Glyoxalbis(2-methylmercaptoanil) complexes of nickel and ruthenium: radical versus non-radical states

Article abstract of DOI:10.1039/c6nj02903e

The coordination chemistry of a N₂S₂ donor α-diimine ligand, glyoxalbis(2-methylmercaptoanil) (gmma), with transition metal ions was explored. The study authenticated that gmma is a redox non-innocent flexidentate ligand. The nickel(

Full text of DOI:10.1039/c6nj02903e

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
Glyoxalbis(2-methylmercaptoanil) complexes of nickel and
ruthenium: radical versus non-radical states†
Pinaki Saha,a Debasish Samantaa and Prasanta Ghosh*a
Received 00th January 20xx,
Accepted 00th January 20xx
The coordination chemistry of a N2S2 donor α-diimine ligand, glyoxalbis(2-methylmercaptoanil) (gmma), with transition
metal ions was explored. The study authenticated that gmma is a redox non-innocent flexidentate ligand. The nickel(II)
and ruthenium(II) complexes of the types trans-[NiII(gmma)Cl2] (1), trans-[RuII(gmma)Cl2] (2) and [RuII(gmma)(PPh3)Cl]Cl
(3+Cl-) were isolated. Single crystal X-ray crystallography established that the diimine fragment particularly in 2 and 3+Cl-
.H2O are severely distorted. EPR spectroscopy and density functional theory (DFT) calculations authenticated that the
octahedral 1− and 12− ions are gmma anion radical (gmma•−) and gmma diimide (gmma2−) complexes of the types trans-
DOI: 10.1039/x0xx00000x
www.rsc.org/
[NiII(gmma•−)Cl2]− (1−) and trans-[NiII(gmma2−)Cl2]2− (12−
) which are unstable in solution. The chemically and
electrochemically reduced ions undergo a chemical change to a dinuclear square planar nickel(II) complex of the type [(μ-
NSNS-gmma)Ni2Cl3(PF6)] (4PF6) in presence of PF6− salt, predicted by ESI mass spectroscopy, where μ-NSNS-gmma is a
bis(methylthio-imine) donor bridging ligand. The CSS solution of 2 is stable. In contrast to 1− and 12− ions, 2− in solution does
not undergo any chemical change and it is defined as a resonance hybrid of trans-[RuII(gmma•−)Cl2]− and trans-
[RuIII(gmma2−)Cl2]− states. Similarly, 3 is defined as a resonance hybrid of [RuII(gmma•−)(PPh3)Cl] and [RuIII(gmma2−)(PPh3)Cl]
states. In 2− and 3 the atomic spin is delocalised over both ruthenium and the α-diimine fragment, authenticated by the
unrestricted DFT calculations. The UV-vis absorption spectra of the isolated complexes and their reduced analogues were
analyzed by spectroelectrochemical measurements and TD DFT calculations.
in coordination chemistry. A redox non-innocent chelate is an
entity that can receive electron from the metal ion, can
transfer electron to the metal ion and can share an electron
Introduction
The participation of the redox non-innocent ligands, either in
paramagnetic or open shell singlet state, in different catalytic
cycles has been documented.1 The role of the redox non-
innocent ligands in different forms to control catalytic
reactions is disclosed.1d It is noteworthy that a redox non-
innocent ligand is an agent that can expand the activity of the
central metal ion, particularly in cases of oxidative addition
reactions.2 The diverse activity of the redox non-innocent
ligands thus is a tool to model functional coordination
complexes. Sharing of an unpaired electron of a coordination
complex by the metal ion as well as the ligand is not common
with the metal ion. The first two phenomena induce the
formation of organic radicals, whereas the third process will
generate a state, in which the contributions of both radical and
non-radical states are present. This particular state can be
defined as a “resonance hybrid” (mixed character) of radical
and non-radical states. Features of the organic radicals
coordinated to transition metal ions as well as the resonance
hybrid states are a subject of investigation.
Notably, the nickel complexes of aliphatic α-diimine which
are redox non-innocent, emerge as promising catalysts for
olefin polymerization and coupling reactions.3 Heterocyclic α-
diimine complexes of ruthenium are numerous. The photo
functionality and catalytic activities of these complexes were
investigated in various aspects.4 However, the aliphatic α-
diimine complexes of ruthenium are limited in scope and in
this study α-diimine complexes of nickel and ruthenium were
explored, particularly to define versatile electronic states
containing ruthenium(II/III) ions and the neutral/mono and di-
reduced diimine fragment. The α-diimine ligand of the type
LRR2′ that exists as neutral diimine (LRR2′), diimine anion radical
(LRR2'•−) and di-anionic diimide (LRR2'2−), as illustrated in
Scheme 1 was persuaded in many cases to explore the anion
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radical states coordinated to transition metal ions.5 The bond
parameters and the spectral features of these three electronic
states, LRR2′, LRR2'•−and LRR2'2‒ in complexes are significantly
different. In this regard, electronic states of the members of
the electron transfer series, [Ni(L)]z (z = 0, 1+, 2+; L = 2-phenyl-
1,4-bis(isopropyl)-1,4-diazabutadiene) are remarkable.6b-e
trans-[NiII(gmma)Cl2] (1)
trans-[RuII(gmma)Cl2] (2)
Scheme 1 Redox series of α-diimine fragments.
Glyoxalbis(2-mercaptoanil) (gma) is a tetradentate ligand
incorporating a stable diimine fragment which coordinates
metal ion as a N2S2-donor as shown in Scheme S1. The
coordination chemistry of gma is rich and the elucidation of
the electronic structures of the transition metal complexes of
gma particularly with iron was a subject of research in last two
decades.7 Eventually gma•− anion radical complexes of
iron(III/II) were successfully isolated.8 The investigation
inferred that the gma is redox non-innocent. Similarly, the
coordination chemistry of the redox non-innocent dianionic
glyoxalbis(2-hydroxyanil) (gha) developed significantly.9
[RuII(gmma)(PPh3)Cl]+ (3+)
Chart 2 Isolated gmma complexes.
neutral bridging ligand. It is defined as a reduction induced
chemical change of an octahedral nickel(II) complex to a
square planar complex. In similar condition, the octahedral 2−
and 3 are stable in solution and these are defined as the
resonance hybrids of [RuII(gmma•−)] ↔ [RuIII(gmma2−)] states.
In this article, syntheses, spectra, electrochemical studies and
the single crystal X-ray structures of gmma,
+Cl−.H2O are reported. The electrochemically/chemically
generated 1- 2- and
were investigated by EPR spectroscopy
1.CH2Cl2, 2 and
3
,
3
and spectroelectrochemical measurements. In addition,
density functional theory (DFT) calculations were employed to
support in elucidating the electronic structures of the
complexes.
Chart 1 gmma ligand and the binding modes.
Experimental section
In this project, the coordination chemistry of glyoxalbis(2-
methylmercaptoanil) (gmma) of nickel and ruthenium was
investigated, to foster the uncommon nickel(I)-(α-
diimine)/nickel(II)-(α-diimine anion radical) and ruthenium(II)-
Physical measurements
Reagents or analytical grade materials were obtained from
the commercial suppliers 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. All analyses
were performed after drying the samples under high vacuum.
Infrared spectra of the samples were measured from 4000 to
400 cm-1 with KBr pellets at room temperature on a Perkin-
(α-diimine)/ruthenium(II)-(α-diimine
anion
radical)/
ruthenium(III)-(α-diimide) states. The search disclosed that
gmma is a redox non-innocent flexidentate ligand acting as a
N2S2-donor tetradentate ligand as gmma and bis(methylthio-
imine) donor bridging ligand as μ-NSNS-gmma as depicted in
Chart 1. It is to be noted that a binuclear ruthenium(II)
complex of μ-NSNS-gmma of the type [(acac)2RuII(μ-NSNS-
gmma)RuII(acac)2] incorporating acetylacetone (acac) as
coligands was reported in a different aspect.10
Elmer Spectrum RX 1 FT-IR spectrophotometer. H and 13C
1
NMR spectra in CDCl3 and DMSO d6 solvents were obtained on
a Bruker DPX 300 and 500 MHz spectrometer. ESI mass spectra
were recorded on a micro mass Q-TOF mass spectrometer and
Shimadzu LCMS-2020. Electronic absorption spectra in solution
at 298 K were obtained on a Perkin-Elmer Lambda 750
spectrophotometer in the range 3300-178 nm. Magnetic
susceptibilities at 298 K were measured on a Sherwood
Magnetic Susceptibility Balance. The X-band electron
paramagnetic resonance (EPR) spectra in a temperature range
of 298 to 113 K were measured on a Magnettech GmbH
Nickel(II) and ruthenium(II) complexes of gmma of the types
trans-[NiII(gmma)Cl2]
(
1
), trans-[RuII(gmma)Cl2]
(
2)
and
[RuII(gmma)(PPh3)Cl]Cl (3+Cl−) were isolated. The notable
observation is that the electro-chemically reduced trans-
[NiII(gmma•−)Cl2]−
( (
1−) and trans-[NiII(gmma2−)Cl2]2− 12−) ions
are not stable in solution and undergo a chemical conversion
to a square planar dinuclear nickel(II) complex, predicted as
[(μ-NSNS-gmma)Ni2Cl3(PF6)] (4PF6), where μ-NSNS-gmma is a
2 | J. Name., 2012, 00, 1-3
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MiniScope MS400 spectrometer (equipped with temperature
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DOI: 10.1039/C6NJ02903E
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[RuII(gmma)(PPh3)Cl]+Cl− (3+Cl−). To a solution of
2 (118 mg,
controller TC H03), where the microwave frequency was 0.25 mmole) in EtOH (30 mL) at 320 K, PPh3 (314.4 mg, 1.2
measured with an FC400 frequency counter. The EPR spectra mmol) was added. The mixture was refluxed for 2 h and
were simulated using EasySpin software package. The electro allowed to cool to room temperature (298 K). Dark-green
analytical instrument BASi Epsilon-EC was used for cyclic microcrystals of 3+Cl− separated out, which were filtered and
voltammetric experiments and spectroelectrochemistry dried in air. 3+Cl− was further purified on a basic alumina
measurements.
column: the unreacted 2 was separated using CH2Cl2 as an
eluent, while 3+Cl− was collected using a mixture of CH2Cl2 and
Materials.
The precursor [RuII(PPh3)3Cl2] was prepared by a reported MeOH (20:1) solvents as an eluent. Yield: 72 mg (~40% with
procedure.11
Syntheses. Glyoxalbis(2-mercaptoanil) (gmma). To a 40% solution of 3+Cl− in CH2Cl2 with few drops of methanol afforded
aqueous solution of glyoxal (3 mmol), 2- single crystals for X-ray structure determination. ESI (positive
(methylmercapto)aniline (1.12 gm, 8 mmol) was added and ion)- MS in CH3OH; m/z: 699.27 [
]+. 1H NMR (CDCl3, 300 MHz,
respect to 2). Slow diffusion of n-hexane to the dark green
3
mixed well with a glass rod. The mixture turned yellow. To the 295 K): δ (ppm) = 8.04 (d, 2H), 7.35 (t, 4H), 7.17-7.26 (m, 19H),
yellow paste, methanol (15 mL) was added and stirred for 1 h 2.96 (s, 6H). Anal. Calcd. for C34H31N2PS2RuCl (3+Cl−): C, 58.40;
at 310 K. It was filtered and the residue was dried in air and H, 4.47; N, 4.01; Found: C, 58.33; H, 4.42; N, 3.96; IR (KBr,
collected. gmma was further re-crystallized in CH2Cl2 and EtOH νmax/cm-1): 3059 (vs, νC-H(aromatic)), 3050 (s), 2922 (s, νC-H(aliphatic)),
mixture (10:1). Slow evaporation of yellow solution of gmma 1646 (s), 1582 (m, CPh=N-), 1452 (s), 1432 (s), 1270 (s) 1088
at 298 K afforded single crystals of gmma, which were (s), 953 (s), 782 (s), 749 (s), 697 (vs, νRu−P(sym)), 530 (vs,
collected for X-ray structure analysis. Yield: 0.62 gm (~69% νRu−P(asym)).
with respect to glyoxal). ESI (positive ion)-MS in CH3OH; m/z:
300.03 (gmma). 1H NMR (CDCl3, 500 MHz, 295 K): δ (ppm) = (PF6)]−
[(μ-NSNS-gmma)Ni2Cl3(PF6)] (4PF6), [(μ-NSNS-gmma•−)Ni2Cl3
(4PF6−), trans-[RuIII(gmma)Cl2]+ (2+),
trans-
8.42 (s, 2H), 7.34 (d, 1H), 7.32 (d, 1H), 7.25 (t, 2H), 7.18 (t, 2H), [RuII(gmma•−)Cl2]− (2−) and [RuII(gmma•−)(PPh3)Cl] (3). These
7.07 (d, 1H), 6.71 (d, 1H), 2.49 (s, 6H). Anal. Calcd. for complexes were not isolated. However, these were generated
C16H16N2S2 (gmma): C, 63.96; H, 5.37; N, 9.32. Found: C, 63.89; chemically and electrochemically for spectroelectrochemical
H, 5.28; N, 9.25. IR (KBr, νmax/cm-1): 3047 (m; νC-H(aromatic)), 2915 measurements, mass and EPR spectra.
(s; νC-H(aliphatic)), 1605 (vs, νCPh=N-), 1571 (s), 1459 (vs), 1437 (vs), X-ray crystallographic data collection and refinement of the
1306 (m), 1276 (m), 1068 (s), 749 (vs), 685 (w).
trans-[NiII(gmma)Cl2] (1). To a solution of gmma (301 mg, 1
structures (CCDC 1497586-1497589)
Single crystals of gmma (yellow), 1.CH2Cl2 (green), 2 (green)
mmol) in EtOH (30 mL) at 320 K, hydrated NiCl2 (238 mg, 1 and 3+Cl−.H2O (dark green) were picked up with nylon loops
mmol) was added. The mixture was refluxed for 45 min and and mounted on a Bruker Kappa-CCD and Bruker AXS D8
allowed to cool to room temperature (298 K). Dark-green QUEST ECO diffractometer (at 296 K) diffractometer equipped
microcrystals of
residue were dried in air. Yield: 0.231 gm (~54% with respect monochromator (Mo Kα, λ = 0.71073 Å). Final cell constants
to nickel). was further re-crystallized in CH2Cl2. Evaporation were obtained from least-squares fits of all measured
of green CH2Cl2 solution of under argon afforded single reflections. Structures were readily solved by Patterson
crystals of .CH2Cl2, which were collected for X-ray structure methods and subsequent difference Fourier techniques. The
analysis. ESI (positive ion)-MS in CH3OH; m/z: 392.91 [
-Cl]+. crystallographic data are given in Table S2. XS. Ver. 2013/1,12a
Anal. Calcd. for C16H16N2S2NiCl2 (
): C, 44.69; H, 3.75; N, 6.51; XT. Ver. 2014/412b and XL. Ver. 2014/712c were used for the
1 separated out, which were filtered and the with a Mo-target rotating anode X-ray source and a graphite
1
1
1
1
1
Found: C, 44.57; H, 3.68; N, 6.40; IR (KBr, νmax/cm-1): 3001 (m, structure solution and refinement. All non-hydrogen atoms
νC-H(aromatic)), 2915 (s, νC-H(aliphatic)), 1578 (vs, CPh=N-), 1470 (s), were refined anisotropically. Hydrogen atoms were placed at
1410 (m), 1378 (s), 942 (m), 917 (m), 760 (vs).
calculated positions and refined as riding atoms with isotropic
trans-[RuII(gmma)Cl2] (2). To a solution of gmma (60 mg, 0.2 displacement parameters.
mmole) in EtOH (30 mL) at 320 K, [RuII(PPh3)3Cl2] (200 mg, 0.2 Density functional theory (DFT) and time dependent (TD) DFT
mmol) was added. The mixture was refluxed for 45 min and calculations
allowed to cool to room temperature (298 K). Dark-green
microcrystals of
All calculations reported in this article were done with the
separated out, which were filtered and dried Gaussian 03W13 program package supported by GaussView
2
in air. Yield: 66 mg (~70% with respect to ruthenium). Single 4.1. The DFT14 and TD DFT15 calculations were performed at
crystals for X-ray structure determination were grown by slow the level of a Becke three-parameter hybrid functional with
diffusion of n-hexane to the dark green CH2Cl2 solution of
2
.
the nonlocal correlation functional of Lee-Yang-Parr (B3LYP).16
ESI (positive ion)- MS in CH3OH; m/z: 436.87 [2
-Cl]+. 1H NMR Gas-phase geometries of the ligands and complexes were
(CDCl3, 500 MHz, 295 K): δ (ppm) = 9.28 (s, 1H, CH=N), 8.00 (s, optimized using Pulay’s direct inversion17 in the iterative
1H, CH=N), 7.67 (d, 2H), 7.65 (d, 2H), 7.54 (t, 2H), 7.47 (t, 2H), subspace (DIIS), “tight” convergent SCF procedure,18 ignoring
3.02 (s, 6H). Anal. Calcd. for C16H16N2S2RuCl2 (
3.41; N, 5.93; Found: C, 40.56; H, 3.33; N, 5.81; IR (KBr,
νmax/cm-1): 3066 (s, νC-H(aromatic)), 2919 (s, νC-H(aliphatic)), 1615 (vs), for the optimizations of other species are: singlet for gmma,
2): C, 40.68; H, symmetry. The gas phase geometries of trans-[Ni(gmma)Cl2]
(
1) was optimized with triplet spin state. The spin states used
1560 (vs, CPh=N-), 1475 (vs), 1418 (vs), 963 (s), 761 (s).
trans-[Ru(gmma)Cl2] (2 (
), [RuII(gmma)(PMe3)Cl]+ 3Me+) and
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Cl
Cl
Cl
trans-[Ni(gmma)Cl2]2− 12−); doublet for trans-[Ni(gmma)Cl2]−
(
H
N
H
N
H
N
H
N
H
N
H
N
(
1−), trans-[Ru(gmma)Cl2]− (2−), trans-[Ru(gmma)Cl2]+ (2+) and
+e
-e
+e
NiII
NiII
NiII
[RuII(gmma)(PMe3)Cl] (3Me). In all calculations, a LANL2DZ basis
set along with the corresponding effective core potential (ECP)
was used for nickel, zinc and ruthenium metals.19-21 The
valence double-ζ basis set 6-31G22 for H was used. For the non-
hydrogen atoms C, N, O, P, S and Cl, valence double-ζ with
diffuse and polarization functions, 6-31+G*23 as basis set was
employed for all calculations. The percentage contributions of
metal, chloride, gmma and gmha ligands to the frontier
orbitals were calculated using the GaussSum program
S
S
S
S
S
S
Me
Me
Me
Me
Me
Me
Cl
Cl
Cl
1-
12-
1
(unstable)
(unstable)
-(gmma + Cl-) +PF6
F
F
F
F
P F
Cl
Ni
F
Me
S
N
N
S Me
Ni
package.24 The 60 lowest singlet excitation energies on each of
Cl
Cl
+
the optimized geometries of gmma,
1,
2
and 3Me were
4PF6
calculated by the TD DFT method.25 The natures of transitions
were calculated by adding the probability of the same type
among α and β molecular orbitals.
Scheme 2 Reduction induced chemical change of
1
.
tetrabutylammonium hexafluorophosphate displayed m/z
peaks due to 4PF6 (major).
Results and discussion
Molecular geometries
Syntheses
Single crystal X-ray structure determinations confirmed the
The α-diimine ligand, glyoxalbis(2-methylmercaptoanil)
(gmma) and the coordination complexes of it reported in this
article are summarized in Chart 2. Details of the syntheses are
outlined in the experimental section. Towards nickel(II) ion
gmma is a flexidentate ligand exhibiting two types of binding
modes: tetradentate N2S2-donor as gmma and bis(methylthio-
imine) donor bridging ligand10 abbreviated as μ-NSNS-gmma.
tetradentate N2S2-binding mode of gmma in 1.CH2Cl2, 2 and
3+Cl−.H2O. To compare the bond parameters of the diimine
fragments of the complexes, single crystal X-ray structure of
gmma was also determined. The crystallographic data are
summarized in Table S1. The significant bond parameters are
summarized in Table 1. The ligand, gmma crystallizes in the
P21/n space group and it exhibits trans geometry (Fig. S3). The
average C=N and NC-CN lengths of gmma are 1.212(3) and
1.436(4) Å.
Reaction of gmma with NiCl2.xH2O afforded 1. 2 was isolated
from a reaction of [RuII(PPh3)3Cl2] with gmma in boiling
ethanol. Reaction of
2
with excess triphenyl phosphine in
.
1.CH2Cl2 crystallizes in the Pnma space group. The molecular
boiling ethanol afforded 3+
structure in the crystals and the atom labeling scheme are
illustrated in Fig. 1(a). The gmma ligand with nickel(II) ion,
excluding the two methyl substituents which are cis to each
other, is approximately planar and the two Cl ligands reside
trans to each other. The average Ni(1)-Nimine and Ni(1)-S(1)
distances are 2.030(2) and 2.436(1) Å. The average NiII-Cl
lengths are 2.395(1) Å. These lengths correlate well to those
reported in the similar types of diimine complexes of nickel(II)
ion.6 The average C=N lengths, 1.282(2) Å, are relatively
longer. However, these bond parameters are quite consistent
to the coordination of neutral gmma ligand to nickel(II) ion.
Notably, the reduced 1− and 12− ions in solution are unstable
and the octahedral complex ions convert to a square planar
dinuclear nickel(II) complex. The chemical conversion of 1− and
12− ions was investigated by ESI mass spectroscopy. The
constant potential coulometric reductions of
1 → 1 →
1− and
12− (respectively at -0.5 V and -0.9 V vs Fc+/Fc couple, vide
infra) in CH2Cl2 using tetrabutylammonium hexafluoro
phosphate as electrolyte were performed. In both cases the
yellowish green solutions of the reduced complexes in air
turned brown due to the formation of 4PF6 as depicted in
Scheme 2. Analyses of these solutions by ESI mass spectra
revel the m/z peaks at 520 and 630 corresponding to
[Ni2(gmma)Cl3]+ and [Ni2(gmma)Cl2(PF6)]+ molecular ions as
illustrated in Fig. S2(a). During the chromatographic
separation, 4PF6 decomposes and isolation of pure 4PF6 did not
succeed. However, the brown coating on the platinum working
electrode obtained during electrolysis was the pure 4PF6
authenticated by the ESI mass spectroscopy (see, Fig. S2(b)).
2
crystallizes in the P21/c space group and iso-structural to
1
.CH2Cl2. The molecular geometry in the crystals and the atom
labeling scheme are shown in Fig. 1(b). The average RuII-Nimine
and RuII-SMe lengths are 1.981(3) and 2.367(2) Å. The extent
of deformation of the α-diimine fragment of
2 is relatively
larger. The average C=N lengths are 1.321(5) Å, while, the NC-
CN length is 1.401(7) Å as listed in Table 1. The similar features
of the bond parameters were established in other α-diimine
Chemical reduction of
1
also results in the formation of the
on addition of
complexes of ruthenium(II).26,27 Thus,
2 is defined as a neutral
[Ni2(gmma)Cl3]+ . The green CH2Cl2 solution of
1
gmma complex of ruthenium(II) ion as defined by the 2Ru(II)L
two equivalent of cobaltocene turned immediately brown that
gave the m/z peak only due to [Ni2(gmma)Cl3]+. However the
ESI mass spectrum of the solution obtained after the chemical
state of Chart 3. The relatively longer C=N and shorter NC-CN
lengths of
the di-radical state, 2Ru(III)L•− as depicted in Chart 3, to the
ground electronic state of
2 can be explained by a resonance contribution of
reduction of 1 by cobaltocene in presence of
2.
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Cl
Cl
H
H
N
H
N
H
N
N
RuII
RuIII
S
S
S
S
Me
Me
Me
Me
X
X
2Ru(II)L
2Ru(III)L
X = Cl
3+Ru(III)L
X = PPh3
3+Ru(II)L
Chart 3 Two possible descriptions of the (one and only) electronic state
the π-acidic PPh3 ligand to 3+ ion. Due to stronger dRu → PPh3
back bonding, dRu→ π* back bonding is less effective in 3+ ion.
Consequently, the average RuII-Nimine lengths, 2.008(3) Å of 3+
ion are relatively longer than those found in
2 (see Table
1).The diimine fragment of 3+ is relatively less deformed
inferring the smaller contribution of 3+Ru(III)L•− state to the
ground electronic state of 3+ ion. The average C=N and NC-CN
lengths are 1.303(5) and 1.432(9) Å.
Redox activities
The redox activities of gmma, 1, 2 and 3
+ were investigated by
cyclic voltammetry in CH2Cl2 at 298 K. The redox potential data
referenced to ferrocenium/ferrocene (Fc+/Fc) couple are
summarized in Table S2. It is observed that both cathodic and
anodic waves due to gmma/gmma•− and gmma•+/gmma redox
couples are irreversible as shown in Fig. 2(a). However, the
cathodic wave due to gmma/gmma•− redox couple in
complexes is reversible.
1 exhibits two cathodic waves at -0.34
V (peak-to-peak separation, 260 mV) and -0.59 V (peak-to-
peak separation, 90 mV). The former wave is assigned to
Fig. 1 Molecular geometries of (a) 1.CH2Cl2, (b) 2 and (c) 3+Cl−.H2O in crystals (40% [NiII(gmma)]/[NiII(gmma•−)]− (
thermal ellipsoids; solvents and anion are omitted for clarity).
1
−) redox couple, while the latter
2−). The EPR and
ESI mass spectra of the reduced species authenticated that 1−
is assigned to [NiII(gmma•−)]/[NiII(gmma2−)]2−
(1
3
+Cl−.H2O that crystallizes in the
and
change to
1
2− ions are not stable in solution and undergo a chemical
The molecular geometry of
)/m space group, and the atom labeling scheme are shown
P6(3
4
PF6. The instability of the 1− and
1
2− ions makes the
−
first redox wave (E ) due to the gmma/gmma• redox couple,
in Fig. 1(c). A split model is used to refine the disordered
phenyl rings and platon/SQUEEZE is used to remove
disordered solvent from a solvent channel (see ESI†). The
approximate geometry of 3+ ion that incorporates a PPh3
1
½
irreversible (ic/ia = 1.19) as shown in Fig. 2(b). However, the
−
2
2−
second cathodic wave (E ) due to gmma• / gmma redox
½
couple in the experimental scan-period is reversible (ic/ia =
ligand, is similar to that of
2. The bond parameters of the
1.0). The redox activity of dinuclear species is different from
−
that of
1. The
μ
-NSNS-gmma/
μ
-NSNS-gmma• redox couple of
coordination sphere reflect the effect of the coordination of
4
PF6 at -1.28 is reversible (ic/ia = 1.0) as depicted in Fig. 2(c).
Table 1 Selected experimental bond lengths (Å) of gmma,
obtained from the B3LYP/DFT calculations
1.CH2Cl2,
2
and 3+Cl−.H2O and the corresponding calculated bond parameters of
1,
2
,
2−
,
3Me+
,
3Me and 3Me−
Bond
Types
1
2
3+
−
−
gmma
1
.CH2Cl2
exptl
1
1−
12
2
2
2−
3+Cl−.H2O
exptl
3Me+
3Me
3Me
(
exptl
)
(
)
(calcd) (calcd) (calcd)
(
exptl
)
(calcd)
(calcd)
)
(
)
(calcd)
(calcd) (calcd)
avg M-Nimine
avg M-SMe
avg M-Cl
M-PPh3
-
-
-
-
2.030(2) 2.084
2.436(1) 2.527
2.395(1) 2.405
2.062
2.597
2.452
1.937
2.270
2.328
-
1.981(3)
2.367(2)
2.391(2)
-
2.001
2.445
2.443
-
2.026
2.439
2.490
-
2.008(3)
2.357 (2)
2.461(2)
2.320(2)
1.303(5)
1.432(9)
2.024
2.449
2.465
2.395
1.320
1.426
2.049
2.439
2.520
2.340
1.351
1.394
2.062
2.448
2.583
2.295
1.385
1.349
-
-
avg C=N
1.212(3) 1.282(2) 1.291
1.436(4) 1.460(3) 1.457
1.333
1.406
1.395
1.379
1.321(5)
1.401(7)
1.327
1.415
1.359
1.385
NC-CN
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ARTICLE
Both anodic and cathodic waves of
Journal Name
2
at +0.48 V due to
[RuIII(gmma)]/[RuII(gmma)] redox couple (ic/ia = 1.0) and -1.18
V due to [RuII(gmma)]/[RuII(gmma•−)]− redox couple (ic/ia = 1.0)
are reversible as illustrated in Fig. 3(a). The similar anodic
wave is absent in 1 as the corresponding nickel(III) state is hard
to achieve with the softer gmma ligand. 3+ ion exhibits two
cathodic waves at -0.73 and -1.36 V. The first one is reversible
(ic/ia = 1.0), while the second wave is irreversible (ic/ia = 1.5) as
illustrated in Fig. 3(b). The potential data implies that 3+ is
Fig. 4 X-band EPR spectra of 1- ion (a) CH2Cl2 solution (298 K) and (b) CH2Cl2 frozen glass
(113 K) ((i) experimental (black), (ii) simulated (red)); (c) chemically generated 4PF6− at
113 K.
easily reducible than 2
. The second reduction of 3+ ion due to
gmma•−/gmma2− redox couple, is not observable in case of
2. It
a metal centred St = ½ state and exhibits an anisotropic EPR
is the effect of introducing π-acidic PPh3 ligand to 3+ ion.
spectrum. However, the EPR spectrum of
reduction of the crude product
PF6 with excess cobaltocene in
CH2Cl2 reveals a signal at g = 1.997 as depicted Fig. 4(c). It is
4
PF6− ion achieved by
Notably, the anodic wave due to [RuIII(gmma)]/[RuII(gmma)]
4
couple of 3
+ ion is completely irreversible.
analyzed that the
of gmma•−.
4
PF6− ion is a square planar nickel(II) complex
Fig. 2 Cyclic voltammograms of (a) gmma, (b) 1 and (c) 4PF6 in CH2Cl2 at 298 K.
Conditions: 0.20 M [N(n-Bu)4]PF6 supporting electrolyte; platinum working electrode;
scan rate 100 mVs-1
.
Fig. 5 X-band EPR spectra of 2− (a) CH2Cl2 solution (298 K) (i) black, experimental
spectrum; (ii) red, simulated spectrum considering the trans-[RuIII(gmma2−)Cl2]− state;
(iii) blue, simulated spectrum considering the trans-[RuII(gmma•−)Cl2]− state; (iv) green,
simulated spectrum considering the trans-[RuII(gmma•−)Cl2]− and trans-
[RuIII(gmma2−)Cl2]− canonical structures and (b) CH2Cl2 frozen glass (113 K) (i) black,
experimental spectrum; (ii) red, simulated spectrum considering the trans-
[RuIII(gmma2−)Cl2]− state; (iii) blue, simulated spectrum considering the trans-
[RuII(gmma•−)Cl2]− state; (iv) green, simulated spectrum considering the trans-
[RuII(gmma•−)Cl2]− and trans-[RuIII(gmma2−)Cl2]− canonical structures.
The EPR spectra of the chemically reduced 2− ion recorded at
different temperature (298-113 K) are shown in Fig. S4. The
fluid solution and the frozen glass spectra with simulations are
depicted in Fig. 5. It is noted that in addition to an isotropic
signal due to trans-[RuII(gmma•−)Cl2]− state at g = 2.000, the
Fig. 3 Cyclic voltammograms of (a) 2 and (b) 3+Cl− in CH2Cl2 at 298 K. Conditions: 0.20 M
[N(n-Bu)4]PF6 supporting electrolyte; platinum working electrode (Scan rate 100 mVs-1).
EPR spectroscopy
Magnetic susceptibility measurements at 298 K confirmed the
fluid solution EPR spectrum of 2
− ion contains another signal at
paramagnetism of
1 (μeff = 2.85). The parameters of the EPR
g = 2.059. In frozen glass the anisotropic component gives a
rhombic signal at g1 = 2.180, g2 = 2.130 and g3 = 1.860. The
frozen glass EPR spectrum of 2− ion was simulated considering
trans-[RuII(gmma•−)Cl2]− and trans-[RuIII(gmma2−)Cl2]− canonical
states. The anisotropic signal is reproducible both
chemically/electrochemically, eliminating the possibility of the
existence of the paramagnetic impurity. The spectra are similar
in presence of tetrabutylammonium chloride precluding the
chloride dissociation. It infers that in 2− ion the spin is shared
by both ruthenium and gmma ligand.
measurements are listed in Table S3 and the simulated g
values and the coupling constants are summarized in Table 2.
In the X-band EPR spectrum no signal of
to large zero field splitting.28 However,
1
was detected, due
1
− ion obtained after
reduction of
1 by cobaltocene in CH2Cl2, exhibits an isotropic
EPR signal due to St = ½ state at g = 2.184 as illustrated in Fig.
4(a). The frozen glass spectrum displays a rhombic signal at g1
= 2.230, g2 = 2.185 and g3 = 2.089 as shown in Fig. 4(b), which
corroborate well to those of the nickel(I) complexes.6 The St =
½ spin state of 1− can be achieved either by reduction of
nickel(II) ion or by reduction of gmma to gmma•− that couples
The g-anisotropy (∆g) of the frozen glass is 0.32 which is
relatively larger than those observed in organic radicals.6,9,26,27
However, the ∆g value correlates well to that observed in the
ruthenium(III) complexes.26,27 Thus the 2− is defined as a
resonance hybrid of trans-[RuII(gmma•−)Cl2]− and trans-
[RuIII(gmma2−)Cl2]− states, the latter state is responsible for the
to St = 1 state of an octahedral nickel(II) ion. In case of
1
reduction occurs at the diimine fragment converting gmma to
gmma•−. The anion radical couples anti-ferromagnetically to
one of the electrons of the nickel(II) ion (vide infra) producing
6 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
Table 2 X-Band EPR spectral parameters of 1−, 2−, 2+, 3 and 4−
The X-band EPR spectra of
3
(CH2Cl2 solution and frozen glass)
at different temperature (298-113 K) are illustrated in Fig. S6.
The spectra are similar to that of 2− ion. Both solution and
Complexes
g1/g2/g3
giso/gav
a∆g
frozen glass EPR spectra of 3 were simulated considering
[RuII(gmma•−)] and [RuIII(gmma2−)] canonical states as
illustrated in Fig. 6(a) and Fig. 6(b). However, the ∆g value in
1−
CH2Cl2 solution (298 K)
CH2Cl2 frozen glass (113 K)
2.184
2.168
0
2.230/2.185/2.089
0.14
case of
1.905, ∆g = 0.22), predicting a smaller contribution of
[RuIII(gmma2−)] state to in comparison to that in 2− ion. It is
the effect of introduction of π acidic PPh3 ligand to
3 is relatively small (g1 = 2.126, g2 = 1.995 and g3 =
2−
CH2Cl2 solution (298 K)
contribution of ccs:
trans-[RuII(gmma•−)Cl2]−
trans-[RuIII(gmma2−)Cl2]−
CH2Cl2 frozen glass (113 K)
contribution of ccs:
3
3.
1.998
2.059
0
0
Density functional theory (DFT) calculations and the electronic
structures of the complexes
trans-[RuII(gmma•−)Cl2]−
trans-[RuIII(gmma2−)Cl2]−
2.002
2.056
In conjunction with the X-ray bond parameters and EPR
spectroscopy, DFT calculations at the B3LYP level of the theory
2.180/2.130/1.860
(bA= 53/76/13 G)
0.32
0.20
were used to elucidate the electronic structures of 1, 2 .
and 3+
2+
gmma, gmma•− and [ZnII(gmma)Cl2]. To analyze the
CH2Cl2 frozen glass (113 K)
2.165/2.089/1.968
(A= 36/10/36 G)
2.074
geometrical features and the bond parameters of the ligand,
the gas phase geometries of the neutral (E form with singlet
3
spin state) and one electron reduced (doublet spin state)
gmma were optimized. The calculated C=N lengths of gmma
and gmma•− are 1.285 and 1.333 Å. The NC-CN lengths of
gmma and gmma•− are 1.458 and 1.405 Å. In the reduced
analogue the atomic spin is dominantly localized on the imine
function inferring the formation of a π-anion radical,
abbreviated as gmma•− as depicted in Fig. S7. The bond
CH2Cl2 solution (298 K)
contribution of ccs:
[RuII(gmma•−)(PPh3)Cl]
[RuIII(gmma2−)(PPh3)Cl]
CH2Cl2 frozen glass (113 K)
contribution of ccs:
[RuII(gmma•−)(PPh3)Cl]
[RuIII(gmma2−)(PPh3)Cl]
2.005
2.068
0
0
2.005
2.009
2.126/1.995/1.905
(A=17/9/17 G)
0.22
0
parameters of the coordinated
Z form were calculated
optimizing [ZnII(gmma)Cl2] complex with singlet spin state. The
calculated C=N and NC-CN lengths of the coordinated Z form
are 1.289 and 1.461 Å.
4PF6−
1.997
aΔg = gmax - gmin bA is due to 99,101Ru = 5/2 nucleus; ccs = canonical states
;
−
trans-[NiII(gmma)Cl2] (1), trans-[NiII(gmma• )Cl2]− (1−) and
cis-[NiII(gmma2−)Cl2]2− (12−). Gas phase geometries of 1− and
1,
12− were optimized respectively with the triplet, doublet and
singlet spin states. The calculated bond parameters of
correlate well to those obtained from the single crystal X-ray
structure determination of .CH2Cl2 (see Table 1). It is to be
1
1
noted that the calculated bond parameters of the coordinated
diimine fragment of these three species are significantly
different. In 1, the calculated average C=N and NC-CN lengths
are 1.291 and 1.457 Å which are similar to those observed in
the optimized geometry of the gmma ligand and
[ZnII(gmma)Cl2]. It infers the coordination of the neutral gmma
Fig. 6 X-band EPR spectra of 3 (a) CH2Cl2 solution at 298 K, (i) black, experimental
spectrum; (ii) red, simulated spectrum considering the [RuIII(gmma2−)(PPh3)Cl] state; (iii)
blue, simulated spectrum considering the [RuII(gmma•−)(PPh3)Cl] state; (iv) green,
simulated spectrum considering [RuIII(gmma2−)(PPh3)Cl] and [RuII(gmma•−)(PPh3)Cl]
canonical structures. (b) CH2Cl2 frozen glass at 113 K, (i) black, experimental spectrum;
(ii) red, simulated spectrum considering the [RuIII(gmma2−)(PPh3)Cl] state; (iii) blue,
simulated spectrum considering the [RuII(gmma•−)(PPh3)Cl] state; (iv) green, simulated
spectrum considering the [RuIII(gmma2−)(PPh3)Cl] and [RuII(gmma•−)(PPh3)Cl] canonical
structures.
ligand to nickel(II) ion in 1. The atomic spin of 1 is shown in Fig.
7(a). On the contrary, the calculated C=N length of 1− ion,
1.333 Å, is relatively longer, while the NC-CN length, 1.406 Å, is
relatively shorter. The trend is consistent with those of diimine
anion radicals coordinated to the transition metal ions.6,26,27 It
establishes that in
1
−, gmma ligand is reduced to gmma•−
which results the anti-ferromagnetic coupling to nickel(II) ion
affording a St = ½ spin state. The atomic spin obtained from
the Mulliken spin population analysis, disperses on gmma as
shown in Fig. 7(b), corroborating to the formation of gmma•−,
coordinated to the nickel(II) ion. Thus, 1− ion is defined as a
anisotropy of the spectrum. The X-ray bond parameters of the
diimine fragment also suggested
a
contribution of
ruthenium(III) state to . The CH2Cl2 frozen glass EPR spectrum
2
of 2+ is anisotropic as illustrated in Fig. S5. The simulated g
parameters as listed in Table 2, are similar to those reported in
cases of ruthenium(III) complexes incorporating redox non-
innocent diimine fragments.26,27 It infers that 2+ ion is a
ruthenium(III) complex of the type trans-[RuIII(gmma)Cl2]+.
octahedral gmma•− complex of nickel(II) ion of the type trans
-
[NiII(gmma•−)Cl2]−. The calculated bond parameters and the
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Journal Name
2-
Cl
H
and NC-CN lengths of the diimine fragment are 1.327 and
1.415 Å (see Table 1). However, the CSS solution of is stable
and no instability due to open shell singlet (OSS) perturbation
was recorded, discarding the possibility of
Ru(III)L•– as a ground
affirmed the mixing
Cl
-
H
N
H
N
H
N
N
H
2
SMe
H
N
N
+e
+e
NiII
NiII
Cl
Cl
S
NiII
S
S
S
Me
Me
2
Me
Me
S
Cl
Me
Cl
state. Analyses of molecular orbitals of
2
12-
1-
of the π* orbital with the ruthenium d-orbitals as depicted in
1
6
Figure S8, resulting in a delocalization of the t2g electrons to
the diimine fragment. The feature promotes
contribute to . The experimental and calculated bond
parameters of the diimine fragment suggest a mixing of 2Ru(II)L
and 2Ru(III)L•– states in 2 29
The features are similar to those
2
Ru(III)L•– state to
Scheme 3
2
.
observed in the diimine and osazone complexes of
ruthenium(II) reported recently.26 The shorter average C=N
lengths, 1.317 Å, and the localization of atomic spin on
ruthenium as illustrated in Fig. 8(a) confirmed that the
paramagnetic 2+ ion is a ruthenium(III) complex of the type
trans-[RuIII(gmma)Cl2]+. The calculated bond parameters of the
Fig. 7 Atomic spin of (a) 1 and (b) 1− (isovalue = 0.004).
diimine fragment and the coordination sphere of
notably different from those of and
+ ion.
The average C=N lengths of the diimine fragment of
2
- ion are
2
2
2
− ion is
1.359 Å which is relatively longer than those of [ZnII(gmma)Cl2]
and 2+ ion. The NC-CN length is relatively shorter, 1.385 Å. The
trend corroborates well to those observed in gma•– and
diimine anion radical complexes of transition metal ions.5,6,8,9
The atomic spin obtained from the Mulliken spin population
analysis, as shown in Fig. 8(b), is consistent to the existence of
(a)
(b)
gmma•− in − ion. However, a significant amount of spin (~30%)
2
shared by one of the t2g orbitals of the ruthenium ion, infers a
contribution of the trans-[RuIII(gmma2−)Cl2]− state to 2− ion.
The contribution of trans-[RuIII(PQ2−)(PPh3)2Cl2]− and trans-
[RuII(PQ•−)(PPh3)2Cl2]− states similarly was assigned to the
reduced species of the 9,10-phenanthrenesemiquinonate
anion radical (PQ•−) complexes of ruthenium(III) of the type
trans-[RuIII(PQ•−)(PPh3)2Cl2].30 Thus, the ground electronic state
of 2- ion is defined as a resonance hybrid of trans-
[RuII(gmma•−)Cl2]− and trans-[RuIII(gmma2−)Cl2]− states. No
contribution of the ruthenium(I) state is predicted in these
chemical systems.31
(c)
Fig. 8 Atomic spin of (a) 2+, (b) 2− and (c) 3Me (isovalue = 0.004).
molecular geometry of the singlet 12− ion are surprisingly
different from those of the octahedral geometries of the
paramagnetic
1
and 1− ion. The closed shell singlet (CSS)
solution converged to a square planar nickel(II) complex as
shown in Scheme 3. The optimized geometry is illustrated in
Chart S1(a). The calculated C=N lengths are 1.395 and 1.359 Å,
while the NC-CN length is 1.379 Å. The calculation infers that
the dianionic gmma2− coordinates the nickel(II) ion as a NS-
donor bidentate ligand. For comparison, the square planar
geometry of 12− with NN-chelate (see Chart S1(b)) was also
optimized with singlet spin state. However, the square planar
complex with NS-chelate is 1.87 kJ/mole, lower in energy than
that the NN-chelate. The DFT calculations reveal that
octahedral 12− ion is not stable and undergoes geometrical
reorganization, which is the origin of the irreversibility of the
[RuII(gmma)(PPh3)Cl]+ (3+), [RuII(gmma•−)(PPh3)Cl]
↔
[RuIII(gmma2−)(PPh3)Cl] (3) and [RuII(gmma2−)(PPh3)Cl]− (3−)
The calculated C=N and NC-CN lengths of the diimine
fragments
of
[RuII(gmma)(PMe3)Cl]+
(
3
3
Me+),
Me−),
[RuII(gmma)(PMe3)Cl] (
3
Me) and [RuII(gmma)(PMe3)Cl]− (
optimized with singlet, doublet and singlet spin states are
significantly different (see Table 1). In 3Me+ 3Me 3Me−
conversions, the C=N lengths gradually increase, while NC-CN
lengths decrease as: C=N, (
Me+, 1.320; Me, 1.351; Me−, 1.385
Å) and NC-CN (
Me+, 1.426; Me, 1.394; Me−, 1.349 Å). The CSS
→
→
first cathodic redox wave of 1.
trans-[RuII(gmma)Cl2] (2), trans-[RuIII(gmma)Cl2]+ (2+) and
trans-[RuII(gmma•−)Cl2]− ↔ trans-[RuIII(gmma2−)Cl2]− (2−). Gas
3
3
3
3
3
3
solution of 3Me+ ion is also stable inferring that 3+ ion is a
ruthenium(II) complex of neutral gmma ligand. Similar to 2−
ion, atomic spin of 3Me scatter on the both diimine fragment
phase geometries of
2,
2+ and 2− ions were optimized
respectively with singlet, doublet and doublet spin states. As
both metal ion and the coordinated gmma ligand are redox
and the ruthenium (~11%) as illustrated in Fig. 8(c). Thus 3 is
also defined as a resonance hybrid of [RuII(gmma•−)(PPh3)Cl]
and [RuIII(gmma2−)(PPh3)Cl] states. In comparison to 2− ion, the
non-innocent, the ground electronic state of
by the resonance structures of CSS (
Ru(II)L) and the diradical
open shell singlet (
Ru(III)L•–) states as illustrated in Chart 3. The
bond parameters of these two electronic states of the diimine
2 can be defined
2
2
atomic spin on ruthenium in
3 is relatively smaller, predicting a
lower stability of the ruthenium(III) state with PPh3 as a co-
ligand. The bond parameters of the gmma ligand of the 3Me−
fragment are significantly different. In 2, the calculated C=N
8 | J. Name., 2012, 00, 1-3
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Table 3 UV-vis absorption spectral data of gmma, 1, 2,
3+Cl−, 1−, 2−, 2+ and 3 in
correspond to those of the diimide state (C=N, 1.385 Å, Table
1) and it is defined as a gmma2− complex of ruthenium(II) of
the type [RuII(gmma2−)(PPh3)Cl]−.
CH2Cl2 at 298 K
Comp
gmma
λmax/nm (ε, 10-4 M-1 cm-1)
406 (0.19), 296 (0.55)
1
2
608 (0.002), 468 (0.14)sh, 414 (0.67), 386 (0.80), 369 (0.75)
648 (0.16), 501 (0.26)sh, 466 (0.61)sh, 437 (0.77), 302 (1.6)
744 (0.05), 646 (0.15), 468 (0.5)sh, 435 (0.76), 301 (1.6)sh
468 (0.10), 411 (0.52), 391 (0.59), 290 (0.50), 267 (0.82)
654 (0.04), 434 (0.08)sh, 287 (0.30)sh
Electronic spectra, spectroelectrochemical measurements and
time dependent (TD) DFT calculations
3+Cl−
1−
The UV-vis absorption spectra of gmma, 1, 2 and 3
+Cl− were
2−
recorded in CH2Cl2 at 298 K. The spectra are shown in Fig. 9
and the spectral data are summarized in Table 3. A qualitative
absorption spectrum of 4PF6 is depicted in Fig. S2. The origins
of the absorption bands were elucidated by the TD DFT
2+
650 (0.12), 416 (0.26)sh, 289 (0.59)
3
730 (0.05)sh, 575 (0.12), 395 (0.41), 287 (1.04)sh
calculations on gmma, 1, 2
and 3Me+ in CH2Cl2 using CPCM
model with the singlet spin state. The excitation energies with
the oscillator strengths and the transition types are also
summarized in Table S4. The absorption spectrum of gmma
Fig. 10 Spectroelectrochemical measurements showing the change of electronic
spectra during (a) 1 → 1− and (b) 3+ → 3 conversions in CH2Cl2 at 298 K.
Conclusion
In this article, the coordination chemistry of glyoxalbis(2-
methylmercaptoanil) (gmma) which is a N2S2 donor α-diimine
ligand, with nickel and ruthenium ions are disclosed. Nickel
and ruthenium complexes of the types trans-[NiII(gmma)Cl2]
(
1
), trans-[RuII(gmma)Cl2] (
(3+Cl−) are reported. The study authenticated that gmma is a
redox non-innocent flexidentate ligand. is a gmma complex
2
) and [RuII(gmma)(PPh3)Cl]+Cl−
Fig. 9 UV-vis spectra of (a) gmma, (b) 1, (c) 2 and (d) 3+Cl- in CH2Cl2 at 298 K.
1
of nickel(II), whereas 1− and 12− ions are gmma•− and gmma2−
complexes of nickel(II). However both 1− and 12− ions are not
stable in solution and undergo a chemical change to a
exhibits bands at 406 and 296 nm that are assigned to πAr-SMe
π* transition (Fig. 9(a)). In
, the similar transitions are
observed at 414 and 386 nm (Fig. 9(b)). The calculated wave
lengths ( cal) for these transitions of are 415.5 and 383.4 nm.
In addition, absorbs at 468 nm and the corresponding cal are
453.3 and 443.0 nm (Table S4) due to pCl→π* transitions.
→
1
−
dinuclear species. In presence of PF6 ion, they afford a
λ
1
dinuclear square planner nickel(II) complex, [(
gmma)Ni2Cl3(PF6)] (
PF6) detected by ESI mass spectra, where
-NSNS-gmma is a bis(methylthio-imine) donor bridging ligand.
μ-NSNS-
1
λ
4
2
μ
absorbs at 648, 501 and 466 nm (Fig. 9(d)). The corresponding
λcal are 646.1 and 492.1 nm respectively due to dRu→π* (MLCT
type) and dRu to mixed-dRu-π* charge transfer (MMLCT)
With ruthenium the chemistry is different. The relatively
longer C=N bonds of the diimine fragments propose a
contribution of [RuIII(gmma•−)] state in
2 2
and 3+ ion. - is a
transitions. The UV-vis absorption spectra of
Fig. 9(e) is similar to that of . In addition to an absorption
3
+ ion as shown in
resonance hybrid of trans-[RuII(gmma•−)Cl2]− and trans
[RuIII(gmma2−)Cl2]− states, while
is a resonance hybrid of
-
2
3
maximum at 578 nm, 3+ ion exhibits a NIR absorption band at
744 nm. The λcal due to the dRu→π* transitions are 754.2 and
547.7 nm.
[RuII(gmma•−)(PPh3)Cl] and [RuIII(gmma2−)(PPh3)Cl] states. 2+ is
a neutral gmma complex of ruthenium(III). The study infers
that the redox chemistry of gmma with harder nickel(II) ion is
different from that of the softer ruthenium(II) ion. Thus, the
redox and the structural chemistry of gmma with transition
metal ion is a subject of investigation.
The UV-vis/NIR absorption spectra of 1− 2− + and
, , 2 3 were
recorded in CH2Cl2 by spectroelectrochemical measurements
at 298 K and the spectral data are summarized in Table 3. The
conversions occur via several isosbestic points. The absorption
− and 3+
spectra of the 1→ 1 → 3 conversions are shown in Fig.
Acknowledgements
10, other are illustrated in Fig. S9. One of the important
features of the spectra of the reduced species is the decrease
Financial support received from Department of Science and
Technology (SR/S1/IC/0026/2012), Council of Scientific and
Industrial Research (2699/12/EMR-II) and University Grants
Commission (F. No. 43-214/2014(SR) New Delhi, India is
of the absorbance at the
analogues. It is due to the partial occupancy of the π* orbitals
in 1− − and and dM→π* transitions are perturbed.
λmax corresponding to the neutral
,
2
3
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ARTICLE
Journal Name
2009, 131, 1208 and relevant references therein; (k) C. C.
Lu , E. Bill , T. Weyhermüller , E. Bothe and K. Wieghardt, J.
Am. Chem. Soc., 2008, 130, 3181-3197; (l) Y. Liu, P. Yang, J.
Yu, X. -J. Yang, J. D. Zhang, Z. Chen, H. F. Schaefer and B. Wu,
Organometallics, 2008, 27, 5830; (m) H. Schumann, M.
Hummert, A. N. Lukoyanov and I. L. Fedushkin,
Organometallics, 2005, 24, 3891; (n) R. J. Baker, R. D. Farley,
gratefully acknowledged. P.S. is thankful to CSIR, New Delhi,
India, for fellowship (SRF) and D.S. gratefully acknowledged
DST (SR/S1/IC/0026/2012) New Delhi, India, for fellowship. We
sincerely acknowledge the support of Dr. Thomas
Weyhermüller,
Energiekonversion, Germany to refine the X-ray structure of
+Cl−.
Max-Planck-Institut
für
Chemische
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DOI: 10.1039/C6NJ02903E
Glyoxalbis(2-methylmercaptoanil) complexes of nickel and ruthenium:
radical versus non-radical states
Pinaki Saha, Debasish Samanta and Prasanta Ghosh*
Graphical abstract
The molecular and electronic structures of nickel(II) and ruthenium(II) complexes of glyoxalbis(2-
methylmercaptoanil) and their reduced and oxidized analouges are reported.