Characteristic Studies of Hexamethylene Diamine Complexes

Preparation and chemical analysis of Mn(II), Fe(III), Co(II), Ni(II), and Zn(II) complexes with Schiff base L [oHOC 6 H 4 CH:N(CH 2 ) 6 N:CHC 6 H 4 OH-o] are the main tasks of this work. The octahedral (M 2 L 2 ⋅nH 2 O⋅X) complexes in 1 : 1 M : L ratio (X = NO3 − or Ac group, L = ligand) were prepared by involving the hydroxylic group in ortho position. All complexes were characterized on the basis of elemental analysis, UV, IR, H NMR, Gc/Ms, thermogravimetric analysis, magnetic measurements, molar conductance, and electrical conductivity. The obtained data indicate that all the investigated compounds behave as semiconductor materials.


Introduction
The chemistry of transition metal complexes of Schiff base compounds hasattracted a lot of interest in the field of bioinorganic and coordination chemistry [1][2][3][4]. The presence of ion pair on the nitrogen atom of imino group enables the coordination of numerous metal cations [5]. Transition metal complexes with oxygen and nitrogen donor Schiff bases are of particular interest because of their ability to possess unusual configuration that is structurally labile and their sensitivity to molecular environments [6,7]. Schiff base can also accommodate different anions of the same center metal involving various coordination modes, thereby allowing successful synthesis of homo-and heterometallic complexes with varied stereochemistry. This feature is employed for modeling active sites in biological system [8][9][10][11]. In regard to importance of these compounds, many literatures have been published in this field. In view of this recently, multicomponent has much attention, and many of them have been reported. The desired Schiff base was obtained when 1,6-hexanediamine was condensed with salicylaldehyde. The structures of Mn(II), Fe(III), Co(II), Ni(II), and Zn(II) complexes were confirmed by elemental analysis, infrared and UV-Visible spectra, thermogravimetric analysis, magnetic measurements, and molar conductance.

Physical Measurements.
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. 1 H-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 eff = 2.84( ) 1/2 B.M., where is molar susceptibility.

Results and Discussion
All  Table 1.

Electronic Spectral and Magnetic Susceptibility
Measurements. The electronic spectrum of Mn(II) complex shows a band at 721 nm. This band is assignable to -transition. The band at 316.52 nm may be attributed to phenolate O(p ) → Mn(d * ) ligand and to metal charge transfer [12]. The band at 256.46 nm is due to - * (azomethine) ligand transitions. The magnetic moment (5.65 B.M.) is additional evidence for octahedral structure. The conductance of Mn(II) complex in DMF is 25.8 S/cm. The low value of conductance indicated that the complex is nonelectrolyte. The electronic spectrum of Fe(III) complex shows a broad band at 415.20 nm. This is mainly due to charge-transfer (CT) band. The absorption bands at 257.7 and 276 nm are attributed to - * (azomethine) ligand and - * transitions [13] (see Table 3).
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 S/cm. The low value of conductance indicated that the complex is nonelectrolyte.
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 3 A 2 g(F)→ 3 T 2 g(F), 3 A 2 g(F)→ 3 T 1 g(F), and 3 A 2 g(F)→ 3 T 1 g(P). The 3 A 2 g(F)→ 3 T 2 g(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 3 A 2 g(F)→ 3 T 1 g(F) transition is observed at 734.91 nm. The third band due to 3 A 2 g(F)→ 3 T 1 g(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 S/cm. The low value of conductance indicated that complex is nonelectrolyte. 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 S/cm. The low value of conductance indicated that complex is nonelectrolyte. Electronic spectral studies, magnetic studies and conductance of the metal complexes of ligand L (HBS) are given in Table 4.

IR Spectra.
Chemical reaction at the amino group of 1,6hexanediamine 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 NH 2 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 CH 2 , 1460 cm −1 corresponding asymmetric CH 2 in plane bending, 1400 cm −1 symmetric CH 2 in plane bending and 881 cm −1 ( CH 2 out of plane deformation). At the expense of vanished amino group species, new spectral absorption 8 International Journal of Inorganic Chemistry   Table 2 in the spectra of all metal complexes, suggesting the coordination of nitrogen of the azomethine group to central metal atom these complexes consistent with this the metal-nitrogen bond are indicated by the absorptions in the region 454-586 cm −1 from IR data [14,15], it can be inferred that the (L) 1,6-hexanediamine function as bidentate at each end of L through their hydroxyl oxygen and azomethine N atom. Also, all the complexes show bands due to the metal-nitrogen and metal-oxygen bonds. The NO 3 − ion is coordinated to the metal ion as unidentate in case of complexes (1), (2), (3), and (4) with C 2 ] symmetry. Each unidentate nitrate group has three nondegenerate modes of vibrations (] s , ] s , and ] as ) which appeared in the ranges (1315-1360), (1040-1028), and (810-830) cm −1 [16].
On the other hand, acetate anion can, however, coordinate in monodentate, bidentate, or bridging bidentate Tc: transition temperature for the ligand and metal complexes; 1 : activation energy in the lower temperature; 2 : activation energy in the higher temperature; 1 : electrical conductivity measured at lower temperature; 2 : electrical conductivity measured at higher temperature.    manner [17]. The monodentate behavior of acetate group in the investigated complex is deduced from the frequency difference (Δ]) between ] asCOO − and ] sCOO − . The value is higher than 185 cm −1 indicating a monodentate behavior.       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 2 depicts 1 H-NMR of ligand L. The Zn(II) complex is diamagnetic as expected, and its geometry is octahedral. The 1 H-NMR spectrum of Zn(II) complex, [Zn 2 (HL) 2 (Ac) 2 (H 2 O) 2 ] in CF 3 COOD + DMSOd 6 , is shown in Figure 3.
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.
TGA curve of [Cu 2 (HL) 2 (CH 3 COO) 2 (H 2 O) 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 C 6 H 14 N 2 O 2 (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 C 8 H 14 N 2 O 2 & C 7 H 7 (Calc./Found %; 41.61/41.63%). Figure 6 shows the TGA curve of [Cu 2 (HL) 2 (CH 3 COO) 2 (H 2 O) 2 ].

The Electrical Conductivity of the Metal Complexes of Ligand L (HBS)
. The values of the electrical conductivity ( ) and activation energies of the metal complexes of ligand L (HBS) with Mn(II), Fe(III), Co(II), and Ni(II) are collected in Table 4. They lie in the range of semiconducting materials. The activation energy of thermal decomposition step is determined from the slope of the straight line of ln and 1/ (K) relationship. Blotting ln against 1/ (K), as shown in Figures 8, 9, and 10, of the investigated complexes yielded two lines over the given temperature ranges and obeyed Arrhenius equation. This may be due to phase transition or packing or change of chemical structure during the increase of temperature.

Conclusion
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 11 for metal chelates under investigation.