Unprecedented oxidation of half-sandwiched ruthenium(II) in the excess of ammonium hexafluorophosphate and formation of nanosized Ru-RuS2

Article abstract of DOI:10.1016/j.jorganchem.2012.05.022

The [{(η⁶-p-cymene)RuCl(μ-Cl)}₂] reacts with N-{2-(phenylthio)ethyl}morpholine (L) and excess NH₄PF₆ in CH₃OH at room temperature (24 h), resulting in [(η⁶- p-cymene)RuCl₂(L)][PF

Full text of DOI:10.1016/j.jorganchem.2012.05.022

Journal of Organometallic Chemistry 715 (2012) 33e38
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Unprecedented oxidation of half-sandwiched ruthenium(II) in the excess
of ammonium hexafluorophosphate and formation of nanosized RueRuS2
*
Pradhumn Singh, G. Mukherjee, Ajai K. Singh
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
a r t i c l e i n f o
a b s t r a c t
6-p-cymene)RuCl(
m
-Cl)}2] reacts with N-{2-(phenylthio)ethyl}morpholine (L) and excess NH4PF6
Article history:
The [{(
in CH3OH at room temperature (24 h), resulting in [(
RuCl(NH3)2][PF6] (2) unexpectedly. The complex 1 is first example of a 17eꢀ half-sandwich complex of
6-arene with Ru(III) formed due to unexpected oxidation of Ru(II) in the presence of excess NH4PF6. The
1 is authenticated by EPR and on the basis of DFT calculations. The single crystal structures authenticate
both 1 and 2. The RudS bond length in 1 is 2.413(3) Å whereas in 2 RudN bond distances are 2.141(3)
and 2.149(3) Å. Attempt to catalyze transfer hydrogenation of ketones with 2-propanol with 1 has given
spherical and block shaped RueRuS2 (70:30 w/w%) nano-particles of average size 5e8 nm.
Ó 2012 Elsevier B.V. All rights reserved.
h
h
6-p-cymene)RuCl2(L)][PF6] (1) and [( 6-p-cymene)
h
Received 24 November 2011
Received in revised form
8 May 2012
h
Accepted 19 May 2012
Keywords:
Half-sandwich ruthenium(II/III)
Morpholine
Synthesis
Crystal structure
RueRuS2 nano-particle
1. Introduction
received considerable attention, particularly from the point of view
of catalysis [17]. Zhang et al. reported that the treatment of [h5
-
Half-sandwich compounds of ruthenium(II) having
important in organometallic chemistry [1,2] and generally stable.
An extensive chemistry of such compounds is known [3].
h
6-arene are
Cp*Ru(CH3CN)3][PF6] with HN[SeP(i-Pr)2]2 afforded
complex, [
5-Cp*Ru{ 2-Se2P(i-Pr)2}{ 2-SeP(i-Pr)2}][PF6] [18]. Elec-
trochemically synthesized complexes of
5-Cp*Ru(IV) with dithio-
a Ru(IV)
h
h
h
h
Numerous half-sandwich complexes of (
h
6-arene)Ru(II) unit with
carbamate and carbonodithiolate ligands are also known [19].
Apart from academic curiosity the current interest in half-
sandwich species of Ru(II) has stemmed from their various appli-
cations e.g. catalytic transfer hydrogenation of ketones [20e23] in
aqueous as well as non-aqueous media. The use of 2-propanol as
hydrogen source in this process is interesting as it avoids inflam-
mable H2 gas [24e29]. The species found suitable for catalyzing
transfer hydrogenation [30e51] in last one decade include half-
hybrid organochalcogen ligands (having N and/or O as other donor
atoms) behaving as monodentate [4,5], bidentate [6e9] and tri-
dentate [10e13], have been reported in last decade. Half-sandwich
complexes of Ru(III) are generally formed by (
and most of them are binuclear. However, monomeric species are
5-Cp*RuCl(
also known. The reaction of [{ -Cl)}2] with 3-
thiapentane-1,5-dithiolate (tpdt
S(CH2CH2Sꢀ)2) results in
a monomeric complex [
5-Cp*Ru(III)(tpdt)] [14]. Becker et al. have
h
5-Cp/Cp*)Ru(III) unit
h
¼
m
h
sandwich species [(
h h
6-arene)Ru(bipy)(OH2)]2þ, [( 6-arene)Ru(N,N)
reported oxidative addition of alkyl or aryl di-sulfides/selenides,
REER (R ¼ t-Bu, Ph, p-tolyl; E ¼ S, Se) with labile cationic
Cl]þ and [RuCl(
h
6-benzene/p-cymene)(N,N)][BPh4] ((N,N) ¼ 2-
hydroxyphenyl bis(pyrazol-1-yl)methane or 2-hydroxyphenyl
bis(3,5-dimethylpyrazol-1-yl)methane). Transfer hydrogenation of
ketones with 2-propanol catalyzed by ruthenium(III) species has
also been reported [52e57].
complex [
5-CpRu(CH3CN)(
tion of [{(
6-p-cymene)RuCl(
[(
6-p-cymene)Ru(S2C2(B10H10))] a mononuclear (16eꢀ) complex
first, which in the presence of an excess of sulfur formed binuclear
complex [( -S2)Ru(III)(S2C2(B10H10))2] [16].
6-p-cymene)Ru(I)(
h
5-CpRu(CH3CN)3][PF6], resulting in binuclear species
[
h
m
-ER)2(CH3CN)Ru(
h
5-Cp)][PF6]2 [15]. The reac-
-Cl)}2] with Li2[S2C2(B10H10)] gives
h
m
h
The first monomeric 17eꢀ species having half-sandwich unit
(h h
6-arene)Ru(III), [( 6-p-cymene)RuCl2(L)][PF6] (1) is formed
h
m
unexpectedly by reaction of [{(h m-Cl)}2] with N-
6-p-cymene)RuCl(
Half-sandwich complexes of Ru(IV) are also known and have
{2-(phenylthio)ethyl}morpholine (L) and NH4PF6 (excess) in
methanol at room temperature for 24 h (Scheme 1). In an attempt
to catalyze hydrogenation of ketones with 2-propanol with 1
spherical and block shaped RueRuS2 (70:30 w/w%) nano-particles
of average size 5e8 nm were formed. In this paper these results are
reported.
* Corresponding author. Tel.: þ91 11 26591379; fax: þ91 11 26581102.
E-mail
addresses:
ajai57@hotmail.com,
aksingh@chemistry.iitd.ac.in
(A.K. Singh).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.022

34
P. Singh et al. / Journal of Organometallic Chemistry 715 (2012) 33e38
EDX system model QuanTax 200 which is based on the SDD tech-
nology and provides an energy resolution of 127 eV at Mn K . The
samples were scanned in different regions in order to minimize the
error in the analysis for evaluating the morphological parameters.
Samples were mounted on a circular metallic sample holder with
a sticky carbon tape.
EtOH / NaOH
N2 atm. / reflux
SH
SNa
a
EtOH / NaOH
N2 atm. / reflux
Cl
.
N
HCl
O
Single crystal diffraction studies were carried out with a Bruker
AXS SMART Apex CCD diffractometer using Mo K
a (0.71073 Å)
6
8
1
S
radiation at 100(2) (for 1)/298(2) (for 2) K. The software SADABS
was used for absorption correction (if needed) and SHELXTL for
space group, structure determination, and refinements [58,59]. All
non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were included in idealized positions with isotropic thermal
parameters set at 1.2 times that of the carbon atom to which they
are attached. The least-squares refinement cycles on F2 were per-
formed until converged. The figures of molecular structures of 1, 2
and secondary interactions were drown using Diamond pro-
gramme [60]. Powder X-ray diffraction studies were carried out on
4
N
5
3
2
O
7
(L)
Cl
Cl
MeOH / r.t. / 24 h
excess NH4PF6
Ru
Ru
Cl
Cl
+
+
a Bruker D8 Advance Diffractometer with Ni-filtered Cu K
a
X-rays
PF6
PF6
of wavelength (
l
) ¼ 1.54065 Å. The data were recorded in a 2
q range
of 10ꢀ70ꢁ with the step size of 0.05ꢁ and step time of 1 s.
Ru(III)
Ru(II)
All DFT calculations were carried out at Supercomputing Facility
for Bioinformatics and Computational Biology of the department
with the GAUSSIAN-03 [61] program with an objective of calcu-
lating the partial charges present on various atoms in 1 and 2. The
geometry of all the compounds was optimized at the B3LYP [62]
level using an SDD basis set for metal atom, and 6e31G* basis
sets for C, N, H, S, O and Cl. Geometry optimizations were carried
out without any symmetry restriction. Harmonic force constants
were computed at the optimized geometries to characterize the
minima. The molecular orbital plots were made using the Chem-
craft program package.
Cl
Cl
NH3
H3N
Cl
S
(2)
N
O
(1)
Scheme 1. Synthesis of L and complexes 1e2.
2.2. Chemicals and reagents
2. Experimental
Thiophenol, (2-chloroethyl)morpholine hydrochloride, NH4PF6,
KOH and all other chemicals procured from SigmaeAldrich (USA)
were used as received. The solvents were dried and distilled before
2.1. Physical measurement
PerkineElmer 2400 Series II C, H, N analyzer was used for
elemental analysis. The 1H and 13C{1H} NMR spectra were recorded
on a Bruker Spectrospin DPX-300 NMR spectrometer at 300.13 and
75.47 MHz respectively. IR spectra in the range 4000ꢀ400 cmꢀ1
were recorded on a Nicolet Protége 460 FT-IR spectrometer as KBr
pellets. The UVevisible spectra were recorded on Shimadzu
UVeviseNIR-1601 spectrometer. The EPR spectrum was recorded
on JEOL JES-FE3XG operated at 1 mV and 9.43 GHz (University of
Delhi, New Delhi, India). The conductivity measurements were
carried out in CH3CN (concentration ca. 1 mM) using ORION
conductivity meter model 162. The cyclic voltammetric studies
were performed on BAS CV 50 W instrument at the University of
Delhi (Department of Chemistry). A three-electrode configuration
composed of a Pt disk working electrode (3.1 mm2 area), a Pt wire
counter electrode, and an Ag/AgCl reference electrode was used for
the measurements. Ferrocene was used as an internal standard
(E1/2 ¼ 0.500 V versus Ag/AgCl) and all the potentials are expressed
with reference to Ag/AgCl.
TEM studies were carried out with a JEOL-2100F electron
microscope operated at 200 kV (Advanced Instrumentation
Research Facility at Jawaharlal Nehru University Delhi, India). The
specimens for TEM were prepared by dispersing the powder in
chloroform by ultrasonic treatment, dropping onto a porous carbon
film supported on a copper grid, and then drying in air. The nano-
structural phase morphology was observed by using a Carl Zeiss
EVO5O Scanning Electron Microscope (SEM). Nanostructures
observed by SEM were analyzed for their elemental composition by
use by standard procedures [63]. The [(h m-Cl)]2
6-p-cymene)RuCl(
was prepared by procedure reported in literature [64]. The ligand L
was synthesized by an earlier reported procedure [8].
2.3. Synthesis of half-sandwich complexes 1 and 2
The solid [{(h m-Cl)}2] (0.12 g, 0.2 mmol) was
6-p-cymene)RuCl(
added to the solution of L (0.045 g, 0.2 mmol) made in CH3OH
(15 cm3). The mixture was stirred for 24 h at room temperature. The
solid NH4PF6 (0.16 g, 10 mmol) was added to the above mixture
which was further stirred at room temperature for 2 h. The
precipitate formed was filtered, washed with cold methanol
(10 cm3) and dried in vacuo. This resulted in 1 as a red microcrys-
talline solid. In the filtrate kept aside for slow evaporation orange
crystals of 2 appeared which were separated out and found suitable
for X-ray diffraction. The single crystals of 1 suitable for X-ray
diffraction were obtained by diffusion of diethyl ether into its
solution (1 cm3) made in a mixture of CH3OH and CH3CN (1:4, v/v).
1 Yield: 0.095 g, 70%. m.p. 178 ꢁC. L ¼ 144.8 S cm2 molꢀ1. Anal.
M
Calc. for C22H31Cl2NORuS$PF6: C, 39.18; H, 4.63; N, 2.08%. Found: C,
39.10; H, 4.60; N, 2.15%. IR (KBr, nmax/cm1): 3034 (m; nCeH(aromatic)),
2970, 2860 (s; nCeH(aliphatic)), 1630 (m; nCeC(aromatic)), 1203, 1115 (w;
nCeN), 845 (s; nPeF), 748 (m; nCeH(aromatic)). UVevis. in CH3CN, lmax
/
nm (
/Mꢀ1 cmꢀ1): 250 (6209), 325 (849), 409 (538).
3
2 Yield: 0.014 g, 15%. m.p. 155 ꢁC. L ¼ 155.5 S cm2 molꢀ1. Anal.
M
Calc. for C10H20ClN2Ru$PF6: C, 26.71; H, 4.48; N, 6.23%. Found: C,
26.70; H, 4.40; N, 6.29%. 1H NMR (CD3CN, 25 ꢁC, vs Me4Si):
d (ppm):

P. Singh et al. / Journal of Organometallic Chemistry 715 (2012) 33e38
35
1.18e1.20 (d, 3JHH ¼ 6.6 Hz, 3H, CH3 of i-Pr),1.89 (s, 6H, NH3), 2.00 (s,
3H, CH3 p to i-Pr), 2.74 (sp, 1H, CH of i-Pr), 5.33e5.72 (m, 4H, AreH
of p-cymene). 13C{1H} NMR (CD3CN, 25 ꢁC, vs Me4Si):
d (ppm): 18.4
(CH3, p to i-Pr), 22.4 (CH3 of i-Pr), 31.5 (CH of i-Pr), 81.3e104.2 (AreC
of p-cymene). IR (KBr, nmax/cm1): 3288 (m; nNeH), 3018 (s;
nCeH(aromatic)), 1596 (m; nCeC(aromatic)), 1441 (w; nNeH) 848(s; nPeF),
744 (m; nCeH(aromatic)).
2.4. Isolation of RueRuS2 nano-particles
A solution of the ketone (acetophenone, 4-chloro/bromoaceto-
phenone or benzophenone) (1 mmol), KOH (0.2 cm3 of a 0.2 M
solution in 2-propanol) and the complex 1 (1 mmol) were heated
under reflux (80 ꢁC) in 10 cm3 of 2-propanol for 1 h and thereafter
cooled to room temperature. The solvent was decanted and black
residue of RueRuS2 nano-particles was washed with 4 cm3 of
acetone and 1 cm3 of water.
3. Results and discussion
The syntheses of L, 1 and 2 are shown in Scheme 1. When
amount of NH4PF6 used was not in excess (i.e. upto equimolar
amount only) Ru(II) complex, [(
h
6-p-cymene)RuCl2(L)] was major
6-p-cymene)RuCl(L)][PF6] was also
Fig. 1. ORTEP diagram of cation of 1 with 50% probability ellipsoids; H-atoms and PF6ꢀ
are omitted for clarity. Bond length (Å): Ru(1)eS(1) 2.413(3), Ru(1)eCl(1) 2.400(3),
Ru(1)eCl(2) 2.419(3), Ru(1)dC 2.175(13)e2.226(13); bond angle (ꢁ): Cl(1)eRu(1)eS(1)
85.05(12), Cl(2)eRu(1)eS(1) 88.15(11), Cl(1)eRu(1)eCl(2) 88.50(11).
product (small amount of [(
h
formed) rather than 1 and largely NH4PF6 remained unconsumed.
The yield of 2 was not complementary to that of 1 as side reaction
and escape of NH3 was unavoidable. The L in the monochloro
complex behaves as (S, N) donor rather than a monodentate ligand
(as in 1). Probably following set of reactions feasible under ambient
conditions and in the presence of excess of NH4PF6 result in Ru(III)
species.
ruthenium. The p-cymene ring occupies one face of octahedron and
co-ligands the other one. In case of 1, co-ligands are L (bonded
through S alone) and two Cl atoms. The data for Ru(III)eS bond
distances in molecular species are not easily available therefore
comparisons are made with Ru(II)eS bond lengths. The RudS bond
length of cation of 1 is 2.413(3) Å, which is longer than the value
NH4PF6#NH3 þ HPF6
HPF6#PFꢀ6 þ Hþ
4RuðIIÞ þ 4Hþ þ O2/4RuðIIIÞ þ 2H2O
2.3815(12) Å reported for Ru(II) species, [(h
6-benzene)RuCl(L)][PF6]
The solubility of L,1 and 2 in common organic solvent was found
to be good but in hexane, diethyl ether and petroleum ether both
complexes could not be dissolved significantly. The solution of 1 in
DMSO showed the sign of decomposition after 24 h. The L was
authenticated with 1H and 13C{1H} NMR and IR spectra. The EPR
spectrum (Figure S4 in Supplementary Information) of 1 (para-
magnetic complex) in solid state was recorded at room tempera-
ture and X-band frequencies. The spectrum is very broad and
unsymmetrical and therefore it can not be converted to very
accurate parameters. However there are two maxima and
approximate ‘g’ values calculated using magnetic field ‘H’ at these
two maxima are w2.07 and w2.73. Further position of EPR signal of
1 appears to be consistent with its low spin octahedral geometry
[8] (L ¼ N-{2-(phenylthio)ethyl}morpholine). This is not surprising
as sulfur ligand in 1 is monodentate whereas it is bidentate in the
later complex. Unexpectedly RudS bond distance of cation of 1 is
also longer than the reported values 2.3978(7) Å for [(
h
6-p-cymene)
6-p-cymene)
RuCl2(MeSC3H5)] [5] and 2.3881e2.3833(7) Å for [(
h
RuCl(SMe2)2][SbF6] [5]. The steric factor of L may be responsible for
[57,65,66]. The molar conductance value of 1 (144.8 S cm2 molꢀ1
)
was found consistent with its 1:1 electrolytic nature. UVevisible
spectrum of 1 recorded in CH3CN (conc. 1e2 mmol) shows bands
at 250, 325 and 409 nm. Their corresponding extinction coefficients
( ) are w6209, w849 and w538 respectively
/L Me1 cme1
3
(Figures S6.1eS6.2 in Supplementary Information), characteristic of
Ru(III) species [65]. The presence of L and p-cymene in 1 is sup-
ported by its IR spectrum. The formation of 2 suggests that NH4PF6
has a role in the oxidation of Ru(II) to Ru(III) and is also a source of
NH3 for it. IR and NMR spectra of 2 were found characteristic. The
molecular structures of 1 and 2 based on single crystal diffraction
studies made on them are shown in Figs. 1 and 2 along with
important bond lengths and angles. For details of crystal data
and refinement parameters of 1 and 2 see Tables S1 and S2 in
Supplementary Information. In cations of 1 and 2, there is a pseudo-
octahedral ‘‘Piano-Stool” disposition of donor atoms around
Fig. 2. ORTEP diagram of 2 with 30% probability ellipsoids; H-atoms are omitted for
clarity. Bond length (Å): Ru(1)eN(1) 2.149(3), Ru(1)eN(2) 2.141(3), Ru(1)eCl(1)
2.4137(9), Ru(1)dC 2.156(3)e2.206(3); bond angle (ꢁ): N(1)eRu(1)eN(2) 82.83(12),
Cl(1)eRu(1)eN(1) 84.53(9), Cl(1)eRu(1)eN(2) 84.26(9).

36
P. Singh et al. / Journal of Organometallic Chemistry 715 (2012) 33e38
it. The RudS bond distance, 2.3409(12) Å for [
h
5-Cp*Ru(III)(tpdt)]
The cyclic voltammetric curve of complex 1 (Figures S5.1 and
S5.2 in Supplementary Information) is not of high quality but
appears to be of Ru(II)/Ru(III) couple, as Ru(III) on applying the
potential to begin experiment may not survive and most likely
reduced to Ru(II). The E1/2 value 0.650 V (vs. Ag/AgCl) (Table S4)
implies that both species, Ru(II) and Ru(III), are equally stabilized by
the same set of ligands. The short lived reduced state of the metal
ion is probably responsible for the nature of CV curve [72], which
shows some signs of reversibility of Ru(II)/Ru(III) process.
The DFT studies reveal that partial atomic charge for 1 and 2
are ꢀ0.240 e and ꢀ0.045 e respectively (Figures S7 and S8 in
Supplementary Information). This supports the easy conversion of
Ru(III) to Ru(II) in CV experiment. The sulphur is softer donor than
nitrogen and its presence in 1 appears to result in the present
variation of atomic charges.
[14] (tpdt ¼ 3-thiapentane-1,5-dithiolate) is significantly shorter
than that of 1 as tpdt is behaving as a chelating ligand. Two RudN
bond lengths of cation of 2 are 2.149(3) and 2.141(3) Å, are shorter
than the values reported for Ru(II) species, 2.192(4) Å for [(h
6-p-
cymene)RuCl(L)][PF6] [6] (L ¼ N-{2-(phenylthio)ethyl}pyrrolidine)
and 2.208(3) Å for [(
h
6-benzene)RuCl(L)][PF6] [8] (L ¼ N-{2-(phe-
nylthio)ethyl}morpholine). The reason for these shorter bond
lengths in 2 may be due to the strong coordination behavior of NH3
(less sterically demanding) than the N of pyrrolidine and mor-
pholine rings. The two RudCl bond lengths of cation of 1 (2.400(3)
and 2.419(3) Å) are longer than the sum of covalent radii of Ru(III)
and Cl (2.20 Å) and the values 2.321(1)e2.351(1) reported for trans-
[Ru(DMSO)3Cl3] [67]. These present values are also consistent with
the reduction of the covalent radius (0.04 Å) when Ru(II) changes to
Ru(III) [68]. The RudCl(terminal) bond distances, 2.3851(8) Å for
[(h h
5-Cp)Ru(III)Cl2]2 [29] and 2.418(2) Å for [ 5-Cp*Ru(III)Cl2]2
3.1. Formation of nanosized RueRuS2
[69,70], are consistent with the bond length of 1. The RudCl bond
length of cation of 2, 2.4137(9) Å is also consistent with earlier
reports on Ru(II)dCl bond distances [6e8], for example 2.4108(8) Å
The attempt was made to catalyze with complex 1 transfer
hydrogenation of ketones (acetophenone, 4-chloro or bromoace-
tophenone and benzophenone) with 2-propanol in the presence of
KOH at 80 ꢁC. The products of transfer hydrogenation reaction
could not be unequivocally detected. The complex decomposes
(almost completely in 1 h) in the course of such an attempt. The
resulting black residue was found amorphous in nature by powder
X-ray diffraction studies. The amorphous powder was annealed in
argon atmosphere at 800 ꢁC for 6 h which led to the formation of
crystalline RueRuS2 nano-particles. The powder X-ray diffraction
pattern of these nano-particles (Table S5 and Figure S9 in Supple-
mentary Information) was indexed on the basis of primitive
hexagonal unit cell [73] (JCPDS # 06-0663) with the refined lattice
for [(
h
6-p-cymene)RuCl2(MeSC2H4Ph)] [5], 2.4104(7) Å for [(
h
6-p-
cymene)RuCl2(MeSC3H5)] [5] and 2.3944(7) Å for [(
h
6-p-cymene)
RuCl(SMe2)2][SbF6] [5]. The RudC bond lengths of cations of 1e2
(2.156(3)e2.226(13) Å) are consistent with earlier reports
[4,6e9,12,14,18,69e71]. The CeRueC bond angles for 1 and 2 are
also normal.
There are interesting secondary interactions in the crystal of 1.
The CdH$$$$
p interaction results in chain formation (Figures S1
and S2 in Supplementary Information) and each PF6 is involved
with in secondary interaction with six cations as shown in Fig. 3
(Figures S3.1 and S3.2 in Supplementary Information).
Fig. 3. Secondary interactions of PFꢀ6 anion.

P. Singh et al. / Journal of Organometallic Chemistry 715 (2012) 33e38
37
Appendix B. Supplementary information
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2012.05.022.
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unit cell [74] (JCPDS # 73-1677) with the refined lattice parameter;
a ¼ 5.609 Å (for RuS2 phase). The d values (Å) (hkl)/2
q
(ꢁ) are:
3.2385 (111)/27.52, 2.8046 (200)/31.88, 2.5088 (210)/35.76, 2.3435
(100)/38.38, 2.2900 (211)/39.31, 2.1420 (002)/42.15, 2.0551 (101)/
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69.41. SEM and SEM-EDX (Figures S10.1eS10.3 in Supplementary
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average size 5e8 nm. TEM-EDX (Figure S12 in Supplementary
Information) analyses further indicate composition of RueRuS2
nano-particles as: Ru nano-particles ¼ 70 (wt.%) and RuS2 nano-
particles ¼ (30 wt.%). The SEM-EDX studies (Figure S10 in Supple-
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RueRuS2 nano-particles.
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