Synthesis and Characterization of the Ligand
2-[(6-Nitro-2-benzothiazolyl )azo]-4,6-dimethylphenol (6-NBTADMP) and It's Complexes with Fe(II), Co(III), Ni(II), Cu(II), Zn(II), Cd(II), Pd(II) and Ag(I) Ions

Abid Allah. M. Ali
College of Education for Women, University of Kufa
(NJC)

(Receivedon 10/6/2007)                  (Accepted for publication on  6/11/2007)

Abstract 
        A new ligand 2-[(6-Nitro-2-benzothiazolyl)azo]-4,6-dimethylphenol (6-NBTADMP = HL) has been synthesized by coupling diazotized 2-amino-6-nitrobenzothiazole  with 2,4-dimethylphenol in alkaline  alcoholic solution.  Metal complexes  have  the general  formula  [FeL2],  [CoL2]Cl . H2O, [NiL2],  [CuL H2O]Cl,  [ZnL2],  [CdL2]. H2O,  [PdLCl],  and  [AgL H2O] . H2O,  were  synthesized from  thiazolylazo  ligand  and metal chloride ( sulfate for Fe(II) and nitrate for Ag(I) ) in 1:1 molar  ratio (metal:ligand) for Cu(II) , Pd(II) and Ag(I) and 1:2 for the  rest metal ions. Based on elemental analysis, molar  conductivity,  magnetic susceptibility  data, IR and UV-Vis  spectra. The data show  that  the ligand  coordinates to the metal ion νia  phenolate O, azo N and with  thiazole N atoms. All complexes are insoluble in water but these are soluble in common organic solvents such as acetone, DMF  and  DMSO.  According  to results obtained  the geometry  for the complexes was suggested.        
  Key words: Synthesis, Thiazolylazo, Ligand, Metal Complexes, Characterization.
الخلاصة                                                                                                                                                        تضمن البحث تحضير الليكاند 2-[(6-نيترو-2-بنزوثيازوليل )آزو]-6,4-ثنائي مثيل فينول (6-NBTADMP=HL) وذلك من  ازواج ناتج أزوتة المركب 2-امينو-6-نيترو بنزو ثيازول مع محلول 4,2- ثنائي مثيل  فينول في محلول قاعـدي كحولي . كما تم تحضير  المعقدات الفلزية ذات الصيغ العامة  [FeL2]  ، [CoL2]Cl. H2O ،[NiL2]  ،  [CuL H2O] Cl ،[ZnL2] ،[CdL2]. H2O ،[PdLCl]  و[AgL H2O] H2O . وذلك من تفاعل ليكاند الثيازوليل آزو مع كلوريدات الأيونات الفلزية )والكبـريتات للـحديد(II)  والنـترات للفضة( (I) ، وقد بلـغت النسـبة الموليـة ) فـلـز: ليكانـد ( 1:1 لأيونات النحاس (II)والبلاديوم(II) والفضـة(I) فيمـا بلغت النسـبة 1:2 لبقـية الأيونات الفلزية.  وا سـتنادا الى معطيات نتـائـج الـتحليل الدقـيق للعـناصـر والـتوصـيل الكـهربـائـي المـولاري والحـساسـية المـغناطيسـية وأطـياف الأشـعة تحـت الحمراء والفوق الـبنفسجية- المرئية فـقـد تبيـن أن الليكـاند ترتبـط مـن خلال مـواقـع الـتناسـق الـمتاحة وهي ذرة الأوكسجين الـفينولية واحدى ذرتي نيتروجين مجموعة الآزو وذرة الـنيتروجين لحلقة الـثيـازول. كـمـا تبـين أن جمـيع الـمـعـقدات المـحضـرة لاتـذوب في الـماء ولكـنها جيـدة الـذوبان فـي أغـلب المـذيبات العـضويـة مـثل الاسـيتـون والـ  DMF والـ DMSO . كـذاك تـم اقـتراح الأشـكال الـفراغـية للـمعـقدات المـحـضرة.             

Introduction 
        The thiazole and its derivatives are of biological important and they are used in the synthesis of drugs(1-3). Heterocyclic amines have been used extensively in the preparation of azo dyes(4-6). Dyes from 2-amino-5-nitrothiazole have been reported to have high extinction coefficient, and they are reddishblue depending upon the substitution pattern in the coupler(7,8). Thiazolylazophenols have attracted much attention as analytical reagent owing to the high sensitivity(9-11). This class of organic ligands that contain two nitrogen atoms coupled in conjugated system of π-bonds, and usually react with metal ions as tridentate ligands(12-15).   
       This paper describe the synthesis of new thiazolylazo ligand and some of it's metal complexes     
Experimental             
Material and Measurements  
        All reagents  used are chemically pure  or  analytical grads,  except  of  2-amino-6-nitrobenzo-thiazole was prepared and purified according to the literature(16). Melting points were taken in open capillaries   on  a Stuart  melting  point  apparatus  and  are uncorrected.  C,H,N  analysis data were obtained at Al-Albayt University, on a Perkin-Elmer 240 elemental  analyzer.  The metal  contents were determined by using a Shimadzu-AA-160,  Atomic absorption spectrophotometer.  All condu- ctivity measurements  were  performed  in  DMSO using  conductivity  Bridge  31A  at 25 °C,  the concentration of the solution  was 10-3 mol L-1. pH  measurements  were carried out using HANNA  pH meter model HI  9321. Magnetic susceptibility measurement  were made by faraday method at room temperature  using Balance Magnetic MSB-MK apparatus, and diamagnetic corrections for  the ligand were calculated using Pascal's constants(17).  IR spectra were recorded on a Pye-Unicom SP3 - 300, spectrophotometer, in the  4000-200 cm-1 using  CsI disc. Electronic spectra from 200-1000 nm were determined in ethanol on a Shimadzu UV-Vis 1700 spectrophotometer
.      
Synthesis of Azo ligand (6-NBTADMP)

    The  azo ligand  (6-NBTADMP) Fig.1,  was  synthesized  as in  the  procedure  described  for thiazolylazo  dyes(18).  The  details are given  as follows; sulfuric acid  96% 10ml  was  cooled  and stirred,  and  sodium nitrite ( 0.84g, 12mmol ) was  added  in  small  portions  at  in  such  rate as to  avoid  the evolution of  nitrous gases.  The solution  was stirred  and  slowly heated  to 50°C  until  the salts were completely dissolved. The solution of nitrosyl sulfuric acid obtained was stirred and cooled to 5-10°C, then (1.95g, 10mmol) of 2-amino-6-nitrobenzothiazole was added, the reaction mixture was then stirred at 0-5°C  for 1hr. The resulting diazonium sulfate solution was added drop-wise with  continuous  stirring to  a solution of  2,4-dimethylphenol  (1.22g ,10m mol)  in  alkaline ethanol 150ml. The reaction mixture was stirred for 3hrs at  0-5°C, and left in the refrigerator over night.  The mixture  was acidified  with  dilute sulfuric acid until (pH=6).  The soiled  product was filtered off, washed with 500ml cold water, air dried and recrystellized twice from hot ethanol then dried in the oven at 70°C for several hrs.    

  

Fig.1: Structure of the ligand (6-NBTADMP) 

Synthesis of Metal Complexes
        The metal complexes were prepared by dissolving (0.328g, 1mmol) from ligand in hot ethanol 50ml and added drop-wise with stirring to a stoiciometric amounts of  1 : 1 (metal : ligand) molar ratio of Cu(II) and Pd(II) chloride and Ag(I) nitrate  or 1 : 2 ratio of Fe(II) ammonium sulfate and Co(II), Ni(II), Zn(II) and Cd(II) chloride salts, dissolving in 10ml hot distilled water. The resulting mixture solution was stirred under reflux for 1h. The solid product thus formed was filtered off from the ice-cooled reaction mixture, washed with 5ml hot ethanol and dried at 80°C over night. 
Results and Discussion    
       The reaction of  azoligand (6-NBTADMP) with the metal ions mentioned above different color crystals, depending on the nature of metal ion. The complexes are  air-stable, insoluble in water, but soluble in common organic solvents. Decomposition accurse with conc.nitric acid, and the resultant solution was used after suitable dilution for metal analysis. The elemental analysis data of the ligand and it's complexes are given in Table (1), they are consistent with the calculated results from the empirical formula of each compound.

Table.1: Analytical and physical data of the ligand and its complexes

No.	Compound	Color	M.p °C	Yield%	Formula	Found (Caled) %	
						C	H	N	M	
1	HL	Reddish-brown	143	62	C15H12N4O3S	54.56   (54.78)	3.52
(3.65)
	16.83
(17.07)	------	
2	[FeL2]         
	Brown	171	67	C30H22N8O6S2Fe	50.51
(50.70)	2.97
(3.09)	15.48
(15.77)	7.64
(7.88)	
3	[CoL2]Cl. H2O 	Dark green 	189	70	C30H24N8O7S2ClCo 	46.82
(46.96)	3.04
(3.13)	14.37
(14.61)	7.41
(7.69)	
4	[NiL2] 	Green	212	63	C30H22N8O6S2Ni 	50.26
(50.49)	3.01
(3.08)	15.39
(15.70)	7.89
(8.27)	
5	[CuL( H2O)]Cl 	Brown	166	62	C15H13N4O4SClCu 	40.32
(40.54)	2.80
(2.92)	12.43
(12.61)	14.06
(14.30)	
6	[PdLCl] 	Brown	223d	63	C15H11N4O3SClPd	38.14
(38.37)	2.23
(2.34)	11.76
(11.94)	------	
7	[ZnL2] 	Red	159 	59	C30H22N8O6S2Zn 	49.78
(50.04)	2.92
(3.05)	15.32
(15.56)	8.72
(9.09)	
8	 [CdL2]. H2O 	Red	198	61	C30H24N8O7S2Cd	45.71
(45.89)	2.89
(3.05)	14.08
(14.27)	------	
9	[AgL(H2O)].H2O	Red	201	64	C15H15N4O5SAg	38.02
(38.21	3.09
(3.18)	11.67
(11.88)	------	
HL=(6-NBTADMP),   d = decompose

Effect of pH and Time  
         The effect on the absorbance of the complex solutions of varying various pH was observed. The absorption of  M+n – (6-NBTADMP) solution of all complexes approach maximum at pH 5.5-7.0. This result agree with the fact of the lower basicity of the thiazole nucleus, will lead to shift of reaction conditions for the formation of complexes towards the more acidic region(19). Also the reaction are complete in 5min at room temperature. This shows that (6-NBTADMP) demonstrates strong coordination with all metal ions.     
Metal : Ligand Ratio   
        The metal : ligand ratio of the complexes were determined by the method of molar ratio at fixed pH, and maximum absorption wavelengths. The results are summarized in Table (2). The ligand was found to form 1:2 chelates with Fe(II), Co(III), Ni(II), Zn(II) and Cd(II),  metal ions and 1:1 chelates with Cu(II), Pd(II) and Ag(I), metal ions. The results are in agreement with the values reported for some thiazolylazo phenol complexes(20,21). 

Table.2: Metal: Ligand ratios and Stability constant values
    
ligand	Metal ion	pH	λmax nm	Metal : Ligand	β	Log β	
 HL	Fe(II)	5.5	622	1 : 2	3.217×105	5.507	
	Co(III)	7.0	628	1 : 2	2.512×107	7.400	
	Ni(II)	6.0	614	1 : 2	2.016×106	6.304	
	Cu(II)	5.5	540	1 : 1	6.332×105	5.801	
	Pd(II)	6.5	423	1 : 1	3.424×106	6.534	
	Zn(II)	6.5	472	1 : 2	1.219 ×104	4.086	
	Cd(II)	6.0	481	1 : 2	2.731×104	4.436	
	Ag(I)	6.0	487	1 : 1	4.526×103	3.655	

Determination of the Metal Complexes Stability Constant 
        Stability constants are obtained spectrophotometrically by measuring the absorbance of solutions of ligand and metal mixture at fixed wavelengths λmax and pH values. The degree of formation of the complexes are obtained from the relationship(22), β = (1 – α)/(α2c) for 1:1 metal chelates and β = (1 – α)/(4α3c2) for 1:2 metal complexes and α = Am – As / Am. Where Am and As are the absorbance's of the fully and partially formed complex respectively at optimum concentration.  The calculated (log β) values of these complexes are given in Table2. 
Infrared Spectroscopic Study        
         The active site of the ligand and their bonding to the metal ions was characterized by careful comparison of the main infrared absorption bands of the free ligand and it's complexes Table3. IR spectra of all metal complexes show that (6-NBTADMP) behaves as monobasic tridentate ligand, coordinating νia (C═N), (N═N) and the phenolic (O─H) groups with  displacement of hydrogen atom from the latter. The absences of a broad band at 3360-3180 cm-1 indicate the deprotonation of the phenolic oxygen and cleavage of the  hydrogen bond with the involvement of the oxygen atom in bonding(23). In the ν(O─H) water region, the spectrum of the Cu(II) complex show strong sharp band at 3455 cm-1 attributed to the coordination of water(24). In the spectra of the Co(III) and Cd(II) complexes show a strong and broad absorption at 3450-3160 cm-1 which may indicates the lattice water(25). The spectrum of Ag(I) complex exhibit, in addition to the band of coordinated water, a broad continuous absorption peak at 3370-3110 cm-1, this is apparently due to both coordinated and crystal water(26). No such band are observed in the spectra of Fe(II), Ni(II), Zn(II) and Pd(II) complexes, this may indicates the absence of coordinated and / or lattice water. The appearance of strong band at 1620 cm-1 in the ligand spectrum assigned to ν(C═N) of thiazole ring(27). It is observed with a little change in shape and shift to lower frequencies 

1600-1590 cm-1 in prepared complexes spectra. These differences indicating coordination of thiazole-N atom(28). The IR spectra of chelat complexes showed considerable reduction in the ν (N═N) stretching frequency, absorption frequencies at 1540-1530 cm-1 as compared to that of the parent free ligand 1560 cm-1. This shift could be attributed to the metal-azo back bonding(29). Another band appeared at 1270 cm-1 in the ligand spectrum, this band is due to ν(C─S) of the thiazole ring(30). The 

existence of this band in all metal complexes means that the sulpher atom of the heterocyclic ring does not participate in coordination(28). Some other new bands appeared in the region of 270-490 cm-1 in the complexes spectra, which are not present in the spectrum of the ligand may be attributed to the ν(M─O), ν(M─N), and ν(M─Cl) bands(31). 
Thus the above IR spectra data lead to suggest that the ligand behaves as a tridentate chelating ligand coordinating through the positions of phenolic oxygen, nitrogen of azo group and thiazole ring nitrogen.
 
Table.3: Characteristic IR absorption bands of the ligand and its complexes in cm-1 units
Compound	ν(O─H)	ν(C═N)	ν(N═N)	ν(C─S)	ν(M─O)	ν(M─N)	ν(M─Cl)	
HL	3360-3180 br	1620 m	1560 m   	1270 m       	------	------	------	
[FeL2]	------	1590 m.br	1530 msh
	1270 m  
	490       w	390        w	------	
[CoL2]Cl.H2O 	3450-3390   s.br	1600  m. br	1535 m
	1270 m     	480        w	380         w	
270  
w
	
[NiL2] 	------	1595  m	1530 m    	1265  m      	490       w	410        w	------	
[CuL( H2O)]Cl	3450 s
	1600 m	1540 m
	1270 m
	470 w	400 w	
270 w

[PdLCl] 	------	1595 m 	1540 m.sh	1270 m      	480       w	410        w	260    
w	
[ZnL2]	------	1600  m. br   	1535 m  	1265 m       	480        w	410        w	------	
[CdL2]. H2O	3440-3180   s.br	1590  m	1540 m.sh	1265 m
	470         w	400        w	------	
[Ag.L(H2O)].H2O	3370-7110	1600 m	1530 m.sh	1270 m	480  
w	390  
w	------	
HL = ligand, v = very, w = weak, s = strong, m = medium, br = broad, shr = sharp

Conductivity Measurements, Electronic Spectra and Magnetic Properties 
       All chelate complexes except of Co(III) and Cu(II) complexes showed the conductivity measurements values rang between 8.45-7.18 S. cm2 mol-1.Table4, in DMSO (10-3M ) at room temperature, the values indicating that non-ionic character(32). But the low values of conductivity 69.44 and 76.35 S. cm2 mol-1 for the  Co(III) and Cu(II) complexes respectively indicating that these complexes is (1:1) ionic structure. 
          The electronic spectrum of Fe(II) complex shows a single absorption band at 10200 cm-1, corresponding to5T2g → 5Eg transition. This complex exhibit magnetic moment of 5.46 B.M, which can be a normal value for high-spin octahedral geometry(33). The UV-Vis spectrum of Co(III) complex show two absorption bands at 15923 cm-1 and 21739 cm-1 characteristic of octahedral stereo absorption(34). They were assigned to the transitions of  1A1g → 1T1g and 1A1g → 1T2g respectively. The magnetic moment of this complex has been found to be diamagnetic the low spin behavior of Co(III) complex indicates that the Co(II) ion is oxidized to the Co(III) ion  during complexation. The change of the oxidation state agrees with the earlier observation of the aqueous solution of Co(II) salts which are spontaneously oxidized to Co(III) in the presence of strong ligand such as thiazolylazo compounds(21). The spectrum of Ni(II) complex exhibit three bands at 10400 cm-1, 16286 cm-1 and 22870cm-1 corresponding to3A2g → 3T2g(F), 3A2g → 3T1g(F), and 3A2g → 3T1g(P) transitions respectively with an octahedral spatial configuration (35). This complex exhibit magnetic moment of  3.17 B.M, which can be a normal value for octahedral high-spin Ni(II) complexes(36). The visible absorption spectrum of Cu(II) complex provide abroad absorption band around 18518 cm-1 corresponding to 2B1g → 2A1g transition. It is reasonable to assign square planer structure (37). The value of magnetic moment of this metal complex was found to be 1.86 B.M, this suggests the presence of one unpaired electron in this complex. The electronic spectrum of Pd(II) complex show absorption band in the visible region around 23130 cm-1, which was attributed to 1A1g → 1B1g transition in square planer environment(38). The zero magnetic value of this complex indicate square planer geometry which is the common stereo chemistry for tetra coordinate Pd(II) complex. The UV-Vis spectra of Ag(I), Zn(II) and Cd(II) complexes with (6-NBTADMP) do not show any d→d transition bands. The magnetic susceptibility show that all complexes have diamagnetic moment for d10 ions. The spectral data and magnetic moments are listed in Table4.   According to the above data the structural formula of metal complexes may be proposed in Figs.2, 3 4 and 5.

Table.4: Molar conductance, Electronic spectra and Magnetic moment of Complexes

Complex	Absorption bands (cm-1)	Transition	Conductivity S.mol-1.cm2	μeff   (B.M)	
[FeL2]	10200
	5A2g → 5Eg
	8.45	5.46	
[CoL2]Cl.H2O	15923
21739
	3A2g → 3T2g(F)
3A2g → 3T1g(F)
	69.35	dia	
[NiL2]	10400             
16286                     22870                     	3A2g → 3T2g(F)
3A2g → 3T1g(F)
3A2g → 3T1g(p)	7.52	3.17	
[CuL( H2O)]Cl	18518	2B1g → 2A1g	76.35	1.86	
[PdLCl]	23130	1A1g → 1B1g	7.77	dia	
[ZnL2]	-----	------	7.63	dia	
[CdL2]. H2O	-----	------	7.25	dia	
[Ag.L(H2O)].H2O	-----	------	7.18	dia	

M = Fe(II), Ni(II) and Zn(II) , n = 0, m = 0
M = Co(III), n = 1, m = 1
M = Cd(II), n = 0, m = 1

Fig.2: The proposed structural formula of Fe(II),Co(III), Ni(II), Zn(II) and Cd(II) complexes

Fig.3: The proposed structural formula of Cu(II) complex

Fig.4: The proposed structural formula of Pd(II) complex

Fig.5: The proposed structural formula of Ag(I) complex

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