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.     

Studies of copper(II) and nickel(II) complexation by bis(1,4,7-triazacyclononane) ligands containing alkene and alkyne bridging groups

The copper(II) and nickel(II) complexes of three new 1,2-bis(1,4,7-triazacyclononane) ligands containing unsaturated four carbon bridging groups is studied by continuous variation UV-Vis spectroscopic and pH potentiometric equilibrium experiments. The cis-butene-2 (L_C) linked ligand may form monomeric MN₆-type complexes while the trans-butene-2 (L_T) and butyne-2 (L_Y) ligands are prevented by their stereochemistry from forming monomeric complexes and form oligomeric complexes. It is determined that the stability of the CuL_C²⁺ complex is not appreciably different from the oligomeric complexes of L_T and L_Y. Single-crystal X-ray structure determinations are made on three square pyramidal Cu₂L⁴⁺ complexes: [Cu₂L_CCl₄] (1), [Cu₂L_YCl₄] (2), and [Cu₂L_T(NO₃)₂(H₂O)₂](NO₃)₂ (3). The structure of [Ni₂(L_C)₂](ClO₄)₄ · 2H₂O (4) is a binuclear dimer that contains two nickel(II) ions sandwiched between two ligands, indicating that bis([9]aneN₃) ligands with four linker atom chains may form either monomeric or oligomeric structures.     

Study of the coordination behaviour of (3,5-diphenyl-1H-pyrazol-1-yl)ethanol against Pd(II), Zn(II) and Cu(II)

A new easily synthetic route with a 96% yield of ligand 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethanol (L) is obtained. The reactivity of L against Pd(II), Zn(II) and Cu(II) leads to [PdCl₂(L)₂] (1), [ZnCl₂(L)] (2) and [CuCl(L′)]₂ (3) (L′ is the ligand L without alcoholic proton), respectively. According to the different geometries imposed by the metallic centre and the capability of L to present various coordination links, it has been obtained complexes with square planar (1 and 3) or tetrahedral (2) geometry and different nuclearity: monomeric (1 and 2) or dimeric (3). Complete characterisation by analytical and spectroscopic methods, resolution of L and 1-3 by single-crystal X-ray diffraction and magnetic studies for complex 3 are presented.     

Bis(O2S2 macrocycle) complexes of palladium(II)

Two isomeric dibenzo-O₂S₂ macrocycles L¹ and L² have been synthesised and their coordination chemistry towards palladium(II) has been investigated. Two-step approaches via reactions of 1:1-type complexes, [cis-Cl₂LPd] (1a: L = L¹, 1b: L = L²), with different O₂S₂ macrocycle systems (L¹ and L²) have led to the isolation of the following bis(O₂S₂ macrocycle) palladium(II) complexes in the solid state: [Pd(L¹)₂](ClO₄)₂ (2a) and a mixture of [Pd(L¹)₂](ClO₄)₂ (2a) + [Pd(L²)₂](ClO₄)₂ (2b).     

Synthesis, crystal structures, and biological evaluation of Cu(II) and Zn(II) complexes of 2-benzoylpyridine Schiff bases derived from S-methyl- and S-phenyldithiocarbazates

Two NNS tridentate Schiff base ligands of 2-benzoylpyridine S-methyldithiocarbazate (HL¹) and 2-benzoylpyridine S-phenyldithiocarbazate (HL²) and their transition metal complexes [Cu₂(L¹)₂(CH₃COO)](ClO₄) (1), [Zn₂(L¹)₂(ClO₄)₂] (2), [Zn(L²)₂](3) have been prepared and characterized by elemental analysis, IR, MS, NMR and single-crystal X-ray diffraction studies. In the solid state, each of two Schiff bases remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. Under similar prepared conditions, three new complexes showed distinctly different coordination modes depending on their coordinating preferences. Each copper atom in S-bridged dinuclear complex [Cu₂(L¹)₂(CH₃COO)](ClO₄) (1) is surrounded by five donor atoms in a square-pyramidal fashion (4 + 1). [Zn₂(L¹)₂(ClO₄)₂] (2) is a dimer in which each zinc atom adopts a seven-coordinate distorted pentagonal bipyramidal geometry, while mononuclear [Zn(L²)₂] (3) has octahedral coordination geometry. Biological studies, carried out in vitro against selected bacteria, fungi, and K562 leukaemia cell line, respectively, have shown that different substituted groups attached at the dithiocarbazate moieties and metals showed distinctive differences in the biological property. Zinc(II) complexes 2 and 3 could distinguish K562 leukaemia cell line from normal hepatocyte QSG7701 cell line. Effect of the title compounds on Mitochondria membrane potential (MMP) and PI-associated fluorescence intensity in K562 leukaemia cell line are also studied. The title compounds may exert their cytotoxicity activity via induced loss of MMP.     

Coordinative versatility of 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L) to different metal ions: syntheses, crystal structures and properties of [Cu(I)L]2 and [ML] (M=Cu(II), Ni(II), Zn(II) and Co(II))

The complexes of Cu(I), Cu(II), Ni(II), Zn(II) and Co(II) with a new polypyridyl ligand, 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L), have been synthesized and characterized. The crystal structures of these complexes have been elucidated by X-ray diffraction analyses and three types of coordination modes for L were found to exist in them. In the dinuclear complex [Cu(I)L(CH₃CN)]₂·(ClO₄)₂ (1), L acts as a tridentate ligand with two Cu(I) centers bridged by two L ligands to form a box-like dimeric structure, in which each Cu(I) ion is penta-coordinated with three nitrogen atoms and a methoxyl oxygen atom of two L ligands, and an acetonitrile. In [Cu(II)L(NO₃)₂]·CH₃CN 2, the Cu(II) center is coordinated to the two nitrogen atoms of the two pyridine rings of L which acts as a bidentate ligand. The structures of [Ni(II)L(NO₃)(H₂O)₂]·2CH₃CN·NO₃ (3), [Zn(II)L(NO₃)₂ (H₂O)]·2CH₃CN (4) and [Co(II)LCl₂(H₂O)] (5) are similar to each other in which L acts as a tridentate ligand by using its half side, and the metal centers are coordinated to a methoxyl oxygen atom and two bipyridine nitrogen atoms of L in the same side. The formation of infinite quasi-one-dimensional chains (1, 4 and 5) or a quasi-two-dimensional sheet (2) assisted by the intra- or intermolecular face-to-face aryl stacking interactions and hydrogen bonds may have stabilized the crystals of these complexes. Luminescence studies showed that 1 exhibits broad, structureless emissions at 420 nm in the solid state and at 450 nm in frozen alcohol frozen glasses at 77 K. Cyclic voltammetric studies of 1 show the presence of an irreversible metal-centered reduction wave at approximately −0.973 V versus Fc^+/0 and a quasi-reversible ligand-centered reduction couple at approximately −1.996 V versus Fc^+/0. The solution behaviors of these complexes have been further studied by UV-Vis and ESR techniques.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Copper(II) complexes with monocarboxylate ligands bearing different substituent groups: Synthesis and spectroscopic studies

In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new Cu^II complexes formulated as [Cu₂(L¹)₄(DMF)₂] (1), {[Cu₂(L¹)₄(Hmta)](H₂O)_0.75}_∞ (2), [Cu₂(L²)₄(2,2′-bipy)₂] (3), [Cu₂(L³)₄(H₂O)₂] (4), [Cu₂(L³)₄(Hmta)]_∞ (5), [Cu₂(L³)₄(Dabco)]_∞ (6) and [Cu₂(L³)₄(Pz)]_∞ (7) with three monocarboxylate ligands bearing different substituent groups HL¹-HL³ (HL¹ = phenanthrene-9-carboxylic acid, HL² = 2-phenylquinoline-4-carboxylic acid, HL³ = adamantane-1-carboxylic acid, Hmta = hexamethylenetetramine, 2,2′-bipy = 2,2′-bipyridine, Dabco = 1,4-diazabicyclo[2.2.2] octane and Pz = pyrazine), have been prepared and characterized by X-ray diffraction. In 1, 2 and 4-7, each Cu^II ion is octahedrally coordinated, and carboxylate acid acts as a syn-syn bridging bidentate ligand. While each Cu^II ion in 3 is penta-coordinated in a distorted square-pyramidal geometry. 1 and 4 both show a dinuclear paddle-wheel block, while 2, 5, 6 and 7 all exhibit an alternated 1D chain structure between dinuclear paddle-wheel units of the tetracarboxylate type Cu₂-(RCO₂)₄ and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and μ_1,1-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2′-bipy. Moreover, complexes 1-6 were characterized by electron paramagnetic resonance (EPR) spectroscopy.     

Mn(II) coordination architectures with mixed ligands of 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons

In our efforts to investigate the factors that affect the formation of coordination architectures, such as secondary coordination donors and pendant skeletons of the carboxylic acid ligands, as well as H-bonding and other weak interactions, two kinds of ligands: (a) 3-(2-pyridyl)pyrazole (L¹) with a non-coordinated N atom as a H-bonding donor, a 2,2′-bipyridyl-like chelating ligand, and (b) four carboxylic ligands with different secondary coordination donors and/or pendant skeletons, 1,4-benzenedicarboxylic acid (H₂L²), 4-sulfobenzoic acid (H₂L³), quinoline-4-carboxylic acid (HL⁴) and fumaric acid (H₂L⁵), have been selected to react with Mn(II) salts, and five new complexes, [Mn(L¹)₂(SO₄)]₂ (1), [Mn(L¹)₂(L²)]_∞ (2), [Mn(L¹)(HL³)₂]_∞ (3), Mn(L¹)₂(L⁴)₂ (4), and [Mn(L¹)₂(L⁵)]_∞ (5), have been obtained and structurally characterized. The structural differences of 1-5 can be attributed to the introduction of the different carboxylic acid ligands (H₂L², H₂L³, HL⁴, and H₂L⁵) with different secondary coordination donors and pendant skeletons, respectively. This result also reveals that the typical H-bonding (i.e. N-H?O and O-H?O) and some other intra- or inter-molecular weak interactions, such as C-H?O weak H-bonding and π?π interactions, often play important roles in the formation of supramolecular aggregates, especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks.     

Zinc(II) and mercury(II) coordination architectures with two pyridyl/benzimidazol-1-yl-based ligands: Crystal structures and photoluminescent properties

In our efforts to investigate the relationships between the structures of ligands and their complexes, two structurally related ligands, 1-(2-pyridylmethyl)-1H-benzimidazole (L¹) and 1-(4-pyridylmethyl)-1H-benzimidazole (L²), and their four complexes, [Zn(L¹)₂Cl₂] (1), [Hg(L¹)Br₂]_∞ (2), {[Zn(L²)Cl₂](CH₃CN)}_∞ (3) and [Hg(L²)Br₂]₂(CH₃CN)₂ (4) were synthesized and structurally characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction analysis. Structural analyses show that 1 has a mononuclear structure, and 2 and 3 both take 1D structure. While 4 takes a dinuclear structure. 1, 2 and 4 were further linked into higher-dimensional supramolecular networks by weak interactions, such as C-H?Cl and C-H?Br H-bonding, C-H?π, and π?π stacking interactions. The structural differences of 1-4 may be attributed to the difference of the spatial positions of the terminal N donor atoms in the pendant pyridyl groups in L¹ and L², in which the pyridine rings may act as the directing group for coordination and the benzimidazole rings act as the directing group for π?π stacking and C-H?π interactions. The luminescent properties of the corresponding complexes and ligands have been further investigated.     

Synthesis, characterization, and anion selectivity of copper(II) complexes with a tetradentate Schiff base ligand

A new mononuclear Cu(II) complex, [CuL(ClO₄)₂] (1) has been derived from symmetrical tetradentate di-Schiff base, N,N′-bis-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L) and characterized by X-ray crystallography.The copper atom assumes a tetragonally distorted octahedral geometry with two perchlorate oxygens coordinated very weakly in the axial positions.Reactions of 1 with sodium azide, ammonium thiocyanate or sodium nitrite solution yielded compounds [CuL(N₃)]ClO₄ (2), [CuL(SCN)]ClO₄ (3) or [CuL(NO₂)]ClO₄ (4), respectively, all of which have been characterized by X-ray analysis.The geometries of the penta-coordinated copper(II) in complexes 2-4 are intermediate between square pyramid and trigonal bipyramid (tbp) having the Addition parameters (τ) 0.47, 0.45 and 0.58, respectively.In complex 4, the nitrite ion is coordinated as a chelating ligand and essentially both the O atoms of the nitrite occupy one axial site.Complex 1 shows distinct preference for the anion in the order in forming the complexes 2-4 when treated with a mixture. Electrochemical electron transfer study reveals Cu^IICu^I reduction in acetonitrile solution.     

Structural variability in manganese(II) complexes of N,N′-bis(2-pyridinylmethylene) ethane (and propane) diamine ligands

Manganese(II) complexes, Mn₂L¹₃(ClO₄)₄, MnL¹(H₂O)₂(ClO₄)₂, MnL²(H₂O)₂(ClO₄)₂, and {(μ-Cl)MnL²(PF₆)}₂ based on N,N′-bis(2-pyridinylmethylene) ethanediamine (L¹) and N,N′-bis(2-pyridinylmethylene) propanediamine (L²) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn₂L²₃(ClO₄)₄ shows that each of the two Mn(II) ion centers with a Mn-Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L¹ and Mn(II) yielded a one-dimensional polymer, MnL¹(H₂O)₂(ClO₄)₂. Ligand L² when reacted with manganese(II) perchlorate gives contrarily to L¹ mononuclear MnL²(H₂O)₂(ClO₄)₂ complex. The analysis of the structural properties of the MnL²(H₂O)₂(ClO₄)₂ lead to the design of dinuclear complex {(μ-Cl)MnL²(PF₆)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn₂Cl₂ core with a Mn-Mn distance of 3.726 Å. At room temperature {(μ-Cl)MnL²(PF₆)} is ferromagnetic with observed μ_eff = 4.04 μ_B per Mn(II) ion. With cooling, μ_eff grows reaching 4.81 μ_B per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.     

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.     

A rare case of solution and solid state inter-conversion of two copper(II) dimers and a copper(II) chain

Three Cu(II)-azido complexes of formula [Cu₂L₂(N₃)₂] (1), [Cu₂L₂(N₃)₂]·H₂O (2) and [CuL(N₃)]_n (3) have been synthesized using the same tridentate Schiff base ligand HL (2-[(3-methylaminopropylimino)-methyl]-phenol), the condensation product of N-methyl-1,3-propanediamine and salicyldehyde). Compounds 1 and 2 are basal-apical μ-1,1 double azido bridged dimers. The dimeric structure of 1 is centrosymmetric but that of 2 is non-centrommetric. Compound 3 is a μ-1,1 single azido bridged 1D chain. The three complexes interconvert in solution and can be obtained in pure form by carefully controlling the synthetic conditions. Compound 2 undergoes an irreversible transformation to 1 upon dehydration in the solid state. The magnetic properties of compounds 1 and 2 show the presence of weak antiferromagnetic exchange interactions mediated by the double 1,1-N₃ azido bridges (J = −2.59(4) and −0.10(1) cm−¹, respectively). The single 1,1-N₃ bridge in compound 3 mediates a negligible exchange interaction.     

Speciation, stability constants and structures of complexes of copper(II), nickel(II), silver(I) and mercury(II) with PAMAM dendrimer and related tetraamide ligands

The acid-base properties and Cu(II), Ni(II), Ag(I) and Hg(II) binding abilities of PAMAM dendrimer, L, and of the simple model compounds, the tetraamides of EDTA and PDTA, L¹, were studied in solution by pH-metric methods and by ¹H NMR and UV-Vis spectroscopy. PAMAM is hexabasic and six pK_a values have been determined and assigned. PAMAM forms five identifiable complexes with copper(II), [CuLH₄]⁶⁺, [CuLH₂]⁴⁺, [CuLH]³⁺, [CuL]²⁺ and [CuLH_-1]⁺ in the pH range 2-11 and three with nickel(II), [NiLH]³⁺, [NiL]²⁺ and [NiLH_-1]⁺ in the pH range 7-11. The complex [CuLH₄]⁶⁺, which contains two tertiary nitrogen and three amide oxygen atoms coordinated to the metal ion, is less stable than the analogous EDTA and PDTA tetraamide complexes [CuL¹]²⁺, which contain two tertiary nitrogen and four amide oxygen atoms, due to ring size and charge effects. With increasing pH, [CuLH₄]⁶⁺ undergoes deprotonation of two coordinated amide groups to give [CuLH₂]⁴⁺ with a concomitant change from O-amide to N-amidate coordination. Surprisingly and in contrast to the tetraamide complexes [CuL¹]²⁺, these two deprotonation steps could not be separated. As expected the nickel(II) complexes are less stable than their copper(II) analogues. The tetra-N-methylamides of EDTA, L¹(b), and PDTA form mononuclear and binuclear complexes with Hg(II). In the case of L¹(b) these have stoichiometries HgL¹(b)Cl₂, [HgL¹(b)H₋₂Cl₂]²⁻, [Hg₂L¹(b)Cl₂]²⁺, Hg₂L¹(b)H₋₂Cl₂ and [Hg₂L¹(b)H₋₅Cl₂]³⁻. Based on ¹H NMR and pH-metric data the proposed structure for HgL¹(b)Cl₂, the main tetraamide ligand containing species in the pH range <3-6.5, contains L¹(b) coordinated to the metal ion through the two tertiary nitrogens and two amide oxygens while the structure of [HgL¹(b)H₋₂Cl₂]²⁻, the main tetraamide ligand species at pH 7.5-9.0, contains the ligand similarly coordinated but through two amidate nitrogen atoms instead of amide oxygens. The proposed structure of [Hg₂L¹(b)Cl₂]²⁺, a minor species at pH 3-6.5, also based on ¹H NMR and pH-metric data, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amide oxygens and a chloride ligand while that of [Hg₂L¹(b)H₋₅Cl₂]³⁻, contains each Hg(II) coordinated to a tertiary amino nitrogen, two amidate nitrogens, a chloride and a hydroxo ligand in the case of one of the Hg(II) ions. The parent EDTA and PDTA amides only form mononuclear complexes. PAMAM also forms dinuclear as well as mononuclear complexes with mercury(II) and silver(I). In the pH range 3-11 six complexes with Hg(II) i.e. [HgLH₄Cl₂]⁴⁺, [HgLH₃Cl₂]³⁺, [Hg₂LCl₂]²⁺, [Hg₂LH₋₁Cl₂]⁺, [HgLH₋₁Cl₂]⁻ and [HgLH₋₂Cl₂]²⁻ were identified and only two with Ag(I), [AgLH₃]⁴⁺ and [Ag₂L]²⁺. Based on stoichiometries, stability constant comparisons and ¹H NMR data, structures are proposed for these species. Hence [HgLH₄Cl₂]⁴⁺ is proposed to have a similar structure to [CuLH₄]⁶⁺ while [Hg₂LCl₂]²⁺has a similar structure to [Hg₂L¹(b)H₋₅Cl₂]³⁻.     

Spectroscopic and electrochemical properties of heteroleptic cationic copper complexes bis-(diphenylphosphino)alkane-(2,2′-biquinoline)copper(I). Crystal structure of bis(diphenylphosphino)ethane-(2,2′-biquinoline)copper(I) perchlorate

A series of [Cu^(I)(2,2′-biquinoline)(L)](ClO₄) complexes (L = bis(diphenylphosphino)methane (bppm), 1,2-bis(diphenylphosphino)ethane (bppe), 1,4-bis(diphenylphosphino)butane (bppb)) have been synthesized and characterized by elemental analysis, conductivity, ESI-mass, NMR and UV-Vis spectroscopies, cyclic voltammetry, X-ray diffraction ([Cu^(I)(2,2′-biquinoline)(bppe)](ClO₄)) and DFT calculations. These compounds are monometallic species in a distorted tetrahedral arrangement, in contrast with related compounds found as dinuclear according to diffraction studies. The spectroscopic properties are not directly correlated with the length of alkyl chain bridge between the bis-diphenylphosphine groups. In this way, the chemical shift of some 2,2′-biquinoline protons and the metal to ligand charge transfer (Cu to 2,2′-biquinoline) follows the order [Cu(2,2′-biquinoline)(bppm)](ClO₄), [Cu(2,2′-biquinoline)(bppb)](ClO₄), [Cu(2,2′-biquinoline)(bppe)](ClO₄). The same dependence is followed by the potentials to Cu(II)/Cu(I) couple. These results are discussed in terms of inter-phosphorus alkane chain length and tetrahedral distortions on copper.     

Copper(II) chloride/1-methylbenzotriazole chemistry: influence of various synthetic parameters on the product identity, structural and magnetic characterization, and quantum-chemical studies

A systematic investigation of the CuCl₂/Mebta (Mebta = 1-methylbenzotriazole) reaction system is described, involving the determination of the influence of the Cu^II:Mebta ratio, the nature of solvent and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cu₂Cl₄(Mebta)₄] (1), [CuCl₂(Mebta)₂] (2), {[Cu₂Cl₄(Mebta)₂]}_n (3), [Cu₄OCl₆(Mebta)₄] · 0.25H₂O (4 · 0.25H₂O) and [Cu₂Cl₂(Mebta)₆](ClO₄)₂ (5) have been isolated and structurally characterized by single-crystal X-ray studies. Mebta behaves as a monodentate ligand binding through N(3). 1 is a dinuclear complex, the structure of 2 consists of discrete monomeric units, and that of 3 is composed of linear, well-separated polymeric chains of Cu^II atoms. The molecules of 4 · 0.25H₂O have a central μ₄-oxide ion surrounded tetrahedrally by four Cu^II atoms. In the cations of 5 the two Cu^II centres are asymmetrically bridged by two chloro ligands, with three Mebta molecules completing five coordination at each metal. Complexes were characterized by spectroscopic (IR, far-IR, solution UV/Vis) and thermal decomposition (TG, DTG, and DTA) techniques. Variable-temperature magnetic susceptibility data for 1, 3 and 5 showed intramolecular (1, 5) and intrachain (3) ferromagnetic exchange interactions. Estimates of the Jparameters, experimentally derived, were in close agreement with a new magneto-structural criterion developed by us, holding for bis(μ-chloro) copper(II) dimers. A comparison between the CuCl₂/Mebta and CuBr₂/Mebta systems is also presented.     

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes

The macrocyclic symmetrical and a series of unsymmetrical binuclear copper(II) complexes have been synthesized by using mononuclear complex [CuL] [3,3′-((1E,7E)-3,6-dioxa-2,7-diazaocta-1,7-diene-1,8-diyl)bis(3-formyl-5-methyl-2-diolato)copper(II)]. Another compartment of the [CuL] have been condensed with various diamines like 1,2-bis(aminooxy)ethane (L¹), 1,2-diamino ethane(L^2a), 1,3-diamino propane(L^2b), 1,4-diamino butane(L^2c), 1,2-diamino benzene(L^2d), 1,8-diamino naphthalene(L^2e) and characterized by elemental, spectroscopic, and X-ray crystallographic methods. The influence of the coordination geometry and the ring size of the binucleating ligands on the electronic, redox, magnetic, catecholase activity, DNA binding and cleavage properties have been studied. The molecular structures of the symmetrical binuclear complex [Cu₂L¹(H₂O)₂](ClO₄)₂ (1) and unsymmetrical binuclear complex [Cu₂L^2b(ClO₄)(H₂O)]ClO₄ (2b) were determined by X-ray crystallography. Both of them were discrete binuclear species in which each Cu(II) ions are in distorted square pyramid. The Cu?Cu distances vary from 3.0308 (2b) to 3.0361 Å (1). Electrochemical studies evidenced that two quasi-reversible one electron-transfer reduction waves −0.91 to −1.01 V, −1.26 to −1.55 V) for binuclear complexes are obtained in the cathodic region. Cryomagnetic investigation of the binuclear complexes reveals a weak antiferromagnetic spin exchange interaction between the Cu(II) ions within the complexes (−2J = 104.4-127.5 cm⁻¹). The initial rate (V_in) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II)complexes are in the range 3.6 × 10⁻⁵ to 7.3 × 10⁻⁵ Ms⁻¹. The binuclear Cu(II) complexes are avid binders to calf thymus DNA. The complexes display significant oxidative cleavage of circular plasmid pBR322 DNA in the presence of mercaptoethanol using the singlet oxygen as a reactive species. The aromatic diamine condensed macrocyclic ligands of copper(II) complexes display better DNA interaction and significant chemical nuclease activity than the aliphatic diamine condensed macrocyclic Cu(II) complexes.     

Zinc(II) tweezers containing artificial peptides mimicking the active site of phosphotriesterase: The catalyzed hydrolysis of the toxic organophosphate parathion

Two new ligand-containing histidine based on N,N′,N″-tris(N-benzyl-l-histidinyl)tri(2-aminoethyl)amine, L¹, namely N,N′,N″-tris[(1S)-2-methoxy-2-oxy-1-(1-benzylimidazol-4-ylmethyl)]nitrilotriacetamide L² and N,N′,N″-tris{N-benzyl-N-[N-benzyl-N-(N-benzyl-l-histidinyl)-l-histidinyl]-l-histidinyl}tri(2-aminoethyl)amine L³ were prepared. Zinc(II) binding studies by these ligand systems were analyzed by means of potentiometric and ¹H NMR titrations in aqueous methanol (33 % v/v). Subsequently their zinc(II) complexes [L¹Zn(H₂O)](ClO₄)₂·HClO₄ (1), [L²Zn(OH₂)](ClO₄)₂·H₂O (2), and ([L³Zn₃(H₂O)₃](ClO₄)₆·3HClO₄·5H₂O (3), respectively were synthesized and characterized. The reactivity of the trinuclear complex (3) toward the hydrolysis of the toxic organophosphate parathion was investigated and compared with that of the mononuclear reference complex (1). From the pH dependence of the apparent rate constants, and the deprotonation constant (pK_a) of the coordinated water molecules in (1), the active species were confirmed to be {[HL¹Zn(OH)]²⁺/[L¹Zn(H₂O)]²⁺} at pH 8.5. The trizinc complex (3) effects hydrolysis of parathion, with three times rate enhancement over the mononuclear (1), indicating that cooperative action of the three zinc centers is limited.