COORDINATION COMPOUNDS OF Cu (II) AND Ni (II) WITH SCHIFF BASES DERIVED FROM FORMYLMENTHONE AND AROMATIC AMINES

The Schiff bases obtained from formylmenthone and o-, m-, p-toluidine behave as bidentate ligands with O and N donor atoms in Ni(ll) and Cu(II) complexes by the type NiL2 and CuL2.(H2O)2. The donor atoms and the possible geometry for the complexes were assigned by means of chemical, thermodifferential analyses and electronic, EPR and IR spectra.

The electronic diffuse reflectance spectra within 300-1100 nm range were obtained with VSU-2P Zeiss-Jena Spectrophotometer, using MgO as a standard. EPR spectra were recorded at room temperature on polycrystalline powders, on ART-5-IFA Spectrograph.
The klystron frequency was 9060 MHz and modulation of the magnetic field 100 KHz. The EPR spectral parameters were calculated against a Mn (ll) standard.

General synthesis of ligands
0.01 mol formylmenthone was dissolved in 200 mL ethylic alcohol. A solution of toluidine dissolved in 40 mL ethyl alcohol is added in hot drop in the reaction mixture, after which it is maintained at the room temperature for 50 hours.

General synthesis of the complexes
The complexes were prepared by mixing warm aqueous methanol solution (50%) of metal acetate (1 mmol) and ligands (2 mmols). The resulting precipitates were filtered and washed with aqueous methanol solution (50%) and dried at room temperature. The metal content was obtained gravimetrically. Compound 5a was synthesized according to general procedure of the complexes.
Compound 5b was synthesized according to general procedure of the complexes.

Synthesis
Five new ligands able to generate complexes have been synthesized (Scheme 1). The presence of the >C=O and >C=N -groups respect to each other favours keto-enolic tautomerism (Scheme 2). This tautomerism has been attributed to an intramolecular hydrogen bond and might explain their chelating ability. NMR studies have shown that such Schiff bases with the carbonyl and azomethine groups exist in solution as the enolic tautomer (4a-c) and that the tautomer distribution was solvent dependent (Scheme 2) [8,9].

Elemental Analyses
The elemental analyses are consistent with their formulation as anhydrous, monomeric Schiff bases chelates CuL2 and NiL2) or hydrated, monomeric complexes with water molecules either as coordinated or as crystalline water. All the metal chelates are colored, readily soluble in organic solvents (chloroform, acetone, methanol), but sparingly soluble in water.

Thermodifferential Analysis
The thermodifferential analysis are consistent with their formulation as anhydrous, monomeric Schiff bases chelates. Curves for compounds Cu(para-L)2.(H2O)2 and Ni(para-L)2 arc shown in detail in Figures 1a and l b. For compound Cu(para-L)2.(H2O) (Figure la) the mass loss observed within 60-215°C range in the TG curve corresponds to the loss of two water molecules per molecule of each copper compound. The TG curve shows that the water molecules are liberated in two steps (weight loss at 170°C, found: 2.98%, calcd., for H2O: 2.88%; weight loss at 215°C, found: 7.03%, calcd., for 2H2O: 5.76%). Hence, the two water molecules are present as coordinated water, in Cu(ll) complexes.

Electronic diffuse reflectance
The electronic diffuse reflectance spectra of the complexes are given in Figures 2 and 3.
The spectra of the Ni (ll) complexes (5d and 5e, Figures 2) are like and are consistent with tetrahedral Ni (ll) complexes [10].
3.5. EPR spectra EPR spectra of the three copper complexes recorded at room temperature on polycrystalline samples present a similar intense EPR signal characteristic monomeric species of Cu (ll) ion with a third order anisotropy for the factor g resulting from distortion of octahedral geometry (Figure 4).
This anisotropy is compatible with Cu (ll) ion in a compressed rhombic-octahedral geometry [12,13] with R>1 and supports the electronic spectra. In a three g value spectrum with g1 < g2< g3, the value of R = (g2 -g1)/(g3-g2) may be significant: if R > 1, a predominant dz 2 ground state is present and would be consistent with compressed axial or rhombic symmetry with slight misalignment of the axex. If R < 1, a predominant dx 2 -y 2 state is present [12,13]. The keto-enolic tautomerism is supported by presence of the bands due to νO-H and νC=N. The band due to νC=O (1700 cm-1) occurs as a very weak band or a shoulder. The band due to νO-H occurs as a broad band (3200-3600 cm-1 range) with two unresolved peaks. The band due to νC=N occurs as a broad band (1500-1600 cm-1 range) with three unresolved peaks.
A comparison of the position of the bands in spectra of the complexes with their position in the IR spectra of free ligands shows changes of the bands due to νO-H and νC=N. Upon coordination, the stretching frequencies, νC=N. are shifted to lower values and stretching frequencies νO-H are shifted to higher values. These changes are generally noticed upon coordination of the Schiff bases containing an N and O donor atoms, by the both donor atoms [14]. The new band near 1111 cm-1 occuring in the IR spectra of the three copper complexes only could be assigned to the coordinated water molecules in agreement with Fujita [15] and is be consistent with the results of the thermodifferential analysis.

Results
On the basis of elemental, differential analyses and spectral measurements, we conclude that Cu (ll) ion is hexacoordinated in a compressed rhombic geometry, while Ni (ll) ion is tetracoordinated in a tetrahedral geomety.
The ligands acted bidentately with both O and N donor atoms by deprotonation of the OH group making evident the participation of the ligands in the enolic tautomeric form.
Cu (ll) coordinates by atom donors, N and O in a plane and by shorter bonds to axial water molecules in a compressed rhombic geometry (