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Article

Synthesis of Some Transition Metal Complexes of a Novel Schiff Base Ligand Derived from 2,2'-bis(p-Methoxyphenylamine) and Salicylicaldehyde

1
College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, P. R.China
2
Chemistry Department, Guangxi University for Nationalities, Nanning, 530006, P. R. China
*
Author to whom correspondence should be addressed.
Molecules 2003, 8(5), 439-443; https://doi.org/10.3390/80500439
Submission received: 25 February 2003 / Revised: 3 April 2003 / Accepted: 5 April 2003 / Published: 31 May 2003

Abstract

:
A novel Schiff base ligand derived from 2,2'-bis(p-methoxyphenylamine) and salicylicaldehyde and its transition metal complexes with Cu (Ⅱ), Co (Ⅱ) and Mn (Ⅱ) have been synthesized. Their spectral properties and electrochemical behavior were investigated.

Introduction

During the past two decades, considerable attention has been paid to the chemistry of the metal complexes of Schiff bases containing nitrogen and other donors [1,2,3,4]. This may be attributed to their stability, biological activity [5] and potential applications in many fields such as oxidation catalysis [6], electrochemistry [7], etc. Herein we report the synthesis of a novel Schiff base ligand (H2L) and its Cu (II), Co (II) and Mn (II) complexes. Their spectral properties and electrochemical behavior were investigated.

Results and discussion

Ligand synthesis

The ligand (H2L) was prepared as outlined in Figure 1.
Figure 1. Synthesis of the ligand
Figure 1. Synthesis of the ligand
Molecules 08 00439 g001

Complexes

Elemental analyses indicate that the complexes of H2L with Cu (II), Co (II) and Mn (II) can be formulated as M·L. The disappearance of the OH band of the free ligand in the IR of the metal complexes indicates that the OH group is deprotonated and coordinated to the metal ion as –O-. On the other hand, the C=N stretching mode is shifted to a lower frequency by about 29 cm-1, compared to the free ligand. These IR results indicate that the ligand is coordinated to Cu (II), Co (II), Mn (II) via both N and O. The new IR bands appearing at 420 ~ 430 cm-1 and 541 ~ 560 cm-1 are assigned to ν (M-O) and ν (M-N) vibrations, respectively. In addition, no new bands at 1610 ~ 1550 cm-1 and 1420 ~ 1300 cm-1 are observed, indicating that the complexes do not contain CH3COO- anions, which is in accordance with the elemental analysis results for the complexes. According to the aforementioned data, we propose for the complexes prepared the structure shown in Figure 2. It is suggested that the complexes are square planar or nearly square planar, coordinated according to the common stereochemistry of this kind of compounds.
Figure 2. The proposed chemical structure for the transition metal complexes
Figure 2. The proposed chemical structure for the transition metal complexes
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Electrochemistry

The electrochemical behaviors of the H2L ligand and the MnL, CuL and CoL complexes were examined by means of cyclic voltammetry in CH2Cl2. A typical cyclic  voltammogram   of H2L and its complexes is shown in Figure 3 and the results are summarized in Table 1.
Table 1. Cyclic  voltammetric  data for ligand and complexes in CH2Cl2 
Table 1. Cyclic  voltammetric  data for ligand and complexes in CH2Cl2 
Ligand and Complexes Ep ,a1/ VE1/2/ mVΔEp1/ mVEp ,a2 / V E 1 / 2 / mV
L0.8579782.475.5
MnL0.580495.0110.00.895800.0
CuL0.830745.0
CoL0.782700.0
The MnL complex shows two oxidation processes at Ep,a = 0.58 and 0.895V. The first wave is nearly reversible with ΔEp=110mV. This process is consistent with a one-electron oxidation to form the mixed valence Mn(II, III) species. The second wave is irreversible at 0.895 V. On the other hand, the complexes of CuL and CoL only show one oxidation process at 0.83 and 0.782V, respectively, which are irreversible. This process is attributed to the oxidation of ligand. The observed reaction voltages of the complexes of CuL and CoL are lower than that of the ligand, while the MnL one is higher.
Figure 3. Cyclic Voltamogram of the Complexes in CH2Cl2; Scan Rate 100mV/s
Figure 3. Cyclic Voltamogram of the Complexes in CH2Cl2; Scan Rate 100mV/s
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Acknowledgments

   We thank National Natural Science Foundation of China (No. 29871014) and the Doctoral
Foundation of Lanzhou University for financial support.

Experimental

General

The C, H, N data were determined using a Varian EL elemental analyzer. IR spectra was recorded on a Nicolet 170SX FT IR spectrophotometer using KBr discs in the range ν = 400- 4000 cm-1. The cyclic voltammetry experiments were carried out using a CHI660A electrochemical workstation (Covarda, USA). All chemicals were analytical grade and used without further purification.

Preparation of the Ligand

Salicylicaldehyde (20 mmol) was added to a solution of 2,2'-bi(p-methoxyphenylamine) (10 mmol) in ethanol (30 mL). The mixture was continuously stirred for 3 h at room temperature, and the resulting yellow product was collected by filtration to give pale white crystals in 94% yield. Calculated for C28H24N2O4 : 74.3 % C, 5.4 % H, 6.2 % N. Found: 73.9 % C, 5.6 % H, 6.1 % N. IR (in KBr pellets) cm-1: 1657 (-C=N-), 3450 (-OH) cm-1.

Preparation of the Complexes

      A mixture of  M(OAc) 2 · nH 2  O (2 mmol) [M = Mn (Ⅱ), Co (Ⅱ), Cu (Ⅱ)], LiOH and ligand in a
1:2:1 molar ratio was stirred in ethanol (20 mL) at 50℃ for 4h. The crude complexes were filtered off
and then recrystallized from 1:1 water-ethanol. The products were dried in vacuo for 48 h.
CuL: brown solid, yield, 85 %; Calculated for C28H22N2O4Cu: 65.4 % C, 4.3 % H, 5.5 % N. Found: 65.2 % C, 4.6 % H, 5.7 % N. IR cm-1: 1628 (-C=N).
CoL: orange solid, yield, 88 %; Calculated for C28H22N2O4C: 66.0 % C, 4.4 % H, 5.5 % N. Found: 65.8 % C, 4.3 % H, 5.7 % N. IR cm-1: 1629 (-C=N).
MnL: dark-brown solid, yield, 88 %; Calculated for C28H22N2O4Mn: 66.5 % C, 4.4 % H, 5.5 % N. Found: 66.8 % C, 4.1 % H, 5.2 % N. IR cm-1: 1628 (-C=N)

Electrochemical Measurements

The cyclic voltammetry experiments were carried out with a three electrode apparatus using a CHI660A electrochemical workstation (Covarda, USA), the working electrode was a glassy carbon disc, polished with an Al2O3 suspension prior to every experiment. Ag/AgCl and Pt foil were used as reference and counter electrodes, respectively. The H2L and complexes solutions (1.0×10-3 mol·L-1) in CH2Cl2, with tetraethylammonium perchlorate (0.1 mol·L-1) as supporting electrolyte were purged of oxygen by bubbling nitrogen for 15 min. and then blanketed with the same gas during the experiments. All compounds were investigated at 25℃.The voltammograms were recorded with a potential scan of 100mV·s-1.

References

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MDPI and ACS Style

Tai, X.; Yin, X.; Chen, Q.; Tan, M. Synthesis of Some Transition Metal Complexes of a Novel Schiff Base Ligand Derived from 2,2'-bis(p-Methoxyphenylamine) and Salicylicaldehyde. Molecules 2003, 8, 439-443. https://doi.org/10.3390/80500439

AMA Style

Tai X, Yin X, Chen Q, Tan M. Synthesis of Some Transition Metal Complexes of a Novel Schiff Base Ligand Derived from 2,2'-bis(p-Methoxyphenylamine) and Salicylicaldehyde. Molecules. 2003; 8(5):439-443. https://doi.org/10.3390/80500439

Chicago/Turabian Style

Tai, Xishi, Xianhong Yin, Qiang Chen, and Minyu Tan. 2003. "Synthesis of Some Transition Metal Complexes of a Novel Schiff Base Ligand Derived from 2,2'-bis(p-Methoxyphenylamine) and Salicylicaldehyde" Molecules 8, no. 5: 439-443. https://doi.org/10.3390/80500439

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