Coordination-organometallic hybrid materials based on the trinuclear M(II)-Ru(II) (M=Ni and Zn) complexes: Synthesis, structural characterization, luminescence and electrochemical properties

Article abstract of DOI:10.1016/j.molstruc.2017.10.042

A new series of trinuclear complexes of the type Ni[R-C₆H₄N[dbnd]CH(O)C₆H₃C[tbnd]CRu(dppe)₂Cl]₂ (1a-c) and Zn[R[sbnd]C₆H₄N[dbnd]CH(O)C₆H₃C[tbnd]CRu(dppe)₂Cl]₂ (2a-c) have been prepared from the reaction of trans-[RuCl(dppe)₂C[tbnd]C[sbnd]C₆H₃(OH)(CHO)] (1) with aniline, 4-nitroaniline and 4-methoxyaniline (R_1-3) in presence of nickel acetate and zinc acetate in CH₂Cl₂/MeOH (1:1) mixture. The structural properties of the complexes have been characterized by elemental analyses and spectroscopic techniques viz. FTIR, UV-Visible, ¹H NMR and ³¹P NMR spectral studies. The crystal structure and morphology of the hybrid complexes was investigated with the help of X-ray powder diffraction (XRPD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The thermal properties of 1a-c and 2a-c were studied by thermogravimetric (TG) analysis. The electrochemical behaviour of the complexes reveals that all complexes displayed a quasireversible redox behaviour corresponding to Ru(II)/Ru(III) and Ni(II)/Ni(III) couples for 1a-c and only Ru(II)/Ru(III) couple for 2a-c. All complexes are emissive in solution at room temperature revealing the influence of substituents and solvent polarity on emission properties of the complexes.

Full text of DOI:10.1016/j.molstruc.2017.10.042

Journal of Molecular Structure 1154 (2018) 131e139
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Coordination-organometallic hybrid materials based on the trinuclear
M(II)-Ru(II) (M¼Ni and Zn) complexes: Synthesis, structural
characterization, luminescence and electrochemical properties
*
S.B. Pawal, S.R. Lolage, S.S. Chavan
Department of Chemistry, Shivaji University, Kolhapur, 416 004, MS, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2017
Received in revised form
A new series of trinuclear complexes of the type Ni[R-C H N]CH(O)C H C^CRu(dppe) Cl] (1a-c) and
6
4
6
3
2
2
Zn[ReC
RuCl(dppe)
presence of nickel acetate and zinc acetate in CH
the complexes have been characterized by elemental analyses and spectroscopic techniques viz. FTIR,
6
H
4
N]CH(O)C
6
H
3
C^CRu(dppe)
(OH)(CHO)] (1) with aniline, 4-nitroaniline and 4-methoxyaniline (R1-3) in
Cl /MeOH (1:1) mixture. The structural properties of
2 2
Cl] (2a-c) have been prepared from the reaction of trans-
[
2
C^CeC
6 3
H
12 October 2017
2
2
Accepted 12 October 2017
1
31
UV-Visible, H NMR and P NMR spectral studies. The crystal structure and morphology of the hybrid
complexes was investigated with the help of X-ray powder diffraction (XRPD), Scanning electron mi-
croscopy (SEM) and Transmission electron microscopy (TEM). The thermal properties of 1a-c and 2a-c
were studied by thermogravimetric (TG) analysis. The electrochemical behaviour of the complexes re-
veals that all complexes displayed a quasireversible redox behaviour corresponding to Ru(II)/Ru(III) and
Ni(II)/Ni(III) couples for 1a-c and only Ru(II)/Ru(III) couple for 2a-c. All complexes are emissive in so-
lution at room temperature revealing the influence of substituents and solvent polarity on emission
properties of the complexes.
Keywords:
Heterometallic complexes
Photoluminescence
Cyclic voltammetry
©
2017 Published by Elsevier B.V.
1
. Introduction
steric, electronic and conformational effects imparted by the Schiff
base ligands which play an essential role in stabilizing the metal ion
and modifying the physical and chemical properties of the syn-
thesized complexes [12e15]. Organometallic compounds particu-
Advances in molecular materials with heteronuclear or multi-
component complexes are strongly motivated because of their
interesting synthetic, structural and magnetic properties [1e3].
Among different strategies used for the synthesis of such systems,
one of the most efficient method is the use of multifunctional
bridging ligand that contain two or more functional groups asso-
ciated with different metal centers. Such heteronuclear and/or
multicomponent systems exhibit remarkable physical and chemi-
cal properties with potential applications in catalysis, molecular
sensing, biological systems as well as in the magnetic and opto-
electronic field [4e7]. Schiff base ligands particularly with N, O
donor atoms have drawn special attention for fabrication of such
molecular assemblies because of their ability to generate a much
greater diversity with potential applications in many fields such as
catalysis [8], pharmaceuticals [9], luminescent [10] and nonlinear
optics [11]. Such systems are more attractive with respect to their
larly with
s-alkynyl ligands have also attracted considerable
attention for their use in the preparation of heteronuclear and/or
multicomponent system with desired electronic and optical prop-
erties. The interest in s-alkynyl complexes are not only due to their
rich structural diversity and interesting chemical reactivity but also
due to their increasing potential applications in nonlinear optics
[16], electronic communication [17], luminescence [18] and liquid
crystalline materials [19]. In order to prepare the heteronuclear
and/or multicomponent complexes, metal-acetylides are attractive
precursor due to their electronic, structural features and their
ability to interact with metal centers via pp-dp overlap. The in-
terest in such multifunctional molecular systems are not only due
to their excellent candidature for exploration of intramolecular
triplet energy transfer between organometallic subunits but also
for achieving materials with long-lived luminescence with high
quantum efficiency [20].
In order to explore new materials with interesting structural
topology and novel physical properties, we have been recently
*
Corresponding author.
E-mail address: sanjaycha2@rediffmail.com (S.S. Chavan).
https://doi.org/10.1016/j.molstruc.2017.10.042
022-2860/© 2017 Published by Elsevier B.V.
0

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S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
engaged in the research of synthesis of new hybrid complexes
composed of coordination and organometallic sites. A previous
report from our laboratory has developed some heterobimetallic
4 4
containing n-Bu NClO as the supporting electrolyte. The peak
potentials reported were referenced to Ag/AgCl and were converted
to the SCE scale.
hybrid
complexes
of
the
type
[Ni(ReC
6
H
H
4
HC ¼ N(O)
0
C
C
6
H
H
3
N ¼ NC
6
H
H
4
C^CRu(dppe)
C^CRu(dppe)
2
Cl) (L )] and [Zn(ReC
6
4
HC ¼ N(O)
2. Synthesis
0
6
4
N ¼ NC
6
4
2
Cl) (L )] by the reaction of
[(ReC
6
H
4
HC ¼ N(O)C
6
H
3
N ¼ NC
6
H
4
C^CRu(dppe)
2
Cl)] with nickel
2.2.1. Synthesis of trans-[RuCl(dppe)
The mixture of 5-ethynylsalicyladehyde
0.619 mmol), cis-RuCl (dppe) (0.500 g, 0.516 mmol) and NaPF
(0.266 g,1.583 mmol) was refluxed in CH
for 16 h. NEt
passed through a short pad of alumina eluting with CH
2
C^C-C
6
H
3
(OH)(CHO)] (1)
acetate or zinc acetate in presence of 8-hydroxyquinoline (where
L' ¼ 8-hydroxyquinoline, R ¼ Cl, Br, I) and reported their promising
application as a luminescent material [21]. As a continuation of our
previous report, we explore herein synthesis of new trinuclear
M(II)/Ru(II) coordination-organometallic hybrid complexes of the
(0.09048 g,
2
2
6
2
Cl
2
/MeOH (30 ml, 2:1 v/v)
3
(1 ml) was added and the solution was immediately
Cl . The
2
2
type Ni[ReC
ReC
N ¼ CH(O)C
reaction of trans-[RuCl(dppe)
line, 4-nitroaniline and 4-methoxy aniline (R1-3) in presence of
Ni(II) and Zn(II) in CH Cl /MeOH (1:1) mixture. These complexes
were characterized by elemental analyses, IR, UVeVisible, H NMR,
6
H
4
N ¼ CH(O)C
C^CRu(dppe)
C^C-C
6
H
3
C^CRu(dppe)
Cl] (2a-c) derived from the
(OH)(CHO)] (1) with ani-
2
Cl]
2
(1a-c) and Zn
solvent was removed from the eluate under reduced pressure and
the resulting yellow powder was stirred with diethyl ether to
[
6
H
4
H
6 3
2
2
2
6
H
3
remove unreacted cis-[RuCl
purified by column chromatography on alumina using 4:1 CH
2
(dppe)
2
]. The product was further
2
Cl :
2
2
2
petroleum ether as eluent to afford yellowish green coloured solid.
Yield: 78% (0.4605 g, 0.426 mmol); Elemental analyses (C, H and
1
3
1
P NMR and ESI-MS spectral studies. X-ray powder diffraction
XRPD), Scanning electron microscopy (SEM) and Transmission
N, Wt %) Anal. Cal for C61
67.63; H, 4.71%; IR (KBr) (cm ): 2076, ʋ(C^C); 3280, ʋ(eOH);
53 2 4
H O RuP Cl: C, 67.93; H, 4.95; Found: C,
ꢀ1
(
1
electron microscopy (TEM) are used for confirmation of
morphology and structural behaviour of the complexes. The influ-
1289, ʋ(C-O); 1474, 1433, 1163, 689, ʋ(dppe); H NMR (CDCl
(300 MHz): 10.68 (s, 1H, OH), 9.66 (s, 1H, O]CH), 6.45e7.53 (m,
43H, Ph), 2.65 (s, 8H, CH
3
)
d
3
1
ence of
p-conjugation, the donor/acceptor substituent on photo-
2
); P NMR:
d
49.43. ESI-MS: 1102
þ
þ
luminescence, electrochemical and thermal properties of the
complexes have also been reported.
([RuCl(dppe)
100).
2
C^C-C
6
H
3
(OH)(CHO)þNa] , 30), 898 ([Ru(dppe)
2
] ,
2
. Experimental
2.2.2. Synthesis of Ni[H-C
6
H
4
N ¼ CH(O)C
H
6 3
2 2
C^CRu(dppe) Cl]
(1a)
2.1. Materials and general methods
To
a
solution of trans-[RuCl(dppe)
2
C^C-C (OH)(CHO)]
6 3
H
(0.200 g, 0.185 mmol) in dichloromethane was added a solution of
All manipulations were carried out under dry nitrogen atmo-
Ni(CH
3
COO) .4H O (0.0230 g, 0.0927 mmol) (5 ml) and aniline
2
2
sphere using standard Schlenk techniques, unless otherwise stated.
All solvents were dried over appropriate drying agents and freshly
distilled by suitable procedures prior to use. All chemicals used
(0.0172 g, 0.185 mmol) (5 ml) in methanol dropwise with constant
stirring. The reaction mixture was then rfluxed for 4 h on water
bath. The resulting solution was then evaporated to small volume
under vacuum. The brown coloured complex was collected by
filtration, washed with ethanol and dried in vacuo.
were of AR grade and used without further purification. NaPF
n-Bu NClO were purchased from Aldrich and used as received.
RuCl (dmso) [22] and cis-RuCl (dppe) [23] were synthesized ac-
cording to standard procedure.
6
and
4
4
2
4
2
2
Yield: 72% (0.2231 g, 0.094 mmol); Elemental analyses (C, H and
114 2 2 2 8 2
N, Wt %) Anal. Cal for NiC134H N O Ru P Cl : C, 68.08; H, 4.86; N,
ꢀ
1
Microanalyses (C, H and N) were performed on a Thermo Fin-
nigan FLASH EA-112 CHNS analyzer. UVeVisible absorption spectra
of the samples were measured at room temperature on a Shimadzu
UV-Vis-NIR-100 spectrophotometer. Infrared spectra were recor-
ded on Perkin Elmer FTIR spectrometer as KBr pellets in the 4000-
1.19. Found: C, 67.85; H, 4.75; N, 1.35%; IR (KBr) (cm ): 2053,
ʋ(C^C); 1581, ʋ(C]N); 1273, ʋ(C-O); 1476, 1436, 1165, 695,
1
y
d
d
(dppe); H NMR (CDCl
3
) (300 MHz):
d
8.37 (s, 2H, C]N),
31
6.53e7.57 (m, 96H, phenyl),
49.46. ESI-MS: 2387 ([Ni{H-C
d
2 2
2.67 (m, 16H, PCH CH P); P NMR:
6
H
H
4
N ¼ CH(O)C
6
6
H
H
3
C^CRu
C^CRu
ꢀ1
1
þ
4
00 cm
spectral range. H NMR spectra of the samples were
(dppe)
(dppe)
2
Cl}
2
þNa] , 29), 1153 ([{H-C
6
4
N ¼ CH(O)C
3
þ
þ
measured on Bruker-300 MHz instrument using TMS [(CH
3
)
4
Si] as
2
Cl}] , 100), 898 ([Ru(dppe)
2
] , 41).
an internal standard. 31P NMR spectra were recorded using a Varian
Mercury-300 FTNMR spectrometer. ESI mass spectra were recorded
using Finnigan LCQ mass spectrometer. Thermal analysis of the
complexes was carried out on a Perkin Elmer thermal analyzer in
2.2.3. Synthesis of Ni[NO
(1b)
2
-C
6
H
4 6 3 2 2
N ¼ CH(O)C H C^CRu(dppe) Cl]
The complex 1b was prepared similar to the procedure per-
formed in the preparation of 1a except that aniline was replaced by
4-nitroaniline (0.0256 g, 0.185 mmol).
ꢁ
nitrogen atmosphere at a heating rate of 10 C/min. The fluores-
cence spectra were collected on Perkin Elmer LS 55 spectrofluo-
rometer equipped with quartz cuvette of 1 cm path length at room
temperature. Luminescence lifetime measurement was carried out
by using time-correlated single photon counting from HORIBA
Jobin Yvon. Scanning electron microscopy (SEM) images were
captured on Carl Zeiss (Ultra plus) field emission scanning electron
microscope using AC voltage of 10 kV. TEM image was obtained on
instruments of Philips CM120 microscope. X-ray powder diffraction
Yield: 67% (0.2132 g, 0.086 mmol); Elemental analyses (C, H and
112 4 6 2 8 2
N, Wt %) Anal. Cal for NiC134H N O Ru P Cl : C, 65.59; H, 4.60; N,
ꢀ1
2.28. Found: C, 65.25; H, 4.45; N, 2.48%; IR (KBr) (cm ): 2056,
ʋ(C^C); 1590, ʋ(C]N); 1275, ʋ(C-O); 1477, 1435, 1164, 696,
1
y
d
d
C
C
(dppe); H NMR (CDCl
3
) (300 MHz):
d
8.40 (s, 2H, C]N),
31
6.60e7.79 (m, 94H, phenyl),
49.47. ESI-MS:
d
2 2
2.68 (m, 16H, PCH CH P); P NMR:
2477
([Ni{NO
2
-C
-C
6
H
H
4
N ¼ CH(O)
þ
(
XRD) spectra were recorded on a Rigaku diffractometer (Cu-K
a
6
6
H
H
3
C^CRu(dppe)
C^CRu(dppe)
2
Cl}
2
þNa] , 32), 1198 ([{NO
2
6
4
N ¼ CH(O)
þ
þ
radiation, k ¼ 0.15418 nm) having angle range 5e70. The electro-
chemical measurements were performed with a CH-400A Elec-
trochemical Analyzer. A three component electrochemical cell was
used with Pt disk as the working electrode, Pt wire counter elec-
trode and Ag/AgCl reference electrode. All the measurements have
3
2
Cl}þNa] , 100), 898 ([Ru(dppe)
2
] , 43).
2.2.4. Synthesis of Ni[OCH
(1c)
3
-C
6
H
4
N ¼ CH(O)C
6 3 2 2
H C^CRu(dppe) Cl]
The complex 1c was prepared similar to the procedure per-
formed in the preparation of 1a except that aniline was replaced by
2 2
been carried out with scan rate 100 mV/s in CH Cl solution

S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
133
4
-methoxyaniline (0.0228 g, 0.185 mmol).
Yield: 75% (0.2366 g, 0.097 mmol); Elemental analysis (C, H and
ʋ(C^C); 1588,ʋ(C]N); 1278, ʋ(C-O); 1481, 1436, 1167, 697
y
(dppe);
1
H NMR (CDCl
94H, phenyl),
2484 ([Zn{NO
1198 ([{NO -C
3
d
) (300 MHz):
2.68 (m, 16H, PCH
-C
N ¼ CH(O)C
N ¼ CH(O)C
þ
2
([Ru(dppe) ] , 46).
d
8.38 (s, 2H, C]N),
d
d
6.85e7.80 (m,
49.47. ESI-MS:
31
N, Wt %) Anal. Cal for NiC136
.16. Found: C, 67.18; H, 4.69; N, 1.33%; IR (KBr) (cm ): 2058,
ʋ(C^C), 1583, ʋ(C]N); 1274, ʋ(C-O); 1479, 1436, 1166, 696,
H
118
N
2
O
Ru
4 2
P
8
Cl
2
: C, 67.39; H, 4.91; N,
2
CH
C^CRu(dppe)
C^CRu(dppe)
2
P); P NMR:
ꢀ1
þ
1
2
6
H
H
4
6
H
3
2
Cl}
2
þNa] , 29),
þ
2
6
4
6
H
3
2
Cl}] , 100), 898
1
y(dppe); H NMR (CDCl
3
) (300 MHz):
d
8.38 (s, 2H, C]N),
), 2.68 (m, 16H,
d
PCH
6.65e7.81 (m, 94H, phenyl),
d
3.88 (s, 6H, OCH
3
d
31
2
CH
2
P);
P
NMR:
d
49.46. ESI-MS: 2447 ([Ni{OCH
3
-
-
] ,
2
(
.2.7. Synthesis of Zn[OCH
2c)
The complex 2c was prepared similar to the procedure per-
formed in the preparation of 2a except that aniline was replaced by
3
-C
6
H
4
N ¼ CH(O)C
6 3 2 2
H C^CRu(dppe) Cl]
þ
C
C
3
6
H
H
4
N ¼ CH(O)C
6
6
H
H
3
C^CRu(dppe)
C^C Ru(dppe)
2
Cl}
2
þNa] , 35), 1183 ([{OCH
3
þ
þ
6
4
N ¼ CH(O)C
3
2
Cl}] , 100), 898 ([Ru(dppe)
2
9).
4-methoxyaniline (0.0228 g, 0.185 mmol).
2
(
.2.5. Synthesis of Zn[H-C
2a)
To
0.200 g, 0.185 mmol) in dichloromethane was added a solution of
COO) .2H O (0.0203 g, 0.092 mmol) (5 ml) and aniline
0.0172 g, 0.185 mmol) (5 ml) in methanol dropwise with constant
6
H
4
N ¼ CH(O)C
6
H
3
C^CRu(dppe)
2
Cl]
2
Yield:87% (0.2114 g, 0.087 mmol); Elemental analyses
ZnC136
H
118
N
2
O
4
Ru
2 8 2
P Cl : C, 67.20; H, 4.89; N, 1.15. Found: C, 66.99;
ꢀ
1
a
solution of trans-[RuCl(dppe)
2
C^C-C
H
6 3
(OH)(CHO)]
H, 4.76; N, 1.37%; IR (KBr) (cm ): 2058, ʋ(C^C); 1586,
1279, ʋ(C-O); 1478, 1437, 1165, 692,
(300 MHz):
(s, 6H, OCH
2454
y
(C]N);
(dppe); H NMR (CDCl
6.74e7.55 (m, 94H, phenyl), 3.87
1
(
y
3
)
Zn(CH
(
3
2
2
d
8.39 (s, 2H, C]N),
2.70 (m,16H, PCH
-C
-C
d
d
31
3
),
d
2
CH
N ¼ CH(O)C
N]CH(O)C
2
P); P NMR:
d
49.49. ESI-MS:
þ
stirring. The reaction mixture was refluxed for 4 h on water bath.
The resulting solution was then evaporated to small volume under
vacuum. The pink coloured complex was collected by filtration,
washed with ethanol and dried in vacuo.
([Zn{OCH
3
6
H
4
6
3
H C^CRu(dppe)
2
Cl}
2
þNa] ,
þ
33), 1183 ([{OCH
3
6
H
4
6
H
3
C^CRu(dppe)
2
Cl}] , 100),
þ
898 ([Ru(dppe)
2
] , 43).
Yield: 83% (0.1971 g, 0.083 mmol); Elemental analyses (C, H and
3
. Results and discussion
N, Wt %) Anal. Cal for ZnC134
.18. Found: C, 67.70; H, 4.65; N, 1.35%; IR (KBr) (cm ): 2055,
ʋ(C^C); 1589, ʋ(C]N); 1276, ʋ(C-O); 1479, 1435, 1164, 693,
114 2 2 2 8 2
H N O Ru P Cl : C, 67.89; H, 4.85; N,
ꢀ
1
1
3.1. Synthesis and characterization
1
ʋ(dppe); H NMR (CDCl
3
) (300 MHz):
6.54e7.60 (m, 96H, phenyl), 2.69 (m, 16H, PCH
2394 ([Zn{H-C
þNa] , 33), 1153 ([{H-C
d 8.39 (s, 2H, C]N),
The synthesis of ruthenium-alkynyl complex 1 and its trime-
tallic hybrid complexes 1a-c and 2a-c is shown in Scheme 1. The
reaction of cis-[RuCl (dppe) ] with 5-ethynylsalicyaldehyde in
CH Cl /MeOH mixture (2:1) assisted by NaPF at room temperature
followed by column chromatography (Al ) afforded trans-
RuCl(dppe) C^C-C
(OH)(CHO)] (1) (dppe ¼ 1,2-bis(diphenyl
phosphinoethane)) as a mononuclear complex in 78% yield. The
31
d
d
C
C
d
2 2
CH P); P NMR:
49.48.
C^CRu(dppe)
C^CRu(dppe)
ESI-MS:
6
6
H
4
N ¼ CH(O)
2
2
þ
6
H
H
3
2
2
Cl}
2
H
4
N ¼ CH(O)
2
2
6
þ
þ
6
3
Cl}] , 100), 898 ([Ru(dppe)
2
] , 38).
2 3
O
[
2
6 3
H
2
(
.2.6. Synthesis of Zn[NO
2b)
The complex 2b was prepared similar to the procedure per-
formed in the preparation of 2a except that aniline was replaced by
2
-C
6
H
4
N ¼ CH(O)C
H
6 3
C^CRu(dppe) Cl]
2 2
trinuclear complexes of the type Ni[ReC
C
C
6
H
H
4
N ¼ CH(O)
6
H
H
3
C^CRu(dppe)
C^CRu(dppe)
2
2
Cl]
Cl]
2
(1a-c),
Zn[ReC
6
4
N ¼ CH(O)
6
3
2
(2a-c) (where R ¼ H, NO
2 3
, OCH ) were
4
-nitroaniline (0.0256 g, 0.185 mmol).
2 6 3
prepared by the reaction of trans-[RuCl(dppe) C^C-C H (OH)(-
Yield: 78% (0.1918 g, 0.077 mmol); Elemental analyses (C, H and
CHO)] (1) with nickel acetate or zinc acetate in the presence of
aniline, 4-nitroaniline and 4-methoxyaniline, respectively. All the
complexes were air stable at room temperature, non-hygroscopic
N, Wt %) Anal. Cal for ZnC134
112 4 6 2 8 2
H N O Ru P Cl : C, 65.41; H, 4.59; N,
ꢀ1
2
.28. Found: C, 65.20; H, 4.29; N, 2.55%; IR (KBr) (cm ): 2060,
CHO
CHO
CHO
PdCl (PPh )
3 2
CH Cl2 + MeOH
2
2
HO
Br
+
Si(CH3)
HO
Si(CH3)
3
CuI, Et N
3
HO
H
3
KOH
CH Cl2 + MeOH RuCl (dppe)2
2
2
Et N NaPF6
3
R
CHO
Ph2P
PPh2
Cl
Ph2P
PPh2
Cl
H N
R
2
N
O
O
N
Ru
HO
Ru
Ph2P
Cl
Ph2P
PPh2
PPh2
M(CH COOH) .XH O
M
3
2
2
Ph2P
PPh2
CH
2
Cl
2
+ MeOH
Ph2P
PPh2
Ru
1
R
R= H, NO , OCH ; M=Ni, Zn
2
3
Scheme 1. The Synthetic route to 1 and its hybrid complexes 1a-c and 2a-c.

134
S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
and soluble in solvents like chloroform, dichloromethane, ethanol,
methanol etc. The composition and identity of the complexes were
confirmed from satisfactory elemental analyses, ESI-MS, IR,
Table 1
UVeVisible absorption data of 1a-c and 2a-c in CH
2
Cl
2
.
3
ꢀ1
ꢀ1
)
Complex
lmax(nm) (ε x10 , M cm
1
31
UVeVisible, H NMR and P NMR spectroscopy.
1
278 (13.3), 320 (3.4)
The IR frequencies of selected groups in the spectra of 1 and its
hybrid complexes 1a-c and 2a-c are given in experimental section.
1a
1b
1c
283 (17.1), 347 (4.3), 516 (0.6)
285 (16.6), 349 (3.9), 521 (0.5)
282 (18.0), 345 (5.4), 513 (0.7)
289 (17.2), 348 (5.3)
292 (15.4), 356 (3.9)
285 (18.1), 347 (6.2)
ꢀ
1
A weak band at 2076 cm due to internal triple bond (C^C) in the
IR spectrum of 1 is slightly shifted to lower frequency region at ca
2
2
2
a
b
c
ꢀ1
ꢀ1
2
053e2058 cm for 1a-c and ca 2055e2060 cm for 2a-c sug-
gesting perturbation of the phenyl site leads to electron dissipation
at the triple bond through conjugation [24]. The band observed at
ꢀ
1
ꢀ1
1
581-1590 cm in 1a-c and 1586-1589 cm in 2a-c indicate the
presence of imine (HC]N) group in the complexes [25]. This view
was further supported by the appearance of a band corresponding
ꢀ
1
to the metal-nitrogen stretching vibration at ca 501-519 cm in
ꢀ
1
1
a-c and ca 515-519 cm in 2a-c. In the IR spectrum of 1, a band
ꢀ
1
observed at 3280 cm due to phenolic eOH proton disappeared in
the spectra of 1a-c and 2a-c upon coordination. The involvement of
deprotonated phenolic moiety in all heteronuclear complexes is
deduced by shifting of ʋ(C-O) stretching frequency observed at
ꢀ1
ꢀ1
1
289 cm in 1 to a lower frequency region by 14e16 cm in 1a-c
ꢀ
1
and 10-13 cm in 2a-c indicating weakening of ʋ(C-O) and for-
mation of strong M ꢀ O bond [26]. Further proof for complexation
of oxygen is obtained from the appearance of (M ꢀ O) band at ca
ꢀ1
ꢀ1
5
37e569 cm for 1a-c and 543-564 cm for 2a-c. The spectra of
ꢀ1
all complexes exhibit bands at around 1478, 1435, 1168, 694 cm
are due to the presence of the dppe ligand. The complexes 1b and
ꢀ
1
ꢀ1
2
b exhibit two bands at ~1565 cm and ~1409 cm which can be
attributed to ʋasym(NO ) and ʋsym(NO ) modes whereas; 1c and 2c
2
2
ꢀ1
3
exhibit band at around 1165 cm ascribed to eOCH group in the
2 2
Fig. 1. UVeVisible absorption spectra of 1 in CH Cl solutions.
complexes [27].
The 1H NMR spectra of mononuclear ruthenium-acetylide
complex 1 and its corresponding trinuclear Ni(II)/Ru(II) (1a-c)
and their corresponding data are summarized in Table 1. The ab-
sorption spectrum of 1 in CH Cl is displayed in Fig. 1. The dppe
phenyl group is primarily responsible for the intraligand
transition band at max at 278 nm while the absorption band at
320 nm are due to the d (Ru)/ *(C≡CR) MLCT transition in 1.
Similar absorption spectra were observed for the complexes
exhibiting two intense bands with max at around 283 and 347 nm
for 1a-c and 288 and 350 nm for 2a-c (Fig. 2) which can be
attributed to an intraligand ( *) transition and MLCT transition,
respectively. A weak absorption at around 516 nm in the spectra of
and Zn(II)/Ru(II) (2a-c) complexes were recorded in CDCl
3
and are
2
2
given in experimental section. Comparison of the chemical shift of
the ruthenium-acetylide complex 1 with its respective Ni(II)/Ru(II)
and Zn(II)/Ru(II) complexes shows that the resonance peaks are
p/p*
l
max
l
p
p
1
shifted at different level in each case. In the H NMR spectrum of 1,
a characteristic resonance observed at
d
10.68 ppm due to phenolic
l
OH proton disappeared in the spectra of 1a-c and 2a-c indicating
deprotonation of 1 and coordination of phenolic eOH to the central
p/p
1
metal ion. Another singlet observed at
d
9.66 ppm in the H NMR
1
1
spectrum of 1 corresponds to aldehydic proton. Upon imine for-
1a-c is assigned to the spin allowed transition ( A1g/ A2g) for
mation this singlet disappeared and a new singlet was observed at
four-coordinated square-planar Ni-Salen complexes [32]. Upon
coordination, absorption bands of the complexes 1a-c and 2a-c are
shifted to longer wavelength region compared to those of their
monometallic precursor 1. The absorption shift and intensity
change in the spectra of 1a-c and 2a-c relative to metallic precursor
around
of the imine proton [28]. However, the signal due to aromatic
protons observed as multiplets in the region 6.45e7.53 ppm in 1
d 8.39 ppm in 1a-c and 2a-c identified as -CH]N resonance
d
shifted towards downfield region in 1a-c and 2a-c confirming the
1
complexation with Ni(II) and Zn(II) ion in the complexes. The H
1 is most likely originated from the metallation, increased p-
NMR spectra of all complexes exhibit single resonance character-
conjugation and increased delocalization of the whole electronic
system [33].
istic of the CH
[
2
protons in the dppe of acetylide ligand at
29]. A sharp singlet observed at 3.87 ppm in the spectra of 1c and
protons in the complexes [30].
The 31P NMR spectra of 1a-c and 2a-c and their mononuclear
d 2.69 ppm
d
Emission spectra of 1 as well as its trimetallic complexes 1a-c
ꢀ5
2
c corresponds to eOCH
3
and 2a-c were recorded in CH Cl solution (10 M) and spectral
2 2
data are displayed in Table 2. The ruthenium-alkynyl complex 1
exhibit emission at 495 nm upon excitation at 371 nm (Fig. 3). This
emission belong to MLCT transition similar to that of other lumi-
nescent ruthenium(II)-alkynyl complexes reported earlier [34].
Upon complexation of 1 with Ni(II) and Zn(II), the trinuclear com-
plexes exhibit strong red shifted emission at 534e552 nm for 1a-c
and 539e554 nm for 2a-c with lifetime of 2.56e2.78 and 3.77e3.91
ns, respectively. The significant red shift observed in 1a-c and 2a-c
in comparison to their metallic precursor 1 results from the for-
mation of trinuclear species which leads to an increased energy gap
between ground state and excited state. These results also confirm
that the emission origin in 1a-c and 2a-c predominantly not only
counterpart 1 displayed a single resonance at ~49.47 ppm corre-
sponding to the phosphine ligand attached to the ruthenium. This
suggests that two dppe ligands of each ruthenium occupy the
ꢀ
equatorial plane with Cl and alkynyl group trans disposed at the
axial sites in all the complexes [31].
3.2. Absorption and emission behaviour
The electronic absorption spectra of ruthenium-acetylide com-
plex 1 and its trinuclear Ni(II)/Ru(II) (1a-c) and Zn(II)/Ru(II) (2a-c)
ꢀ
4
2 2
complexes were recorded in CH Cl (10 M) at room temperature

S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
135
(A)
(B)
Fig. 2. UVeVisible absorption spectra of (A) 1a-c (B) 2a-c in CH
2
Cl
2
solutions.
Table 2
electron withdrawing eNO
donating eOCH
tensities in 1a and 2a with 'H group in the complexes are in be-
tween above two intensities. The emission quantum yield ( ) of all
the complexes was determined with reference to quinine sulfate
group as compared to electron
group in 1c and 2c. However, the emission in-
2
ꢀ
5
Photoluminescence data of 1a-c and 2a-c in CH
2
Cl
2
(10 M).
3
0
(s 1/107)
ꢀ
nr(sꢀ1/109)
K
Complex
l
ex (nm)
l
em (nm)
f
t
(ns)
K
r
f
1
371
380
383
378
390
393
388
495
538
552
534
549
554
539
0.049 1.90
0.056 2.60
0.059 2.78
0.053 2.56
0.068 3.85
0.069 3.91
0.064 3.77
2.578
2.153
2.122
2.070
1.766
1.764
1.697
0.500
0.363
0.338
0.369
0.242
0.238
0.248
1
1
1
2
2
2
a
b
c
a
b
c
(
f
¼ 0.52) and are listed in Table 2. The fluorescence quantum yield
) of the complexes is approximately at 0.053e0.059 for 1a-c and
.064e0.069 for 2a-c which are higher than for their mononuclear
(f
0
counterpart 1 (0.049). These values are in conformity with the
values reported in the literature [37].
3.3. Solvatochromism of the complexes
The solubility of the complexes in variety of organic solvents
allowed a detailed investigation of its solvatochromism behaviour.
Thus in order to study the solvatochromism of the complexes their
emission spectra were obtained in different solvents (chloroben-
zene, dichloromethane and tetrahydofuran). It was observed from
Fig. 4 that, emission band maxima of the complexes 1a-c and 2a-c
shows clear differences. The complexes 1a-c shows their emission
peak at 524e539 nm in chlorobenzene, 534e552 nm in dichloro-
methane and 544e565 nm in tetrahydrofuran whereas, the com-
plexes 2a-c shows emission peak at 528e540 nm in chlorobenzene,
539e554 nm in dichloromethane and 551e564 nm in tetrahydro-
furan. From Table 3 it is revealed that emission maxima increases
with increase in solvent polarity in the order chloroben-
zene < dichloromethane < tetrahydrofuran. The observed shift of
band maxima to higher wavelength in the solvents of increasing
polarity were indicative of, excited states are more stabilized with
increasing polarity of the solvents which leads to a red shifted
emission [38].
2 2
Fig. 3. Emission spectra of 1 in CH Cl solutions.
due to MLCT transition but also due to chelation enhanced fluo-
rescence (CHEF) caused by coordination of imine group to Ni(II) and
Zn(II) ion in the complexes [35]. The remarkable increase in fluo-
rescence emission by CHEF is attributed to the formation of
comparatively rigid structure by strong complexation with central
metal ion which minimizes the nonradiative energy loss [36].
Compared to 1a, 1c, 2a and 2c the slight red shift of the absorption
and emission wavelengths observed in 1b and 2b is probably as a
3.4. SEM and TEM studies
The SEM analysis of representative complexes 1a and 2c was
carried out in order to evaluate the surface morphology and particle
size of the trimetallic complexes. From the SEM image in Fig. 5(A)
and 5(B) it is observed that, the shape of complex 1a is irregular
with crushed ice like morphology having average size of ~110 nm.
On other hand the SEM of 2c exhibit plate like morphology with
average size of ~200 nm. Fig. 6 shows various TEM images with
different magnifications and the calculated histogram for zinc
complex. The TEM image indicate the sphere-like structure for
Zn(II)/Ru(II) hybrid complex (2c) with well dispersed spherical
particle size between 200 and 300 nm without agglomeration.
result of the higher electron withdrawing ability of eNO
2
group
which offers an extra conjugated backbone which lower the
*
p
(C^CH) orbital energy and lead to narrowing the HOMO-LUMO
energy gap. The substituent's on the coordinated imine group also
affect the emission intensities in the complexes. The fluorescence
intensity is significantly quenched in 1b and 2b due to presence of

136
S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
Fig. 4. Emission spectra of 1a-c and 2a-c in different solvents: chlorobenzene, dichloromethane and tetrahedrofuran.
3
.5. X-ray powder diffraction studies
of d ¼ 7.012 Å. The diffractogram of 2c consists of six reflections
ꢁ
with maxima at 2
q
¼ 10.44 corresponding to value of d ¼ 8.470 Å.
Single crystal X-ray technique is a powerful analytical tool
The main peaks of 1a and 2c have been indexed by using computer
which provides detailed information about internal lattice, unit cell
dimensions, particle size, crystal system, bond length and bond
angles of crystalline substances. However, the difficulties in
obtaining crystalline complexes in proper symmetric form
rendered us to study the X-ray powder diffraction method of pre-
pared complexes. The X-ray diffraction pattern of representative
complexes 1a and 2c revealed well defined crystalline peaks indi-
cating that the complexes 1a and 2c are crystalline in nature
software by trial and error method [39] keeping in mind charac-
teristics of various symmetry systems till good fit could be obtain
2
between observed and calculated 2
q
and sin
q
values. The method
also yielded hkl values. The relative intensities corresponding to the
prominent peaks have been measured. The indexing of the dif-
fractogram of 1a and 2c are identical. Based on this it can be pro-
posed that these compounds belong to same structural class. A
2
comparison of values of 2
q
and sin
q
for the 1a and 2c reveals that,
(
Fig. 7). The diffractogram of 1a records eight reflections between 5
there is good agreement between the calculated and observed
values of 2q and sin q on the basis of assumption of monoclinic
ꢁ
ꢁ
2
and 80 (2
q
) with maximum at 2
q
¼ 12.61 corresponding to value

S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
137
Table 3
Emission maxima and Quantum yield data in various solvents of 1a-c and 2a-c.
(a)
(b)
Complex
Solvent
lex (nm)
lem (nm)
Quantum Yield (f)
1
1
1
2
2
2
a
b
c
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
379
380
382
383
383
386
375
378
379
388
390
391
392
393
397
387
388
390
531
538
553
539
552
565
524
534
544
536
549
557
540
554
564
528
539
551
0.057
0.056
0.054
0.061
0.059
0.058
0.053
0.053
0.052
0.069
0.068
0.065
0.069
0.069
0.067
0.068
0.064
0.061
a
b
c
Fig. 6. TEM photograph of 2c.
total loss of salicylidine moiety (calcd. 18.52 (1a), 21.51(1b) and
0.54 (1c). All the complexes collapse due to release of dppe ligand
2
ꢀ
ꢁ
along with Cl per formula unit between 351 and 535 C with an
observed weight loss of 70.28 (1a), 67.69 (1b) and 68.40 (1c),
respectively (calcd. 70.41 (1a), 67.83 (1b) and 68.66 (1c)). The
Zn(II)/Ru(II) complexes 2a, 2b and 2c shows very similar behaviour
to the above; once again an absence of water or solvent is indicated
structure [40]. The structure of 1a yields values for lattice constant
ꢁ
a ¼ 10.9308 Å, b ¼ 8.8289 Å, and c ¼ 15.2709 Å;
a
¼
g
¼ 90 and
ꢁ
by stability of the complexes up to ca. 243, 246 and 251 C for 2a, 2b
ꢁ
3
b
¼ 103.7 , unit cell volume V ¼ 1431.92 Å . However, the structure
and 2c respectively. For 2a-c the decomposition stage with mass
loss of 17.97 in 2a, 21.03 in 2b and 20.18 in 2c can be ascribed to the
loss of coordinated salicylidine moiety (calcd 18.47 (2a), 21.45 (2b)
of 2c yields values for lattice constant a ¼ 14.6848 Å, b ¼ 8.4702 Å
ꢁ
ꢁ
and c ¼ 11.4494 Å;
a
¼
g
¼ 90 and
b
¼ 99.035 , unit cell volume
3
V ¼ 1406.45 Å . In conjunction with these parameters the condi-
and 20.48 (2c)) in the temperature ranges 244e353, 247e357 and
tions such as asb sc and
a
¼
gsb required for the samples to be
ꢁ
2
3
6
52e362 C, respectively. Another stage at 354e569, 358e567,
monoclinic were tested and found to be satisfactory. The particle
size of 1a and 2c was determined using Scherrer's formula [41] and
was found to be 231.62 and 247.13 Å, respectively.
ꢁ
63e615 and 363e620 C with observed mass loss of 69.89 (2a),
7.27 (2b) and 68.08 (2c) respectively due to loss of the remaining
dppe ligands (calcd 70.21 (2a), 67.64 (2b) and 68.48 (2c)).
3.6. Thermogravimetric analysis
3.7. Cyclic voltammetry
To characterize the compounds in terms of thermal stability, the
thermal properties of 1a-c and 2a-c complexes were studied by
In order to gain insight into the electronic environment; the
thermogravimetric analysis. For TG measurement the samples were
heated in the range of 25e800 C at heating rate of 10 C min
electrochemical properties of all complexes were probed by cyclic
voltammetry. All measurements were performed in dichloro-
ꢁ
ꢁ
ꢀ1
ꢀ
3
under nitrogen atmosphere. TG curve of Ni(II)/Ru(II) complexes
methane solution (10 M) containing 0.05 M n-Bu NClO as a
4 4
ꢁ
showed that the complexes are thermally stable upto ca 245 C
supporting electrolyte at room temperature in the potential
range þ1.50 to ꢀ1.50 V. The electrochemical behaviour of all the
complexes is characterized by a well defined redox process on the
positive potential side in dichloromethane and the representative
cyclic voltammogram of 1c and 2c are presented in Fig. 8. The
revealing absence of either water or solvent molecules. In the
ꢁ
temperature range of 246e350 C, the complexes were then un-
derwent complicated and significant multiple weight loss of 18.19
(1a), 21.35(1b) and 20.22 (1c), respectively corresponding to the
(A)
(B)
Fig. 5. Scanning electron micrographs of (A) 1a and (B) 2c.

138
S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
(A)
(B)
Fig. 7. Powder X-ray diffraction patterns of 1a and 2c.
ruthenium-acetylide complex 1 oxidized at a potential 1.021 V (E1/
) ascribed to the Ru(II)/Ru(III) couple. Cyclic voltammetry studies
Table 4
Electrochemical data of the complexes 1a-c and 2a-c.
2
on Ni(II)/Ru(II) complexes (1a-c) reveal that, all complexes undergo
quasireversible oxidation processes in the range 0.528e0.549 V
assigned to the Ni(II)/Ni(III) couple by analogy with earlier obser-
vations [42]. Another oxidation process observed at 1.051e1.078 V
Compound Ni(II)/Ni(III) Ru(II)/Ru(III)
pa(V) pa(V) pc(V)
E
E
pc(V)
E1/2(V)
E
E
E1/2(V)
1
1
1
2a
2b
a
b
c
0.587
0.610
0.575
e
0.486
0.488
0.482
e
0.536
0.549
0.528
e
1.079
1.087
1.063
1.085
1.096
1.075
1.044
1.069
1.039
1.019
1.027
1.006
1.061
1.078
1.051
1.052
1.061
1.040
(
E
1/2) in 1a-c is attributed to Ru(II)/Ru(III) couple. However, the half
wave potential for Ru(II)/Ru(III) couple is only observed at
.040e1.061 V (E1/2) for 2a-c. On comparing cyclic voltammetry
1
e
e
e
2c
e
e
e
data of mononuclear precursor 1 with its respective Ni(II)/Ru(II)
and Zn(II)/Ru(II) complexes, it was found that the oxidation of
ruthenium(II) units shifted to more positive value which is pre-
sumably due to increase in electron density around Ni(II) and Zn(II)
in the complexes [43]. It is noticeable from Table 4 that, the elec-
trochemical properties of all the complexes are interdependent
with the substituent groups on the coordinating ligands. The
electron donating eOCH shifts both oxidation and reduction to-
3
2
wards cathode while electron withdrawing eNO groups shift the
redox potentials towards anode.
Supporting electrolyte: n-Bu
1/2 ¼ ½(Epa þ Epc); scan rate: 100 mVs . All potentials vs. SCE.
4 4 2 2
NClO (0.05 M); complex: 0.001 M; solvent: CH Cl ;
ꢀ
1
E
studies of representative complexes 1a and 2c are used to investi-
gate the crystal structure and morphology of the complexes. The
electrochemical study of the complexes showed quasireversible
redox behaviour corresponding to Ni(II)/Ni(III) and Ru(II)/Ru(III) for
1
a-c and only Ru(II)/Ru(III) for 2a-c. Oxidation of Ru(II) unit in 1a-c
and 2a-c is shifted towards more positive value than their mono-
nuclear precursor 1 upon coordination to Ni(II) and Zn(II). All the
complexes are photoluminescent in solution state at room tem-
perature which can be tuned by the variation of the substituent
4
. Conclusion
In summary, some trimetallic complexes of the type Ni
2 3
group and follow the trend NO >H > OCH whereas; reverse effect
was found in emission intensity of the complexes. Emission max-
ima increases with increase in polarity of the solvent indicative of
excited states of all the complexes are more stabilized in polar
[
[
ReC
ReC
6
H
H
4
N ¼ CH(O)C
6
H
H
3
C^CRu(dppe)
C^CRu(dppe)
2
Cl]
Cl]
2
(1a-c)
(2a-c) have been syn-
and
Zn
6
4
N ¼ CH(O)C
6
3
2
2
thesized and characterized. X-ray powder diffraction, SEM and TEM
(A)
(B)
ꢀ
3
Fig. 8. Cyclic voltammograms of 1c and 2c measured in CH Cl (10 M) and 0.05 M n-Bu NClO as supporting electrolyte. Potentials vs. SCE.
2
2
4
4

S.B. Pawal et al. / Journal of Molecular Structure 1154 (2018) 131e139
139
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We gratefully acknowledge financial support from Science and
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