Synthesis and Spectral Properties Studies of Novel Hetrocyclic Mono Azo Dye Derived from Thiazole and Pyridine With Some Transition Complexes

Introduction

Azo dyes of thiazole and pyridine compounds are  very important class of chemical constituents having  enormous applications in multiple fields such as polymer ,paper , paint and coating industries as a dyeing pigments [1-4] . Thiazolyl azo and pyridyl azo compounds are important in  intermediates for the preparation of some applications such as biological activity [5,6] , clinical fields [7,8] , analytical reagents [9,10] and some drugs including discouraging the growth of germs[11,12] . Most hetrocyclic azo dyes such as pyridyl azo and thiazolylazo compounds of technical interest for application to textiles are derived from mono and diazo components  consisting of five – membered metallo ring consisting of  one sulphur  or nitrogen hetero atom and to which a diazotisable amino group is  directly attached ,the ring may also possess one or two nitrogen hetro atoms such as pyridyl azo ,imidazolylazo and benzimidazolyl azo [13-15] , or one nitrogen and one sulpher hetro atoms such as thiazolylazo and benzothiazolylazo and be fused to another aromatic ring[16,17] . The  thiazolylazo and pyridyl azo reagents have an important role in spectral determination field to determine metal ions because of high sensitivity  and selectivity [18,19] . Thus azo dyes compounds from this intermediate have achieved significant commercial success for the dyeing of cellulose acetate fibers in which  gas fastness  is a higher  priority than light fastness .  In the present study, the synthesis of mono azo dye ligand (NTAPy) which contains two hetrocyclic ring thiazole  and pyridine and its metal complexes with Cr(III) , Mn(II) , Fe(III) , Co(II) , Ni(II) , Cu(II), and Zn(II) ions  are reported. Moreover spectral and analytical identification studies have been investigated for comparative purposes.

Materials and Methods

2-Amino-4-methyl pyridine  , 2-amino-5-nitro thiazole and other chemicals were equipped from Aldrich , BDH and sigma chemical companies and used without further purification .All chemicals  and solvents used in the preparation and characterization were of analytical grade. ¹H-NMR and ¹³C-NMR spectra were obtained with a model Bruker AM(400MHz)spectrometer for using DMSO-d6 solution in an appropriate deuterated  solvent .The chemical shift are reported in ppm using tetra methyl silane(TMS)as the internal reference.Mass spectrum of azo ligand (NTAPy)were recovrded on a shimadzu Agilent Technologies 5975^oC at 70ev and MSD energy using a direct insertion probe (Acqmethod low energy) at 90-110^oC  temperature .Elemental analysis (C.H.N.S) was carried out using a C.H.N EA-99 mth instrument.  The metal contents of metal complexes were measured by using atomic absorption technique by shimadzu AA-6300. IR spectro were recorded as KBr discs in range (4000-400)cm^-1 on a shimadzu 8400FT-IR spectrophotometer .The electronic spectra were measured in 1cm quartz cells on a spectraphotometer a UV-Visb.   T80-PG by using 10^-3 M solution absolute ethanol at room temperature in the rang (200-1100) nm . Magnetic susceptibility measurements of the metal complexes in powder form were carried out on Balance Magnetic (MSB-MKi) apparatus by using farady  method at room temperature Diamagnetic correction for the metal complexes was calculated using pascals constant. Molar conductivity measurements were recorded at room temperature in DMF solution (10^-3M) by using a 31 A digital conductivity meter . Melting points of azo dye ligand  and its metal complexes are un corrected and were determined using open capillary tube method which uses Electro thermal melting point 9300 apparatus . The purity of the azo dya ligand was assessed by thin layer chromatography (TLC) using whatman 250m silicegel plates as the stationary phase and methanol as developing solvent .

Synthesis of Novel  Hetrocyclic Mono azo dye Ligand (NTAPy)

The novel heterocyclic mono azo dye ligand (NTAPy) ,(Scheme 1) was synthesized by dissolved 2-amino-5-nitro thiazole(1.45gm,0.01mol) in 50 ml distilled water and 4 ml hydrochloric acid . The solution was diazotized with (0.75 gm, 0.01 mol in 25 ml distilled water) sodium nitrate (NaNO₂)was cooled and added drop – wise to solution of 2-amino-5-nitro thiazole .The resulting  reaction mixture was stirred  of 20 minutes ,formed a clear yellow solution .In the resulting diazonium chloride solution,drop-wise, with cooled condition and stirring continuously at(0-5)^oC,was added  to solution of 2-amino-4-methyl pyridine (1.08 gm,0.01 mol) dissolved in 100 ml ethanol .The color of the reaction mass was changed from yellow to brown red color.The reaction mixture was stirred for another 2 hours at (0-5)^oC in ice-bath. After completion of reaction ,the reaction mixture was added to the ice cold water (200ml) with stirring .The crude product was separated by filtration , washed with distilled water  and dried .The solids obtained recrystallized  with ethanol to get  brown crystals colored .The purity of the azo dye ligand (NTAPy) was determined by thin layer chromatography (TLC). The yield of the reaction was 76% and m.p =122^oC . The molecular structure of  the azo dye ligand and  was characterized by ¹H-NMR ,  ¹³C-NMR ,mass spectrum ,UV-Vis , FT-IR and C.H.N.S elemental analysis.

Scheme 1: Synthesis of mono azo dye ligand 5-[2-(5-Nitro thiazolyl)azo]-2-amino-4-methyl pyridine(NTAPy) Click here to View scheme

 

Synthesis of Metal Complexes

The metal complexes of mono azo dye ligand (NTAPy)were synthesized by adding 0.528gm(0.002 mol)of ligand dissolved  in 50 ml hot ethanol in the form of drop-wise with  stirring stoichiometric amount of 1:2 ,[M:L] mole ratio  (0.001mol) for Cr(III), Mn(II) , Fe(III) , Co(II) , Ni(II) , Cu(II) and Zn(II) Chloride salts  which dissolved in 30 ml hot buffer solution (ammonium acetate) at pH=6.5-7.5 for each metal ions .The reaction mixture was heated and stirred for another 40 minutes at (60-70) ^oC until the precipitated product ,than left over night , The crude precipitate was filitered off and washed several time with distilled water , then washed by 10 ml absolute ethanol to remove any trace of unreacted organic material  to get crystals product purple ,orange, green and red solids , dried and preserved in desiccators over anhydrous CaCl₂ . The yields, melting points, color and analytical data are collected in table(1).

Table 1: physical and analytical data of novel azo dye of ligand (NTAPy) and its metal  complexes

Compound	PH	color	m.p oC	Yield%	Molecular formula	Found (calc.)%
					(Mol.wt)	C	H	N	S	M
Ligand=NTAPy	6	Brown	122	76	C9H8N6O2S	-40.9	-3.05	-31.8	-12.13	–
					-264.26	40.68	2.97	31.35	12.34
[Cr(L)2Cl2]Cl.H2O	7.5	Purple	183	74	C18H18N12O5S2Cl3Cr	-29.9	-2.5	-23.25	-8.87	-7.19
					-722.897	30.09	2.39	23.6	9.11	7.48
[Mn(L)2Cl2].H2O	7	Dark purple	168	63	C18H18N12O5S2Cl2Mn	-32.16	-2.69	-24.99	-9.536	-8.17
					-672.499	31.75	2.75	25.42	9.84	8.39
[Fe(L)2Cl2]Cl.H2O	6.5	Reddish orange	194	58	C18H18N12O5S2Cl3Fe	-30.51	-2.55	-23.71	-9.04	-7.87
					-708.8596	30.74	2.46	23.95	8.83	8.21
[Co(L)2Cl2].H2O	7.5	Dark green	203	72	C18H18N12O5S2Cl2Co	-31.19	-2.68	-24.84	-9.48	-8.71
					-676.451	31.51	2.56	25.01	9.75	8.85
[Ni(L)2Cl2].H2O	7	Purple	206	77	C18H18N12O5S2Cl2Ni	-31.98	-2.68	-24.84	-9.49	-8.67
					-676.311	32.44	2.75	24.99	9.67	8.78
[Cu(L)2Cl2].H2O	6.5	Green	172	81	C18H18N12O5S2Cl2Cu	-31.75	-2.66	-24.46	-9.41	-9.32
					-681.104	31.93	2.74	24.79	9.7	9.75
[Zn(L)2Cl2].H2O	7	pink	188	69	C18H18N12O5S2Cl2Zn	-31.67	-2.65	-24.61	-9.38	-9.58
					-682.967	31.91	2.71	24.77	9.65	9.79

NTAPy=L

Result and Discussion

Mass Spectrum of the Novel Azo dye Ligand (NTAPy)

The mass spectrum fragmentation of novel azo dye ligand (NTAPy) shown in schem-2 and figure 1 . The base peak of azo dye ligand at m/Z⁺ =264.0 is a ttributed to the original molecular weight of ligand [C₉H₈N₆O₂S] , 264.29 . The peak at m/Z⁺= 234.0 is due to loss of methyl and amine groups [C₈H₄N₅O₂S]⁺ ion , while a peak at  m/Z⁺=188.0 is attributed  to the loss of nitro group(NO₂) to give groups [C₈H₄N₄S]⁺. The loss of azo group  give a peak at m/Z⁺=160.0 [C₈H₄N₂S]⁺. The peak at  m/Z⁺=84.0 is analogous to the loss of [C₅H₄N]⁺ (pyridine ring) and gives thiazole molecule[C₃H₂NS]^{+ ,} [20,21].

Figure 1: Mass spectrum of novel azo dye ligand (NTAPy) Click here to View figure

 

Scheme 2: Mass spectrum fragmentation of novel azo dye ligand (NTAPy) Click here to View scheme

 

¹H-NMR Spectrum of Novel Azo dye Ligand (NTAPy)

The ¹H-NMR spectrum of novel azo dye ligand (NTAPy), figure 2 ,was measured using in CDCl₃ solvent with TMS as an internal reference .The ¹H-NMR spectrum data of the azo dye ligand showed  δ =1.3 ppm ( S,3H,CH₃ ) ,  δ =6.8 ppm (S,2H,NH₂)  and  δ =7.1-8.1 ppm (m,3H,Ar-H) [20,22,23].

Figure 2: 1H-NMR spectrum of novel azo dye ligand ( NTAPY) Click here to View figure

 

¹³C-NMR  Spectrum of Novel Azo dye Ligand (NTAPy)

The ¹³C-NMR spectrum of novel azo ligand (NTAPy) , figure 3, was measured by using  DMSO as solvent .The  ¹³C-NMR spectrum of azo dye ligand show  δ=149.3 ppm (C₂), δ =124 ppm (C₅), δ=145 ppm (C₄), δ=24.4 ppm (C₇) , δ=128 ppm (C₄^–), δ=125 ppm (C₅^–),δ=131 ppm (C₆^–),δ=144 ppm (C₂^–)and δ=114ppm (C₃^–) [24,25].

Figure 3: 13C-NMR spectrum of novel azo dye ligand ( NTAPY) Click here to View figure

 

Infrared Spectral Studies

The IR spectral data of the prepared azo dye ligand (NTAPy) and their Cr(III) ,Mn(II) ,Fe(III) ,Co(II), Ni(II) , Cu(II) and Zn(II) complexes (KBr disc) are presented in Table 2.   The IR spectrum of the free azo dye ligand exhibited a band at 3402 cm^-1 which is assigned to Ʋ(-NH₂) group in the ligand (NTAPy) . This band does not  change in position in all metal complexes because of  non coordination with metal ion [26] . The IR spectrum of azo dye ligand shows characteristic bands at 3263 cm^-1 and 3101 cm^-1 was attributed to  Ʋ(-CH₃) and Ʋ(-CH) pyridine ring respectively [27] . This band did not show any frequency shift in IR spectra of all metal complexes [20,27,28] .The spectra of all metal complexes show a broad band around at(3440-3496) cm^-1 indicated the presence of water molecule Ʋ(H₂O) in these complexes[14,15]. The strong band observed at 1628 cm^-1 in the free azo dye ligand was attributed to Ʋ(-C=N) stretching of the thizole ring [30] . This band shifted to a lower wave number side (1605- 1620) cm^-1  in all metal complexes suggesting  the participation of the  Ʋ(-C=N-) of thiazole ring in bonding with metal ions [15,31] . A strong to medium in tensity band at 1512 cm^-1  in free ligand and (1512-1519) cm^-1  in all metal complexes which is assigned to Ʋ(-NO₂) group [16] . A medium intensity band at 1473 cm^-1  in the free ligand was attributed to Ʋ(-N=N) stretch of the azo group [32,33] .The band shifts to lower wave number side (1458-1434) cm^-1 in all metal complexes indicating the coordination with metal ions[34] . Another bands appeared at 1257 cm^-1 in free ligand spectrum . attributed to Ʋ(-C-S) of the thiazole ring [15,20,27,35] .The existence of this band in all metal complexes means that the suphur atom of thiazole ring does not participate in coordination [36] . New absorption the range of (512-493) cm^-1 which are not present in the spectrum of the free ligand are due to Ʋ(M-N) band vibrate ion [37] .IR spectra  data lead to suggest that the ligand behaves as a bidentate chelating agent coordination through the nitrogen atom of thiazole ring nitrogen of azo group nearest to pyridine ring to give five membred metalo ring .Some representative spectra are given in figures 4,5 and 6.

Table 2: Selected IR data (KBr disc, Ʋ cm^-1) for novel azo dye ligand (NTAPy) and their metal  complexes

Compound	Ʋ(NH2)	Ʋ(CH3)	Ʋ(C=N)	Ʋ(NO2)	Ʋ(N=N)	Ʋ(C=C)	Ʋ(C-S)	Ʋ(M-N)
Ligand=(NTAPy)	3402	3263	1628	1512	1473	1335	1257
	S.	m.	s.	m.br	m.	w.	m.	–
				1365
				S.
[Cr(L)2Cl2]Cl.H2O	3438*	3271	1620	1518	1458	1157	1248	509
	s.br.	w.	m.	w.	w.	w.	w.	w.
				1342
[Mn(L)2Cl2].H2O	3425*	3217	1620	1512	1434	1303	1227	486
	w.	w.	m.sh	m.sh	w.	w.	s.
				1345
[Fe(L)2Cl2]Cl.H2O	3406*	3214	1620	1519	1434	1203	1275	508
	w.	w.	w.	m.sh	m.	m.	s.	w.
				1335
[Co(L)2Cl2].H2O	3440*	3224	1620	1516	1448	1203	1268	493
	s.br.	w.	m.sh	M	m.	m.	m.
				1334
				w.
[Ni(L)2Cl2].H2O	3428*	3215	1604	1527	1443	1296	1228	502
	m.br.	w.	m.	w.	m.	w.	w.	w.
				1357
				w.
[Cu(L)2Cl2].H2O	3340*	3225	1618	1512	1434	1287	1218	485
	m.(NH2)	w.	m.	w.	w.	w.br.	m.br	w.
	3441			1368
	m.br.(H2O)			m.
[Zn(L)2Cl2].H2O	3741	3226	1605	1520	1442	1296	1203	509
	w.br	w.	m.sh	m.br.	w.	w.	m.sh	w.
	(H2O)			1358
	3332			m.br.
	m.br
	(NH2)

 

*This band attributed to ^Ʋ(NH₂) and ^Ʋ(H₂O) molecule because of interference between this bands in this reagan ; w=weak  , m=medium , s=strong , sh=sholder , b=broad.

Figure 4: IR spectrum of azo dye ligand (NTAPY) Click here to View figure

 

Figure 5: IR spectrum of the  [Cr(L)2Cl2]Cl.H2O complex  Click here to View figure

 

Figure 6: IR spectrum of the  [Cu(L)2Cl2].H2O complex  Click here to View figure

 

Electronic Spectral Studies

The electronic absorption spectra of the novel azo dye ligand (NTAPy) and its prepared  metal complexes with some metal ions such as of Cr(III) , Mn(II) , Fe(III) , Co(II) , Ni(II) ,Cu(II) and Zn(II) ions were recorded in freshly absolute ethanol(10^-3M)at room temperature .The spectral data are summarized in table (3) and show the spectra in figures 7,8,9 and 10.

The electronic spectrum of the free ligand (NTAPY) exhibited two absorption bands at 384 nm (26042cm^-1) and 239nm (41841cm^-1) assignable to π→* π and n→* π transition respectively due to the azo group (-N=N-) and (C=C) groups of thiazole and pyridine rings [20,38]. The absorption band of azo group showed a red shift because of coordination between ligand and metal ion [15,39].The electronic spectrium of the   Cr(III) complex displayed three bands at 532nm (18797cm^-1), 412nm(24272cm^-1)and 349nm(28653cm^-1) which may be d-d transitions of Cr(lll)ion, these bands are assignable to ⁴A₂g →⁴T₂g(F), ⁴A₂g→⁴T₁g(F) and ⁴A₂g →⁴T₁g(p) transitions respectively [27]. The electronic absorption spectrum of Mn(II)-complex(d⁵) exhibited one term apree ion (⁶s) in addition to several times dubline and quarter there for any transition between the crystal field cases will be prohibited multplicity ,and as a result the spectra of ions(d⁵) are very weak and the colors are faint [40]. The Mn(II)- complex where showed two absorption bands at 907nm (11025cm^-1) and 537nm (18622cm^-1) which may be attributed to ⁶A₁g→⁴T₂g and ⁶A₁g→⁴Eg,⁴A_Ig(G) transitions respectively [41] . The absorption band at 238 nm(42017 cm^-1) is attributed to center ligand transition.  The electronic spectrum of Fe(III)-complex showed three absorption band at 963nm (10384cm^-1) , 468nm(21367cm^-1) and 317nm(31546cm^-1) attributed to ²A₂g→⁴T₁g(G) , ²A₂g→⁴Eg, ⁴A₁g(G) and ²A₂g→⁴T₁g(p) transitions respectively [27] .  The Co(II)-complex exhibited  three absorption band at 637nm(15698cm^-1) ,500nm (20000cm^-1) and 402nm (24876cm^-1) assignable to ⁴T₁g(F) →⁴T₂g(F) , ⁴T₁g→⁴A₂g and ⁴T₁g(F) →⁴T₁g(p) transition respectively [40,43] ,while the absorption bands at 296nm (33784cm^-1) and 251(39841cm^-1) attributed to center ligand transitions. The electronic spectrum of the Ni(II)-complex exhibited three absorption bands at 968 nm(10330cm^-1) ,535nm (18691cm^-1) and 340nm(29412cm^-1) assignable to³A₂g(F)→³T₂g(F)f , ³A₂g(F)→³T₁g(F) and  ³A₂g→³T₁g(p) transition respectively  while the absorption band at 252nm(39682cm^-1) attributed to center ligand   transition [32,43] . The green colored of Cu-complex exhibited a single broad asymmetric band around at 618 nm (1618cm^-1) ,the broodiness of this band indicates the three transition  ²B₁g→²A₂g(Ʋ₁) , ²B₁g→²B₂g(Ʋ₂) and ²B₁g→³Eg(Ʋ₃) ,which are of similar energy and give rise to only one broad absorption band due to ²B₂g→²A₂g transition . The broadness of the band may be attributed to dynamic Jahn- Teller distortion [20,23].The electronic spectrum of the Zn(II)- complex did not show any d-d transition because it is saturated with electron (d¹⁰) .The absorption band at longer wavelength 416nm (24038cm^-1) is due to a charge transfer (M→L,CT) transition.This transition where d π(Zn⁺²)→ *π(L)is belived to be primarily dominated by the LUMO of the azoimine chromophory [44,45].

Magnetic Moments Studies

The magnetic moments obtained at room temperature for Cr(III),Mn(II),Fe(III), Co(II),Ni(II), Cu(II) and Zn(II) complexes are listed in table 3 . The Cr(III)- Complex exhibited the magnetic moment value of 3.78 B.M, this value is too close to the theoretical of magnetic moment for the Cr(III)ion (³t₂g eg⁰), (M_eff=3.87B.M) which indicates an octahedral geometry and d²sp³ hybridization[27].The magnetic moment value of Mn(II)-complex has been found 5.63 B.M. The larger variation in the magnetice moment for a high spin has a d⁵, (t₂g³  eg²) configuration depends on the magnituede of the orbital contribution . The high value of magnetic moment is  because of five electrons unpaired which may suggest a regular  octahedral geometry and sp³d² hybridization [27,46] .The Fe(III)-complex showed the magnetic moment value of 1.84 B.M due presence of one electron unpaired for alow  spin has a d⁵(t₂g⁵  eg⁰) configuration which indicates a distorted octahedral geometry (Z-out) and d²sp³ hybridization [47] . The Co(II)-complex exhibited three absorption bands at  637nm (15698 cm^-1), 500nm (20000 cm^-1) and 402nm(24876 cm^-1) assignable to ⁴T₁g(F) →⁴T₂g(F) , ⁴T₁g→⁴A₂g and ⁴T₁g(F) →⁴T₂g(p) transitions respectively [40,42],while the absorption bands at 296nm (33784 cm^-1) and 251 nm (39841 cm^-1) is attributed to center ligand transition . The Ni(II)-complex showed the magnetic moment  value of 3.04 B.M with the range of 2.8-3.5B.M for high spin (t₂g⁶ eg²) configuration suggesting a regular octahedral geometry and sp³d² hybridization [50,51]. The Cu(II)-complex has a d(t₂g⁶  eg³) configuration show magnetic moment of 1.83 B.M is slightly higher than the spin –only value of 1.73B.M which offers possibility of an octahedral geometry because of the presence of one electron unpaired and sp³d² hybridization [52] .The magnetic moment value of Zn(II)-complex is diamagnetic consistent d¹⁰,(t₂g⁶ eg⁴) configuration which indicates an octahedral geometry with sp³d²  hybridization [53].

Table 3: Electronic absorption spectra (nm,cm^-1),magnetic moments ,geometry and hydridization

Compound	λmax nm	Absorption bands(cm-1)	Trensitons	Meff	Geometry	Hybridization
				(B.M)
Ligand=(NTAPy)	384	26042	n→π*	–	–	–
(L)	239	41841	π →π*
[Cr(L)2Cl2]Cl.H2O	532	18797	4A2g→4T2g(F) (Ʋ1)	3.78	Octahedral	d2sp3
	412	24272	4A2g→4T1g(F)( Ʋ2)		(Regular)
	349	28653	4A2g→4T1g(p)(Ʋ3)
[Mn(L)2Cl2].H2O	907	11025	6A1g→4T2g(F) (Ʋ1)		Octahedral	Sp3d2
	537	18622	6A1g→4Eg,4A1g(G)(Ʋ2)	5.63	(Regular)	(High spin)
[Fe(L)2Cl2]Cl.H2O	963	10384	2A2g→4T1g(G) (Ʋ1)		Octahedral	d2sp3
	468	21367	2A2g→4Eg,4A1g(G) (Ʋ2)	1.84	distorted	(low spin)
	317	31546	2A2g→4T1g(p) (Ʋ3)		(Z-out)
[Co(L)2Cl2].H2O	637	15698	4T1g→4T2g(F) (Ʋ1)		Octahedral	Sp3d2
	500	20000	4T1g→4A2g(F) (Ʋ2)	4.23	(regular)	(High spin)
	402	24876	4T1g→4T1g(P) (Ʋ3)		z-out or z in
[Ni(L)2Cl2].H2O	968	10330	2A2g→2T2g(F) (Ʋ1)	3.04	Octahedral	Sp3d2
	535	18691	2A2g→2T1g(F) (Ʋ2)		(Regular)	(High spin)
	340	29412	2A2g→2T1g(P) (Ʋ3)
[Cu(L)2Cl2].H2O	618	16181	2B2g→2A2g	1.83	Octahedral	Sp3d2
					distorted (Z in-z out)
[Zn(L)2Cl2].H2O	416	24088	dπ(Zn)+2→π*(L)	Dia	Octahedral	Sp3d2
					(Regular)

 

(Figure 7: UV-Visible spectrum of azo dye ligand (NTAPy     Click here to View figure

 

Figure 8: UV-Visible spectrum of Cr(III)-Complex Click here to View figure

 

Figure 9: UV-Visible spectrum of Ni(II)-Complex Click here to View figure

 

Figure 10: UV-Visible spectrum of Zn(II)-Complex Click here to View figure

 

Molar Conductivity Studies

The molar conductance( Ʌ_m) studies  of the metal complexes were measured in DMF solvent in 10^-3M concentration at room temperature.The high values of molar conductivity of the Cr(III)- complex and Fe (III)-complex give 73.85 S.mol^-1 .cm² and 79.37 S.mol^-1.cm² respectively which indicates that the complexes are 1:1 electrolyte with ionic nature because of  the presence of the chloride ion (Cl^–)which is located outside the coordination sphere [20,27], but showed the values of molar conductivity of the Mn(II) , Co(II) , Ni(II) , Cu(II) and Zn(II) complexes ranged between (16.08-24.17)S.mol^-1 .cm² ,this indicates that non –electrolyte and no conductive species exist because of the chloride ions (2Cl^–)which are located in side the coordination sphere [14,32,42,54]. The values of molar conductivity of this metal complexes are listed in table 4.

Metal: Ligand Ratio

The metal : ligand ratio [M:L]of metal complexes were determined by molar ratio method at fixed concentration at wavelength maximum absorption (λ_max).     The solution of prepared metal complexes increase the intensity of the colors as approach point of intersection ratio and color continus constant at passing the point which indicates that the metal complexes formed [15,20,32,39]. The azo dye ligand (NTAPY)which was found to form 1:2 [M:L] mole ratio with all metal ions suggested the formation of metal complexes to give two five- membered chelate rings.

Calculation of Metal Complexes Stability Constant

The stability constant(β and logβ) of metal complexes are determined spectrophotometrically  by measure  the absorbance of mixture of solution of azo dye ligand (NTAPY) and metal ions at fixed wavelength (λ_max)and optimum concentration values .  The degree of formation of metal complexes are calculated depending on the relation- ship β=1-α/4α³c²and α= Am-As/Am , where  As and Am are the absorbance of the partially and fully  formed complexes respectively .The calculated  β and log β values for prepared metal complexes are listed in table 4 . The listed stability constant follows the arrangement Cu(II) ˃Ni(II) ˃Co(II)˃Zn(II) ˃ Mn(II) ˃Cr(III)˃Fe(III) the sequence of metal ions of the first row transition metals agree with Irving-Williams of stability constant[55,56] .

Table 4: stability constant values (  β and log β ) , molar conductivity optimal concentration , maximum wavelength  (λmax) and molar absorptivity (ϵ) of metal complexes

Ligand	Metal ion	Maximum Wavelength (λmax)nm	Optimal Molar Conc.x10-4	Moler Absorpitivity (ϵ)x10-3  L.mol.cm-1	Stability Constant β,L2.mol-2	Log β	Molar conductivity S.cm2.mol-1
λ max=384nm	Cr(III)	532	1.75	2.25	3.77×109	9.58	73.85
ϵ=4.09×103	Mn(II)	537	1.5	0.39	4.18 x109	9.62	16.08
L.mol-1.cm-1	Fe(III)	468	2	8.64	2.49 x109	9.4	79.37
Conc.=1.50×10-4M	Co(II)	637	1.75	1.41	4.57 x1010	10.41	18.58
	Ni(II)	535	2	4.49	5.64 x1010	10.75	24.17
	Cu(II)	618	1.5	1.38	6.73 x1010	10.83	21.88
	Zn(II)	416	2.25	5.32	5.69 x109	9.76	17.89

 

The Proposed Structures of Metal Complexes

Acoording to the results and discussion through different techniques , the proposed structures of the prepared metal complexes are suggested and shown in figure 11 . Depending on the analytical and spectral data, the novel azo dye ligand (NTAPy) behaves as a bidentate chelating agent coordination through the nitrogen atom (N₃)of azo group nearest to pyridine ring and nitrogen atom (N3) of thiazole ring to give one-five membered chelate ring.

Figure 11: The prosed structural formula of metal complexes Click here to View figure

 

Conclusion

In this paper we report the synthesis and spectral properties studies of a bidentate azo dye ligand  derived from thiazole  and pyridine ring (NTAPy) and its metal complexes with Cr(III) , Mn(II) , Fe(III) , Co(II) , Ni(II) , Cu(II) and Zn(II) ions. The azo dye ligand and its metal complexes were characterized by using several physical techniques such as elemental analysis , ¹H-NMR .¹³C-NMR ,Mass spectroscopy ,IR ,UV-Visb and molar conductivity .The geometry proposed for all metal complexes  were octahedral stereo   chemistry .  All metal complexes are not effected by air ,light and a moisture ,suggesting  high stability  plus degrees of melting point that  give  another evidence of the stability of the prepared metal complexes.

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