Synthesis and Structural Views on New Azo Ligand and Its Metal Complexes with Some of their Application

In this work, we presented a study of the structural formula for a new series of complexes with Ag(I), Cu(II), Zn(II), and Cd(II) derived from the guanine azo dye ligand 2-amino-8-((3-hydroxyphenyl)diazinyl)-1,7-dihydro-6H-purin-6-one (HAG), which is investigated using various physicochemical analyses, spectroscopic techniques (FT-IR, U.V-VIS, and 1 H NMR), thermogravimetric analysis (TGA). In addition, elemental analyses, magnetic susceptibility, and molar conductance measurements were all stabilized. As well as the mole ratio, stability constant, and Gibbs free energy were studied for all complexes, where they showed high stability and spontaneous synthesis. The Cu(II) complex was suggested to have octahedral stereochemistry, while the Ag(I), Zn(II), and Cd(II) complexes were suggested to have tetrahedral stereochemistry. The ligand has been demonstrated to be a useful acid-base indicator, and it has been shown that the ligand (HAG) and its complexes exhibit high photostability and have various colors that can be used to dye wool materials.


Introduction
Guanine is an organic compound that belongs to the purine group, which is made up of a fused pyrimidine-imidazole ring system comprising carbon and nitrogen atoms.Azo dyes make up most dye chemistry production today, and in the future, their relative importance might increase.They are necessary for developing the printing and dye markets.These dyes are produced using a simple coupling of the diazotization process.A number of changes and detours are taken in order to achieve the desired results.Greater dispensability, yield, and dye particle size are important dye characteristics.Azo dyes provide more than 60% of the colors used in contemporary dyes [1].The majority of industrial colors-roughly 70% are synthetic azo dyes.These substances are distinguished by the functional group (-N=N-) connecting symmetrical or asymmetrical fragments.Azo dyes are utilized as a more important material for the textile and printing industries that disperse colors.Additionally, they have been used in various fields, including electro-optical devices, liquid crystal displays, nonlinear optics, cosmetics, food coloring, acid-base indicators, and polymers [2].The study aims to synthesize and characterize a new ligand (HAG) and its complexes with Ag(I), Cu(II), Zn(II), and Cd(II), as well as to investigate its ability to dye cotton fabric.Acid-base indicators and photostability were investigated.

Experimental 2.1. Materials and instruments
All chemicals were purchased from commercial sources and used without additional purification unless stated otherwise.Elemental microanalysis of the HAG ligand were recorded on a Eure EA 3000 Elemental Analyzer.The pH values of the samples were measured using HANNA instruments.The FT-IR spectral data were recorded using a Shimadzu 8400s spectrophotometer.The UV-Vis spectral data were recorded using a Shimadzu 1800 UV-Vis spectrophotometer. 1 H NMR spectral data were recorded using a Bruker AV400 Avance-III spectrometer.Thermal gravimetric analysis (TGA) was utilized to measure the metal content of the synthetic ligand and complexes by SDT, Q600 V20.9 Build.Melting points are uncorrected and were recorded in open capillary tubes using a Gallenkamp instrument.The molar conductance of metal ion complexes was examined at 10 -3 M in deionized distilled water.The Mohr method was used to determine the chloride concentrations in the complexes.The magnetic susceptibilities of the complexes were assessed at room temperature using a Sherwood scientific auto-magnet susceptibility balance model.

Metal complex synthesis
All new complexes were synthesized in a mole ratio of M:L (1:1), except (Cu-HAG), which had a mole ratio of 1:2.The HAG ligand (0.306 g, 1 mmol) was dissolved in a minimal amount of deionized distilled water (Scheme 2).The ligand solution was gradually added to the appropriate aqueous solution of metal salts [AgNO3 (0.1698 g, 1 mmol), ZnCl2 (0.1362 g, 1 mmol), CdCl2 (0.183 g, 1 mmol), or CuCl2.6H2O(0.8524 g, 0.5 mmol)] in deionized distilled water.The reaction mixture was then heated to reflux for 3 hours, and the reaction was monitored by TLC using a mixture of solvents (0.8 mL of methanol, 1.2 mL of ammonia, and 4 mL of butanol).The solid crude material was filtered after washing the mixture with a mixture of deionized distilled water and ethanol.The physicochemical properties of the HAG ligand and its complexes are listed in Table 1 [4].

Result and discussion
All the synthesized compounds are stable across moisture, non-hygroscopic, and have bright colors.The structural formulae of the azo ligand and its metal complexes were confirmed by utilizing different physicochemical and spectroscopic techniques such as elemental analysis (C.H.N and M), molar conductivity, FT-IR, 1 H NMR, UV-Vis spectroscopy, magnetic magerment and thermal analysis.The elemental analysis and analytical results for metal complexes confirmed the formation of a M:L (1:2) mole ratio for the Cu(II) complex and were consistent with their suggested molecular formula, whereas the other complexes (M:L) have the mole ratio (1:1).By studying the molar conductivity of the complexes, it was found that all complexes are non-electrolytes, except for the silver complex, which has a 1:1 electrolyte (Table 1).The mole ratio approach, which was used, is the most common method for determining the composition of a complex in solution.The solutions were prepared at a concentration of 10 -4 M. Figure 1 depicts the procedure and the locating outcomes, and Table 2 presents the data on the results.Spectrophotometric analysis can be used to estimate the stability constant [5].The following formula was used to calculate the stability constant for Cu(II) complexes: where Where: α = The mole fraction of the reactant that submits dissociation is equal to the degree of dissociation.
As = the absorption of a solution with a stoichiometric (1:1) ratio (M: L).Am = A solution's absorption, including excess ligand.C = The mole/L concentration of the synthesized solution.
The stability constant for complexes Ag(I), Zn(II), and Cd(II) at a 1:1 ratio, on the other hand, was calculated using the following equation [6]: According to the findings in Table 3, the stability is as follows, in ascending order: The thermodynamic coefficient of ΔG (Gibbs free energy) was obtained from the equation below [7]: ΔG = -RT ln K Where: R is the gas's constant, and it is 8.31 J. mole -1 .K (T) is the temperature (Kelvin).The formations we obtained from G indicate that all complexes are synthesized spontaneously.

Thermogravimetric analysis (TGA)
The thermal behavior of the synthetic HAG ligand and its complexes is explored in Figure 2. Table 4 lists the estimated and discovered phase mass losses.In the four exothermic phases, the ligand HAG breakdown occurs in the 50-800 °C range.The first stage of decomposition occurs between 25 and 100 °C, resulting in a weight loss of 12.13%.The second stage occurs between 100 and 310 °C, resulting in a weight loss of 19.80%, and the third stage occurs between 310 and 400 °C, resulting in a weight loss of 8.958%.The final step of disintegration begins between 400 and 800 °C (25.39% weight loss) (as recommended in Figure 2A).In the case of [Ag(HAG)(H2O)2]NO3.2H2Ocomplex breaks down in the five stapes (Figure 2B).The initial stage of decomposition begins at 25 to 90 °C, resulting in a weight loss of 3.642% decomposed of water.At 90-249 °C, the second stages of breakdown were noticed (9.527% weight loss).Decomposition begins in its third stage at 249-390 °C (13.78% weight loss), moves to a range of 390-760 °C (25.22% weight loss) in the fourth stage.In the last stage (760-800 °C), the weight decreased by 44.13%.The chemical compound [Cu(HAG)2Cl2].H2O, in contrast, breaks down into seven different components (Figure 2C).With a weight loss of 3.202%, the first stage of decomposition begins between 25 and 62 °C.The second stage of decomposition was recorded between 62 and 200 °C.Decomposition begins in its third stage between 200 and 400 °C (9.47% weight loss).In the fourth stage (400-500 °C), it was lost 10.79% of the weight.The fifth stage (weight loss of 19.30% at 500-625 °C).The sixth stage loses weight by 13.13% between 625-700 °C and 19.19% between 700-800 °C during the final stage of disintegration [6].The Zn(HAG)Cl2.H2O complex is divided into five stapes (Figure 2D).At 25 to 60 °C, the first stage of decomposition begins, and a loss of 1.626 pounds results.The second stage of breakdown (14.17% weight loss) was noticed between 60 and 400 °C.Decomposition begins in its third stage between 400 and 475 °C (6.80% weight loss).Starting at the range 475-600 °C, the fourth stage lost weight by 10.51%, and the last stage reached 600-800 °C (weight loss of 22.0%).Considering Cd(HAG) Cl2.2H2O in five states, the complex breaks down (Figure 2E).At 25 to 85 °C, the first stage of breakdown begins, resulting in a weight loss of 2.74%.The second stage of disintegration (5.24% weight loss) was seen between 85-220 °C.During weight loss of 220-400 °C (10.44%), the third stage of breakdown begins.At the range from 400 to 560 °C, the fourth stage started, losing weight by 11.93%.The final stage at 560-800 °C (weight loss of 27.69% [7].The HAG ligand and its complexes (thermal stability) are reduced in the following order:

FT-IR spectroscopy
FT-IR can help predict the binding mode for the HAG ligand with the metal ions in the complexes that have been generated.For identification, the FT-IR spectra of all synthesized metal ion complexes and the HAG ligand were contrasted.The spectra of the complexes showed absorption bands back to the ligands, with some variations because of the chelating.Table 5 summarizes the principal bands for the HAG ligand and its metal complexes.Figure 3 shows the highest number of moieties vibrations using the CsI disk.The following points summarize the most important information about the linkage between the metal ion and the ligands and the accompanying changes: The bands at 1573 and 1562 cm -1 in the HAG ligand spectrum are associated with C=N in the imidazole ring for guanine.This band's structure and position changed because of its coordination with the metal ion.The bands of O-H, N-H, and C=O [3] were unaffected in the complex spectra (Table 5).Suggesting that no chelating occurred via these moieties [8,9], however, small alterations in location or form were occasionally attributed to a decrease or increase in resonance because of chelating [10,11].The azo compounds' distinct feature bands (N=N) [12].This band appears at 1413 cm -1 in the spectrum of the HAG ligand.However, the stretching absorption of C-N=N-C at 1373 and 1342 cm -1 .The posture and intensity of these bands are minified in the complex spectra by chelating [13,14].Several additional bands that were not present in the free-ligand spectrum were discovered.However, the most noticeable changes occurred in the 405-622 cm -1 range.These bands, which appeared in this region may be related to the stretching absorptions of M-Nazo, M-Nimidazole), and M-OH2O.This will support our results regarding the chelation sites of the ligands with metal ions, and from the above, we conclude that the HAG ligand acts as a neutral N,Nbidentate ligand forming penta-chelating ring [15,16].

Dying performance
The effectiveness of the HAG ligands' complex dyes on wool was examined.Most protein filaments that make up wool fibers have complex structure amino groups and are called keratin.It has the general formula [H2N.CHR.COOH], where R is an independent chain with a distinct character, and is composed of lengthy polypeptide chains with 18 different amino acids.The bridges are composed of cysteine and connect chains [24].These theories provided a holistic explanation strictly in terms of the ionic theory [25], the mechanism of wool dyeing under acidic conditions, interactions with the fibers' positively charged amino groups, and the colored anions with a negative charge [26].The placement of the substituted present, the diazotized chemical, and the outcomes cause differences in the tones of the azo dye textile.Grayscale tests were performed on the complexes chosen for color fastness and standing time.The replicas were colored with a fixative, the color fastness of the fabrics was evaluated during washing using soap powder (2%) at 260 °C for 30 minutes, and the responsiveness was excellent to water (Table 9).The HAG ligand and its complexes have various colors when used for dying wool fiber (Figure 8).[27,28].As a result, acid-base titrations were used to test this feature in all azo dyes .All synthetic azo dyes exhibited reversible and abrupt color changes when transitioning from an acidic condition to a basic condition or vice versa.They also possessed a stable color in both acidic and basic solutions.Each azo compound accurately identified the endpoint.Table 10 shows the data of acid-base titrations that are used to assess the indicator property of azo dyes that should be included.Figure 9 displays the hues of azo dye solutions in both acidic and basic environments.

Photostability
By dissolving the HAG ligand in water at a concentration of (10 -4 M) and subjecting them to ultraviolet (UV) radiation for two hours at room temperature, their photostability was examined (Table 11).The photostability was calculated [15,29] using the difference between the initial absorbance (i.e., before irradiation and the final absorbance to the beginning absorbance).The following findings were obtained from the photostability test:

Conclusion
Different spectroscopic techniques are used to characterize and study Ag(I), Cu(II), Zn(II), and Cd(II) complexes that are formed from the HAG azo ligand (2-amino-8-((4-chloro-3hydroxyphenyl)diazenyl)-1,7-dihydro-6H-purin-6-one).The complexes formed at different stoichiometric rates.All have tetrahedral geometry with the exception of the Cu(II) complex, which has a distorted octahedral structure, and the ligand acts as a bidentate ligand.It can also be used as an indicator for the titrimetric assay in both strong acid/strong base and weak acid/strong base titrimetric analyses.The ligand and its complexes have various colors confirmed to be used to dye wool fabrics.The ultraviolet protection factor's findings support the material's excellent UV absorption capacity to support various analytical works in teaching and research laboratories, which remains our goal.

Figure 4 :
Figure 4: 1 H NMR spectrum of the HAG ligand

6 .
Azo dyes as acid-base indicators The organic dyes with distinct colors in solutions with different pH values are known as acid-base indicators.They are frequently used in acid-base titrations to establish the equivalency point.When the pH changes, they exhibited a striking color change.Due to their capacity to alter color in response to pH, azo dyes are the most widely used chemical molecules as acid-base indicators

Table 1 :
Some physical and chemical properties of the HAG ligand and its complex

Table 2 :
HAG-Metal ion solution absorbance vs mole ratio

Table 3 :
The behavior of the thermodynamic parameters of ΔG (Gibbs free energy)

Table 4 :
TGA of HAG ligand and their complexes

Table 7 :
The data of the spectrum of UV-Vis for HAG ligand and their complexes

Table 9 :
Dying properties Where the values 4-5 are good, 3 is moderate, and 1-2 are not good.According to woolen textile standard No. 3616

Table 10 :
The data of acid-base titrations of HAG ligand

Table 11 :
The photostability data of HAG ligand and its complexes