N-Morpholine-N'-benzoylthiourea as an extractant for Pb(II) and Cu(II) in aqueous media: Crystal structure of bis(N-morpholine-N′-4-benzoylthioureato)lead(II) European Journal of Chemistry 15 (3) (2024) 266-273 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2024 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.15.3.266-273.2550 European Journal of Chemistry View Journal Online View Article Online N-Morpholine-N'-benzoylthiourea as an extractant for Pb(II) and Cu(II) in aqueous media: Crystal structure of bis(N-morpholine-N′-4-benzoylthioureato)lead(II) Kenechukwu Johncross Ifeanyieze 1, Obinna Chibueze Okpareke 1, Uchechukwu Susan Oruma 1, Nkechinyere Nwanneka Ukwueze 1, Ilknur Babahan Bircan 2, and Jonnie Niyi Asegbeloyin 1,* 1 Department of Pure and Industrial Chemistry, Faculty of Physical Sciences, University of Nigeria, Nsukka, Enugu State, 410001, Nigeria 2 Department of Chemistry, Faculty of Arts and Science, Adnan Menderes University, Aydin 09010, Turkey * Corresponding author at: Department of Pure and Industrial Chemistry, Faculty of Physical Sciences, University of Nigeria, Nsukka, Enugu State, 410001, Nigeria. e-mail: niyi.asegbeloyin@unn.edu.ng (J.N. Asegbeloyin). 10.5155/eurjchem.15.3.266-273.2550 Received: 14 March 2024 Received in revised form: 20 May 2024 Accepted: 12 July 2024 Published online: 30 September 2024 Printed: 30 September 2024 The reaction of N-morpholine-N′-benzoylthiourea (L: HBMOR) and lead(II) acetate gave a neutral, stable metal(II) complex of type ML2. The Pb(II) complex crystallized in a monoclinic crystal system with P21/n space group. The complex was further characterized by spectroscopic and microanalytic analyses. The solvent extraction behaviors of Pb(II) and Cu(II) ions were investigated in aqueous media containing HBMOR/CHCl3 as extracting reagents. The solvent extraction of Pb(II) and Cu(II) ions from solutions of varying pH, varying concentrations of mineral acids (HCl, HNO3 and H2SO4), varying concentrations of masking agents (EDTA, KCN and KH[C8H6O4]) and varying concentrations of salting-out agents (NaCl, Na2SO4, KNO3) in chloroform solutions of HBMOR were studied. Pb(II) and Cu(II) ions were quantitatively extracted at pH = 7 in 10 min (HCl = 0.01 M) and pH = 8 in 5 min (H2SO4 = 0.01 M), respectively. The Pb(II) ions were quantitatively extracted with minimal interference from EDTA (0.01 M), KCN (0.50 M), and potassium hydrogen phthalate (1.0 M), while the Cu (II) ions were extracted with EDTA (1.0 M), KCN (1.0 M) and potassium hydrogen phthalate (0.01 M). The order of increasing interference for the extraction of Pb(II) and Cu(II) ions was KCN > potassium hydrogen phthalate > EDTA. Sodium sulfate (0.01 M) in HCl enhanced the extraction of Pb(II) ions, while sodium chloride (0.50 M) in HCl enhanced the extraction of Cu(II) ions. pH0.5 values of 0.67 and 2.70 were obtained for Pb(II) and Cu(II) ions, respectively, indicating that the separation of the two metal ions is favorable with HBMOR. Selectivity Acylthiourea Spectroscopy Metal complex Crystal structure Solvent extraction Cite this: Eur. J. Chem. 2024, 15(3), 266-273 Journal website: www.eurjchem.com 1. Introduction Aqueous effluents from many technological processes often contain Cu(II) and Pb(II) ions. For example, Cu(II) ions are found in effluents from the electroplating and brass manufac- turing industries, printed circuit boards, and copper-based agrochemical run-off from agricultural lands [1]. The presence of these effluents discharged into the environment has serious negative consequences on the ecosystem due to the persistence and nondegradable nature of the metal ions and their tendency to accumulate [2,3]. Lead has been implicated in a number of adverse health effects, including cancer, haematological, neuro- logical, cardiac, renal, and digestive disorders [4-8]. Copper is a valuable metal due to its low toxicity, and it plays an essential biological role in the survival of life [9,10]; it also has antibacterial properties. However, very high concentrations of copper in the human body have been reported to cause adverse health effects such as lung cancer [10], stomach and intestinal cancer, liver, and kidney damage [11,12]. The extraction, detection, and analysis of Pb(II) and Cu(II) ions are still considered necessary since the allowed limits in the aqueous effluent become progressively low. Solvent extraction has continued to be very attractive as a method for extracting and concentrating metal ions from aqueous media because of its ease of handling, high extraction efficiency, and good selectivity. Organic molecules that are often used for the extraction of metal ions from aqueous solutions are expected to have high chelating ability and selectivity. 1-(Acyl/aroyl)-3-(mono- substituted)thioureas and 1-(acyl/aroyl)-3,3-(di-substituted) thioureas, with the general formula R1-C(O)-N(1)H-C(S)- N(3)R2R3 form metal complexes with ease [13-20], several reports are also available on the formation of stable Cu(II) complexes of these group of compounds [14-17,19]. Some 1- (acyl/aroyl)-3-(mono-substituted)thioureas and 1-(acyl/ aroyl)-3,3-(di-substituted)thioureas have been reported in ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.15.3.266-273.2550 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.15.3.266-273.2550 mailto:niyi.asegbeloyin@unn.edu.ng http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.15.3.266-273.2550&domain=pdf&date_stamp=2024-09-30 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 267 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 Figure 1. Molecular structure of PbBMOR with atom numbering scheme, H atoms were omitted for clarity. effective liquid-liquid extraction of Au (III)[21] and potential extractants for Cd(II), Cu(II), Hg(II), Pd(II) and Pt(II) ions [22]. The ease of isolation of the thiourea ligands and the observed attractive metal-dependent colors of the metal complexes have prompted our interest in exploring the use of thiourea derivatives for the extraction and determination of metal ions in aqueous media. Herein, we present the solvent extraction studies of N-morpholine-N′-benzoylthiourea toward Pb(II) and Cu(II) ions in aqueous media. In addition, the crystal structure of bis(N-morpholine-N′-benzoylthioureato)lead (II) is repor- ted. 2. Experimental 2.1. Chemicals and instrumentation All reagents were used without further purification. Benzoylchloride and morpholine were obtained from Sigma- Aldrich Chemicals, USA, while lead(II)acetate trihydrate, copper(II)acetate dihydrate, and potassium thiocyanate were obtained from Fluka Chemicals. Dichloromethane, ethanol, methanol, hydrochloric acid, chloroform, sulphuric acid, nitric acid, sodium chloride, sodium sulphate, potassium hydrogen phthalate, potassium cyanide, EDTA, potassium nitrate, boric acid and sodium hydroxide were obtained from Fine Laboratory Chemicals, China. The 1H NMR and 13C NMR spectrum of bis(N-morpholine- N′-benzoylthioureato)lead (II) was obtained on a Bruker spectrometer; DMSO-d6 was used as a solvent. The mass spectrum was obtained using micrOTOF ESI-MS. Infrared spectra were recorded in the range of 4000-400 cm-1 using KBr pellets on a Perkin Elmer 100 infrared spectrophotometer. The melting point was obtained with a Fisher-John melting point apparatus. UV/vis spectra were obtained using a UV-2500 PC series model spectrophotometer. Metal ion concentrations were measured using an atomic absorption spectrometer 210 VGP. Single crystal X-ray diffraction data of bis(N-morpholine- N′-benzoylthioureato)lead (II) were obtained on an XtaLAB Synergy, Dualflex, Pilatus 200K diffractometer. 2.2. Synthesis of bis(N-morpholine-N′-benzoylthioureato) lead(II) complex N-Morpholine-N′-benzoylthiourea (HBMOR) was synthe- sized as previously reported [23]. Bis(N-morpholine-N′- benzoylthioureato) lead(II) complex (PbBMOR) was synthe- sized as follows: A solution of lead acetate trihydrate (0.95 g, 0.0025 mol) in ethanol (20 mL) was added dropwise to a solution of the ligand (HBMOR) (0.46 g, 0.005 mol) in dichloromethane (30 mL) at room temperature and the resulting mixture was stirred for 60 min, and a light gray solid product was formed. The precipitate was filtered and crystals suitable for X-ray studies were obtained by slow evaporation of a 1:1 dichloromethane:ethanol solution of PbBMOR for a few days. Color: Light gray. M.p.: 169-170 °C. Yield: 78.23 %. FT-IR (KBr, ν, cm-1): 1479 (νC=O), 1349 (νC=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 8.02 (d, J = 7.2 Hz, 4H, Ar-H), 7.46 (t, J = 7.2 Hz, 2H, Ar-H), 7.37 (t, J = 7.5 Hz, 4H, Ar-H), 3.93 (t, J = 4.4 Hz, 8H, O-CH2), 3.55 (t, J = 4.4 Hz, 8H, N-CH2). 13C NMR (101 MHz, DMSO-d6, δ, ppm): 178.0 (quat, N=C-N,S), 169.7 (quat, O=C- N,Ar), 137.7 (Ar-ipso), 130.9 (Ar-para), 129.1 (Ar-ortho), 127.8 (Ar-meta), 66.2 (O-CH2), 47.8 (N-CH2). MS (ESI, m/z (%)): calculated for [M+Na]+ 728.83; found [M+Na]+ 728.816. UV/Vis (CHCl3, λmax, nm): 285 nm. 2.3. X-ray crystallography Crystal of bis(N-morpholine-N′-benzoylthioureato)lead(II) complex suitable for X-ray crystallography were mounted on the glass fibre with epoxy cement for X-ray measurement. The diffraction data was collected at 111.7(4) K on a XtaLAB SynergyDuaflex Pilatus 200K diffractometer. Graphite monochromated Cu-Kα radiation (λ = 1.54184 Å) was used. Data integration, scaling, and empirical absorption corrections were carried out using the CrysAlisPro program package [24]. The structure was solved with the SHELXT [25] structure solution program using intrinsic phasing and refined with the SHELXL [26] refinement package using least squares minimi- zation in Olex2 [27]. 2.4. Extraction studies 2.4.1. Preparation of metal stock and buffer solutions 1000 ppm of Pb(II) stock solution was prepared by dissolving 0.915 g of Pb(CH3COO)2·3H2O in 500 mL of deionized water. 1000 ppm Cu(II) stock solution was prepared by dissolving 1.71 g of Cu(CH3COO)2·2H2O in 500 mL of deionized water. A working solution of 18 μg/mL was prepared from the stock solution, which was used for the extraction process. Clark and Lubs procedures [28] were used to prepare buffer solutions of pH values 1-13 with standard solutions of the following acid/salt systems; hydrochloric acid/potassium chloride, hydrochloric acid/potassium hydrogen phthalate, potassium hydrogen phthalate/sodium hydroxide, and boric acid/sodium hydroxide [29]. They were standardized with Jenway 3510 pH meter. 268 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 Table 1. Crystal data and refinement parameters of PbBMOR. Empirical formula C24H26N4O4PbS2 Formula weight 705.80 Temperature (K) 100.00(10) Crystal system Monoclinic Space group P21/n a, (Å) 13.3922(2) b, (Å) 7.97550(10) c, (Å) 23.3368(3) α (°) 90 β (°) 92.5820(10) γ (°) 90 Volume (Å3) 2490.06(6) Z 4 ρcalc (g/cm3) 1.883 μ (mm-1) 15.072 F(000) 1376.0 Crystal size (mm3) 0.22 × 0.2 × 0.16 Radiation CuKα (λ = 1.54184) 2Θ range for data collection (°) 7.468 to 148.802 Index ranges -16 ≤ h ≤ 16, -9 ≤ k ≤ 9, -28 ≤ l ≤ 29 Reflections collected 29913 Independent reflections 5010 [Rint = 0.0343, Rsigma = 0.0213] Data/restraints/parameters 5010/0/316 Goodness-of-fit on F2 1.251 Final R indexes [I≥2σ (I)] R1 = 0.0248, wR2 = 0.0637 Final R indexes [all data] R1 = 0.0250, wR2 = 0.0638 Largest diff. peak/hole (e.Å-3) 1.28/-1.81 2.4.2. Preparation of acids, salting-out agents, and masking agents The 5 M HCl, H2SO4, and HNO3 solutions were prepared by the dilution method. Solutions of 2 M NaCl, Na2SO4, and KNO3 were prepared by dissolving an appropriate amount of salts (11.89 g of NaCl, 28.409 g of Na2SO4, 20.221 g of KNO3) in 100 mL of deionized water. 1.0 M solutions of KCN and potassium hydrogen phthalate (KH(C8H6O4)) were prepared by dissolving an appropriate amount of salts (3.26 g of KCN and 10.21 g of KH(C8H6O4)) in 50 mL of deionized water. 0.4 M solution of EDTA-disodium salt dehydrate was prepared by dissolving 7.45 g of the salt in 50 mL of deionized water. 2.4.3. Extraction procedure Equal volumes (6 mL) of aqueous phase containing 18 ppm of either Pb(II) or Cu(II) ions and 1% solution of HBMOR in chloroform were shaken mechanically in stoppered extraction bottles at time intervals of 5, 10, 20, 30, 40, 50, 60 and 70 minutes. For each extraction process; after centrifugation, the phases are separated and the concentration of solutes in aqueous raffinate was determined by atomic absorption spectroscopy (AAS). Equal volumes (6 mL) of aqueous phase containing 18 ppm of either Pb(II) or Cu(II) ions and the relevant buffer solution (adjusted to the required pH using either dilute hydrochloric acid or ammonia solution) and 1% HBMOR solution in chloroform were mechanically shaken in stoppered extraction bottles at the appropriate time deter- mined for each metal. For each extraction process; after centrifugation, the phases are separated and the concentration of solutes in aqueous raffinate was determined using AAS. These processes were repeated for equal volumes (6 mL) of aqueous phase containing 18 ppm of Pb(II) or Cu(II) ions and the appropriate acids, masking agents and salting-out agents and 1% solution of HBMOR in chloroform. 3. Results and discussion 3.1. Physical properties and spectroscopic analysis of PbBMOR PbBMOR was isolated by recrystallization using suitable solvents. It is a light gray and non-hygroscopic, and an air stable solid. It is insoluble in water and diethyl ether, slightly soluble in ethanol and methanol, but soluble in acetone, chloroform, dichloromethane, DMF and DMSO. It has a low molar conduc- tivity value of 21 μS/cm indicating that it is non-electrolyte. In the 1H NMR spectra of the metal complex, there are characteristic peaks in the aromatic regions. Multiplets at δ 7.37-8.02 ppm were assigned to the aromatic protons of the phenyl moiety, however there were no peaks that are charac- teristic of NH protons because the ligand was deprotonated on complexation [30-33]. The δ 3.55-3.93 ppm bands have been assigned to the protons of the morpholine moiety. The 13C NMR spectra are also consistent with the structural information provided by the single crystal X-ray diffraction studies. The C=O group was observed at δ 169.7 ppm and the peak for C=N was observed at δ 178.0 ppm, while the O-CH2 and N-CH2 carbons were observed at δ 66.2 and 47.8, respectively. Chemical shifts of aromatic carbons were observed in the range δ 127.8-137.7. In the IR spectra, there are no characteristic vibration peaks of the N-H stretching [30-33]. The peak at 1479 cm-1 has been assigned to the C=O stretching vibration. The UV/vis spectra of PbBMOR were recorded in acetone. The absorption band (nm) observed at 285 was assigned to the n → π* electronic transition of the C=S bond [16]. 3.2. Structural analysis of PbBMOR The complex PbBMOR was synthesized and isolated at room temperature, showing a favorable energy interaction between Lewis acid Pb(II) and the thiourea derivative with a combination of hard O and soft S donors, consistent with Pearson's hard-soft acid-base principle [34]. PbBMOR crystal- lized in a monoclinic crystal system with P21/n space group. The molecular structure and unit cell packing of PbBMOR are presented in Figures 1 and 2, respectively. Crystallographic refinement parameters are presented in Table 1, while selected bond angles and bond length are shown in Table 2. Lead is in a +2 oxidation state and is coordinated to the S and O atoms of the BMOR with a four-coordination number. However, the Pb(II) complex was neither square planar nor tetrahedral geometry, which is commonly observed for p-block transition metals [31,32]. Pb is a p-block element in the periodic table, Pb(II) has an electronic configuration of [Xe]4f145d106s2 , the coordination geometry is affected by the lone pair of Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 269 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 Table 2. Bond lengths (Å) and bond angles (°) of PbBMOR. Atom Atom Bond lengths (Å) Atom Atom Atom Bond angles (°) Pb S1 2.680(1) S2 Pb1 S1 96.24(3) Pb S2 2.679(1) S2 Pb1 O2 76.07(7) Pb O1 2.441(3) S2 Pb1 O1 85.35(7) Pb O2 2.452(3) S1 Pb1 O2 76.90(7) S1 C1 1.747(4) S1 Pb1 O1 79.53(7) S2 C13 1.747(4) O2 Pb1 O1 148.0(1) O1 C2 1.254(5) Pb1 S2 C13 98.2(1) O2 C14 1.265(5) Pb1 S1 C1 103.6(1) N1 C1 1.329(5) Pb1 O2 C14 132.8(3) N1 C2 1.333(5) Pb1 O1 C2 127.4(3) N3 C9 1.471(5) S1 C1 N1 124.0(3) N3 C12 1.470(5) S1 C1 N3 118.2(3) N3 C1 1.345(5) S2 C13 N2 122.9(3) N2 C14 1.324(5) S2 C13 N4 119.8(3) N2 C13 1.345(5) N2 C13 N4 116.9(3) N4 C13 1.329(5) C1 N1 C2 124.8(3) N4 C24 1.470(5) C9 N3 C12 112.0(3) O3 C10 1.433(5) C12 N3 C1 121.5(3) O3 C11 1.414(5) C13 N4 C24 123.1(3) O4 C23 1.427(5) C24 N4 C21 111.7(3) O4 C22 1.428(5) N2 C14 C15 116.7(3) C11 C12 1.517(6) C20 C15 C16 119.6(4) C5 C6 1.386(7) N3 C9 C10 108.0(3) Figure 2. Molecular packing arrangement of PbBMOR in the unit cell, showing intramolecular and intermolecular contacts. electrons on the 6s orbital. Thus, Pb(II) in PbBMOR is in a square pyramidal geometry distorted mainly by the repulsion between the 6s2 electrons and the Pb-S and Pb-O bonding electrons as clearly predicted by the valence shell electron pair repulsion theory. As a result of this distortion, the bond angles of S2-Pb1-O2, S2-Pb1-O1, S1-Pb1-O2, and S1-Pb1-O1 were 76.07, 85.35, 76.90 and 79.53°, respectively, which deviated from the 90° angle expected for an ideal square pyramidal geometry. Because of the large orbital size of sulfur compared to that of oxygen, the Pb-S bonding electrons experienced more repulsion than the Pb-O bonding electrons. This led to the shrinking of the S2-Pb-S1 bond angle from 180° to 96.24°, whereas the O2-Pb-O1 bond angle was 148.0°. The Pb(II) complex adopted a trans geometry with the S atoms, morpholine, and phenyl rings on alternate sides to minimize repulsion. Acylthioureas are known to form metal complexes by deprotonation of the N-H group of the thiourea moiety [16]. This hypothesis is supported by the elongated C1-S1 bond of 1.747 Å and the C14-O2 bond of 1.265 Å compared to the average length of the C-S and C-O bond in acyl thioureas of 1.67 and 1.23 Å [16]. The elongation of the C-S and C-O bonds indicated that the deprotonation of the N-H protons was followed by the delocalization of electrons around the OC-N-CS moiety prior to coordination to Pb(II) as demonstrated in an earlier report [13], thus metal complexation and potential extraction will be favored above neutral pH. The C-N bonds in the acylthiourea moiety were C1-N3, C1-N1, C2-N1, C13-N2, and C13-N4 of 1.345, 1.333, 1.324, 1.345 and 1.329 Å, respectively. The Pb-S bond length in PbBMOR of ~1.680 Å is much shorter than that reported for Pb(II) coordinated to thiourea with Pb-S bond length of 2.65-3.23 Å [35]. This might be due to the stronger interaction between Pb(II) and negatively charged S in PbBMOR compared to (NH2)2C=S coordinated to Pb(II) through the lone pair of electrons on the sulfur. The four-molecule aggregate packing structure of the molecule in Figure 2 does not show any conventional hydrogen bond, but some phenyl-C-H···O (morpholine) intermolecular contacts link the four-aggregate structure in the three- dimensional space and are stabilized by some intramolecular phenyl-C-H···N (morpholine) and phenyl-C-H···S (thiol) contacts. 3.3. Extraction studies 3.3.1. Equilibration time The equilibration time for efficient extraction of Pb(II) and Cu(II) ions was examined in the presence of 1% HBMOR in chloroform. The percentage yield of the extracted ions at different time intervals were determined. For the extraction of Pb(II) ions, the optimum extraction was obtained at an equilibration time of 10 min, while for the extraction of Cu(II) ions, the optimum extraction was obtained at an equilibration time of 5 min. All subsequent extraction processes were conducted in the appropriate time for each metal ion. 3.3.2. Effect of pH on the extraction of Pb(II) and Cu(II) The extraction of Pb(II) and Cu(II) ions with HBMOR was studied as a function of pH in the range of 1-13. 270 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 Figure 3. The effect of pH on the extraction of Pb (II) and Cu(II) ions. Figure 4. The effect of mineral acids on the extraction of Pb(II) and Cu(II) ions. Figure 3 shows the profile of the effect of pH on the extraction of Pb(II) and Cu(II) ions. Between pH = 1 and 4, the percentage of Pb(II) ions extracted ranged from 55.13-73.23%. However, the percentage extraction increased at pH = 5, reaching a peak at pH = 7 where a quantitative extraction of 77.37% was observed. The low extraction between pH = 1 and 4 is likely due to incomplete dissociation of the ligand leading to poor formation of the extractable metal complex [36]. Quantitative extraction at pH = 7 is likely due to the formation of a complex completely extractable into the organic phase. Furthermore, between pH = 8 and 13, a decrease in the amount of Pb(II) ions extracted was observed. The low extraction in this pH range could be attributed to the ease of hydrolysis of the metal ion, and the masking effect of the buffer contributes to decreasing metal extraction [37]. The extraction of Cu(II) ions with HBMOR was also studied as a function of pH in the range 1-13. There was quantitative extraction at pH = 8 with 83.10% extraction. The low extraction at pH = 1-5 may be due to competition between proton and Cu(II) ions for the ligand coordination sites. A pH0.5 for Pb was observed at 0.67 while that of Cu was observed at 2.70. The difference in the pH0.5 value of 2.03 indicated the possibility of separating Pb and Cu in aqueous medium [38]. 3.3.3. Effect of mineral acids on the extraction of Pb(II) and Cu(II) The variation of the acid concentration on the percentage of extracted Pb (II) and Cu(II) ions is shown in Figure 4. The result shows that acid concentrations of 0.01-0.10 M support the formation of extractable complex of Pb(II). In addition, it shows that there is a decrease in the amount of Pb(II) extracted as the acidity increases. The % extraction was up to 73.33 in 0.01 M HNO3. Low extraction was observed in HCl as compared to that in any other acid. The acid concentrations of 0.01-0.10 M also support the formation of extractable complex of Cu(II) ions. At an acid concentration of 0.01 M H2SO4, 73.37% of Cu(II) ions were extracted. It also shows that the percentage extraction decreases with an increase in acidity. Low extraction was also observed in HCl than in any other acid; however, the extraction efficiency is better than in 0.01 M HNO3. 3.3.4. Effect of salting-out agents on the extraction of Pb(II) and Cu(II) The effect of salting-out agents on the extraction of Pb(II) and Cu(II) ions at varying concentrations of salting-out agents was studied. Figure 5 shows the profile of the effect of the salting-out agents on the extraction of Pb(II) and Cu(II) ions. The extraction of Pb(II) ions with HBMOR in chloroform was studied between 0.01 and 1.00 M concentration of salting-out agents (NaCl, Na2SO4 and KNO3) and different acid concent- rations. The results show that HCl/NaSO4 showed an improve- ment in the percentage extraction of 41.87 to 87.83%. This is attributable to the formation of extractable species. The percentage extracted decreased with an increase in the concentration of the salting-out agents. In HCl/KNO3, a relati- vely small percentage of extraction was observed (41.87- 51.53%). Generally, it was observed that the amount of metal ions extracted was higher at a lower concentration of the salting-out agent. Therefore, 0.01 M Na2SO4 and NaCl are good salting-out agents for the extraction of Pb(II) ions. Extraction of Cu(II) ions with 1% HBMOR was studied at different concentrations of salting-out agents (NaCl, Na2SO4 and KNO3) at an acid concentration where partial extraction was obtained. 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 M et al e xt ra ct io n ra te (% ) pH PbBMOR CuBMOR 40 45 50 55 60 65 70 75 80 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 M et al e xt ra ct io n ra te (% ) Concentration (M) PbBMOR - HCl CuBMOR - HCl PbBMOR - H2SO4 CuBMOR - H2SO4 PbBMOR - HNO3 CuBMOR - HNO3 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 271 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 Figure 5. The effect of salting-out agents on the extraction of Pb(II) and Cu(II) ions. Figure 6. The effect of masking agents on the extraction of Pb(II) and Cu(II) ions with HBMOR. The results show that the percentage extraction increased from 47.27 to 72.67% in 0.01 M HCl with the addition of 0.5 M NaCl. This may be due to the decrease in the activity of water, consequent on the hydration of the added salt, enabling the formation of extractable species. The amount extracted decreased with an increase in the concentration of Na2SO4, and the reverse was the case in other salts. In HCl/ Na2SO4, there was an enhancement in percentage extraction from 47.27 to 70.07%. This may likely be due to the increase in the dielectric constant of the aqueous medium, which enhances the extractability of the metal complex into the organic phase [36]. Analysis of the results revealed that 0.50 M NaCl and 0.10 M Na2SO4 are good salting-out agents for the extraction of Cu(II) ions. 3.3.5. Effect of masking agents on the extraction of Pb(II) and Cu(II) The effect of masking agents on the degree of extraction was investigated at an acid concentration for quantitative extraction of the metal ions. Figure 6 shows the effects of masking agents on the extraction of Pb(II) and Cu(II) ions. EDTA, potassium cyanide and potassium hydrogen phthalate greatly contributed to decrease in the % extraction of Pb(II) ions in 0.01 M acid concentration. 0.5 M KCN reduced the % extraction of Pb(II) to 31.67. The % extraction of Pb(II) was decreased to 43.57 at 1.0 M potassium hydrogen phthalate. Potassium cyanide and potassium hydrogen phthalate greatly decreased the % extraction of Cu(II) ions. 1.0 M potassium cyanide reduced the % extraction of Cu(II) to 26.23, while 0.01 M potassium cyanide reduced the % extraction to 52.77. For potassium hydrogen phthalate, at 0.01 M, the % extraction of Cu(II) was reduced to 32.03, and at 0.5 M, it was reduced to 46.67. EDTA 1 M, on the other hand, reduced the %extraction of Cu(II) to 38.9. The high reduction in extraction as observed in both metals is likely to be the result of the formation of non-extractable complex species formed in the aqueous phase [36]. 4. Conclusions The crystal structure of the bis(N-morpholine-N′-benzoyl thioureato)lead(II) complex has been reported. The complex crystallized in a monoclinic crystal system with P21/n space group, as an ML2 type metal complex. Expectedly, the four- coordinate complex has a square pyramidal geometry distorted mainly by the repulsion between the 6s2 electrons and the Pb-S and Pb-O bonding electrons, considering the fact that the lead belongs to the p block in the periodic table, with an electronic configuration of [Xe]4f145d106s2 and the coordination geometry is mainly affected by the lone pair of electrons in the 6s orbital. Extraction studies at a pH range 1-13, indicated that maximum extraction of Pb(II) ions using 1% HBMOR/CHCl3 was attained at pH = 7 in 10 minutes. Furthermore, quantitative extraction was observed at acid concentrations of 0.01 to 2.00 M. HNO3 and HCl quantitatively extracted Pb(II) ions at lower concentrations, with an observed decrease in percentage extraction as the acid concentration increased. Na2SO4 proved to be a good salting-out agent at 0.01 M for the extraction of Pb(II) ions. The interference of potassium cyanide was high at 0.5 M and low for EDTA at 1.0 M. The Cu(II) ion was extracted using 1% HBMOR/CHCl3 under a pH range of 1-13 and maximum extraction was observed at pH = 8 under 5 minutes. Quantitative extraction of Cu(II) ions was observed at 0.01 M to 2.0 M acid concentrations. H2SO4 and HCl quantitatively extracted Cu(II) ions at lower 0 10 20 30 40 50 60 70 80 90 100 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 M et al e xt ra ct io n ra te (% ) Concentration (M) PbBMOR - NaCl CuBMOR - NaCl PbBMOR - Na2SO4 CuBMOR - Na2SO4 PbBMOR - KNO3 CuBMOR - KNO3 0 10 20 30 40 50 60 70 80 90 100 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 M et al e xt ra ct io n ra te (% ) Concentration (M) PbBMOR - EDTA CuBMOR - EDTA PbBMOR - KCN CuBMOR - KCN PbBMOR - KH(C8H6O4) CuBMOR - KH(C8H6O4) 272 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 concentrations, with an observed decrease in percentage extraction as the acid concentration increased. Na2SO4 also proved to be a good salting-out agent at 0.1 M for the extraction of Cu(II) ions. Potassium hydrogen phthalate had a high masking action on the extraction of Cu(II), but EDTA and potassium cyanide had a moderate effect. 1% HBMOR/CHCl3 has been shown to be a promising extractant for the extraction of Pb(II) ions at pH = 7, 0.01 M HCl, and 0.01 M Na2SO4. The optimal extraction conditions for the extraction of Cu(II) ions with 1% HBMOR/CHCl3 are pH = 8, 0.01 M H2SO4, and 0.01 M Na2SO4. The pH0.5 values of 0.67 and 2.70 were obtained for Pb(II) and Cu(II) ions, respectively, indicating that the two ions can be effectively extracted in aqueous media. Acknowledgements The authors are thankful to Tania Groutso, and the School of Chemical Sciences, University of Auckland, New Zealand, for the crystal diffraction data of PbBMOR. Many thanks to the National Centre for Energy Research and Development, University of Nigeria, Nsukka, for infrastructure support. Supporting information CCDC-2102001 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, or by e-mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Jonnie Niyi Asegbeloyin, Kenechukwu Johncross Ifeanyieze; Methodology: Kenechukwu Johncross Ifeanyieze, Obinna Chibueze Okpareke; Software: Kenechukwu Johncross Ifeanyieze, Obinna Chibueze Okpareke; Validation: Obinna Chibueze Okpareke, Kenechukwu Johncross Ifeanyieze; Formal Analysis: Kenechukwu Johncross Ifeanyieze, Obinna Chibueze Okpareke; Investigation: Kenechukwu Johncross Ifeanyieze, Jonnie Niyi Asegbeloyin; Resources: Kenechukwu Johncross Ifeanyieze, Nkechinyere Nwanneka Ukwueze; Data Curation: Kenechukwu Johncross Ifeanyieze, Uchechukwu Susan Oruma; Writing - Original Draft: Kenechukwu Johncross Ifeanyieze, Jonnie Niyi Asegbeloyin; Writing - Review and Editing: Jonnie Niyi Asegbeloyin, Ilknur Babahan Bircan, Uchechukwu Susan Oruma; Visualization: Uchechukwu Susan Oruma, Nkechinyere Nwanneka Ukwueze; Supervision: Jonnie Niyi Asegbeloyin, Ilknur Babahan Bircan; Project Administration: Jonnie Niyi Asegbeloyin, Ilknur Babahan Bircan. ORCID and Email Kenechukwu Johncross Ifeanyieze kenechukwu.ifeanyieze.pg00135@unn.edu.ng https://orcid.org/0000-0002-3801-872X Obinna Chibueze Okpareke obinna.okpareke@unn.edu.ng https://orcid.org/0000-0003-0815-8198 Uchechukwu Susan Oruma susan.oruma@unn.edu.ng https://orcid.org/0000-0002-9226-2512 Nkechinyere Nwanneka Ukwueze nkechinyere.ukwueze@unn.edu.ng https://orcid.org/0000-0003-1707-0438 Ilknur Babahan Bircan ibabahan@adu.edu.tr https://orcid.org/0000-0002-1336-671X Jonnie Niyi Asegbeloyin niyi.asegbeloyin@unn.edu.ng https://orcid.org/0000-0002-5710-7613 References [1]. Boujelben, N.; Bouzid, J.; Elouear, Z. Adsorption of nickel and copper onto natural iron oxide-coated sand from aqueous solutions: Study in single and binary systems. J. Hazard. Mater. 2009, 163, 376–382. [2]. Khan, M. A.; Ahmad, I.; Rahman, I. U. Effect of environmental pollution on heavy metals content of Withania somnifera. J. Chin. Chem. Soc. 2007, 54, 339–343. [3]. Ahmaruzzaman, M. Industrial wastes as low-cost potential adsorbents for the treatment of wastewater laden with heavy metals. Adv. Colloid Interface Sci. 2011, 166, 36–59. [4]. Mudgal, V.; Madaan, N.; Mudgal, A.; Singh, R. B.; Mishra, S. Effect of toxic metals on human health. Open Nutraceuticals J. 2010, 3, 94–99. [5]. Tandon, S. K.; Chatterjee, M.; Bhargava, A.; Shukla, V.; Bihari, V. Lead poisoning in Indian silver refiners. Sci. Total Environ. 2001, 281, 177– 182. [6]. Pizent, A.; Čolak, B.; Kljaković, Z.; Telišman, S. Prostate-Specific Antigen (PSA) in serum in Relation to Blood Lead Concentration and Alcohol Consumption in men. Arh. Hig. Rada Toksikol. 2009, 60, 69– 78. [7]. Lindbohm, M. L.; Sallmen, M.; Anttila, A.; Taskinen, H.; Hemminki, K. Paternal occupational lead exposure and spontaneous abortion. Scand. J. Work Environ. Health 1991, 17, 95–103. [8]. Tang, S.; Yu, X.; Wu, C. Comparison of the levels of five heavy metals in human urine and sweat after strenuous exercise by ICP-MS. J. Appl. Math. Phys. 2016, 04, 183–188. [9]. Rai, P. K.; Lee, S. S.; Zhang, M.; Tsang, Y. F.; Kim, K.-H. Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environ. Int. 2019, 125, 365–385. [10]. Yu, B.; Zhang, Y.; Shukla, A.; Shukla, S. S.; Dorris, K. L. The removal of heavy metal from aqueous solutions by sawdust adsorption — removal of copper. J. Hazard. Mater. 2000, 80, 33–42. [11]. Wuana, R. A.; Okieimen, F. E. Heavy metals in contaminated soils: A review of sources, chemistry, risks and best available strategies for remediation. ISRN Ecol. 2011, 2011, 1–20. [12]. Dixit, R.; Wasiullah; Malaviya, D.; Pandiyan, K.; Singh, U.; Sahu, A.; Shukla, R.; Singh, B.; Rai, J.; Sharma, P.; Lade, H.; Paul, D. Bioremediation of heavy metals from soil and aquatic environment: An overview of principles and criteria of fundamental processes. Sustainability 2015, 7, 2189–2212. [13]. Saeed, A.; Flörke, U.; Erben, M. F. A review on the chemistry, coordination, structure and biological properties of 1-(acyl/aroyl)-3- (substituted) thioureas. J. Sulphur Chem. 2014, 35, 318–355. [14]. Binzet, G.; Gumus, I.; Dogen, A.; Flörke, U.; Kulcu, N.; Arslan, H. Nickel(II) and copper(II) complexes of N,N-dialkyl-N′-3- chlorobenzoylthiourea: Synthesis, characterization, crystal structures, Hirshfeld surfaces and antimicrobial activity. J. Mol. Struct. 2018, 1161, 519–529. [15]. Binzet, G.; Kavak, G.; Külcü, N.; Özbey, S.; Flörke, U.; Arslan, H. Synthesis and characterization of novel thiourea derivatives and their nickel and copper complexes. J. Chem. 2013, 2013, 1–9. [16]. Oyeka, E. E.; Asegbeloyin, J. N.; Babahan, I.; Eboma, B.; Okpareke, O.; Lane, J.; Ibezim, A.; Bıyık, H. H.; Törün, B.; Izuogu, D. C. Synthesis, crystal structure, computational analysis and biological properties of 1-(4-chlorobenzoyl)-3-[2-(2-2-[3-(4-chlorobenzoyl)-thioureido]- ethoxyethoxy)ethyl]-thiourea and its Ni(II) and Cu(II) complexes. J. Mol. Struct. 2018, 1168, 153–164. [17]. Oyeka, E. E.; Babahan, I.; Eboma, B.; Ifeanyieze, K. J.; Okpareke, O. C.; Coban, E. P.; Özmen, A.; Coban, B.; Aksel, M.; Özdemir, N.; Groutso, T. V.; Ayogu, J. I.; Yildiz, U.; Dinçer Bilgin, M.; Halil Biyik, H.; Schrage, B. R.; Ziegler, C. J.; Asegbeloyin, J. N. Biologically active acylthioureas and their Ni(II) and Cu(II) Complexes: Structural, spectroscopic, anti- proliferative, nucleolytic and antimicrobial studies. Inorganica Chim. Acta 2021, 528, 120590. [18]. Ghazal, K.; Shoaib, S.; Khan, M.; Khan, S.; Rauf, M. K.; Khan, N.; Badshah, A.; Tahir, M. N.; Ali, I.; Rehman, A.-U.- Synthesis, characterization, X- ray diffraction study, in-vitro cytotoxicity, antibacterial and antifungal activities of nickel(II) and copper(II) complexes with acyl thiourea ligand. J. Mol. Struct. 2019, 1177, 124–130. [19]. Arslan, H.; Külcü, N.; Flörke, U. Synthesis and characterization of copper(II), nickel(II) and cobalt(II) complexes with novel thiourea derivatives. Transit. Met. Chem. 2003, 28, 816–819. [20]. Binzet, G.; Flörke, U.; Külcü, N.; Arslan, H. Crystal and molecular structure of bis(4-bromo-N-(diethylcarbamothioyl)benzamido) nickel(II) complex. Eur. J. Chem. 2012, 3, 37–39. [21]. Luckay, R. C.; Mebrahtu, F.; Esterhuysen, C.; Koch, K. R. Extraction and transport of gold(III) using some acyl(aroyl)thiourea ligands and a crystal structure of one of the complexes. Inorg. Chem. Commun. 2010, 13, 468–470. [22]. Koch, K. R. New chemistry with old ligands: N-alkyl- and N,N-dialkyl- N′-acyl(aroyl)thioureas in co-ordination, analytical and process chemistry of the platinum group metals. Coord. Chem. Rev. 2001, 216– 217, 473–488. http://www.ccdc.cam.ac.uk/%20data_request/cif http://www.ccdc.cam.ac.uk/%20data_request/cif mailto:data_request@ccdc.cam.ac.uk https://orcid.org/0000-0002-3801-872X mailto:obinna.okpareke@unn.edu.ng https://orcid.org/0000-0003-0815-8198 mailto:susan.oruma@unn.edu.ng https://orcid.org/0000-0002-9226-2512 mailto:nkechinyere.ukwueze@unn.edu.ng https://orcid.org/0000-0003-1707-0438 mailto:ibabahan@adu.edu.tr https://orcid.org/0000-0002-1336-671X mailto:niyi.asegbeloyin@unn.edu.ng https://orcid.org/0000-0002-5710-7613 Ifeanyieze et al. / European Journal of Chemistry 15 (3) (2024) 266-273 273 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.3.266-273.2550 [23]. Cunha, S.; Macedo, F. C., Jr; Costa, G. A. N.; Rodrigues, M. T., Jr; Verde, R. B. V.; de Souza Neta, L. C.; Vencato, I.; Lariucci, C.; Sá, F. P. Antimicrobial activity and structural study of disubstituted thiourea derivatives. Monatsh. Chem. 2007, 138, 511–516. [24]. Agilent (2014). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England. [25]. Sheldrick, G. M. SHELXT– Integrated space-group and crystal- structure determination. Acta Crystallogr. A Found. Adv. 2015, 71, 3– 8. [26]. Sheldrick, G. M. Crystal structure refinement withSHELXL. Acta Crystallogr. C Struct. Chem. 2015, 71, 3–8. [27]. Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339–341. [28]. Bower, V. E.; Bates, R. G. pH values of the Clark and Lubs buffer solutions at 25 C. J. Res. Natl. Bur. Stand. (1934) 1955, 55, 197. [29]. Kolthoff, I. M.; Sandell, E. B.; Mecham, E. J.; Eastern, S. P. Quantitative chemical analysis; Macmillian: London, 1969. [30]. Binzet, G.; Arslan, H.; Flörke, U.; Külcü, N.; Duran, N. Synthesis, characterization and antimicrobial activities of transition metal complexes of N,N -dialkyl- N′ -(2-chlorobenzoyl)thiourea derivatives. J. Coord. Chem. 2006, 59, 1395–1406. [31]. Keskin, E.; Solmaz, U.; Binzet, G.; Gumus, I.; Arslan, H. Synthesis, characterization and crystal structure of platinum(II) complexes with thiourea derivative ligands. Eur. J. Chem. 2018, 9, 360–368. [32]. Gumus, I.; Solmaz, U.; Celik, O.; Binzet, G.; Balcı, G. K.; Arslan, H. Synthesis, characterization and crystal structure of cis-bis[4-fluoro-N- (diethylcarbamothioyl)benzamido-κ2O,S]platinum(II). Eur. J. Chem. 2015, 6, 237–241. [33]. Plutín, A. M.; Ramos, R.; Mocelo, R.; Alvarez, A.; Castellano, E. E.; Cominetti, M. R.; Oliveira, K. M.; Donizeth de Oliveira, T.; Silva, T. E. M.; S. Correa, R.; Batista, A. A. Antitumor activity of Pd(II) complexes with N,S or O,S coordination modes of acylthiourea ligands. Polyhedron 2020, 184, 114543. [34]. Housecroft, C. E.; Sharpe, A. G. Inorganic Chemistry; Pearson Education: Philadelphia, PA, 2008. [35]. Schwade, V. D.; Kirsten, L.; Hagenbach, A.; Schulz Lang, E.; Abram, U. Indium(III), lead(II), gold(I) and copper(II) complexes with isophthaloylbis(thiourea) ligands. Polyhedron 2013, 55, 155–161. [36]. Ukoha, P. O.; Ekere, N. R.; Opara, I. J. Studies on extraction of Co(II) ions from aqueous solution using 1,5-dimethyl-2 phenyl-4-[(e)-(2,3,4- trihydroxylphenyl)diazenyl]-1,2-dihydro-3h-pyrazol-3-one. Journal of Chemical Society of Nigeria 2017, 40, 12–18. www.journals.chemsociety.org.ng/index.php/jcsn/article/view/4 [37]. Opara, I. J.; Ukoha, P. O.; Onunze, E. O. Extractive spectrophotometric determination of Fe(III) and Co(II) from steel sample using azo ligand 1,5-dimethyl-2-phenyl-4-[(E)-(2, 3, 4-trihydroxyl phenyl)diazenyl]- 1,2-dihydro-3H-pyrazole-3-one. Int. J. Chem. Mater. Environ. Res. 2018, 5(1), 148-154. [38]. Sinha, M.; Sahu, S.; Meshram, P.; Pandey, B.; Kumar, V. Solvent extraction and separation of copper and zinc from a pickling solution. Int. J. Met. Eng. 2012, 1, 28–34. Copyright © 2024 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at https://www.eurjchem.com/index.php/eurjchem/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). http://www.journals.chemsociety.org.ng/index.php/jcsn/article/view/4 https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Experimental 2.1. Chemicals and instrumentation 2.2. Synthesis of bis(N-morpholine-N′-benzoylthioureato) lead(II) complex 2.3. X-ray crystallography 2.4. Extraction studies 2.4.1. Preparation of metal stock and buffer solutions 2.4.2. Preparation of acids, salting-out agents, and masking agents 2.4.3. Extraction procedure 3. Results and discussion 3.1. Physical properties and spectroscopic analysis of PbBMOR 3.2. Structural analysis of PbBMOR 3.3. Extraction studies 3.3.1. Equilibration time 3.3.2. Effect of pH on the extraction of Pb(II) and Cu(II) 3.3.3. Effect of mineral acids on the extraction of Pb(II) and Cu(II) 3.3.4. Effect of salting-out agents on the extraction of Pb(II) and Cu(II) 3.3.5. Effect of masking agents on the extraction of Pb(II) and Cu(II) 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: