Synthesis of zinc(II)/cadmium(II)/mercury(II) thiocyanate and azide complexes of a new bidentate Schiff-base ligand (L) with general formula of MLX2 (M = Zn(II), Cd(II), and Hg(II)) in ethanol solution at room temperature is reported. The ligand and metal complexes were characterized by using ultraviolet-visible (UV-visible), Fourier transform infrared (FT-IR), 1H- and 13C-NMR spectroscopy and physical characterization, CHN analysis, and molar conductivity. 1H- and 13C-NMR spectra have been studied in DMSO-d6. The reasonable shifts of FT-IR and NMR spectral signals of the complexes with respect to the free ligand confirm well coordination of Schiff-base ligand and anions in an inner sphere coordination space. The conductivity measurements as well as spectral data indicated that the complexes are nonelectrolyte. Theoretical optimization on the structure of ligand and its complexes was performed at the Becke’s three-parameter hybrid functional (B3) with the nonlocal correlation of Lee-Yang-Parr (LYP) level of theory with double-zeta valence (LANL2DZ) basis set using GAUSSIAN 03 suite of program, and then some theoretical structural parameters such as bond lengths, bond angles, and torsion angles were obtained. Finally, electrochemical behavior of ligand and its complexes was investigated. Cyclic voltammograms of metal complexes showed considerable changes with respect to free ligand.
Schiff bases are very important class of ligands in coordination chemistry due to the wide applications of them in synthesis of a large variety of transition-metal complexes with various structural architectures [
All solvents and chemicals used in synthesis and analysis were provided from Aldrich, Merck, and/or BDH companies. Metal thiocyanate and azide salts were freshly prepared according to our previous report [
The ligand of N,N′-bis((E)-3-(2-nitrophenyl)allylidene)propane-1,3-diamine has been synthesized by the reaction between 2-nitrocinnamaldehyde (2 mmol, 0.354 g) and propane-1,3-diamine (1 mmol, 0.074 g) in ethanol under severe stirring for 4 h. The yellowish solution so obtained was subjected to evaporation for obtaining yellowish white precipitate. Then, the product was recrystallized from dichloromethane to afford the pure Schiff base in 76% yield. %C21H20N4O4: calc. C, 64.28%; H, 5.14%; N, 14.28%; found: C, 63.7%; H, 5.3%; N, 14.6%. Characteristic FT-IR and UV-visible spectral data have been summarized in Table
FT-IR (cm−1) and UV-visible (nm) spectral data of the Schiff base and their complexes.
Compounds |
|
|
|
|
|
|
|
–SCN/–N3 |
|
---|---|---|---|---|---|---|---|---|---|
Ligand | 3067 (w) | 2935 (w) | 2843 (w) | 1635 (s) | 1615 (m) | 1522 (vs) | 1345 (s) | — | 298 (6927) |
ZnL(NCS)2 | 3062 (w) | 2935 (w) | 2863 (w) | 1633 (s) | 1610 (m) | 1520 (vs) | 1343 (s) | 2065 | 323 (8737) |
ZnL(N3)2 | 3057 (w) | 2918 (w) | 2850 (w) | 1633 (vs) | 1611 (s) | 1518 (vs) | 1347 (s) | 2062 | 293 (3566) |
CdL(SCN)(NCS) | 3059 (w) | 2917 (w) | 2844 (w) | 1632 (vs) | 1612 (s) | 1518 (vs) | 1339 (s) | 2058 |
339 (12697) |
CdL(N3)2 | 3052 (w) | 2924 (w) | 2854 (w) | 1636 (vs) | 1616 (s) | 1520 (vs) | 1342 (s) | 2046 | 333 (8840) |
HgL(SCN)2 | 3057 (w) | 2924 (w) | 2854 (w) | 1626 (vs) | — | 1520 (vs) | 1346 (s) | 2117 | 335 (10494) |
HgL(N3)2 | 3057 (w) | 2921 (w) | 2854 (w) | 1632 (vs) | — | 1520 (vs) | 1343 (s) | 2034 | 331 (10660) |
All Schiff-base complexes were synthesized by gradual addition of ethanolic solution of ligand (0.5 mmol) to solution of metal (II) thiocyanate or azide salts in ethanol. The mixture was stirred for 2-3 hours severely at room temperature. The complexes as precipitate were filtered, washed with ethanol twice, dried under vacuum and finally recrystallized from dichloromethane/methanol or chloroform/ethanol. Characteristic FT-IR and UV-visible spectral data were summarized in Table
(1)
(2)
(3) [CdL(SCN)(NCS)]. Yield: 58%; yellowish white precipitate, %C23H20Cd S2N6O4: calc. C, 44.49%; H, 3.25%; N, 13.53%; found: C, 44.9%; H, 3.4%; N, 13.7%. 1H NMR (DMSO-d6): 8.21 (d, 2H,
(4)
(5)
(6)
Herein, the synthesis and spectral identification of a new symmetrical bidentate Schiff-base ligand of N,N′-bis((E)-3-(2-nitrophenyl)allylidene)propane-1,3-diamine and its complexes with zinc, cadmium, and mercury ions in general formula of MLX2 (X = SCN−,
The structure of ligand and MLX2 complexes (M = Zn(II), Cd(II), Hg(II); X = SCN−,
The low molar conductivities of 10−3 M solutions of ligand and its complexes in DMF solvent were in the range of 2.53–46.67 cm2 Ω−1 M−1 at room temperature indicate that all of them are nonelectrolytes [
Some important FT-IR absorption frequencies of the bidentate Schiff-base ligand and its zinc, cadmium, and mercury complexes have been collected in Table
UV-visible spectra of the free ligand and complexes were recorded in DMF (Table
The 1H NMR spectroscopy has been used for confirmation of the binding of ligand to metal ions for all complexes. The 1H and 13C NMR spectral data have been summarized in Section
1H-NMR and 13C-NMR of ligand ((a) and (b)) and ZnL(N3)2 ((c) and (d)), respectively.
The initial structures of ligand and its complexes were sketched with HyperChem 8.0.8 software and PM3 semiempirical method. All geometries were optimized at the Becke’s three-parameter hybride functional (B3) with the nonlocal correlation of Lee-Yang-Parr (LYP) level of theory with double-zeta valence (LANL2DZ) basis set using GAUSSIAN 03 suite of program, working on 2.3 GHz dual processors. Calculations were followed in the gas phase. Density functional theory (DFT) calculations were done in order to find the optimized geometry of the ligand and its complexes. For instance, the optimized structures of ligand, zinc thiocyanate, and azide complexes have been shown in Figure
Some selected structural data derived from theoretical optimization.
Selected data | ZnL(NCS)2 | ZnL(N3)2 | CdL(SCN)(NCS) | CdL(N3)2 | HgL(SCN)2 | HgL(N3)2 |
---|---|---|---|---|---|---|
Bond length (°A) | ||||||
M–N (imine) | 2.1150 | 2.1226 | 2.3311 | 2.3599 | 2.4672 | 2.5162 |
M–N′ (imine) | 2.1150 | 2.1225 | 2.3453 | 2.3448 | 2.4498 | 2.4879 |
M–X | 1.9700 | 1.9735 | 2.5953 | 2.1330 | 2.6680 | 2.2460 |
M–X′ | 1.9535 | 1.9507 | 2.1564 | 2.1662 | 2.6821 | 2.2246 |
| ||||||
Bond angle (°) | ||||||
N′–M–N | 89.8163 | 88.1673 | 83.2459 | 81.0377 | 80.0201 | 74.6799 |
N′–M–X | 109.8485 | 101.4402 | 100.9224 | 102.1950 | 111.1427 | 94.1154 |
N′–M–X′ | 103.5345 | 107.7474 | 106.5551 | 97.1403 | 110.2779 | 94.8796 |
N–M–X | 109.8436 | 101.4219 | 117.3905 | 110.3509 | 112.0082 | 90.5492 |
N–M–X′ | 103.5413 | 107.7841 | 100.9224 | 94.6580 | 101.5451 | 104.3265 |
X–M–X′ | 132.0564 | 138.8475 | 134.4819 | 150.3185 | 130.0291 | 164.2183 |
| ||||||
Torsion angle (°) | ||||||
N–C9–C8–C7 | −176.6223 | −178.3666 | −179.6795 | −179.6153 | −179.7008 | −178.9212 |
|
176.6320 | 178.3640 | 178.5942 | 179.0566 | 176.8017 | 177.7678 |
|
−67.07 | −66.39 | −68.49 | −68.05 | −73.23 | −66.75 |
|
67.07 | 66.41 | 71.63 | 70.41 | 70.29 | 69.43 |
C8–C7–C6–C5 | −149.97 | −152.57 | 151.95 | −153.48 | 155.17 | −154.47 |
|
149.98 | 152.57 | −154.52 | 153.12 | −153.16 | 153.30 |
Optimized structure of ligand (a), ZnL(N3)2 (b), and ZnL(NCS)2 (c).
The electrochemical properties of a substance in solution are investigated by cyclic voltammetry technique. In this paper, cyclic voltammograms of ligand and its zinc, cadmium, and mercury complexes were obtained in dry acetonitrile solutions on glassy carbon electrode with a scan rate of 0.1 V/S and are depicted in Figure
Electrochemical data of ligand and complexes.
Compounds |
|
|
|
|
---|---|---|---|---|
L | −0.78 (−0.70), −1.54 (−1.47) | −0.08 | −0.07 | −0.63 (−0.71) |
ZnL(NCS)2 | −0.76 (−0.67), −1.57 (−1.49) | −0.09 | −0.13 | −0.59 (−0.68) |
ZnL(N3)2 | −0.73 (−0.62), −1.50 (−1.44) | −0.09 | −0.06 | −0.57 (−0.66) |
CdL(SCN)(NCS) | −0.86 (−0.75) | −0.09 | — | −0.61 (−0.74) |
CdL(N3)2 | −0.77 (−0.67) | −0.1 | — | −0.57 (−0.71) |
HgL(SCN)2 | −0.93 (−0.82) | −0.09 | — | −0.72 (−0.83) |
HgL(N3)2 | −0.90 (−0.78) | −0.12 | — | −0.70 (−0.82) |
a
Cyclic voltammograms of ligand (a), ZnL(N3)2, ZnL(NCS)2, CdL(SCN)(NCS), CdL(N3)2, HgL(N3)2, and HgL(SCN)2 ((b): a, b, c, d, e, and f, resp.).
In this work, we reported the synthesis, full spectroscopic characterization, electrochemical and theoretical investigation of a new symmetric bidentate Schiff-base ligand and its new zinc(II), cadmium(II), and mercury(II) azide and thiocyanate four coordinated compounds. The physical, spectral, and theoretical results predict pseudotetrahedral geometry for all coordination compounds. The ligand and its complexes structures were optimized at the nonlocal correlation of Lee-Yang-Parr (LYP) level of theory with double-zeta valence (LANL2DZ) basis set using Gaussian 03 suite of program, and finally some theoretical structural parameters such as bond lengths, bond angles, and torsional angles were extracted. Electrochemical behavior of ligand and its complexes was investigated by cyclic voltammetry technique. The cyclic voltammogram of ligand illustrated two reduction and one oxidation peaks. The zinc complexes exhibited a similar behavior with respect to ligand, but cadmium and mercury complexes showed a reversible electrochemical process.
Partial support of this research by Yasouj University is acknowledged. The authors do not have a direct financial relation with the commercial identity companies mentioned in this work.