Synthesis , Characterization and Thermal Study of New Transition Metall Complexes Derived from 3-Acetylcoumarine

The synthesis, structure, physico-chemical and thermal investigation studies of some transition metal complexes ofCo(II),Ni(II) Cu(II) and Cd(II),withtwo ligands derived from 3-acetyl coumarine. The two ligands ligands(L and L) were synthesizedvianucleophilic substitution of 3-bromoacetylcoumar with potassium thiocyanateandethanolic solution of 1,2-phenlendiaminein respectively. The metal complexes of Co(II), Ni(II) Cu(II) and Cd(II),with Land Lwere prepared and isolated in the solid state then characterized by CHNM elemental spectral FT-IR, H, C NMR , Mass spectra,UV-Visible spectra. The thermal study (TG-DSC) of some complexes was carried out in nitrogen gas which assisted in determination the proper structure and formula of such complexes. The ligand acts as bidentate, through OO or NO, neutral in coordinating the metal ions under study. The results obtained from elemental analyses,magnetic susceptibility and electronic spectra suggested that all metal complexes were formed in 2:1 molar ratio of ligand to metal with octahedral structures. The complexes are found to be soluble in DMF and DMSO. The TG-DSC study revealed that the metal complexes were thermally stable with point decomposition over 350 C as well as the percent in loss of weight up on decomposition at inert conditions of nitrogen atmosphere has reported the proposed formula.


Introduction
Transition metal complexes of cumarineligandshave been studied and attract attention against the antitumor activity [1][2][3].In particular metal chelates of cumarine have been known for some time to be antitumor agents [4,5].Because of their biological activity and analytical application,thiosemicarbazidesandthiosemicarbazones, as well as theirmetal complexes have been the subject of many studies [6,7].The Schiff bases of coumarins comprise a very large class of Lewis bases that have interested in the field of coordination chemistry [8].The antimicrobial activity of coumarin nucleus and related derivatives [9] has a great important effects like antibacterial, antithromboticandvasodilators [10].As it hasinvestigated in the literature the biological activity of some coumarinderivatives significantly enhances by binding to metal ions [11,12].In continuation with this interest of cumarine chelates, we report the synthesis, characterization and thermal study of some first row transition metal complexes with two ligands derived from 3-bromoacetyl-cumarine-2-one.

Experimental
All chemicals were of reagent grade, and solvents were dried and distilled before useaccording to the standard procedures.3-Acetylcoumar-2one in was purchased from Sigma-Aldrich company and other starting materials like potassium thiocyanate and 1,2-phenylenediamine were supported from laboratories of chemistry department,college of science-Al-Mustansiriyauniversity.The hydrated chloridesCoCl 2 .6H 2 O,NiCl 2 .6H 2 O,CuCl 2 .2H 2 O,CdCl 2 .2H 2 O and Cd(CH 3 COO) 2 were purchased from Alfa company, and were used without further purification as received .The measurements of molar conductivity were made on an Hanna conductivity bridge with cell constant 1.0 cm -1 .The magnetic susceptibilitymeasurements were made on a Gouy balance at room temperature using Hg[Co(SCN)4]as calibrant on Sherewood magnetic balance.The vibration spectra were recorded in a KBr and CsI matrix using a Shimadzu FTIR spectrometer model 983 .The electronic spectra in the range (200-1000 nm) were done for all complexes and the free ligands complexes in DMF and ethanol solutions were scanned on aCarry 2390 instrument.1H and 13C-NMR spectra were determined on Burker DMX-500 NMRSpectrophotometer on a 300 MHz, with TMS as standard and DMSO as solvent (Alalbayt University-Jordan).TG and DSC( Differential Scanning Colurimetry) thermo grams in different ranges were carried out at (R.T) heating rate = 10C 0 / min (Linseis STA PT-1000) were run in Baghdad university Abinhitham collage.The metal contents of the complexes were determined by Atomic Absorption measurements were performed by using the instrument Analytic Jena / A Spect LS /FL 1.3.0.0,Ibn-CinaCenter, Ministry of Industry.Magnetic moment for prepared complexes in the solid state at room temperature were measured according to Faraday's method using: Auto Magnetic susceptibility Balance Sherwood Scientific.AL-Mustansiriyah University.The chloride content for complexes were determined by Mohr's method.Mass spectra were performed using the instrument: GC MS -QP 2010 VLTRA, AL-Mustansiriyah University.

Analyses and physical measurements
All the complexes are sparingly soluble in common organic solvents but highly soluble in DMF and DMSO.The analytical data (Table 1) indicate that the complexes are mononuclear with 2:1 molar ratio of ligand to metal ion.The molar conductance in DMF fall in the expected range for their non-electrolytic behaviour, indicating that the chloride ions are inside the coordination while the Cd(II) complexfall in the expected range for their electrolytic behaviour, indicating that the chloride ions are outside the coordination sphere and

Infrared spectra
The bromination of 3-acetylcumarine have proved by the medium bands at 780 and 870 cm -1 that are attributed to H 2 C-Br moiety [12].The distinct bands at 2962, 1710, and 1630 cm 1-in the IR spectra of L2 may be assigned to aliphatic -CH 2 -,carbonyl of chromone and -C=C-moiety respectively [12].As well as the spectra of ligand L 1 formed from cyclo addition of A with 1,2-phenylenediamine was approved from appearance singlet absorption at 3370 cm-1 and strong absorptions at 1712 and 1630 cm-1 which are assigned to -C=O and -C=N-of quinoxaline moiety [13].Main characteristic infrared absorption bands of the 3-acetylcumarine A and their derived ligands L1 and L2 with their Ni(II), Co(II), Cu(II) and Cd(II) complexes, along with their assignments, are presented in Table 2.
The free 3-acetylcoumarin) shows band at 1730cm-1 is attributed to (C=O) of the lactone ring [13].The stretching vibration is observed at 2130 cm-1 with a shoulder on lower wave number side may be assigned to -S-CN moiety.The observed medium intensity band at 912 cm−1 in the free L 2 ligand, which is ascribed to δ(CSC) of -SCN-moiety vibration [15], did not subject to remarkable changes in the spectra of solid complexes suggesting no involvement of the sulfur atom in the bonding with the metal's ions [15].The medium intensity band observed at 1570 cm-1 is assigned to (C=C) of the chromoneringThe comparison of the positions of these bands with those observed in the infrared spectra of its Ni(II), Co(II), Cu(II) and Cd(II) complexes indicated that the band at 1670-1705 cm−1 showed   [5] a marked shift, this discussed that carbonyl group shared in the complexation toward Ni(II), Co(II), Cu(II) and Cd(II) ions, while that bands at 3328 and 3306 cm−1 which assigned to stretching vibration motions -O-H moiety is good proof for presence of coordinated water molecules [14].This fact suggests the coordination of L2 through the nitrogen -S-CN and oxygen of lactone -C=O together and tending to form stable complexes.The observed medium intensity band at 912 cm−1 in the free HL ligand, which is ascribed to δ(CSC) of thiocyanato group attached directly to -CH2-moiety [15], shifted to lower values for the five HL complexes, suggesting the involvement of the sulfur atom in the bonding with the metal's ions.The band assigned to the stretching of ν(C−S) is similarly shi ed to lower frequencies.This also confirms that the sulfur atom is taking part in the complex formation [16].On the other hand, the weak to medium intensity absorptions in the regions 400-470 and 490-544 cm1-are ascribed to M-O and M-N bonds [17].

Magnetic measurements
The magnetic susceptibilities of the complexes, recorded at room temperature (Table-3) show low magnetic moments indicating the presence of a spin exchange interactions between the metal ions.The values obtained of copper(II) complexes lie in the 1.73-1.85BM range and corresponds to one unpaired electron.As well as the orbital contributions of cobalt (II) and nickel(II) complexes in the ranges 4.2-4.6 and 3.50-3.22BM respectively indicated the high spin octahedral structures around Co(II) and Ni(II) ions [18,19].

Electronic spectral studies
Electronic spectral data of the complexes in DMSO solution are listed in Table (3).The ligands L 1 and L 2 exhibited similar spectral features in the UV-Vis region with bands around 255, 310 and 440 nmrespectively.The first band below 310 nm is assigned to a ligand transition (n-π*) and(π-π*) [10,14] .The other two bands, 370 and 440 nm are attributed to charge transfer processes.The visible spectra of all the complexes are similar and show an intense absorption band near ~360 nm and moderately intense shoulder band near 395-415 nm and distinct band at ~656 nm.The separated weak energy bands of copper (II) complex in the range 550-871 nm could be attributed to 2 B 1 g→ 2 B 2 g and 2 B 1 g→ 2 Eg transitions respectively and support the formation of distorted octahedral around Cu(II) ion [17].The weak absorptions at 810,650 and 440 nm of cobalt(II) complex formed with L 1 ligand may be assigned to 4 T 1 g→ 4 T 2 g , 1 T 1 g → 4 A 2 g and 4 T 1 g→ 4 T 1 g(P) respectively [18].The spectrum of the green complex of Co(II) formed with L2 ligand exhibited the following absorptions at 860 nm ,690 nm and 567 nm these peaks are characteristic of octahedral cobalt (II) complex respectively [12,17].By the same way, the nickel(II) complex formed with L1 and L2 ligands showed two spin-allowed transitions at 410 , 395 nm and 840and550 nm that are remarkably belonged to 3 A 2 g→ 3 T 2 g and 3 A 2 g→ 3 T 1 g suggesting the octahedral geometry around Ni(II) ion respectively [18].However, the cadmium(II) complexes formed with L1 showed only absorptions in the 393,361nm and 401,365 nm indicating the charge transfer and the benzenoid bands of coumarine ring [10,11].The absorptions in the regions 378,340 and 393,363nm attributed to the cadmium chloride and cadmium acetate(II) complexes formed with L2

NMR Spectra
The 1 H-NMR spectra of the L1 ligand in d6-DMSO solventTable.3shows multiple signals at 6.5-7.90 ppm, corresponding to the eight protons aromatic ring protons of the phenyl and pyrazine moieties [15].The singlet at 4.60 ppm was attributed to the two protons of the -CH2-Br group [10].The signal of the -NH proton in the quinoxaline moiety was observed at 9.55 ppm, and the singlet peak at 8.77 ppm is attrinuted to H-C=C-in position 4 of coumarinering,figure (4).As well as the figure (5) shows the C 13 NMR of L1 in d6-DMSO which displays resonance peaks related to aromatic -C=C-in the regions 113-125 ppm and 127-131 ppm are assigned to -C=O, -C=N-and -C-N moieties respectively.The figures (5,6) show the 1 H and 13 C nmr spectra of L2 in d6-DMSO where the absorptions in the region 6.2-7.80 ppm are ascribed to Ar-H protons and the chemical shift at 8.04-8.70ppm is assigned to protons of annulated coumarine ring [12,13].The singlet peak at 11.40-11.50ppm may be attributed to H-C=C of coumarine ring in C4 position.However, the weak peak at 4.10 ppm could be assigned to CH2-Br due to effect of electron withdrawing effect of bromine and thiocyanato groups on the deshielding of aliphatic protons toward the weak magnetic field [20].[7]  [8]

Thermal analysis
The thermal degradation of Co(II), Cu(II) and Cd(II)fig.9,10complexes was studied using thermo gravimetric techniques and a temperature range of 25-360 °C.The thermal stability data are listed in Table 6.The data from the thermo gravimetric analysis clearly indicated that the decomposition of the complexes proceeds in three or four steps.Ethanol molecules were lost between 50-63.[9]  [10]

Conclusions
According to the results obtained from elemental analyses, spectral, magnetic susceptibility measurements and the TG-DSC analyses, the octahedral geometry around cobalt, nickel,copper and cadmium (II) ions were suggested and the IR dataadopted the chelation of the two ligands of coumarine derivative via nitrogen of quinoxalinemoiet and carbonyl of chromone ring, Scheme 7.
[14] 1/2C 2 H 5 OH.The thermal analyses of complexes shows significant weight losses corresponding to the elimination of ethanol and water molecules per mononuclear unit in the 650C and 100-120 0 C ranges respectively.Therefore, onewater molecule are outside coordination sphere, whereas the Cd(II) are outside the coordination sphere for both it's chloride and acetate complexes.
figure(1) clearly exhibits the molecular ion peak m/e=188 which agree well with the formula C 11 H 8 O 3 [13].As well as the bromination of 3-acetyl cumarine (A) by Br 2 in chloroform solution leads to A2 derivative which it's mass spectra in figure(2) displays base peak at 267 that is consistent with C 10 H 7 O 3 Br.However the other peaks at 186 and 88 are extremely attributed M-Br+ ion.The ring closure of 1,2-phenylenediamine with A2derivative,scheme(3) results in ligand L1 which shows molecular ion m/e=274 at relative intensity 100% then supports the proposed structure of L 1 ligand.On the other hand the figure(3) represents the mass spectra of L2 ligand which shows absorptions at245, 244,192,160,128 and 81 that are assigned to C 12 H 7 NSO 3 and fragments of M-SCN,M-CH 2 SCN and base peak of C 5 H 5 O+ respectively[14,15],figure(3).

Figure 11 .
Figure 11.DSC analysis of Cu(II) complex with L 1 ligand.

Table 1 .
The physical properties and elemental analysis of the prepared metal complexes.Decomposed,calc :Calculated, b Content of metal was done by flame atomic absorption spectroscopy.
a Dec:

Table 2 .
FT-IR absorptions of the ligands L 1 and L 2 and theirmetal complexes in cm -1 .

Table 3 .
The electronic spectra and molar conductance of the prepared complexes.

Table ( 4
) .Decomposition steps with the temperature range and weight loss for some complexesof L 1 .