Synthesis, characterization, and antimicrobial activity of Cu(II) and Zn(II) complexes with N,N-bis(4-methoxybenzylidene)ethylenediamine or N-(4-methoxybenzylidene)ethylenediamine Schiff base European Journal of Chemistry 16 (2) (2025) 169-177 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2025 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.16.2.169-177.2651 European Journal of Chemistry View Journal Online View Article Online Synthesis, characterization, and antimicrobial activity of Cu(II) and Zn(II) complexes with N,N-bis(4-methoxybenzylidene)ethylenediamine or N-(4-methoxybenzylidene)ethylenediamine Schiff base Adrienne Ndiolene 1, Tidiane Diop 1,*, Mouhamadou Sembene Boye 2, Bruno Faure 3, Aminata Diasse-Sarr 1 and Michel Giorgi 4 1 Département de Chimie, Université Cheikh Anta Diop de Dakar, BP 5005 Fan-Dakar, Sénégal 2 Département de Physique Chimie, Faculté des Sciences et Technologies de l’Education et de la Formation, Université Cheikh Anta Diop, Boulevard Habib, Bourguiba, BP 5036 Fann-Dakar, Sénégal 3 ISM2 - Institut des Sciences Moléculaires de Marseille, Campus Saint Jérôme Av. escadrille Normandie Niemen BP 531 13397 Marseille Cedex 20, France 4 AMU SPEC - Spectropôle - Aix Marseille Université, Campus Scientifique de Saint Jérôme Service 511 13397 Marseille Cedex 20, France * Corresponding author at: Département de Chimie, Université Cheikh Anta Diop de Dakar, BP 5005 Fan-Dakar, Sénégal. e-mail: tidiane3.diop@ucad.edu.sn (T. Diop). 10.5155/eurjchem.16.2.169-177.2651 Received: 22 January 2025 Received in revised form: 26 March 2025 Accepted: 2 May 2025 Published online: 30 June 2025 Printed: 30 June 2025 Seven mononuclear complexes were synthesized by mixing N,N'-bis(4-methoxy benzaldehyde)ethylenediamine (L) or N-(4-methoxybenzylidene)ethylenediamine (L1) and copper or zinc salts. These compounds were characterized by IR, 1H NMR, UV-vis, fluorescence spectroscopy, molar conductimetric, and elemental (CHN) analysis techniques. The crystal structures of the zinc complexes were determined by single crystal X-ray diffraction studies. Crystal data for C18H20I2N2O2Zn: Monoclinic, space group P21/c (no. 14), a = 10.45670(10) Å, b = 13.28610(10) Å, c = 15.43490(10) Å, β = 96.4300(10)°, V = 2130.86(3) Å3, Z = 4, Dcalc = 1.919 g/cm3, 46801 reflections measured (8.51° ≤ 2Θ ≤ 145.92°), 4231 unique (Rint = 0.0565, Rsigma = 0.0185) which were used in all calculations. Crystal data for C18H20Br2N2O2Zn: Monoclinic, space group P21/c (no. 14), a = 10.30071(17) Å, b = 13.00839(18) Å, c = 15.0084(2) Å, β = 97.3057(14) °, V = 1994.74(5) Å3, Z = 4, Dcalc = 1.737 g/cm3, 103282 reflections measured (4.158° ≤ 2Θ ≤ 59.492°), 5360 unique (Rint = 0.0394, Rsigma = 0.0161) which were used in all calculations. Crystal structures show a distorted tetrahedral geometry around the zinc metal. The ligand is bidentate chelating with imine nitrogen atoms. Fluorescence spectroscopy shows a reduction in the fluorescence intensity of the complexes relative to the ligand. This reduction is due to the presence of metal-coordinated halides. The in vitro antimicrobial activities of the ligand and complexes were elaborated by screening them against Gram(+) bacteria (Streptococcus pyogenes), Gram(-) bacteria (Pseudomonas aeruginosa), and a fungus (Candida albicans). All compounds showed weak activity against the tested bacterial and fungal strains. Synthesis Schiff base Characterization Crystal structure Antimicrobial activity Cu(II) and Zn(II) complexes Cite this: Eur. J. Chem. 2025, 16(2), 169-177 Journal website: www.eurjchem.com 1. Introduction Schiff bases derived from primary amines are excellent chelating agents for metal ions via azomethine nitrogen (>C=N-) [1-4]. Metal complexes with Schiff bases have antibacterial, antifungal, antitumor, and antianalgesic activities [5-9]. Macrocyclic derivatives of Schiff bases have countless ultimate functions, such as photosynthesis, oxygen transport in mammals, and other respiratory patterns [10]. A considerable number of Schiff base complexes have been used as biological models to understand the structure of biomolecules and biological processes [11]. These compounds are active against a wide range of organisms such as Candida albicans, Escherichia coli, Staphylococcus aureus, Bacillus polymxa, Trychophyton gypseum, Mycobacteria, Erysiphe graminis, and Plasmopara viticola [12-16]. In recent years, zinc compounds with a stable d10 electronic configuration have received considerable attention in the fields of inorganic chemistry, biochemistry, and environmental chemistry. Approximately ten zinc-based enzymes are known, in which zinc is generally tetrahedral and is linked to donor nitrogen atoms [17,18]. In this work, Cu(II) and Zn(II) complexes with symmetric Schiff bases of ethylenediamine and benzaldehyde (4-methoxybenzaldehyde) were synthesized to explore their antimicrobial activity. 2. Experimental 2.1. Instrumentation The elemental analyses for carbon, hydrogen, and nitrogen of the metal complexes were carried out using a Flash EA 1112 Elementary Analyzer. Electronic spectra were recorded with a CARY 50 BIO UV-Vis spectrometer from 200 to 800 nm. The 1H and 13C NMR spectra were recorded on a Bruker AV2 (400 MHz) spectrometer using DMSO-d6 as a solvent. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.16.2.169-177.2651 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.16.2.169-177.2651 mailto:tidiane3.diop@ucad.edu.sn http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.16.2.169-177.2651&domain=pdf&date_stamp=2025-06-30 170 Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 1. Crystal data and structure refinement for the zinc complexes. Compound A6 A7 Empirical formula C18H20I2N2O2Zn C18H20Br2N2O2Zn Formula weight (g/mol) 615.53 521.55 Temperature (K) 295 295 Crystal system Monoclinic Monoclinic Space group P21/c P21/c a (Å) 10.45670(10) 10.30071(17) b (Å) 13.28610(10) 13.00839(18) c (Å) 15.43490(10) 15.0084(2) α (°) 90 90 β (°) 96.4300(10) 97.3057(14) γ (°) 90 90 Volume (Å3) 2130.86(3) 1994.74(5) Z 4 4 ρcalc (g/cm3) 1.919 1.737 μ (mm-1) 24.455 5.251 F(000) 1176.0 1032.0 Crystal size (mm3) 0.2 × 0.08 × 0.08 0.26 × 0.26 × 0.08 Radiation Cu Kα (λ = 1.54184) Mo Kα (λ = 0.71073) 2Θ range for data collection (°) 8.51 to 145.92 4.158 to 59.492 Index ranges -12 ≤ h ≤ 12, -16 ≤ k ≤ 16, -19 ≤ l ≤ 19 -13 ≤ h ≤ 14, -17 ≤ k ≤ 17, -20 ≤ l ≤ 20 Reflections collected 46801 103282 Independent reflections 4231 [Rint = 0.0565, Rsigma = 0.0185] 5360 [Rint = 0.0394, Rsigma = 0.0161] Data/restraints/parameters 4231/0/228 5360/0/228 Goodness-of-fit on F2 1.045 1.023 Final R indexes [I≥2σ (I)] R1 = 0.0359, wR2 = 0.0980 R1 = 0.0285, wR2 = 0.0589 Final R indexes [all data] R1 = 0.0374, wR2 = 0.1000 R1 = 0.0462, wR2 = 0.0650 Largest diff. peak/hole (e.Å-3) 1.42/-0.65 0.69/-0.55 O O H2N NH2 N N O O 2 2H2OEtOH Scheme 1. Synthesis of the ligand N,N’-bis(4-methoxybenzaldehyde)ethylenediamine. The IR spectra were recorded in the region 4000-200 cm-1 by using a FT-IR Bruker Tensor 27 spectrometer and fluorescence spectra were recorded on a Horiba Jobin Ivon Fluoromax-4 spectrofluorometer. X-ray diffraction measurements of Zn(II) complexes were performed using a SuperNova Dual AtlasS2 diffractometer with graphite- monochromated CuKα radiation (λ = 1.54184 Å) for complex A6 and MoKα radiation (λ = 0.71073 Å) for complex A7. The structures were solved by direct methods with SHELXT [19] using Olex2 [20]. structure solution program using intrinsic phasing and refined with the SHELXL [19] refinement package using least squares minimization. The experimental parameters related to single-crystal X-ray analysis of complexes are given in Table 1. 2.2. Synthesis 2.2.1. Synthesis of the Schiff base (L) The Schiff base ligand (L) was synthesized by mixing solutions of ethylenediamine (30 mmol; 1.8 g) and para- anisaldehyde (60 mmol; 8.169 g) in 30 mL of ethanol (Scheme 1). The yellow mixture obtained, stirring, is brought to reflux for 5 hours at a temperature of 80 °C, then filtered and placed under slow evaporation. After a few days, a mass of 6.345 g of crystals is obtained with a yield of 80.9% [21]. 2.2.2. General procedure for the synthesis of the complexes The metal complexes were synthesized by reacting a methanolic solution of ligand L (296.36 mg, 1 mmol) with an equimolar amount of the corresponding metal salt in a 1:1 molar ratio. The reaction mixture was stirred for 3 hours at room temperature. For the zinc chloride complex (A4), 0.296 g (1 mmol) of L was dissolved in 96% ethanol, followed by the addition of 1 mmol of zinc chloride. The mixture was refluxed at 80 °C for 21 hours. After stirring for two hours, the precipitates were filtered, washed, and dried, while the filtrates were subjected to slow evaporation (Table 2). The melting temperatures of the synthesized complexes were determined as follows: [Cu(L)(ClO4)(CH3OH)]·ClO4 (A1) melted at 184.0 °C, [Cu(L)(CH3COO)2]· 3H2O (A2) at 189.7 °C, and [Cu(L1)Cl2]·H2O (A3) at 216.0 °C. The complexes [Zn(L)Cl2] (A5), [Zn(L)I2] (A6) and [Zn(L)Br2] (A7) exhibited melting temperatures of 235.4 °C, 207.2 °C, and 235.9 °C, respectively. The powders of A4, A5, A6, and A7 were recrystallized from methanol, and the resulting crystals were analyzed by X-ray diffraction [22]. N-(4- Methoxybenzylidene)ethylenediamine ligand (L) was obtained in situ by hydrolysis of N,N-bis(4-methoxybenzylidene) ethylenediamine ligand (L1). 2.3. Antimicrobial activity The antibacterial activity of the ligand and its metal complexes was determined against two wild-type bacterial strains responsible for certain serious infectious diseases: a Gram-negative strain (Pseudomonas aeruginosa) and a Gram- positive strain (Streptococcus pyogenes). The fungus used for antifungal activity is Candida albican. The solutions of the ligand and their complexes were prepared in DMSO at concentrations 100, 50, 30 and 25 mM. The evaluation of the preliminary antibacterial and antifungal effect of the Schiff base ligand and these metal derivatives is carried out by the method of serial dilution in microplates according to the recommendations of the protocol described in a previous study [23]. Bacteria (Pseudomonas aeruginosa and Streptococcus pyogenes) and the fungus (Candida albicans DSM) were exposed to increasing concentrations of complexes and ligand with a final volume of each well equal to 150 μL. Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 171 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 2. Main characteristics of complexes derived from L *. Complex Metal salt Color and nature Yield (%) Found (Calcd.) % C H N [Cu(L)(ClO4)(CH3OH)]·ClO4 (A1) Copper(II) perchlorate Blue (Powder) 79.42 38.55(38.62) 4.12(4.09) 3.77(4.74) [Cu(L)(CH3COO)2]· 3H2O (A2) Copper(II)acetate Blue (Powder) 68.51 48.20(49.66) 5.62(6.06) 6.61(5.27) [Cu(L1)Cl2]·H2O (A3) Copper(II) chloride Blue (Powder) 36.44 36.53(36.32) 4.59(4.88) 8.97(8.47) [Zn(L1)Cl2] (A4) Zinc chloride Yellow (Crystal) 61.00 - - - [Zn(L)Cl2] (A5) Zinc chloride Yellow (Crystal) 38.34 49.87(49.97) 4.67(4.66) 6.49(6.47) [Zn(L)I2] (A6) Zinc iodide Yellow (Crystal) 56.30 34.90(35.12) 3.26(3.27) 4.48(4.55) [Zn(L)Br2] (A7) Zinc bromide Yellow (Crystal) 65.49 41.26(41.45) 3.85(3.87) 5.36(5.37) * L = N,N'-bis(4-Methoxybenzaldehyde)ethylenediamine, L1 = N-(4-Methoxybenzylidene)ethylenediamine. Table 3. IR spectral bands (cm-1) of the Schiff base and its metal complexes. Compound ν(NH2) ν(OH) ν(COO-) ν(C=N) ν(ClO4-) ν(M-N) L - - - 1639 - - [Cu(L)(ClO4)(CH3OH)]·ClO4 (A1) - 3199 - 1678 1075, 1016, 619 515 [Cu(L)(CH3COO)2]·3H2O (A2) - 3298 1553, 1416 1683 - 514 [Cu(L1)Cl2]·H2O (A3) 3261 - - 1637 - 524 [Zn(L1)Cl2] (A4) 3281 - - 1628 - 473 [Zn(L)Cl2] (A5) - - - 1635 - 464 [Zn(L)I2] (A6) - - - 1631 - 421 [Zn(L)Br2] (A7) - - - 1634 - 422 The experiments were carried out in independent triplicate (n = 3). The volume of DMSO corresponding to the highest dose of the compounds tested (final concentration of 1, 2, 3.2, 3.8% DMSO) was used as a negative control and was found to be inactive, showing that the latter is not involved in the results obtained from the compounds. The plates were incubated for 24 hours at a temperature of 37 °C before reading for the antibacterial test and at 35 °C for the antifungal tests. At the end of the incubation, the optical density (OD) 600 nm was measured using a microplate reader (Synergy Mx, Biotek) [24]. The antibacterial activity was evaluated by determination of the minimum inhibitory concentration (MIC) values of the compounds. The MIC is defined as the lowest concentration inhibiting the visible growth of the organism. 2.4. Kinetic of the hydrolysis of phosphodiesters of complexes The solutions used, the substrate bis(4-nitrophenyle) phosphate (50 mm, BNPP), potassium chloride (KCl, 0.25 M) and a borate buffer solution (0.1 M) at pH = 8.5 are prepared in distilled water. Due to the low solubility in water, the complexes studied are prepared in a mixture of water and methanol in the proportions (1/10, v/v, 100 mΜ). The study of the catalytic activity of phosphodiesters was carried out using sterile 96 well polypropylene microplates filled with a micropipette according to the protocol described by Selmeczi et al. [25]. In a typical experiment, freshly prepared solutions of complexes (50 μL), a KCl (50 μL) solution are injected to maintain the ionic strength and the medium buffered by 50 μL of a borate buffer solution. 50 μL of the substrate is added to this mixture; the transparent solution turns yellow after adding the substrate. The final volume of each well is 200 μL. BNPP hydrolysis of the studied complexes gives p-nitrophenol (PNP) and p-nitrophenyl phosphate (PNPP). The progress of the reaction was monitored by the absorbance change visible at 400 nm due to the release of the 4-nitrophenolate anion for 2 h at a temperature of 27 °C. 3. Results and discussion 3.1. Characterization of the Cu(II) and Zn(II) complexes The IR spectra show the appearance of characteristic bands of the ligand and those of the the molecules of water, acetate, and perchlorate groups (Table 3). Among the bands of the L ligand, we are particularly interested in those related to the ν(C=N) vibrations of the azomethine group. This absorption band has undergone a shift compared to that of the ligand, which is located at 1639 cm-1. This shift occurs at high frequencies for the perchlorate and copper acetate complexes, respectively, at 1669 and 1683 cm-1 [26-29], and towards low frequencies for the zinc and copper chloride complexes, respectively, at 1635, 1631, 1634, and 1629 cm-1 [30-33]. The shift of this band and the presence of weak bands towards low frequencies confirm the coordination of the nitrogen atom N of the imine group with the different metals. In the infrared spectrum of the A1 complex, in addition to the L ligand bands, absorption bands are observed at 1075, 1013 and 619 cm-1 attributed to vibrations of the bound perchlorate ion. We also note the ν(OH) absorption band of methanol at 3197 cm-1. On the A2 complex spectrum, the νas(COO) and νs(COO) bands are located at 1597 and 1416 cm-1, respectively [34,35]. The difference between νas(COO) and νs(COO) equal to 181 cm-1 proves that acetate is monodentate [36]. Band at 3296 cm-1 is attributed to ν(OH) water molecules [37,38]. In the spectra of the A3 and A4 complexes, the two fine bands at 3261 and 3281 cm-1 are attributed to ν(NH2) of the amine group, respectively [39,40]. The appearance of this band with that of the azomethine group and the absence of the ν band (C=O) show a partial hydrolysis of the L ligand. The conductivity measurements (A1, A2 and A3) of the complexes were carried out in a millimolar solution (1×10-3 M) of DMSO. Two measurements are taken within a fortnight interval to monitor the stability of the complexes in DMSO. The molar conductance values of the copper complexes were measured both when freshly prepared and after 15 days. For [Cu(L)(ClO4)(CH3OH)]·ClO4 (A1), the molar conductance was initially 54 μS/cm and slightly decreased to 51 μS/cm after 15 days. In the case of [Cu(L)(CH3COO)2]·3H2O (A2), the value remained constant at 17 μS/cm over the same period. Interestingly, [Cu(L1)Cl2]·H2O (A3) exhibited a slight increase in molar conductance, from 24 to 27 μS/cm after 15 days. These conductimetric results of fresh solutions indicate that the A2 and A3 complexes are neutral electrolytes, which indicates the coordination of acetates and chloride atoms with copper [41]. For complex A1, the value of the conductivity obtained is 54 μS/cm. These data are in agreement with an electrolyte type 1:1 and indicate that one of the perchlorate ions is free and plays a role of counter-ion [42]. These results complete the infrared data of the complexes. After 15 days, a slight shift in the conductimetric data of these complexes is observed, which shows the stability of the complexes in DMSO. The analysis of the 1H NMR spectra shows the presence of five signals present in the ligand. Singlets at δ 3.7 and 3.8 ppm that incorporate 6 and 4 protons, respectively, are assigned to protons of the methoxyl (CH3-) and ethyl (CH2-CH2) groups. The doublets at δ 7.66-6.98 ppm or δ 7.65 and 6.98 ppm are attributed to the protons of the aromatic nucleus. 172 Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 4. UV-vis spectra of the Schiff base ligand and its Cu(II) and Zn(II) complex. Compound Absorption (nm) Band assignments L 215, 270 π-π*, n-π* [Cu(L)(ClO4)(CH3OH)]·ClO4 223, 275 π-π*, n-π* 402 LMCT 620 d–d [Cu(L)(CH3COO)2]·3H2O 220, 270 π-π*, n-π* 660 d–d [Cu(L1)Cl2]·H2O 220, 285 π-π*, n-π* 360 LMCT 690 d–d [Zn(L)Cl2] 216, 2764 π-π*, n-π* [Zn(L)I2] 221, 279 π-π*, n-π* [Zn(L)Br2] 220, 275 π-π*, n-π* (a) (b) Figure 1. Molecular structure of the zinc (a) iodide and (b) bromide complexes. The singlet attributed to imine protons at δ 8.19 ppm for the ligand and at δ 8.25 ppm (δ 8.24 ppm) for the complexes confirms the participation of imine nitrogen in the zinc coordination [43,44]. The electronic spectra of the complexes are recorded in freshly prepared ethanol solution at different concentrations, 1×10-5 M for low absorbances (200-400 nm) and 1×10-3 M for high absorbances (500-800 nm) (Table 4). These spectra show absorption bands between 200 and 300 nm attributed to the π → π* absorptions of the aromatic nucleus and n → π* transitions of the imine group contained in the ligand [45]. These transition bands undergo a bathochromic effect compared to those of the ligand because of the presence of different acid, basic or halide auxochromes (OH, NH2, Cl, I, and Br) in the complexes. The bands at 402 and 360 nm on the spectra of the A1 and A3 complexes are attributed to ligand-metal charge transfer (LMCT) [46]. In addition to these bands, the d–d transitions of the copper complexes are also observed at 620 nm (A1), 660 nm (A2) and 690 nm (A3). These bands correspond to the transition bands of an octahedral or square-plane copper complex [47]. For complexes A5 A6 and A7 the d - d transitions of zinc cannot be observed because the d subshell is full (d10). 3.2. Crystallographic study of zinc complexes The crystallographic study of the zinc iodide and bromide complexes shows that they crystallize in the monoclinic system of space group P21/c. The lattice parameters are as follows: a = 10.4567(10) Å; b = 13.28610(10) Å; c = 15.4349(10) Å; β = 96.4300(10) for the A6 complex and a = 10.3007(17) Å; b = 13.0071(18) Å; c = 15.0084(2) Å; β = 97.3057(2) ° for the A7 complex. The unit cell of each complex consists of four molecules (Z = 4). The crystal structure of the complexes shows that zinc is tetracoordinated with the two nitrogen atoms of the azomethine group contained in the ligand, stabilized by two halide atoms (Figure 1). The crystal structure of the zinc chloride complexes A4 and A5 has been reported in a previous article [48]. The values of the bond angles around zinc(II) I2– Zn–I1, I2–Zn–N2, I1–Zn–N1, N2–Zn–N1, N1–Zn–N2, N1–Zn– Br2, N2–Zn–Br1 and Br2–Zn–Br1 are, respectively, 118.62(2)°, 108.64(10)°, 116.17(10)°, 84.71(15)°, 84.54(7)°, 114.94(6)°, 108.89(6)° and 117.58(14)° (Table 5). To explain the geometry around the Zn(II) ion, we used the distortion index or the tetragonality parameter (τ4) [49] calculated from the formula: τ4 = [360 ° - (α + β)]/141°, where α and β are the two largest angles formed by the donor atoms and the metal center (Figure 1). A value of τ4 = 1 gives a regular tetrahedral geometry, while for a value of τ4 = 0 we have a perfect square plane [50]. In our study, the value of τ4 is 0.8878 for the A6 complex and 0.9041 for the A7 complex, which indicates a slightly distorted tetrahedral geometry. On the other hand, the sum of the angles around the zinc(II) is equal to 428.14° (A6) and 425.95° (A7), we also note the variation of the angles around the Zn(II) ion with respect to the valence angle of 109.5°. These data agree with the value of τ4 found and confirm the slightly distorted tetrahedral geometry of the zinc complexes. This variation in the bond angles around the zinc compared to those around a regular tetrahedron is due to the steric effects of the halide atoms (I, Br). The bond lengths Zn–N1, Zn–N2, Zn–I1 and Zn–I2 in the complex A6 are, respectively, equal to 2.078(3), 2.088(4), 2.5461(16) and 2.5387(16) Å (Table 6) and are in good agreement with the lengths of the corresponding bonds in other zinc(II) complexes with a tetrahedral ZnN2I2 chromophore [51]. For the bromide complex, the Zn–N1 (2.0836(18) Å) and Zn–N2 (2.0693(18) Å) bond lengths are similar to those previously reported by Khalaji [52]. Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 173 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 5. Selected bond angles for the zinc complexes. A6 A7 Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) I2 Zn1 I1 118.62(2) Br1 Zn2 Br2 117.576(14) N1 Zn1 I1 116.17(10) N1 Zn2 Br1 109.16(5) N1 Zn1 I2 108.67(10) N1 Zn2 Br2 114.94(6) N1 Zn1 N2 84.71(15) N2 Zn2 Br1 108.89(6) N2 Zn1 I1 114.96(10) N2 Zn2 Br2 116.99(5) N2 Zn1 I2 108.64(10) N2 Zn2 N1 84.54(7) C6 O1 C9 117.2(5) C6 O1 C9 117.3(2) C15 O2 C18 117.7(5) C15 O2 C18 117.6(2) C1 N1 Zn1 104.7(3) C1 N1 Zn2 106.77(14) C2 N1 Zn1 138.5(3) C2 N1 Zn2 134.66(16) C2 N1 C1 116.6(4) C2 N1 C1 117.54(19) C10 N2 Zn1 106.1(3) C10 N2 Zn2 105.08(14) C11 N2 Zn1 134.5(3) C11 N2 Zn2 138.16(16) C11 N2 C10 118.1(4) C11 N2 C10 116.41(19) N1 C1 C10 108.9(4) N1 C1 C10 108.9(2) N1 C2 C3 128.5(4) N1 C2 C3 126.9(2) Figure 2. Infinite chain structure of the zinc iodide complex stabilized by hydrogen bonds of the C–H···I type (dI2-H1A = 3.096 Å). Figure 3. Structure of complex zinc bromide showing C–H···Br and C–H···O intermolecular hydrogen bonds (dashed) (dBr2-H4 = 3.005 Å, dBr2-H7 = 3.029 Å, dO2-H18 = 2.633 Å). The dihedral angles of the complex A6 C1–N1–C2–C3 and C10–N2–C11–C12 are respectively equal to 179.1(2)° and 179.9(2)° indicate an almost planar configuration of this fraction of the complex. The monomers of the zinc complexes are linked by intermolecular hydrogen bonds of type C1– H1A···I2, C10–H···Br1 and C18–H···O2 (Figure 2 and 3). These intermolecular hydrogen bonds strengthen the cohesion and stability of the complex, thus giving it a supramolecular structure. 3.3. Study of the fluorescence of ligand and zinc complexes The fluorescence spectra of ligand L and these zinc complexes at 8×10-4 M are represented in Figure 4. These spectra show the presence of two emission bands: the fine band towards 392 nm attributed to the fluorescence band due to the group OH in methanol and the broad band towards 400 nm due to the emission of the different compounds tested. These emission spectra reveal that the intensity of the fluorescence varies according to the concentration, this variation increases with increasing concentration [53]. The analysis of the fluorescence spectra of the ligand and of the zinc complexes shows a decrease in the intensity of the fluorescence of the complexes of chloride, iodide and bromide of zinc compared to that of the ligand passing from 225610 to 187540; 161510; 436160, respectively. It appears from the emission spectra that the intensity of the fluorescence decreased considerably during the formation of zinc complexes. The decrease in intensity is due to magnetic disturbance and electronic energy transfers, but also to the presence of halide atoms in complexes [54]. 174 Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 6. Selected bond lengths for the zinc complexes. A6 A7 Atom Atom Length (Å) Atom Atom Length (Å) I1 Zn1 2.5461(6) Br1 Zn2 2.3449(4) I2 Zn1 2.5387(6) Br2 Zn2 2.3535(4) Zn1 N1 2.078(3) Zn2 N1 2.0836(18) Zn1 N2 2.088(4) Zn2 N2 2.0693(18) O1 C6 1.353(6) O1 C6 1.354(3) O1 C9 1.449(7) O1 C9 1.434(3) O2 C15 1.348(7) O2 C15 1.353(3) O2 C18 1.440(8) O2 C18 1.441(3) N1 C1 1.468(6) N1 C1 1.474(3) N1 C2 1.272(6) N1 C2 1.267(3) N2 C10 1.471(6) N2 C10 1.472(3) N2 C11 1.262(6) N2 C11 1.276(3) Figure 4. Fluorescence emission spectra of the ligand and of the zinc complexes. Scheme 2. Proposed structure for zinc complexes (A1-A7). 3.4. Proposed structures for complexes Based on infrared, UV-visible spectroscopic data and elemental analysis of the complexes, we have proposed the structures of copper complexes A1, A2, A3 shown in Scheme 2, the geometry around the copper is square plan. This geometry is supported by the presence of the d-d band around 600 nm characteristic of a square planar copper complex. For the zinc complexes, we note a tetrahedral geometry in which the zinc is coordinated via the two nitrogen atoms of the imine group. 3.5. Antimicrobial activity 3.5.1. Antibacterial activity The results of the preliminary tests of ligand L and its metal compounds are listed in Table 7. The results of this study reveal that the compounds tested have weak antibacterial activity on the two bacteria used with MIC, which are greater than 1000 μM. These values obtained are very high compared to those obtained by Kumar [55], but they are comparable to those found by Matar [56] on Schiff base ligands synthesized from condensation of benzaldehyde derivatives and 3,3'- diaminodipropylamine on different bacterial strains. The high inhibitory concentrations found compared to certain antibiotics such as standard ciprofloxacin allow us to conclude that the compounds tested have very weak antibacterial activity on Gram (-) Pseudomonas aeruginosa and Gram (+) Streptococcus pyogenes bacteria [57]. 3.5.2. Antifungal activity The MICs of the compounds tested against Candida albicans (DSM 10697) fungus are listed in Table 7. Analysis of these results shows that the copper complexes have significant activity with MIC equal to 245.1 μM. Their antifungal activity is much higher than that of zinc complexes and the free ligand (MIC ˃ 900 μM). This decrease may be due to the presence of water molecules in the structure of these complexes [58]. 0 100000 200000 300000 400000 365 415 465 515 565 615 Fl uo re sc en ce in te ns ity Emission wavelength (nm) L Zn(L)Cl2 Zn(L)I2 Zn(L)Br2 MeOH Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 175 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 Table 7. Antimicrobial activity of ligand L and its metal complexes. Compound Concentration (mM) P. aeruginosa S. pyogenes C. albicans L 100 ˃1000 ˃1000 ˃990.1 [Cu(L)(ClO4)(CH3OH)]·ClO4 50 ˃1000 ˃1000 245.1 [Cu(L)(CH3COO)2]·3H2O 50 ˃1000 ˃1000 245.1 [Cu(L1)Cl2]·H2O 50 ˃1000 ˃1000 245.1 [Zn(L)Cl2] 100 ˃1000 ˃1000 990.1 [Zn(L)I2] 100 ˃1000 ˃1000 990.1 [Zn(L)Br2] 100 ˃1000 ˃1000 990.1 Ciprofloxacin 100 0.18 6.25 - Fluconazole 100 - - 7.8 Table 8. Kinetic data of BNPP hydrolysis of zinc complexes of ligand L. Complex V (mol/L s) kobs (1/s) [Zn(L)Cl2] 1.00×10-5 8.00×10-4 [Zn(L)I2] 1.18×10-5 9.44×10-4 [Zn(L)Br2] 8.94× 10-6 7.15×10-4 Figure 5. Comparative absorption profile due to para-nitrophenol formation (λmax = 400 nm) after the addition of BNPP to the complexes. The values obtained are very high, compared to those of Sani et al. [59] in the study of the antifungal activity of the tetradentate ligand derived from ethylenediamine and 4- (benzeneazo)salicylaldehyde and its Cu(II) complexes; Ni(II) and Zn(II) on the fungi A. flavus and C. albicans. The antifungal tests found, compared to those of a standard antibiotic, fluconazole, are very high, which shows their low activity on the fungus C. albicans [59]. 3.6. Study of the hydrolysis of phosphodiesters by complexes A5, A6, and A7 Reactions were determined from the slope of the absorbance versus time curve (Figure 5). The values of the observed initial rates (V) and first-order rate constants (kobs = V/[BNPP]) for the appearance of the para-nitrophenolate anion are listed in Table 8. The comparative study of these values of kobs and formation speeds shows that the zinc iodide complex of the ligand has a constant of 9.44×10-4 1/s higher than that of the zinc chloride and zinc bromide complexes (8×10-4 mol/L s; 7.15×10-4 1/s). These formation rate values show that the compounds tested have a catalytic activity for the BNPP hydrolysis reaction. This allows us to say that the complexes studied can considerably accelerate the breaking of the phosphoester bond of BNPP. 4. Conclusions In summary, we have prepared a series of seven new metal complexes with a Schiff base obtained by condensation of p- anisaldehyde and ethylenediamine using alcohol as the solvent. The synthesized complexes have a distorted tetrahedral environment around zinc and a square plane for copper complexes. We also studied the fluorescence of ligand L and its zinc complexes. This decrease in fluorescence intensity is due to the presence of halide ions in the complex structures or to photo-induced energy transfer. It has also been shown that the synthesis of complexes of this ligand by reflux heating or vigorous agitation leads to hydrolysis of the ligand. The results of the microbial activity reveal that the ligands and complexes studied have very low antimicrobial activity in bacterial strains (Gram-negative Pseudomonas aeruginosa and Gram-positive Streptococcus pyogenes) and the fungus Candida albicans. Analysis of the data obtained from absorbance vs. time curves shows that the zinc complexes tested can accelerate the breakdown of the P-O bond of bis-para-nitrophenylphosphate. Acknowledgements The authors gratefully acknowledge Aix Marseille University, The Laboratoire Bioscience Service 332, especially Dr. Michel Giorgi, Dr. Gregory Excoffier, Dr. Marc Maresca, Dr. Bruno Faure and Dr. Jalila Simaan for the XRD analyses, elemental microanalyses, antimicrobial studies, and follow-up of the work. Supporting information CCDC-2112981 (C18H20I2N2O2Zn) and CCDC-2063276 (C18H20Br2N2O2Zn) contain 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. y(ZnLI2) = 1.18E-05x + 8.32E-02 y(ZnLCl2) = 1.00E-05x + 8.09E-02 y(ZnLBr2) = 8.94E-06x + 8.24E-02 0.05 0.07 0.09 0.11 0.13 0.15 0.17 0 1000 2000 3000 4000 5000 6000 7000 8000 Ab so rb an ce Time (s) MeOH Zn(L)I2 Zn(L)Cl2 Zn(L)Br2 Linear (Zn(L)I2) Linear (Zn(L)Cl2) Linear (Zn(L)Br2) http://www.ccdc.cam.ac.uk/data_request/cif mailto:data_request@ccdc.cam.ac.uk 176 Ndiolene et al. / European Journal of Chemistry 16 (2) (2025) 169-177 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.169-177.2651 CRediT authorship contribution statement Conceptualization: Tidiane Diop, Aminata Diasse-Sarr; Methodology: Adrienne Ndiolene, Tidiane Diop; Software : Mouhamadou Sembene Boye, Michel Giorgi; Validation : Adrienne Ndiolene, Tidiane Diop; Formal Analysis: Adrienne Ndiolene; Investigation : Adrienne Ndiolene, Tidiane Diop; Resources: Tidiane Diop, Aminata Diasse-Sarr ; Data Curation: Adrienne Ndiolene, Michel Giorgi; Writing – Original Draft : Adrienne Ndiolene, Tidiane Diop; Writing - Review and Editing: Mouhamadou Sembene Boye, Aminata Diasse-Sarr; Visualization: Adrienne Ndiolene; Supervision : Tidiane Diop, Aminata Diasse-Sarr, Bruno Faure; Project Administration: Aminata Diasse- Sarr. Funding This scientific work was supported by the cooperation of Senegal Marseille with the Erasmus International Credit Mobility bourse for nine months. ORCID and Email Adrienne Ndiolene adrienne.ndiolene@ucad.edu.sn https://orcid.org/0009-0004-2411-8836 Tidiane Diop tidiane3.diop@ucad.edu.sn https://orcid.org/0000-0003-1098-451X Mouhamadou Sembene Boye mouhasboye@hotmail.com https://orcid.org/0009-0000-8447-6409 Bruno Faure bruno.faure@univ-amu.fr https://orcid.org/0000-0003-2117-8310 Aminata Diasse-Sarr aminatadiasse.sarr@ucad.edu.sn https://orcid.org/0000-0002-4143-4281 Michel Giorgi michel.giorgi@univamu.fr https://orcid.org/0000-0002-4367-1985 References [1]. Golcu, A.; Tumer, M.; Demirelli, H.; Wheatley, R. A. Cd(II) and Cu(II) complexes of polydentate Schiff base ligands: synthesis, characterization, properties and biological activity. Inorg. Chim. Acta 2005, 358 (6), 1785–1797. [2]. Justin Dhanaraj, C.; Sivasankaran Nair, M. 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Synthesis, characterization and antibacterial studies of tetradentate schiff base and their metal (II) complexes derived from 4-(Benzeneazo salicylaldehyde and ethylenediamine). Bayero J. Pure Appl. Sci. 2019, 11, 176. Copyright © 2025 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). https://doi.org/10.1007/BF00207949 http://www.e-journals.in/pdf/V2N3/711-726.pdf http://www.e-journals.in/pdf/V2N3/711-726.pdf https://doi.org/10.4314/bcse.v31i1.7 https://doi.org/10.1002/aoc.5593 https://doi.org/10.1039/B617136B https://doi.org/10.5812/jjnpp.67179 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. Instrumentation 2.2. Synthesis 2.2.1. Synthesis of the Schiff base (L) 2.2.2. General procedure for the synthesis of the complexes 2.3. Antimicrobial activity 2.4. Kinetic of the hydrolysis of phosphodiesters of complexes 3. Results and discussion 3.1. Characterization of the Cu(II) and Zn(II) complexes 3.2. Crystallographic study of zinc complexes 3.3. Study of the fluorescence of ligand and zinc complexes 3.4. Proposed structures for complexes 3.5. Antimicrobial activity 3.5.1. Antibacterial activity 3.5.2. Antifungal activity 3.6. Study of the hydrolysis of phosphodiesters by complexes A5, A6, and A7 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement Funding ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: