Six-Coordinated CoII Single-Molecule Magnets: Synthetic Strategy, Structure and Magnetic Properties.

The pursuit of molecule-based magnetic memory materials contributes significantly to high-density information storage research in the frame of the ongoing information technologies revolution. Remarkable progress has been achieved in both transition metal (TM) and lanthanide based single-molecule magnets (SMMs). Notably, six-coordinated CoII SMMs hold particular research significance owing to the economic and abundant nature of 3d TM ions compared to lanthanide ions, the substantial spin-orbit coupling of CoII ions, the potential for precise control over coordination geometry, and the air-stability of coordination-saturated structures. In this review, we will summarize the progress made in six-coordinated CoII SMMs, organized by their coordination geometry and molecular structure similarity. Valuable insights, principles, and new mechanism gleaned from this research and remaining issues that need to be addressed will also be discussed to guide future optimization.

The role of intermolecular interactions in [Fe(X-salEen)2]ClO4 spin crossover complexes.

Two new spin crossover (SCO) Fe(III) compounds were prepared, their structures were analysed and their magnetic properties were investigated. An exhaustive analysis of the effects of halogen substitution and aromatic ring functionalisation on the magnetic properties of non-solvated Fe(III) perchlorate complexes has been performed. Through comparative analysis, different magnetic profiles were found for the compounds studied, namely F (1), Cl (2), H (3), Br (4a, 4b), and I (5). Using tools like Hirshfeld analysis, the study revealed patterns in octahedral distortions and deviations from the ideal octahedral geometry. The SCO phenomenon as the conducting wire in this study, emphasises the influence of intermolecular interactions on the low spin (LS) to high spin (HS) transitions in these halogen-substituted complexes. The prevalence of H⋯H contributions has been demonstrated, albeit being the weakest and an inverse strength relationship in H⋯X interactions ranging from F to I. The findings not only interpret the intricate balance between halogen substitution, functionalisation, and intermolecular interactions in modulating magnetic properties but also direct future works in designing similar molecular systems.

Synthesis, Crystal Structures, Genotoxicity, and Antifungal and Antibacterial Studies of Ni(II) and Cd(II) Pyrazole Amide Coordination Complexes.

In this study, we synthesized two coordination complexes based on pyrazole-based ligands, namely 1,5-dimethyl-N-phenyl-1H-pyrazole-3-carboxamide (L1) and 1,5-dimethyl-N-propyl-1H-pyrazole-3-carboxamide (L2), with the aim to investigate bio-inorganic properties. Their crystal structures revealed a mononuclear complex [Ni(L1)2](ClO4)2 (C1) and a dinuclear complex [Cd2(L2)2]Cl4 (C2). Very competitive antifungal and anti-Fusarium activities were found compared to the reference standard cycloheximide. Additionally, L1 and L2 present very weak genotoxicity in contrast to the observed increase in genotoxicity for the coordination complexes C1 and C2.

Spin-state versatility in FeII4L6 supramolecular cages with a pyridyl-hydrazone ligand scaffold modulated by solvents and counter anions.

Discrete spin crossover (SCO) tetranuclear cages are a unique class of materials that have potential use in next-generation molecular recognition and sensing. In this work, two new edge-bridged SCO FeII4L6 (L = 2,7-bis(((E)-pyridin-2-ylmethylene)amino)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) supramolecular cages with different counter anions: ClO4- (2) and CF3SO3- (3) were constructed via subcomponent self-assembly to investigate both solvent and anion influences on their magnetic properties and compare them to cage 1 with a BF4- anion. Pyridyl-hydrazone bidentate ligand scaffolds were employed to replace the 'classical' imidazole/thiazolyl-imine coordination units to induce SCO behaviour in these cages. 2 and 3 were structurally characterized by single-crystal X-ray diffraction analysis and electrospray ionization time-of-flight mass spectrometry. Magnetic susceptibilities of 1-3 and 1-3·desolvated indicate that the solvents' presence is in favor of the low-spin (LS) state. While different counter anions in 1-3·desolvated affect the spin-state configurations of the four FeII metal centers. According to the 57Fe Mössbauer spectral analysis, the spin-state distributions in 1-3 at 80 K are [2 high-spin (HS)-2LS], [1HS-3LS] and [2HS-2LS], respectively and density functional theory calculations were employed to investigate the reasons. These findings provide insights to regulate the spin-state versatility of SCO FeII cage systems in the solid state.

New triazole-based coordination complexes as antitumor agents against triple negative breast cancer MDA-MB-468 cell line.

The present work describes the synthesis of a new triazole based ligand 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1-methyl-1H-1,2,4-triazole (LM) and demonstration of its coordination diversity giving rise to a family of seven new coordination complexes, namely: [Ni(LM)3](ClO4)2·C2H6OS (5), [Co2(LM)6](ClO4)4·(C2H5)O (6), [Cd(LM)2Cl2] (7), [Cu(LM)2NO3]NO3 (8), [Fe(LM)3](BF4)2 (9), [Zn(LM)3](BF4)2 (10) and [Zn(LM)2NO3]NO3 (11), whose crystal structure was determined by single-crystal X-ray diffraction. Cytotoxic activity was evaluated against the MDA-MB-468 cancer cell line, which serves as a model for triple-negative breast cancer, and compared to the precursor molecule (L), as well as their coordination complexes (H3O){[NiL3](ClO4)3} (1), [CoL3](ClO4)2·2H2O (2), [CdL2Cl2] (3) and [CuL3](NO3)2 (4), for which the crystal structure was earlier determined. Notably, cadmium complexes 3 and 7 exhibit remarkable cytotoxicity and demonstrated a high selectivity index towards cancer cells when compared to peripheral blood mononuclear cells. Such activity highlights their potential function as anticancer agents.

Incorporation of Photo- and Thermoresponsive N-Salicylidene Aniline Derivatives into Cobalt and Zinc Layered Hydroxides.

In search of new multifunctional hybrid materials and in order to investigate the influence of chemical modification on the possible synergy between properties, the carboxylate and sulfonate derivatives of photo- and thermochromic N-salicylidene aniline were successfully inserted into Co(II)- and Zn(II)-based layered simple hydroxides, resulting in four novel hybrids: Co-N-Sali-COO, Co-N-Sali-SO3, Zn-N-Sali-COO, and Zn-N-Sali-SO3. All synthesized hybrids adopt a double organic layered configuration, which prevents the cis-trans photoisomerization ability of N-Sali-R molecules in the hybrids. However, the Zn hybrids exhibit fluorescence upon exposure to UV light due to the excited-state intramolecular proton transfer (ESIPT) mechanism. The thermally stimulated keto-enol tautomerization of N-salicylidene aniline in the hybrids was related with the changes in interlamellar spacings observed by temperature-dependent PXRD. This tautomerization process was prominently evident in the Co-N-Sali-SO3 hybrid (about 11% increase in d-spacing upon decreasing the temperature to -180 °C). Finally, the Co-N-Sali-R hybrids exhibit the typical magnetic behavior associated with Co(II)-based LSHs (ferrimagnetic ordering at TN = 6.8 and 7.7 K for Co-N-Sali-COO and Co-N-Sali-SO3, respectively). This work offers insights into isomerization in LSHs and the ESIPT mechanism's potential in new luminescent materials and prospects for designing new multifunctional materials.

Coordination Complexes Built from a Ditopic Triazole-Pyrazole Ligand with Antibacterial and Antifungal Performances.

Four mononuclear complexes (H3O){[NiL3](ClO4)3} (1), [CoL3](ClO4)2·2H2O (2), [CdL2Cl2] (3) and [CuL3](NO3)2 (4) have been prepared employing a newly synthesized 1,2,4-triazole ligand: 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1H-1,2,4-triazole (L). The structures of the complexes, which crystallized in P63/m (1), P-1 (2), P1 (3), and P21/c (4), are reviewed within the context of the cooperative effect of the hydrogen bonding network and counter anions on the supramolecular formations. Moreover, within the framework of biological activity examination, these compounds showed favorable antibacterial performances compared to those of various species of bacteria, including both Gram-positive and Gram-negative strains. Significant antifungal inhibitory activity towards Fusarium oxysporum f. sp. albedinis fungi was recorded for 3 and 4 over the ligand L.

CuII Pyrazolyl-Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity.

Three dinuclear coordination complexes generated from 1-n-butyl-2-((5-methyl-1H-pyrazole-3-yl)methyl)-1H-benzimidazole (L), have been synthesized and characterized spectroscopically and structurally by single crystal X-ray diffraction analysis. Reaction with iron(II) chloride and then copper(II) nitrate led to a co-crystal containing 78 % of [Cu(NO3 )(µ-Cl)(L')]2 (C1 ) and 22 % of [Cu(NO3 )(µ-NO3 )(L')]2 (C2 ), where L was oxidized to a new ligand L' . A mechanism is provided. Reaction with copper chloride led to the dinuclear complex [Cu(Cl)(µ-Cl)(L)]2 (C3 ). The presence of N-H⋅⋅⋅O and C-H⋅⋅⋅O intermolecular interactions in the crystal structure of C1 and C2 , and C-H⋅⋅⋅N and C-H⋅⋅⋅Cl hydrogen bonding in the crystal structure of C3 led to supramolecular structures that were confirmed by Hirshfeld surface analysis. The ligands and their complexes were tested for free radical scavenging activity and ferric reducing antioxidant power. The complex C1 /C2 shows remarkable antioxidant activities as compared to the ligand L and reference compounds.

Interpenetration Phenomena via Anion Template Effects in Fe(II) and Co(II) Coordination Networks with a Bis-(1,2,4-triazole) Ligand.

Seven new coordination networks, [Fe(tbbt)3](BF4)2 (1), [Co(tbbt)3](BF4)2 (2), [Fe(tbbt)3](ClO4)2 (3), [Co(tbbt)3](ClO4)2 (4), [Fe(NCS)2(tbbt)2] (5), [Co(NCS)2(tbbt)2] (6), and [Fe(H2O)2(tbbt)2]Br2·2H2O (7), were synthesized with the linker 1,1'-(trans-2-butene-1,4-diyl)bis-1,2,4-triazole (tbbt) and structurally investigated. The structure of complexes 1-4 is composed of three interpenetrating, symmetry-related 3D networks. Each individual 3D network forms a primitive, nearly cubic lattice (pcu) with BF4- or ClO4- anions present in the interstitial spaces. The structure of compounds 5 and 6 is composed of two-dimensional sql layers, which are parallel to each other in the AB stacking type. These layers are interpenetrated by one-dimensional chains, both having the same formula unit, [M(NCS)2(tbbt)2] (M = Fe, Co). The structure of compound 7 consists of parallel, two-dimensional sql layers in the ABCD stacking type. The interpenetration in 1-6 is not controlled by π-π-interactions between the triazole rings or C=C bonds, as could have been expected, but by (triazole)C-H⋯F4B, C-H⋯O4Cl, and C-H⋯SCN anion hydrogen bonds, which suggests a template effect of the respective non-coordinated or coordinated anion for the interpenetration. In 7, the (triazole)C-H⋯Br anion interactions are supplemented by O-H⋯O and O-H⋯Br hydrogen bonds involving the aqua ligand and crystal water molecules. It is evident that the coordinated and non-coordinated anions play an essential role in the formation of the networks and guide the interpenetration. All iron(II) coordination networks are colorless, off-white to yellow-orange, and have the metal ions in the high-spin state down to 77 K. Compound 5 stays in the high spin state even at temperatures down to 10 K.

A spin crossover FeII4L6 cage based on pyridyl-hydrazone sites.

Reported here is the first FeII based supramolecular cage with pyridyl-hydrazone ligand scaffolds that exhibits temperature induced spin crossover behaviour. Density functional theory calculations were employed to investigate the cause of the occurrence of this phenomenon based on the ligand structure. These results indicate that the reported low-spin cages with pyridyl-imine sites could be reconsidered for spin crossover by carefully manipulating the functional groups in the ligand system.

A non-porous Fe(II) complex for the colorimetric detection of hazardous gases and the monitoring of meat freshness.

Food quality monitoring and freshness assessment are critical for ensuring food safety at a large scale. Ammonia is used as an important indicator of protein rich food spoilage state. However, current ammonia gas sensors suffer from insufficient sensitivity and selectivity, or sophisticated instrumentation, hindering their practical application in in-situ and real-time food quality monitoring. To overcome such limitations, an innovative nonporous colorimetric complex 1 has been synthesized and investigated for the detection of NH3(g) and its volatile organic derivatives including aliphatic amines, 1,2-diaminopropane(g), isobutylamine(g) and ethylenediamine(g), etc. The sensor operates colorimetrically at room temperature without energy input, with a detection limit to ammonia(g) of 105 ppb, and show excellent reusability. The colorimetric detection mechanism involves a partial spin state change of Fe(II) ions upon exposure to amines in the gas phase. In addition, the complex was utilized as real-time monitoring of meat freshness using a smartphone. Thus, chemosensor 1 is considered as a ground breaking new-generation portable electronic nose for vapors of volatile organic compounds discrimination at room temperature.

Novel family of bis-pyrazole coordination complexes as potent antibacterial and antifungal agents.

A new pyrazole ligand, N,N-bis(2(1',5,5'-trimethyl-1H,1'H-[3,3'-bipyrazol]-1-yl)ethyl)propan-1-amine (L) was synthesized and characterized by 1H-NMR, 13C-NMR, FT-IR and HRMS. The coordination ability of the ligand has been employed for the construction of a new family of coordination complexes, namely: [Cu2LCl4] (1), [ML(CH3OH)(H2O)](ClO4)2 (MII = Ni (2), Co (3)) and [FeL(NCS)2] (4). The series of complexes were characterized using single-crystal X-ray diffraction, HRMS, FT-IR and UV-visible spectroscopy. Moreover, the iron(ii) analogue was investigated by 57Fe Mössbauer spectroscopy and SQUID magnetometry. Single-crystal X-ray structures of the prepared complexes are debated within the framework of the cooperative effect of the hydrogen bonding network and counter anions on the supramolecular formations observed. Furthermore, within the context of biological activity surveys, these compounds were reviewed against different types of bacteria to validate their efficiency, including both Gram-positive as well as Gram-negative bacteria. Enhanced behaviour towards Fusarium oxysporum f. sp. albedinis fungi, were detected for 1 and 4.

New Cathode Materials in the Fe-PO4 -F Chemical Space for High-Performance Sodium-Ion Storage.

Sodium and iron make up the perfect combination for the growing demand for sustainable energy storage systems, given the natural abundance and sustainability of the two building block elements. However, most sodium-iron electrode chemistries are plagued by intrinsic low energy densities with continuous ongoing efforts to solve this. Herein, the chemical space of a series of (meta)stable, off-stoichiometric Fe-PO4 -F phases is analyzed. Some are found to display markedly improved electrochemical activity for sodium storage, as compared to the amorphous or thermodynamically stable phases of equivalent composition. The metastable crystalline Na1.2 Fe1.2 PO4 F0.6 delivers a reversible capacity of more than 140 mAh g-1 with an average discharge potential of 2.9 V (vs Na+ /Na0 ) resulting in a practical specific energy density of 400 Wh kg-1 (estimated at the material level), outperforming many developed Fe-PO4 analogs thus far, with further multiple possibilities to be explored toward improved energy storage metrics. Overall, this study unlocks the possibilities of off-stoichiometric Fe-PO4 -F cathode materials and reveals the importance to explore the oft-overlooked metastable or transient state materials for energy storage.

Coordination complexes constructed from pyrazole-acetamide and pyrazole-quinoxaline: effect of hydrogen bonding on the self-assembly process and antibacterial activity.

Two mononuclear coordination complexes of N-(2-aminophenyl)-2-(5-methyl-1H-pyrazol-3-yl)acetamide (L1), namely [Cd(L1)2Cl2] (C1) and [Cu(L1)2(C2H5OH)2](NO3)2 (C2) and one mononuclear complex [Fe(L2)2(H2O)2](NO3)2·2H2O (C3), obtained after in situ oxidation of L1, have been synthesized and characterized spectroscopically. As revealed by single-crystal X-ray diffraction, each coordination sphere made of two heterocycles is completed either by two chloride anions (in C1), two ethanol molecules (in C2) or two water molecules (in C3). The crystal packing analysis of C1, C2 and C3, revealed 1D and 2D supramolecular architectures, respectively, via various hydrogen bonding interactions, which are discussed in detail. Furthermore, evaluation in vitro of the ligands and their metal complexes for their antibacterial activity against Escherichia coli (ATCC 4157), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923) and Streptococcus fasciens (ATCC 29212) strains of bacteria, revealed outstanding results compared to chloramphenicol, a well-known antibiotic, with a normalized minimum inhibitory concentration as low as 5 µg mL-1.

Thin Films of Nanocrystalline Fe(pz)[Pt(CN)4] Deposited by Resonant Matrix-Assisted Pulsed Laser Evaporation.

Prior studies of the thin film deposition of the metal-organic compound of Fe(pz)Pt[CN]4 (pz = pyrazine) using the matrix-assisted pulsed laser evaporation (MAPLE) method, provided evidence for laser-induced decomposition of the molecular structure resulting in a significant downshift of the spin transition temperature. In this work we report new results obtained with a tunable pulsed laser, adjusted to water resonance absorption band with a maximum at 3080 nm, instead of 1064 nm laser, to overcome limitations related to laser-target interactions. Using this approach, we obtain uniform and functional thin films of Fe(pz)Pt[CN]4 nanoparticles with an average thickness of 135 nm on Si and/or glass substrates. X-ray diffraction measurements show the crystalline structure of the film identical to that of the reference material. The temperature-dependent Raman spectroscopy indicates the spin transition in the temperature range of 275 to 290 K with 15 ± 3 K hysteresis. This result is confirmed by UV-Vis spectroscopy revealing an absorption band shift from 492 to 550 nm related to metal-to-ligand-charge-transfer (MLCT) for high and low spin states, respectively. Spin crossover is also observed with X-ray absorption spectroscopy, but due to soft X-ray-induced excited spin state trapping (SOXIESST) the transition is not complete and shifted towards lower temperatures.

A Highly Efficient Environmental-Friendly Adsorbent Based on Schiff Base for Removal of Cu(II) from Aqueous Solutions: A Combined Experimental and Theoretical Study.

Removal of heavy metals from drinking water sources and rivers is of strategic health importance and is essential for sustainable ecosystem development, in particular in polluted areas around the globe. In this work, new hybrid inorganic-organic material adsorbents made of ortho- (Si-o-OR) or para-Schiff base silica (Si-p-OR) were synthesized and characterized in depth. These hybrid adsorbents show a high selectivity to Cu(II), even in the presence of competing heavy metals (Zn(II), Cd(II), and Pb(II)), and also demonstrate great reusability after five adsorption-desorption cycles. Maximum sorption capacity for Cu(II) was found for Si-o-OR (79.36 mg g-1) and Si-p-OR (36.20 mg g-1) in no less than 25 min. Energy dispersive X-ray fluorescence and Fourier transform-infrared spectroscopy studies demonstrate that this uptake occurs due to a chelating effect, which allows these adsorbents to trap Cu(II) ions on their surfaces; this result is supported by a theoretical study for Si-o-OR. The new adsorbents were tested against real water samples extracted from two rivers from the Oriental region of Morocco.

Auxiliary alkyl chain modulated spin crossover behaviour of [Fe(H2Bpz2)2(Cn-bipy)] complexes.

Three new alkyl chain substituted complexes [Fe(H2Bpz2)2(Cn-bipy)] (pz = pyrazolyl, Cn-bipy = bipyridine alkyl chain diester, n = 3 (3), 4 (4) and 5 (5)) show versatile spin state switching behaviour with different "tail" lengths as revealed by structural and magnetic analyses. The most striking phenomenon is observed for 5 which undergoes an abrupt spin transition accompanied by thermal hysteresis of ca. 10 K, which is attributed to crystal packing effects derived from the competition between π⋯π and C-H⋯O interactions. Interestingly, each of the complexes exhibits similar gradual and complete spin crossover in methanol solution with a transition temperature around 249 K, as deduced from temperature-dependent UV-vis spectroscopy. This highlights the differences between the solid state (ligand field; crystal packing) and solution (ligand field; solvation) effects on spin crossover. This work demonstrates that the length of the complex's alkyl chain substituents on the complex can have a large impact on the transition temperature and profile of solid state spin crossover, offering a potential path to the fabrication of soft matter spin crossover materials.

Synthesis and cytotoxicity against tumor cells of pincer N-heterocyclic ligands and their transition metal complexes.

The complexes: [CoL2](ClO4)2 (1), [FeL2](ClO4)2 (2), [NiL2](ClO4)2 (3) and [MnLCl2] (4), with L = diethyl-1,1'-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazole-3-carboxylate), were synthesized and fully characterized. Structural analysis revealed two distinct patterns influenced by the counter ions where L acts as a tridentate chelating ligand. The in vitro antitumor activity of L and L' (diethyl 2,2'-(pyridine-2,6-diylbis(5-methyl-1H-pyrazole-3,1-diyl)) diacetate) as well as their metal complexes, was tested by the measurement of their cytostatic and cytotoxic properties towards the blood cancer mastocytoma cell line P815. We have also investigated their interactions with the antioxidant enzyme system. As a result, [MnL'Cl2] (1') exhibited the strongest activity compared to reference cis-platin with no cytotoxicity towards normal cells PBMCs (Peripheral Blood Mononuclear Cells). On the other hand, the antioxidant enzyme activity showed that the efficiency of metal complex 1' against P815 tumor cells was via the rise in the SOD activity and inhibition of CAT enzyme activity. This proof of concept study allows disclosure of a new class of molecules in cancer therapeutics.

Kinetics, thermodynamics, equilibrium, surface modelling, and atomic absorption analysis of selective Cu(ii) removal from aqueous solutions and rivers water using silica-2-(pyridin-2-ylmethoxy)ethan-1-ol hybrid material.

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment. In this investigation, a new adsorbent based on silica functionalized with pyridin-2-ylmethanol (SiPy) was successfully synthesized to yield to a hybrid material. FTIR, SEM, TGA, and specific surface area analysis were used to characterize the structure and morphology of the SiPy hybrid material. Various heavy metal ions such as Cu(ii), Zn(ii), Cd(ii), and Pb(ii) were selected to examine the adsorption efficiency of the newly prepared adsorbent, optimized at varying solution pH, contact time, concentration, and temperature. The adsorbent SiPy displayed good adsorption capacity of 90.25, 75.38, 55.23, and 35.12 mg g-1 for Cu(ii), Zn(ii), Cd(ii), and Pb(ii), respectively, at 25 min and pH = 6. The adsorption behaviors of metal ions onto the SiPy adsorbent fitted well with the pseudo-second-order kinetic mode and the isotherm was better described by the Langmuir isotherm. The thermodynamic studies disclose spontaneous and endothermic adsorption process. Furthermore, the SiPy adsorbent retained good selectivity and regeneration properties after five adsorption-desorption cycles of Cu(ii). A computational investigation of the adsorption mechanism indicates that the N-pyridine, O-hydroxyl, and ether O-atoms play a predominant role during the capture of Cu(ii), Zn(ii), Cd(ii), and Pb(ii). This study proposes the SiPy adsorbent as an attractive material for the selective removal of Cu(ii) from real river water and real industrial wastewater.

Efficient and Environmentally Friendly Adsorbent Based on ß-Ketoenol-Pyrazole-Thiophene for Heavy-Metal Ion Removal from Aquatic Medium: A Combined Experimental and Theoretical Study.

A new sustainable and environmentally friendly adsorbent based on a ß-ketoenol-pyrazole-thiophene receptor grafted onto a silica surface was developed and applied to the removal of heavy-metal ions (Pb(II), Cu(II), Zn(II), and Cd(II)) from aquatic medium. The new material SiNPz-Th was well characterized and confirms the success of covalent binding of the receptor on the silica surface. The effect of environmental parameters on adsorption including pH, contact time, temperature, and the initial concentration were investigated. The maximum adsorption capacities of SiNPz-Th for Pb(II), Cu(II), Zn(II), and Cd(II) ions were 102.20, 76.42, 68.95, and 32.68 mg/g, respectively, at 30 min and pH = 6. The adsorption isotherms, kinetics, and thermodynamic process were investigated and showed efficiency and selectivity toward Pb(II) and good regeneration performance. Density functional theory, noncovalent-interaction, and quantum theory of atoms in molecules calculations were used to study and to gain a deeper understanding of both the adsorption mechanism and selectivity of metal ions onto the adsorbent. Accordingly, metal ions such as Pb(II), Cu(II), and Zn(II) were bidentate coordinated with the adsorbent by nitrogen and oxygen atoms of the Schiff base C=N and hydroxyl group -OH, respectively, to form stable complexes. Whereas Cd(II) was coordinated in a monodentate fashion with oxygen atom of the hydroxyl group. Furthermore, the affinity of SiNPz-Th toward the metal ions was decreased in the order of Pb(II) > Cu(II) > Zn(II) > Cd(II), in good agreement with the experimental results. All these results highlight that SiNPz-Th has good potential to be an advanced adsorbent for the removal of lead ions from real water.