INTRODUCTION:

The Pyrimidine’s are aromatic heterocyclic compounds that resemble benzene and pyridine; they contain nitrogen atoms located at positions 1 and 3 within a six-membered ring structure. The heterocyclic ring of pyrimidine is significant due to its role as a crucial category of both natural and synthetic substances, many of which demonstrate valuable biological effects and potential uses in clinical settings¹. Substituted purines and pyrimidines are found extensively in various living organisms. In medicinal chemistry, pyrimidines hold a crucial role due to their wide array of biological functions.

Additionally, their fused heterocyclic variants, such as pyrimido-pyrimidines and their derivatives, have garnered attention as promising bioactive compounds.

Pyrimidine compounds have been noted to exhibit a variety of medicinal effects, including properties that help prevent seizures², antihypertensive activity³, analgesic⁴, anti-depressive⁵, antipyretic⁶, anti-inflammatory⁷, Chemotherapeutic agents⁸, antiviral⁹, anti HIV¹⁰, antimicrobial¹¹ and anti-tumor activities. Pyrimidine nucleus is an integral part of biomolecules like DNA and RNA and plays an important role in several biological processes and also has considerable pharmacological uses such as antibiotics, antibacterial¹², cardiovascular as well as agrochemical and veterinary product.

By considering all these importance we are synthesized fused pyrimido pyrimidine and its derivatives with simple path. In the presence of the pyrimidine base thymine, cytosine, and uracil, which are vital for therapeutic uses. The review of existing literature showed that the compound containing the pyrimidine structure demonstrates a broad spectrum of pharmacological effects. Furthermore, different derivatives of pyrimidine have been discovered to have antibacterial¹³, antifungal¹⁴, antioxidant¹⁵, antihistaminic¹⁶, antiallergy¹⁷, antiviral¹⁸, anticancer properties¹⁹, and also function as calcium channel blockers.

The Heterocyclic compounds are abundant in the environment and hold significant importance for life due to their structural components found in numerous natural substances like vitamins, hormones, and antibiotics. Consequently, they attract substantial interest in the creation of biologically active molecules and the field of advanced organic chemistry²⁰. Within heterocyclic compounds, those that contain nitrogen are a crucial category in medicinal chemistry and have made valuable contributions to society through both biological and industrial uses²¹. An unsaturated six-membered ring featuring nitrogen is referred to as an azine or pyridine; when there are two nitrogen atoms, it is classified as diazine, with nitrogen at the 1,2-position known as pyridine, at the 1,3-position as pyrimidine, and at the 1,4-position as pyrazine. Nevertheless, this review aims to explore and conduct an in-depth investigation into the significance of the pyrimidine group of antimicrobial agents, as well as the clinical and in vitro applications of pyrimidine derivatives, to facilitate the development of more effective and potent antimicrobial agents²².

A literature of existing literature demonstrates that there has been no research conducted on Schiff base transition metal compounds made from 2,6 diamino 4-hydroxy pyrimidine and P-Methoxysalicylaldehyde. In this report, we present the creation of a bidentate Schiff base that results from the reaction between 2,6 diamino 4-hydroxy pyrimidine and P-Methoxysalicylaldehyde (Figure 5). Solid complexes of these ligands with Ni(II), Cu(II), and Mn(II) have been synthesized and examined through various physicochemical techniques.

MATERIALS AND METHODS:

Reagents and solvents:

The 2,6 diamino 4-hydroxy pyrimidine (Aldrich sigma), P-Methoxysalicylaldehyde, metal nitrate of AR grade was used for synthesis of ligand and metal complex.

Synthesis of ligand:

The ligand was synthesized by altering the existing techniques that have been documented^23-25. The Schiff base ligand has been synthesized by refluxing a mixture of 0.01 mol (1.2015g) of P-Methoxysalicylaldehyde and 0.01 mol (1.2710 g) of 2, 6 diamino 4-hydroxy pyrimidine in 50 ml super dry ethanol refluxed for about 4h. The Schiff base that was created was allowed to cool to ambient temperature and then gathered through filtration, after which it underwent recrystallization in ethanol and was subsequently dried under vacuum using anhydrous calcium chloride. (Yield:79%).

Synthesis of metal complexes:

In a heated solution of ethanol measuring (25ml) containing 2 moles of the ligand, (25ml) of metal nitrate with a concentration of 1 mole was incorporated while continually stirring. The pH level of the resulting mixture was modified to fall between 7-8 by the addition of a 10% solution of alcoholic ammonia, and then the mixture was kept at boiling for approximately 3 hours. The solid metal complex that formed was filtered out while still warm, rinsed with hot ethanol, and subsequently dried using calcium chloride in vacuum desiccators. (Yield: 73%)

Physical Measurement:

IR spectra were recorded on FTIR(ATR)-BRUKER -TENSOR37 spectrometer using KBr pellets in the range of 4000-400 cm^-1. 1HNMR Varian mercury 300MHZ spectra of ligand were measured in CDCl₃ using TMS as internal standard. X-RD were recorded on BRUKER D8 Advance. TGA- DTA were recorded on Shimadzu. The carbon, hydrogen and nitrogen contents were determined on Elementar model vario EL-III. The UV-visible spectra of the complexes were recorded on model Jasco V-530 UV-Vis spectrometer. Molar conductance of complexes was measured on Elico CM 180 conductivity meter using 10^-4 M solution in DMSO. Magnetic susceptibility measurements of the metal chelates were done on a Guoy balance at room temperature using Hg[Co(SCN)₄] as a calibrant.

RESULTS AND DISCUSSION:

Schiff bases of 2,6 diamino 4-hydroxy pyrimidine and its complexes have a variety of applications including biological, clinical and analytical. The coordinating possibility of 2,6 diamino 4-hydroxy pyrimidine has been improved by condensing with a variety of carbonyl compounds. An attempt has been made to synthesize Schiff bases from 2,6-diamino-4-hydroxy pyrimidine with P-Methoxysalicylaldehyde. Physical characteristics, micro analytical, and molar conductance data of ligand and metal complexes are given in (Table 1 and 2). The analytical data of complexes revels 2:1 molar ratio (ligand: metal) and corresponds well with the general formula [ML(H₂O)₂] [where M= Cu(II), Ni(II), And Mn(II)]. The magnetic susceptibilities of Cu(II), Ni(II), And Mn(II) complexes at room temperature are consistent with high spin octahedral structure with two water molecules coordinated to metal ion. The existence of two aligned water molecules was verified through TGA-DTA analysis. The metal chelate solutions in DMSO show low conductance and supports their non-electrolyte nature. (Table 1)

Molar Conductivity Measurements:

The metal (II) complexes were dissolved in DMSO and the molar conductivity of 10^-4M of their solution at room temperature was measured. The lower conductance values of the complexes support their non-electrolytic nature of the compounds.

Table 1. Physical characterization, analytical and molar conductance data of compounds

Compound Molecular formula	Molecular Weight	M.P. Decomposition Temp. ⁰C	Colour	Molar Conduc. Mho. Cm²mol^-1
L	260.25	96	Yellow	---
Cu-L	620.09	>300	Dark Yellow	13.22
Ni-L	615.23	>300	Yellow	14.25
Mn-L	611.48	>300	Yellow	12.30

Table 2. Elemental Analysis of Cu(II), Ni(II) and Mn(II) Complex:

Compound	% Found (Calculated)
Compound	C	H	N	M
L	55.36(55.20)	4.65 (4.58)	21.53 (21.41)	----
Cu-L	46.31 (46.48)	4.49 (4.55)	17.95 (18.08)	10.12 (10.25)
Ni-L	46.67 (46.85)	4.51 (4.59)	18.10 (18.22)	9.41 (9.54)
Mn-L	46.96 (47.14)	4.54 (4.66)	18.21 (18.33)	8.85 (9.98)

¹H-NMR spectra of ligand:

The ¹H-NMR. Spectra of free ligand at room temperature show the following signals. 2.35 δ (s, 3H, Methyl hydrogen bonded to pyrimidine ring), 2.35 δ (s, 3H, Methyl hydrogen bonded to phenyl ring), 5.47 δ (s, 1H, Phenolic (OH) hydrogen of pyrimidine ring), 6.77 δ(s, 1H, Hydrogen bonded to pyrimidine ring ), 7.84 δ (s, 1H, hydrogen attached to azomethine carbon), 7.2-7.42 δ (D, 4H, Aromatic Ha, Hb, hydrogen atoms of phenyl ring)

IR Spectra:

The IR spectra of the complexes are compared with that of the ligand to determine the changes that might have taken place during the complexation. The bands at 3363, 1678, 1516, 1309, and 1186 cm^-1assignable to OH (intramolecular hydrogen bonded), C=C(aromatic), C=N (azomethine), C-N (aryl azomethine) and C-O (phenolic) stretching modes respectively^26-28. The lack of a weak broad band in the range of 3200-3400 cm^-1 in the spectra of the metal complexes indicates that the intramolecular hydrogen-bonded OH group undergoes deprotonation upon complex formation, leading to the coordination of phenolic oxygen with the metal ion. This observation is further corroborated by a decrease in the υ C-O (phenolic)²⁹ compared to the free ligand. Upon complexation, the (C=N)³⁰ band shifts to a lower wavenumber compared to the free ligand, indicating that the nitrogen from the azomethine group is bonded to the metal ion. There is also a decrease in the C-N band wavenumber when compared to the free ligand. The IR spectra of the metal chelates reveal new bands in the ranges of 500-600 and 400-500 cm^-1 that can be attributed to M-O and M-N³¹ vibrations, respectively. The IR spectra of Cu (II) show a prominent band within the range of 3050-3600 cm^-1, suggesting the existence of coordinated water within these metal complexes. The coordination of water is further validated by the detection of a non-ligand band in the 830-840 cm^-1 region, which corresponds to the rocking motion of water. The coordination of water is also confirmed by TGA/DTA results pertaining to these complexes. Therefore, it can be concluded that coordination occurs through the phenolic oxygen and azomethine nitrogen of the ligand molecule.

Thermogravimetric analysis:

The dynamic TGA with the percentage mass loss at different steps have been recorded. The simultaneous TGA/DTA analysis of Cu(II) was studied from ambient temperature to 1000 0C in nitrogen atmosphere using α-Al₂O₃ as reference. An examination of the thermogram for the complexes demonstrated that Cu(II) complexes with ligand L (Figure 1) exhibit a two-step breakdown process. The initial weight loss 5.61 %, in between temp. 50-1950C could be correlated with the loss of two molecules of lattice water (calcd 6.50 %). The anhydrous compound does not remain stable at higher temperature, it undergoes rapid decomposition in the range 195-570°C, and with 79.45 % mass loss corresponds to decomposition of the complex (calcd. 79.14 %) in second step. The decomposition is completed leading to the formation of stable residue of metal oxide CuO obs. 11.23 % (calcd. 14.35 %). kinetic and thermodynamic viz the energy of activation (Ea), frequency factor (Z), entropy change (-ΔS) and free energy change (ΔG) for the non-isothermal decomposition of complexes have been determined by employing Horowitz-Metzger method³² values are presented in Table 3. The derived values for the activation energy of the complexes are comparatively low, suggesting that the metal ion has an autocatalytic influence on the thermal breakdown of the complex. The negative activation entropy value implies that the activated complexes exhibited greater order compared to the slower reaction. This increased order might be attributed to the polarization of bonds during the activated phase, which could take place through transitions involving charge transfer³³.

Table 3: The kinetic and thermodynamic parameters for decomposition of metal complexes

Complex

Step

Decomp. Temp. (⁰C)

(kJmole^-1)

(S^-1)

(JK^-1mole^-1)

(kJmole^-1)

Correlation coefficient

Cu-L

374

1.4

12.80

2.26 ´ 10⁴

-167.87

24.84

0.943

Ni-L

377

1.5

11.98

2.23 ´ 10⁴

-168.91

24.76

0.933


Fig. 1: TGA-DTA Curve of Cu(II) Complex of Ligand L	Fig. 2: TGA-DTA Curve of Ni(II) Complex of Ligand L

	Wavelength	Absorption
	788	0.225
	742	0.206
	724	0.226
	502	0.239
	483	0.236
	402	0.233
	392	0.235
	362	0.23
	345	0.096

Fig. 3: Electronic Absorption Spectra of Mn(II) Complex of Ligand L

Magnetic measurements and electronic absorption spectra:

The electronic spectral studies as shown below Fig. 3 of metal complexes of Mn (II) with Schiff bases were carried out in DMSO solution. The absorption spectrum of the Mn(II) complex shows bands at 13812 cm^-1and 30030 cm^-1 are assigned to ²B_1g→ 2A_1g and charge transfer respectively in an octahedral field³⁴. The Ni (II) complexes were diamagnetic in nature.

Powder x-ray diffraction:

The x-ray diffractogram of Cu (II) complexes of L8 was scanned in the range 20-80° at wavelength 1.543 Å (Figure 4). The diffractogram and associated data depict the 2θ value for each peak, relative intensity and inter-planar spacing (d-values). The diffractogram of Cu(II) complex of L had fifteen reflections with maxima at 2θ = 12.89° corresponding to d value 6.86Å. The x-ray diffraction pattern of these complexes with respect to major peaks of relative intensity greater than 10% has been indexed by using computer programmed³⁵. The above indexing method also yields Miller indices (hkl), unit cell parameters and unit cell volume. The unit cell of Co(II) complex of L yielded values of lattice constants, a= 9.76 Å, b=10.24 Å, c = 27.24 Å and unit cell volume V=2722.43096 Å³. In alignment with the specified cell parameters, the requirements such as a = b = c and α = β = γ = 90, necessary for a sample to be classified as Monoclinic, were examined and deemed acceptable. Thus, it can be deduced that the Cu(II) complex exhibits an Orthorhombic crystal structure. Consequently, it can also be inferred that the Cu(II) complex of L possesses a monoclinic crystal formation. The density values of the complexes were measured using the specific gravity technique and found to be 0.8968 g/cm³ for the Cu(II) complexes³¹. Using the obtained density values, the molecular weight of the complexes, Avogadro's number, and the volume of the unit cell were calculated. The number of molecules in each unit cell was determined using the equation ρ = nM/NV, and it was found for the Cu(II) complexes. Utilizing these data, theoretical density was calculated, resulting in a value of 0.8858 g/cm³ for the corresponding complexes. A comparison between the experimental and theoretical densities indicates a strong correspondence within the experimental error margins³³.

Fig. 4: X-ray Diffractogram of Cu (II) complex of L

ANTIBACTERIAL ACTIVITY:

The antifungal and antibacterial properties of ligand and metal complexes were evaluated in vitro against fungi such as Aspergillus niger, Penicillium chrysogenum, Fusarium moneliforme, Aspergillus flavus, and bacteria including E. coli, B. subtilis, S. aureus, and Bacillus subtilis using the paper disc diffusion method^36-39. The substances were assessed at concentrations of 1% and 2% in DMSO and were compared to established antibiotics such as Griseofulvin and Penicillin. The results demonstrate that the inhibitory effects of metal chelates are greater than those of the ligand, aligning well with earlier studies concerning the comparative effectiveness of the free ligand and its complexes⁴⁰.

Table 4: Antifungal activity of ligands

Test Compound	Antifungal Growth
	*Aspergillus niger*		*Penicillium chrysogenum*		*Fusarium moneliforme*		*Aspergillus flavus*
	1%	2%	1%	2%	1%	2%	1%	2%
L	-ve	-ve	-ve	-ve	-ve	-ve	-ve	-ve
Cu-L	-ve	-ve	-ve	-ve	-ve	-ve	-ve	+ve
Ni-L	-ve	-ve	-ve	-ve	-ve	-ve	-ve	-ve
Mn-L	-ve	-ve	RG	-ve	-ve	-ve	-ve	-ve
+ve control	+ve	+ve	+ve	+ve	+ve	+ve	+ve	+ve
-ve control (Griseofulvin)	-ve	-ve	-ve	-ve	-ve	-ve	-ve	-ve

Ligand & Metal: +ve – Growth (Antifungal Activity absent)

-ve - Growth (Antifungal Activity present)

RG - Reduced Growth (More than 50% reduction in growth observed)

Table 5: Antibacterial activity of ligands and their metal complexes

Test Compound	Diameter of inhibition zone (mm)
	*E. coli*		*Salmonella typhi*		*Staphylococcu saureus*		*Bacillus subtlis*
	1%	2%	1%	2%	1%	2%	1%	2%
L	13mm	18mm	14mm	19mm	19mm	23mm	18mm	21mm
Cu-L	14mm	17mm	12mm	16mm	17mm	24mm	16mm	19mm
Ni-L	13mm	16mm	18mm	20mm	20mm	26mm	19mm	22mm
Mn-L	18mm	21mm	19mm	23mm	21mm	24mm	19mm	25mm
DMSO	-ve	-ve	-ve	-ve	-ve	-ve	-ve	-ve
Penicillin	16mm	17mm	19mm	19mm	32mm	32mm	24mm	24mm

Ligand & Metal: - ve - No Antibacterial Activity

Zone of inhibition - --mm

Fig. 5: Structure of Schiff Base Ligand L

Fig. 6: The proposed Structure of the Metal complexes. [When M= Cu(II), Ni(II), And Mn(II)]

CONCLUSION:

Considering the prior conversation, we have suggested an octahedral arrangement for the Ni(II), Cu(II), and Mn(II) complexes. Based on the previously examined physical and chemical properties along with spectral data, it can be inferred that the ligand functions as a dibasic, NO bidentate, and coordinating through phenolic oxygen and imino nitrogen, as demonstrated in Fig.6. These complexes exhibit biological activity and possess improved antimicrobial effects compared to the unbound ligand. The thermal analysis indicates that the complexes are thermally stable. According to the X-ray analysis, the crystal system for the Ni(II), Cu(II), and Mn(II) complexes is orthorhombic.

ACKNOWLEDGEMENTS:

The writers express their gratitude to the sophisticated analytical instrument facility (SAIF) and the sophisticated test and instrument center (STIC) in Kochi for their support in elemental analysis (CHN). Furthermore, we appreciate the Department of Chemistry at Pune University for offering IR, NMR spectroscopy, and TGA-DTA services, as well as the Department of Physics at Pune University for granting access to X-RD facilities. We also extend our thanks to the Department of Microbiology at N. S. B. College in Nanded for their assistance with antibacterial and antifungal activities.

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Received on 27.09.2025 Revised on 22.11.2025

Accepted on 30.12.2025 Published on 27.05.2026

Available online from May 30, 2026

Asian J. Research Chem.2026; 19(3):221-227.

DOI: 10.52711/0974-4150.2026.00034

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