Heterometallic Cu(I)/Ru(II) halide and pseudohalide hybrid complexes composed of coordination and organometallic sites: Synthesis, spectroscopic characterization, electrochemical and luminescence properties

Article abstract of DOI:10.1016/j.poly.2017.03.001

A new series of heterometallic halide/pseudohalide hybrid complexes of the type [Cu(L₁)NC₅H₄–C[tbnd]C–C₆H₃–1,3-{C[tbnd]C-trans-RuCl(dppe)₂}₂X] (1a–d) and [Cu(L₂)NC

Full text of DOI:10.1016/j.poly.2017.03.001

Accepted Manuscript
Heterometallic Cu(I)/Ru(II) halide and pseudohalide hybrid complexes com-
posed of coordination and organometallic sites: Synthesis, spectroscopic char-
acterisation, electrochemical and luminescence properties
S.B. Pawal, S.R. Lolage, S.S. Chavan
PII:
S0277-5387(17)30167-5
DOI:
http://dx.doi.org/10.1016/j.poly.2017.03.001
POLY 12512
Reference:
Polyhedron
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Received Date:
Revised Date:
Accepted Date:
18 January 2017
26 February 2017
1 March 2017
Please cite this article as: S.B. Pawal, S.R. Lolage, S.S. Chavan, Heterometallic Cu(I)/Ru(II) halide and pseudohalide
hybrid complexes composed of coordination and organometallic sites: Synthesis, spectroscopic characterisation,
electrochemical and luminescence properties, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.03.001
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Heterometallic Cu(I)/Ru(II) halide and pseudohalide hybrid complexes
composed of coordination and organometallic sites: Synthesis, spectroscopic
characterisation, electrochemical and luminescence properties
S. B. Pawal, S. R. Lolage, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS) India-416 004
Abstract
A new series of heterometallic halide/pseudohalide hybrid complexes of the type [Cu(L1)NC5H4-
C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2X] (1a-d) and [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2X] (2a-d) have been prepared by the reaction of [NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2] (1) with copper(I) salts in presence of L1 and L2 (Where L1 = 4-methoxy-
N-(2-pyridylmethylene) phenylamine and L2 = 4-nitro-N-(2-pyridylmethylene)phenylamine; X=
Cl, I, N3, and NCS) in CH2Cl2/MeOH mixture. Thermal stability of 1a-d and 2a-d has been
investigated by using thermogravimetric analysis (TGA). The electrochemical behaviour of 1a-d
and 2a-d reveals that all complexes display a quasireversible redox behaviour corresponding to
Cu(I)/Cu(II) and Ru(II)/Ru(III) couples. The room temperature luminescence is observed for all
complexes in dichloromethane solution indicating that the emission wavelength is finely tuned
by the variation of the substituent group on iminopyridine ligand and quenching ability of halides
and pseudohalides in the complexes. Further, the excited state of 1a-d and 2a-d are stabilized and
red shifted in their emission wavelength with increasing polarity of the solvents.
Keywords: heterometallic complexes, cyclic voltammetry, photoluminescence
Corresponding author: Tel.: +91 231 2609381; fax: +91 231 2691533.
E-mail: sanjaycha2@rediffmail.com
1

1. Introduction
In the past several decades, there has been a growing interest in the design and synthesis of
heterometallic or multicomponent complexes that exhibit rich photophysical and electrochemical
properties [1-2]. An attractive pursuit in this area is to design the structural rigid building blocks with
readily tuneable electronic, steric and photophysical characteristics by virtue of coordinated metal
centre or by modifying the backbone substituent’s of the coordinated ligands [3]. A good example for
the fabrication of such heterometallic or multicomponent complex is use of Schiff base ligands that
contain two or more functional groups associate with different metal centres [4, 5]. An important
feature of these system is that, they have ability to generate a much greater diversity with many
attractive properties such as magnetism [6], electrochemical [7], catalysis [8] and luminescence [9].
Because of the widespread utility of Schiff base ligands and their ability to act as polyfunctional
ligands many studies on its metal complexes have been carried out [10,11]. Similar to coordination
compounds organometallic compounds particularly, metal-alkynyl complexes have emerged as a
prominent tool for construction of heterometallic or multicomponent with attractive spectroscopic
and optical properties [12, 13]. The interest in metal alkynyl complexes is not only from their rich
structural diversity and interesting chemical reactivity but also due to their increasing potential
applications in material science [14]. The favourable electronic and structural features of the alkynyl
units and their ability to interact with metal centres via significant pπ-dπ overlap have made them
attractive for the preparation of heterometallic or multicomponent complexes with unique properties
such as optical nonlinearity [15], electrical conductivity [16] and liquid crystallanity [17]. This field
has recently been stimulated by the attractive photochemical and photophysical properties with
potential applications in light emitting diodes [18], optical sensors [19], molecular devices [20] etc.
Compared to simple alkynes functionalized -alkynes are more favourable for fabrication of
heteronuclear or multicomponent complexes with desired electronic and optical properties. Upon
complexation such metallo-ligands provide an easy access to various kinds of molecular architectures
with unique properties for intramolecular energy transfer between organometallic subunit as well as
attending long lived luminescence with high quantum efficiency [21].
2

With the aim of understanding the potential applications of coordination and organometallic
compounds and preparing new materials with interesting structural topology and novel physical
properties, we have been recently engaged in the research of synthesis of new heterometallic
complexes composed of organometallic and coordination sites. Previous report from our laboratory
have developed some heterobinuclear Cu/Ru hybrid complex material derived by the reaction of
trans-[RuCl(dppe)2(C≡CC6H4(C≡C-py-3) with Cu(I) in presence of 2-(pyrrole-2-yl-methylidine)
aminophenol and 5-bromo-2-(pyrrole-2-ylmethyldine)aminophenol as ligands [22] and reported their
promising application as a luminescent and nonlinear optical material in solid state. In this paper, we
report the synthesis of some trinuclear Cu(I)/Ru(II) halide and pseudohalide hybrid complexes
composed of coordination and organometallic sites of the type [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2X] (1a-d) and [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2X]
(2a-d) derived from the reaction of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (1) with
copper(I) salts in presence of iminopyridine ligands L1 and L2 in CH2Cl2/MeOH mixture. All the
complexes were characterized by elemental analyses, IR, UV-visible, 1H NMR, 31P NMR and mass
spectral studies. The influence of π-conjugation, donor-acceptor substituents as well as coordinated
halides and pseudohalides on photophysical, thermal and electrochemical properties of the complexes
have been studied.
2. Experimental
2.1. Materials and general methods
All reactions were performed under dry nitrogen using standard Schlenk techniques. Reaction
solvents dichloromethane and triethylamine were dried by distilling over calcium hydride and
methanol was dried by distilling over Mg/I2; other solvents were used as received. All chemicals used
were of AR grade and used without further purification. The Schiff base ligands 4-methoxy-N-(2-
pyridylmethylene)phenylamine (L1) and 4-nitro-N-(2-pyridylmethylene)phenylamine (L2) were
prepared as previously reported [23]. RuCl2(dmso)4 [24], cis-RuCl2(dppe)2 [25], [C6H3-1,3-{C≡C-
trans-[RuCl(dppe)2]}2-5-(C≡CH)] [26] were prepared according to the literature procedure.
Elemental analyses (C, H and N) were performed on a Thermo Finnegan FLASH EA-112 CHNS
analyzer. Electronic spectra were recorded on a Shimadzu UV-Vis-NIR-100 spectrophotometer.
3

Infrared spectra were recorded on Perkin Elmer FT-IR spectrometer as KBr pellets in the 4000-400
cm-1spectral range. 1H NMR spectra of the samples were measured on Bruker-300 MHz instrument
31
using TMS [(CH3)4Si] as an internal standard. P NMR spectra were recorded using a Varian
Mercury-300 FT-NMR spectrometer. ESI mass spectra were recorded using Finnegan LCQ mass
spectrometer. Thermal analysis of the complexes was carried out on a Perkin Elmer thermal
analyzer in nitrogen atmosphere at a heating rate of 10°C/min. Luminescence properties were
measured using a Perkin Elmer LS 55 spectrofluorometer equipped with quartz cuvette of 1 cm3
path length at room temperature. Luminescence lifetime measurements were carried out by using
time-correlated single photon counting from HORIBA Jobin Yvon. Cyclic voltammetry
measurements were performed with a CH-400A Electrochemical Analyzer. A standard three
electrode system, consisting of Pt disk working electrode, Pt wire counter electrode and Ag/AgCl
reference electrode were used. All potentials were converted to SCE scale. Tetrabutyl ammonium
perchlorate (TBAP) was used as supporting electrolyte and all measurements were carried out in
CH2Cl2 solution at room temperature with scan rate 100 m Vs-1.
2.2. Synthesis
2.2.1. Synthesis of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (1)
A flask was charged with [C6H3-1,3-{C≡C-trans-[RuCl(dppe)2]}2-5-(C≡CH)] (1.000g, 0.496
mmole), 3-iodopyridine (0.102g, 0.496 mmole), PdCl2(PPh3)2 (0.007 g, 2% mole ratio) and CuI
(0.008g, 8% mole ratio) and then 25 ml of triethylamine was added to it. The reaction mixture was
refluxed for 17 h at 60 0C. The solvent was reduced to small volume under vacuum and then passed
through a short pad of neutral alumina using 3:1 CH2Cl2:Pet.ether as eluent. Removal of the solvent
under vacuum yielded a brown coloured solid.
Yield: 72%; Elemental analyses (C, H and N, Wt %) Anal.Calc. for C121H103NCl2P8Ru2: C,
69.47; H, 4.96; N, 0.67. Found: C, 69.37; H, 4.72; N, 0.75%; IR (KBr) (cm-1): 2074, ʋ(C≡C);
1
1487, 1441, 1172, 699, ʋ(dppe); H NMR (CDCl3) (300MHz):  8.76 (s, 1H, Py-HoN, C≡C),
o
8.62 (s, 1H, Py-HoN, C≡C),  2.72 (m, 16H, PCH2CH2P),  6.62–7.80 (m, 85H, phenyl); 31P
p
NMR:  53.93. ESI MS: 2115 ([NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2+Na]+ 26),
,
898 ([RuCl(dppe)2]+ 100).
,
4

2.2.2. Synthesis of [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2Cl] (1a)
To a solution of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (0.400g, 0.191 mmol) in
dichloromethane (10 ml), the Schiff base ligand L1 in 5 ml methanol (0.041g, 0.191 mmol) and
CuCl (0.019g, 0.191 mmol) were added. The reaction mixture was refluxed for 3 h and then
the solution was evaporated to a small volume under vaccum. The reddish brown colored
complex was developed by diffusion of diethyl ether in to the solution.
Yield: 68%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C134H115N3OCl3P8CuRu2:
C, 66.97; H, 4.82; N, 1.75. Found: C, 66.87; H, 4.76; N, 1.79%; IR (KBr) (cm-1): 2051,
ʋ(C≡C); 1583, ʋ(C=N); 1478, 1436, 1165, 689, (dppe); 1H NMR (CDCl3) (300 MHz):  9.20 (s,
1H, HC=N),  8.79 (s, 1H, Py-HoN, oC≡C), 8.63 (s, 1H, Py-HoN, pC≡C),  3.88 (s, 3H, OCH3), 
2.74 (m, 16H, PCH2CH2P),  6.82-7.98 (m, 93 H, phenyl); 31P NMR:  53.96. ESI MS: 2426
([Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2Cl+Na]+, 26), 2191 ([Cu(NC5H4-C≡C-
C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2Cl]+, 100) , 898 ([RuCl(dppe)2]+, 38).
2.2.3. Synthesis of [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2I] (1b)
The complex 1b was prepared similar to the procedure performed in the preparation of 1a except that
CuCl was replaced by CuI (0.036g, 0.191 mmol).
Yield: 76%; Elemental analysis (C, H and N, Wt %) Anal. Cal for C134H115N3OCl2IP8CuRu2: C,
64.52; H, 4.65; N, 1.68. Found: C, 64.39; H, 4.61; N, 1.87%; IR (KBr) (cm-1): 2056, ʋ(C≡C), 1587,
ʋ(C=N); 1481, 1433, 1159, 693, (dppe); 1H NMR (CDCl3) (300 MHz):  9.18 (s, 1H, HC=N), 
8.79 (s, 1H, Py-HoN, oC≡C), 8.65 (s, 1H, Py-HoN, pC≡C),  3.87 (s, 3H, OCH3),  2.73 (m, 16H,
31
PCH2CH2P),  6.83–7.96 (m, 93H, phenyl); P NMR:  53.96. ESI MS: 2517 ([Cu(L1)NC5H4-
C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2I+Na]+, 28), 2282 ([Cu(N C5H4-C≡C-C6H3-1,3-
{C≡C-trans-RuCl(dppe)2}2I]+, 100), 898 ([RuCl(dppe)2]+, 43).
2.2.4. Synthesis of [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3] (1c)
To a solution of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (0.400g, 0.191 mmol) in
dichloromethane (10 ml), a solution of Schiff base ligand L1 (0.041g, 0.191 mmol) in methanol (5 ml)
5

and CuI (0.036 g, 0.191 mmol) was added while stirring. To this a solution of NaN3 (0.012 g, 0.191
mmol) in warm methanol (5 ml) was added. The resultant mixture was stirred for 6 hrs at room
temperature. The solid product was obtained by evaporation of solvent under vacuum over CaCl2.
Yield: 71%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C134H115N6OCl2P8CuRu2: C,
66.79; H, 4.81; N, 3.49. Found: C, 66.74; H, 4.76; N, 3.56%; IR (KBr) (cm-1): 2058, ʋ(C≡C);
1
1585, ʋ(C=N); 2049, 1345 ʋ(N3); 1482, 1435, 1164, 693, ʋ(dppe); H NMR (CDCl3)
(300MHz):  9.19 (s, 1H, HC=N),  8.77 (s, 1H, Py-HoN, C≡C), 8.63 (s, 1H, Py-HoN, C≡C),
o
p
31
 3.88 (s, 3H, OCH3),  2.73 (m, 16H, PCH2CH2P),  6.89–8.05 (m, 93 H, phenyl); P NMR: 
53.94. ESI MS: 2433 ([Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3+Na]+, 27), 2198
([Cu(NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3]+, 100), 898 ([RuCl(dppe)2]+, 39).
2.2.5. Synthesis of [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2NCS] (1d)
To a solution of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (0.400g, 0.191 mmol) in
dichloromethane (10 ml) a solution of Schiff base ligand L1 (0.041g, 0.191 mmol) in methanol
(5 ml) and CuI (0.036g, 0.191 mmol) was added while stirring. To this a solution of NH4SCN (0.014 g,
0.191 mmol) in warm methanol (5 ml) was added. The resultant mixture was stirred for 6 hrs at room
temperature. The solid product was obtained by evaporation of solvents under vacuum over CaCl2.
Yield: 69%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C135H115N4OSCl2P8CuRu2:
C, 66.84; H, 4.78; N, 2.31. Found: C,66.67; H,4.76; N, 2.40%; IR (KBr) (cm-1): 2057, ʋ(C≡C);
1589, ʋ(C=N); 2073 ʋ(NCS); 1481, 1434, 1163, 690, (dppe); 1H NMR (CDCl3) (300MHz): 
9.18 (s, 1H, HC=N),  8.80 (s, 1H, py-HoN, C≡C), 8.64 (s, 1H, Py-HoN, C≡C),  3.87 (s, 3H,
o
p
OCH3), 2.75 (m, 16H, PCH2CH2P),  6.90–8.07 (m, 93 H, phenyl); 31P NMR:  53.93. ESI MS:
2449 ([Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2NCS+Na]+, 29), 2214 ([Cu(NC5H4-
C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2NCS]+, 100), 898 ([RuCl(dppe)2]+, 42).
2.2.6. Synthesis of [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2Cl] (2a)
The complex 2a was prepared similar to the procedure performed in the preparation of 1a except that
L1 was replaced by L2 (0.043g, 0.191 mmol).
6

Yield: 68%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C133H112N4O2Cl3P8CuRu2: C,
66.06; H, 4.67; N, 2.32. Found: C, 66.01; H, 4.56; N, 2.45%; IR (KBr) (cm-1): 2063, ʋ(C≡C); 1596,
1
ʋ(C=N); 1482, 1435, 1163, 694, (dppe); H NMR (CDCl3) (300 MHz):  9.22 (s, 1H, HC=N),
 8.83 (s, 1H, Py-HoN, C≡C), 8.65 (s, 1H, Py-HoN, C≡C),  2.75 (m, 16H, PCH2CH2P),  6.85-
o
p
7.99 (m, 93 H, phenyl); 31P NMR:  53.95. ESI MS: 2441 ([Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2Cl+Na]+, 21), 2191([Cu(NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2Cl]+,
100), 898 ([RuCl(dppe)2]+, 47).
2.2.7. Synthesis of [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2I] (2b)
The complex 2b was prepared similar to the procedure performed in the preparation of 1b except that
L1 was replaced by L2 (0.043 g, 0.191 mmol).
Yield: 72%; Elemental analysis (C, H and N, Wt %) Anal. Cal for C133H112N4O2Cl2IP8CuRu2: C,
63.65; H, 4.50; N, 2.23. Found: C, 63.58; H, 4.46; N, 2.37%; IR (KBr) (cm-1): 2060, ʋ(C≡C),
1589, ʋ(C=N); 1481, 1432, 1159, 693, (dppe); 1H NMR (CDCl3) (300 MHz):  9.21 (s, 1H, HC=N),
 8.85 (s, 1H, Py-HoN, oC≡C), 8.64 (s, 1H, Py-HoN, pC≡C),  2.74 (m, 16H, PCH2CH2P),  6.85–
7.98 (m, 93H, phenyl); 31P NMR:  53.96. ESI MS: 2532 ([Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2I+Na]+, 31), 2282 ([Cu(NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2I]+,
100), 898 ([RuCl(dppe)2]+, 38).
2.2.8. Synthesis of [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3] (2c)
The complex 2c was prepared similar to the procedure performed in the preparation of 1c
except that L1 was replaced by L2 (0.043 g, 0.191 mmol).
Yield: 76%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C133H112N7O2Cl2P8CuRu2:
C, 65.88; H, 4.66; N, 4.04. Found: C, 65.74; H, 4.59; N, 4.15%; IR (KBr) (cm-1): 2058,
1
ʋ(C≡C); 1590, ʋ(C=N); 2057, 1349 ʋ(N3); 1481, 1435, 1165, 693, ʋ(dppe); H NMR (CDCl3)
(300MHz):  9.22(s, 1H, HC=N),  8.84 (s, 1H, Py-HoN, C≡C), 8.63 (s, 1H, Py-HoN, C≡C), 
o
p
31
2.73 (m, 16H, PCH2CH2P),  6.90–8.09 (m, 93H, phenyl); P NMR:  53.95. ESI MS: 2448
([Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3+Na]+, 23), 2198 ([Cu(NC5H4- C≡C-
C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2N3]+, 100), 898 ([RuCl(dppe)2]+, 43).
7

2.2.9. Synthesis of [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2NCS] (2d)
The complex 2d was prepared similar to the procedure performed in the preparation of 2d
except that L1 was replaced by L2 (0.043 g, 0.191 mmol).
Yield: 74%; Elemental analyses (C, H and N, Wt %) Anal. Cal for C134H112N5O2SCl2P8 CuRu2: C,
65.94; H, 4.63; N, 2.87. Found: C, 65.87; H, 4.59; N, 2.97%; IR (KBr) (cm-1): 2061, ʋ(C≡C); 1592,
1
ʋ(C=N); 2078 ʋ(NCS); 1481, 1434, 1163, 690, (dppe); H NMR (CDCl3) (300MHz):  9.20 (s,
1H, HC=N),  8.82 (s, 1H, Py-HoN, oC≡C), 8.64 (s, 1H, Py-HoN, pC≡C),  2.75 (m, 16H, PCH2CH2P),
31
 6.90–8.08 (m, 93H, phenyl); P NMR:  53.95. ESI MS: 2464 ([Cu(L2)N C5H4-C≡C-C6H3-
1,3-{C≡C-trans-RuCl(dppe)2}2NCS+Na]+, 26), 2214 ([Cu(NC5H4-C≡C-C6H3- 1,3-{C≡C-trans-
RuCl(dppe)2}2NCS]+, 100), 898 ([RuCl(dppe)2]+, 46).
3. Results and discussion
3.1. Synthesis of complexes
A synthesis of ruthenium-alkynyl complex [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2]
(1) was achieved by following the reaction sequence depicted in Scheme 1. The starting material
1, 3, 5-triethynylbenzene was prepared by Pd(II)/Cu(I)-catalyzed coupling reaction of 1,3,5-
tribromobenzene followed by reaction with KOH in methanol according to the procedure
reported earlier [24]. The complex 1 was synthesized by the reaction of 1,3,5-triethynylbenzene
with cis-[RuCl2(dppe)2] assisted by NaPF6. The reaction was controlled by steric hindrance as
only two RuCl2(dppe)2 units will add to 1,3,5-triethynylbenzene. Further reaction of [C6H3-1,3-
{C≡C-trans-[RuCl(dppe)2]}2-5-(C≡CH)] with 3-iodopyridine in presence of Pd(II)/Cu(I) as a
catalyst at reflux temperature followed by column chromatography (Al2O3) afforded [NC5H4-C≡C-
C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] as a binuclear complex 1 (dppe=1,2-bis(diphenyl
phosphinoethane)). Further, reaction of equimolar quantities of 1 with a copper(I) salt CuX (X =
Cl-, I-, N3- and NCS) in presence of iminopyridine ligand L1 and L2 in dichloromethane under
ambient conditions afforded the heterometallic complexes of the type [Cu(L1)NC5H4-C≡C-
C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2X] (1a-d) and [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-
8

RuCl(dppe)2}2X] (2a-d). The complexes prepared show a great thermal stability and are moisture
insensitive in solid phase. They are freely soluble in dichloromethane, chloroform and methanol.
Composition and identity of all complexes were deduced from satisfactory elemental analysis,
FT-IR, UV-Vis, 1H NMR, and mass spectral studies.
3.2. IR and NMR spectroscopy
The IR spectra of 1 exhibit a medium intensity band at 2074 cm-1 corresponds to stretching
frequency of (C≡C). Upon coordination this band observed in lower frequency region at 2051-
2058 for 1a-d and 2058-2063 for 2a-d suggesting perturbation of the phenyl site leads to electron
dissipation at triple bond through conjugation [27]. A strong band observed at ~1625 cm-1 in
iminopyridine ligands L1 and L2 corresponds to ʋ(HC=N) shifted to lower frequency at 1583 -
1589 cm-1 in 1a-d and 1589-1596 cm-1 in 2a-d indicating π-back bonding from the electron rich
copper(I) centre to vacant imine π* orbital [28]. This view was further supported by appearance
of a new band at ~482 cm-1 in the spectra of all complexes corresponding to ʋ(Cu-N) stretching
mode vibration [29]. The spectra of all complexes exhibit expected bands due to dppe ligand at
around 1484, 1436, 1169 and 693 cm-1. The azido complexes 1c and 2c exhibit asymmetric
stretching ʋas(N3) at ~2053 cm-1 and symmetric ʋs(N3) vibration mode at ~1347 cm-1 are
corresponds to presence of a terminally coordinated azido group in the complexes [30]. The
thiocynato complexes 1d and 2d exhibit a very sharp and strong band at ~2075 cm-1, a medium
intensity band at ~762 cm-1 and a weak band at ~485 cm-1 which can be assigned to ʋ(CN),
ʋ(CS) and ʋ(NCS), respectively. The intensities and position of these bands indicate monodentate
coordination of the thiocynate group through nitrogen [31].
The 1H NMR spectra of all compounds were recorded in CDCl3 and are given in section 2. The
1H NMR spectroscopic properties of 1a-d and 2a-d are consistent with their formulation as
heterometallic ruthenium-acetylide based complexes. An important observation is the shifting
1
of some resonance in 1a-d and 2a-d as compared to their metallic precursor 1. The H NMR
spectra of 1 exhibit a broad multiplet in the region 6.62-7.80 ppm assigned to phenyl protons of
the dppe ligand together with ring protons of organometallic moiety. After coordination to
9

copper(I) along with iminopyridine ligand L1 or L2 the values of these resonance shifted to
lower frequency region and observed at 6.82-8.07 ppm in 1a-d and 6.85-8.09 ppm in 2a-d
where; additional peaks were observed due to iminopyridine ligand. Aside from the aromatic
protons, the imine proton appears as a singlet at 9.19 ppm in 1a-d and 9.21 ppm in 2a-d. The
downfield shift of imine proton in 1a-d and 2a-d relative to free ligands L1 and L2 can be attributed
1
to deshielding effect resulting from the coordination of the ligand to copper(I) ion [32]. The H
NMR spectra of all complexes exhibit a broad singlet at approximately 2.74 ppm due to CH2
protons of the dppe ligand [33]. In addition to these, a sharp singlet at 3.88 ppm in the spectra of
1a-d corresponds to methoxy proton in the complexes [34].
31P NMR spectra of 1a-d and 2a-d and their metallic precursor 1 display only a single
resonance at ~53.95 ppm. 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 [35].
3.3. Absorption and emission properties
The electronic absorption spectra of all complexes were recorded in dichloromethane solution
(10-4 M) at 298 K and data are summarized in Table 1. The absorption spectra of 1 exhibit an
intense band at 285 nm (Fig. 1) caused by intraligand (π→π*) transitions (within pyridine
cycles). Another intense band at λmax 327 nm in 1 is assigned to dπ(Ru)π*(CCR) metal to
ligand charge transfer (MLCT) transition. The electronic absorption spectra of Cu(I)/Ru(II) hybrid
complexes show intense absorption band at ca 295-298 nm for 1a-d and 293-299 nm for 2a-d
which are tentatively assigned as phosphine centred intraligand transition. In addition to high
energy band a low energy absorption band at ca 334-350 nm in 1a-d and 348-351 nm in 2a-d (Fig.
2) are likely assigned as a mixture of intraligand (π→π*) transition with metal to ligand charge
transfer transition. The observed bathochromic shift in these complexes relative to 1 is in
accordance with the coordination of pyridyl nitrogen to the copper (I) centre.
The emission properties of all compounds were explored at room temperature in CH2Cl2 solution
(10-4 M) and the data are summarized in Table 2. The ruthenium-alkynyl complex 1 exhibit
intense broad emission band at 435 nm upon excitation at 370 nm (Fig. 3). The emission origin in
complex 1 has been ascribed to originate from triplet excited state of intra-ligand(ππ* CCR)
10

Table 1. UV-Visible absorption data of 1a-d and 2a-d in CH2Cl2
Complex
λmax(nm)(ε x103, M-1 cm-1)
295 (14.1), 334 (6.1)
1a
297 (15.8), 337 (7.5)
295 (18.2), 348 (7.5)
298 (18.8), 350 (8.6)
293 (17.3), 349 (6.6)
295 (18.2), 348 (7.5)
293 (17.3), 349 (6.6)
299 (19.2), 351 (8.9)
1b
1c
1d
2a
2b
2c
2d
character predominantly localized on the phenyl ring with mixing of metal character through
the interaction of ruthenium dπ-orbital with pπ-orbital of alkynyl ligand [36]. The
heterometallic complexes 1a-d exhibit a broad emission at 476-517 nm upon excitation at 353-
379 nm whereas; 2a-d exhibit emission at 486-531 nm upon excitation at 356-378 nm. On
comparing the emission maxima of 1a-d and 2a-d with their metallic precursor 1, a red shift to
a tune of 62 and 73 nm, respectively has been observed. These results confirm the formation of
heterometallic species which leads to formation of comparatively rigid structure by
complexation of 1 with copper(I) ion and thus reduces the nonradiative energy loss [37,38]. It
was observed that the emission properties of 1a-d and 2a-d appears at longer wavelength (476-
517 nm and 486-531 nm) as compared to previously reported similar Cu/Ru complexes.
Moreover, the substituted group on coordinated iminopyridine ligands have significant
influence on emission intensities as well as wavelength of the complexes. A red shift of ~10
nm was observed when -NO2 group was introduced instead of -OCH3 group forming the
complexes 2a-d. The observed red shift in wavelength in these complexes might be due to
extra conjugation backbone offered by -NO2 group which lower the π*(C≡CH) orbital energy
and lead to narrowing the HOMO-LUMO energy gap. It was also observed that, the emission
intensity is significantly quenched in 2a-d by the presence of electron withdrawing
-NO2
group [39]. No significant effect was observed on emission energies in the complexes due to
different halogens from the copper(I) halide adduct (1a, 1b, 2a and 2b). However,
11

pseudohalide complexes (1c, 1d, 2c and 2d) show high emissivity as compare to halide
complexes and follow the sequence ClI<N3<NCS presumably due to better quenching ability
of the halogens [40]. The emission quantum yield (ϕ) of all the complexes was determined with
reference to quinine sulfate (ϕ = 0.52 at 298 K) and appears approximately at 0.053-0.069 for
1a-d and 0.055-0.071 for 2a-d [41]. It is noticeable from Table 2 that the pseudohalide
complexes 1c, 1d, 2c and 2d shows high quantum yields as compare to other halide complexes
1a, 1b, 2a and 2b. Life time data of all the complexes were obtained upon excitation at 320 nm
and are summarized in Table 2. Compare to halide complexes, the average lifetime of
pseudohalide complexes is longer than those observed for halide complexes (Table 2). These
results could be attributed to red shifted emission and reduced emission intensity observed in
halide complexes as compare to pseudohalide complexes.
Table 2. Photoluminescence data of 1a-d and 2a-d in CH2Cl2
Complex λex(nm) λem(nm)
τ (ns) Kr(s−1/107) Knr(s−1/109)

353
356
373
379
356
359
374
378
476
479
516
517
486
488
527
531
0.053
2.66
2.59
3.79
3.75
2.84
2.91
3.76
3.74
1.992
2.084
1.715
1.840
1.936
1.958
1.808
1.898
0.356
0.365
0.246
0.248
0.332
0.324
0.247
0.248
1a
1b
1c
1d
2a
2b
2c
2d
0.054
0.065
0.069
0.055
0.057
0.068
0.071
3.4. Solvatochromism of the complexes
A good solubility of the complexes in a wide range of organic solvents makes them notable
solvatochromic compounds. However, solvatochromism studies of Cu(I)/Ru(II) halide and
pseudohalide hybrid complexes were carried out by dissolving the complexes in
chlorobenzene, dichloromethane and tetrahydrofuran with a 10-4 M concentration. The
absorption peaks of complexes 1a-d and 2a-d in different solvents are almost same. This
suggests that the polarity of the solvents has very little influence on the energy levels of all
molecules. The differences in emission maxima of the complexes in solvents with different
polarities were summarized in Table 3. As shown in Fig. 4, the position of emission band in
12

1a-d and 2a-d is sensitive to polarity of the solvents. Complexes 1a-d exhibit emission at 470-
512 nm in chlorobenzene, 476-517 nm in dichloromethane and 496-537 nm in tetrahydrofuran.
However, the complexes 2a-d exhibit emission peak at 475-523 nm emission peak at 475-523
nm in chlorobenzene, 486-531 nm in dichloromethane and 498-545 nm in tetrahydrofuran.
These results confirm that the excited state of all Cu(I)/Ru(II) hybrid complexes are more
stabilized with increasing polarity of the solvents which leads to a red shift in emission with
increasing solvent polarity [42].
Table 3: Emission maxima and Quantum yield data of 1a-d and 2a-d in various solvents
Complex
Solvent
λex (nm)
352
353
355
356
356
358
371
373
374
378
379
382
355
356
358
357
359
360
373
374
374
375
378
379
λem (nm)
470
476
496
474
479
499
509
516
534
512
517
537
475
486
498
477
488
501
518
527
539
523
531
545
Quantum Yield (ϕ)
0.055
0.053
0.049
0.055
0.054
0.051
0.069
0.065
0.063
0.074
0.069
0.067
0.059
0.055
0.054
0.060
0.057
0.052
0.073
0.068
0.061
0.076
0.071
0.069
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
Chlorobenzene
Dichloromethane
Tetrahydrofuran
1a
1b
1c
1d
2a
2b
2c
2d
13

3.5. Thermogravimetric analysis
To examine the thermal stability of the complexes 1a-d and 2a-d, thermo gravimetric analysis
(TGA) were performed between 25-800°C under nitrogen atmosphere with controlled heating
o
rate 10 C min-1. TGA curve of 1a, 1b, 1c and 1d shows that the complexes are stable up to
243, 244, 257 and 259 0C revealing absence of water or solvent molecules. The complexes then
undergo a weight loss of 19.61 (1a), 22.56 (1b), 19.80 (1c) and 20.31 (1d) % in the
temperature range of 244-349, 245-351, 258-359 and 260-3600C, respectively due to
iminopyridine, pyridylacetyl moiety and halide or pseudohalide (calcd. 19.67 (1a), 22.62(1b),
19.89 (1c) and 20.42(1d)%). The second stage keep losing weight from 350-553, 352-555,
o
360-603 and 361-611 C accompanied by mass loss of 69.12 (1a), 66.57 (1b), 68.87 (1c) and
68.49 % (1d) attributed to decomposition of dppe along with Cl- ligand (calcd. 69.26 (1a),
66.72 (1b), 69.07 (1c) and 68.61 % (1d)). The complexes 2a, 2b, 2c and 2d shows very
similar behaviour to the above; once again an absence of water or solvent is indicated by
stability of the complexes up to 245, 248, 255 and 258 0C for 2a, 2b, 2c and 2d, respectively.
However, the first decomposition stage occurs in the range 246-357, 249-359, 256-363 and
0
259-365 C with mass loss of 20.09, 23.01, 20.25 and 20.71 for 2a, 2b, 2c and 2d attributed
loss of iminopyridine, pyridylacetyl moiety and halide or pseudohalide (calcd 20.17 (2a),
23.08 (2b), 20.39 (2c) and 20.91 % (2d)). The complexes then undergo a rapid and significant
weight loss of 68.73 (2a), 66.19 (2b), 68.59 (2c) and 68.01 % (2d) in the temperature range
o
358-560, 360-568, 364-612 and 366-619 C, respectively (calcd 68.83 (2a), 66.32 (2b), 68.64
(2c) and 68.19 % (2d)) indicating decomposition of dppe and Cl- ligand.
3.6. Cyclic Voltammetry
In order to gain insight into the electronic environment of all complexes the electrochemical
properties of 1 and its trinuclear Cu(I)/Ru(II) hybrid complexes 1a-d and 2a-d were studied by
cyclic voltammetry. All the measurements were performed in dichloromethane solution
(10-3 M) containing 0.05 M n-Bu4NClO4 as a supporting electrolyte at room temperature in the
potential range +1.50 to -1.50 V with a scan rate of 100 mVs-1. The electrochemical data for
the Cu(I)/Ru(II) hybrid complexes are given in Table 4 and cyclic voltammogram of 1a and 2a
are shown in Figure 5.
14

The cyclic voltammetry data for ruthenium acetylide compound 1 reveals two reversible
oxidations with narrow range at 0.54 and 0.75 assigned to Ru(II)/Ru(III) processes at
ruthenium atom separated by 1,3-diethynylbenzene unit. The electrochemical behaviour of
1a-d and 2a-d revealing that all complexes undergo quasireversible oxidation processes in the
range 0.721-0.727 V (E1/2) for 1a-d and 0.723-0.732 V (E1/2) for 2a-d corresponds to
Cu(I)/Cu(II) couple. Another oxidation process observed at 0.877-0.886 V and 1.070-1.079 V
(E1/2) in 1a-d and 0.881-0.889 V and 1.075-1.081 V (E1/2) for 2a-d assigned to Ru(II)/Ru(III)
couple. These values are slightly shifted towards negative potentials as compared to previously
reported similar Cu(I)/Ru(II) complexes due to incorporation of one more ruthenium atom into
1a-d and 2a-d. Compare to 1 the complexes 1a-d and 2a-d shows an increase in the ease of
oxidation which is due to coordination of pyridyl group to copper(I) centre which increases the
electron density around copper(I) and ruthenium(II) centres through an inductive effect. It is
evident from Table 4 that, the electrochemical properties correlate well with the nature of
substituent group on the iminopyridine ligand. The complexes with electron donating -OCH3
group (1a-d) shifted to more negative potential as compared to complexes with electron
withdrawing -NO2 group (2a-d). Moreover, the redox responses for thiocynato (1d and 2d)
Table 4: Electrochemical data of 1a-d and 2a-d
Ru(II)/Ru(III)
Cu(I)/Cu(II)
I
II
Compound Epa(V) Epc(V) E1/2(V) Epa(V) Epc(V) E1/2(V) Epa(V) Epc(V) E1/2(V)
0.775
0.780
0.785
0.782
0778
0.668
0.669
0.670
0.668
0.669
0.673
0.675
0.669
0.721
0.724
0.727
0.725
0.723
0.728
0.732
0.726
0.916
0.920
0.928
0.925
0.919
0.923
0.930
0.927
0.838
0.839
0.845
0.841
0.843
0.844
0.848
0.844
0.877
0.879
0.886
0.883
0.881
0.883
0.889
0.885
1.129
1.133
1.135
1.128
1.135
1.136
1.138
1.130
1.011
1.018
1.024
1.018
1.015
1.021
1.025
1.022
1.070
1.075
1.079
1.073
1.075
1.078
1.081
1.076
1a
1b
1c
1d
2a
2b
2c
2d
0.783
0.789
0.783
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.001 M; solvent: CH2Cl2; E1/2 = ½( Epa +
Epc); scan rate: 100 mVs-1. All potentials vs. SCE.
15

complexes appear at less positive potential (0.725-1.073 V and 0.726-1.076 V) analogue than
for azido complexes (1c and 2c) complexes (0.727-1.079 V and 0.732-1.081 V). These results
are in good agreement with those are reported in the literature [43].
4. Conclusion
A new series of heterometallic complexes of the type [Cu(L1)NC5H4-C≡C-C6H3-1,3-{C≡C-
trans-RuCl(dppe)2}2X] (1a-d) and [Cu(L2)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2
X] (2a-d) derived from the reaction of [NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (1)
with copper(I) salts in the presence of L1 and L2 in CH2Cl2/MeOH mixture. TGA studies of the
complexes reveals that the pseudohalide complexes are thermally more stable than the halide
complexes. The electrochemical behaviour of 1a-d and 2a-d suggest that all complexes display
a quasireversible redox behaviour corresponding to Cu(I)/Cu(II) and Ru(II)/Ru(III) couples.
Room temperature luminescence is observed for all Cu(I)/Ru(II) hybrid complexes with high
quantum yield in dichloromethane solution. The variation of the substituent groups with
different electronic properties on iminopyridine ligand and quenching ability of halide and
pseudo halides shows marked effect on emission wavelength and intensity of the complexes.
The effects of different polarities of the solvents on absorption properties suggest that the
polarity of the solvents has very little influence on the energy levels of all molecules. However,
excited state of all complexes is stabilized and red shifted in their emission wavelength with
increasing polarity of the solvent
Acknowledgements
We gratefully acknowledge financial support from Science and Engineering Research Board (SERB
No. SB/EMEQ-267/2013 dated 01/08/2013), New Delhi, Govt. of India. SBP is thankful to Science
and Engineering Research Board (SERB), New Delhi for awarding Project Fellowship
16

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18

Figure captions:
Scheme 1: Synthetic route to metal-alkynyl complex 1 and complexes 1a-d and 2a-d.
Fig. 1:
Fig. 2:
Fig. 3:
Fig. 4:
UV-Visible absorption spectra of 1 in CH2Cl2 solution.
UV-Visible absorption spectra of (A) 1a-d (B) 2a-d in CH2Cl2 solution.
Emission spectra of 1 in CH2Cl2 solution.
Emission spectra of 1a-d and 2a-d in different solvents: chlorobenzene,
dichloromethane and tetrahedrofuran.
Fig. 5:
Cyclic voltammogram of 1a and 2a measured in CH2Cl2 (10-3 M) and 0.05 M
n-Bu4NClO4 as supporting electrolyte. Potentials vs. SCE.
19

Scheme 1
Si(CH3)3
H
Br
KOH
(CH3)3SiC
CH
CH2Cl2, MeOH
PdCl2(PPh3)2/CuI
NEt3, CH2Cl2
Br
Br
Si(CH3)3
Si(CH3)3
H
H
NaPF6
cis-
RuCl2(dppe)2
CH2Cl2/NEt3
N
H
I
N
PPh2
PPh2
Ru
Ph2P
Ru
Ph2P
Ph2P
Cl
PdCl2(PPh3)2/CuI
NEt3, CH2Cl2
Ph2P
Cl
PPh2
Cl
Ru
PPh2
Cl
Ru
PPh2
Ph2P
PPh2
Ph2P
Ph2P
PPh2
Ph2P
PPh2
1
N
N
R
MeOH
CH2Cl2
CuX
PPh2 Cl
Ru
PPh2
PPh2
PPh2
Where, X= Cl, I, N3 and NCS
R= OCH3 (1a-d), NO2(2a-d)
N
N
Cu
PPh2
PPh2
X
N
Ru
PPh2
PPh2
Cl
R
1a-d and 2a-d
Fig. 1
20

Fig.2
(A)
(B)
Fig. 3
21

Fig. 4
22

23

Fig. 5
(A)
(B)
24

Graphical Abstract- Pictogram:
PPh2 Cl
Ru
PPh2
PPh2
PPh2
X= Cl, I, N3 and NCS
N
Cu
N
N
R= OCH3 (1a-d), NO2(2a-d)
PPh2
X
Ru
PPh2
PPh2
PPh2
Cl
R
25