Springer 2006
Transition Metal Chemistry (2007) 32:102–106 DOI 10.1007/s11243-006-0134-x
Synthesis and spectral characterization of some new azo dyes and their metal complexes Rafet Kılınc¸arslan and Emin Erdem* Department of Chemistry, Pamukkale University, Kınıklı Campus, Denizli, Turkey Hasan Kocaokutgen Department of Chemistry, Ondokuz Mayıs University, Kurupelit, Samsun, Turkey Received 25 July 2006; accepted 20 September 2006
Abstract A series of azo-metal chelate dyes have been synthesized by coupling substituted o-nitroaniline and p-t-/s-butylphenol. The spectral characterization of the azo dyes containing o-hydroxy group and azo-metal(II) chelate [metal(II): Cu, Ni, Co] dyes by IR spectra, UV–VIS spectra, NMR spectra, elemental analysis and magnetic susceptibility techniques are reported. The stoichiometry of the azo-metal chelates was determined by the spectroscopic titration method to be 1:2 (ML2).
Introduction
Result and discussion
Azo dyes are an important class of organic colorants which consist of at least a conjugated chromophore azo (–N=N–) group and the largest and most versatile class of dyes. It has been known for many years that azo compounds are the most widely used class of dyes due to their versatile application in various fields such as the dyeing of textile fiber and coloring of different materials, and for plastics, biological-medical studies, and advanced applications in organic synthesis [1–4]. Potentiometric and spectrophotometric studies of Co2+, Ni2+ and Cu2+ chelates with azo dyes have been reported [5]. They are most commonly used for dyeing textiles. Besides, recently, azo conjugated transition metal complexes have been shown to provide new opportunities towards redox, magnetic and optical properties originating from the d-orbitals [6–9]. In this work, we synthesized some new azo dyes containing the o-hydroxy group and azo-metal chelates using different diazo coupling components and metal (II) ions (copper, nickel and cobalt). Their chemical structures are shown in Figures 1 and 2. The structures were confirmed by IR spectra, UV-VIS spectra, NMR, elemental analysis and magnetic susceptibility techniques.
The present article describes the synthesis of azo dye ligands (HL1-3) and their azo-metal chelates having the metal:ligand ratio of 1:2 (M(L1-3)2Æ2H2O). Suggested structures of the ligands and complexes are given in Figures 1 and 2. The physical properties of ligands and their complexes are given in Table 1.
* Author for correspondence: E-mail:
[email protected]
Infrared spectra study Absorption in the 4000–2600 cm)1 region involves the bands of –OH, –NH and SO3H groups as well as those of the C–H phenyl and C–H aliphatic and associated water molecules in the compounds. The IR data of azo dyes and their azo-metal chelates are given in Table 2. In the IR spectra of azo dye ligands, the band at 3540–3460 cm)1 can be attributed to O–HÆÆÆN intramolecular hydrogen bonding and their absence in the metal complexes indicates deprotonation of phenolic –OH groups, thereby showing its coordination to the metal ions [10]. The sharp band observed at 2870–2965 cm)1 (HL1) and 2865–2950 cm)1 (HL3) can be suggested for mt-bu vibrations, 2875–2969 cm)1 (HL2) for msec-bu. The band of vibration for NO2 in azo dyes and azo-metal chelates observed at 1530 cm)1. The spectrum of azo dye ligands contains a band at ca. 3500 cm)1 which is weakly –OH, the band 3480–3512 cm)1 which is a strongly –OH stretching frequency of coordinated water molecules when the azo-metal chelates.
103 changes to ca. 1040 cm)1. The bathochromic shifts at the vibration spectra of the azo-metal chelates showed bands between 1328 and 1340 cm)1 which azo dyes ligands indicated phenolic C–O stretching vibration to occur between 1336 and 1343 cm)1 [13]. Absorption in the 1000–400 cm)1 region, the out of plane deformation frequencies of aromatic C–H band, are expected where it is observed at ca. 810 cm)1 for azo dye ligands and slightly change to ca. 807 cm)1 on complexation. In this region three new bands were noticed at ca. 760 cm)1 which were assigned as ringdef + m(M–OH)2, i.e., a coordinate water molecule in azo-metal chelates, another band at ca. 500 cm)1 which was assigned as m(M–N), while the band at ca. 450 cm)1 was assigned as m(M–O) [14, 15].
Fig. 1. Chemical structure of the azo ligands.
UV–VIS spectra study
Fig. 2. Chemical structure of the azo-metal chelates.
Absorption in the 2600–1400 cm)1 region is interesting, since it contains bands of > C–O, > –N=N– and > C=C. The bands at 1418 (HL1), 1420 cm)1 (HL2), 1421 (HL3) and around 1400 cm)1 described the N=N and phenolic C–O [11, 12] vibrations, respectively. The bathochromic shift of these bands to between 1394–1406 for N=N respectively, indicates the bonding of ligand to the metal ions through both the azo nitrogen [13]. Absorption in the 1400–1000 cm)1 region involves other bands such as the aromatic C–H in plane deformation vibration, C–N stretching vibration and C–C stretching vibration. Two bands were noticed at this region, one at about 1200 cm)1 which changes to ca. 1196 cm)1 while the other band at about 1045 cm)1
Table 1. The colors, formulas, formula weights, melting points, yields and results of magnetic susceptibilities of the azo dye ligands (HL1-3) and azo-metal chelates (M(L1-3)2 Æ 2H2O) Compounds
F. W. (g/mol)
Color
M.p.C
Yield (%)
l eff [B.M.]
HL1 HL2 HL3 Cu(L1)2 Æ 2H2O Cu(L2)2 Æ 2H2O Cu(L3)2 Æ 2H2O Ni(L1)2 Æ 2H2O Ni(L2)2 Æ 2H2O Ni(L3)2 Æ 2112O Co(L1)2 Æ 2H2O Co(L2)2 Æ 2H2O Co(L3)2 Æ 2H2O
299.3 333.8 333.8 696.2 765.1 765.1 691.4 760.3 760.3 691.6 760.5 760.5
Orange Red Red Brown Brown Brown Brown Brown Brown Dark brown Dark brown Dark brown
184 164 172 278 290 286 262 275 263 226 215 247
64 60 58 65 67 64 58 60 62 56 58 54
– – – 1.69 1.98 1.88 2.66 2.65 2.63 3.74 3.70 3.72
The UV–VIS spectral behavior of azo dyes and their azo-metal chelates were investigated in DMF. The compared dates of the UV–VIS spectrum for azo dyes and azo-metal chelates are shown in Table 3. Comparing data of the UV spectra, it was found that all of the spectra show a strong absorption maximum in the 343–434 nm range with high extinction coefficients. The azo compound HL1 gives two absorption bands 414 nm (n fi p*) and 343 nm (p fi p*); HL2 gives two absorption bands 433 nm (n fi p*) and 351 nm (p fi p*) and HL3 gives two absorption bands 434 nm (n fi p*) and 356 nm (p fi p*). The complex formation equilibrium and formation constant of the complex can be represented by equations (1) and (2) [16], M þ nL ¡ MLn
ð1Þ
½MLn ½M½Ln
ð2Þ
K¼
in which [M], [L] and [MLn] represent the molar equilibrium concentrations of the metal ion, ligand dye and the complex, respectively. The azo-metal chelates of Cu(L1)2, Cu(L2)2 and Cu(L3)2 reveal one broad asymmetric ligand field band at 654, 662 and 661 nm assignable to 2Eg fi 2T2g transition in a distorted octahedral geometry, respectively [17]. The azo-nickel chelates reveals three bands at 746, 512 and 341 nm for Ni(L1)2, 748, 516 and 343 nm for Ni(L2)2 and 746, 516 and 345 nm for Ni(L3)2 assignable to 3A2g (F) fi 3T2g (F) fi 3T1g (F) and 3T1g (P) transitions, respectively. This is in accordance with the earlier reported values for the octahedral Ni2+ complexes [18]. The azo-cobalt chelates shows three d–d transitions at 985, 546 and 453 nm for Co(L1)2, 994, 551 and 462 nm for Co(L2)2, 992, 552 and 460 nm for Co(L3)2 attributed to 4T1g (F) fi 4T2g (F) fi 4A2g (F) and 4T1g (P), respectively. These transitions suggest an octahedral symmetry around the metal ion.
104 Table 2. Characteristic IR bands of the azo dyes and their azo-metal chelates as KBr pellets (cm)1) Compounds
(–C–O)
(–OH2)
(–C1)
(–N=N–)
(–NO2)
(–Butyl)
(M–O)
(M–N)
(M–OH2)
HL1 Cu(L1)2 Ni(L1)2 Co(L1)2 HL2 Cu(L2)2 Ni(L2)2 Co(L2)2 HL3 Cu(L3)2 Ni(L3)2 Co(L3)2
1336 1328 1330 1332 1343 1336 1339 1340 1343 1335 1334 1340
– 3480 3486 3486 – 3490 3496 3512 – 3490 3498 3512
– – – – 743 742 743 743 743 743 742 743
1418 1394 1396 1402 1420 1401 1403 1406 1421 1398 1400 1402
1530 1530 1530 1530 1530 1530 1530 1530 1530 1530 1530 1530
2870–2965 (tert-) 2869–2968 2866–2962 2865–2962 2875–2969 (sec-) 2870–2952 2872–2959 2870–2960 2865–2950 (tert-) 2865–2950 2862–2949 2864–2950
– 446 438 442 – 455 440 452 – 456 438 452
– 496 496 498
– 762 768 759 – 764 765 762 – 759 762 764
Table 3. UV–VIS dates for azo dyes and their azo-metal chelates in DMF Compounds
n fi p*
kmax/nm p fi p*
dfid
HL1 Cu(L1)2 Ni(L1)2 Co(L1)2 HL2 Cu(L2)2 Ni(L2)2 Co(L2)2 HL3 Cu(L3)2 Ni(L3)2 Co(L3)2
414 434* 413 432* 433 434* 429 432 434 434* 423 430*
343 343 347 352* 351 351 350 352 356 354 350* 350*
– 654* 746,* 985,* – 662* 748,* 994,* – 661* 746,* 992,*
510 512 508 512 512 508
Magnetic susceptibility The azo-metal chelates exhibit leff values of 1.69–1.98 B.M. for Cu(L1-3)2, 2.63–2.66 B.M. for Ni(L1-3)2 and 3.72–3.74 B.M. for Co(L1-3)2 indicating a high spin distorted octahedral structure.
512, 341 546, 453
Experimental 516, 343 551, 462
516, 345 552, 460
* Shoulder.
The Job’s diagram, in the case of the azo-cobalt chelate, is obtained by plotting the absorbance (A) at 620 nm. It consist roughly of two straight lines intersecting at fmetal = 0.36, indicating that a 1:2 complex (ML2) is formed (Figure 3).
IR spectra of the dyes were recorded as KBr pellets in the 400–4000 cm)1range on an ATI UNICAM 2000 spectrometer. NMR spectra were recorded at 297 K on Varian at 400 MHz (1H), 100.56 MHz (13C). The UV–VIS absorption spectra were recorded using a Shimadzu UV-1601 Spectrometer. For determining the stoichiometry and formation constant of the azometal chelate, the absorbance of a series of metal salt + ligand [in DMF] mixtures, which were prepared from their 10)4 mol/L solutions, were measured. The data were analyzed using Job’s method [19–20]. Elemental analyses were carried out by the analytical service of TUBITAK with a Carlo Erba Strumentazione Model 1106 apparatus. Magnetic susceptibilities were determined on a Sherwood Scientific Magnetic Susceptibility Balance (Model MK1) at room temperature (20 C) using Hg[Co(SCN)4] as a calibrant; diamagnetic corrections were calculated from Pascal’s constants [21]. All chemicals were obtained from Aldrich. Synthesis of the azo dye ligands (HL1-3) (Diazotization and coupling)
Fig. 3. Job’s diagram for the azo-cobalt chelate (k = 620 nm).
Synthesis of HL1 The diazotization of 4-nitroaniline and coupling with 4-tert-butyl-phenol was carried out according to the published methods [22, 23]. A mixture of 4-nitroaniline (0.81 g, 5.84 mmol), water (10.0 mL) and concentrated hydrochloric acid (1.5 mL, 18.0 mmol) was stirred until a clear solution was obtained. This solution was cooled to 0–5 C and a solution of sodium nitrite (0.47 g, 6.84 mmol) in
105 4 mL water was then added dropwise, maintaining the temperature below 5 C. The resulting mixture was stirred for an additional 30 min in an ice bath and was buffered with solid sodium acetate. 4-t-Butyl phenol (0.88 g, 5.84 mmol) was dissolved in 3 mL of water and cooled to 0–5 C in an ice bath. This solution was then gradually added to the solution of the cooled 4-nitrobenzene diazonium chloride and the resulting mixture was continually stirred at 0–5 C for 2 h. The resulting orange crude precipitate was filtered, washed several times with water, and crystallized from hot glacial acid. Yield: 64%. m.p.: 184 C. Anal. Calcd. for C16H17N3O3; C: 64.2; H: 5.7; N: 14.0; found C:64.6; H: 5.2; N: 14.2%. 1 H NMR (d, CDCl3): 1.36 [s, 9H, C(CH3)3]; 6.98–8.51 (m, 7H, subst. azobenzene); 12.52 (s, H, OH). 13C- NMR (d, CDCl3): 31.3 [C(CH3)3]; 34.1 (C(CH3)3); 117.6, 122.1, 125.0, 129.6, 130.7, 136.8, 142.7, 146.9, 150.1, 156.4 (subst. benzene). Synthesis of HL2 This compound was prepared in the same manner as HL1 using 2-chloro-4-nitroaniline (1.0 g, 5.84 mmol) and 4-s-butyl-phenol (0.87 g, 5.84 mmol). The red product was obtained Yield: 60%. m.p.: 164 C. Anal. Calcd. for C16H16ClN3O3; C: 57.6; H: 4.8; N: 12.6; found C: 58.0; H: 4.7; N: 13. 1%. 1 H-NMR (d, CDCl3): 1.15–1.40 [m, 3H, CH(CH3) (CH2CH3)]; 1.51–1.72 [m, 3H, CH(CH3)(CH2CH3)]; 2.58–2.72 [m, H, CH(CH3)(CH2CH3)]; 6.92–8.50 (m, 6H, subst. azobenzene); 12.70 (s, H, OH). 13C NMR (d, CDCl3): 11.1 (CH(CH3)(CH2CH3)); 21.8 [CH(CH3) (CH2CH3)]; 31.3 [CH(CH3)(CH2CH3)]; 42.5 [CH(CH3) (CH2CH3)]; 118.5, 122.7, 125.0, 125.7, 126.7, 134.8, 136.9, 138.4, 139.7, 147.9, 150.1, 153.6 (subst. azobenzene).
crude precipitate was isolated by filtration, washed several times with water. Synthesis of L1-CopperII complex Yield: 65%. m.p.: 278 C.. Anal. Calcd. for C32H32N6O6Cu; C: 58.2; H: 4.9; N: 12.7; found C: 58.9; H: 4.8; N: 12.1%. Synthesis of L2-CopperII complex Yield: 67%. m.p.: 290 C. Anal. Calcd. for C32H30Cl2N6O6Cu; C: 52.7; H: 4.15; N: 11.5; found C: 53.2; H: 4.0; N: 11.2%. Synthesis of L3-CopperII complex Yield: 64%. m.p.: 286 C. Anal. Calcd. for C32H30Cl2N6O6Cu; C: 52.7; H: 4.15; N: 11.5; found C: 3.0; H: 4.2; N: 11.1%. Synthesis of L1-Nickel II complex Yield: 58%. m.p.: 262 C. Anal. Calcd. for C32H32N6O6Ni; C: 58; H: 4.9; N: 12.8; found C: 58.7; H: 5.1; N: 12.8%. Synthesis of L2-Nickel II complex Yield: 60%. m.p.: 275 C. Anal. Calcd. for C32H30Cl2N6O6Ni; C: 53.1; H: 4.2; N: 11.6; found C: 52.7; H: 4.3; N: 11.45%. Synthesis of L3-Nickel II complex Yield: 62%. m.p.: 263 C. Anal. Calcd. for C32H30Cl2N6O6Ni; C: 53.1; H: 4.2; N: 11.6; found C: 53.1; H: 4.1; N: 11.7%. Synthesis of L1-Cobalt II complex Yield: 56%. m.p.: 226 C. Anal. Calcd. for C32H36N6O8Co; C: 55.6; H: 5.25; N: 12.15; found C: 56.1; H: 5.9; N: 11.9%.
Synthesis of HL3 This compound was prepared in the same manner as HL1 using 2-chloro-4-nitroaniline (1.0 g, 5.84 mmol) and 4-t-butyl-phenol (0.88 g, 5.84 mmol). The red product was obtained Yield: 58%. m.p.: 172 C. Anal. Calcd. for C16H16ClN3O3; C: 57.6; H: 4.8; N: 12.6; found C: 57.2; H: 4.9; N: 13.6%. 1 H-NMR (d, CDCl3): 1.37 [s, 9H, C(CH3)3]; 7.0–8.52 (m, 6H, subst. azobenzene); 12.70 (s, H, OH). 13 C NMR (d, CDCl3): 31.3 [C(CH3)3]; 34.1 (C(CH3)3); 117.6, 122.7, 124.9, 125.8, 129.5, 131.3, 138.9, 139.8, 142.7, 147.8, 150.1, 152.9 (subst. azobenzene).
Synthesis of L2-Cobalt II complex Yield: 58%. m.p.: 215 C. Anal. Calcd. for C32H34Cl2N6O8Co; C: 50.5; H: 4.5; N: 11.05; found C: 51.3; H: 4.6; N: 10.6%.
Preparation of azo-metal chelate compounds (Metallization)
Spectroscopic studies of the complexation of metal ions with an azo dye showed that the absorption maxima of the complexes are bathochromically shifted compared with azo dyes. It was found that geometric forms of the complexes do not actually become square planar structures actually, the high-spin and form of distortion of octahedral configuration of the complexes are deduced by magnetic
Azo dye (1.0 equiv.) was heated with metal(II) chloride (0.5 equiv.) and sodium acetate (1.0 equiv.) under reflux for 4 h in 15 mL DMF. After cooling to room temperature, the mixture was poured into cold NaCl solution and then kept for 30 min in an ice bath. The
Synthesis of L3-Cobalt II complex Yield: 54%. m.p.: 247 C. Anal. Calcd. for C32H34Cl2N6O8Co; C: 50.5; H: 4.5; N: 11.05; found C: 51.15; H: 4.6; N: 10.5%.
Conclusion
106 susceptibility and UV–VIS spectra. The stoichiometry of the complex was determined by Job’s titration method to be 1:2 (ML2). The chelates described to include water molecules from IR spectrum dates investigated.
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