Transition-Metal Chelates of Terpyridine-Fullerene/Nanotube Diads: Synthesis and Redox Properties

Article abstract of DOI:10.1080/15533174.2014.963249

The authors discuss the synthesis of two carbon cluster-based chelating tridentate ligands, terpyridyl-pyrrolidine-fullerene (C₆₀-tpy) and terpyridyl-pyrrolidine multiwalled carbon nanotube (MWCNT-tpy), by 1,3-dipolar cycloaddition. The two che

Full text of DOI:10.1080/15533174.2014.963249

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Transition-Metal Chelates of Terpyridine-Fullerene/
Nanotube Diads: Synthesis and Redox Properties
Zhen-Yi Wu & Wei Wang
To cite this article: Zhen-Yi Wu & Wei Wang (2016) Transition-Metal Chelates of
Terpyridine-Fullerene/Nanotube Diads: Synthesis and Redox Properties, Synthesis and
Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 46:3, 428-436, DOI:
10.1080/15533174.2014.963249
To link to this article: http://dx.doi.org/10.1080/15533174.2014.963249
Accepted author version posted online: 05
Oct 2015.
Submit your article to this journal
Article views: 71
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=lsrt20
Download by: [University of Nebraska, Lincoln]
Date: 04 December 2015, At: 04:12

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2016) 46, 428–436
Copyright © Taylor and Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2014.963249
Transition-Metal Chelates of Terpyridine-Fullerene/
Nanotube Diads: Synthesis and Redox Properties
ZHEN-YI WU and WEI WANG
State Key Lab for Physical Chemistry of Solid Surfaces, Department of Chemistry and College of Chemistry and Chemical
Engineering, Xiamen University, Xiamen, P. R. China
Received 13 April 2014; accepted 24 August 2014
The authors discuss the synthesis of two carbon cluster-based chelating tridentate ligands, terpyridyl-pyrrolidine-fullerene (C60-tpy)
and terpyridyl-pyrrolidine multiwalled carbon nanotube (MWCNT-tpy), by 1,3-dipolar cycloaddition. The two chelating ligands
further coordinate with Ru(III) ions to yield two carbon cluster-based ruthenium complexes, C60-tpyRu(H2O)3Cl3 and MWCNT-
tpyRu(H2O)3Cl3. The synthesized ligands and complexes were characterized by mass spectroscopy, nuclear magnetic resonance
spectroscopy, infrared spectroscopy, ultraviolet/visible spectroscopy spectrometry, Raman spectroscopy, X-ray photoelectron
spectroscopy, thermogravimetric analysis, and differential pulse voltammetry. Results show that grafting of carbon-clusters with the
terpyridine ligand decrease the p* orbital energy level of the terpyridine moiety, and the electron-withdrawing ability of C60 is
stronger than that of MWCNTs. This work aims to lay the foundation for the practical application of fullerenes and carbon
nanotubes as functional materials.
Keywords: fullerene, carbon nanotubes, ruthenium polypyridyl complex
Introduction
toluidine-modified CNTs possess excellent optical and electri-
cal properties[15]; DNA modified CNTs can be used to fabri-
Carbon nanotubes (CNTs) show extremely high mechanical cate biosensors.[16] Consequently, functionalized CNTs have
strength,[1] have low density,[2] and exhibit unique electro- potential applications in many fields such as catalyst car-
chemical,[3] magnetic,[4,5] optical,[6,7] and catalytic[8,9] proper- riers,[17] nanosensors,[18] nanoelectrodes,[19] photoelectro-
ties. These outstanding properties offer CNTs great potential chemical nanotransistors,[20,21] and nonlinear optical
for wide applications. However, CNTs easily form twisted materials.[22,23] To date, the synthesis and property study of
aggregate[1] and are difficult to disperse in most solvent sys- functionalized CNTs has gradually developed into a means
tems due to their low interfacial adhesion[11] and strong :-: of preparing the CNT composites with a specific function,
interaction. This hinders their practical exploration and utili- and bridged the gap between molecule and materials. The
zation. It is thus necessary to carry out the surface modifica- research in this area aims to lay the foundation for the CNTs’
tion for interrupting the strong van der Waals forces, and application as materials.
improving their solubility and processability in organic and/
Strategies for functionalizing CNTs mainly include cova-
or inorganic solvents. Accordingly, the surface chemical lent and noncovalent chemical strategies. Noncovalent sur-
modification of CNTs is the premise of their further function- face modification is based on the supramolecular
alization. In addition, novel properties will be introduced to complexation,[24–27] and is realized through ways of p stack-
CNTs by further grafting with molecules possessing special ing, van der Waals forces, or through the polymer wrap-
properties. For example, the metal phthalocyanine-grafted ping.[28,29] Whereas the covalent modification is realized by
CNTs show significant photoelectric conversion perfor- either the “grafting to”[30] or the “grafting from”[31,32] strate-
mance[12,13]; ferromagnetic material-filled CNTs exhibit good gies. Nucleophilic aromatic substitution reaction of fluori-
electrical transport and magnetic propertie[14]; poly p- nated CNTs and esterification/amidation reaction of the
carboxyl group-modified CNTs have been used in the “graft-
ing from” method. Because the surface oxidation mainly
occurs at the CNT defects or port sites, the major drawback
of the approach is that functional groups cannot be uniformly
Physical Chemistry of Solid Surfaces, Department of Chemistry
Address correspondence to Zhen-Yi Wu, State Key Lab for
dispersed on the CNT surface. The “grafting to” method is
mainly involved in cycloadditions of aryl diazonium salts,
free radical reactions, and the 1,3-dipolar cycloaddition of
methyl amine. Wherein the 1,3-dipolar cycloaddition is the
most effective method for the CNT functionalization. By
and College of Chemistry and Chemical Engineering, Xiamen
University, Xiamen, 361005, P. R. China. E-mail: zywu@xmu.
edu.cn
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.

Terpyridine-Fullerene/Nanotube Diads
429
1
using 1,3-dipolar additions, functional groups can be uni- product. Yield: 2.59 g (52.1%). H NMR (CDCl3): d (ppm)
formly grafted onto the CNT surface to achieve stable cova- 4.58 (s, 2H), 6.74 (s, 2H), 7.28 (s, 2H), 7.42 (dd, 2H, J D
lently modified CNTs.
6.4 Hz, J D 4.4 Hz), 7.95 (t, 2H, J D 7.2 Hz), 8.79 (s, 4H),
Polypyridine (bipyridine and terpyridine) ligands have 8.76 (t, 2H, J D 7.6 Hz). ESI-MS (positive): m/z 402.4
strong coordination ability to form stable complexes with (100%).
most metal ions. These complexes have a variety of excellent
Synthesis of 40-(p-formylphenyl)-2,20:60,200-terpyridine
performances, such as optical, electromagnetic, and catalytic (tpy-PhCHO)[37]: tpy-PhCH2-Br (2.24 g, 5.57 mmol) and
properties. For example, ruthenium polypyridyl complexes HMT (2.34 g, 16.71 mmol) were dissolved in a mixture of
are the most common light-absorbing dyes in DSSC for the deionized water and ethanol (1:1). The mixture was stirred
solar cell technology. As an example, the photoelectric con- and refluxed for 6 h. 10 mL of concentrated hydrochloric
version efficiencies of dyes N3 and N719 that bipyridine acid was added, and refluxed for other 30 min. After cooling
derivatives act as ligands have reached 10% and more.[33]
to room temperature, the solution was neutralized with a satu-
Currently, the covalent linkage between CNTs and metal rated aqueous solution of sodium bicarbonate, extracted with
complexes is mainly achieved following two strategies: (a) dichloromethane. The organic phase was washed with deion-
metal complexes are firstly synthesized, and then covalently ized water and dried over anhydrous sodium carbonate. The
attached to CNTs. For example, the phthalocyanine[12] or solvent was removed by rotary evaporation to give a yellow
porphyrin-modified[34] CNTs are synthesized by using this solid. The crude product was purified by recrystallization
method. (b) Ligands covalently anchored to CNTs first, fol- from a mixture of chloroform-ethanol. This gave the product
lowing further coordination with metal ions.
tpy-PhCHO. Yield: 2.59 g (87.9%). 1H NMR (CDCl3): d
In this study, the ligand of terpyridine was covalently (ppm) 7.25–7.40 (m, 2H), 7.89 (t, 2H, J D 7.6 Hz), 8.03 (dd,
attached to C60 and MWCNTs by 1,3-dipolar addition based 4H, J D 8.4 Hz, J D 8.4 Hz), 8.67 (d, 2H, J D 8.0 Hz), 8.74
on our early works of the grafting pyridines to CNTs,[35] and (d, 2H, J D 4.0 Hz), 8.76 (s, 2H), 10.10(s, 2H). ESI-MS (posi-
then the fullerene or MWCNT-based terpyridyl ligand coor- tive): m/z 338.4 (100%).
dinated with Ru(III) ion to form the carbon cluster-based
complex.
Synthesis of C60–tpy (4): Toluene (80 mL) was added to
C60 (288 mg, 0.40 mmol), sarcosine (214 mg, 2.4 mmol), and
tpy-PhCHO (161.7 mg, 0.4 mmol) under an inert atmo-
sphere. After ultrasonic dissolution, the mixture was stirred
and refluxed at 140–150ꢀC in an oil bath for 12 h. The resul-
tant brown solution was centrifuged to remove the insoluble
Experimental
Pristine MWCNTs (95% nanotube purity, p-MWCNTs) impurities, and concentrated to approximately 15 mL by vac-
grown by chemical vapor deposition were purchased from uum distillation. The concentrated solution was applied to a
Shenzhen Nanotech Port Co., Ltd. (Shenzhen, China) (purity column of alumina (neutral alumina, 15% deactivated). Tolu-
>95%, diameter: 0–30 nm; length: 1–2 mm). [60]Fullerene ene was the initial eluant to remove the unreacted C60, and
(C60) was purchased from Wuda three-dimensional Carbon was followed by toluene-acetonitrile (10:1, v/v). The second
Cluster Materials Co., Ltd. in Wuhan City. These carbon running fraction was collected and concentrated to about
materials were used directly without further processing.
10 mL by removing the solvent through distillation under
Synthesis of tpy-PhCH3[36]: A mixture of 4-methylbenzal- nitrogen. n-hexane (20 mL) is added to precipitate C60–tpy
dehyde (2.40 g, 0.02 mol), 2-acetylpyridine (4.85 g, (176 mg, 0.162 mmol) as a brown solid. 1H NMR (CDCl3): d
0.04 mol), potassium hydroxide (3.08 g, 0.55 mol) and con- (ppm) 1.28 (s,3H), 2.99 (s,3H), 4.33 (d,1H,J D 9.6), 5.05
centrated ammonia (50 mL, 25%) in anhydrous ethanol (t,2H,J D 6.4), 7.39 (dd,2H,J D 5.2,J D 6.0), 7.92 (t, 2H, J D
(100 mL) was stirred at room temperature under air atmo- 7.6 Hz), 8.00 (s, 2H), 8.71 (d, 2H, J D 8.0 Hz), 8.75 (d, 2H, J
sphere for 24 h. Other concentrated ammonia (10 mL 25%) D 4.0 Hz), 8.79 (s, 2H). ESI-MS (positive): m/z 1084.2
was added and stirred at 60ꢀC for another 12 h. The precipi- (100%).
tate was separated by centrifugation, washed three times with
Synthesis of MWCNT–tpy: Toluene (100 mL) was added
deionized water (5 mL) and anhydrous ethanol (5 mL), and to MWCNTs (288 mg), sarcosine (856 mg, 9.6 mmol), and
crystallization from ethanol to yield tpy-PhCH3 (4.51 g, tpy-PhCHO (439.2 mg, 1.3 mmol) under an inert atmo-
69.8% yield) as a white solid. 1H NMR (CDCl3): d (ppm) 2.43 sphere. The mixture was sonicated for 30 min to obtain a sus-
(s, 3H), 7.32 (dd, 2H, J D 1.2 Hz, J D 2.2 Hz), 7.34 (t, 2H, J pension that was stirred and refluxed at 140–150ꢀC in an oil
D 2.4 Hz), 7.85 (t, 2H, J D 2.0 Hz), 7.86 (d, 2H, J D 1.6 Hz), bath for two days. Another 100 mg of tpy-PhCHO (100 mg,
8.68 (d, 2H, J D 8.0 Hz), 8.74 (d, 2H, J D 0.8 Hz), 8.75 (s, 0.3 mmol) was added. The suspension was stirred and
2H). ESI-MS (positive): m/z 324.4 (100%)
refluxed for another 3 days, cooled, and then filtered using a
Synthesis of tpy-PhCH2-Br[36]: A mixture of tpy-PhCH3 0.22 mm pore-sized polycarbonate membrane. The filter
(4.0 g, 12.38 mol), NBS (4.41 g, 24.78 mmol) and benzoyl cake was transferred to a 100 mL beaker, and ultrasonic
peroxide (BPO; 0.12g, 0.496 mmol) in dry carbon tetrachlo- washing three times using distilled water (10 mL), methanol
ride (60 mL) was stirred and refluxed at 100ꢀC in an oil bath (10 mL), and chloroform (10 mL) as detergents, respectively.
for 6 h, and filtered while hot. The filtrate was concentrated This gave MWCNT–tpy (306 mg) as a black solid.
by rotary evaporation, and cooled to room temperature. A
Synthesis of C60-tpyRu(H2O)3Cl3 (3): C60–tpy (90 mg,
yellow precipitate was obtained, and recrystallization from 0.083 mol) was dissolved in 10 mL of o-dichlorobenzene.
ethanol-acetone yielded tpy-PhCH2-Br as a pale yellow To this solution was added dropwise RuCl3 (25.8 mg) in

430
Wu and Wang
a mixture of methanol and H2O (6C6 mL) under an inert (DPV) were recorded with a CHI 660 C electrochemical ana-
atmosphere. This solution was stirred and refluxed at lyzer (Chen Hua Instrument Co., Shanghai, China) in deaer-
120ꢀC in an oil bath for 6 h. Methanol was removed at ated CHCl3-acetonitrile (4: 1, v/v) solution containing
80ꢀC by vacuum distillation. To the remaining solution 0.10 M n-Bu4NBF4 at room temperature.
was added 20 mL of toluene. A brown precipitate formed
at once. The precipitated C60-tpyRu(H2O)3Cl3 was centri-
fuged and washed three times with distilled water (5 mL), Results and Discussion
methanol (5 mL), and chloroform (5 mL). This gave C60-
tpyRu (H2O)3Cl3 (288 mg) as a brown solid. ESI-MS (pos- MWCNT-tpyRu(H2O)3Cl3
(complex
1),
C60-tpyRu
itive): m/z 1347.0(100%).
(H2O)3Cl3 (complex 3) and MWCNT-tpy (ligand 2), C60-tpy
Synthesis of MWCNT-tpyRu(H2O)3Cl3 (1): A mixture of (ligand 4) were synthesized according to the synthesis route
MWCNT–tpy (230 mg) and o-dichlorobenzene (20 mL) was shown in Figure 1. The one-pot method, which can proceeds
sonicated under an inert atmosphere for 30 min to obtain a smoothly under mild conditions, was used to synthesize 40-(p-
suspension. A solution of RuCl3 (60.6 mg) in a mixture of tolyl)-2,20:60,200-terpyridine (tpy-PhCH3) according to the
methanol and water (3C3 mL) was added. The mixture was literature,[36] and provides pure product. The aldehyde-deco-
stirred and refluxed at 120ꢀC in an oil bath for 2 h. Methanol rated terpyridine was prepared by using N-bromosuccinimide
was removed at 80ꢀC by vacuum distillation, and then filtered (NBS) as bromine source to bromide tpy-PhCH3 to get 40-(p-
using a 0.22 mm pore-sized polycarbonate membrane. The bromomethylphenyl)-2,20:60,200-terpyridine (denoted as tpy-
filter cake was transferred to a 100 mL beaker, and ultrasonic PhCH2Br) following nucleophilic substitution with hexa-
wash three times using distilled water (5 mL), methanol methylenetetramine (HMT) and hydrolysis under acidic con-
(5 mL), and chloroform (10 mL) as detergents, respectively. ditions. Up to date, the linkage of CNTs and polypyridine is
This gave MWCNT-Ru(H2O)3Cl3 (288 mg) as a black solid.
realized mainly by the reaction of aryl diazonium salt,[38] also
The samples were characterized by various standard ana- by introducing carboxylate acid groups onto the surface of
lytical techniques, including mass spectrometry (MS), nuclear CNTs and further derivatization.[39] However, the carboxyl
magnetic resonance (NMR) spectra, ultraviolet/visible spec- groups are mostly distributed in the CNT rupture sites, and
troscopy (UV-Vis), infrared spectroscopy (IR), Raman spec- the modification is very finite in extent. The use of 1,3-dipolar
troscopy, X-ray photoelectron spectroscopy (XPS), and cycloaddition reaction improve the CNT modification
thermogravimetric analysis (TGA). The MS spectra were degree. At the same time, the introduction of functional
recorded using a Daltonics mass spectrometer of Bruker (Bre- groups to the CNT sidewalls destroys the molecular forces
men, Germany); 1H NMR spectra were recorded on a Varian among CNTs, thus improve the dispersion property of CNTs
Unity 400 spectrometer (400 MHz); The UV-vis absorption in solution. Presently, the covalent attachment of the ruthe-
spectra were measured on a Shimadzu UV-2501 spectropho- nium terpyridyl complex with CNTs via a pyrrolidine bridge
tometer. For a typical sample preparation, the suspension of has not been reported. Using 1,3-dipolar cycloaddition reac-
the MWCNT-based ligand/complex in chloroform was soni- tion of the aldehyde-containing terpyridine and MWCNTs,
cated for 1 h. The IR spectra were recorded on a Nicolet we prepared two ligands of the CNT-grafted terpyridine. The
Avatar 360 Fourier transform infrared spectrometer using crude product was washed with ultrasound using water and
KBr pellets. The resonance Raman spectra were measured dichloromethane as the detergent to remove the water-soluble
using a Renishaw 1000 Raman spectroscope equipped with a sarcosine and the chloroform-soluble tpy-PhCHO to provide
514.5 nm laser at room temperature. The solid samples were the pure CNT-grafted terpyridine. The ligand of the CNT-
mounted on a glass slide. The maximum laser power on the based terpyridine can be dispersed in chloroform for a long
samples was about 6 mW. The XPS spectra were recorded on time. We got the complex 1 through stirring and refluxing the
a Quantum-2000 scanning ESCA microprobe with AlKa mixture of the MWCNT-based terpyridine ligand and RuCl3
radiation. All the spectra were calibrated with the C1s photo- in N2 atmosphere. A pure product can be obtained facilely
emission peak at 284.5 eV for sp2 hybridized carbon and ana- because the terpyridine moiety is a chelating ligand and easy
lyzed using a standard Gaussian curve fitting routine with a to coordinate with metal ions to form a single chelate.
Shirley background subtraction. TGA was conducted with a
WCT-1C medium-temperature computer differential thermal spray ionization (ESI), and matrix-assisted laser desorption–
balance under flowing air at a scan rate of 10ꢀC min¡1
ionization (MALDI) mass spectrometry have been important
In recent years, fast atom bombardment (FAB), electro-
.
Electrochemical experiments were carried out in a conven- soft ionization techniques in the research on complexes. The
tional three-electrode system, by using a platinum ball (d D high sensitivity, specificity, and speed of these techniques
2.2 mm) as the working electrode, a square platinum sheet offer many advantages over other techniques. In the ESI-MS
(1 cm2) as the auxiliary electrode, and a saturated calomel spectrum of ligand 4 (Figure 2), a maximum relative intensity
electrode (SCE) as the reference electrode. Tetrabutylammo- peak at m/z 1084.2 was detected as the molecular ion peak of
nium tetrafluoborate (TBATFB; from Alfa Aesar) was used ligand 4, its sotopic distributions are consistent with the simu-
as the supporting electrolyte, and chloroform and acetonitrile lated distributions, and a peak at m/z 777.0 corresponded to
(chromatography pure, from China National Pharmaceutical the N–methylfullopyrrolidine fragmentation. The ESI-MS
Group Chemical Reagent Co., Ltd) were used without fur- mass spectrum of complex 3 exhibits a molecular ion peak at
ther purification. All other chemicals were reagent grade. m/z 1347.0 with the maximum relative intensity. However,
Cyclic voltammetry (CV) and differential pulse voltammetry we did not observe any fragment peaks of complexes bearing

Terpyridine-Fullerene/Nanotube Diads
431
Fig. 1. Synthesis route of complexes 1 and 3 and ligands 2 and 4.
chlorine and C60-tpy as ligands, indicating that the ligands of conducted to determine the composition and the content of
the product are water molecules and C60-tpy rather than chlo- modified groups on the MWCNT surface. Figure 3 shows
rine and C60-tpy.
the XPS survey spectra of complex 1, ligand 2, and p-
The X-ray photoemission spectroscopy (XPS) is a very MWCNTs. In the spectrum of 1, the characteristic XPS
useful technique for the determination of elemental composi- peaks of C1s, Cl2p, N1s, O1s, and Ru3p were detected at
tion, content and oxidation states of a compound. The XPS 284.78, 198.65, 400.44, 532.87, and 462.95 eV, respectively,
tests of complex 1, ligand 2, and p-MWCNTs were indicating complex 1 contains five elements: C, Cl, N, O, and
Fig. 2. Mass spectra of ligand C60-tpy (a, inset: Experimental and simulated isotopic pattern of the molecular ion of ligand C60-tpy)
and complex C60-tpyRu (H2O)3Cl3 (b).

432
Wu and Wang
Fig. 3. Wide-scan XPS spectra of MWCNT-based complex 1, ligand 2, and p-MWCNTs; C1s, N1S, Cl2p, Ru3p core level spectra for
complex 1 and N1s core level spectrum for ligand 2.
Ru3p, wherein the oxygen element comes from groups of
It can be deduced that there are one ruthenium atom, eight
-OH, -COOH, and H2O on the MWCNT surface. The char- nitrogen atoms, and three chlorine atoms for every 142 car-
acteristic peaks of C1s (284.78eV), N1s (399.85eV), and O1s bon atoms in the complex 1. After subtracting the number of
(532.25eV) were observed in the spectrum of 2, showing that carbon atoms of the grafted groups and taking into account
the ligand 2 consisted of three elements, C, N, and O. Simi- the charge-neutrality principle, it can be concluded that there
larly, the measured survey spectrum of p-MWCNTs indicates are two pyrrolidine terpyridine moieties for every about 94
that p-MWCNTs contains elements of C (C1s XPS, MWCNT carbon atoms. One of the two terpyridine moieties
284.82eV) and O (O1s, 533.4 eV). In order to investigate the did not undergo coordination reaction with ruthenium(III)
content and oxidation state of each element in 1 and 2, the ion. Another terpyridine moiety, together with three water
XPS narrow scans for elements that the two samples con- molecules, coordinated with a ruthenium(III) ion to form a
tained were conducted. The C1s XPS peak of 1 was fitted to six-coordinate complex MWCNT-tpyRu(H2O)3Cl3.
five Gaussian-Lorentzian curves centered at 284.75, 285.29,
The thermogravimetric behaviors of compounds 1, 2, and
285.22, 286.71, and 291.02 eV, which are ascribed to the sp2- p-MWCNTs were investigated from room temperature to
hybridized graphite-like carbon of CNT, sp3-hybridized dia- 750ꢀC under a standard atmosphere (Figure 4). The TG
mond-like carbon of CNT, sp3-hybridized carboxyl carbon curve of 1 shows that there are three obvious weight-loss
of CNT, the sp2-hybridized carbon of the terpyridine moiety, stages from room temperature to 750ꢀC. Weight loss of about
and p–p*.
2.75% from room temperature to 214ꢀC was the decomposi-
Peak decomposition and subsequent area integration for tion of the three coordinated water molecules. This is consis-
the narrow scan XPS peaks of the above-mentioned elements tent with the XPS test results (Relative content of 2.55% for
were performed using the software XPSPEAK. By taking the three coordinated water molecules). The second weight
into account the relative sensitivity factors for each element, loss stage (10.30%) from 214 to 418ꢀC was ascribed the com-
the relative atomic content in 1 and 2 can be calculated. The bustion of three pyridine rings (XPS test result was 10.7%).
data in Table 1 show the peak area, relative sensitivity factor, The third weight loss stage (418–595ꢀC) accounted for
and relative atom number of each element.
80.0%. This was attributed to the combustion of both the
MWCNT skeleton and the uncoordinated terpyridine moiety
on the MWCNT surface. The initial decomposition tempera-
ture of the MWCNT skeleton was 483ꢀC for the complex 1.
As against, the decomposition temperatures of the MWCNT
skeleton of ligand 2 and p-MWCNTs were 555 and 586ꢀC,
respectively. Obviously, the thermal stability decreases from
p-MWCNTs, 2 to 1. The ligand 2 is less thermally stable than
p-MWCNTs. This is attributed to the destruction of the
MWCNT conjugated structure and to the introduction of
more sp3 hybridized carbon atoms after the grafting of ter-
pyridine to MWCNTs by 1,3-dipolar addition. However, the
Table 1. XPS elemental ratio analysis for 1 and 2
Peak
C1s
Ru3p N1s
Cl2p O1s
Relative sensitivity
factor
0.296 3.696 0.477 0.77 0.57
Peak area
1
2
1
2
17038 1494 1518 912 2989
17146 1499 7078
Relative atom number
142
1.00
7.90
2.93 10.40
18.43 1.00
thermal stability further decrease after the ligand
2

Terpyridine-Fullerene/Nanotube Diads
433
Fig. 6. IR spectra of MWCNT-based complex 1, ligand 2, tpy-
phCH3, and p-MWCNTs.
D mode and G mode (ID/IG) reflects the defect extent of
CNTs, the change of ID/IG in the Raman spectra of function-
alized CNTs is strong evidence of the successful sidewall cova-
lent modification. The ID/IG values of 1, 2, and p-MWCNTs
were 0.817, 0.858, and 0.660 respectively. Apparently, ID/IG
value decreased after the MWCNT sidewall was modified,
indicating the number of sp3 hybridized carbon atoms on the
MWCNT sidewall surface increase. This was ascribed to the
change of the hybridization of C atoms on the nanotubes
from sp2 to sp3 after the 1,3-dipolar addition reaction.
Most of absorption peaks observed in the infrared spec-
trum of ligand 2 were retained in the infrared spectrum of
complex 1 (Figure 6). Moreover, a broad peak appears in the
range 3290–3620 cm¡1, indicating the existence of H2O mole-
cules in the complex 1. An antisymmetric in-plane rocking
motion of the coordinated water molecule was observed at
about 560 cm¡1, indicating that the H2O molecule involved
in coordination. Peaks appeared at 2918 and 2847 cm¡1 were
attributed to the CDC stretching vibration of the MWCNT.
Absorptions at 2360, 1630, 1380, and 832 cm¡1 were
assigned to the characteristic peaks of pyridine rings.
Wherein peaks at 2360, 1630 cm¡1 were ascribed to the
CDN-stretching vibration of pyridine rings; the peak at
1380 cm¡1 was attributed to the skeleton vibration of pyri-
dine rings and peak at 832 cm¡1 was assigned to the CꢁꢁH
Fig. 4. Thermogravimetric analysis of MWCNT-based complex
1, ligand 2, and p-MWCNTs.
coordinate with and Ru (III) ions. This is ascribed to the
decrease in the charge density of the nitrogen atoms of the
three pyridine rings.
Figure 5 shows the Raman spectra of 1, 2 and p-
MWCNTs. In the Raman spectrum of p-MWCNTs, The G
band was observed at 1565.3 cm¡1. This band is tangential
stretching mode of carbon material caused by the CDC vibra-
tion of sp2-hybridized carbon atom in the two-dimensional
graphene sheets of CNTs. The D band was observed at
1339.9cm¡1, due to the sp3-hybridized carbon of the defect/
disorder sites on the CNT walls. The D band shifted to lower
frequencies after both MWCNTs covalently grafting with tpy
and further coordinatting with metal ions. The D band of
ligand 2 is red-shifted to 1337.2 cm¡1, and is further red-
shifted to 1336.7cm¡1 for complex 1. The relative intensity of
Fig. 5. Raman spectra of MWCNT-based complex 1, ligand 2,
Fig. 7. IR spectra of C60-based complex 3, ligand 4, tpy-phCH3,
and p-MWCNTs.
and C60.

434
Wu and Wang
Fig. 8. Differential pulse voltamograms of complexes 1 and 3 and ligands 2 and 4 in deaerated CHCl3-acetonitrile (4:1, v/v) solution
containing 0.10 M n-Bu4NBF4 at room temperature with a pulse amplitude 50 mV.
out-of-plane bending vibration of pyridine rings. After ligand fullerene-centered reduction of ligand 4 shift toward more
2 coordinated with Ru(III) ion, the CDN stretching vibration negative potentials with respect to that of the pristine C60,
peak shifted to higher wave number from 1583 cm¡1 for 2 to indicating that C60 have a strong electron withdrawing prop-
1630 cm¡1 for 1, and the CꢁꢁH out-of-plane bending vibra- erty. Peak III was assigned to terpyridine-centered tpy0/¡1
tion of pyridine rings also shifted to higher wave number couple. Two reduction peaks of II and III and an oxidation
from 782 cm¡1 for 2 to 832 cm¡1 for 1, indicating the coordi- peak of I were observed in the DPV curve of complex 3.
nation of the N atoms in the pyridine ring with Ru(III) ion.
Peak III was assigned to the terpyridine-centered tpy0/¡1
Absorptions of C60 at 525.2, 574.8, 1181.9, and couple. It cathodically shifted by 31 mV compare to that of
1427.6 cm¡1 were basically remained in the infrared spectra the ligand 4, indicating that the energy level of p* orbital of
of complex 3 and ligand 4 (Figure 7). However, their relative tpy moiety decreased after ligand 4 coordinate with metal
intensity decreased in spectra of 4 and 3. A broad absorption ions. Oxidation peak I was assigned to the metal centered
peak at about 3440.2 cm¡1 was observed in the IR spectrum Ru(III)/Ru(II) couple. Radical ion pairs, namely the one-
ꢂ C
of complex 3, this originates from H2O molecules, showing electron oxidation of Ru (III) tpy
and the one-electron
that the complex 3 contains water molecules. Characteristic reduction of C60ꢂ ¡, exist in the complex 3. The energy gap
absorption peaks of the pyridine ring appeared at 2358.3, (DEcs) between the charge separated state of Ru(III) tpyꢂC
-
ꢂ–
1581.1, 1399.2, and 988 cm¡1 in the spectrum of ligand 4. C60 can be obtained to be 2.05 eV by the calculation of
These peaks disappeared or the relative intensity decreased the difference between the metal-centered oxidation poten-
after the ligand 4 coordinate with the Ru(III) ion. This is tial and the fullerene-centered reduction potential.
attributed to the change in the molecular symmetry after the
Two reduction peaks (peak II and peak III) were observed
ligand 4 coordinate with Ru(III) ion and result in the change in the DPV curve of ligand 2. Peak II was the onset potential
of the vibration mode from infrared active vibrations to non- that electrons begin to fill in the MWCNT successive band,
infrared active vibrations.
which is related to the van Hove singularity,[40] and the reduc-
The redox properties of complexes 1 and 3 and ligands 2 tion peak III was assigned to tpy0/¡1 couple. The half-wave
and 4 were studied by CV and DPV (Figure 8), and the potential of peak III of 1 anodically shifted by 240mV com-
energy level structures of the nano-carbon cluster-based pare to that of the ligand 2, indicating that the energy level of
ligands/complexes were studied. Ligand 4 shows four reduc- p* orbital of tpy moiety decreased after ligand 2 coordinate
tion peaks with half-wave potential (E1/2) at ¡0.640 (peak with metal ions. Obviously, the influence of the coordination
II), ¡1.071 (peak III), ¡1.245 (peak IV), and 1.651 V (peak on the reduction potential of the tpy0/¡1 couple for ligand 2
V) in range from 0 to ¡1.7 V (Table 2). Wherein peaks II, was greater than that for ligand 4, namely, the coordination
0/¡1
IV, and V were¡2a/s¡si3gned to fullerene-centered C60
,
of metal ions with ligands have a greater impact on the p*
C60¡1/¡2, and C60
couples. The half-wave potentials of orbital energy level of tpy moiety for ligand 2 than for ligand
Table 2. Cyclic voltammetry data for C60 and differential pulse voltammetry data for 1–4
E1/2
III
Complex
I
II
IV
V
C60
C60-tpy
C60-tpyRu(H2O)3Cl3
MWCNT-tpy
MWCNT-tpyRu(H2O)3Cl3
¡0.495
¡0.640
¡0.666
¡0.202
¡0.513
¡0.939
¡1.245
¡1.450
¡1.651
4
3
2
1
¡1.071
¡1.040
¡1.083
¡0.842
1.379
1.089

Terpyridine-Fullerene/Nanotube Diads
435
to longer wavelengths compared with that of the tpy-PhCH3,
indicating that the MWCNT has the electron withdrawing
property. Absorptions at 499.0 nm for complex 3 and at
433.7 nm for complex 1 were ascribed to the metal to ligand
electron transitions (MLCT). The absorption of complex 3
was at a longer wavelength (redshift by 66 nm) with respect
to that of complex 1, this was attributed to a greater delocali-
zation : system of complex 3, and showed that C60 has a
stronger electron withdrawing property compare with
MWCNT.
Conclusions
Carbon cluster-based ligands C60-tpy and MWCNT-tpy were
synthesized by 1,3-dipolar cycloaddition. As tridentate che-
lating ligands, C60-tpy and MWCNT-tpy can coordinate
with a variety of metal ions to fabricate novel carbon cluster-
based hybrid materials with specific properties. Synthesized
carbon cluster-based ligands further coordinate with Ru(II)
ions to synthesize carbon-based ruthenium complexes.
Wherein the terpyridine moiety and three water molecules
act as ligands, and three chloride ions as counterions. Experi-
mental results show that the linkage between the carbon clus-
ter and the terpyridine makes an increase in the electron
density of C60 and MWCNTs, and resulted in a negative shift
of the reduction potentials. The grafting of carbon cluster to
terpyridine also led to a decrease of the p* orbital energy level
of the terpyridine moiety. The low-energy MLCT band in
C60tpyRuCl complex red shift by 6 nm compared to in the
MWCNT-tpyRu(H2O)3Cl3 complex, suggesting a stronger
electron-withdrawing ability of C60.
Fig. 9. Absorption spectra of complexes 1 and 3, ligands 2 and 4,
and tpyPh-CH3.
4. Oxidation peak I was assigned to the metal centered Ru
(III)/Ru(II) couple. The Ru(III)/Ru(II) oxidation peak of
complex 1 was at a less positive potential with respect to that
of complex 3, indicating the electron-withdrawing property
of C60 was stronger than that of MWCNTs. The charge sepa-
rated state Ru(III)tpyꢂC-MWCNTꢂ– was also exit in complex
1. The energy gap (DEcs) can be calculated to be 1.602 eV.
The UV-visible spectra of 1–4 were measured in NMP in
the investigated range 200–800 nm (Figure 9). Wavelengths
of maximum absorption for the five ligands/complexes were
shown in Table 3. The characteristic absorption of the mono-
addition C60-derivative with a [6,6] closed-loop structure were
observed at 430.0 nm for ligand 4 and at 432.3 nm for com-
plex 3, indicating the existence of covalent linkages between
C60 and tpy moiety. Absorptions at 327.5 nm for ligand 4
and at 325.2 nm for complex 3 were attributed to the ligand
centered-p-p* transition of the tpy moiety. Both of them
shifted to longer wavelengths with respect to that of the tpy-
PhCH3. This is attributed to the stabilization of the ligand p*
LUMO orbital of the tpy moiety after the tpy-PhCH3 cova-
lently grafting C60. Similarly, the ligand centered :-p* transi-
tion of the tpy moiety for ligand 2 and complex 1 also shifted
Funding
The authors gratefully acknowledge the financial support
from the Natural 5 Science Foundation of the Fujian Prov-
ince of China (Grant Number: 2013J01057; 2009J01039).
References
1. Lee, D.; Cui, T. H. Nanotechnology 2011, 22.
2. Balasubramanian, K.; Burghard, M. Small 2005, 1, 180–192.
3. Yamada, Y.; Tanaka, T.; Machida, K.; Suematsu, S.; Tamamitsu,
K.; Kataura, H.; Hatori, H. Carbon 2012, 50, 1422–1424.
4. Morales-Cid, G.; Fekete, A.; Simonet, B. M.; Lehmann, R.; Carde-
nas, S.; Zhang, X. M.; Valcarcel, M.; Schmitt-Kopplin, P. Anal.
Chem. 2010, 82, 2743–2752.
5. Vermisoglou, E. C.; Pilatos, G.; Romanos, G. E.; Devlin, E.;
Kanellopoulos, N. K.; Karanikolos, G. N. Nanotechnology 2011,
22.
Table 3. Absorption data of complexes 1 and 3 and ligands 2 and
4, tpy-PhCH3
Complex
1LC MLCT
λmax
6. Beuerle, F.; Herrmann, C.; Whalley, A. C.; Valente, C.; Gamburd,
A.; Ratner, M. A.; Stoddart, J. F. Chemistry 2011, 17, 3868–3875.
7. Ostojic, G. N. ChemPhysChem 2011, 13, 2102–2107.
8. Cui, R. J.; Han, Z. D.; Zhu, J. J. Chemistry 2011, 17, 9377–9384.
9. Rocha, R. P.; Sousa, J. P. S.; Silva, A. M. T.; Pereira, M. F. R.;
Figueiredo, J. L. Appl. Catal. B–Environ. 2011, 104, 330–336.
10. Grossiord, N.; Regev, O.; Loos, J.; Meuldijk, J.; Koning, C. E.
Analytical Chemistry 2005, 77, 5135–5139.
C60-tpy
255.4, 275.2, 327.5,
430.0
292.2, 325.2, 432.3
254.9, 279.7, 322.5
284.2, 328.7
C60-tpyRu(H2O)3Cl3 tpy
499.0
433.7
MWCNT-tpyRu(H2O)3Cl3
MWCNT-tpy
254.1, 280.9, 327.3

436
Wu and Wang
11. Yesil, S.; Winkelrnann, C.; Bayram, G.; La Saponara, V. Mater. 26. Llanes-Pallas, A.; Yoosaf, K.; Traboulsi, H.; Mohanraj, J.; Sel-
Sci. Eng. A 2010, 527, 7340–7352.
drum, T.; Dumont, J.; Minoia, A.; Lazzaroni, R.; Armaroli, N.;
12. Campidelli, S.; Ballesteros, B.; Filoramo, A.; Diaz, D. D.; de la
Bonifazi, D. J. Am. Chem. Soc. 2011, 133, 15412–15424.
Torre, G.; Torres, T.; Rahman, G. M. A.; Ehli, C.; Kiessling, D.; 27. Ozawa, H.; Ide, N.; Fujigaya, T.; Niidome, Y.; Nakashima, N.
Werner, F.; Sgobba, V.; Guldi, D. M.; Cioffi, C.; Prato, M.; Bour-
goin, J. P. J. Am. Chem. Soc. 2008, 130, 11503–11509.
13. Ballesteros, B.; de la Torre, G.; Ehli, C.; Rahman, G. M. A.;
Agullo-Rueda, F.; Guldi, D. M.; Torres, T. J. Am. Chem. Soc.
2007, 129, 5061–5068.
14. Leonhardt, A.; Ritschel, A.; Kozhuharova, R.; Graff, A.; Muhl, T.;
Huhle, R.; Monch, I.; Elefant, D.; Schneider, C. M. Diamond Relat.
Mater. 2003, 12, 790–793.
15. Bavastrello, V.; Carrara, S.; Ram, M. K.; Nicolini, C. Langmuir
2004, 20, 969–973.
16. Williams, K. A.; Veenhuizen, P. T. M.; de la Torre, B. G.; Eritja,
R.; Dekker, C. Nature 2002, 420, 761–761.
17. Wang, C.; Li, B. D.; Lin, H. Q.; Yuan, Y. Z. J. Power Sources 2012,
202, 200–208.
18. Cusano, A.; Consales, M.; Crescitelli, A.; Penza, M.; Aversa, P.;
Veneri, C. D.; Giordano, M. Carbon 2009, 47, 782–788.
19. Gooding, J. J.; Chou, A.; Liu, J. Q.; Losic, D.; Shapter, J. G.; Hib-
bert, D. B. Electrochem. Commun. 2007, 9, 1677–1683.
Chemistry 2011, 17, 13438–13444.
28. Naito, M.; Nobusawa, K.; Onouchi, H.; Nakamura, M.; Yasui,
K.; Ikeda, A.; Fujiki, M. J. Am. Chem. Soc. 2008, 130, 16697–
16703.
29. Yi, W. H.; Malkovskiy, A.; Chu, Q. H.; Sokolov, A. P.; Colon,
M. L.; Meador, M.; Pang, Y. J. Phys. Chem. B 2008, 112,
12263–12269.
30. Peng, M.; Liao, Z. J.; Zhu, Z. M.; Guo, H. L. Macromolecules
2010, 43, 9635–9644.
31. Qin, S. H.; Qin, D. Q.; Ford, W. T.; Resasco, D. E.; Herrera, J. E.
Macromolecules 2004, 37, 752–757.
32. Sakellariou, G.; Ji, H. N.; Mays, J. W.; Baskaran, D. Chem. Mater.
2008, 20, 6217–6230.
33. Vougioukalakis, G. C.; Philippopoulos, A. I.; Stergiopoulos, T.;
Falaras, P. Coord. Chem. Rev. 2011, 255, 2602–2621.
34. Palacin, T.; Le Khanh, H.; Jousselme, B.; Jegou, P.; Filoramo, A.;
Ehli, C.; Guldi, D. M.; Campidelli, S. J. Am. Chem. Soc. 2009, 131,
15394–15402.
20. Hasobe, T.; Fukuzumi, S.; Kamat, P. V. Angew. Chem. Int. Ed. 35. Wu, Z. Y.; Huang, R. B.; Xie, S. Y.; Zheng, L. S. Dalton Trans.
2006, 45, 755–759. 2011, 40, 8353–8360.
21. Magadur, G.; Lauret, J. S.; Charron, G.; Bouanis, F.; Norman, E.; 36. Tang, B.; Yu, F.; Li, P.; Tong, L. L.; Duan, X.; Xie, T.; Wang, X. J.
Huc, V.; Cojocaru, C. S.; Gomez-Coca, S.; Ruiz, E.; Mallah, T. J.
Am. Chem. Soc. 2009, 131, 3016–3023.
Am. Chem. Soc. 2012, 134, 7896–7901.
22. Kim, H.; Sheps, T.; Collins, P. G.; Potma, E. O. Nano Lett. 2009, 9,
37. Winter, A.; Egbe, D. A. M.; Schubert, U. S. Org. Lett. 2007, 9,
2345–2348.
2991–2995.
38. Pan, Y. X.; Tong, B.; Shi, J. B.; Zhao, W.; Shen, J. B.; Zhi, J. G.;
Dong, Y. P. J. Phys. Chem. C 2010, 114, 8040–8047.
39. Martin, R.; Jimenez, L.; Alvaro, M.; Scaiano, J. C.; Garcia, H.
Chemistry 2010, 16, 7282–7292.
23. Wang, J.; Chen, Y.; Blau, W. J. J. Mater. Chem. 2009, 19, 7425–
7443.
24. Cortez, M. L.; Ceolin, M.; Azzaroni, O.; Battaglini, F. Anal. Chem.
2011, 83, 8011–8018.
25. Imin, P.; Imit, M.; Adronov, A. Macromolecules 2011, 44, 9138–
40. Paolucci, D.; Franco, M. M.; Iurlo, M.; Marcaccio, M.; Prato, M.;
Zerbetto, F.; Penicaud, A.; Paolucci, F. J. Am. Chem. Soc. 2008,
130, 7393–7399.
9145.