Synthesis and characterization of complex of copper(II) with hydantoin

This study aims to find out the way of synthesis, formulas, electronic spectra, magnetic properties, and infrared spectra formed from copper(II) with hydantoin. Copper(II)-hydantoin complex has been synthesized with a mole ratio of 1:2 metal to ligand in methanol. The empirical formula of the complex estimated from the analysis of copper content in the complex was Cu(hydantoin)3SO4(H2O)n (n = 3, 4 or 5). Electrical conductivity showed the ratio of the cation: anion charge in the complex was 1:1. Thermal analysis estimated the existence of four water molecules as both ligand and hydrate. The proposed formula of the complex was [Cu(hydantoin)3(H2O)]SO4·3H2O. The electronic spectra showed an absorption peak at 795 nm. Measurement of magnetic moment with Magnetic Susceptibility Balance (MSB) shows that the complex is paramagnetic with μeff of 1.81 B.M. This indicates that the complex has a square planar structure. IR spectra data showed a shift in the absorption of one of the N-H functional groups on the hydantoin which showed coordination on the central atom.


Introduction
Antimicrobial infection becomes a severe problem in the world [1][2][3].The development of new compounds with promising biological activities is imperative.Therefore, a study of new antimicrobial agents attracts the interest of scientists.In this context, transition metal complexes have been studied as antibacterial due to having potential biological properties and multiple mechanism actions [4][5].Copper is one of the metals that are often used as antimicrobial agents [6].Many copper(II) complexes have been created recently and studied in relation to biological processes [7].The complexation of copper with several ligands forming new complexes often increases their biological activity [8][9].This enhancement was also related to the synergistic effects of the ligands used.
Copper(II) is expected to form complexes with the simplest form of hydantoin.The existence of N and O donor atoms with various positions causes several possible coordinated groups in the central ion.Therefore, the formation of copper(II) ions with hydantoin needs to be studied.In this work, copper(II)hydantoin complexes was synthesized and characterized using several spectroscopic methods.

Synthesis of Copper(II) Complex with Hydantoin
The complex was obtained from the synthesized solution of CuSO4•5H2O (1.748 g; 7 mmol) in methanol (30 mL) added to a hydantoin solution (1.400 g; 14 mmol) in hot methanol (60 mL) and then refluxed for 2 hours.Furthermore, a precipitate formed after the solution was left to stand for 24 hours.After filtering and washing with methanol, the precipitate was overnight desiccated to finish drying.

Physical measurements
A Shimadzu AA-6650 Atomic Absorption Spectrophotometer (AAS) was used to measure the copper content in the Cu(II)-hydantoin complex.A Shimadzu 50 Differential Thermal Analyzer was used to measure the complex's water content and water position.Determination of the molar conductivity of a 10 -3 M solution dissolved in water was determined using a Jenway CE 4071 conductivity meter at 25 o C. Shimadzu Prestige-21 spectrophotometers captured the infrared absorption bands of the functional groups as KBr pellets in the frequency range of 4000-450 cm -1 .A UV-Vis Double Beam Shimadzu PC 1601 spectrophotometer was used to record the UV-Vis absorption areas of complexes and CuCl22H2O solutions.Complexes' magnetic characteristics can be determined with the Auto Sherwood Scientific 10169 Magnetic Susceptibility Balance.

Determination of Copper Content in the Complex
AAS result and copper content in the complex theoretically are shown in Table 1.The copper content in the complex experimentally is 11.750.40.If the copper content of the experimental result is compared with the copper content theoretically, it can be predicted that the complex formula for Cu(II)-hydantoin is Cu(hydantoin)3SO4(H2O)n (n = 3, 4, or 5).

Thermal analysis of Cu(II)-Hydantoin
The curve of the TG/DTA analysis of the Cu(II)-hydantoin complex is shown in Figure 5. ).This reduction in mass marks the release of three and one water molecules, respectively, in the complex (theory: 10.14 and 3.38%).Water molecules in the complex can be bound as both a ligand and a hydrate.At 30-84 o C, lattice water was evaporated.Coordinated water is released at a higher temperature compared to uncoordinated water.Water released at 84-107 o C acted as a ligand [16].Other mass reduction of 21% at a temperature of 107-214 o C indicates the release of one hydantoin in the complex (theory 18.81%).Furthermore, the remaining 63.7% is estimated to be Cu(hydantoin)2SO4.If the complex has one water molecule as the ligand and three water molecules as the crystal water, and then the possible complex formula is [Cu(hydantoin)3H2O]SO4•3H2O.

Molar Conductivity of Cu(II)-Hydantoin
The electrical conductivity of standard solutions and complex solutions in DMSO is shown in Table 2.The table exhibits that the electrical conductivity of Cu(II)-hydantoin near to the electrical conductivity esteem of CuSO4•5H2O and NiSO4•6H2O which has a charge ratio of cation:anion = 1: 1.This shows the position of the anion SO4 2-in the Cu(II)-hydantoin complex as a counter ion so that it isn't facilitated to the Cu(II) central ion.Thus, it strengthens [Cu (hydantoin)3H2O]SO4•3H2O as the proposed complex formula.

Infrared Analysis of Complex Cu(II)-Hydantoin
The IR spectra of the N-H and C=O functional groups of the hydantoin and Cu(II)-hydantoin are shown in Table 3. Table 3 shows that the absorption of the N( 1)-H group in hydantoin (3263 cm -1 ) experienced a shift in the Cu(II)-hydantoin complex (3487 and 3572 cm -1 ).The absorption of the carbonyl group did not experience a significant shift, so the C=O group was not coordinated to the copper ion and only one N-H group was coordinated to the copper ion.Actually, there are two groups of amines, N(1)-H and N(2)-H (Figure 3).Due to the smaller steric effect, the amine group N(1)-H has the highest possibility of being coordinated with the copper ion.Similarly, monodentate hydantoin ligands were coordinated through N(1)-H in the cis-[Pt(C6H8N2O2)2(NH3)2](NO3)2•4H2O complex [17].The magnitude of the transition energy (10 Dq) is 146.12 ± 0.14 kJ mol -1 for CuSO4•5H2O and 150.50 ± 0.49 kJ mol -1 for the complex.Both compounds have nearly the same value of 10 Dq.This shows that the strength of the hydantoin ligand is a weak ligand.The maximum wavelength of the complex at 795 nm is estimated to form square planar geometry.Similarly, square planar complex, Cu(II)-( 5(3)-amino-2-chloro-3(5)-methylpyridine), had a maximum wavelength of 788 nm which then indicates a shift in the d-d electronic absorption band [18].Square planar geometries exhibit the absorption bands corresponding to 2 B → 2 A1g, 2 B1g → 2 B2g and 2 B1g → 2 Eg) [19].Square planar Cu(II) complexes often give a broad absorption, due to Jahn-Teller distortions, generally only one broadband is observed [20].

Magnetic moment of Cu(II)-hydantoin
The result of measuring the effective magnetic moment (μeff) of the Cu(II)-hydantoin complex was 1.81 BM.The value of the magnetic moment indicates that the complex is paramagnetic, having one unpaired electron, and no interaction between metals and metals (Cu-Cu) in complex compounds.If there is an interaction between metals, the electrons will pair up so that they are diamagnetic and have an effective magnetic moment value less than 1.73 BM as in complex (Cu(CH3CuO)2•H2O)2 with an effective magnetic moment value of 1.4 BM each Cu atom [20].The Cu(II)-hydantoin complex has an effective magnetic moment value approaches to that of some copper complexes with a square geometry [22][23].Thus, the complex is also estimated to have square planar geometry.The proposed structure of [Cu(hydantoin)3(H2O)]SO4•3H2O is shown in Figure 5.

Conclusion
Copper(II)-hydantoin complex, [Cu(hydantoin)3(H2O)]SO4•3H2O, has been successfully synthesized with a mole ratio of 1:2 metal to ligand in methanol.The molar conductivity of the complex showed the ratio of the cation: anion charge was 1:1.The electronic spectra appeared as one wide absorption with a maximum wavelength of 795 nm.The complexes are paramagnetic with μeff of 1.81 B.M. The complex was estimated to have a square planar structure.N-H functional groups on the hydantoin showed a coordination bond to the central atom.

Figure 2 .
Figure 2. TG/DTA Curve of Cu(II)-hydantoin.The TG/DTA curve shows an endothermal peaks at 83 o C, 110 o C, 188 o C.There are two steps of mass reduction at 30-84 o C (10.4%) and 84-107 o C (4.9%).This reduction in mass marks the release of three and one water molecules, respectively, in the complex (theory: 10.14 and 3.38%).Water molecules in the complex can be bound as both a ligand and a hydrate.At 30-84 o C, lattice water was evaporated.Coordinated water is released at a higher temperature compared to uncoordinated water.Water released at 84-107 o C acted as a ligand[16].Other mass reduction of 21% at a temperature of 107-214 o C indicates the release of one hydantoin in the complex (theory 18.81%).Furthermore, the remaining 63.7% is estimated to be Cu(hydantoin)2SO4.If the complex has one water molecule as the ligand and three water molecules as the crystal water, and then the possible complex formula is [Cu(hydantoin)3H2O]SO4•3H2O.

Figure 4 .
Figure 4. Electronic spectra of Cu(II) and the complex solution in DMSO.

Figure 5 .
Figure 5. Proposed structure of the complex.

Table 1 .
Copper Contents with Various Possible Theoretically Complex Empirical Formulas and AAS result.

Table 2 .
Electrical Conductivity of Standard Solutions and Complex Solutions in DMSO.

Table 3 .
Infrared spectra of hydantoin (a) and the complex (b).