand respectively are 1.25 0.01 and
1.30 0.01 Å, while that of the o-iminosemiquinonate anion
radical are 1.30 0.01 and 1.35 0.01 Å.6 However, the C-N
lengths of the o-iminoquinone and o-iminosemiquinonate anion
radical forms of a tri-dented o-aminophenol ligand are relatively
longer and span the ranges of 1.34 0.01 Å and 1.37 0.01 Å.17
Considering the trend of the C-N lengths of a tri-dented o-
0
iminoquinone ligand and the C-O length, existence of the LIQ
with a minor contribution of LISQ●- states in 1 has been predicted.
The C-C lengths of the aminophenol ring of LIQ0 exhibit quinoidal
distortion with shorter C(2)-C(3), 1.340(10) and C(4)-C(5),
1.352(8) Å, lengths. In conjunction with the trend of the Ru-Cl
0
lengths and a major contribution of the LIQ form of the LAPH2
ligand, 1•MeOH has been defined as a diruthenium (II, III)
Robin-Day Class-II complex (where the +2 and +3 oxidation
states are assigned to Ru(1) and Ru(2) centres respectively)
with a minor contribution of diruthenium (III, III) state containing
●-
LISQ radical anti-ferromagnetically coupled to the chelated
ruthenium (III) ion as shown in Scheme 1.
Metrical oxidation state (MOS) of LIQn (n = 0, -1, -2) has been
calculated by the method introduced by Brown2c using X-ray
bond parameters of 1•MeOH. The calculated MOS is -0.82 that
corresponds to the dominant contribution of the LIQ●- state of the
ligand. However the assignment differs significantly as the LIQn is
a tri-dented bridging ligand and the metrical parameters of the
three redox states of these ligands are quite different17 from
those observed for a bi-dented ligand.2c, 18
Cyclic Voltammetry. The redox activity of 1 was investigated
by cyclic voltammetry at 298 K using tetrabutylammonium
hexafluorophosphate or tetrabutylammonium chloride as
a
supporting electrolyte. The cyclic voltammograms and the redox
potential data referenced to the ferrocenium/ferrocene, Fc+/Fc,
couple are given in Figure 2. In CH2Cl2 and CH3CN (10:1)
mixture 1 exhibits two reversible cathodic waves at -0.38 and -
0.82 V respectively due to [RuII(LIQ0)(µ-Cl)2RuIII]/[RuII(LIQ0)(µ-
Cl)2RuII] and [RuII(LIQ0)(µ-Cl)2RuII]/[RuII(LISQ●-)(µ-Cl)2RuII] redox
couples (Figure 2(a)), however, in this condition no reversible
anodic wave was discernible due to the dissociation of the labile
PPh3 ligands. The anodic waves of the voltammogram of 1
recorded in CH2Cl2 containing 1.5×10-4 M PPh3 as shown in
Figure 2(b) are reversible. In presence of PPh3, the cyclic
voltammogram of 1 displays anodic waves respectively at +0.52
and +0.85 V, that are assigned to [RuIII(LIQ0)(µ-Cl)2RuIII]/
[RuII(LIQ0)(µ-Cl)2RuIII] and [RuIII(LIQ0)(µ-Cl)2RuIV]/ [RuIII(LIQ0)(µ-
Cl)2RuIII] redox couples. To restrict the effect of the chloride
dissociation, the cyclic voltammogram of 1 was recorded using
tetrabutylammonium chloride as a supporting electrolyte (Figure
2(c)). However, no reversible anodic wave was discernible in
this medium too, precluding any effect of the chloride
dissociation. In presence of tetrabutylammonium chloride salt,
the cathodic waves shift positively by around 100 mV and a new
cathodic wave at -0.97 V due to LISQ●-/ LAP2- redox couple was
detected. The 1+, 12+, 1- and 12- forms were not isolated, but
characterized by EPR spectroscopy, NIR absorption bands and
BS DFT calculations.
Figure 2. Cyclic voltammograms of 1 in (a) CH2Cl2 and CH3CN (10:1) solvents
mixture (b) CH2Cl2 containing 1.5×10-4 M PPh3 using 0.2 M [N(n-Bu)4]PF6 as a
supporting electrolyte (c) CH2Cl2 containing 0.2 M [N(n-Bu)4]Cl as a supporting
electrolyte at 298 K (potential is referenced to Fc+/Fc couple).
EPR Spectroscopy. The paramagnetic complexes were also
analyzed by EPR spectroscopy. The X-band EPR spectra of the
powder sample of 1 and the CH2Cl2 solutions of 1, 12- and 12+
recorded at variable temperatures (298-113 K) are illustrated in
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Figure S5. The powder sample of 1 at 113 K exhibits a Ru(2)
centre based rhombic spectrum that displays hyperfine splitting
due to 35,37Cl nucleus (I = 3/2) as illustrated in Figure 3(a). The
simulated g and the hyperfine coupling constant (ACl) are g1 =
2.476, g2 = 2.339 (ACl = 40.0) and g3 = 2.068 (ACl = 230.0 MHz)
with the anisotropy (∆g), 0.41. The ∆g is larger as the RuPNCl4
octahedron is severely distorted. The frozen glass EPR
spectrum of 1 in CH2Cl2 at 113 K (Figure 3(b)) is similar to that of
the powder sample and the simulated g and ACl parameters are
g1 = 2.481, g2 = 2.360 (ACl = 125.0) and g3 = 2.049 (ACl = 190.0
MHz) with ∆g = 0.43. The similar EPR spectra of the powder and
frozen glass confirm that in CH2Cl2 1 is stable. The pattern of the
EPR spectra of
1
is similar to those reported for
[Ru3C16(PR3)6][BPh4] by Cotton et. al.19 Notably, the frozen glass
EPR spectrum for the 12+ ion in CH2Cl2 at 113 K is also similar to
that of 1, inferring that the EPR signal of 12+ ion is also based on
the spin centred on Ru(2). The assigned g values for 12+ ion are
g1 = 2.484, g2 = 2.391 and g3 = 2.061 with ∆g = 0.42. The S = ½
state of Ru(2) of 12+ ion is achieved by an anti-ferromagnetic
coupling interaction between Ru(1)3+ (↓) and Ru(2)4+ (↑↑) ions.
The EPR spectrum of 12- is different from those of the 1 and 12+.
The fluid solution EPR spectrum of 12- at 298 K displays a strong
signal at g = 2.008 due to iminobenzosemiquinonate anion
radical and a broader signal at g = 2.2 (Figure 4(a)) due to
ruthenium (III) ion, while the frozen CH2Cl2 glass spectrum of the
12- at 113 K is well resolved and exhibits a rhombic EPR signal
due to +3 state of Ru(1) ion as given in Figure 4(b). The variable
temperature EPR spectra of 12- confirming a contribution of
ruthenium(III) ion were illustrated in Figure S6. However, no
temperature dependent thermal equilibrium between [RuII(LISQ●-)]
and [RuIII(LAP2-)] forms was established.
Figure 3. X-band EPR spectra of (a) powder sample of 1 at 113 K (frequency,
9.46827 MHz) (b) frozen CH2Cl2 glass of 1 at 113 K (frequency 9.47580 MHz)
(experimental, black and simulated, red) and (c) 12+ ion, fluid solution (in
CH2Cl2 containing 1.5×10-4 M PPh3) at 273 K (frequency 9.47117 MHz) (green)
and frozen glass at 113 K (frequency 9.47667 MHz) (black).
Figure 4. X-band EPR spectra of 12-, (a) CH2Cl2 solution at 298 K (frequency,
9.46130 MHz) and (b) CH2Cl2 frozen glass at 113 K (frequency 9.47655 MHz)
(experimental, black and simulated, red; simulated spectra was achieved by a
combination of two sub-spectra due to [RuII(LAP2-)(µ-Cl)2RuIII] (33.3%) and
[RuII(LISQ●-)(µ-Cl)2RuII] (66.7%) electronic states).
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distribution predicts the contributions of both [RuII(LIQ0)(µ-
●
Cl)2RuIII ↔ RuIII(LISQ -)(µ-Cl)2RuIII] forms (Chart 5) to the ground
electronic state of 1. The quantum chemical result on 1
predicting the nearly equal spin density on both ruthenium ions
seems to be a consequence of an over-delocalization.21
The gas phase geometry of 1- was optimized with singlet spin
state. It is noteworthy that no significant change of the C(1)-O(1)
and C(6)-N(1) lengths were observed during the 1 → 1-
conversion. However, in 1- the calculated Ru(1)-Cl(1), 2.387 Å,
Ru(2)-Cl(4), 2.389 and Ru(2)-Cl(5), 2.393 Å, are significantly
longer than those found for 1. In 1-, the Ru(1)-Cl and Ru(2)-Cl
terminal and bridging bond lengths (Table 1) are similar and the
diruthenium (II, II) state, [RuII(LIQ0)(µ-Cl)2RuII] has been assigned
to 1-. The gas phase geometry of 12- was optimized with a
doublet spin state. The calculated lengths for 12- ion have a
different trend. In the transformation of 1- → 12-, the Ru(1)-Cl(1),
Ru(2)-Cl(4) and Ru(2)-Cl(5) lengths increase, while Ru(1)-P(1)
and Ru(2)-P(2) lengths decrease significantly. It infers that 12-
promotes stronger Ru → PPh3 back-bonding. In 12- the C(1)-O(1)
and C(6)-N(1) lengths respectively are 1.307 and 1.385 Å that
Chart 4. Two electronic states of 12-
●-
Chart 5. [RuII(LIQ0)(µ-Cl)2RuIII] and [RuIII(LISQ )(µ-Cl)2RuIII] forms of 1
●-
are consistent with the LISQ form of the ligand.13 The spin
The frozen glass spectrum was convoluted into two sub-spectra
and simulated considering [RuII(LAP2-)(µ-Cl)2RuIII] (33.3%) and
[RuII(LISQ●-)(µ-Cl)2RuII] (66.7%) components. The simulated g
values for the ruthenium(III) component are g1 = 2.201, g2
2.005 and g3 = 1.955, and that for the organic radical component
is 2.009.
density obtained from the Mulliken spin population analysis is
dominantly localized on Ru(1) and the NO-chelate as illustrated
in Figure 5(b). Thus contributions of both [RuIII(LAP2-)(µ-Cl)2RuII]
and [RuII(LISQ●-)(µ-Cl)2RuII] forms to the electronic ground state of
12- was anticipated. The existence of these two components
(Chart 4) to the ground electronic state of 12- was confirmed by
fluid solution and frozen glass EPR spectra (vide supra).
=
The two component EPR spectra of the ruthenium(II/III)
complexes containing redox noninnocent ligands were reported
in several aspects.20 Notably, the frozen glass spectrum due to
radical component of 12- displays hyperfine splitting due to 14N (I
= 1) nucleus and the simulated hyperfine coupling constant (AN)
is 16.5 MHz. The study infers that both [RuIII(LAP2-)(µ-Cl)2RuII]
and [RuII(LISQ●-)(µ-Cl)2RuII] components coexist in 12- ion.
Expectedly, in fluid solution at 298 K, the spectrum due to
ruthenium (III) ion is not resolved. However, the frozen glass
reveals a well resolved rhombic spectrum. Thus the ground
The gas phase geometry of 1+ was optimized with singlet and
triplet spin states and these were compared with the broken
symmetry (BS) MS = 0 solution. The triplet solution is 81.9
kJ/mol lower in energy than the singlet solution, while the energy
of the BS (1,1) solution is similar to that of the triplet solution
(only 0.52 kJ/mol higher in energy), inferring the presence of the
ruthenium (III, III) state in the 1+ ion. In the BS state of 1+, the
calculated Ru(1)-Cl(1), 2.266 Å, Ru(2)-Cl(4), 2.286 Å and Ru(2)-
Cl(5), 2.302 Å terminal lengths are comparable and relatively
shorter. Notably the Ru(1)-PPh3, 2.375 Å and Ru(2)-PPh3, 2.343
Å, lengths increase significantly correlating well with the
oxidation of Ru(1)II to Ru(1)III. The C(1)-O(1) and C(6)-N(1)
lengths in 1+ are also relatively shorter than those of 1.
Considering these bond parameters, 1+ ion has been defined by
the [RuIII(LIQ0)(µ-Cl)2RuIII] state.
electronic state of 12- is defined as a hybrid state of [RuIII(LAP
2-
)(µ-Cl)2RuII] ↔ [RuII(LISQ●-)(µ-Cl)2RuII] forms as depicted in Chart
4.
Broken Symmetry (BS) DFT Calculations. The electronic
structures of 1 and the oxidized and reduced analogues were
further confirmed by BS DFT calculations using the ORCA
program package.6 The gas phase geometry of 1 with a doublet
spin state was optimized by the hybrid PBE0 DFT method and
the gas phase optimized geometry is shown in Figure 1(b). The
calculated bond lengths are summarized in Table 1. For
comparison geometry of 1 was also optimized in CH2Cl2 and the
calculated bond parameters of the gas phase and solution
geometries are similar. In 1, the calculated Ru(1)-Cl(1) length is
marginally longer than Ru(2)-Cl(4) and Ru(2)-Ru(5) lengths. The
calculated C(1)-O(1) length,1.283 Å, is an intermediate of that
expected for semiquinone (~1.30 Å) and quinone (~1.25 Å)
forms. Similarly, the C(6)-N(1) length, 1.350 Å, is relatively
longer than that reported for a tri-dentate o-iminoquinone
ligand.18 The calculated spin density obtained from Mulliken spin
The gas phase geometry of 12+ was optimized with doublet and
quartet spin states. The energy of the BS MS = ½ of 12+ was
calculated by a flip spin method. Notably, the energy of the high
spin quartet solution is 26.9 kJ/mol lower than the doublet
solution, while the BS (III, IV) MS = ½ solution is 0.71 kJ/mol
lower in energy than that of high spin quartet solution. Thus, 12+
ion is described by a [RuIII(LIQ0)(µ-Cl)2RuIV] state. In 1+ → 12+
transformation, the Ru(1)-Cl(1) length decreases to 2.252 Å,
while the Ru(1)-PPh3 length changes to 2.367 Å. The Ru(2)-
Cl(4) and Ru(2)-Cl(5) lengths respectively are 2.255 and 2.240 Å
which are distinctly shorter than those of the 1+ ion. The
calculated lengths are also shorter than those reported for
ruthenium (IV) complexes.22 In 12+, the C(1)-O(1) and C(6)-N(1)
lengths, 1.264 and 1.333 Å, are shorter and have been
0
population analysis scatters on both ruthenium ions and LIQ
ligand as depicted in Figure 5(a). The trend of the calculated Ru-
Cl, C-O and C-N lengths in conjunction with the spin density
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(a)
(b)
(c)
(d)
Figure 5. Mulliken spin density plots with isovalue 0.01 obtained from unrestricted DFT calculations on (a) 1 [PBE0, Ru(1), 0.65; Ru(2), 0.88; O(1), -0.10; N(1), -
0.25; C(1), -0.13; C(2), 0.04; C(3), -0.10; C(4), -0.06; C(6), -0.07; Cl(1), 0.05; Cl(4), 0.06; Cl(5), 0.07] and (b) 12- [Ru(1), 0.63; Ru(2), 0.02; O(1), 0.12; N(1), 0.07;
C(2), 0.04; C(4), 0.03]. Spin density plot obtained from broken symmetry DFT calculations on (c) 1+ [Ru(1), 1.05; Cl(1), 0.19; Cl(2), +0.07; Ru(2), -0.85; Cl(4), -
0.08; Cl(5), -0.08; Cl(3), -0.04; C(1), -0.07; C(4), -0.09; C(5), 0.06; C(6), -0.11] and (d) 12+ [Ru(1), -1.08; Cl(1), -0.20; Ru(2), +1.59; Cl(4), +0.24; Cl(5), +0.14; C(4),
+0.11; O(1), +0.04] (red, alpha spin; yellow, beta spin).
Table 2. UV-Vis-NIR Absorption Spectral Data of LAPH2, 1, 1+, 12+, 1- and 12- in
CH2Cl2
considered as the markers for the LIQ state of LAPH2 in this
dinuclear core. The spin density obtained from Mulliken spin
population analysis is dominantly localized on Ru(1), -1.08 (beta
spin) and Ru(2), +1.59 (alpha spin) centres as shown in Figure
5(d) and is consistent with the dinuclear ruthenium (III, IV) state
of 12+ ion.
Compounds
λmax, nm (ε, 103 M-1cm-1)
LAPH2
1
425 (3.23), 290 (7.19)
1300 (0.14), 560 (1.40), 500 (1.30), 360 (1.67)
560 (0.88), 375 (1.11)
UV-Vis-NIR Absorption Spectra. The UV-Vis-NIR absorption
spectra of LAPH2, 1 and 1+, 12+, 1- and 12- obtained from constant
potential bulk electrolysis experiments in CH2Cl2 at 298K were
recorded and are illustrated in Figure 6. LAPH2 exhibits strong
absorption bands at 425 and 290 nm. The absorption spectrum
of 1 displays a NIR band at 1300 nm (Figure 6(b)) due to a RuII
→ RuIII intervalence charge transfer (IVCT) transition. Similarly,
the 12+ ion exhibits a RuIII → RuIV IVCT transition at 1370 nm.
The IVCT transitions correlate with the Robin-Day class II
electronic states of 1 and 12+ ion. Notably, the lower energy
band is absent in the 1+ and 1- ions containing (RuIII, RuIII) and
(RuII, RuII) cores. The 12- ion exhibits a broader absorption band
at 1000 nm.
a1+
a12+
1-
1370 (0.17), 550 (1.42), 425 (1.75)
570 (1.16), 380 (2.00)
12-
540 (0.50), 375 (0.88)
a containing 1.5×10-4 M PPh3
All these dinuclear complexes exhibit a stronger absorption band
at 540-560 nm (Figure 7) which are ubiquitous for RuII-quinone
complexes.17, 20 The origin of the transition was elucidated by TD
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Figure 6. UV-Vis-NIR absorption spectra of LAPH2, 1, 1- and 12- in CH2Cl2 and 1+, 12+ in CH2Cl2 containing 1.5×10-4 M PPh3.
DFT calculation on 1 in CH2Cl2. The calculated wave lengths are
listed in Table 3. The DFT calculation confirms that the
absorption band at 500-600 nm is due to the metal to ligand
charge transfer (MLCT) and metal to mixed metal-ligand charge
transfer (MMMLCT) transitions. Notably, this MLCT transition is
significantly perturbed during 1 → 1+ and 1 → 1- conversions.
The changes of UV-vis absorption pattern during 1 → 1+, 1 →
12+, 1 → 1- and 1- → 12- conversions were recorded by
spectroelectrochemical measurements (Figure 7) in CH2Cl2. It
was recorded that in 1 → 1- conversion, where [RuII(LIQ0)(µ-
Cl)2RuIII] is reduced to [RuII(LIQ0)(µ-Cl)2RuII] state, the MLCT
band at 560 nm gradually diminishes and a broader band at 750
nm appears showing two isosbestic points at 650 and 480 nm.
In the 1-
→
12- conversion due to the reduction of
iminobenzoquinone to iminobenzosemiquinonate anion radical
the MLCT transition gradually diminishes and the spectrum
changes showing one isosbestic point at 390 nm. In 1 → 1+
conversion, where [RuII(LIQ0)(µ-Cl)2RuIII] is oxidised to
[RuIII(LIQ0)(µ-Cl)2RuIII] state, the MLCT band changes showing
two isosbestic points at 515 and 660 nm. However, during 1+ →
12+ conversion, the major bands disappear generating a peak at
550 nm.
Figure 7. Change of absorption spectra during (a) 1 → 1- (CH2Cl2) (b) 1- → 12-
(CH2Cl2) and (c) 1 → 1+ (CH2Cl2 containing 1.5×10-4 M PPh3) and (d) 1+ → 12+
M PPh3) conversions achieved by constant
potential spectroelectrochemical measurements at 298 K (initial spectrum, red
and final spectrum, dark blue) .
(CH2Cl2 containing 1.5×10-4
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Table 3. Calculated Excitation Energies (λ/nm), Oscillator Strengths (f) and Transition Types Obtained from TD DFT Calculation on 1 in CH2Cl2 using PBE0 hybrid
functional
λcal
f
λexp
Significant Transitions
(>10%)
Transitions Types
597.6
0.014
560
α-HOMO-3 → LUMO (18%)
β-HOMO-3 → LUMO (12%)
β-HOMO-1 → LUMO (12%)
d
Ru → π* (MLCT)
dRu → π*+dRu (MMMLCT)
dRu+ pCl → π*+dRu (MMMLCT)
PPh3 → π* (LLCT)
490.7
0.068
500
α-HOMO-5 → LUMO (28%)
MLCT = metal to ligand charge transfer; MMMLCT = metal to mixed metal-ligand charge transfer; LLCT = ligand to ligand charge transfer.
Conclusions
References
Coordination of redox noninnocent ligands to transition metal
[1]
(a) M. Parthey, J. B. G. Gluyas, M. A. Fox, P. J. Low, M. Kaupp, Chem.
ions is common for natural electron transfer proteins those
undergo with various mixed-valence states. In this study, it is
disclosed that a combination of redox non-innocent and innocent
donor cites in a ligand is significant in modelling mixed valence
complexes of transition metal ions. In this context, a N-pyridyl-o-
aminophenol derivative containing a redox non-innocent NO-
and a redox innocent pyridine nitrogen donor sites, abbreviated
as (LAPH2) and a mixed valence diruthenium (II, III) complex,
[(PPh3)Cl2RuII(LIQ0)(µ-Cl)2RuIIICl(PPh3)] (1) were successfully
Eur. J. 2014, 20, 6895-6908. b) A. Heckmann, L. Christoph, Angew.
Chem. Int. Ed. 2012, 51, 326-392. c) B. Sarkar, S. Patra, J. Fiedler, R.
B. Sunoj, D. Janardanan, G. K. Lahiri, W. Kaim, J. Am. Chem. Soc.
2008, 130, 3532-3542. d) R. C. Rocha, F. N. Rein, H. Jude, A. P.
Shreve, J. J. Concepcion, T. J. Meyer, Angew. Chem. 2008, 120, 513-
516. e) K. D. Demadis, C. M. Hartshorn, T. J. Meyer, Chem. Rev. 2001,
101, 2655-2685.
[2]
Ligand Mixed Valency: a) S. D. J. McKinnon, B. O. Patrick, A. B. P.
Lever, R. G. Hicks, Inorg. Chem. 2013, 52, 8053-8066. b) C. P. Kubiak,
Inorg. Chem. 2013, 52, 5663-5676. c) S. N. Brown, Inorg. Chem. 2012,
51, 1251-1260. d) C. G. Pierpont, Inorg. Chem. 2011, 50, 9766-9772.
e) A. Das, T. Scherer, S. T. K. Maji, S. M. Mobin, F. A. Urbanos, R.
Jimenez-Aparicio, W. Kaim, G. K. Lahiri, Inorg. Chem. 2011, 50, 7040-
7049. f) T. J. Mooibroek, G. Aromí, M. Quesada, O. Roubeau, P.
Gamez, S. DeBeer George, J. van Slageren, S. Yasin, E. Ruiz, J.
Reedijk, Inorg. Chem. 2009, 48, 10643-10651. g) P. H. Dinolfo, S. J.
Lee, V. Coropceanu, J. L. Brédas, J. T. Hupp, Inorg. Chem. 2005, 44,
5789-5797. h) A. P. Meacham, K. L. Druce, Z. R. Bell, M. D. Ward, J. B.
Keister, A. B. P. Lever, Inorg. Chem. 2003, 42, 7887-7896. i) H. C.
Chang, K. Mochizuki, S. Kitagawa, Inorg. Chem. 2002, 41, 4444-4452.
a) E. I. Solomon, X. Xie, A. Dey, Chem. Soc. Rev. 2008, 37, 623-638.
b) J. Stubbe, W. A. van der Donk, Chem. Rev. 1998, 98, 705-762.
Creutz and Taube Complex: a) C. Creutz, H. Taube, J. Am. Chem. Soc.
1973, 95, 1086-1094. b) C. Creutz, H. Taube, J. Am. Chem. Soc. 1969,
91, 3988-3989.
0
isolated (LIQ is the 2e oxidized o-iminobenzoquinone form of
LAPH2). 1/1- and 1-/12- redox couples are reversible, while 1+/1
and 12+/1+ redox couples are not due to PPh3 dissociation,
however they are reversible in CH2Cl2 containing 1.5×10-4
M
PPh3 solution. Single crystal X-ray crystallography, EPR
spectroscopy, spectroelectrochemical measurement, inter
valence charge transfer (IVCT) transition and broken symmetry
(BS) DFT calculations confirm that 1 and 12+ are respectively
diruthenium (II, III), [RuII(LIQ0)(µ-Cl)2RuIII] and diruthenium (III, IV),
[RuIII(LIQ0)(µ-Cl)2RuIV], mixed valence complexes, while 1+ and 1-
are diruthenium (III, III), [RuIII(LIQ0)(µ-Cl)2RuIII] and diruthenium (II,
II), [RuII(LIQ0)(µ-Cl)2RuII] complexes of (LIQ0). The ground
[3]
[4]
●-
electronic state of 12- is analyzed by a hybrid state of [RuII(LISQ
)(µ-Cl)2RuII] ↔ [RuIII(LAP2-)(µ-Cl)2RuII] forms. The NIR absorption
spectra of 1+ and 12+ display IVCT transition at 1300 and 1370
nm, while the IVCT bands are absent in other analogues. The
study ushers that a combination of redox innocent and redox
noninnocent donor sites in a ligand is worthy in stabilizing
different redox states of a metal ion in the dinuclear and poly-
nuclear forms and makes the theme of isolating mixed valence
complexes of a transition metal ion successful.
[5]
a) F. F. Khan, J. Klein, J. L. Priego, B. Sarkar, R. J. Aparicio, G. K.
Lahiri, Inorg. Chem., 2018, 57, 12800-12810. b) A. Mandal, A. Grupp,
B. Schwederski, W. Kaim, G. K. Lahiri, Inorg. Chem. 2015, 54, 10049-
10057. c) A. Mandal, H. Agarwala, R. Ray, S. Plebst, S. M. Mobin, J. L.
Priego, R. J. Aparicio, W. Kaim, G. K. Lahiri, Inorg. Chem. 2014, 53,
6082-6093. d) A. K. Das, B. Sarkar, J. Fiedler, S. Zális, I. Hartenbach,
S. Strobel, G. K. Lahiri, W. Kaim, J. Am. Chem. Soc. 2009, 131, 8895-
8902. e) S. Maji, B. Sarkar, S. M. Mobin, J. Fiedler, F. A. Urbanos, R. J.
Aparicio, W. Kaim, G. K. Lahiri, Inorg. Chem. 2008, 47, 5204-5211. f) B.
Sarkar, S. Patra, J. Fiedler, R. B. Sunoj, D. Janardanan, G. K. Lahiri, W.
Kaim, J. Am. Chem. Soc. 2008, 130, 3532-3542. g) M. Koley, B. Sarkar,
S. Ghumaan, E. Bulak, J. Fiedler, W. Kaim, G. K. Lahiri, Inorg.
Chem., 2007, 46, 3736-3742. h) M. Koley, B. Sarkar, S. Ghumaan, E.
Bulak, J. Fiedler, W. Kaim, G. K. Lahiri, Inorg. Chem. 2007, 46, 3736-
3742. i) S. Ghumaan, S. Kar, S. M. Mobin, B. Harish, V. G. Puranik, G.
K. Lahiri, Inorg. Chem. 2006, 45, 2413-2423. j) S. Patra, B. Sarkar, S.
Ghumaan, J. Fiedler, W. Kaim, G. K. Lahiri, Inorg. Chem. 2004, 43,
6108-6113. k) N. Chanda, B. Sarkar, S. Kar, J. Fiedler, W. Kaim, G. K.
Lahiri, Inorg. Chem. 2004, 43, 5128-5133. l) S. Kar, N. Chanda, S. M.
Mobin, A. Datta, F. A. Urbanos, V. G. Puranik, R. Jimenez-Aparicio, G.
K. Lahiri, Inorg. Chem. 2004, 43, 4911-4920. m) S. Patra, T. A. Miller, B.
Acknowledgements
The authors acknowledge the financial support received from
DST (EMR/2016/005222). DD is an INSPIRE fellow of DST
(IF131158), New Delhi, India.
Keywords: • di-ruthenium mixed valence complex • organic
radical • IVCT transition • broken symmetry DFT • asymmetric
bridging ligand.
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Sarkar, M. Niemeyer, M. D. Ward, G. K. Lahiri, Inorg. Chem. 2003, 42,
4707-4713. n) S. Patra, B. Mondal, B. Sarkar, M. Niemeyer, G. K. Lahiri,
Inorg. Chem. 2003, 42, 1322-1327.
[6]
a) P. Sarkar, M. K. Mondal, A. Sarmah, S. Maity, C. Mukherjee, Inorg.
Chem. 2017, 56, 8068-8077. b) R. Rakshit, S. Ghorai, S. Biswas, C.
Mukherjee, Inorg. Chem. 2014, 53, 3333-3337. c) S. Kundu, S. Maity, A.
N. Maity, S-C. Ke, P. Ghosh, Dalton Trans. 2013, 42, 4586-4601. d) A.
S. Roy, P. Saha, N. D. Adhikary, P. Ghosh, Inorg. Chem. 2011, 50,
2488-2500. e) C. Mukherjee, T. Weyhermüller, E. Bothe, P. Chaudhuri,
Inorg. Chem. 2008, 47, 2740-2746. f) S. Kokatam, T. Weyhermüller, E.
Bothe, P. Chaudhuri, K. Wieghardt, Inorg. Chem. 2005, 44, 3709-3717.
a) G. M. Sheldrick, Acta Crystallogr. Sect. C: Struct. Chem. 2015, 71, 3-
8. b) G. M. Sheldrick, Acta Cryst. 2008, A64, 112-122.
[7]
[8]
[9]
F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2, 73-78.
a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648-5652. b) B. Miehlich, A.
Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1989, 157, 200-206. c) C.
Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785-789.
[10] F. Neese, J. Phys. Chem. Solids 2004, 65, 781-785.
[11] a) F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297-
3305. b) F. Weigend, F. Furche, R. Ahlrichs, J. Chem. Phys. 2003,
119(24), 12753-12762. c) K. Eichkorn, F. Weigend, O. Treutler, R.
Ahlrichs, Theor. Chem. Acc. 1997, 97, 119-124. d) A. Schaefer, C.
Huber, R. Ahlrichs, J. Chem. Phys. 1994, 100, 5829-5835. e) A.
Schaefer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97, 2571-2577.
[12] a) S. Kossmann, F. Neese, J. Chem. Theory Comput. 2010, 6, 2325-
2338. b) H. B. Schlegel, J. J. McDouall, In Computational Advances in
Organic Chemistry. C. Ogretir, I. G. Csizmadia, Eds. Kluwer Academic:
The Netherlands, 1991.
[13] a) R. E. Stratmann, G. E. Scuseria, M. Frisch, J. Chem. Phys. 1998,
109, 8218−8224. b) M. E. Casida, C. Jamoroski, K. C. Casida, D. R.
Salahub, J. Chem. Phys. 1998, 108, 4439-4449. c) R. Bauernschmitt,
M. Haser, O. Treutler, R. Ahlrichs, Chem. Phys. Lett. 1996, 256, 454-
464. d) M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem.
2003, 24, 669-681. e) V. Barone, M. Cossi, J. Phys. Chem. A 1998, 102,
1995-2001.
[14] M. P. de Araujo, Transition Metal Chem. 2002, 27, 110-114.
[15] M. Laing, L. Pope, Acta Cryst. 1976, B32, 1547.
[16] I. S. Thorburn, S. J. Rettig, B. R. James, Inorg. Chem. 1986, 25, 234-
240.
[17] a) S. Maity, S. Kundu, S. Mondal, S. Bera, P. Ghosh, Inorg. Chem.
2017, 56, 3363-3376. b) S. Maity, S. Kundu, S. Bera, T. Weyhermüller,
P. Ghosh, Eur. J. Inorg. Chem. 2016, 3691-3697. c) S. Bera, S. Mondal,
S. Maity, T. Weyhermüller, P. Ghosh, Inorg. Chem. 2016, 55, 4746-
4756. d) M. Bubrin, D. Schweinfurth, F. Ehret, S. Záliš, H. Kvapilová, J.
Fiedler, Q. Zeng, F. Hartl, W. Kaim, Organometallics 2014, 33, 4973-
4985. e) R. Hübner, S. Weber, S. Strobel, B. Sarkar, S. Záliš, W. Kaim,
Organometallics 2011, 30, 1414-1418.
[18] S. Kundu, S. Maity, T. Weyhermüller, P. Ghosh, Inorg. Chem. 2013, 52,
7417-7430.
[19] F. A. Cotton, R. C. Torralba, Inorg. Chem. 1991, 30, 4386-4391.
[20] a) S. Kundu, D. Dutta, S. Maity, T. Weyhermüller, P. Ghosh, Inorg.
Chem., 2018, 57, 11948-11960. b) M. K. Biswas, S. C. Patra, A. N.
Maity, S-C. Ke, N. D. Adhikary, P. Ghosh, Inorg. Chem. 2012, 51,
6687-6699.
[21] M. Parthey, M. Kaupp, Chem. Soc. Rev. 2014, 43, 5067-5088.
[22] J. Díez, J. Gimeno, I. Merino, E. Rubio, F. J. Suarez, Inorg. Chem.
2011, 50, 4868-4881.
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Debarpan Dutta,[a] Suman Kundu[a] and
Prasanta Ghosh*[a]
Page No. – Page No.
A Di-ruthenium Complex of a N-
Pyridyl-o-Aminophenol Derivative: A
Route to Mixed Valency
Mixed valence di-ruthenium complexes of 2-((3-nitropyridin-2-yl)amino)phenol
containing redox innocent and non-innocent coordination sites are disclosed.
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