Tripodal Schiff Base Research Articles

The Synthesis of Melamine Cored Schiff Bases and Investigation of Heteronuclear Metal Complexes

In this study, 2,4,6-triamino-s-triazine (melamine) is the starting material. The condensation reaction of melamine and 4-hydroxybenzaldehyde resulted in the formation of the monopodal Schiff base. An oxygen-bridged monopodal complex of [(Fe(III)Salophen)Cl] ligand complex with monopodal Schiff base ligand was then obtained. Tripodal Schiff base ligand was obtained by condensing 2-hydroxybenzaldehyde with a monopodal complex and this ligand in some transition metal complexes were synthesized. As a result, the ligand and complexes of this ligand were isolated, as well as elemental analyses, FT-IR, 1H-NMR, TGA and magnetic susceptibility measurements of the obtained compounds were taken to elucidate their structures.

Highly Selective Turn-on Fluorescence Sensor for Cd2+ Ions by TripodalOrganic Ligand.

Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd2+ (10- 4M) addition exhibited a strong enhancement of fluorescence at 450nm. Interestingly, other metal ions including Zn2+, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd2+ showed the detection limit of 6.78 × 10- 8M. NMR spectra of 1 with Cd2+ and computational studies were performed to understand the mechanism of sense.

Tripodal Schiff Base Compounds Containing Triazole and Mn3+ and Fe3+ Complexes: Synthesis, Characterization, and Investigation of Their Spectral Properties

In this study, it was aimed to synthesize and elucidate the structure of tripodal Schiff bases, which are used in the fields of materials science, chemistry, and pharmacology, and especially for the synthesis of chemical sensor materials due to their very good tendency to form complexes with metals. For the synthesis of new Schiff base tripodal compounds and their complexation with metals; Tripodal compound was synthesized as a result of the reaction of 2-hydroxy-4-(prop-2-yn-1-yloxy) benzaldehyde and N1, N1-bis(2-aminoethyl) ethane-1,2-diamine. The obtained compounds were complexed with Fe3+ and Mn3+ metals. The structures of synthesized tripodal ligands and metal complexes were tried to be elucidated using IR, UV-vis, Photoluminescence, 1H-NMR, 13C-NMR spectroscopic methods.

Aggregation-Induced Emission, Mechanofluorochromism, and Selective Fluoride Detection by a Tripodal Salicylaldimine.

Fluoride ions are indispensable in biology and environmental science and hence the selective and sensitive detection of fluoride is important. This work reports the design and synthesis of a tripodal Schiff's base 1 through a simple condensation reaction between a commercially available aldehyde and an amine. Single crystal X-ray crystallography revealed that compound 1 is a planar entity with the three salicylidene derivatives on the three arms of the central phenyl moiety linked by imine groups. Compound 1 forms a molecular dimer that resembles a six-petal flower and is stabilized through multiple intermolecular interactions such as C-H.π and π.π interactions. Compound 1 exhibited moderately good emission in the solid state with aggregation induced emission and reversible mechanofluorochromic properties. Moreover, 1 was observed to selectively detect fluoride among various anions with a limit of detection of ∼9 ppm. Compound 1 was also capable of detecting fluoride under a variety of conditions such as in thin films and under cellular conditions.

Photo-induced atom transfer radical polymerization of styrene using a highly active claw-type Schiff-base ligand

The use of a tripodal Schiff base, tris[N-(2-(4-(dimethylamino)pyridylmethyl)-2-iminoethyl]amine (PyNMe23Tren), as a highly active claw-type ligand for photo-induced atom transfer radical polymerization (Photo-ATRP) is reported. CuBr2 / PyNMe23Tren is employed as the catalyst for Photo-ATRP of styrene (St) under the irradiation of visible or ultraviolet light. Well-defined polystyrene (PSt) could be synthesized with high chain-end functionality confirmed by in situ chain extension and PSt-Br macroinitiator for the secondary polymerization of St. Through switching the light “on” and “off”, temporal control of Photo-ATRP was successfully demonstrated. After the polymerization, the reaction system appeared stratification and the upper layer PSt could be facilely separated from the system.

Silver(I) complexes with a luminescent tripodal Schiff base ligand derived from fluorene-2-carboxaldehyde

A new tripodal Schiff base ligand was obtained by reacting tris(2-aminoethyl)amine with fluorene-2-carboxaldehyde. The ligand and five mononuclear Ag(I) complexes, resulted from the reactions of the ligand with AgNO3, AgCF3SO3, AgSbF6, AgBF4 and AgClO4, were structurally characterized by X-ray diffraction on single crystals. Within complexes, the Ag(I) ions are tetracoordinated with a distorted tetrahedral placement of the donating atoms. The metal ions are located outside of the tetrahedron formed by the four nitrogen atoms of the ligand (three imino and one amino nitrogen atoms). Luminescent properties of the ligand L and complexes were investigated in solid-state.

Selective crystallization of dysprosium complex from neodymium/dysprosium mixture enabled by cooperation of coordination and crystallization.

Designing a molecular-level Ln3+ separation system remains a challenge for developing next-generation separation methodologies. Herein, we report crystallization-based Nd3+/Dy3+ separation using a tripodal Schiff base ligand. Highly selective crystallization of the Dy3+ complex was enabled by cooperation between the coordination and crystallization processes.

Synthesis, Biological and In Silico Studies of a Tripodal Schiff Base Derived from 2,4,6-Triamino-1,3,5-triazine and Its Trinuclear Dy(III), Er(III), and Gd(III) Salen Capped Complexes.

A tripodal Schiff base ligand, 2,4,6-Tris(4-carboxybenzimino)-1,3,5-triazine (MT) and its trinuclear Dy(III), Er(III), and Gd(III) complexes were synthesized. These were characterized using UV-visible, IR, 1H, and 13C NMR spectroscopies, elemental analysis, and molar conductivity measurements. The spectral studies indicate that the ligand is hexadentate and coordinates to the Ln(III) ions through the oxygen atoms of the carboxylic group. The trinuclear complexes were characterized as being bridged by carboxylate anions to the Dy(III), Er(III), and Gd(III) salen centers and displaying a coordination number of six. Biological studies revealed that MT is more active against the test micro-organisms relative to the trinuclear complexes. Acute toxicity studies revealed that MT is safe and has a wide range of effective doses (ED50). In vivo antimalarial studies indicate that MT could serve as an effective antimalarial agent since it has parasitemia inhibition of 84.02% at 50 mg/kg and 65.81% at 25 mg/kg, close to the value (87.22%) of the standard drug—Artesunate. Molecular docking simulation studies on the compounds against SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN) revealed effective binding interactions through multiple bonding modes. The binding energy calculated for Er(III)MT-6Y84 and Er(III)MT-5MMN complexes showed active molecules with the ability to inhibit SARS-CoV-2 and E. coli DNA gyrase.

Enhanced TbIII-centered Luminescence due to Elongated Methylene Arms of Tripodal Schiff Base Ligand

LnIII-tripodal Schiff base complex TbIIILtrpn was prepared, in which the three arms of the ligand were extended by one methylene based on the tris(2-aminoethyl)amine in TbIIILtren. TbIIILtrpn showed enhanced TbIII-centered luminescence compared to TbIIILtren. Crystallographic analysis revealed that the symmetry of the seven-coordination environment of the TbIII center in TbIIILtrpn was diminished compared to that in TbIIILtren, resulting in the increased radiative transition rate and/or decreased back energy transfer rate and, thus, the increased luminescence.

Short Radiative Lifetime and Non-Triplet Sensitization in Near-Infrared-Luminescent Yb(III) Complex with Tripodal Schiff Base.

We prepared Ln(III) (Ln=Eu, Gd, and Yb) complexes with a tripodal Schiff base, tris[2‐(5‐methylsalicylideneimino)ethyl]amine (H3L) and studied their photophysical properties. Upon ligand excitation, YbL showed Yb(III)‐centered luminescence in the near‐infrared region. While the overall quantum yield (0.60(1)%) of YbL in acetonitrile was moderate among the reported values for Yb(III) complexes, its radiative lifetime (0.33(2) ms) was significantly shorter than those reported previously. We propose that the ligand‐to‐metal charge‐transfer (LMCT) state mediated the sensitization in YbL. The emission and excitation spectra of EuL indicated the participation of the LMCT state in the sensitization. The radiative lifetime (0.84(7) ms) for EuL in the solid state was rather short compared to those of reported Eu(III) complexes. Our results show that the Yb(III) complex with the Schiff base ligand has two features: the short radiative lifetime and the non‐triplet sensitization path.

A Quasi-Liner {MnIIDyIIIMnII} Cluster Featuring In Situ Schiff Base Ligand Transformation

Employing tripodal Schiff base ligand of tris[4-(2-hydroxy-3-methoxyphenyl)-3-aza-3-butenyl]amine (H3L1) and auxiliary ligand of 2-hydroxy-5-chlorobenzaldehyde, a 3d–4f cluster of $$\left[ {{\text{Dy}}^{{{\text{III}}}} {{{\text{Mn}}}}_{ 2}^{{{\text{II}}}} \left( {{{\text{L}}}^{ 2} } \right)_{ 2} } \right]\left[ {{{\text{NO}}}_{ 3} } \right] \cdot 5 {{{\text{CH}}}}_{ 3} {{{\text{OH}}}}$$ (1) was synthesized. Intriguingly, the H3L1 ligand has transformed into another Schiff base ligand of {N-[4-(2-hydroxy-5-chlorophenyl)-3-aza-3-butenyl]-N′,N′′-bis[4-(2-hydroxy-3-methoxyphenyl)-3-aza-3-butenyl]}amine (H3L2) in situ during the coordination process, that one of terminal groups of H3L1 ligand was substituted. A pair of such (L2)3− ligands chelate a DyIII and two MnII ions to form a quasi-liner {MnIIDyIIIMnII} skeleton of 1, in which the adjacent MnII and DyIII ions were bridged by three Ophenol. To the best of our knowledge, this in situ substitution of the terminal group of Schiff base ligand has not been reported in previous literature. DC magnetic susceptibility measurements were conducted on 1, revealing the weak antiferromagnetic interactions between the DyIII and MnII centers. A quasi-liner a {MnIIDyIIIMnII} cluster has been constructed from tripodal Schiff base ligand of H3L1. The H3L1 ligands underwent an in situ substitution in the coordination, which has been not reported in previous literature so far as we known. Magnetic studies reveal the weak antiferromagnetic interactions between DyIII and MnII ions.

New Cr, Mo, W, and Fe Metal Complexes with Potentially Heptadentate (S3N4) Tripodal Schiff Base Ligand: Synthesis, Characterization, and Antibacterial Activity

Reactions of Cr, Mo, W, and Fe metal carbonyls with potentially heptadentate (S3N4) tripodal Schiff base ligand, (thio)3tren, have been studied. The Schiff base (thio)3tren has been prepared by condensation of thiophene-2-carboxaldehyde with tris(2-aminoethyl)amine. The Schiff base and its metal complexes have been characterized by IR, UV-Vis, 1H and 13C NMR spectra, TGA, and elemental analysis. According to the spectroscopic data, (thio)3tren is coordinated to the metal centers as a potentially heptadentate ligand. The products have been tested in vitro against the bacterial species, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Bacillus cereus by the disc diffusion and micro-broth dilution methods, and characterized by antibacterial activity higher than that of the ligand. The lowest MIC was determined for Fe complex against Bacillus cereus and the highest for Mo complex against Escherichia coli.

Structural Evidence of Spin State Selection and Spin Crossover Behavior of Tripodal Schiff Base Complexes of tris(2-aminoethyl)amine and Related Tripodal Amines

A review of the tripodal Schiff base (SB) complexes of tris(2-aminoethyl)amine, Nap(CH2CH 2NH2)3 (tren), and a few closely related tripodal amines with Cr(II), Mn(III) (d4), Mn(II), Fe(III) (d5), Fe(II) (d6), and Co(II) (d7) is provided. Attention is focused on examination of key structural features, the M-Nimine, M-Namine, or M-O and M-Nap bond distances and Nimine-M-N(O) bite and C-Nap-C angles and how these values correlate with spin state selection and spin crossover (SCO) behavior. A comparison of these experimental values with density functional theory calculated values is also given. The greatest number, 132, of complexes is observed with cationic mononuclear iron(II) in a N6 donor set, Fe(II)N6. The dominance of two spin states, high spin (HS) and low spin (LS), in these systems is indicated by the bimodal distribution of histogram plots of Fe(II)-Nimine and Fe(II)-Nazole/pyridine bond distances and of Nimine–Fe(II)-Nazole/pyridine and C-Nap-C bond angles. The values of the two maxima, corresponding to LS and HS states, in each of these histograms agree closely with the theoretical values. The iron(II)-Nimine and iron(II)-Nazole/pyridine bond distances correlate well for these complexes. Examples of SCO complexes of this type are tabulated and a few of the 20 examples are discussed that exhibit interesting features. There are only a few mononuclear iron(III) cationic complexes and one is SCO. In addition, a significant number of supramolecular complexes of these ligands that exhibit SCO, intervalence, and chiral recognition are discussed. A summary is made regarding the current state of this area of research and possible new avenues to explore based on analysis of the present data.

Studies of a Tripodal Biomimetic Siderophore Analog: An Efficient Encapsulation for Fe(III) Ion

A new tris-(2-aminoethyl)amine (TREN) capped tripodal Schiff base ligand has been developed by mimicking structural features of a natural siderophore, Bacillibactin, by substituting the catechol units with salicylaldehyde and employing amino acid as a spacer. Synthesis of the ligand N-[2-[bis[2-[[2-[(2-hydroxyphenyl)methylamino]acetyl] amino]ethyl]amino]ethyl]-2-[(2-hydroxyphenyl)methylamino]acetamide(TRENglySAL) includes condensation of salicylaldehyde and amino acid (glycine) followed by an in-situ reduction of the produced Schiff base, followed by further condensation with TREN. The complexation behavior of the ligand with Fe(III) has been investigated by potentiometric and UV-Vis spectrophotometric method at temperature 25±1oC and 0.1 M ionic strength. Seven protonation constants were obtained of the ligand: three each for secondary amine and phenolic protons and one for tertiary nitrogen of capping TREN moiety. The formation constants (log β11n) of different complex species MLH3, MLH2, MLH, ML and MLH-1 are found to be 35.15, 32.09, 27.91, 25.32 and 17.32 respectively. These results indicate that the ligand is an excellent iron-binding chelator. Significant electronic spectral variations during complex formation at higher pH also provide a scope for the ligand to act as an optical pH sensor towards Fe (III) metal ion in biological systems. Structures of the ligand and metal complexes are proposed through experimental findings along with the theoretical semi-empirical PM3 calculation. The theoretical spectroscopic results are found to be comparable with the experimental finding.

Synthesis, characterization, and antibacterial activities of some metal complexes with tripodal Schiff base ligand derived from pyrrole-2-carboxaldehyde

The tripodalheptadentate Schiff base ligand, C21H27N7, was derived from pyrrole-2-carboxaldehyde with tris(2-aminoethyl)amine (tren) and its complexes with Cd(II), Co(II), Mn(II) and Ni(II) metal ions have been synthesized. The Schiff base and its metal complexes have been identified by IR, UV-Vis, 1H-NMR, 13C-NMR spectroscopy, elemental analysis and thermo gravimetric analysis (TGA). According to the spectroscopic and elemental analyses data, it was found that the Schiff base was coordinated to the metal ions as a potentially heptadentate ligand. All compounds showed antibacterial properties against the gram-positive bacteria; Bacillus cereus, Staphylococcus aureus, and gram-negative bacteria; Pseudomonas aeruginosa, Escherichia coli by using disc diffusion and micro-broth dilution methods. Also, the metal complexes showed a greater inhibitory effect than their individual ligand. Bacillus cereus was the most susceptible bacterial species to Co(II) complex while Escherichia coli required a relatively higher minimum inhibition concentration of Mn(II) complex.

A highly fluorescent tri-nuclear boron complex with large Stokes shifts based on tripodal Schiff base: synthesis and photophysical properties

In this study, a new imine-based tripodal ligand and its difluoroboron complex were designed and synthesized. This trinuclear-boron complex was prepared for the first time and fully characterized by common spectroscopic techniques such as $$^{1}$$ H-NMR, $$^{13}$$ C-NMR, FT-IR, UV–Vis and MS analysis. The optical and fluorescence properties of complex were examined in $$\hbox {CHCl}_{{3}}$$ , THF, acetonitrile, EtOAc, DMF and DMSO. It was revealed that the obtained boron complex showed intense emission with large Stokes shifts in the range from 83 nm to 96 nm. As a result of quantification of fluorescence quantum yields, it has been observed that it has high quantum yield values up to 48%. The large Stokes shifts and high efficient emissions in the solutions of boron complex make it precious fluorophore for potential applications in materials science. SYNOPSIS: The synthesis and characterization of a new four coordinated trinuclear boron complex and its optical properties are reported. The results show that the obtained new fluorophore could be beneficial for fluorescent materials due to presenting large Stokes shifts and high efficient blue emissions.

Synthesis, Characterization, Antimicrobial Screening, and Computational Studies of a Tripodal Schiff Base Containing Pyrimidine Unit

A novel tripodal Schiff base ligand, 5‐amino‐2,4,6‐tris(4‐carboxybenzimino)‐1,3‐pyrimidine (TTPS), was synthesized for the first time by the reaction of 2,4,5,6‐tetraaminopyrimidine with 4‐carboxybenzaldehyde. The ligand was characterized by means of ultraviolet–visible, Fourier transform infrared, one‐dimensional 1H‐NMR, and one‐dimensional 13C‐NMR spectroscopies and elemental microanalysis. The Fourier transform infrared and NMR studies revealed that one of the NH2 group in 2,4,5,6‐tetraaminopyrimidine is not involved in bonding. The in vitro antimicrobial activities of the ligand were investigated against Gram‐negative bacteria: Escherichia coli (ATCC 6749) and Pseudomonas aeruginosa (ATCC 9027), Gram‐positive bacteria: Staphylococcus aureus (ATCC 6538P) and Bacillus cereus (ATCC 14579), and fungi: Candida albicans and Aspergillus niger by the agar well diffusion technique. TTPS exhibits good activity against the test microorganisms. The minimum inhibitory concentrations of TTPS against S. aureus were compared with tetracycline and gentamicin, which are conventional bacterial drugs. The upper level of Lorke's method was used to determine the acute toxicity of the compound. The acute toxicity test indicates that TTPS is toxic at doses above 2154 mg/kg. The in vivo antimalarial assay was carried out on Plasmodium berghei based on the 4‐day suppressive method. The result shows a general dose‐dependent significant parasitemia inhibition compared with the negative control with TTPS having inhibition of 72.20% at 50 mg/kg and 65.81% at 25 mg/kg close to the value (87.22%) of the standard drug artesunate 5 mg/kg. Density functional theory method was used to complement this experimental investigation.

New triphenyltin(IV) complexes of flexible tripodal Schiff base ligands: X-ray structural characterization of Ph3SnCl.(H3trensal)

New triphenyltin(IV) complexes of flexible tripodal Schiff base ligands, viz. tris(2-(2-hydroxybenzylidene)ethyl)amine) (H3saltren), tris(2-(2-hydroxyacetophenylidene)ethyl)amine) (H3hatren), and tris(2-(5-chloro-2-hydroxybenzylidene)ethyl)amine (H35-Cl-saltren) have been synthesized. The coordination behaviour of Schiff bases towards triphenyltin(IV) moiety is discussed on the basis of electronic, infrared, multinuclear (1H, 13C, and 119Sn) magnetic resonance (NMR) spectroscopic studies, and electrospray mass spectrometry (ESMS). Detailed single crystal X-ray studies demonstrate that adduct, Ph3SnCl.(H3trensal) crystallizes in orthorhombic space group, ‘P 21 21 21’ with cell parameters (a (Å) = 13.803(5), b (Å) = 21.117(5), c (Å) = 28.815(5)). The tin atom adopts a slightly distorted trigonal bipyramidal geometry wherein most electronegative chlorine and oxygen atoms are apically arranged, and ipso carbons of three phenyl rings of tin are aligned to constitute an equatorial plane around it. Thermal studies of all of the synthesized triphenyltin(IV) chloride adducts have also been carried out using TG, DTG and DTA techniques.

Extending photophysical behavior of Schiff base tripod for the speciation of iron and fabrication of INHIBIT type molecular logic gate for fluorogenic recognition of Zn(II) and Cd(II) ions

A tripodal Schiff base derived by the condensation of tris(2-aminoethyl)amine and 2-hydroxynaphthaldehyde, and characterized by single crystal X-ray diffraction has been explored herein as a chemosensor for metallic species. Although, its fluorogenic response towards Zn2+ (in 95:5 ethanol–water solvent) has been already reported, however, its utilization for the naked eye speciation of iron and fluorogenic response towards Cd2+ ions needs to be explored. It exhibits pronounced fluorescence signaling for Zn2+ and Cd2+ as well as chromogenic response towards Fe3+, Fe2+, Zn2+ and Cd2+ ions. The addition of metallic cations induces a remarkable colorimetric response from yellow to colorless (for Zn2+, Cd2+), purple (for Fe2+) and light green (for Fe3+) visible to naked eye. Interestingly, the sensor can easily differentiate two states of iron (Fe3+ from Fe2+) by revealing distinctive colors and different absorption maxima. The detection limit of the sensor towards Zn2+/Cd2+ is low down to nanomolar concentration (86nM and 50nM, respectively). Moreover, the sensor can be applied for the fabrication of fluorogenic molecular switch, which turns “ON” upon selective binding with Zn2+/Cd2+ ions and turns “OFF” in the simultaneous presence of Zn2+/Cd2+ and IO4- ion. Thus, it is potentially significant sensor and should be explored further for environmental applications.

Synthesis, crystal structure, and antibacterial activity of a mononuclear cerium(III) complex derived from tris(2-((5-chlorosalicylidene)amino)ethyl)amine

ABSTRACTA new mononuclear cerium(III) complex, [CeL(H2O)]·0.5CH3OH, where L is the deprotonated form of tris(2-((5-chlorosalicylidene)amino)ethyl)amine, was prepared by the reaction of 5-chlorosalicylaldehyde, tris(2-aminoethyl)amine, and cerium(III) trifluoromethanesulfonate in methanol. The complex was characterized by physicochemical methods and single-crystal X-ray determination. The asymmetric unit of the complex contains a mononuclear cerium(III) complex molecule and a half methanol molecule of crystallization. The tripodal Schiff base ligand coordinates to the Ce atom through all the phenolate oxygen, imino nitrogen, and amino nitrogen atoms. The Ce atom is eight coordinated by the seven donor atoms of the Schiff base ligand, and one water molecule. The complex has effective activity against the bacteria Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescens.