Monomeric Metal Complexes Research Articles

Coordination compounds of carbonyl oxygen polychelate ligand; synthesis, physicochemical characterization and biological evaluation

The work covers the formation of the bisaldehyde ligand 2,2'-[ethane-1,2diylbis(oxy)] dibenzaldehyde (M) and its metal complexes. The synthesis of M was achieved via two steps in which two equivalents of the salicylaldehyde were reacted with KOH in an ethanolic medium. Subsequently, the resulting compound dissolved in DMF and one equivalent of 1,2-dibromoethane was added. Adding an ethanolic solution of metal chloride of a range of metal ions to the ligand in a 1:1 (M:L) mole ratio resulted in preparing a new five monomeric complexes. The entity of the isolated structure for the prepared compounds was confirmed using physicochemical methods (FT-IR, electronic spectroscopy, mass and 1H, 13C-NMR spectra, elemental microanalysis, magnetic susceptibility and molar conductance). The characterization data indicated the isolation of six and four-coordinate monomeric complexes with the general formula; [Cr(M)(Cl)2(H2O)2]Cl, [M(M)(Cl)2].H2O (where M= Fe(II), Co(II) and Cu(II)) and [Ni(M)]Cl2.H2O. The anti-microbiological activity of the title compounds (ligand and complexes) was tested against various bacterial and fungal microorganisms. The acquired data revealed that the metal complexes became potentially more active than the M. Keywords: Bisaldehyde ligand; Novel monomeric metal complexes; Structural study; Antimicrobial activity.

A Biodegradable Iridium(III) Coordination Polymer for Enhanced Two‐Photon Photodynamic Therapy Using an Apoptosis–Ferroptosis Hybrid Pathway

AbstractThe clinical application of photodynamic therapy is hindered by the high glutathione concentration, poor cancer‐targeting properties, poor drug loading into delivery systems, and an inefficient activation of the cell death machinery in cancer cells. To overcome these limitations, herein, the formulation of a promising IrIII complex into a biodegradable coordination polymer (IrS NPs) is presented. The nanoparticles were found to remain stable under physiological conditions but deplete glutathione and disintegrate into the monomeric metal complexes in the tumor microenvironment, causing an enhanced therapeutic effect. The nanoparticles were found to selectively accumulate in the mitochondria where these trigger cell death by hybrid apoptosis and ferroptosis pathways through the photoinduced production of singlet oxygen and superoxide anion radicals. This study presents the first example of a coordination polymer that can efficiently cause cancer cell death by apoptosis and ferroptosis upon irradiation, providing an innovative approach for cancer therapy.

A Biodegradable Iridium(III) Coordination Polymer for Enhanced Two-Photon Photodynamic Therapy Using an Apoptosis-Ferroptosis Hybrid Pathway.

The clinical application of photodynamic therapy is hindered by the high glutathione concentration, poor cancer-targeting properties, poor drug loading into delivery systems, and an inefficient activation of the cell death machinery in cancer cells. To overcome these limitations, herein, the formulation of a promising IrIII complex into a biodegradable coordination polymer (IrS NPs) is presented. The nanoparticles were found to remain stable under physiological conditions but deplete glutathione and disintegrate into the monomeric metal complexes in the tumor microenvironment, causing an enhanced therapeutic effect. The nanoparticles were found to selectively accumulate in the mitochondria where these trigger cell death by hybrid apoptosis and ferroptosis pathways through the photoinduced production of singlet oxygen and superoxide anion radicals. This study presents the first example of a coordination polymer that can efficiently cause cancer cell death by apoptosis and ferroptosis upon irradiation, providing an innovative approach for cancer therapy.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL SCREENING OF Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) IONS WITH SCHIFF BASE POSSESSING THIOSEMICARBAZONE MOIETY

Para-chlorobenzaldehyde and thiosemicarbazide react in 1:1 molar ratio in MeOH and form the Schiff base, LH (1). The Schiff base reacts with divalent Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions in 1:2 molar ratio in MeOH and forms the corresponding non-electrolytic, monomeric metal complexes, [MnL2(MeOH)2](2), [ML2] (3, M = Ni, Zn) and [ML2] (4, M = Co, Cu) respectively. The stereochemistry of Coordination compounds has been reported on the basis of elemental analyses, magnetic susceptibility and molar conductance, IR, electronic and 1H NMR spectral studies. The synthesized Schiff base and metal complexes were tested for antimicrobial activities and they show significant biological activities. An octahedral structure to 2, a tetrahedral structure to 3 (M = Ni, Zn) and a squareplanar structure to 4 (M = Co, Cu) are proposed.

The synthesis and characterization of s-Triazine polymer complexes containing epoxy groups

Abstract It has been synthesized in this study that s-triazine based monomeric complexes including epoxy groups and their polymeric structures. For this reason, cyanuric chloride (I) has been used as starting material. 5-(4,6-dicholoro-2-1,3,5-triazine-2-ylamino)isophtalic acid coded as “III” has been obtained from the reaction of 5-aminoisophtalic acid II and I at −5 °C with sodium bicarbonate in aqua/acetone media. Bis(oxiran-2-ylmethyl)-5-(4,6-dichloro-1,3,5-triazine-2-ylamino)izophtalate coded as “V” was synthesized from the reaction of epichlorohydrin (IV) and III in aqua/acetone media with KOH at 2 °C. In aqua/ethanol media at 60 °C, monomeric metal complexes (VI, VII and VIII) were obtained from the reaction of V and/or Mn+2, Co+2 and Ni+2. s-Triazine based polymeric metal complexes (IX-XIV) were obtained from the reaction of the monomeric metal complexes and 3,4-dihydroxybenzaldehyde/o-phenylenediamine in 1,4-diaxane media with DIPEA at 60 °C. The structure of ligands, monomers and polymers were characterized using 1H NMR and 13C NMR, FTIR, ESI-MS, UV–vis spectrophotometers, TGA and elemental analyses. Metal contents in the prepared monomeric and polymeric complexes were determined by inductively coupled plasma atomic emission spectrophotometer (ICP-AES). Magnetic behaviors of the synthesized novel monomeric and polymeric complexes were also investigated. And, these compounds were determined to be high-spin distorted octahedral Mn(II), distorted octahedral Co(II) and distorted octahedral Ni(II).

Oxidant-responsive ferrocene-based cyclodextrin complex coacervate core micelles

ABSTRACT Coacervate-core micelles are considered promising materials for several applications, from catalysis to drug delivery. However, oxidant-responsive coacervate-core micelles, able to undergo structural changes upon specific oxidation stimuli, are not well reported. Here, we present a novel ferrocene–dipicolinic acid derivative as redox-responsive subcomponent to be incorporated in cyclodextrin-based coacervate core micelles, C4Ms, with tuneable core structure and responsiveness towards H2O2 treatment. The Fc-C4Ms are formed combining three orthogonal supramolecular interactions, namely (i) metal-to-ligand coordination between europium(III) ions and dipicolinic acid molecules, (ii) host-guest interaction between beta cyclodextrins and ferrocenes and (iii) electrostatic coacervation interaction. The micelle stability against oxidation can be controlled by varying three main parameters: (a) the core-unit structure, from monomeric metal complexes to supramolecular oligomers, (b) the H2O2 equivalents and c) the ratio between redox-responsive and non-redox-responsive bislinker. The H2O2-responsive ferrocene-based systems might have an interesting application, e.g. reactive oxygen species-mediated drug delivery.

Alkyl-sulfur versus aryl-sulfur bond cleavage in tridentate alkylthiophenylazonaphthols by group 9 metal ions

The reactions of monoanionic tridentate alkylthiophenylazonaphthols featuring both C(sp3)–S and aryl C(sp2)–S bonds with low-valent group 9 metal compounds afforded monomeric metal complexes via either C(sp2)–S or C(sp3)–S cleavage. Rhodium(I) and iridium(I) selectively cleave C(sp2)–S bond of 2-hydroxy-1-(2′-alkylthiophenylazo) naphthalenes (HL1-HL5) and 1-hydroxy-2-(2′-alkylthiophenylazo) naphthalenes (HL6-HL10) with concomitant two-electron metal based oxidation resulting in the formation of novel M(III) cyclometallates. The molecular structures of the resulting complexes have been determined by single crystal X-ray crystallography. Rhodium(III) or iridium(III) binds desulfurized modified HL1-HL10 ligands via O, N, C(aryl) donor set. Cobalt(I), the remaining member of the group 9, regiospecifically cleaves the C(sp3)–S bond of the diazene ligands with concomitant two-electron oxidation leading to the formation of novel cobalt(III) complexes. The molecular structures of one of the resulting cobalt(III) complex has been determined by single crystal X-ray crystallography. The cobalt(III) center binds one monoanionic ligand (HL) via O, N,S donor set along with a dianionic modified HL through O, N, S(thiolato) donor set.

Formation of small volatile complexes during copper film growth by the combined synthesis-transport method

Stable heterogeneous synthesis products in combined synthesis-transport processes for the growth of thin copper films have been studied by ESR, X-ray photoelectron, and IR spectroscopies. The results demonstrate that the synthesized volatile compounds condensed on solid surfaces have the form of formate-like metal complexes of copper(I). We have identified the mechanisms underlying the formation of volatile monomeric metal complexes on the surface of copper-containing precursor particles and the mechanism of the thermal decomposition of metal complexes on a heated substrate.

Spectroscopic and pH-metric studies on the complexation of a novel tripodal amine-phenol ligand towards Al(III), Ga(III) and In(III)

The aqueous coordination chemistry of a newly synthesized tripodal amine-phenol ligand, cis,cis-1,3,5-tris{(2-hydroxybenzyl)aminomethyl}cyclohexane (THAC) towards H+, Al3+, Ga3+ and In3+ ions have been investigated in aqueous medium of 0.1M KCl ionic strength and 25±1°C by potentiometric and spectrophotometric methods. Three protonation constants assigned to phenolic hydroxyl groups were determined and were used as input data to evaluate the formation constants of the metal complexes. The ligand formed various monomeric metal complex species MLH3, MLH2, MLH, ML and MLH-1 with Ga(III) and In(III); MLH3, ML and MLH−1 with Al(III). The calculated stability constants followed the order Ga(III)>In(III)>Al(III), and their pM values at physiological condition were found to be higher than the corresponding transferrin complexes.

Spectrophotometric and Potentiometric Studies on the Binding Abilities of Two Novel Tripodal Imine-Phenol Ligands Towards Al(III) and Ga(III)

The aqueous coordination behavior of two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L1) and cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me3- TMACHSAL, L2) with Al3+ and Ga3+ has been investigated at an ionic strength of 0.1 mol⋅dm−3 KCl and 25±1 °C by potentiometric and spectrophotometric methods. Both ligands formed various monomeric metal complex species MLH3, MLH2, MLH, ML and MLH−1 with Ga(III); and MLH3, ML and MLH−1 with Al(III). The Ga(III) complexes showed higher thermodynamic stability than the Al(III) complexes. Semi-empirical PM6 calculations along with TDDFT/B3LYP/3-21G calculations have been performed to complement the experimental measurements. The calculated structure of the metal complexes predicted a distorted octahedral geometry where favorable ring-flipping from the equatorial conformation in uncomplexed ligands to the axial conformation was observed upon chelation.

Novel Molecular Building Blocks Based on the Boradiazaindacene Chromophore: Applications in Fluorescent Metallosupramolecular Coordination Polymers

We designed and synthesized novel boradiazaindacene (Bodipy) derivatives that are appropriately functionalized for metal-ion-mediated supramolecular polymerization. Thus, ligands for 2-terpyridyl-, 2,6-terpyridyl-, and bipyridyl-functionalized Bodipy dyes were synthesized through Sonogashira couplings. These fluorescent building blocks are responsive to metal ions in a stoichiometry-dependent manner. Octahedral coordinating metal ions such as Zn(II) result in polymerization at a stoichiometry corresponding to two terpyridyl ligands to one Zn(II) ion. However, at increased metal ion concentrations, the dynamic equilibria are re-established in such a way that the monomeric metal complex dominates. The position of equilibria can easily be monitored by (1)H NMR and fluorescence spectroscopies. As expected, although open-shell Fe(II) ions form similar complex structures, these cations quench the fluorescence emission of all four functionalized Bodipy ligands.

Excited state intramolecular proton transfer (ESIPT) in a dioxotetraamine derived schiff base and its complexation with Fe(III) and Cr(III)

The excited state intramolecular proton transfer (ESIPT) process in a symmetric Schiff base derived from dioxotetraamine and salicylaldehyde, N, N′-Bis{2-[(2-hydroxybenzylidine)amino]ethyl}malonamide (BHAEM) has been investigated experimentally by the fluorescent method and a two step proton transfer mechanism from dienol to ketoenol and then to diketo tautomer has been proposed on the basis of the theoretical evidence obtained through semi-empirical MO/CI calculations using the AM1 Hamiltonian. BHAEM on interaction with Fe(III) and Cr(III), in an aqueous medium of 0.1N ionic strength and 25 ± 1 °C forms monomeric metal complexes of the type ML and MLH −2 with both metal ions, whereas with Cr(III) it forms two more additional species, MLH and MLH −1. The stabilities of these metal complexes have been evaluated using potentiometric and spectrophotometric methods and the relative stabilities of the complexes formed with this ligand are rationalized. At low pH, the ligand coordinates to the metal ions through bis-imine nitrogen and bis-phenolate oxygen atoms but with an increase of pH, further coordination occurs through two amide nitrogen atoms of the ionized amide groups. The structures of the metal complexes were predicted from minimum strain energy calculations employing molecular mechanics using the MM3 force field and from their theoretical electronic spectra obtained through semi-empirical AM1/ZINDO method.

Monomeric Magnesium and Calcium Complexes containing the Rigid, Dianionic 1, 2‐Bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene (dtb‐BIAN) and 1, 2‐Bis[(2‐biphenyl)imino]acenaphthene (bph‐BIAN) Ligands

AbstractThe new rigid bidentate nitrogen ligands 1, 2‐bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene (1) (dtb‐BIAN) and 1, 2‐bis[(2‐biphenyl)imino]acenaphthene (2) (bph‐BIAN) have been synthesized by condensation of 1, 2‐acenaphthylenedione with 2, 5‐di‐tert‐butylaniline and 2‐aminobiphenyl, respectively. Reduction of 1 and 2 with magnesium and calcium results in the formation of the monomeric metal complexes [(dtb‐BIAN)Mg(THF)2] (3), [(bph‐BIAN)Mg(DME)2] (4), and [(bph‐BIAN)Ca(THF)3] (5). Compounds 1 — 5 have been characterized by C/H analyses, IR, 1H NMR, and 13C NMR spectra, the structures of 2, 3, and 5 have been estimated by single crystal X‐ray diffraction.

Synthesis of titanium-TADDOLate complexes containing bidentate nitrogen donors and the asymmetric ethylation of benzaldehyde

Reaction of TiCl 2(TADDOLate)L 2 (L=THF ( 1) or AcOEt ( 2)) with a bidentate nitrogen-containing ligand such as 2,2 ′-bipyridine (bipy) or 1,10-phenanthroline (phen) affords six-coordinate complexes TiCl 2(TADDOLate)(L 2) (L 2=bipy ( 3) or phen ( 4)). Complexes 3 and 4 can also be obtained from reaction of 1.3 eq. of TiCl 4 with a TADDOL (α,α,α ′,α ′-tetraphenyl-1,3-dioxolane-4,5-dimethanol) ligand in diethyl ether followed by the addition of the bidentate ligand. The complex 3 reacts further with 2.2 eq. of MeLi in toluene to give the mono-methyl complex TiCl(Me)(TADDOLate)(bipy) ( 5). Complexes 3 and 4 were subjected to X-ray structural analyses and both structures reveal the same C 2 molecular symmetry with the bidentate bipy or phen ligand trans to the TADDOLate ligand. In the asymmetric reaction of diethylzinc addition to benzaldehyde, the monomeric metal complex 3 or 4 alone shows good catalytic reactivities with low to moderate enantioselectivities of 31% or 52% ee, respectively. However, with the addition of excess Ti(O- i-Pr) 4, the reaction gives nearly quantitative yields of the desired product with good enantioselectivities up to 88% ee.

Voltammetric and spectroscopic investigation of binding in complexes of divalent metal ions with styrene–maleic acid-copolymer and monomeric analogues

The interaction of divalent metal ions with styrene–maleic acid-copolymer (SMA copolymer) has been studied. Polarography, voltammetry on a hanging mercury electrode and UV-VIS spectroscopy were applied to evaluate formation constants for complexation of Cu(II), Zn(II) and Ni(II) ions with the polyelectrolyte SMA copolymer as well as monomeric dicarboxylic acids in aqueous solution. Considering adsorption of the polymer on the Hg electrode the studies show that SMA acts as strong ligand for Cu(II) ions while complexation with Zn(II) is less strong. Voltammetric behavior of Ni(II) in polymer solutions was found to be rather complex. Formation constants of Cu(II) and Zn(II) polymer complexes are considerably greater compared to the corresponding monomeric metal complexes. The results reported point to a strong influence of metal dissolution on the mechanism of deposition of MA copolymers on copper, zinc and nickel electrodes.

Surprising Titanium Complexes Bearing η2-Pyrazolato Ligands: Synthesis, Structure, and Molecular Orbital Studies

As part of a program relating to the preparation of molecular precursors to early transition metal nitride films,2 we have been pursuing the synthesis of complexes that possess only nitrogen ligands in the coordination sphere. Pyrazolato (pz) ligands are particularly attractive nitrogen donors,3 since the ligands themselves are easily prepared and the properties of resultant complexes should be readily modified by appropriate choice of substituents at the carbon atoms. However, application of such complexes as CVD precursors requires monomeric species to achieve the highest possible volatility. Monomeric metal complexes with η2-pz ligands are known for lanthanide and actinide complexes,4,5 but there is only one example of a d-block complex ([Cp2Zr(C3H3N2)(THF)]BPh4) bearing an η2-pz ligand.6 All other structurally characterized d-block metal complexes have shown the ligand to be present either in the bridging mode or with only one nitrogen atom coordinated to the metal.7 With these considerations in mind, we report the synthesis and characterization of several homoleptic pz complexes of titanium(IV). These species are the first homoleptic monomeric pz complexes of any metal and contain exclusively η2-pz ligands. The results of molecular orbital calculations rationalize why the η2-bonding mode is preferred and suggest that η2-pz complexes should be common in early to middle transition metals. Treatment of tetrakis(dimethylamido)titanium(IV) with 4 equiv of 3,5-dimethylpyrazole8 or 3,5-diphenylpyrazole8 in refluxing toluene afforded tetrakis(3,5-dimethylpyrazolato)titanium(IV) (1; 83%) and tetrakis(3,5-diphenylpyrazolato)titanium(IV) (2; 76%) as yellow and light red solids, respectively (eq 1).9 Compounds 1 and 2 were characterized by spectro-

Third order NLO properties of PMMA films co-dispersed with metal dithiolene oligomers

Metal dithiolene oligomers show enhanced third order NLO properties compared with films containing monomeric metal complexes.

Preparation and characterization of paramagnetic polychelates and their protein conjugates

The gadolinium complexes of poly-L-lysine-poly(diethylenetriamine-N,N,N',N",N"-pentaacetic acid) (Gd-PL-DTPA) and poly-L-lysine-poly(1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetr aacetic acid) (Gd-PL-DOTA) and their conjugates with human serum albumin (HSA) have been prepared and characterized. Poly-L-lysine (PL, degree of polymerization approximately 100) was N-acylated with a mixed anhydride of the chelating ligand (DTPA or DOTA). Sixty to ninety chelating groups per molecule of PL could be attached in this way. Following purification of the polychelate by size-exclusion chromatography, the gadolinium complexes were prepared by standard methods and conjugated to HSA with heterobifunctional cross-linking reagents. The molar relaxities of these macromolecular species were 2-3-fold higher than those of the corresponding monomeric metal complexes [( Gd(DTPA)] and [Gd(DOTA)]). The conjugation conditions were optimized to produce conjugates containing 60-90 metal centers per molecule of HSA (ca. one polychelate per protein).

Stability and response studies of multicolor electrochromic polymer modified electrodes prepared from tris(5,5′-dicarboxyester-2,2′-bipyridine)ruthenium(II)

A monomeric metal complex, tris(5,5′-dicarbo(3-acrylatoprop-1-oxy)-2,2′-bipyridine)ruthenium(II) as its p-toluene sulfonate salt, can be spin coated onto optically transparent SnO 2 and thermally polymerized to yield a polymer modified electrode with multicolor (7 color) electrochromic properties. The polymer shows rapid electrochemical response (as short as 250 ms for total conversion through seven oxidation states) and good stability. The response and stability characteristics of the polymer have been examined with respect to polymerization conditions, electrode substrate pretreatment, solvent, supporting electrolyte, and potential excitation vs. time program