Two multidentate ligands utilizing triazolyl, pyridinyl and phenolate groups as donors for constructing dinuclear copper(II) and iron(III) complexes: Syntheses, structures, and electrochemistry

Article abstract of DOI:10.1016/j.ica.2014.08.051

Two multidentate ligands 2,2′-(1,1′-(pyridine-2,6-diylbis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)bis(methylene)diphenol (H₂L^I) and N,N′-((1,1′-(pyridine-2,6-diylbis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))bis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) (L^II) containing triazolyl, phenolate and pyridinyl groups were prepared by click reaction between diazide and terminal alkynes in the presence of catalyst CuI. Both ligands were reacted with Cu²⁺and Fe³⁺salts to give three dinuclear complexes [L^ICu₂](BPh₄)₂·2DMF (1), [L^II(DMF)₂Cu₂](ClO₄)₄·H₂O (2) and [L^II(FeCl₂)₂](PF₆)₂(3). All complexes were characterized by IR, UV-Vis spectra and element analysis. X-ray analysis revealed that the Cu²⁺centers in complexes 1 and 2 adopted the distorted trigonal bipyramidal geometry, and the Fe³⁺center in complex 3 chose an octahedral geometry. In addition, the electrochemistry of complexes 1-3 was investigated.

Full text of DOI:10.1016/j.ica.2014.08.051

Inorganica Chimica Acta 423 (2014) 332–339
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Two multidentate ligands utilizing triazolyl, pyridinyl and phenolate
groups as donors for constructing dinuclear copper(II) and iron(III)
complexes: Syntheses, structures, and electrochemistry
Xiuli You a,b, Zhenhong Wei a,
⇑
a Department of Chemistry, Nanchang University, Nanchang 330031, China
b Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University, Nanchang, 330013 China
a r t i c l e i n f o
a b s t r a c t
Two multidentate ligands 2,20-(1,10-(pyridine-2,6-diylbis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))bis(meth-
ylene)bis((pyridin-2-ylmethyl)azanediyl)bis(methylene)diphenol (H2LI) and N,N0-((1,10-(pyridine-2,6-diyl-
bis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))bis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)
methanamine) (LII) containing triazolyl, phenolate and pyridinyl groups were prepared by click reaction
between diazide and terminal alkynes in the presence of catalyst CuI. Both ligands were reacted with
Cu2+ and Fe3+ salts to give three dinuclear complexes [LICu2](BPh4)2ꢀ2DMF (1), [LII(DMF)2Cu2](ClO4)4ꢀH2O
(2) and [LII(FeCl2)2](PF6)2 (3). All complexes were characterized by IR, UV–Vis spectra and element anal-
ysis. X-ray analysis revealed that the Cu2+ centers in complexes 1 and 2 adopted the distorted trigonal
bipyramidal geometry, and the Fe3+ center in complex 3 chose an octahedral geometry. In addition,
the electrochemistry of complexes 1–3 was investigated.
Article history:
Received 22 June 2014
Received in revised form 30 July 2014
Accepted 10 August 2014
Available online 6 September 2014
Keywords:
Click reaction
Triazolyl group
Multidentate ligand
Transition metal complex
Electrochemistry
Ó 2014 Published by Elsevier B.V.
1. Introduction
[32–35]. For example, a multidentate ligand N,N-bis[[1-(phenyl-
methyl)-1H-1,2,3-triazol-4-yl]methyl]-2-pyridinemethaneamine based
Huisgen 1,3-dipolar cycloaddition of azide–alkyne, one of the
so-called click reactions, catalyzed by Cu(I) could easily afford a
1,2,3-triazole ring system with high efficiency and excellent region
selectivity [1–5]. Its mild reacting conditions and wide substrate
scope have led to a tremendous degree of attention due to the fact
it has been applied in a remarkably wide range of setting and appli-
cations [6–15]. Indeed, the development of the click reaction has
also led to an explosion of interest in the coordination chemistry
of 1,2,3-triazoles due to their ability to as a donor ligand itself
but also act as chelating ligand [16–23]. As shown in Scheme 1,
the N2 and N3 atoms in 1,2,3-triazole group both have one lone
electron pair to participate in the coordination with metals, so
introducing another coordination site in 1 or 4 subsistent or both
can easily form a chelating ligand [24–26]. This kind of ligands
have been intensively investigated and employed in many fields
such as sensors, bio-conjugates, anticancer complexes, catalysts
or fluorescent materials [27–31].
on two triazole groups was obtained through click chemistry,
and its versatile coordination chemistry towards transition metals
Cu2+ and Fe2+ was also investigated [36]. In this paper, to shed light
on the different nature of coordinating properties of pyridine and
phenol groups when both were incorporated into the 1,4-substi-
tuted-1,2,3-triazoles moiety, two multidentate ligands 2,20-(1,10-
(pyridine-2,6-diylbis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))
bis(methylene)bis((pyridin-2-ylmethyl)azanediyl)bis(methylene)
diphenol (H2LI) and N,N0-((1,10-(pyridine-2,6-diylbis(methylene))
bis(1H-1,2,3-triazole-4,1-diyl))bis(methylene))bis(1-(pyridin-2-yl)-
N-(pyridin-2-ylmethyl)methanamine) (LII) were designed and
synthesized. Continuous investigation on their coordinated reac-
tions with Cu2+ and Fe3+ ions gave three dinuclear complexes [LICu2]
(BPh4)2ꢀ2DMF (1), [LII(DMF)2Cu2](ClO4)4ꢀH2O (2) and [LII(FeCl2)2]
(PF6)2 (3). Herein we reported the synthesis, crystal structures and
electrochemistry of complexes 1–3 based on ligands H2LI and LII.
Recently, we are interested in the design and synthesis of
multidentate ligand due to their diverse potential application in
catalysis, mimics of metalloenzymes, ions recognition, and so on
2. Experimental
2.1. Instrument and materials
⇑
Reactions were performed under an argon atmosphere
using standard Schlenk techniques when necessary. Solvents were
Corresponding author.
E-mail address: weizh@ncu.edu.cn (Z. Wei).
http://dx.doi.org/10.1016/j.ica.2014.08.051
0020-1693/Ó 2014 Published by Elsevier B.V.

X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
333
(0.17 g, 1.0 mmol) in MeCN (100 mL) give the finial yellow oily
liquid (1.49 g, 63%). 1H NMR (d, ppm, 400 M, CDCl3): 8.48–8.47
(d, 2H, Py), 7.75–7.71 (t, 2H, Py), 7.50–7.48 (d, 2H, Py), 7.23–7.19
(t, 2H, Py), 4.15 (s, 4H, CH2), 3.40 (s, 2H, CH2), 2.33 (s, 1H, „CH).
13C NMR: 157.8, 148.3, 138.8, 124.6, 121.8, 78.0, 73.2, 58.6, 46.6.
IR (dichloromethane, cmꢂ1): 3290 (m), 3015 (m), 2839 (s), 2118
(s), 1598 (s).
Scheme 1. The simple structure of 1,4-subsituted 1,2,3-triazole as a chelating
ligand.
2.2.4. Ligand H2LI
To a solution of 2-((prop-2-yn-1-yl(pyridin-2-ylmethyl)amino)
methyl)phenol (151.2 mg, 0.6 mmol) in MeCN (80 mL), 2,6-bis(azi-
domethyl)pyridine (56.7 mg, 0.3 mmol), CuI (6 mg, 0.03 mmol) and
Et3N (0.4 mL, 0.36 mmol) were added under Ar atmosphere. After
being refluxed for two days under the continually stirring, the mix-
ture was cooled to room temperature. Removal of the solvent
under reduced pressure gave a crude product which was further
purified using flash chromatography on silica gel column with
ethyl acetate as eluent to give a light brown solid (75.17 mg,
36%). Anal. Calc. for C39H39N11O2 (FW = 693.8), calc. (%): C, 67.51;
H, 5.67; N, 22.21. Found: C, 67.53; H, 5.69; N, 22.53%. 1H NMR (d,
ppm, 400 M, CDCl3): 8.58–8.57 (d, 2H, Py), 7.78 (s, 2H, triazole),
7.74–7.49 (m, 3H, Py), 7.31,7.30 (d, 2H, Py), 7.20–7.14 (m, 4H,
Py), 7.03–7.01 (d, 4H, Ph), 6.86–6.84 (d, 2H, Ph), 6.79–6.75 (t, 2H,
Ph), 5.54 (s, 4H, 2CH2), 3.90–3.87 (d, 8H, 4CH2), 3.80 (s, 4H, 2CH2).
13C NMR: 157.6, 157.1, 154.4, 149.2, 144.3, 138.5, 136.8, 129.6,
129.0, 124.1, 123.4, 122.4, 122.1, 121.5 119.1, 116.4, 58.6, 56.6,
55.1, 47.7. IR (KBr, cmꢂ1): 3424 (s), 3142 (w), 3066 (w), 2929
(w), 2830 (w), 1588 (s), 1486 (s), 1462 (m), 1432 (s), 1249
(m), 1049 (s), 758 (s), 460 (m). UV–Vis (MeCN, kmax/nm
freshly distilled by using appropriate drying agents prior to use. 1H
NMR and 13C NMR spectra were recorded on an AVANCE DRX 400
(Bruker) in CDCl3. UV–Vis spectra were collected on a Shimadzu
UV2550 spectrophotometer. Infrared data were recorded on an
FTIR spectrometer (Scimitar 2000, Varian). Micro-analysis service
was recorded on a Heraeus CHNORapid. Electrochemical measure-
ments were performed on an Echo Chemie Autolab PGESTAT 30 in
dry acetonitrile with [NBu4][BF4] as supporting electrolyte; plati-
num and Ag/AgCl were used as working and reference electrodes,
respectively. Compounds 2,6-bis(bromomethyl)pyridine [37], 2-
(((pyridin-2-ylmethyl)amino)methyl)phenol [38] and bis(pyridin-
2-ylmethyl)amine [39] were synthesized according literatures
with little modification.
Caution! In the course of preparation of benzyl azide, sodium
azide must be handled with care to avoid explosion.
2.2. Synthesis
2.2.1. 2,6-Bis(azidomethyl)pyridine (A) [40]
(e
/mol Lꢂ1 cmꢂ1)): 216 (66585), 255 (31073).
To a suspension of NaN3 (3.25 g, 50 mmol) in DMF (50 mL), 2,6-
bis(bromomethyl)pyridine (1.85 g, 10 mmol) was added. After
being heated at 80 °C for 10 h under the continually stirring, the
mixture was cooled to room temperature and distilled water
(100 mL) was added. The obtained aqueous solution was extracted
successively with diethyl ether (50 mL ꢁ 3). The organic layers
were separated, combined, washed with water and dried with
MgSO4. Removal of the solvent under the reduced pressure gave
a crude product which was further purified using flash chromatog-
raphy on silica gel column with ethyl acetate/petroleum ether = 1/
3 as eluent to give a colorless oily liquid (1.22 g, 96%). (d, ppm,
400 M, CDCl3): 7.71–7.67 (t, 1H, Py), 7.25–7.20 (d, 2H, Py,
J = 7.60 Hz), 4.42 (s, 2H, CH2). IR (liquid, cmꢂ1): (ꢂN3) 2104.
2.2.5. Ligand LII
According to the procedures for synthesis ligand H2LI starting
from the materials N,N-bis(pyridin-2-ylmethyl)prop-2-yn-1-amine
(142.2 mg, 6 mmol), 2,6-bis(azidomethyl)pyridine (56.7 mg,
0.3 mmol), CuI (6 mg, 0.03 mmol) and Et3N (0.4 mL,0.36 mmol) in
MeCN (80 mL) gave the ligand LII (75.70 mg, 38%). Anal. Calc. for
C
37H37N13 (FW = 663.3), calc. (%): C, 66.95; H, 5.62; N, 27.43.
Found: C, 69.58; H, 5.88; N, 27.49%. 1H NMR (d, ppm, 400 M,
CDCl3): 8.39, (d, 4H, Py), 7.86 (s, 2H, triazole), 7.67–7.62 (m, 5H,
Py), 7.53–7.51 (d, 4H, Py), 7.13–7.07 (m, 6H, Py), 5.58 (s, 4H,
2CH2), 3.88 (s, 4H, 2CH2), 3.85 (s, 8H, 4CH2). IR (KBr, cmꢂ1): 3142
(w), 3059 (w), 2933 (w), 2837 (w), 1645 (m), 1595 (s), 1452 (s),
2.2.2. 2-((Prop-2-yn-1-yl(pyridin-2-ylmethyl)amino)methyl)phenol
(B)
1219 (s), 761 (s), 623 (w), 487 (w). UV–Vis (MeCN, kmax/nm (e/
mol Lꢂ1 cmꢂ1)): 212 (56375), 250 (42170).
To a solution of 2-(((pyridin-2-ylmethyl)amino)methyl)phenol
(2.56 g, 11.23 mmol) in MeCN (100 mL), K2CO3 (1.56 g, 11.28 mmol),
KI (1.88 g, 11.34 mmol) and propargyl bromide (1.37 g, 11.5 mmol)
were added. After being refluxed for 24 h, the reacted mixture was
cooled to room temperature and then filtered. The filtrate was
removed of solvent under reduced pressure to give a crude
product, which was further purified using flash chromatography
on silica gel column with ethyl acetate as eluent to give a yellow
oily liquid (1.83 g, 65%). 1H NMR (d, ppm, 400 M, CDCl3): 10.51
(s, 1H, OH), 8.63–8.62 (d, 1H, Py), 7.70–7.67 (t, 1H, Py), 7.31–7.29
(d, 1H, Py), 7.26–7.17 (m, 2H, Py, Ph), 7.09–7.07 (d, 1H, Ph), 6.89–
6.87 (d, 1H, Ph), 6.81–6.77 (t, 1H, Ph), 3.96 (s, 2H, CH2), 3.87 (s,
2H, CH2), 3.42 (s, 2H, CH2), 2.34 (s, 1H, C„CH). 13C NMR: 157.6,
157.1, 149.3, 136.8, 129.6, 129.1, 123.1, 122.5, 121.8, 119.1,
116.4, 77.0, 74.2, 58.6, 55.3, 41.6. IR (dichloromethane, cmꢂ1):
3295 (m), 3013 (m), 2839 (s), 2106 (s), 1594 (s).
2.2.6. Complex [LICu2](BPh4)2ꢀ2DMF (1)
To a solution of ligand H2LI (69.4 mg, 0.1 mmol) in methanol
(10 mL), Cu(ClO4)2ꢀ6H2O (74.2 mg, 0.2 mmol) and Et3N (0.15 mL,
1.0 mmol) were added to give a blue solution. After being stirred
for five minutes, Na[BPh4] (68.4 mg, 0.2 mmol) solid was added
to give much blue precipitate, which was collected via filtration
and washed with dichloromethane (5 mL ꢁ 3). Recrystallisation
of the precipitate in DMF/Et2O systems gave the blue crystals in
four days (96.2 mg, 60%). Anal. Calc. for
C93H91B2Cu2N13O4
(FW = 1603.5), calc. (%): C, 69.66; H, 5.72; N, 11.36. Found: C,
69.35; H, 5.96; N, 11.45%. IR (KBr, cmꢂ1): 3059 (m), 2997 (w),
2860 (w), 1672 (m), 1598 (m), 1574 (m), 1480 (s), 1452 (m),
1276 (s), 743 (s), 704 (s), 609 (m), 494 (w). UV–Vis (DMF, kmax
/
nm (
e
/mol Lꢂ1 cmꢂ1)): 210 (37731), 258 (22195), 850 (332).
2.2.7. Complex [LII(DMF)2Cu2](ClO4)4ꢀH2O (2)
2.2.3. N,N-Bis(pyridin-2-ylmethyl)prop-2-yn-1-amine (B0) [41]
According to the similar procedures for synthesis B starting
from bis(pyridin-2-ylmethyl)amine (1.99 g, 10 mmol), propargyl
bromide (1.19 g, 10 mmol), K2CO3 (1.56 g,11.28 mmol) and KI
To a solution of ligand LII (66.3 mg, 0.1 mmol) in methanol
(10 mL), Cu(ClO4)2ꢀ6H2O (74.2 mg, 0.2 mmol) was added to give
much blue precipitate. After being stirred for five minutes, the pre-
cipitate was collected via filtration, washed with CH2Cl2 and dried

334
X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
in vacuum. Recrystallisation of the solid in DMF/Et2O systems gave
the light blue crystal 2 in four days (77.4 mg, 58%). Anal. Calc. for
sodium to give the finial A. On the other hand, the synthesis of
compounds B (B0) was started from the reaction between pyri-
din-2-ylmethanamine and 2-hydroxybenzaldehyde or between
pyridin-2-ylmethanamine and picolinaldehyde to give the Schiff
bases 2-(((pyridin-2-ylmethyl)imino)methyl)phenol, or 1-(pyridin-
2-yl)-N-(pyridin-2-ylmethylene)methenamine. Both Schiff bases
were reduced by NaBH4 to give the middle products 2-(((pyridin-
2-ylmethyl)amino)methyl)phenol or bis(pyridin-2-ylmethyl)amine,
which were further reacted with propargyl bromide to give the prod-
ucts 2-(((pyridin-2-ylmethyl)amino)methyl)phenol (B) or 2-(((pyri-
din-2-ylmethyl)amino)methyl)phenol (B0). Click reactions between
diazide A and B or (B0) catalyzed by CuI in the presence of Et3N gave
the finial ligands H2LI or LG, respectively. Their identities were con-
firmed using NMR spectra, and element analysis. Besides triazolyl
and pyridinyl groups, ligand H2LI contains two phenolate groups,
which was deprotonated by Et3N before it reacted with Cu(ClO4)2
and followed by anion exchange with [BPh4]ꢂ to give the solid com-
plex [LICu2](BPh4)2ꢀ2DMF (1), Scheme 3. Ligand LII is only consisted
with pyridinyl and triazolyl rings. Direct reactions of ligand LII with
Cu(ClO4)2 in methanol or FeCl3 in THF gave a blue precipitate of cop-
per complex or a yellow precipitate of iron complex. Recrystalliza-
tion of these two precipitates in DMF or MeCN gave the
corresponding complexes [LII(DMF)2Cu2](ClO4)4ꢀH2O (2) and [LII
(FeCl2)2](PF6)2 (3). Complexes 1–3 are relatively air and moisture
stable in the solid state, and they are all soluble well in polar solvents
such as MeCN and DMF, but not soluble in nonpolar solvents such as
THF, hexane and toluene.
C
43H51Cl4O18Cu2N15, (Mw = 1334.9), calc (%): C, 38.69; H, 3.85; N,
10.62. Found: C, 38.81; H, 3.35; N, 10.46%. IR (KBr, cmꢂ1): 3469
(m), 3142 (w), 2941 (w), 1652 (m), 1612 (m), 1442 (m), 1110 (s),
836 (s), 772 (s), 626 (s), 423 (w). UV–Vis (DMF, kmax/nm (e/
mol Lꢂ1 cmꢂ1)): 217 (57707), 261 (13317), 288 (8878), 860 (256).
2.2.8. Complex [LII(FeCl2)2](PF6)2 (3)
To a solution of ligand LII (66.3 mg, 0.1 mmol) in THF (10 mL),
FeCl3 (32.4 mg, 0.2 mmol) solid was added to give much deep yel-
low precipitate. After being stirred for five minutes, the precipitate
was filtered, washed with THF, and dried in vacuum. After the
obtained precipitate was dissolved in methanol (5 mL), NH4PF6
(32.6 mg, 0.2 mmol) was added to produce much deep yellow pre-
cipitate, which was collected via filtration, washed with methanol,
and dried in vacuum. Recrystallisation of the solid in MeCN/Et2O
systems gave the deep yellow crystals of 3 in two weeks (83.3 mg,
69%). Anal. Calc. for C37H37N13Cl4P2F12Fe2 (Mw = 1207.24), calc. (%):
C, 36.81; H, 3.09; N, 15.08. Found: C, 36.53; H, 3.43; N, 15.64%. IR
(KBr, cmꢂ1): 3432 (m), 3165 (w), 2944 (w), 2868 (w), 1652 (m),
1608 (m), 1446 (s), 843 (s), 768 (m), 558 (m), 419 (w). UV–Vis
(DMF, kmax/nm (e
/mol Lꢂ1 cmꢂ1)): 210 (35512), 255 (19975), 296
(11097), 380 (6658).
2.3. X-ray crystallography
In the IR spectrum of compound A, the strong absorption at
2095 cmꢂ1 is charaꢂcteristic for the asymmetric stretching vibration
of azide group N3 . In compounds B or B0, the absorption at
3295 cmꢂ1 is belonged to the stretching vibration of the terminal
alkyne hydrogen bond „CAH, and the strong absorptions at
2106, 2118 cmꢂ1 are belonged to the stretching vibration of C„C
triple bond. After the click reaction, these characteristic peaks in
the obtained ligands H2LI and LII are disappeared, and instead of
In the crystallographic data collection of complexes 1–3, stan-
dard procedures were used for mounting the crystals on a Bruker
SMART CCD diffractometer with graphite-monochromated Mo K
a
0
radiation (k = 0.71073 ÅA). The structures were solved by the direct
methods routines in the SHELXS program and refined on F2 in SHELXL
[42]. The crystal quality of complex 2 was poor and its perchlorate
anions, pyridinyl ring, methylene group and water oxygen atom
were severely disordered. The O(2)–O(5) atoms, bonded to Cl(1)
atom in one ClOꢂ4 group, were split into two fragments O(2)–
O(5)/O(2A)–O(5A) with an occupancy factors of 0.70/0.30; the
O(6)–O(9) atoms, bonded to Cl(2) atom in the other ClOꢂ4 group,
were split into two fragments O(6)–O(9)/O(6A)–O(9A) with an
occupancy factors of 0.39/0.61; the atoms C(8)–C(11) and N(2) in
pyridinyl ring and the three methylene C(6), C(7) and C(13) atoms
were split into two fragments C(6)–C(13), N(2)/C(6A)–C(13A),
N(2A) with an occupancy factors of 0.53/0.47. The site-occupation
factor for water O(10) atom was fixed at 0.5 due to the part evap-
oration of solvated water molecules. In crystal 3, the PFꢂ6 group was
also disorder over two directions and was split into two fragments
F(1)–F(6)/F(1A)–F(6A) with an occupancy factors of 0.48/0.52. In
crystals 1–3, all non-hydrogen atoms were modeled anisotropi-
cally. Except that the hydrogen atoms on water molecule in crystal
2 were not added, all other hydrogen atoms were placed in ideal-
ized positions and treated as riding atoms. Details of the data col-
lection and refinement are given in Table 1.
producing a group of new triazole peaks at 1462 and 1452 cmꢂ1
.
This successfully proved the occurrence of azide alkyne Huisgen
cycloaddition.
The absorption spectra of free ligands H2LI, LII and complexes 13
in MeCN are shown in Fig. 1. For ligands H2LI and LII, the strong
absorption peaks at 215 and 250 nm are assigned to
p–p⁄ transi-
tions of the aromatic rings. For complexes 13, the ligand-based
absorption bands at about 215 and 250 nm are also observed. Com-
pared with complex 1, whose spectral profile in the short wave-
length region shows no significant difference with that of free
ligand, the absorption bands in complexes 2 and 3 show new
shoulder peaks with 288 nm for complex 2, 296 nm for complex
3, which are possibly assigned to the ligand to metal charge trans-
fer (LMCT) absorption [44]. Furthermore, the new peak at 380 nm
in complex 3 is assigned to the metal to ligand charge transfer
(MLCT) [44], which was not observed in complexes 1 and 2. In
the long wave length range, the weak absorptions between
510800 nm in complexes 1 and 2 are assigned to dd transitions
of Cu2+ atoms, Fig. 1-insert.
3. Results and discussion
3.2. Structural analysis
3.1. Synthesis and characterization
In crystal 1, the asymmetric unit contains a dinuclear copper
cation [Cu2LI]2+, two independent [BPh4]ꢂ anions and two solvated
DMF molecules. As shown in Fig. 2, the two central copper cores
are surrounded by ligand LI 2ꢂ, with each adopts the distorted tri-
gonal bipyramidal geometry coordinated by one pyridinyl nitro-
gen, one triazole nitrogen, one tertiary amine nitrogen and two
phenolate oxygen atoms of ligand LI 2ꢂ. The two phenolate rings
are cis to each other, in which the deprotonated phenolate oxygen
atoms are acted as the bridges with O(2) serves as the axial ligand
As shown in Scheme 2, both ligands H2LI and LII were synthe-
sized according to the modified procedures by click reaction
between a diazide A and two tridentate compounds B or B0 which
appending with the terminal alkynes [43]. The synthesis of diazide
A was started from the reaction of 2,6-bis(methyl)pyridine with
the brominated reagent N-bromosuccinimide (NBS) in the pres-
ence of the initiators azodiisobutyronitrile to give 2,6-bis(bromo-
methyl)pyridine, which was further substituted with azide

X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
335
Table 1
Crystallographic data for complexes 13.
Complexes
1
2
3
Chemical formula
Fw
Crystal system
Space group
a (Å)
C
93H91B2N13O4Cu2
C43H53Cl4N15O19Cu2
1352.89
monoclinic
C2/c
22.999(9)
20.585(9)
13.206(5)
90
C37H37N13Cl4P2F12Fe2
1207.24
orthorhombic
Fdd2
25.7627(19)
27.964(2)
13.3747(10)
90
1603.51
monoclinic
P21
10.6035(16)
14.891(2)
26.140(4)
90
b (Å)
c (Å)
a
(°)
b (°)
95.092(2)
90
4111.1(11)
2
1.295
1680
110.150(7)
90
5870(4)
4
1.529
2768
90
90
c
(°)
V (Å3)
9635.4(12)
8
1.664
4864
0.982
Z
Dcalc (g cmꢂ3
F(000)
)
l
(Mo K
a
, mmꢂ1
)
0.578
0.989
Total number of reflections
39,144
18,300
22,212
hmax
28.36
28.52
28.22
Number of unique reflections
Number of observed reflections
Number of variables
R1, wR2 (observed data)
R1, wR2 (all data)
19,938 [R(int) = 0.0358]
12,528
1031
0.0461, 0.0862
0.1024, 0.1060
0.994
0.434, ꢂ0.336
7259 [R(int) = 0.0652]
2340
438
0.0989, 0.2715
0.2417, 0.3539
0.975
0.847, ꢂ0.522
5869 [R(int) = 0.0324]
4638
372
0.0360, 0.0817
0.0539, 0.0904
1.030
0.334, ꢂ0.265
GOF, S
Maximum/minimum peak (e Åꢂ3
)
Scheme 2. The synthesized routes for ligands H2LI and LII.

336
X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
Scheme 3. The synthesized routes for complexes 1–3.
Fig. 1. UV–Vis absorptions of free ligands H2LI, LII and complexes 1–3 (1.0 ꢁ 10ꢂ4
mol Lꢂ1 in MeCN).
for Cu(2) and as the equatorial ligand for Cu(1), and O(1) acts as the
equatorial ligand for Cu(1) and as the axial ligand for Cu(2). Inter-
estingly, the tertiary amine nitrogen atoms N(5), N(10) act as
the axial ligand for Cu(1), and Cu(2), with the angles \O(2)ꢂ
Cu(1)ꢂN(5) and \O(1)ꢂCu(2)ꢂN(10) at the axial directions are
169.68 (5)° and 169.83 (5)°. The dihedral angle between planes
Cu(1)O(1)O(2) and Cu(2)O(1)O(2) is 13.06 (5)°, indicating the four
atoms Cu(1), Cu(2), O(1) and O(2) are nearly in the same plane. To
be noted that the middle pyridinyl N(1) is not coordinated to metal
center, which may be caused by the big steric effect of ligand. As
shown in Table 2, the average Cu–Namine bond at 2.2125 Å in axial
direction is longer than that of Cu–Npy at 2.0344 Å and Cu–Ntriazole
Fig. 2. The crystal structure of cation of complex 1. Hydrogen atoms were omitted
for clarity.
[Cu(II)L(H2O)]I2 (L = 5,11,17,23-tetrakis(trimethylammonium)-25,26,
27,28-tetrahydroxycalix[4]arene) [45]. The distance between two
neighboring copper ions is 3.0303(6) Å, indicating a weak interaction
between them.
at 2.0472 Å in equatorial position due to the
r-only bonding in the
former is weaker than the -back bonding in the latter two. The
four CuAO bonds vary in the range of 1.9980 (12) to 2.0098
(11) Å, which are comparable to those found in complex
p
In crystal 2, the asymmetric unit contains a half dinuclear
copper cation [(CuDMF)2LII]4+, two independent [ClO4]ꢂ anions
and one half solvated water molecule. As shown in Fig. 3 (above),

X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
337
Table 2
corresponding bond lengths in complex 1. The average Cu–Npy
bond lengths at 2.0035 Å are slightly longer than those found in
complexes [Cu2(bppyH)2(NO3)2] at 1.956(5) Å, (bppyH = 2-(pyra-
zol-3-yl)-6-(pyrazolate)pyridine) [46] and [Cu(bdmpp)(MeCN)2]
(ClO4)2 at 1.947(2) Å, (bdmpp = bis(3,5-dimethyl-1H-pyrazol-1-yl)
pyridine) [47].
In crystal 3, the asymmetric unit contains a half dinuclear iron
cation [(FeCl2)2LII]2+ and one independent [PF6]ꢂ anion. As shown
in Fig. 3 (below), the central metal Fe3+ atoms in the cation are
adopted the octahedral geometry coordinated by four nitrogen
atoms from ligand LII and two Clꢂ atoms, in which the atoms
The selected bonds (Å) and angles (°) for complex 1.
Cu(1)–O(1) = 1.922(2)
Cu(1)–O(2) = 1.997(2)
Cu(1)–N(11) = 2.002(3)
Cu(1)–N(9) = 2.179(3)
Cu(2)–N(5) = 2.043(2)
Cu(2)–O(2) = 1.928(2)
Cu(1)–N(10) = 2.032(2)
Cu(2)–N(6) = 2.024(3)
Cu(2)–N(4) = 2.015(3)
Cu(2)–O(1) = 2.087(2)
Cu(1)–Cu(2) = 3.0303(6)
O(1)–Cu(1)–O(2) = 81.05(9)
O(2)–Cu(1)–N(11) = 142.31(11)
O(2)–Cu(1)–N(10) = 91.04(10)
O(1)–Cu(1)–N(9) = 102.71(11)
N(11)–Cu(1)–N(9) = 114.77(12)
O(2)–Cu(2)–N(4) = 102.50(11)
N(4)–Cu(2)–N(6) = 130.10(12)
N(4)–Cu(2)–N(5) = 82.35(11)
O(2)–Cu(2)–O(1) = 78.66(9)
N(6)–Cu(2)–O(1) = 114.26(10)
O(1)–Cu(1)–N(11) = 100.81(10)
O(1)–Cu(1)–N(10) = 171.95(11)
N(11)–Cu(1)–N(10) = 84.48(11)
O(2)–Cu(1)–N(9) = 101.17(10)
N(10)–Cu(1)–N(9) = 80.24(11)
O(2)–Cu(2)–N(6) = 99.21(11)
O(2)–Cu(2)–N(5) = 170.33(11)
N(6)–Cu(2)–N(5) = 83.55(11)
N(4)–Cu(2)–O(1) = 113.79(11)
N(5)–Cu(2)–O(1) = 91.74(10)
Table 3
The selected bonds (Å) and angles (°) for complexes 2 and 3.
Complex 2
Complex 3
Cu(1)–N(2) = 1.988(13)
Cu(1)–N(5) = 2.030(7)
Cu(1)–N(8) = 1.992(7)
Cu(1)–N(1) = 2.019(8)
Cu(1)–O(1) = 1.933(7)
Fe(1)–N(2) = 2.102(2)
Fe(1)–N(5) = 2.160(2)
Fe(1)–N(1) = 2.140(2)
Fe(1)–N(8) = 2.245(2)
Fe(1)–Cl(2) = 2.2547(8)
Fe(1)–Cl(1) = 2.2088(9)
N(2)–Fe(1)–N(5) = 89.54(9)
N(2)–Fe(1)–Cl(1) = 103.18(7)
N(1)–Fe(1)–Cl(1)=103.40(7)
N(5)–Fe(1)–Cl(1) = 91.21(7)
Cl(1)–Fe(1)–N(8) = 168.32(7)
N(2)–Fe(1)–Cl(2) = 93.39(7)
N(1)–Fe(1)–Cl(2) = 93.97(7)
N(5)–Fe(1)–Cl(2) = 168.89(7)
Cl(1)–Fe(1)–Cl(2) = 98.53(4)
N(8)–Fe(1)–Cl(2) = 93.15(7)
the central Cu2+ atoms in the cation are adopted the trigonal bipy-
ramidal geometry with each is coordinated with two pyridinyl N
atoms, one triazole N atom, one tertiary amine N atom of ligand
LII, as well as a solvated DMF molecule, in which the four ligating
nitrogen atoms are chosen a nearly perfect trigonal pyramidal
geometry with the tertiary amine nitrogen atom as the vertex,
trans to this tertiary amine is loosely bound a DMF molecule. It is
interesting to note that there is a C2 axis passing through the mid-
dle pyridinyl ring of ligand LII. As shown in Table 3, the angle
\O(1)–Cu(1)–N(8) is 179.0(3)°, indicating the atoms N(8), Cu(1)
and O(1) in the axial direction are near in a straight line. The
bond lengths between Cu and N atoms are comparable to the
O(1)–Cu(1)–N(2) = 94.7(5)
N(2)–Cu(1)–N(8) = 86.3(5)
N(2)–Cu(1)–N(1) = 121.9(6)
O(1)–Cu(1)–N(5) = 98.0(3)
N(8)–Cu(1)–N(5) = 81.4(3)
O(1)–Cu(1)–N(8) = 179.0(3)
O(1)–Cu(1)–N(1) = 97.1(3)
N(8)–Cu(1)–N(1) = 82.5(3)
N(2)–Cu(1)–N(5) = 117.6(6)
N(1)–Cu(1)–N(5) = 116.6(3)
Fig. 3. The crystal structures of cations of complexes 2 (above) and 3 (below). Hydrogen atoms were omitted for clarity. Symmetric codes for 2: A = ꢂx, y, ꢂ0.5 ꢂ z; for 3:
A = 0.5 ꢂ x, 0.5 ꢂ y, z.

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X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
3.3. Electrochemistry
The cyclic voltammograms of complexes 1–3 are shown in
Fig. 4. Complex 1 exhibits three reduction processes with the first
one at ꢂ0.34 V, the second one at ꢂ0.55 V, and the third one at
ꢂ1.65 V. The three reductions are assigned to the processes of CuII-
CuII/CuIICuI, CuIICuI/CuICuI and CuICuI/Cu0Cu0, respectively. The
assignment of the third process is supported by the observation
of a sharp stripping peak at ꢂ0.13 V during the reverse scanning,
Fig. 4-above. The peak potential separation of the first process is
0.08 V, which is supportive of the one-electron assignment. The
ratio of the cathodic over the anodic peak currents (ipc/ipa), 0.43,
suggests the quasi-reversibility of the first redox process, Fig. 4-
above (insert). Complex 2 exhibits two reduction processes, one
reversible at 0.20 V, and one irreversible at ꢂ1.27 V. The first
reduction is assigned to the CuIICuII/CuICuI couple and the second
to the process of CuICuI/Cu0Cu0. The first reduction potential at
0.20 V is more positive than that in complex 1 (ꢂ0.34 V), which
may be ascribed to the stronger donor atom of phenolate oxygen
compared with the pyridinyl nitrogen in complex 1. The nearly
one unit ratio of the cathodic over the anodic peak currents (ipc
/
ipa), 0.56, suggests the quasi-reversibility of the first redox process.
The assignment of the latter process is also supported by the obser-
vation of a sharp stripping peak at ꢂ0.21 V during the reverse scan-
ning, Fig. 4-middle. Whereas complex
3 shows four redox
processes, with the reduction peaks at 0.25, 0.06, ꢂ0.13 and
ꢂ1.63 V, and their corresponding oxidation peaks at 0.44, 0.15
ꢂ0.06 and ꢂ0.44 V. The former three redox processes are quasi-
reversibility and may be assigned to the FeIIIFeIII/FeIIFeII, FeIIFeII/FeII-
FeI and FeIIFeI/FeIFeI, respectively. The last redox process is irre-
versibility and can be ascribed to FeIFeI/Fe0Fe0, Fig. 4-below.
4. Conclusions
In this paper, two multidentate ligands H2LI and LII containing
triazolyl, phenolate and pyridinyl groups have been synthesized.
Their coordinated chemistry to Cu2+ and Fe3+ ions gave three dinu-
clear complexes [LICu2](BPh4)2ꢀ2DMF (1), [LII(DMF)2Cu2](ClO4)4ꢀH2
O (2) and [LII(FeCl2)2](PF6)2 (3). In complex 1, the phenolate groups
in ligand H2LI have been deprotonated and coordinated to the Cu2+
atoms, leading to the two Cu2+ centers close to each other. While in
complexes 2 and 3, the ligand LII contains no phenolate ligand and
only connects with the Cu2+ or Fe3+ atoms with its triazole and
pyridinyl groups, thus leading to the two metal centres far away
from each other. Electrochemistry of complexes 1–3 revealed a
quasi-reversibility redox process CuIICuII/CuIICuI in complex 1, a
reversible redox process CuIICuII/CuICuI in complex 2 and three
quasi-reversible redox processes FeIIIFeIII/FeIIFeII, FeIIFeII/FeIIFeI and
FeIIFeI/FeIFeI in complex 3.
Fig. 4. Cyclic voltammograms of complexes 1 (top), 2 (middle), and 3 (bottom) in
0.1 mol Lꢂ1 [NBu4]BF4/MeCN (scanning rate = 0.1 V sꢂ1).
Acknowledgement
The authors thank the Education Department of Jiangxi Prov-
ince (Grant No.: GJJ13106) for financial support.
N(2)–N(4) and Cl(2) are at a nearly square geometry and the ter-
tiary amine nitrogen atom N(1) and Cl(1) atoms are at the axial
direction. The two Clꢂ atoms are cis to each other, and the two
pyridinyl nitrogen atoms are trans to each other. Also there is a
C2 axis passing through the N(7) and C(19) atoms of the middle
pyridinyl ring. As shown in Table 3, the bond lengths of FeꢂNtriazole
and FeꢂNpy are shorter than that of FeꢂNamine which is also due to
Appendix A. Supplementary material
CCDC 1008684ꢂ1008686 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.ca-
m.ac.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.ica.2014.08.051.
the different nature between
p-back bond and r-only bond. The
two Fe–Cl bond lengths are comparable to each other, but both
are shorter than that found in complex [Fe(bppyH2)Cl2]
(bppyH2 = 2,6-di(1H-pyrazol-3-yl)pyridine) at 2.3302 Å [48].

X. You, Z. Wei / Inorganica Chimica Acta 423 (2014) 332–339
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