Chemicals were purchased from Sigma-Aldrich and used without further purification. Methanol, and ethanol, were of HPLC grade and were purification using standard methods described in the literature [21] .

The prepared ligand complexes were subjected to (C, H, and N) elemental analyses using a 2400 Series II CHNS/O elemental analyzer. Molar conductance measurements were carried out in DMSO using CMD650 digital conductivity meter. Electronic absorption spectra were measured in DMSO using a Shimadzu NIR3101PC Uv-Vis spectrometer. Infrared spectra were obtained asKBr disks on a IFS-25 DPUS/IR spectrophotometer (Bruker) in the range of 4000 - 500 cm⁻¹. ¹H NMR spectra of the ligands were recorded at 25˚C on a Bruker 600 MHz spectrometer equipped with a cryoprobe.

Equimolar amounts of 4-(dimethylamino)benzaldehyde (1.49 g, 10 mmol) and 4-(amino-3-hydroxynaphthalene-1-sulfonic acid (2.39 g, 10 mmol) were mixed together and cooked at reflux for an hour over a water bath. When the combination reached room temperature, a solid of yellow color developed. It was filtered, rinsed with methanol, then crystallized once more in ethanol [22] . Using TLC, the reaction was observed (Scheme 1).

The ligand (Z)-4-((4-(dimethylamino)benzylidene)amino))-3-hydroxynaphthalene-1-sulfonic acid; 3.70 g) was mixed in the same ratio with CoCl₂·6H₂O and CrCl₃·6H₂O salts to create the ligand complexes in identical amounts (0.01 mol). For three hours, the mixes were refluxed. To change the pH at which the point was, a few drops of an ammonia solution were introduced. The resultant complexes were rinsed with hot ethanol multiple times until the filtrate cleared out. The filtrate was vacuum-dried on anhydrous CaCl₂ after first being dried in the air. The yield varied between 79% and 86%. The dried complexes were examined using spectroscopic and elemental analysis. The produced complexes are DMSO-soluble but insoluble in C₂H₅OH. The purity of the ligand complexes was examined using the TLC method.

The elemental analysis data of the ligand complexes shown in Table 1, confirm the formation of the 1:1 [M:L] complexes.

The molar conductance values of the synthesized Cr(III) and Co(II) ligand

*Unit of molar conductance Ω⁻¹·cm²·mol⁻¹. ( ) Calculated values in parentheses.

complexes were shown in the Table 1. These values suggest the presence of an electrolyte nature [23] . From the molar conductivity values we come to know of the total number of ions in the complex from which we can arrive at the correct formulation.

The ¹H NMR spectrum of the ligand in CDCl₃ (Figure 1) agrees with the suggested structure. The singlets at 9.75 and 7.25 ppm were assigned to the proton of a hydroxyl group (s, H, C—OH) and the proton of an azomethine group (s, H, N=CH), respectively [24] . The chemical shifts observed as singlets at 1.5 ppm (s, H, CH₃) could be responsible for the proton of a methyl group attached to dimethylamino moiety [25] . The aromatic protons of antipyrine moiety appeared at 6.87 - 7.50 ppm. The singlets that appeared at 3.10 ppm (s, H, N—CH₃) were assigned to the proton of the methyl group of dimethylamino moiety [26] .

Figures 2-4 displays the infrared spectrum data for the complexes of Co(II) and Cr(III). The ligand has broad, strong to medium peaks at 1649 and 487 cm⁻¹. These belong to the azomethine group and the phenolic ν(OH) stretching vibration, respectively [27] [28] . By contrasting the IR spectra of the ligands and their

complexes, the bonding behavior of the ligand was determined. Through a deprotonated hydroxyl group and the ligand’s azomethine nitrogen atom, L coordinates with the metal ion to behave as a bidentate ligand, as demonstrated by this comparison [29] .

The same spectra, however, show the bands at 1595 cm⁻¹ caused by the ligand’s υ(CH=N) azomethine group (1450 cm⁻¹) and the potent band of phenolic C-O stretching vibration at 1158 cm⁻¹. As the complex forms, these bands shift, showing that they participated in coordination with the Cr(III) and Co(II) ions. The free ligands allocated to the υ(M-O) and υ(M-N) vibrations lack another band in the ranges of 610 - 630 cm⁻¹ and 545 - 575 cm⁻¹. The presence of this vibration provides evidence that chelation involves the coordination groups −O−, −CH=N, and water [30] .

In DMSO solution, the electronic spectrum was captured. The glossy yellow (Z)-4-((4-(dimethylamino)benzylidene)amino))-3-hydroxynaphthalene-1-sulfonic acid (L) displayed two distinct, highly intense absorption bands at 275 nm, (36363 cm⁻¹) and 288 nm, (34722 cm⁻¹). These belong to the benzene ring’s (π → π*) and the azomethine group’s (n → π*) electronic transitions, respectively [27] . The electronic transition of the Schiff base azomethine group is attributed to the weak intensity absorption band at 237 nm (42194 cm⁻¹) [28] . The spectral absorption data of the [CoL]. Cl complex shows several bands at (288 nm,

34,722 cm⁻¹), (365 nm, 27397 cm⁻¹) and (720 nm, 13889 cm⁻¹) attributed to an intra-ligand π-π* transition (phenyl ring), a charge transfer band, and ⁴T₁g(F) → ⁴T₂g(F), ⁴T₁g(F) → ⁴T₁g(P) and ⁴T₁g(F) → ⁴A₂g(F) transitions, which indicate an octahedral structure [31] . A low intensity broad band found in the electronic spectra at wavelengths of 410 and 570 nm is attributed to the Cr(III) ion’s d-d transitions. In this complex, two transition bands ⁴T₂g ← ⁴A₂g, and ⁴T₁g ← ⁴A₂g, as well as a third transition ⁴T₁g(P) ← ⁴A₂g(F) are seen. The transitions’ associated energies are 17,544 and 24,390 cm⁻¹, respectively. The complex’s shape appears to be octahedral around the central Cr³⁺ ion, according to the spectrum changes [32] .