A new tyrosinase model with 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene: Binuclear copper(I) and phenoxo/hydroxo-bridged dicopper(II) complexes

The ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) reacts with [Cu(MeCN)₄][ClO₄] to form a binuclear copper(I) complex . Crystal structure analysis reveals that the distorted tetrahedral coordination of each copper(I) center is satisfied by one bidentate arm of each ligand. The complex undergoes ready aromatic ring hydroxylation at position 2 of the phenyl ring when reacted with molecular oxygen in MeCN/MeOH/CH₂Cl₂, producing a four-coordinate μ-phenoxo- and μ-hydroxo-bridged dicopper(II) complex, [Cu₂(baib-O)(OH)(OClO₃)₂] · 1.5H₂O (2) (baib-OH: 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol). This reaction mimics the reactivity of the copper monooxygenase tyrosinase. A trend is observed for the extent of aromatic ring hydroxylation (25 °C): MeCN > MeOH > CH₂Cl₂. Cyclic voltammetric experiment of 1 in MeCN reveals an appreciably high redox potential (anodic peak potential, E_pa = 0.69 V versus SCE) for the redox process. Complex 2 has been characterized by single-crystal X-ray crystallography. Variable temperature (60-300 K) magnetic susceptibility measurements on 2 establish that the copper(II) centers in 2 are antiferromagnetically coupled (2J = −280 cm⁻¹).     

Synthesis, crystal structure, spectroscopic and magnetic properties of copper(II) complexes with 2-(2-pyridyl)imino-N-(2-thiazolin-2-yl)thiazolidine (PyTT)

The copper(II) complexes [Cu(PyTT)₂(H₂O)](NO₃)₂ (A) and [CuCl₂(μ-PyTT)₂CuCl(H₂O)]Cl · 3H₂O (B) were synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, UV-Vis-NIR diffuse reflectance and magnetic susceptibility measurements. In the mononuclear compound A the copper ion is in a distorted square pyramidal geometry, with the equatorial plane formed by two thiazoline nitrogen atoms, one imino nitrogen atom and one water molecule, whereas the axial site is occupied by one imino nitrogen atom. The compound B is dinuclear and both Cu(II) centres present environments that can be described as slightly distorted square pyramidal geometries. The observed molar magnetic susceptibility for A (μ=2.13 BM) allows to exclude metal-metal interactions, supporting a monomeric structural formulation for this compound. In compound B, magnetic susceptibility measurements in the temperature range 6.2-288 K show an intradimer antiferromagnetic interaction (J=−11.8 cm⁻¹).     

Trinuclear and tetranuclear adduct formation between sodium perchlorate and copper(II) complexes of salicylaldimine type ligands: Structural characterization and theoretical investigation

The synthesis of two new sodium perchlorate adducts (1:2 and 1:3) with copper(II) “ligand-complexes” is reported. One adduct is trinuclear [(CuL¹)₂NaClO₄] (1) and the other is tetranuclear [(CuL²)₃Na]ClO₄·EtOH (2). The ligands are the tetradentate di-Schiff base of 1,3-propanediamines and salicylaldehyde (H₂L¹) or 2-hydroxyacetophenone (H₂L²). Both complexes have been characterized by X-ray single crystal structure analyses. In both structures, the sodium cation has a six-coordinate distorted octahedral environment being bonded to four oxygen atoms from two Schiff-base complexes in addition to a chelated perchlorate anion in 1 and to six oxygen atoms from three Schiff-base complexes in 2. We have carried out a DFT theoretical study (RI-B97-D/def2-SVP level of theory) to compute and compare the formation energies of 1:2 and 1:3 adducts. The DFT study reveals that the latter is more stabilized than the former. The X-ray crystal structure of 1 shows that the packing of the trinuclear unit is controlled by unconventional C-H···O H-bonds and Cu²⁺-π non-covalent interactions. These interactions explain the formation of 1 which is a priori disfavored with respect to 2.     

Synthesis, characterization, and crystal structures of hydrotris(2-mercapto-1-imidazolyl)borate-based zinc(II) and copper(I) complexes

The reaction of the tripod ligand hydrotris(2-mercapto-1-imidazolyl)borate Tm^xylyl with zinc(II) perchlorate in methanol afforded the mononuclear complex of the type [Tm^xylyl-Zn(mim^xylyl)]ClO₄ (1). Whereas under the same conditions, the reaction with copper(II) perchlorate gives rise to the simultaneous formation of the dinuclear copper(I) complex [Tm^xylylCu]₂ (2). The chemical formulae of the complexes have been characterized by elemental chemical analysis, IR-NMR spectroscopies, and single crystal X-ray methods. In complex 1, the zinc(II) atom displays a distorted tetrahedral environment. While in complex 2, the Tm^xylyl ligand bridges the two copper(I) atoms in an asymmetric manner with trigonal geometry. The inverted conformation of the ligand Tm^xylyl at the boron center, allows the B-H units to be directed towards the copper centers. The greater reactivity of the borohydride groups towards metal centers enhances the reduction of Cu(II) to Cu(I). The obtained kinetic results for the methylation reactions of 1 and 2 indicate that these bound thione complexes are less suitable to electrophilic attack than the thiolate ligand.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

Structural variations and spectroscopic properties of copper(I) complexes with bis(schiff base) ligands

Six copper(I) complexes {[Cu₂(L1)(PPh₃)₂I₂] · 2CH₂Cl₂}_n (1), {[Cu₂(L2)(PPh₃)₂]BF₄}_n (2), [Cu₂(L3)(PPh₃)₄I₂] · 2CH₂Cl₂ (3), [Cu₂(L4)(PPh₃)₄I₂] (4), [Cu₂(L5)(PPh₃)₂I₂] (5) and [Cu₂(L6)(PPh₃)₂I₂] (6) have been prepared by reactions of bis(schiff base) ligands: pyridine-4-carbaldehyde azine (L1), 1,2-bis(4′-pyridylmethyleneamino)ethane (L2), pyridine-3-carbaldehyde azine (L3), 1,2-bis(3′-pyridylmethyleneamino)ethane (L4), pyridine-2-carbaldehyde azine (L5), 1,2-bis(2′-pyridylmethyleneamino)ethane (L6) with PPh₃ and copper(I) salt, respectively. Ligand L1 or L2 links (PPh₃)₂Cu₂(μ-I)₂ units to form an infinite coordination polymer chain. Ligand 3 or 4 acts as a monodentate ligand to coordinate two copper(I) atoms yielding a dimer. Ligand 5 or 6 chelates two copper(I) atoms using pyridyl nitrogen and imine nitrogen to form a dimer. Complexes 1-4 exhibit photoluminescence in the solid state at room temperature. The emission has been attributed to be intraligand π-π* transition mixed with MLCT characters.     

Imidazole derivatives of binuclear copper (II) and nickel (II) complexes incorporating bis(1,4,7-triazacyclononan-1-yl) ligands

A series of new binuclear copper (II) and nickel (II) complexes of the macrocyclic ligands bis(1,4,7-triazacyclononan-1-yl)butane (L^but) and bis(1,4,7-triazacyclononan-1-yl)-m-xylene (L^mx) have been synthesized: [Cu₂L^butBr₄] (1), [Cu₂L^but(imidazole)₂Br₂](ClO₄)₂ (2), [Cu₂L^mx(μ-OH)(imidazole)₂](ClO₄)₃ (3), [Cu₂L^but(imidazole)₄](ClO₄)₄ · H₂O (4), [Cu₂L^mx(imidazole)₄](ClO₄)₄ (5), [Ni₂ L^but(H₂O)₆](ClO₄)₄ · 2H₂O (6), [Ni₂L^but(imidazole)₆](ClO₄)₄ · 2H₂O (7) and [Ni₂L^mx (imidazole)₄(H₂O)₂](ClO₄)₄ · 3H₂O (8). Complexes 1, 2, 7 and 8 have been characterized by single crystal X-ray studies. In each of the complexes, the two tridentate 1,4,7-triazacyclononane rings of the ligand facially coordinate to separate metal centres. The distorted square-pyramidal coordination sphere of the copper (II) centres is completed by bromide anions in the case of 1 and/or monodentate imidazole ligands in complexes 2, 4 and 5. Complex 3 has been formulated as a monohydroxo-bridged complex featuring two terminal imidazole ligands. Complexes 6-8 feature distorted octahedral nickel (II) centres with water and/or monodentate imidazole ligands occupying the remaining coordination sites. Within the crystal structures, the ligands adopt trans conformations, with the two metal binding compartments widely separated, perhaps as a consequence of electrostatic repulsion between the cationic metal centres. The imidazole-bearing complexes may be viewed as simple models for the coordinative interaction of the binuclear complexes of bis (tacn) ligands with protein molecules bearing multiple surface-exposed histidine residues.     

Syntheses and characterization of mono- and di-N-hydroxyethylated tetraaza macrocycles containing eight C-methyl groups and their nickel(II) and copper(II) complexes

New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L²) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L³) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L¹) with 2-hydroxyethyl bromide. The complexes [NiL³]²⁺, [CuL²]²⁺, and [CuL³]²⁺ have been prepared and characterized. The complex [CuL²](ClO₄)₂ has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL³](ClO₄)₂ containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL²](ClO₄)₂. Unexpectedly, the nickel(II) complex [NiL³](ClO₄)₂ has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The Ni---O bond distance of the nickel(II) complex is shorter, or not longer, than the Ni---N bond distances. The ligand in [CuL²]²⁺ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL³]²⁺ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL³]²⁺ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.     

The synthesis, crystal and molecular structures of two saccharinate-metal complexes with dipyridylamine (dipyr) as a co-ligand

The complexes [Cd(dipyr)₂(sac)(H₂O)] sac·H₂O 1 and [Hg(dipyr)(sac)₂] 2, where dipyr = dipyridylamine and sac = saccharinate, have been synthesised, and fully characterised by single-crystal X-ray diffraction at 120 K. The geometry around Cd in 1 is approximately octahedral, with the metal coordinated by two bidentate dipyr ligands, one N-bonded sac and one H₂O molecule; the second sac forms the counter-ion, and there is also a water of crystallisation. An extensive H-bonded network is formed. In the anhydrous Hg complex 2, the metal has approximately tetrahedral geometry, with coordination from a bidentate dipyr ligand and two N-bonded sac groups. H-bonding interactions are again extensive, even without the presence of H₂O molecules in the structure, leading to chains along the a-axis.     

Organocyanide coordination chemistry: Syntheses, structural characterisations and magnetic properties of copper (II) complexes with a di-imine/pyridine ligand

The reactions between the copper (II) salts [CuXL]PF₆ (L: 2,6-[1-(2,6-diisopropylphenylimino)ethyl]pyridine) (X = Cl 1, X = Br 2) and LiTCNQ, in a DMF/water mixture, or Et₃NH(TCNQ)₂, in acetone, produced the new complexes [CuXL(TCNQ)] (X = Cl 3, X = Br 4). For both compounds, crystallographic studies have clearly evidenced the existence of dimeric complexes [{CuClL}(TCNQ)]₂ owing to π-π overlap between two adjacent TCNQ⁻ radical anions. Compound 1 reacted with Et₄N(C₁₀N₇) to afford the mononuclear derivative [CuClL(C₁₀N₇)] (5), while its reaction with K₂C₁₀N₆ produced the dinuclear complex [(CuClL)₂(C₁₀N₆)] (6). The crystal structures of complexes 5 and 6 have been determined by X-ray crystallography. Magnetic studies have revealed that compound 6 displays weak antiferromagnetic interactions between the two metal centres, conversely compounds 3 and 5 exhibit purely paramagnetic behaviours.     

Structural and magnetic properties of O-bridged tetranuclear and binuclear Cu(II) complexes

Two copper(II) complexes [Cu₄(L¹)₄] (1) and [Cu₂(phen)₂(HL²)₂] (ClO₄)₂ (2) have been synthesized from two potentially tridentate ligands N-(2-hydroxybenzyl) propanolamine (H₂L¹) and N-(2-hydroxybenzyl) ethanolamine (H₂L²). X-ray analyses revealed that 1 contains a Cu₄O₄ cubane core, with each two Cu(II) atoms bridged by a pair of alkoxides; 2 has a bis(μ₂-phenoxo)-bridged dicopper(II) structure. Variable temperature magnetic measurements of 1 have revealed that the correlation between 2J and the bridge angles φ for 1 shows a very strong antiferromagnetic tendency, i.e. the ferromagnetic and antiferromagnetic interactions cross at the φ of 94.5°. The relatively weak antiferromagnetic interactions (2J=−226.8 cm⁻¹) with respect to the bridge angles (φ=100.4°) for 2 have been ascribed to the pyramidal distortions at the phenoxide oxygen atoms in addition to the unfavorable overlaps of the magnetic orbitals for the highly distorted copper coordination polyhedra.     

Dinuclear and mononuclear copper(II) carboxylate complexes with cis-chelating diacids

The synthesis and crystal structures of two new copper complexes with chelating dicarboxylic acids are described. Reaction of copper(II) acetate with diacid H₂L2 (HO₂CC(Me)₂OArOC(Me)₂CO₂H, Ar=1,3-substituted phenyl) gave a bischelate complex (L2)₂Cu₂ · 2MeOH with the normal paddlewheel structure and tilted, trans-oriented chelate rings with skewed conformations. The overall structure was reasonably well reproduced by density functional calculations on (L2)₂Cu₂. Treatment of the product from reaction of Cu₂(OAc)₄ and diacid H₂L3 (Ar=1,3-substituted 2,4-dibromophenyl) with pyridine gave a six-coordinate mononuclear chelate (L3)Py₂Cu · H₂O in which one chelate carboxylate is monodentate, the other is unsymmetrically bidentate, and the pyridines are cis-coordinated.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Synthesis, crystal structures and magnetic studies of dicyanamide bridged two new 1D copper(II) complexes

Two new dicyanamide bridged 1D polynuclear copper(II) complexes [Cu(L¹){μ_1,5-N(CN)₂}]_n (1) [L¹H = C₆H₅C(O)NHNC(CH₃)C₅H₄N] and [Cu(L²){μ_1,5-N(CN)₂}]_n (2) [L²H=C₆H₅C(O)CHC(CH₃)NCH₂CH₂N(CH₃)₂] have been synthesised and structures of both the complexes and their crystal packing arrangements have been established by X-ray crystallography. For complex 1, a tridentate hydrazone ligand (L¹H) obtained by the condensation of benzhydrazide and 2-acetylpyridine is used, whereas a tridentate Schiff base (L²H) derived from benzoylacetone and 2-dimethylaminoethylamine is employed for the preparation of complex 2. Variable temperature magnetic susceptibility measurement studies indicate there are weak antiferromagnetic interactions with J values −0.10 and −1.41 cm⁻¹ for 1 and 2, respectively.     

Complexes of copper(II) dihalide with 2,2′-dipyridylamine. X-ray diffraction structures of the [dibromo-bis(dipyam)copper(II)]–water (1:2) and di[chloro-bis(dipyam)copper(II)]diiodide–acetonitrile (1:2) complexes

The formation of complexes between copper(II) halides and 2,2′-dipyridylamine (dipyam) has been studied systematically. Only complexes with a 1:1 and 1:2 metal-to-ligand ratio are formed. Some mixed chloro–iodide and halide–PF₆ compounds have also been isolated. The X-ray diffraction structures of the [Cu(dipyam)₂Br₂] · 2H₂O (I) and the [Cu(dipyam)₂Cl]₂I₂ · 2CH₃CN (II) complexes are reported. I is a rare example of an octahedral coordination among the copper(II) halide complexes of dipyam. The two bromo atoms, which occupy the apical positions, are H-bonded to the water molecules of crystallization. II is a dimer, where each copper forms a cationic chloro-complex of approximately trigonal bipyramidal geometry, the dimerization being due to hydrogen bonds formed by the NH group of one of the two dipyams coordinated to each metal atom with the chlorine atom of the centrosymmetric cationic complex. The iodide anions are hydrogen-bonded to the NH groups of the dipyams not involved in the dimerization.     

Syntheses, structures and properties of copper(II) complexes containing N-(2-hydroxybenzyl)-amino amide ligands

Four copper(II) complexes containing the reduced Schiff base ligands, namely, N-(2-hydroxybenzyl)-glycinamide (Hsglym) and N-(2-hydroxybenzyl)-l-alaninamide (Hsalam) have been synthesized and characterized. The crystal structures of [Cu₂(sglym)₂Cl₂] (1), [Cu₂(salam)₂(NO₃)₂] · H₂O (3), [Cu₂(salam)₂(NO₃)(H₂O)](NO₃) · 1.5H₂O (4), [Cu₂(salam)₂](ClO₄)₂ · 2H₂O (5) show that the Cu(II) atoms are bridged by two phenolato oxygen atoms in the dimers. The sglym ligand bonded to Cu(II) in facial manner while salam ligand prefers to bind to Cu(II) in meridonal geometry. Variable temperature magnetic studies of 3 showed it is antiferromagnetic. These Cu(II) complexes and [Cu₂(sglym)₂(NO₃)₂] (2), exhibit very small catecholase activity as compared to the corresponding complexes containing acid functional groups.     

The effect of organic acid on self-assembly process: Syntheses and characterizations of six novel cadmium(II)/zinc(II) complexes derived from mixed ligands

Using the principle of crystal engineering, six metal-organic coordination polymers, [Cd(bdc)(3-pytpy)]_n · 2nH₂O (1), [Cd(bdc)_0.5(3-pytpy)]_n · n(ClO₄) (2), Cd(ndc)_0.5(3-pytpy)]_n · n(ClO₄) (3), [Zn(ndc)(3-pytpy)]_n (4), [Cd(bqdc)(3-pytpy)]_n (5), and [Zn(pam)(3-pytpy)]_n · 2nH₂O (6) (H₂bdc = benzene-1,4-dicarboxylic acid, H₂ndc = naphthalene-2,6-dicarboxylic acid, H₂bqdc = 2,2′-biquinoline-4,4′-dicarboxylic acid, H₂pam = pamoic acid), were synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Compounds 1-6 crystallize in the presence of organic-acid linkers as well as multi-functional N-donor ligand 4′-(3-pyridyl)-2,2′:6′,2′′-terpyridine (3-pytpy). In complexes 1, 4, 5, and 6, the dicarboxylate as bridging ligand connects metal atoms to form the main body of 1D zigzag chains for 1 and 4, nearly linear chain for 5 and helical chain for 6, while 3-pytpy as tridentate chelating ligand is just like lateral arm grafting on both sides of these chains. In complexes 2 and 3, both the dicarboxylate and 3-pytpy as bridging ligands connect metal atoms into 2D polymeric structure for 2 and 1D chain of alternating loops and rods for 3. The weak interactions such as hydrogen bonding and π···π stacking were investigated on the formation of superamolecular structures and the influence of organic acid on the formation of the final structures was discussed. In addition, the photoluminescent properties of 1-6 were also determined.     

Crystal structures and magnetic properties of tetranuclear copper(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine with a defective double-cubane core

Tetranuclear Cu(II) complexes of N-(2-hydroxymethylphenyl)salicylideneimine (H₂L1-H) and its homologues (5-CH₃: H₂L1-Me, 5-Cl: H₂L1-Cl), [Cu(L1-H)]₄ · 3H₂O (1), [Cu(L1-Me)]₄ · 2CH₂Cl₂ (2), and [Cu(L1-Cl)]₄ · 2CH₂Cl₂ (3), have been characterized by X-ray crystal structure analyses and magnetic measurements. The structure analyses revealed that the complexes 1-3 have a defective double-cubane tetra copper(II) core connected by μ₃-alkoxo bridges. The intramolecular Cu?Cu distances are in the range from 5.251(2)-5.256(3) Å for the longest to 3.0518(9)-3.092(2) Å for the shortest. Each Cu(II) ion has a square-pyramidal geometry and the dihedral angles between adjacent Cu(II) basal planes are almost right angles. Magnetic measurements of the present complexes indicate that weak antiferromagnetic interactions (J=−15 to −19 cm⁻¹) between neighboring copper(II) ions are dominant in these tetracopper cores.     

DNA interaction of new copper(II) complexes with sulfonamides as ligands

New copper(II) complexes with sulfonamide ligands have been prepared and characterized. Sulfonamide ligands were prepared through a reaction between 8-aminoquinoline and either 2-mesitylene (Hqmesa), 4-tert-butylbenzene (Hqtbsa), or alpha-toluene (Halphaqtsa) sulfonyl chlorides. The structural analysis carried out for complex [Cu(alphaqtsa)(2)] indicated that the local environment of the Cu(II) cation is between a square planar and a tetrahedral geometry, with stacking of the benzene rings of the sulfonyl ligands between neighbor molecules. Powder EPR spectra at room temperature gave rhombic spectra for the [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] complexes and an axial spectrum for the [Cu(qtbsa)(2)] complex, probably due to the steric hindrance of the methyl groups. Complexes [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] are artificial chemical nucleases that degrade DNA in the presence of sodium ascorbate. A study of the radical scavengers revealed that the ROS (reactive oxygen species) involved in the DNA damage were hydroxyl, singlet oxygen-like species, and superoxide anion.     

Copper(II) complexes with 2-N-(picolinylidene)-n-R-phenols: Solvatochromism, self-assembly and supramolecular structures

A series of copper(II) complexes having the formula [Cu(n-R-pyp)X] with the N,N,O-donor Schiff base system 2-N-(picolinylidene)-n-R-phenol (n-R-Hpyp) (where n = 3, 4, 5 and 6, when R = Me and n = 4 when R = Cl) and halide (X⁻ = Cl⁻ or Br⁻) as an ancillary ligand have been synthesized. The complexes are characterized by microanalytical, magnetic and various spectroscopic measurements. They display solvatochromic behavior. Single crystal X-ray structures of all the complexes are determined. In coordinatively unsaturated species such as a square-planar complex, the metal ion can interact with a fifth atom and if this atom is metal bound, dimeric or polymeric aggregate is formed. In the present series of complexes, the metal ions are square-planar and distorted square-pyramidal when there is an intermolecular Cu···X interaction. In addition to this Cu···X interaction, presence of intermolecular weak non-covalent interactions namely O-H···O, C-H···O, C-H···X and π···π are perceived. The supramolecular architectures formed by the molecules of these complexes via these interactions are scrutinized. The observed supramolecular structural motifs can be classified as staircase, ladder, brick-wall and square-grid. Except for R = Cl the analogous chloride and bromide coordinated complexes show similar structural features.