Binuclear Zinc Complexes Research Articles

An asymmetric binuclear zinc(ii) complex with mixed iminodiacetate and phenanthroline ligands: synthesis, characterization, structural conversion and anticancer properties

A water-soluble asymmetric binuclear zinc(ii) complex with mixed iminodiacetate and 1,10-phenanthroline ligands exhibited promising anticancer activity and low toxicity, suggesting potential as a chemotherapeutic agent.

New pyridazine-based binuclear nickel(ii), copper(ii) and zinc(ii) complexes as prospective anticancer agents

The complexes containing diethylamino substituents exhibit promising cytotoxicity against the estrogen receptor (ER) negative MDA-MB-231 breast cancer cell line.

Phenoxy-bridged binuclear Zn(II) complex holding salen ligand: Synthesis and structural characterization

A novel binuclear phenoxo-bridged zinc complex obtained from the interaction of ligand, 2,2-(1E,1E)-(2,2-dimethylpropane-1,3-diyl)bis(azanylylidene) bis(methanylylidene)diphenol with zinc chloride is reported. The synthesized and isolated zinc complex has been characterized by FT-IR, 1H- and 13C- NMR, ESI-MS, TGA/DTA and single crystal X-ray diffraction studies. The phenoxo-bridge in this binuclear Zn(II) complex is due to the phenolic oxygen of the salen liagnd. The complex crystallizes in monoclinic P-1 space group, and different geometry has been assigned for both zinc ions in the complex.

Spectral and Electroluminescent Properties of Binuclear Zinc Complexes with Halogen-Substituted Derivatives of 1,2,4-Triazole

Spectral properties of binuclear zinc complexes in chloroform solutions and polyvinylcarbazole (PVC) films are investigated. It is demonstrated that incorporation of a halogen atom (chlorine or bromine) in a ligand benzene ring leads to a small shift of the spectrum toward the red region and a reduction of the fluorescence quantum yield. The fluorescence and phosphorescence spectra at T = 77K are investigated. The fluorescence undergoes a blue shift of about 30 nm and multiply increases in the intensity, and the phosphorescence is observed at 540–580 nm. The phosphorescence lifetime is estimated. The electroluminescent properties of metal complexes in structures with thermal vacuum spin coating of complexes and in PVC films are investigated.

Crystal structure of di-μ-hydroxido-bis{[N,N'-bis-(2,6-di-methyl-phen-yl)pentane-2,4-diiminato(1-)]zinc}.

The title compound, [Zn2(C21H25N2)2(OH)2], is a binuclear zinc complex formed by two bidentate β-diketiminate (nacnac) ligands and two μ-hydroxide O atoms, bridging two mononuclear units into a centrosymmetric dimeric unit. Each Zn2+ cation is coordinated by two N-donor atoms from the nacnac ligand and two O-donor atoms of hydroxide anions to give a distorted tetra­hedral coordination environment. The Zn—O bond lengths are 1.9643 (13) and 2.0022 (14) Å, and the two Zn—N bond lengths are 1.9696 (14) and 1.9823 (14) Å. The distance between the two Zn2+ cations in the dimer is 2.9420 (4) Å. Although hydroxide groups are present in the complex, no classical hydrogen-bonding inter­ations are observed because of the bulky β-diketiminate ligands.

Theoretical studies of ground and excited states in a series of Zn(II) complexes, derived from thiourea and thiosemicarbazide

Theoretical studies for a series of mono- and binuclear zinc (II) complexes Zn(CH3COO)(2)(H2L)(2) [H2L = N-2-propenyl-N'-2-pyridinylthiourea] (A), Zn-2(CH3COO)(2)(H3L-a)(2) [H3L-a=2-[(2-hydroxy-phenyl)methylene]hydrazine-N-phenylcarbothioamide] (B), and Zn(H3L-b)(2) [H3L-b = 2-[(2-hydroxy-phenyl) methylene]hydrazine-N-(2-propenyl)carbothioamide] (C) have been performed on their structures and excited-state absorption spectra. The singlet ground-state geometries are fully optimised at three DFT levels, i.e., B3LYP, B3PW91, and M06. Different geometries, i.e., strongly distorted tetrahedral coordination environment in complex A, distorted square-pyramidal environment in complex B, and irregular octahedral mode in complex C are identified. Consequently, the spectroscopic properties are calculated by means of time-dependent density functional theory (TDDFT) with the Polarisable Continuum Model (PCM) based on the optimised gas-phase geometries. Three absorption peaks are identified for every complex, which are in good agreement with the experimental ones. For complex A, all three absorption peaks centered at 280.33 nm, 268.09 nm, and 250.87 nm, respectively, are ascribed to the (p, pi) -> pi* transition with a mixed intraligand charge-transfer (ILCT)/ligand-ligand charge-transfer (LLCT) character. The composition of frontier orbitals involved in major absorption bands for the three complexes shows similarities, which results in the almost homologous transition attributions and characteristics. A remarkable bathochromic shift in the lowest-lying absorption band is observed for complexes B and C as compared with complex A, which is attributed to the decreased H (HOMO)-L (LUMO) energy gap (Delta E vertical bar HOMO-LUMO vertical bar) by the formation of conjugate metallocycles in complexes B and C.

Synthesis, structural features, and methyl methacrylate polymerisation of binuclear zinc(II) complexes with tetradentate pyrazolyl ligands

The reaction of ZnCl2 with ancillary ligands, including 1,4-bis-(N,N-di-(1H-pyrazolyl-1-methyl)amine)benzene (L1) and 4,4′-bis-(N,N-di(1H-pyrazolyl-1-methyl)phenyl)methane (L2), in ethanol yields Zn(II) chloride complexes, i.e., 1,4-bis-(N,N-di-(1H-pyrazolyl-1-methyl)amine)benzene(dichloro)Zn(II) [L1Zn2Cl4] and 4,4′-bis-(N,N-di-(1H-pyrazolyl-1-methyl)phenyl)methane(dichloro)Zn(II) [L2Zn2Cl4]. The X-ray crystal structures of Zn(II) complexes revealed that they are binuclear, and each zinc atom has a distorted tetrahedral geometry which involves a nitrogen atom from two pyrazole groups and two chloro ligands. The catalytic activity of [L1Zn2Cl4] and [L2Zn2Cl4] for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) increased by twofold compared to the corresponding monomeric Zn(II) complex, N,N-bis(1H-pyrazolyl-1-methyl)aniline(dichloro)Zn(II) [LZnCl2], at 60°C.

Crowded Bis-(M-salphen) [M = Pt(II), Zn(II)] Coordination Architectures: Luminescent Properties and Ion-Selective Responses

For binuclear luminescent host systems, cooperativity between metal-organic moieties becomes feasible with regards to photophysical properties and sensing behavior. A new class of conformationally rigid binuclear platinum(II) and zinc(II) complexes bearing tetradentate aromatic Schiff base (salphen) ligands with limited rotational freedom has been prepared and characterized, and the molecular structure of a (Pt-salphen)2 derivative has been determined by X-ray crystallography. Their UV-vis absorption and emission properties have been investigated and are tentatively ascribed to different excited states depending on the metal and the extent of intramolecular π-stacking interactions. Colorimetric and phosphorescent responses by the bis-Pt(II) complexes in the presence of selected metal ions have been observed. The nature of the host-guest interactions has been examined by quantitative binding studies, mass spectrometry and DFT calculations, and through comparisons with control complexes.

Synthesis, Crystal Structure, and Luminescence Property of a New Zinc(II) Complex With Schiff-Base Containing Triazole Propane Ancillary Ligand

A new binuclear zinc complex, namely [Zn(Salpn)4(1,3-btp)]n (1, H2salpn = N,N′- bis(salicylidene)-1,3-diaminopropane, while 1,3- btp = 1,3-bis (triazole) propane) has been synthesized under one-pot reaction conditions in high yield, and has been characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. The complex 1 crystallizes in the monoclinic system, space group of C2/c with a = 18.2270(17), b = 10.7435(10), c = 20.2896(19) Å, β = 92.9780(10)°. The two adjacent zinc-Salpn moieties were connected through the flexible 1,3-btp ligand into a binuclear unit. The bulk purity of the materials of 1 was confirmed through the powder X-ray diffraction (PXRD) experiments. Furthermore, the luminescent property of the complex 1 has also been investigated. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Binuclear and chain-structure zinc(II) complexes constructed from 3,4-dimethoxy-trans-cinnamic acid andN-donor coligands 4-(1H-pyrazol-3-yl)pyridine and 4,4′-bipyridine

3,4-Dimethoxy-trans-cinnamic acid (Dmca) reacts with zinc sulfate in the presence of 4-(1H-pyrazol-3-yl)pyridine (L1) or 4,4'-bipyridine (L2) under hydrothermal conditions to afford two mixed-ligand coordination complexes, namely tetrakis(μ-3,4-dimethoxy-trans-cinnamato-κ(2)O:O')bis[[4-(1H-pyrazol-3-yl)pyridine]zinc(II)] heptahydrate, [Zn2(C11H11O4)4(C8H7N3)2]·7H2O or [Zn2(Dmca)4(L1)2]·7H2O, (I), and catena-poly[[bis(3,4-dimethoxy-trans-cinnamato-κO)zinc(II)]-μ-4,4'-bipyridine-κ(2)N:N'], [Zn(C11H11O4)2(C10H8N2)]n or [Zn(Dmca)2(L2)]n, (II). The Zn(II) centres in the two compounds display different coordination polyhedra. In complex (I), the Zn(II) cation is five-coordinated with a pseudo-square-pyramidal geometry, while in complex (II) the Zn(II) cation sits on a twofold axis and adopts a distorted tetrahedral coordination environment. Complex (I) features a centrosymmetric binuclear paddle-wheel-like structure, while complex (II) shows a chain structure. This study emphasizes the significant effect of the coordination mode of both carboxylate-group and N-donor coligands on the formation of complex structures.

Exchange and dative coordinate bonds in binuclear zinc complex

The high-resolution X-ray diffraction study of dizinc bis(pyridine)-bis{[μ2-(2-oxybenzylidene)amino]-4,6-di(tert-butyl)phenoxide} and the analysis of the structures of related compounds refuted the data on the effect of the exchange or dative mechanism of the metalbridging ligand bond formation on the bond strength and revealed the factors controlling the energy of these bonds.

Theoretical Approach Towards the Understanding of Asymmetric Additions of Dialkylzinc to Enals and Iminals Catalysed by [2.2]Paracyclophane‐Based N,O‐Ligands

The 1,2- and 1,4-asymmetric additions of dialkylzinc reagents (ZnMe(2) and ZnEt(2)) to cinnamaldehyde and N-formylbenzylimine catalysed by [2.2]paracyclophane-based N,O-ligands were studied with quantum chemical methods. High level LPNO-CEPA/1 (local pair natural orbital coupled electron pair approximation 1) calculations were performed to obtain reliable reaction barriers and binding energies. The calculations supported the experimentally observed selectivities. In the reaction, the alkyl transfer takes place on a binuclear zinc complex. Regioselectivity can be traced back to changes in π-conjugation. Because the less conjugated N-formylbenzylimine is more flexible, it is better suited for 1,4-additions. Moreover, bulky ligands were shown to be important for stereoselectivity. The reason is that the tricyclic motif present in the transition states is sterically less hindered in the anti conformation. Based on the LPNO-CEPA/1 data, a set of popular theoretical methods are validated. Although it was possible to set up a procedure to obtain the stereoselectivities with computationally less demanding methods, this was not possible for the regioselectivity of the reactions.

Metal Complexes of Bridging Neutral Radical Ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.

Novel photoluminescent mesogenic Schiff-base ligands bearing [N4O4] donors and their bimetallic Zn(II) complexes

Novel photoluminescent salicylaldimine ligands condensed from 3/, 3/, 4/, 4/-tetraminobiphenyl and 4-substituted long alkoxy salicylaldehyde possessing two sets of tetradentate [N2O2] donor site and their binuclear zinc(II) complexes have been synthesized. The mesogenic and photophysical properties were investigated. The compounds were characterized by FT-IR, 1H and 13C NMR, UV–vis, elemental analyses, solution electrical conductivity measurements and FAB mass spectrometry. The mesomorphic behavior of these compounds was probed by differential scanning calorimetry and polarized optical microscopy. The ligand with six carbon chain length showed monotropic nematic mesomorphism at 128°C. However, the ligand with alkoxy tail of carbon length 12 showed enantiotropic SmC phase. The complexes are devoid of any mesomorphism. The low molar conductance values in CH2Cl2 indicate that the complexes are non-electrolytes. At 330nm excitation, the ligand emits green light at ~516nm (Φ=30%) and ~549nm (Φ=16%) in solution and solid state, respectively. At similar excitation wavelength, the complexes exhibit blue light in solution at ~452nm (Φ=20%) and green light in solid state ~555nm (Φ=11%). The DFT calculations were performed using DMol3 program at BLYP/DNP level to ascertain the stable electronic structure of the complex.

DNA binding, DNA hydrolase and phosphatase like activity of new polyaza macrobicyclic binuclear copper(II), nickel(II) and zinc(II) complexes

A new class of mono, polyaza macrobicyclic binuclear copper(II), nickel(II) and zinc(II) complexes 1–6 are synthesized and characterized. The redox, phosphate hydrolysis, DNA binding and cleavage properties of complexes 1–6 are studied. The mononuclear Cu(II)-complex 1 is structurally characterized by single-crystal X-ray diffraction study. They exhibit a quasi-reversible cyclic voltammetric response near −0.65V versus Ag/AgCl in CH3CN-0.1M TBAP assignable to the M2II/M2I redox couple. The initial rate values for the hydrolysis of 4-nitrophenylphosphate to 4-nitrophenolate by the complexes 1–6 are in the range from 1.82×10−6 to 1.25×10−4s−1. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range from 1.1 to 9.5×105M−1. The binding site size and viscosity data suggest the DNA groove binding of the complexes. The complexes display significant hydrolytic cleavage of supercoiled pBR322 DNA at pH 7.2 and 37°C. The hydrolytic cleavage mechanism is further supported by free radical quenching and T4 ligase ligation results. The pseudo-Michaelis–Menten kinetic parameters kcat=2.13±0.3h−1 and KM=5.12×10−5M for macrobicyclic binuclear zinc(II) complex (6) were obtained.

One-Pot Synthesis and Unpredicted Hydrogen Bonds of the Guanidinium Triflates from Readily Available Amines, Carbodiimides, and Zn(OTf)2

The first synthesis of trisubstituted guanidinium triflates has been achieved by a simple one-step procedure from readily available amines, carbodiimides, and Zn(OTf)2. X-ray analysis revealed they adopt 1-D chain-like or novel 3-D hydrogen-bonded networks, which have not been reported previously in the solid structure of guanidinium salts. Isolation of a binuclear zinc complex and its subsequent carbodiimide insertion provide the insight into the mechanism for the formation of guanidinium triflates.

Binuclear zinc(II) complexes with the anti-inflammatory compounds salicylaldehyde semicarbazone and salicylaldehyde-4-chlorobenzoyl hydrazone (H 2LASSBio-1064)

Complexes [Zn 2(HL 1) 2(CH 3COO) 2] ( 1) and [Zn 2(L 2) 2] ( 2) were synthesized with salicylaldehyde semicarbazone (H 2L 1) and salicylaldehyde-4-chlorobenzoyl hydrazone (H 2LASSBio-1064, H 2L 2), respectively. The crystal structure of ( 1) was determined. Upon recrystallization of previously prepared [Zn 2(HL 2) 2(Cl) 2] ( 3) in 1:9 DMSO:acetone crystals of [Zn 2(L 2) 2(H 2O) 2]·[Zn 2(L 2) 2(DMSO) 4] ( 3a) were obtained. The crystal structure of 3a was also determined. All crystal structures revealed the presence of phenoxo-bridged binuclear zinc(II) complexes.

Preparation, Crystal Structure and Spectroscopic Properties of Dimeric [Zn(2-bromobenzoato)2(phenazone)]2 and Monomeric [Zn(2-bromobenzoato)2(thiourea)2]·2H2O

The binuclear zinc complex bis(2-bromobenzoato-O)-bis(μ 2 -2-bromobenzoato-O,O′)-bis(phenazone-O)-dizinc(II) (I) and the mononuclear dihydrate bis(2-bromobenzoato-O)-bis(thiourea-S)-zinc(II) (II) have been synthesized and characterized by means of elemental analysis and spectroscopic methods (IR, 1H and 13C NMR, EDS). The solid state structures of both compounds were determined by single-crystal X-ray diffractometry. Compound [Zn(2-BrC6H4COO)2(phen)]2 (phen—phenazone) (I) crystallized as a dimeric compound with a triclinic lattice (space group P − 1), where both zinc atoms, interconnected by two carboxylate groups, possess a distorted tetrahedral coordination environment. The crystallographic data of complex I: a = 9.9410(3) A, b = 10.7309(3) A, c = 12.9237(4) A, α = 93.6004(17)°, β = 92.5898(11)°, γ = 116.2192(16)°, V = 1230.26(6) A3, Z = 1. Complex [Zn(2-BrC6H4COO)2(tu)2]·2H2O (tu—thiourea) (II) crystallized with an orthorhombic lattice (space group Aba2) as a monomeric compound, where the coordination environment of the central zinc atom is a distorted tetrahedron. The crystallographic data of complex II are: a = 9.8595(3) A, b = 19.7052(5) A, c = 12.5908(3) A, V = 2446.18(11) A3, Z = 4. The modes of the carboxylate binding were assigned from the IR spectra using the magnitude of the separation between the carboxylate stretches (Δ), which correlated well with the crystal structures. The computed theoretical IR spectrum agreed well with the experimental data. Two new compounds bis(2-bromobenzoato-O)-bis(μ 2 -2-bromobenzoato-O,O′)-bis(phenazone-O)-dizinc(II) and bis(2-bromobenzoato-O)-bis(thiourea-S)-zinc(II) have been prepared and characterized by means of spectral analyses and X-ray single crystal structure determination; furthermore the correlation of IR spectra and structures of the prepared compounds has been done.

Fluorescent Zinc(II) Complex Exhibiting “On-Off-On” Switching Toward Cu2+ and Ag+ Ions

Binuclear zinc(II) and copper(II) complexes based on a new Schiff base ligand N,N'-bis(2-hydroxybenzilidene)-2,4,6-trimethylbenzene-1,3-diamine (H(2)L) have been synthesized. The ligand H(2)L and complexes under investigation have been characterized by elemental analyses, spectral (FT-IR, (1)H, (13)C NMR, ESI-MS, electronic absorption, emission), and electrochemical studies. The structures of H(2)L and complexes [{Zn(C(23)H(18)N(2)O(2))}(2)] (1) and [{Cu(C(23)H(18)N(2)O(2))}(2)]·H(2)O (2) have been determined crystallographically. Selective "On-Off-On" switching behavior of the fluorescent complex 1 has been studied. The fluorescence intensity of 1 quenches (turns-off) upon addition of Cu(2+), while enhances (turns-on) in the presence of Ag(+) ions. The mechanisms of "On-Off-On" signaling have been supported by (1)H NMR, ESI-MS, electronic absorption, and emission spectral studies. Job's plot analysis supported 1:1 and 1:2 stoichiometries for Cu(2+) and Ag(+) ions, respectively. Association and quenching constants have been estimated by the Benesi-Hildebrand method and Stern-Volmer plot. Moreover, 1 mimics a molecular keypad lock that follows correct chemical input order to give maximum output signal.

Selective anion binding by a cofacial binuclear zinc complex of a Schiff-base pyrrole macrocycle.

The synthesis of the new cofacial binuclear zinc complex [Zn(2)(L)] of a Schiff-base pyrrole macrocycle is reported. It was discovered that the binuclear microenvironment between the two metals of [Zn(2)(L)] is suited for the encapsulation of anions, leading to the formation of [K(THF)(6)][Zn(2)(μ-Cl)(L)]·2THF and [Bu(n)(4)N][Zn(2)(μ-OH)(L)] which were characterized by X-ray crystallography. Unusually obtuse Zn-X-Zn angles (X = Cl: 150.54(9)° and OH: 157.4(3)°) illustrate the weak character of these interactions and the importance of the cleft preorganization to stabilize the host. In the absence of added anion, aggregation of [Zn(2)(L)] was inferred and investigated by successive dilutions and by the addition of coordinating solvents to [Zn(2)(L)] solutions using NMR spectroscopy as well as isothermal microcalorimetry (ITC). On anion addition, evidence for deaggregation of [Zn(2)(L)], combined with the formation of the 1:1 host-guest complex, was observed by NMR spectroscopy and ITC titrations. Furthermore, [Zn(2)(L)] binds to Cl(-) selectively in THF as deduced from the ITC analyses, while other halides induce only deaggregation. These conclusions were reinforced by density functional theory (DFT) calculations, which indicated that the binding energies of OH(-) and Cl(-) were significantly greater than for the other halides.