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Journal of Chemical Crystallography

, Volume 44, Issue 4, pp 185–189 | Cite as

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
Original Paper
First Online:
Received:
Accepted:

Abstract

A new binuclear complex [Ag2(ntb)2](NO3)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.

Keywords

Binuclear complex Ag(I) complex Crystal structure Photoluminescence Cyclic voltammogram 

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, 5, 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 C 3 symmetry 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 π···π interaction. In recent literature, a large number of coordination complexes with many metal ions have been synthesized [8], but the complexes about silver(I) are rare. In this paper, we report the synthesis and characterization of a binuclear Ag(I) complex with the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (ntb).

Experimental

Materials and Measurement

All the chemical reagents for synthesizing the ligand OBimB and the title complex were purchased commercially 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 pressed KBr pellets. 1H NMR spectra were measured on a Bruker DOX 300 instrument using DMSO-d 6 as solvent 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 auxiliary electrode. The electrochemical measurement was carried out in a 10 mL electrolyte cell with 0.1 M NaNO3 as supporting electrolyte.

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 literature [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)2·(CH3OH)1.5·(CH3CN)0.5·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 C53H57Ag2N17O9: 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-d 6 ): δ 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 Kα radiation (λ = 0.071073 nm) and a φ/ω scanning mode at 293(2) K. Intensities were corrected for Lorentz and polarization effects and empirical absorption. The structures were solved by direct methods via SHELXS 97 program [10] and refined by full-matrix least squares on F 2 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 positioned from difference Fourier maps and a riding mode. Crystallographic data for the complex are listed in Table 1.
Table 1

Crystals and structures refinement data for the complex

Empirical formula

C23H23Cl2N5O2Zn

µ (mm−1)

0.794

Formula weight

1291.90

F(000)

1,320

Temperature (K)

293(2)

Crystal size (mm)

0.54 × 0.48 × 0.19

Crystal system

Triclinic

Theta range for data collection (°)

3.01–25.50

Space group

P−1

Limiting indices

−13 ≤ h ≤ 12, −17 ≤ k ≤ 17, −23 ≤ l ≤ 23

a (nm)

1.07974(2)

Reflections collected

22,404

b (nm)

1.44650(3)

Independent reflections

10,038 [R(int) = 0.0137]

c (nm)

1.95899(4)

Reflection observed

8,773

α (°)

100.9380(1)

Refinement method

Full-matrix least-squares on F 2

β (°)

101.6890(1)

Data/restraints/parameters

10,038/6/762

γ (°)

109.1910(1)

Goodness-of-fit on F 2

1.035

V (nm3)

2.3672(3)

Final R indices [I > 2σ(I)]

R 1 a  = 0.0264, wR 2 b  = 0.0682

Z

2

R indices (all data)

R 1 a  = 0.0327, wR 2 b  = 0.0752

Dc (Mg m−3)

1.578

Largest diff. peak and hole (e nm−3)

1121 and −684

a R = Σ||F o| − |F c||/Σ|F o|

b R w  = [Σ[w(F o 2  − F c 2 )2]/Σw(F o 2 )2]1/2

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.

Results and Discussion

Description of the Crystal Structure

The crystal structure of the title compound crystallizes with two complexes in an asymmetric unit. Each complex consists of a binuclear [Ag2(ntb)2]2+ dication, two free NO3 − 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 conformation in the bridging mode, so the Ag(I) ion is encapsulated. The Ag(I) ions are each displaced by 0.363 and 0.371 Å from the plane defined by the three nitrogen donors toward the other, leading to short Ag···Ag distances (Ag1···Ag1 = 2.920 Å, Ag2···Ag2 = 2.958 Å), which are closed to that in metallic silver (2.89 Å) and trigonally coordinated binuclear silver(I) complexes [12, 13, 14] with nitrogen donors. The Ag···Ag 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) Å, which are similar to those of Ag–N (pyrimidine) bonds (2.271 Å) [16] but longer than those of Ag–N (pyrazole) (ranging from 2.353 to 2.408 Å) [17, 18]. The bond angles of N–Ag–N are in the range of 104.71(7)°–127.62(7)°.
Fig. 1

Cationic dimeric structures of [Ag2(ntb)2]2+ of the complex

Table 2

Selected bond lengths (Å) and bond angles (°) for the title compound

Ag(1)–N(1)

2.229(2)

Ag(2)–N(8)

2.2141(2)

Ag(1)–N(5)#1

2.2571(2)

Ag(2)–N(10)

2.223(2)

Ag(1)–N(3)

2.267(2)

Ag(2)–N(12)#2

2.236(2)

Ag(1)–Ag(1)#1

2.9196(4)

Ag(2)–Ag(2)#2

2.9578(4)

N(1)–Ag(1)–N(5)#1

127.62(7)

N(8)–Ag(2)–N(10)

121.23(7)

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

In the title compound, the complex units are extended to a 1-D chain by hydrogen bonds formed by the two amine NH groups of the ntb ligand with NO3 − anion [d(O5···H4 N-N4) = 2.997(3) Å; d(O6···H4 N–N4) = 2.989(3) Å; d(N13–H13 N···O5) = 2.814(3) Å; d(O9···H6 N–N6) = 2.820(3) Å] (Table 3) (Fig. 2).
Table 3

Hydrogen bonds of the title compound (Å and °)

D–H···A

d(D–H)

d(H···A)

d(D···A)

∠D–H···A

N(4)–H(4 N)···O(5)#1

0.855(1)

2.420(3)

2.997(3)

125(3)

N(4)–H(4 N)···O(6)#2

0.855(1)

2.240(2)

2.989(3)

146(2)

N(6)–H(6 N)···O(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

Fig. 2

1-D chain formed by N–H···O hydrogen bonds

UV–Vis Spectra

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 (ε 280 = 57600 M−1 cm−1) is about two times to the ligand ntb (ε 280 = 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 π → π* 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 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 ascribe to LMCT process [20], corresponding to the absorption band at 350–400 nm from the above UV–Vis spectra for the complex.
Fig. 3

Emission spectra of the ligand ntb and the complex in the solid state at room temperature

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 E 1/2 = (E pa + E pc)/2 is 0.030 V, corresponding to the Ag+/Ag electrochemical process [21]. The separation of the cathodic and anodic peak potentials, ΔE = 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 (i pc/i pa = 1.802), indicating a slow electron transfer process (Fig. 4).
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

Conclusion

A new Ag(I) complex based on a tripodal ligand tris(2-benzimidazolylmethyl)amine (ntb), [Ag2(ntb)2](NO3)2·(CH3OH)1.5·(CH3CN)0.5 has been synthesized and structurally characterized by X-ray diffraction analyses. In the structures of the complex, two ligands with endo configuration 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.

Notes

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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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • Yue-Yi Deng
    • 1
  • Dong Zhang
    • 1
  • Xiao-Qun Duan
    • 1
  • Xue-Song Shen
    • 1
  • Fa-Qian Liu
    • 2
  1. 1.College of PharmacyGuilin Medical UniversityGuilinPeople’s Republic of China
  2. 2.Key Laboratory of Advanced MaterialsQingdao University of Science and TechnologyQingdaoPeople’s Republic of China

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