Trinuclear Zinc Complex Research Articles

Synthesis, Crystal Structures and Urease Inhibition of Copper(II) and Zinc(II) Complexes Derived from N,N'-Bis(4-bromosalicylidene)-1,3-propanediamine.

A new tetranuclear copper(II) complex [Cu4L2(N3)2(CH3OH)2](NO3)2·4CH3OH (1) and a new trinuclear zinc(II) complex [Zn3L2(CH3COO)2] (2) have been prepared from the bis-Schiff base N,N'-bis(4-bromosalicylidene)-1,3-propanediamine (H2L) with copper nitrate and zinc acetate, respectively, in the presence of sodium azide. The complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. Molecular structures of both complexes were confirmed by single crystal X-ray determination. The Cu(II) atoms in complex 1 are bridged by phenolate oxygen atoms and end-on azide ligands. The Zn(II) atoms in complex 2 are bridged by phenolate oxygen atoms and acetate ligands. The Cu(II) atoms in complex 1 are in square planar and square pyramidal coordination. The Zn(II) atoms in complex 2 are in square pyramidal and octahedral coordination. The Schiff base ligand coordinates to the metal atoms through two phenolate O and two imino N atoms. The biological assay reveals that the copper(II) complex has effective urease inhibition.

Synthesis, characterization, and structures of mononuclear and phenoxo-/acetato-bridged trinuclear zinc(II) complexes from salan ligands: Study of their hydrolytic activity

Synthesis of one mononuclear [ZnL1] (1) and two trinuclear phenoxo-/acetato-bridged zinc(II) complexes [Zn3Cl2(L2)2] (2) and [Zn3(OAc)2(L1)2] (3) containing tetradentate diaminobis(phenolato) “salan” ligands are reported. The ligand precursors and their corresponding zinc complexes are characterized by elemental analysis, NMR, IR, and UV–vis spectroscopy. Molecular structures of complexes 2 and 3 are solved by single-crystal X-ray crystallography, while the fate of the complexes in solution is assessed by ESI-MS spectrometry analysis. All complexes (1–3) were studied for their phosphoesterase activity by using para-nitrophenyl phosphate (PNPP) and bis(2,4–dinitrophenyl) phosphate (BNPP) as substrates. While complex 1 has no activity for these substrates, complex 3 effectively hydrolyses PNPP (1.6 × 10−3 s−1), and complex 2, which is less reactive than 3, displays comparable activities towards both substrates (2.0 × 10−4 s−1 and 5.4 × 10−4 s−1, respectively). The importance of evaluating the speciation of Zn-species present for the understanding of the mechanism of the phosphoesterase reaction is discussed.

Zn(II) complexes with mefenamic acid: Synthesis, characterization, and anticancer activity

In this study, three Zn(II) complexes were synthesized by reacting Zn(CH3COO)2· 2H2O or Zn(ClO4)2· 6H2O with mefenamic acid in the presence of imidazole and pyridine-based co-ligands. The resulting complexes were [Zn(mef)2(imi)2]; (1), [Zn(mef)(py)3]· (ClO4); (2), and [Zn3(mef)6(apy)2]; (3), where mef represents deprotonated mefenamic acid/mefenamato, imi represents imidazole, py represents pyridine and apy represents 2-aminopyridine. Elemental analysis, spectroscopic techniques (FTIR, UV–Vis, 1H and 13C NMR, fluorescence), PXRD (1) and (3), thermal analysis (TG-DSC) (1) and (3), and single crystal X-ray crystallography were employed to characterize the complexes. The Zn(II) in (1) and (2) are in a distorted tetrahedral coordination environment. In (1), the Zn(II) is coordinated by two mefenamato ligands, each coordinating via a monodentate carboxylate oxygen atom and two nitrogens of the imidazole ligands. In (2), the Zn(II) is coordinated by one mefenamato and three pyridine ligands. Complex (3) is a trinuclear zinc complex in which the central Zn(II) is coordinated by six oxygen atoms from six bridging carboxylate groups of the mefenamato ligands. Three mefenamato ligands and a monodentate 2-aminopyridine ligand also coordinate to two terminal Zn(II) ions in a tetrahedral coordination environment in (3). The cytotoxicity of the complexes was evaluated using an MTT assay against MCF-7 (human breast cancer cell line). The complexes demonstrated dependent cell cytotoxicity, with (2) showing the highest anticancer activity.

Insight into the role of pseudo-halides as multiple hydrogen bond acceptors in the formation of supramolecular 1D assembly of di and trinuclear zinc complexes

In this manuscript we report the synthesis of two new zinc(II) complexes, [(DMSO)2 ZnL1Zn(NCS)2] (1), and [{(N3)ZnL2}2Zn(DMSO)2] (2) that were characterized by elemental and spectral analyses {H2L1 is 2,2-dimethyl-1,3-propanediylbis(iminomethylene)bis(phenol), and H2L2 is 1,2-propanediylbis(iminomethylene)bis(4-chlorophenol)}. The structures have been confirmed by single crystal X-ray diffraction analysis. Both complexes form 1D supramoelcular assemblies where the pseudohalides act as multiple H-bond acceptors (CH•••S,N and NH•••S,N). These assemblies have been analyzed theoretically using DFT calculations, and the energy associated to each contact has been estimated using the quantum theory of atoms-in-molecules. The importance of long-range van der Waals interactions is emphasized. This manuscript, where two new complexes are synthesized and the H-bonding contacts individually estimated, is expected to attract the attention not only of synthetic inorganic chemists, but also theoreticians and chemists working in crystal engineering and supramolecular chemistry.

Trinuclear Zinc(II) Complexes Derived from N,N'-Bis(5-bromosalicylidene)-1,2-cyclohexanediamine: Syntheses, Crystal Structures and Antimicrobial Activity.

Two new trinuclear zinc(II) complexes, [Zn3I2L2(H2O)2] (1) and [Zn3(CH3OH)(DMF)L2(NCS)2] (2), where L is the dianionic form of N,N'-bis(5-bromosalicylidene)-1,2-cyclohexanediamine (H2L), have been synthesized and characterized by elemental analyses, IR and UV spectra. Structures of the complexes were further confirmed by single crystal X-ray diffraction. Both complexes are trinuclear zinc compounds. Both compounds are solvated, with water ligand for 1 and methanol ligand for 2. The outer two Zn atoms are in square pyramidal coordination, while the inner one is in octahedral coordination. The effect of the complexes on the antimicrobial activity against Staphylococcus aureus, Escherichia coli and Candida albicans were evaluated, and gave interesting results.

Impact of the zinc complexation of polytopic polyaza ligands on the interaction with double and single stranded DNA/RNA and antimicrobial activity.

Metal complexes have gained a huge interest in the biomedical research in the last decade because of the access to unexplored chemical space with regards to organic molecules and to present additional functionalities to act simultaneously as diagnostic and therapeutic agents. Herein, we evaluated the interaction of two polytopic polyaza ligands and their zinc complexes with DNA and RNA by UV thermal denaturation, fluorescence and circular dichroism spectroscopic assays. The zinc coordination was investigated by X-ray diffraction and afforded the structure of the binuclear zinc complex of PYPOD. Thermal denaturation of DNA and RNA and fluorimetry analysis revealed preferential binding of the zinc-PHENPOD complexes towards GC-containing DNA in contrast to the free ligands. On the other hand, PYPOD metal complexes, compared to the free ligand, stabilized AT-based DNA (B-form) better than AU-RNA (A-form). With regards to single stranded RNA, the binuclear complex of PHENPOD and the free ligand can efficiently identify polyadenylic acid (poly A) among other RNA sequences by circular dichroism spectroscopy. The antimicrobial activity in S. aureus and E. coli bacteria showed the highest activity for the free ligands and their trinuclear zinc complexes. This work can provide valuable insights into the impact of the nuclearity of polytopic polyaza ligands in the binding to DNA/RNA and the antimicrobial effect.

Synthesis, Crystal Structure, and Optical Properties of a Trinuclear Zinc(II) Complex with Rhodamine B

A heteroleptic homotrinuclear complex, [Zn3(valhydr)2(RhB)2(EtOH)2](ClO4)2 (H2valhydr = 1,2-bis(2-hydroxy-3-methoxybenzylidene)hydrazine, RhB = rhodamine B), was synthesized and structurally characterized by X-ray diffraction on single crystal. In the centrosymmetric complex, the zinc ions are positioned in a linear manner. The external zinc ions are pentacoordinated with a distorted square pyramidal stereochemistry, while the central zinc ion presents an elongated octahedral geometry. Luminescent properties of the complex were investigated in solid state and solution.

Synthesis, structural analysis, and docking studies with SARS-CoV-2 of a trinuclear zinc complex with N-phenylanthranilic acid ligands.

The structure of a trinuclear zinc complex, hexakis(μ2‐2‐anilinobenzoato)diaquatrizinc(II), [Zn2(C13H10NO2)6(H2O)2] or (NPA)6Zn3(H2O)2 (NPA is 2‐anilinobenzoate or N‐phenylanthranilate), is reported. The complex crystallizes in the triclinic space group P and the central ZnII atom is located on an inversion center. The NPA ligand is found to coordinate via the carboxylate O atoms with unique C—O bond lengths that support an unequal distribution of resonance over the carboxylate fragment. The axial H2O ligands form hydrogen bonds with neighboring molecules that stabilize the supramolecular system in rigid straight chains, with an angle of 180° along the c axis. π stacking is the primary stabilization along the a and b axes, resulting in a highly ordered supramolecular structure. Docking studies show that this unique supramolecular structure of a trinuclear zinc complex has potential for binding to the main protease (Mpro) in SARS‐CoV‐2 in a different location from Remdesivir, but with a similar binding strength.

Large interaction energy for the homodimer and the heterodimer extracted from the supramolecular chain of a bent trinuclear zinc(ii) complex with a reduced Schiff base ligand

The coordinated amino groups in a trinuclear zinc complex participate in strong H-bonding interactions that have been analysed. The dimerization energy is very large for both the homodimer and the heterodimer in the 1D supramolecular chain.

Acetonitrile-induced structure fine-tuning of a trinuclear zinc complex showing multistimuli responsive luminescence

A trinuclear zinc complex (1) exhibits mechanochromic and acidochromic luminescence properties with five-color switching. The structure of complex 2 shows that the acetonitrile molecules induce fine-tuning of the structures compared with 1.

Copper(II) and Zinc(II) Complexes Derived from N,N’-Bis(4-bromosalicylidene)propane-1,3-diamine: Syntheses, Crystal Structures and Antimicrobial Activity

A mononuclear copper(II) complex, [CuL] (1), and a phenolato-bridged trinuclear zinc(II) complex, [Zn3Cl2L2(DMF)2] (2), where L is the deprotonated form of N,N'-bis(4-bromosalicylidene)propane-1,3-diamine (H2L), have been prepared and characterized by elemental analyses, IR and UV-Vis spectroscopy, and single crystal X-ray diffraction. The Cu atom in complex 1 is in square planar coordination, while the terminal and central Zn atoms in complex 2 are in square pyramidal and octahedral coordination, respectively. The antibacterial activities of the complexes have been tested on the bacteria Staphylococcus aureus and Escherichia coli, and the yeast Candida parapsilosis.

A trinuclear Zn(ii) Schiff base azido compound: synthesis, structure and exploration of antimicrobial activity

The synthesis, characterization, X-ray crystal structure and antimicrobial activity of a trinuclear zinc(ii) complex have been explored.

Synthesis, structure and nitroaromatic sensing ability of a trinuclear zinc complex with a reduced Schiff base ligand: Assessment of the ability of the ligand to sense zinc ion

A trinuclear zinc complex, [Zn{Zn(N3)L}2] {H2L = 2,2′-[(1-ethyl-1,3-propanediyl)bis(iminomethylene)]bis[6-ethoxyphenol]}, has been synthesized and characterized. Its structure has been confirmed by X-ray crystallographic analysis. The complex acts as a sensor for the detection of nitroaromatics in CH3CN solution via turn-off fluorescence response. The solution phase sensing phenomenon has been studied and a strong quenching efficiency has been observed with a quenching constant (KSV) 13.7952 × 102 M−1 for 2-chloro-4-nitrobenzoic acid. H2L displayed high specificity, sensitivity as well as selectivity for zinc ion in its turn-on fluorescence activity. The mechanism of fluorescence enhancement has been proposed, while the metal–ligand binding stoichiometry and binding constant have also been determined. The detection limit of zinc ion is 7.74 × 10−7 M., with the binding constant K = 2.857 × 105 M−1.

A series of trinuclear zinc(ii) complexes with reduced Schiff base ligands: turn-off fluorescent chemosensors with high selectivity for nitroaromatics

A series of trinuclear zinc(ii) complexes have been synthesized and characterized by X-ray crystallography. The ability of the complexes to act as sensors for the detection of nitroaromatics in DMF has been assessed.

Bimetallic and trimetallic zinc amino-bis(phenolate) complexes for ring-opening polymerization of rac-lactide.

The synthesis and structural characterization of bimetallic and trimetallic zinc complexes of amino-bis(phenolate) ligands are described. Bimetallic complexes (ZnEt)2[L1] (1a), its THF adduct (ZnEt)2[L1]·THF (1a·THF), and (ZnEt)2[L2] (1b) (where [L1] = n-propylamine-N,N-bis(2-methylene-4,6-di-t-butylphenolate) and [L2] = n-propylamine-N,N-bis(2-methylene-6-t-butyl-4-methylphenolate) were prepared via reaction of the proligands H2[L1] and H2[L2] with ZnEt2. The addition of isopropanol to complex 1a to replace the ethyl groups with more nucleophilic alkoxyl groups afforded trimetallic zinc complex Zn3(i-PrO)2[L1]2 (3). Their structures were confirmed by X-ray crystallography. Their catalytic activity towards ring-opening polymerization (ROP) of rac-lactide with or without exogenous alcohol as a co-initiator was studied. These complexes exhibit moderate to good activity for ROP of rac-lactide both in the melt phase and solution. The influence of catalyst and co-initiator loadings were studied and thermodynamic activation parameters were determined. Characterization of the polymers by Gel Permeation Chromatography (GPC) and Matrix-Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrometry showed controlled and living polymerizations for rac-lactide in the presence of alcohol.

A trinuclear centrosymmetric zinc(II) Schiff base complex: Exploration of its photocatalytic and phosphatase mimicking activity

A new trinuclear zinc(II) complex, [Zn(μ1,1-N3)2{Zn(L)(N3)}2] {HL = [2-((3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol]} has been synthesized and characterized by X-ray crystallography. The excellent phosphatase mimicking activity {kcat 176 h−1 at 298 K} on disodium 4-nitrophenylphosphate (4-NPP) hexahydrate substrate has been exhibited by the complex. Phosphatase mimicking activity has been evaluated by monitoring the increase in absorbance at ~425 nm (spectrophotometrically) indicating gradual release of p-nitrophenolate by the hydrolysis of 4-nitrophenylphosphate ester with time. The complex has also been found to be efficient photocatalyst for the degradation of methylene blue (MB) under visible light irradiation.

The ability of a trinuclear zinc(II) Schiff base complex to act as a photocatalyst for the degradation of methylene blue and to mimic phosphatase

A new trinuclear zinc(II) complex, [Zn(µ1,1-N3)2{Zn(L)(N3)}2]·0.5CH3OH {HL = [2-((3-(dimethylamino)propylimino)methyl)-6-methoxyphenol]} has been synthesized and characterized. X-ray crystallographic analysis has confirmed its structure. The central zinc(II) is hexa-coordinated and both of the terminal zinc(II) centers are penta-coordinated. The complex has shown excellent phosphatase mimicking activity {kcat ∼ 190 h−1 at 298 K}, evaluated by monitoring the increase in absorbance at ∼425 nm (spectrophotometrically) indicating gradual release of p-nitrophenolate by the hydrolysis of 4-nitrophenylphosphate ester with time, when 4-NPP (disodium 4-nitrophenylphosphatehexahydrate) has been used as substrate. The complex has also been found to be efficient photocatalyst for the degradation of methylene blue (MB).

Structural analysis of a dimeric trinuclear zinc(II) complex based on a preorganized yet flexible strap porphyrin

We report the solid-state structure of an unexpected trinuclear zinc dimeric porphyrin complex resulting of zinc insertion into a single strap porphyrin. The latter bears an overhanging carboxylic acid which usually interacts with metal cations either in out-of-plane (OOP) or in hanging-atop (HAT) coordination mode by changing its location above the porphyrin coordination site. However, in the present studies, the overhanging carboxylic group acts as a bidentate ligand and binds the OOP-bound zinc cation together with another zinc cation bridging two porphyrin units.

Synthesis of di- and trinuclear zinc complexes bearing pyrrole-based ligands and their catalysis toward the ROP of rac-lactides

Di(aminomethylpyrrolyl)methane derivatives [2-{5-R′2NCH2(C4H2NH)}]2CR2 (2a R = Et, R′ = Me; 2b R = Ph, R′ = Me; 2c R = Ph, R′ = Et; 2d R2 = 1,1′-biphenyl-2,2′-diyl, R′ = Me; 2e R2 = 1,1′-biphenyl-2,2′-diyl, R′2 = (CH2)4) were prepared through reaction of di(1H-pyrrol-2-yl)methane derivatives (2-C4H3NH)2CR2 (1a R = Et; 1b R = Ph;1c R2 = 1,1′-biphenyl-2,2′-diyl) with formaldehyde and amines. Treatment of 2a with 3 equiv. of ZnEt2 in toluene afforded trinuclear zinc conplex 3a, while respective reaction of 2b-2e with 3 equiv. of ZnEt2 in toluene or THF produced dinuclear zinc complexes 3b-3e. Each of the complexes was characterized by 1H and 13C NMR spectroscopy and elemental analysis. Structures of complexes 3a and 3b were additionally characterized by single crystal X-ray diffraction. Catalysis of complexes 3a-3e toward the ROP of rac-lactides was evaluated in both toluene and THF. Each complex was active in the catalysis in the presence of benzyl alcohol (BnOH). 3a showed the highest activity in toluene and 3c was the most active in THF. Kinetic study of complexes 3a and 3e was carried out and the results showed that the polymerization catalyzed by 3e/BnOH follows a first-order kinetics, while 3a/BnOH-catalyzed polymerization followed neither first-order nor second-order kinetics.

A new end-on (μ1,1) azido bridged [Zn2(L)2(Na)N3]n 1D chain derived from a trinuclear zinc complex: syntheses, crystal structures, photoluminescence properties and DFT study

A bicompartmental N2O4 donor symmetric Schiff base ligand has been deployed to synthesize a trinuclear zinc complex [Zn3(L)2Cl2], which upon treatment with sodium azide produces a new μ1,1-azido-bridged 1-D polymer [Zn2(L)2(Na)N3]n. Both complexes have been characterized using IR, NMR, UV–vis, and X-ray diffraction techniques. In order to have better understanding of electronic transitions of the complexes, a time-dependent DFT study has been performed. Lifetime measurements have also been performed to learn about the stability of excited states of both complexes. The average fluorescence decay lifetime has been found to be 1.42 and 0.59 ns for 1 and 2, respectively. In Hirshfeld surface mapping, X⋯H/H⋯X (X = O, Cl) contacts are found to be only 2.7% of the total surface, which indicates that no significant X⋯H/H⋯X contacts are present in either of the complexes. Unconventional interactions such as C–H⋯π and π⋯π stacking interactions are found in supramolecular architectures of both complexes.