Preparation and chemical analysis of Mn(II), Fe(III), Co(II), Ni(II), and Zn(II) complexes with Schiff base L [o-HOC6H4CH:N(CH2)6N:CHC6H4OH-o] are the main tasks of this work. The octahedral (M2L2·
The chemistry of transition metal complexes of Schiff base compounds hasattracted a lot of interest in the field of bioinorganic and coordination chemistry [
Infrared measurements were carried out on Perkin Elmer spectrophotometer model 1430 in range from 200 to 4000 cm−1. Ultraviolet and visible spectra were carried out on a Perkin Elmer Lambda 35 UV-Vis spectrophotometer in the range 190–500 nm. The solution spectra of ligands and complexes were carried out in 10−6 M of DMF. 1H-NMR spectra were recorded using a Varian spectrometer, 200 MHz. Thermal gravimetric analysis (TGA) data were measured from room temperature to 650°C at heating rate of 10°C/min. The data were obtained using a Shimadzu TGA-50H instrument. Mass spectra of the compounds were recorded on a Hewlett Packard mass spectrometer model MS 5988. Samples were introduced directly to the probe; fragmentations were carried out at 300°C and 70 eV. Molar conductivities were measured using WAP, GMP 500 conductivity meter. Magnetic susceptibilities of the complexes were measured by the Gouy method at room temperature using a magnetic susceptibility balance, Sherwood Scientific, Cambridge Science Park, Cambridge, UK. Effective magnetic moments were calculated from the expression
The ligand was synthesized by slowly adding salicylaldehyde (5.47 mL, 44.86 mmole) in 100 mL methanol to 1,6-hexanediamine (3 g, 25.81 mmole). The reaction mixture was heated to reflux for 2 hr. The yellow product obtained was filtered off and washed with few amount of methanol and then diethylether, and fine crystals were obtained by recrystallization from methanol. The ligand obtained was soluble in 1,2-dichloromethane, chloroform, and partially soluble in methanol and ethanol. The yield was (7 g, 83.73%), m.p. 72°C, Calc. for C20H24N2O2: C, 74.07; H, 7.41; N, 8.64, Found: C, 73.65; H, 7.77; N, 8.59%. The reaction for the formation of L (HBS) is illustrated in Scheme
Schematic representation for the formation of Schiff base ligand L (HBS).
A pink solution of Mn(NO3)2
A yellow solution of Fe(NO3)3
A red solution of Co(NO3)2
A green solution of Ni(NO3)2
A solution of Zn(CH3COO)2
All the complexes provide satisfactory C, H, N, and metal analyses and confirm the general composition [M2L2(H2O)] and [M2L2X2(H2O)], where L = ligand, X =
Physical data of ligand (HBS) and corresponding metal complexes.
Ligand/complex |
(Yield) % M.wt | Colour |
M.P. °C |
Elemental analyses (Found) Calc. % | |||
---|---|---|---|---|---|---|---|
C | H | N | M | ||||
L (HBS) |
(83.73) |
Yellow | 72 | (73.65) |
(7.77) |
(8.59) |
|
1-[Mn2(L)2(H2O)4] |
(43.64) |
Dark |
>300 |
(57.59) |
(5.76) |
(6.51) |
(12.67) |
2-[Fe2(H2L)(NO3)6(H2O)2] |
(66.25) |
Reddish brown | >300 |
(24.6) |
(3.95) |
(10.9) |
(12.08) |
3-[Co2(HL)2(NO3)2(H2O)2] |
(30.23) |
Dark |
>300 |
(50.67) 51.95 | (5.35) |
(9.70) |
(13.08) |
4-[Ni2(L)(NO3)2(H2O)6] |
(35.43) |
Green | >300 |
(36.12) |
(4.19) |
(8.76) |
(17.83) |
5-[Cu2(HL)2(Ac)2(H2O)2] |
(47.00) |
Dark |
>300 |
(57.06) 56.95 | (5.94) |
(6.70) |
(13.80) |
6-[Zn2(HL)2(Ac)2(H2O)2] |
(78.63) |
Yellowish white | >300 |
(57.55) |
(5.10) |
(6.24) |
(13.41) |
The electronic spectrum of Mn(II) complex shows a band at 721 nm. This band is assignable to
The value of the magnetic moment of the Fe(III) complex is 5.08 B.M. which falls in the range of values corresponding to low-spin octahedral complexes of Fe(III) ions. The conductance of Fe(III) complex in DMF is 7.18
The electronic spectrum of the green Ni(II) complex showed three bands. The spectrum of octahedral Ni(II) consists of three bands which are accordingly assigned as 3A2g(F)→3T2g(F), 3A2g(F)→3T1g(F), and 3A2g(F)→3T1g(P). The 3A2g(F)→3T2g(F) transition was not observed due to the fact that it occurs in the near infrared and is out of the range of the used instrument. The 3A2g(F)→3T1g(F) transition is observed at 734.91 nm. The third band due to 3A2g(F)→3T1g(P) is observed at 369.73 nm, which refers to the charge-transfer transition.
The value of the magnetic moment of Ni(II) complex is 2.52 B.M. The conductance of Ni(II) complex in DMF is 4.20
Zn(II) chelate is diamagnetic and has octahedral geometry, and the electronic spectra show absorption bands at 367.24 nm attributed to charge transfer. The conductance of Zn(II) and complexes in DMF is 6.12
Chemical reaction at the amino group of 1,6-hexanediamine with salicylaldehyde would affect massively the molecular symmetry of 1,6-hexanediamine. The infrared spectrum of 1,6-hexanediamine is therefore basically retained for the reaction product. Some spectral changes are expected to appear as being associated with the formation of new species at the expense of vanished amino group. Confirming this is the disappearance of the vibrational absorptions characteristic of the amino group at 3200 cm−1 and 3120 cm−1 (asymmetric and symmetric of NH2 group, resp.). Consistent with the shift and change of intensity for methylene group at 2930 cm−1 and 2854 cm−1 asymmetric and symmetric of CH2, 1460 cm−1 corresponding
Important IR bands of HBS ligand and its complexes
Ligand/complex |
|
|
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|---|
L (HBS) | 3445 (br) | 3061 (w) | 2931 (m) |
1631 (v.s) | 1162 (w) | — | — | — | — |
1-[Mn2(L)2(H2O)4] | 3399 (br) | 3052 (v.w) | 2927 (m) |
1608 (v.s) | 1145 (m) | 454 (v.w) | 407 (w) | — | — |
2-[Fe2(H2L)(NO3)6(H2O)2] |
3356 (br) | — | 2919 (w) |
1629 (m) | 1047 (w) | 581 (v.w) | 427 (m) | 1382 (s) |
— |
3-[Co2(HL)2(NO3)2(H2O)2] | 3425 (br) | 3056 (v.w) | 2924 (m) |
1614 (v.s) | 1139 (w) | 586 (w) | 463 (v.w) | 1320 m |
— |
4- |
3424 (br) | — | 2925 (m) |
1616 (s) | 1142 (w) | 462 (w) | 395 (w) | 1323 (w) |
— |
5-[Cu2(HL)2(Ac)2(H2O)2] | 3446 (br) | 3020 (v.w) | 2919 (m) |
1624 (v.s) | 1147 (m) | 522 (w) | 470.(w) | — | 1535 (s) |
6-[Zn2(HL)2(Ac)2(H2O)2] | 3418 (br) | 3011 (v.w) | 2922 (m) |
1622 (v.s) | 1188 (m) | 457 (w) | 411 (m) | — | 1535 (s) |
Electronic spectral data of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II)-HBS complexes.
Complex |
|
|
Magnetic moment | Conductance |
---|---|---|---|---|
1-[Mn2(L)2(H2O)4] | 256, 316 | 987.19 | 5.65 | 25.8 |
2-[Fe2(H2L)(NO3)6(H2O)2] |
257, 276, 415 | — | 5.08 | 7.18 |
3-[Co2(HL)2(NO3)2(H2O)2] | 247, 271 | — | 1.87 | 3.22 |
4-[Ni2(L)(NO3)2(H2O)6] | 267, 322, 369 | 656 |
2.52 | 4.20 |
5-[Cu2(HL)2(Ac)2(H2O)2] | 272, 305, 363 | 697 | 2.73 | 4.86 |
6-[Zn2(HL)2(Ac)2(H2O)2] | 298, 367 | — | 0.93 | 6.12 |
Solid State of the Elictrical Conductivity for ligand (HBS) and its metal complexes(1-6)
Compound | Tc (°K) |
|
|
|
|
|
---|---|---|---|---|---|---|
L (HBS) | — | — | 0.0116 |
|
|
339 |
Mn(II) | 378 K | 0.062 | 1.945 |
|
|
404 |
Fe(III) | 369 K | 0.098 | 0.540 |
|
|
530 |
Co(II) | 488 K | 0.0039 | 1.848 |
|
|
504 |
Ni(II) | — | — | 0.0109 |
|
|
475 |
Cu(II) | — | — | 0.0059 |
|
|
478 |
Zn(II) | — | 0.0042 | — |
|
|
472 |
Tc: transition temperature for the ligand and metal complexes;
Infrared spectra of L (HBS), Mn(II), Fe(III), Co(II), and Ni(II)-HBS complexes.
The
On the other hand, acetate anion can, however, coordinate in monodentate, bidentate, or bridging bidentate manner [
The 1H-NMR of L shows four types of signals: methylene protons, aromatic protons, hydroxyl, and azomethine proton at 1.194–3.519 ppm, 6.6–7.4 ppm, 8.3–8.5 ppm, and 13.4–13.6 ppm, respectively. The signals of methylene are not influenced corresponding to chelation, but the multiplet due to the aromatic protons is broader and shifts to lower field, indicating that the chelation perturbs the electron density distribution through the phenyl ring to some extent. The hydroxyl signal at 13.4 ppm disappeared and azomethine signal was shifted, thus indicating that CH=N and OH group are involved in chelation. Figure
1H-NMR spectrum of ligand L (HBS).
The Zn(II) complex is diamagnetic as expected, and its geometry is octahedral. The 1H-NMR spectrum of Zn(II) complex, [Zn2(HL)2(Ac)2(H2O)2] in CF3COOD + DMSO-d6, is shown in Figure
1H-NMR spectrum of [Zn2(HL)2(Ac)2(H2O)2].
It is observed that the signals of methylene are influenced by chelation, but the multiplet due to the aromatic protons is broader and shifts to lower field, indicating that the chelation perturbs the electron density distribution through the phenyl ring to some extent. The hydroxyl signal and the azomethine signal are shifted, thus indicating that CH=N and OH groups are involved in chelation.
The electron impact mass spectrum of the free ligand confirmed the proposed formula of ligand by showing a peak at 324 due to molecular ion (parent peak). The series of peaks, in the ranges of 65, 76, 77, 91, 93, 94, 107, 123, 121, 121, 119, 120, 134, 148, 162, 176, 190, 204, 230, and 231, may be corresponding to various fragments, and their intensity gives an idea of stability fragments (Figure
Mass fragmentation pattern of the Schiff base L (HBS), ligand.
Mass fragmentation pattern of [Co2(HL)2(NO3)2(H2O)2].
Mass spectrum of the Schiff base L (HBS), ligand.
The mass spectrum of Ni(II) complex [Ni2(L)(NO3)2(H2O)6] confirms the proposed formula of the complex by showing a base peak at 380.7
Mass fragmentation pattern of [Ni2(L)(NO3)2(H2O)6].
TGA curve of [Co2(HL)2(NO3)2(H2O)2] shows four stages. The first one from 25 to 252°C corresponds to loss of two coordinated water molecules and N2O4 (Calc./Found %; 13.855/13.734%) from the total weight of the complex. The second stage from 252 to 335°C corresponds to the loss of C7H5NO2 (Calc./Found %; 16.964/16.852%). Third stage from 335 to 359°C corresponds to the loss of C14H18N2O (Calc./Found %; 34.806/33.865%). The last stage from 359 to 800°C corresponds to loss of C5H10 (Calc./Found %; 16.248/16.867%). Figure
TGA curve of [Co2(HL)2(NO3)2(H2O)2].
TGA curve of [Cu2(HL)2(CH3COO)2(H2O)2] complex shows three stages. The first one is from 25 to 258°C with loss of coordinated water molecules (Calc./Found %; 3.88/3.38%) from the total weight of the complex. The second stage from 258 to 296°C corresponds to the loss of two acetate groups and C6H14N2O2 (Calc./Found %; 29.62/29.11%). The third stage is from 296 to 650°C and due to the gradual decomposition of the complex it corresponds to the loss of C8H14N2O2 & C7H7 (Calc./Found %; 41.61/41.63%). Figure
TGA curve of [Cu2(HL)2(Ac)2(H2O)2].
TGA curve of [Zn2(HL)2(CH3COO)2(H2O)2] complex shows four stages. The first one from 25 to 400°C corresponds to the loss of two coordinated water molecules, two acetate groups, and two N=CH (Calc./Found %; 22.346/22.530%) from the total weight of the complex. The second stage from 400 to 500°C corresponds to the loss of C3H6 (Calc./Found %; 5.811/5.344%). The third stage from 500 to 581°C corresponds to the loss of C2H4 (Calc./Found %; 4.112/3.856%). The last stage from 581 to 800°C corresponds to loss of C2H3N (Calc./Found %; 6.280/6.734%). Figure
TGA curve of [Zn2(HL)2(Ac)2(H2O)2].
The values of the electrical conductivity (
Electrical conductivity of [Mn2(L)2(H2O)4].
Electrical conductivity of [Fe2(H2L)(NO3)6(H2O)2]
Electrical conductivity of [Co2(HL)2(NO3)2(H2O)2].
In conclusion, the Schiff bases derived from 1,6-hexanediamine are bonded to the metal ions as tetradentate ligand. The two bonding sites are the oxygen of the deprotonated hydroxyl group of benzene ring and nitrogen of azomethine which lead to stable six-membered chelating ring. The experimental data suggest the structure shown in Figure
Representative structures of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II)-HBS complexes.