A binuclear ag(I) complex based on a tripodal ligand tris(2- benzimidazolylmethyl)amine: Synthesis and characterization

Article abstract of DOI:10.1007/s10870-014-0498-2

A new binuclear complex [Ag₂(ntb)₂](NO ₃)₂·(CH₃OH) _1.5·(CH₃CN)_0.5 based on a tripodal ligand ntb (ntb = tris(2-benzimidazolylmethyl)amine) has been synthesized and structurally characterized by X-ray single crystal diffractometry. In the structure of the complex each center Ag(I) ion is coordinated by two N atoms from two benzimidazole arm of one ntb ligand and one N atoms from one benzimidazole arm of the other in a trigonal coordinated geometry, resulting in the construction of a binuclear complex. The complex units are further linked into a 1-D chain by hydrogen bonds. The emission spectrum of the complex has been investigated and shows a red-shift of the emission peak compared to the ligand and the existence of ligand-to-metal charge transfer process (emission peak at 468.2 nm). Cyclic voltammogram of the complex indicates a pair of quasi-reversible redox couple, corresponding to the Ag⁺/Ag electrochemical process. Graphical Abstract: In the structure of the complex each center Ag(I) ion is coordinated by two N atoms from two benzimidazole arm of one ntb ligand and one N atoms from one benzimidazole arm of the other in a trigonal coordinated geometry, resulting in the construction of a binuclear complex.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-014-0498-2

J Chem Crystallogr
DOI 10.1007/s10870-014-0498-2
ORIGINAL PAPER
A Binuclear Ag(I) Complex Based on a Tripodal Ligand Tris
(2-Benzimidazolylmethyl)amine: Synthesis and Characterization
•
Yue-Yi Deng Dong Zhang Xiao-Qun Duan
•
•
•
Xue-Song Shen Fa-Qian Liu
Received: 14 September 2013 / Accepted: 17 January 2014
Ó Springer Science+Business Media New York 2014
Abstract A new binuclear complex [Ag2(ntb)2](NO3)2Á
(CH3OH)1.5Á(CH3CN)0.5 based on a tripodal ligand ntb
(ntb = tris(2-benzimidazolylmethyl)amine) has been syn-
thesized and structurally characterized by X-ray single
crystal diffractometry. In the structure of the complex each
center Ag(I) ion is coordinated by two N atoms from two
benzimidazole arm of one ntb ligand and one N atoms from
one benzimidazole arm of the other in a trigonal coordi-
nated geometry, resulting in the construction of a binuclear
complex. The complex units are further linked into a 1-D
chain by hydrogen bonds. The emission spectrum of the
complex has been investigated and shows a red-shift of the
emission peak compared to the ligand and the existence of
ligand-to-metal charge transfer process (emission peak at
468.2 nm). Cyclic voltammogram of the complex indicates
a pair of quasi-reversible redox couple, corresponding to
the Ag?/Ag electrochemical process.
Introduction
The tripodal ligand tris(2-benzimidazolylmethyl)amine
(ntb) and their complexes with metal ions have attracted
much attention in recent years. These complexes exhibit
not only special supramolecular networks [1, 2], but also
some potential applications as catalysts [3], models for
biological systems [4–6] and luminescent materials [7].
The tetradentate tripodal tetraamine ligand ntb thus contain
a single tertiary N atom, which ‘caps’ the tripod, and one
N-donor atom on each arm. Ntb have nominal C3 sym-
metry about the central N atom and three arms can each
rotate freely around an Napical–C bond, so all kinds of
supramolecular networks can be formed by coordination
bonds, hydrogen bonds and pÁÁÁp interaction. In recent lit-
erature, a large number of coordination complexes with
many metal ions have been synthesized [8], but the com-
plexes about silver(I) are rare. In this paper, we report the
synthesis and characterization of a binuclear Ag(I) com-
plex with the tripodal tetradentate ligand tris(2-benzimid-
azolylmethyl)amine (ntb).
Keywords Binuclear complex Á Ag(I) complex Á Crystal
structure Á Photoluminescence Á Cyclic voltammogram
Experimental
Materials and Measurement
All the chemical reagents for synthesizing the ligand
OBimB and the title complex were purchased commer-
cially and used without further purification. Elemental
analyses (C, H and N) were carried out on a Perkin-Elmer
1400C analyzer. IR spectra were recorded in the range of
400–4,000 cm-1 on a Nicolet 170SX spectrometer with
Y.-Y. Deng Á D. Zhang Á X.-Q. Duan Á X.-S. Shen
College of Pharmacy, Guilin Medical University, Guilin 541004,
People’s Republic of China
F.-Q. Liu (&)
Key Laboratory of Advanced Materials, Qingdao University of
Science and Technology, Qingdao 266042, People’s Republic of
China
1
pressed KBr pellets. H NMR spectra were measured on a
Bruker DOX 300 instrument using DMSO-d6 as solvent
e-mail: faqianliu@yahoo.com
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J Chem Crystallogr
and TMS as an internal standard at room temperature. UV–
Vis spectra were measured on a Perkin-Elmer UV–Vis
spectrometer. Voltammetry was performed using a CHI
832B electrochemical analysis system (China) with a three-
electrode system consisting of the modified electrode as the
working electrode, a saturated calomel electrode (SCE) as
the reference electrode, and a platinum wire as the auxil-
iary electrode. The electrochemical measurement was
carried out in a 10 mL electrolyte cell with 0.1 M NaNO3
as supporting electrolyte.
Ag2N17O9: C 49.28, H 4.45, N 18.43; found(%): C 49.37, H
4.54, N 18.48. IR(KBr): 3165 (w, vNH), 1625(w), 1543 (m,
vCN), 1441(m, vC=N–C=C). 1H NMR (DMSO-d6): d
13.02(2H, s, NH), 12.85(H, s, NH), 7.8(1H, d, Ar),
7.6–7.0(11H, m, Ar), 4.76(1H, d, CH2), 4.58 (1H, d, CH2),
4.15(4H, d, CH2).
X-ray Crystallography
Block shaped crystals of the complex was mounted on a
Bruker SMART 1000 CCD area detector X-ray single
crystal diffractometer with graphite-monochromated Mo
Ka radiation (k = 0.071073 nm) and a u/x scanning mode
at 293(2) K. Intensities were corrected for Lorentz and
polarization effects and empirical absorption. The struc-
tures were solved by direct methods via SHELXS 97
program [10] and refined by full-matrix least squares on F2
via SHELXL 97 program [11]. The correct positions for the
metal atoms were deduced from E-map. Subsequent least-
squares refinement and difference Fourier calculations
revealed the positions of the remaining non-hydrogen
atoms. Non-hydrogen atoms were refined with independent
anisotropic displacement parameters. H atoms were posi-
tioned from difference Fourier maps and a riding mode.
Crystallographic data for the complex are listed in Table 1.
Crystallographic data for the structural analysis have been
deposited to the Cambridge Crystallographic Data Centre,
Nos. CCDC 958929. Copies of this information can be
obtained free of charge from: The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK. Fax: ?44(1223)336-033,
email: deposit@ccdc.cam.ac.uk, or WWW: www.ccdc.cam.
ac.uk.
Preparation of the Complexes
The ligand tris(2-benzimidazolylmethyl)amine (ntb) was
synthesized by condensing o-diaminobenzene with
nitrilotriacetic acid according to the method of the litera-
ture [9] with minor revisions. o-Diaminobenzene (27 g,
250 mmol) and nitrilotriacetic acid (15.3 g, 80 mmol) in
150 mL of propylene glycol were heated and refluxed for
18 h, then cooled to room temperature. 50 mL of ice cold
water was added to force the precipitation of a brown solid.
The brown solid was recrystallized from hot methanol to
give pinkish white product (yield, 85 %). IR(KBr): 3143
(w, vNH), 1625(w), 1539 (m, vCN), 1446(m, vC=N–C=C).
Synthesis of [Ag2(ntb)2](NO3)2Á(CH3OH)1.5Á(CH3CN)0.5
Á
Ag(NO3)2 (0.051 g, 0.3 mmol) and ntb (0.12 g, 0.3 mmol)
were added to methanol (15 mL) and acetonitrile (15 mL),
and the mixture was stirred and refluxed for half an hour. The
resulting colorless solution was filtered and the filtrate was
allowed to stay at ambient temperature for a period of about
2 days, to give colorless block crystals (yield: 30 %) suitable
for structural determinations. Anal. Calcd(%) for C53H57
Table 1 Crystals and structures refinement data for the complex
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (nm)
C23H23Cl2N5O2Zn
1291.90
l (mm-1
)
0.794
F(000)
1,320
293(2)
Crystal size (mm)
0.54 9 0.48 9 0.19
Triclinic
Theta range for data collection (°)
Limiting indices
3.01–25.50
P-1
-13 B h B 12, -17 B k B 17, -23 B l B 23
22,404
1.07974(2)
1.44650(3)
1.95899(4)
100.9380(1)
101.6890(1)
109.1910(1)
2.3672(3)
2
Reflections collected
b (nm)
Independent reflections
Reflection observed
10,038 [R(int) = 0.0137]
c (nm)
8,773
Full-matrix least-squares on F2
10,038/6/762
a (°)
b (°)
c (°)
V (nm3)
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I [ 2r(I)]
R indices (all data)
1.035
Ra1 = 0.0264, wRb2 = 0.0682
Ra1 = 0.0327, wRb2 = 0.0752
1121 and -684
Z
Dc (Mg m-3
)
1.578
Largest diff. peak and hole (e nm-3
)
a
R = R||Fo| - |Fc||/R|Fo|
Rw = [R[w(F2o - F2c)2]/Rw(F2o)2]1/2
b
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J Chem Crystallogr
˚
Results and Discussion
Description of the Crystal Structure
Table 2 Selected bond lengths (A) and bond angles (°) for the title
compound
Ag(1)–N(1)
2.229(2)
2.2571(2) Ag(2)–N(10)
2.267(2) Ag(2)–N(12)#2
Ag(2)–N(8)
2.2141(2)
2.223(2)
2.236(2)
2.9578(4)
121.23(7)
Ag(1)–N(5)#1
Ag(1)–N(3)
The crystal structure of the title compound crystallizes with
two complexes in an asymmetric unit. Each complex con-
sists of a binuclear [Ag2(ntb)2]2? dication, two free NO3
Ag(1)–Ag(1)#1
2.9196(4) Ag(2)–Ag(2)#2
-
N(1)–Ag(1)–
N(5)#1
127.62(7) N(8)–Ag(2)–N(10)
anions, and lattice methanol and acetonitrile molecules. The
molecular structure of the two centrosymmetric dications
[Ag2(ntb)2]2? is shown in Fig. 1. The selected bond lengths
and bond angles are listed in Table 2. In the crystal structure
of each dications, the center Ag(I) ion is coordinated by two
N atoms from two benzimidazole arm of one ntb ligand and
one N atoms from one benzimidazole arm of the other in a
trigonal coordinated geometry, resulting in the construction
of a M2L2 complex. The ntb ligand adopts an endo con-
formation in the bridging mode, so the Ag(I) ion is encap-
sulated. The Ag(I) ions are each displaced by 0.363 and
N(1)–Ag(1)–N(3)
119.83(7) N(8)–Ag(2)–N(12)#2 122.34(7)
N(5)#1–Ag(1)–
N(3)
104.71(7) N(10)–Ag(2)–
N(12)#2
108.18(8)
Symmetry code: #1 -x ? 1, -y ? 1, -z ? 1, #2 -x ? 1, -y ? 1,
-z ? 2
˚
Table 3 Hydrogen bonds of the title compound (A and °)
D–HÁÁÁA
d(D–H) d(HÁÁÁA) d(DÁÁÁA) \D–HÁÁÁA
˚
0.371 A from the plane defined by the three nitrogen donors
N(4)–H(4 N)ÁÁÁO(5)#1 0.855(1) 2.420(3) 2.997(3) 125(3)
N(4)–H(4 N)ÁÁÁO(6)#2 0.855(1) 2.240(2) 2.989(3) 146(2)
N(6)–H(6 N)ÁÁÁO(9)#3 0.853(3) 2.039(1) 2.820(3) 152(3)
Symmetry code: #1: 2 - x, 1 - y, 2 – z, #2: 2 - x, 1 - y, 2 – z, #3:
1 - x, 1 - y, 1 - z
toward the other, leading to short AgÁÁÁAg distances
˚
˚
(Ag1ÁÁÁAg1 = 2.920 A, Ag2ÁÁÁAg2 = 2.958 A), which are
˚
closed to that in metallic silver (2.89 A) and trigonally
coordinated binuclear silver(I) complexes [12–14] with
nitrogen donors. The AgÁÁÁAg interactions [15] may result in
the aggregation of the two ntb ligands to generate the
binuclear complexes. The Ag–N bond distances are in the
˚
range of 2.214(2)–2.267(2) A, which are similar to those of
˚
Ag–N (pyrimidine) bonds (2.271 A) [16] but longer than
˚
those of Ag–N (pyrazole) (ranging from 2.353 to 2.408 A)
˚
˚
N4) = 2.997(3) A; d(O6ÁÁÁH4 N–N4) = 2.989(3) A; d(N13–
˚ ˚
H13 NÁÁÁO5) = 2.814(3) A; d(O9ÁÁÁH6 N–N6) = 2.820(3) A]
(Table 3) (Fig. 2).
[17, 18]. The bond angles of N–Ag–N are in the range of
104.71(7)°–127.62(7)°.
In the title compound, the complex units are extended to a
UV–Vis Spectra
1-D chain by hydrogen bonds formed by the two amine NH
-
groups of the ntb ligand with NO3 anion [d(O5ÁÁÁH4 N-
UV–Vis spectra of the ligand ntb and the title complex in
DMF solution exhibit similar transition at 280 nm, which
suggests that the absorption is owned to the ligand. The
absorbance of the complex (e280 = 57600 M-1 cm-1) is
about two times to the ligand ntb (e280 = 28,500 M-1 cm-1),
which shows the complex contains two ntb ligand and is
consistent with crystal structure of the complex. The
absorption band can be assigned to intramolecular charge
transfer transitions of the ligand (IL) and ascribed to p ? p*
transitions in the ligand. The weak absorption band at
350–400 nm for the complex are as a result of ligand-to-
metal charge transfer (LMCT) character [19, 20].
Photoluminescence
The emission spectra of the ligand and the complex were
investigated in the solid state at room temperature. As
shown in Fig. 3, the ligand displays a narrow emission
band around 306.2 nm upon excitation at 280 nm and the
complex exhibits a broad emission peak at 346.8 nm. The
Fig. 1 Cationic dimeric structures of [Ag2(ntb)2]2? of the complex
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J Chem Crystallogr
Fig. 2 1-D chain formed by
N–HÁÁÁO hydrogen bonds
ascribe to LMCT process [20], corresponding to the
absorption band at 350–400 nm from the above UV–Vis
spectra for the complex.
Cyclic Voltammetry
The electrochemical behavior of 1 mmol L-1 the complex
in DMSO solution with 0.1 mmol L-1 NaNO3 as the
supporting electrolyte at a scan rate of 0.1 V s-1 on the
surface of glassy carbon electrode is shown in Fig. 3. The
complex displays a pair of well-defined redox peaks with
large currents; an anodic peak is observed at 0.250 V and a
cathodic peak at -0.190 V. The mean peak potential
E1/2 = (Epa ? Epc)/2 is 0.030 V, corresponding to the
Ag?/Ag electrochemical process [21]. The separation of
the cathodic and anodic peak potentials, DE = 0.440 V,
indicates that the electrochemical behavior of the complex
is a quasi-reversible process. The anodic peak current is
larger than the cathodic current (ipc/ipa = 1.802), indicating
a slow electron transfer process (Fig. 4).
Fig. 3 Emission spectra of the ligand ntb and the complex in the
solid state at room temperature
Conclusion
A new Ag(I) complex based on a tripodal ligand tris(2-
benzimidazolylmethyl)amine (ntb), [Ag2(ntb)2](NO3)2Á
(CH3OH)1.5Á(CH3CN)0.5 has been synthesized and struc-
turally characterized by X-ray diffraction analyses. In the
structures of the complex, two ligands with endo configu-
ration afford six coordination sites to chelate two metal
ions, resulting in a binuclear structure. The complex units
are further linked into a 1-D chain by hydrogen bonds. The
electronic absorption of the complex mainly exhibits
LMCT character. Cyclic voltammogram of the complex
indicates a pair of quasi-reversible redox couple, which is
ascrible to the Ag?/Ag electrochemical process.
Fig. 4 Cyclic voltammogram of 1 mmol L-1 the complex in DMSO
solution with 0.1 mmol L-1 NaNO3 as the supporting electrolyte at a
scan rate of 0.1 V s-1
complex shows weak emission and the emission peak has a
red-shift of 40.6 nm compared to that of the ligand, which
can be as a result of the coordination of N atoms with Ag
atom. The emission peak of the complex at 468.2 nm is
Acknowledgments This work was supported by the NSF of China
(No. 21371105), Science and Technology Plan of Qingdao (13-1-4-
209-jch) and University and Doctoral Foundation of Guilin Medical
University.
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J Chem Crystallogr
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