الفهرس 
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Abstract
The objective of the present study is to investigate the reactions of two Schiff base ligands (L1 and HL2) with the metal hexacarbonyls M(CO)6 (M= Cr, Mo or W) and with some transition metal ions (Cu(II), Ni(II), Co(II), La(III) and Sm(III)). The two ligands (L1 and HL2) have been prepared by the reaction of pyridine-2-carboxaldehyde with an amine compound (2,6-diaminopyridine or 2-aminophenol) in 1:1 molar ratio.
The ligands and metal complexes are characterised by elemental analysis, spectroscopic studies such as IR, UV–Vis, 1H NMR, fluorescence, mass, molar conductance and magnetic susceptibility measurements.
Three complexes with molecular formulas [Cr(L1)3], 1, [MoO2(L1)2], 2 and [WO2(L1)2], 3 are isolated from the reaction of the metal hexacarbonyls with L1. These complexes give no 1H NMR signals indicating paramagnetic characterist- ics. The infrared spectrum of chromium complex, displays the characteristic bands of L1 with appropriate shifts due to complex formation. The effective magnetic moment of chromium complex, 1, is indicated to the spin-only moment of spectroscopic data, it can be concluded that the chromium
complex has the tris configuration. This structural arrangement
would give a chromium species with zero (d6) oxidation state.
The infrared spectra of complexes 2 and 3 display two
symmetric stretching bands at 974 and 938 cm-1 as well as two
asymmetric stretching bands at 897 and 935cm-1
corresponding to the presence of two terminal cis M=O
(M=Mo or W) bonds, respectively. The infrared spectra of the
two complexes also displayed non-ligand bands due to M-N
bonds confirming the coordination of the metal to L1 via
azomethine and pyridyl nitrogen atoms. So, it is expected that
the metal atom may exist in +4 formal oxidation state.
Magnetic measurements of 2 and 3 indicate the presence of
two unpaired electrons in the valence shell of the metals.
The corresponding reactions with HL2 produced the
complexes [Cr(HL2)2], 4, [Mo2(CO)4O2(HL2)2], 5 and
[W(CO)4(HL2)], 6. The infrared spectrum of the chromium
complex, 4, exhibits vibrational bands due to ν(OH), ν(C-O)
and υ(C=N) bonds with proper shifts with respect to that of the
free ligand. The 1H NMR spectrum of 4 displays a lower shift
signal at 9.96 ppm indicating the coordination of the ligand
HL2 to chromium atom through the oxygen of OH group
without oxidation. Therefore, it can be concluded that phenolic oxygen, pyridyl nitrogen and azomethine nitrogen
acting as a tridentate ligand.
The IR spectrum of the complex 5 displays non-ligand
two stretching bands corresponding to the presence of two
terminal CO groups bonded to molybdenum in trans positions
and also displays asymmetric and symmetric characteristic
stretching bands due to the presence of two bridged CO
groups. The two strong stretching bands at 925 and 903 cm-1
refer to the presence of two terminal Mo=O bonds in trans
positions. Therefore, complex 5 could be considered as
dinuclear with the two molybdenum atoms in distorted
octahedral environment. Each molybdenum atom has +2
formal oxidation state with a low-spin d4 electronic
configuration due to further splitting of the t2g orbitals in the
low-symmetry complex.
The IR spectrum of complex 6 shows a vibrational band
due to ν(OH) frequency with the proper shift with respect to
the HL2 ligand . The 1H NMR spectra of complex 6 confirm
the presence of shifted OH group. These shifts proposed the
coordination of tungsten to HL2 ligand through the oxygen of
the hydroxyl group without oxidation. The IR spectrum of
complex, 6, displays a pattern of four CO bands in the terminal metal carbonyl region. Therefore, it could be concluded that
the complex is mono nuclear complex with the tungsten atom
existing in a distorted octahedral environment. This structural
arrangement would give a tungsten species with zero (d6)
oxidation state.
The solid complexes of the Schiff base ligand L1 are also
prepared by the reaction with Cu2+, Ni2+, Co2+, La3+ and
Sm3+forming the complexes [M(L1)Cl2(H2O)2] where M=
Cu2+, Ni2+, Co2+, and the two complexes
[La(L1)3](NO3)3.3H2O and [Sm(L1)(ClO4)3].3H2O. The
ligand L1 acts here as a bidentate ligand where it is coordinated
to the metal through its nitrogen atoms of the pyridine and
azomethine group. The molar conductivity data for complexes
indicate that the complexes have non electrolytic nature except
La(III) complex.
The IR spectra of these complexes show bands due to
ν(-C=N) and δ(Py). Also, the IR spectrum of Sm(III) complex
show that perchlorate groups are coordinated to the metal in a
bidentate manner. The band at 1383 cm-1 in the spectrum of
the La(III) complex indicats the existence of ionic nitrate
group in the complex. The measured values of the magnetic
moment of Cu(II), Ni(II) and Co(III) complexes have been
found to be 1.98, 3.81 and 4.42 B.M., respectively, which are in the normal range observed for octahedral complexes. The diffused reflectance spectra of the Ni(II) and Co(II) complexes show three bands, while Cu(II) complex show one band due to d-d transitions.
The mixed ligands complexes are prepared from the reactions of the metal ions Cu2+, Ni2+, Co2+or La3+ with the Schiff base HL2 in the presence of 2-aminopyridine (2-AP) to give the complexes: [M(HL2)(2-AP)Cl2].H2O where M= Cu2+, Ni2+, Co2+ ions in addition to the complex [La(HL2)(2-AP)(NO3)2].NO3. The molar conductivity data for 1mM solutions of all complexes suggest that they have non electrolytic nature except La(III) complex. The IR spectra of the complexes show characteristic bands due to OH, C–O, and C=N functional groups indicating the coordination of HL2 to the metal ions in a tridentate manner with NNO donor sites of the pyridine-N, nitrogen atom of the azomethine group and the oxygen atom of hydroxyl group. Magnetic moment and diffused reflectance spectra of Cu(II), Ni(II) and Co(II) complexes suggest an octahedral structure around metal ions.
The fluorescence spectral results reveal that the fluorescence emission intensity of Schiff bases increases dramatically on complexation. Therefore, all synthesized compounds can potentially serve as photoactive materials as indicated from their characteristic fluorescence properties.
Thermal studies indicate high thermal stability of the complexes. The activation thermodynamic parameters, such as activation energy, enthalpy, entropy and Gibbs free energy change of decomposition are calculated and discussed.
The catalytic activities of the complexes towards hydrogen peroxide decomposition reaction are investigated.
The ligands and their metal chelates have been screened for their antibacterial activities and the findings have been reported, explained and compared with some known antibiotics.