EXPERIMENTAL:

Instrumentation:

The carbon, hydrogen and nitrogen contents were determined on Carlo-Erba1108 CHNS elemental analyzer. IR spectra were recorded on Shimadzu FT-IR-8100 spectrometer using KBr and CsI pellets at al-Mustansiriya university. 1H-NMR spectra of ligand were measured in d6-D.M.S.O. solvent using TMS as internal standard on Bruker 300MHz HNMR spectrometer at Al-bait University, Jordan.The electronic spectra of the ligands and its complexes in various solvents (0.001M) were recorded on a Shimadzu Uv-Vis spectrophotometer 1650 having wavelength range 190-1100nm and spectral bandwidth 2nm. Spectra of the complexes were recorded at room temperature in the wavelength range 200-900 nm with a scanning rate 200 nm/minute. The Magnetic susceptibility measurements of the metal chelates were done on a Guoy balance at room temperature usingHg[Co(SCN)4] as a calibration MK-Magnetic balance at al-Nahrain university. Molar conductance of complexes was measured on Philips 180 conductivity meterusing 10^-3 M solution in DMF.The metal contents of the complexes were determined by atomic absorption type Shimadzu (A.A-670) .

Preparation of the compound (A)

The compound (A) was prepared according to method published in literature¹⁰, scheme (1)

Scheme (1) -Synthesis of A compound

Preparation of the ligand (H₂L)

A symmetric tetra dentate ligand was prepared by mixing (1.63 g, 0.01 mol ) of (A) compound in 20 ml absolute ethanol and add (1.22 g, 0.02 mol) from salicylaldehyde in 10 ml of ethanol in the presence of few drops of conc. glacial acetic acid and refluxed the mixture with constant stirring on water bath for 72 hours. The isolated brown precipitate was filtered. It was washed with cold ethanol and di ethyl ether dried under vacuum over anhydrous calcium chloride. Yield (65%), scheme (2),the element analysis data is shown in Table (1).

Scheme (2)- Synthesis of ligand H₂L

Synthesis of metal complexes:

An ethanolic solution (100 ml.) of metal(II) chloride[CoCl2_6H2O (0.237 g, 0.01 M), NiCl2_6H2O (0.237 g,0.01 M), CuCl2_2H2O (0.170 g, 0.01 M) , MnCl2. 4H2O (0.198 g, 0.01 M) and CdCl2(0.227g,o.o1M] was added with stirring to an ethanolic solution of the ligand [H2L (0.267 g, 0.01 M)] and refluxed on water bath temperature for 5-6 hours, then a crude solid complex was separated by filtration under suction, washed several times with hot ethanol to afford colored purified metal complexes, scheme (3).

Scheme (3)-Preparation of metal(II) complexes

RESULTS OF DISCUSSION:

The transition metal complexes prepared in this work were non-hygroscopic (stable at the room temperature) and in the form of amorphous solids. These are soluble easily in DMSO, DMF and sparingly in ethanol and methanol, whereas they are insoluble in chlorinated hydrocarbons. The found/experimental C, H, N values of ligand and its metal complexes are nearly agreed with the calculated values, suggested that the proposed structures of the compounds are acceptable,table(1). The molar conductivity values are compiled in table (2). The, molar ratio method, is especially applicable in determining stochiometry of the prepared metal complexes. The complex was observed to bind in metal-to-ligand ratio equal to 1:1 which was clear from mole ratio plot showing maximum absorbance at 1:1 metal to ligand concentrations¹³,figure (1).

Figure (1)-Stoichiometry of Cu(II) complex with H2L via molar ratio method at λ=380 nm.

Table (1)-Physical properties and analytical data of the prepared compounds

Molecular formula	symbol	Molecular weight	M.p⁰C dec	Calca (Found)%
Molecular formula	symbol	Molecular weight	M.p⁰C dec	C	H	N	M
C₃₇H₃₃N₅O₂	H₂L	579.69	166-162	76.66 (75.66)	5.74 (5.00)	12.08 (11.88)	-
C₃₇H₃₁N₅O₂Mn	MnL	632.6	>260	70.25 (69.77)	4.94 (4.37)	11.07 (12.00)	8.68 (7.66)
C₃₇H₃₁N₅O₂Co	CoL	636.6	>270	69.81 (68.44)	4.91 (4.05)	11.0 (11.09)	9.26 (9.00)
C₃₇H₃₁N₅O₂Ni	NiL	636.3	>260	69.83 (67.99)	4.91 (4.22)	11.01 (12)	9.22 (8.88)
C₃₇H₃₁N₅O₂Cu	CuL	640	>250	69.30 (68.21)	4.87 (4.00)	10..92 (11.99)	9.91 (9.09)
C₃₇H₃₁N₅O₂Cd	CdL	691.0	>290	64.40 (63.99)	4.53 (3.88)	10.15 (11.21)	16.29 (15.98)

UV-Visible spectra:

The electronic spectroscopy is a valuable tool for coordination chemists to obtain important information regarding structure of complexes. Ligands usually being organic compounds show absorption in UV region, which may extend to longer wavelengths in case of extended conjugation. On formation the metal complexes in solution,the electronic properties of ligands change which may give new bands in UV-Vis. spectra due to d-d transitions and MLCT/LMCT transitions and this data can be used to obtain information regarding structure and geometry of complexes^11-12.All the metal complexes solutions in DMF recorded low values of molar conductance falling in the range 22-40 ohm-1.cm2.mol-1,suggesting no chloride ion in the outer sphere of complexes12-13.The UV-Visible spectra of ligand solution in 10^-3 M ethanol exhibits two absorption bands at 332 and 269 nm. which are due to π ®π* and n®π* of C= N and C=C groups in the structures^13-14 . These transitions are also found in the spectra of metal complexes but they shifted towards lower and higher wavelengths, confirming the coordination of C=N to metal ion. All the metal complexes solutions in DMF showed d-d transitions in the visible region that confirm the binding of active sites of ligan like –C=N- to empty orbitals of metal ions,table(2).The copper(II) complex solution exhibits two low energy resolute bands in the regions 570 and 675 nm that may be assigned to A₁g²®B₁g² and A₁g²®B₁g² transitions respectively¹⁴,this supports the z-out elongated octahedral geometry¹⁵.The cobalt(II) complex shows two spin-allowed transitions at 422 and 533 nm which ascribed to T₁g⁴(F)®A₂g⁴(F) and T₁g⁴(F)®T₂g⁴(F) respectively. However, the nickel(II) complex in DMF exhibits weak and sharp bands in the regions 400-480 nm and 366 nm that are attributed to A₂g³®T₂g³(F) and A₂g³®T₁g³ and LMCT respectively^15-16.On the other hand,the cadmium(II) complex showed two high intensity absorptions in the 290-385 nm regions that are assigned to ligand field of ligand and LMCT transitions respectively.

Table(2)-Electronic spectral, magnetic moment and molar conducatance data of the metal(II) complexes

Geometry	Mµ	^mλ	Tentative assignment	λ max (nm)	Compound
_		17	n®π n®π*	269 332	H2L
Octahedral	5.5	26	⁶A₁g(F)®⁴T₁g(F) ⁶A₁g(F)®⁴T₂g(F)	544 422	[MnL]
Octahedral	3.98	18	⁴T₁g®⁴A₂g(F) ⁴T₁g®⁴T₂g(F) LMCT	533 422 390	[CoL]
Octahedral	2.80	22	³A₂g_(F)®³T₂g(F) ³A₂g_(F)®³T₁g(p) LMCT	480 400 366	[NiL]
Distorted octahedral	1.33	19	LMCT ²B₁g®²B₂g ²B₁g®²A₂g	380 675 570	[CuL]
Octahedral	0	43	LMCT n®π*	385 290	[CdL]

C.T=Charge Transfer, m=molar conductivity in DMF solutions(ohm^-1.cm².mol.^-1),and LMCT=ligand to metal charge transfer.

IR Spectra:

The IR spectrum of free ligand show a strong band in the 1614cm-1 region, which may be due to C=N groups formed up on condensation of diacetyl pyridine with 4-methyl-1,2-phenylene diamine¹⁷. There is no -absorption in the 1700-1690 cm^-1 region , indicating the absence of any free carbonyl groups in the ligand on in the formed metal complexes. It is also clear that the six-member rings containing the hydrogen bonding are greatly stabilized by conjugation¹⁷.The other strong absorptions at 1633-1480 cm^-1 in the ligand accompanied by a weaker absorption at 1384-1416 cm^-1, can be assigned to 𝜐(C=C),𝜐(C=N) of pyridine rings. All the complexes displayed downshifts in the 𝜐(C=N) modes in range 1540-1615cm^-1, and exhibited new bands in the far-IR spectrum (420-480 cm^-1) confirming the linkage of C=N to metal ion ^17-18.The value of 𝜐(C=N) is lower than that usually found for imino linkage which may be explained on the basis of drift of lone pair density of -C=N toward metal ion. However, the far-infrared spectra sowed weak to medium bands in the ranges 407-450 and 490-577 cm^-1 that are attributed to M-O and M-N bonds respectively ¹⁸.

Table(3)-IR spectra of the prepared compounds

Compound	C=N,Py^b C=N	υ C-O,C=C-	M-O	M-N	Other bands
H2L	1633,1480	1233,1384-1416	433-410	554-490	3050,2966^a
MnL	1588,1500	1210,1385	418-450	533-501	3100,2890^a
CoL	1615,1499	1198,1422-1378	466	577	3060(w)^a,2988
NiL	1550,1470	1195,1414-1376	407	566	3000(w),2967(m)
CuL	1567,1473^b	1200,1420-1382	429	544	3060^a,2970
CdL	1540,1488^b	1192,1450-1380	455	511	3020(w),2966(m)

A=stretching of –C-H of pyridine and –CH3 moiety and b= vibrational modes of –C=N-of pyridine ring

NMR and Mass spectra:

The ¹H and ¹³C NMR data of the H2L were recorded in DMSO-d6 solution using TMS as internal standard at room temperature. The ligand H2Lshowed the resonance signals at 2.0-2.4 δ (s, 3H,C₆-CH3), 2.40-2.55 δ (s, 3H, N=C-CH3), 5.75 δ (s, 2H, phenolic OH), 5.80 δ (s, 1H, C5-H), 6.5-7.9 δ (m, Ar-H), 8.4 δ (s, 1H, N=C-H) and 2.5 and 3.4 ppm, respectively. The resonance of methyl protons attached to imine moiety (H₃C-C=N) were appeared at 2.07-2.39 ppm in free ligand confirming the condensation of 2,6-diacetyl pyridine with 4-methyl-1,2-phenylenediamine in the first step of formation the Schiff base.As well as,the disappearance of –NH2 resonance of A derivative supports ita condensation with salicyaldehyde¹⁹,figure(2).Furthermore, the figure(3) showed the resonances peaks at 19,45,60,122,128,133-140,150,154,158-160 ppm that assigned to –CH3,-CH=N-,Ar-C,C-N-(Pyridine) and –C-O moiety respectively¹⁹.The communication of carbon atom numbers with resonances of protons assists in the investigation the expected formula of acyclic poly dentate H₂L ligand.However,the figures(4-5) showed the mass spectra of free ligand and MnL complex which revealed the presence of molecular ion peaks that reveals the expected structure and agree well with other data of CHNM elemental analyses and NMR spectra.

Figure (2)-H NMR spectra of free H2L ligand in DMSO-d6 solution

Fgure (3)-¹³C NMR spectra of free H2L ligand in DMSO-d6 solution

Figure(4)-Mass spectra of H2L ligand

Figure(5)-Mass spectrum of MnL complex

INTRODUCTION: