Bi- and Trinuclear Copper(II) Complexes of a Sterically Constrained Phenol-Based Tetradentate Ligand: Syntheses, Structures, and Magnetic Studies

Catechol oxidation promoted by bridging phenoxo moieties in a bis(μ-phenoxo)-bridged dicopper(ii) complex

A dinuclear copper(ii) complex [Cu₂(papy)₂(CH₃OH)₂] has been synthesized by reaction of one equiv. of Cu(OAc)₂·2H₂O with one equiv. of the tetradentate tripodal ligand H₂papy [N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] and has been characterized by various spectroscopic techniques and its solid state structure has been confirmed by X-ray crystal structure analysis. The single-crystal structure of the complex reveals that the two copper centers are hexa-coordinated and bridged by two O-atoms of the phenoxo moieties. The variable temperature magnetic susceptibility measurement of the complex reveals weak ferromagnetic interactions among the Cu(ii) ions with a J value of 1.1 cm⁻¹. The catecholase activity of the complex has been investigated spectrophotometrically using 3,5-di-tert-butyl catechol as a model substrate in methanol solvent under aerobic conditions. The Michaelis–Menten kinetic treatment has been applied using different excess substrate concentrations. The parameters obtained from the catecholase activity by the complex are K_M 2.97 × 10⁻⁴ M, V_max 2 × 10⁻⁴ M s⁻¹, and k_cat 7.2 × 10³ h⁻¹. A reaction mechanism has been proposed based on experimental findings and theoretical calculations. The catechol substrate binds to dicopper(ii) centers and subsequently two electrons are transferred to the metal centers from the substrate. The bridging phenoxo moieties participate as a Brønsted base by accepting protons from catechol during the catalytic cycle and thereby facilitating the catechol oxidation process.

A bis(μ-phenoxo)-bridged dicopper(ii) complex capable of oxidizing catechol with the highest efficiency amongst any bis(μ-phenoxo)-bridged dicopper(ii) complexes is reported.

Unusual chemistry of Cu(ii) salan complexes: synthesis, characterization and superoxide dismutase activity

Cu(ii)-salan complexes: structural and spectral characterization, solvent assisted ring cleavage and correlation of superoxide dismutase activity with cyclic voltammetry data and steric effects.

Crossover from Antiferromagnetic to Ferromagnetic Exchange Coupling in a New Family of Bis-(μ-phenoxido)dicopper(II) Complexes: A Comprehensive Magneto-Structural Correlation by Experimental and Theoretical Study

Five neutral bis(μ-phenoxido)dicopper(II) complexes, [Cu₂(L^Me,Me,Me)₂] (1), [Cu₂(L^Me,Me,Et)₂]·CH₂Cl₂ (2), [Cu₂(L ^{i-Pr,i-Pr,i-Pr})₂]·2H₂O (3), [Cu₂(L ^t-Bu,Me,i-Pr)₂] (4), and [Cu₂(L ^{t-Bu,t-Bu,i-Pr})₂]·H₂O (5) have been synthesized and characterized by single-crystal X-ray diffraction analyses, magnetic studies, and density functional theory (DFT) calculations, in which the ligands [H₂L^Me,Me,Me = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L^Me,Me,Et = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N',N'-dimethylethylene-1,2-diamine, H₂L ^{i-Pr,i-Pr,i-Pr} = N,N-bis(2-hydroxy-3,5-diisopropylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, H₂L ^t-Bu,Me,i-Pr = N,N-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-N',N'-diisopropylethylene-1,2-diamine, and H₂L ^{t-Bu,t-Bu,i-Pr} = N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'-diisopropylethylene-1,2-diamine] contain the same [O,N,N,O]-donor atoms combination but differ in substituents at phenol rings and at an amino nitrogen atom. The effect of these remote substituents on the nature of exchange coupling interactions (ferromagnetic vs antiferromagnetic) between the copper(II) ions has been investigated. The average Cu-O-Cu angle, Cu-O-Cu-O torsion angle, and Cu···Cu separation in 1-5 are varied systematically by these remote ligand substituents in the range 98.6-83.3°, 26.0-46.5°, and 2.982-2.633 Å, respectively. As a result, the intramolecular spin-spin coupling in these complexes are changing gradually from a strong antiferromagnetic (J = -395 cm^-1, where Ĥ = -JŜ ₁ Ŝ ₂) to a moderate ferromagnetic (J = +53.2 cm^-1) regime. The crossover angle at which the magnetic interaction changes from antiferromagnetic to ferromagnetic (J = 0) is determined to be ca. 87° for this series of dicopper(II) complexes. DFT calculations support the experimentally determined crossover angle and disclose various magneto-structural correlations in the series 1-5.

Varying structural motifs, unusual X-band electron paramagnetic spectra, DFT studies and superoxide dismutase enzymatic activity of copper(ii) complexes with N′-[(E)-phenyl(pyridin-2-yl)methylidene]benzohydrazide

A diverse set of new copper(ii) complexes synthesized as possible models for antioxidant superoxide dismutase mimics.

Copper (ii) dimers stabilized by bis(phenol) amine ligands: theoretical and experimental insights

Comparative structural and magnetic studies on the binuclear Cu complexes of ¹L(2−)/²L(2−) have been done and their electronic structures and observed electronic transitions (DFT and TD-DFT calculations) rationalized. The dimer complex can be converted into the corresponding monomeric Cu(ii) complex, [¹L₂CuII2(X)] (X = py), by adding an exogenous ligand such as pyridine (py).

Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO₂L^1-7] (1-7) derived from various tetradentate diamino bis(phenolato) "salan" ligands, N,N'-dimethyl-N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H₂L¹); X=Me, YCl, Z=H (H₂L²); X=ⁱPr, Y=Cl, Z=Me (H₂L³)} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=^tBu, Z=H (H₂L⁴); X=Y=Me, Z=H (H₂L⁵); X=ⁱPr, YCl, Z=Me (H₂L⁶); X=Y=Br, Z=H (H₂L⁷)} containing O-N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV-vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O₂N₂ donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC₅₀ values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC₅₀ values of 6 are 2.62 and 10.74μM and that of 7 is 11.79 and 30.48μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.

Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes

Three new copper(ii) complexes, viz., [Cu(L)(NO₃)(H₂O)]H₂O 1, [Cu(L)(H₂O)₂]NO₃2 and [Cu₂(L)₂(pyrazine)](ClO₄)₂·4H₂O 3, were prepared using a biomimetic synthesis strategy [HL = 4-chloro-2-{(E)-[2-(pyridin-2-yl)hydrazinylidene]methyl}phenol]. In complex 3, stacking of chelates rings was observed.

Unprecedented copper(ii) mediated in situ formation of gem-diol binuclear complexes: a combined experimental and computational study

The two alkoxo bridged complexes [Cu₂(L¹)₂(HL²)₂(H₂O)](NO₃)₂·2H₂O 1 and [Cu₂(L¹)₂(HL²)₂](NO₃)₂·H₂O 2 have been synthesized by metal assisted hydrolysis with two Schiff bases, where L¹ is 2-benzoylpyridine and HL² is phenyl(pyridin-2-yl)methanediol.

The structure, magnetism and EPR spectra of a (μ-thiophenolato)(μ-pyrazolato-N,N') double bridged dicopper(II) complex

A new binuclear copper(ii) complex, namely [Cu2L(pz)(DMSO)], where L = 2,6-bis[(2-phenoxy)iminomethyl]-4-methylthiophenolate(3-) and pz = pyrazolate ligand, has been synthesized by a one-pot synthesis involving copper(ii) acetate monohydrate, the S-protected ligand precursor 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2'-hydroxy anil, (), and pyrazole, in which a metal-promoted S-deprotection reaction occurs during the formation of the complex. This was characterized by routine physicochemical studies, single crystal X-ray diffraction and electron paramagnetic resonance (EPR) techniques. The structure analysis reveals that there are copper centres in two different environments, a slightly distorted square planar and a distorted square-pyramidal, arranged in binuclear units. The EPR study of these binuclear units performed at 9.4 GHz in the temperature range between 4 and 293 K shows an antiferromagnetic interaction between Cu(II) ions, and allows evaluating g factors gx = 2.068(1), gy = 2.091(1) and gz = 2.165(1), with <g> = 2.108(1), an exchange coupling parameter J0 = -26(1) cm(-1) (defined as ), and a zero field splitting of the ground triplet state described by D = 86(2) × 10(-4) cm(-1) and E = -48(3) × 10(-4) cm(-1). These results are discussed and compared with the existing literature.

Unprecedented structural variations in trinuclear mixed valence Co(ii/iii) complexes: theoretical studies, pnicogen bonding interactions and catecholase-like activities

Cis–trans configurational changes of trinuclear mixed valence Co(ii/iii) complexes of a Schiff base ligand and an unusual structure with its reduced form are reported.

Synthesis, Structure, Luminescent Property and Theoretical studies of 4-Chloro-2,6-Bis[(3,5-Dimethyl-1H-pyrazol-1-yl)methyl]phenol

4-Chloro-2,6-bis[(3,5-dimethyl-1 H-pyrazol-1-yl)methyl]phenol has been synthesised and characterised, including by single-crystal X-ray diffraction. The benzene ring system is planar and makes dihedral angles of 88.90°(0.14) and 59.84°(0.11) with two pyrazole rings, respectively, and the two pyrazole rings are arranged trans to each other with the dihedral angles 87.22°(0.15). The luminescent property of the title compound was investigated. The molecular structure of the title compound has been optimised by density functional theory with B3LYP/6-31G (d, p) level, the optimised geometer parameters and vibrational frequencies are consistent with the experiment data.

Synthesis, characterization and reactivity of trinuclear Cu(II) complexes derived from disalicylaldehyde malonoyldihydrazone

Three new homotrinuclear copper(II) complexes [Cu3(slmh)(μ-Cl)2(CH3OH)3]⋅0.5CH3OH (1), [Cu3(slmh)(NO3)2(CH3OH)5]⋅1.5CH3OH (2) and [Cu3(slmh)(μ-ClO4)2(CH3OH)3]⋅2CH3OH (3) from disalicylaldehyde malonoyldihydrazone have been synthesized and characterized. The composition of the complexes has been established on the basis of data obtained from analytical and thermoanalytical data. The structure of the complexes has been discussed in the light of molar conductance, electronic, FT-IR and far-IR spectral data, magnetic moment and EPR spectral studies. The molar conductance values for the complexes in DMSO solution indicate that all of them are non-electrolyte. The magnetic moment values for the complexes suggest considerable metal-metal intramolecular interaction between metal ions in the structural unit of the complexes. The EPR spectral features reveal that at RT, the ground state for the complexes is a mixture of the quartet state (S=3/2) and doublet state (S=1/2). At lower temperature, the ground state for the complexes is dx(2)-y(2) with considerable contribution from dz(2) orbital. Dihydrazone ligand is present in enol form in all of the complexes. The complexes have distorted square pyramidal stereochemistry. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry. Hydrogen peroxide mediated oxidation of benzyl alcohol catalyzed by complex 1 has been studied.

Limiting nuclearity in formation of polynuclear metal complexes through [2 + 3] cycloaddition: synthesis and magnetic properties of tri- and pentanuclear metal complexes

The cycloaddition reaction between [Ni(L)(N₃)] and different organonitriles afforded tetrazolate bridged tri- and pentanuclear nickel(ii) complexes.

Heteroleptic titanium(IV) catecholato/piperazine systems and their anti-cancer properties

In this paper we report the synthesis and full characterisation of a range of Ti(IV)-catecholato systems complexed to piperazine or homopiperazine salan ligands. The steric/electronic environment of the catecholate moiety has been varied and the effect this has on cytotoxicity discussed. It was observed that the 7-membered homopiperazine complexes are more stable to hydrolysis than their piperazine cousins in biological media. In general the homopiperazine complexes show higher cytotoxicity than the piperazine complexes, with the most cytotoxic complex exhibiting IC50 (μM) values of 3 ± 0.5 μM (HT-29) and 4 ± 1 μM (OVCAR).

Synthesis and characterization of homotrimetallic copper complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Copper (II) complexes [Cu(3)(nph)(μ(2)-X)(2)(H(2)O)(6)]·2H(2)O [X=Cl (1), (ClO(4)) (3)] and [Cu(3)(nph)(NO(3))(2)(H(2)O)(6)] (2) have been synthesized from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone in methanol medium and characterized. The structures of the complexes have been discussed in the light of data obtained from analytical, thermoanalytical, mass spectral studies, molar conductance, magnetic moment, electronic, EPR, IR, FT-IR spectroscopic studies. The molar conductance values for the complexes fall in the region 0.5-0.9 Sm(2) mol(-1) in DMSO solution indicating that all of them are non-electrolyte. The magnetic moment values for the complexes suggest weak M-M interaction in the structural unit of the complexes. The dihydrazone ligand is present in enol form in all of the complexes. Copper centre has tetragonally distorted octahedral stereochemistry in chlorido and perchlorato complexes while in nitrato complex, copper has mixed square-pyramidal and distorted-octahedral stereochemistry. The EPR parameters of the complexes indicate that the copper centre has the doublet state as the ground state.

Aqua-{4,4',6,6'-tetra-fluoro-2,2'-[(piperazine-1,4-di-yl)dimethyl-ene]diphenolato}copper(II)

In the title compound, [Cu(C₁₈H₁₆F₄N₂O₂)(H₂O)], the Cu^II atom shows a distorted square-pyramidal coordination geometry with the N,N′,O,O′-tetra­dentate piperazine–diphenolate ligand forming the basal plane. The apical site is occupied by the O atom of a coordinated water mol­ecule. Neighbouring complexes are associated through inter­molecular O—H⋯O and O—H⋯F hydrogen bonds between the water mol­ecule and a phenolate O atom or an F atom from an adjacent ligand, respectively, forming a centrosymmetric dimer. Dimers are linked by additional inter­molecular C—H⋯O and C—H⋯F hydrogen bonds, giving infinite chains propagating along the a axis.

Magnetic properties of a novel quasi-2D Cu(II)-trimer system

We present structural and magnetic data of a new Cu(2+)(S = 1/2)-containing magnetic trimer system 2b·3CuCl(2)·2H(2)O (b = betaine, C(5)H(11)NO(2)). The trimers form a quasi-2D quantum spin system with an unusual intra-layer exchange coupling topology, which, in principle, supports diagonal four-spin exchange. To describe the magnetic properties, a 2D effective interacting-trimer model has been developed including an intra-trimer coupling J and two inter-trimer couplings J(a) and J(b). The low-energy description and effective parameters are obtained from numerical calculations based on four coupled trimers (with periodic boundary conditions). Fits to the experimental data using this model yield the magnetic coupling constants J/k(B) = -15 K and J(a)/k(B) = J(b)/k(B) = -4 K. These parameters describe the susceptibility and magnetization data very well over the whole temperature and field range investigated. Moreover, the model calculations indicate that, for certain ranges of the ratio J(b)/J(a), which might be accessible by either chemical substitution and/or hydrostatic pressure, the low-energy properties of 2b·3CuCl(2)·2H(2)O will be dominated by non-trivial four-spin exchange processes.