The synthesis, structure and properties of copper(II) complexes of asymmetrically functionalized derivatives of 1,4,7-triazacyclononane

Reaction of 1-propylamino-4-acetato-1,4,7-triazacyclononane (L1), 1-benzyl-4-acetato-1,4,7-triazacyclononane (L2) and 1-benzyl-4-propylamino-1,4,7-triazacyclononane (L3) with a copper(II) salt gave Na2[CuL1](ClO4)3(1a), [CuL2]Cl (2) and [Cu2L32](ClO4)4.5H2O (3), respectively. [CuL4]ClO4 (4) was formed by reacting 1-formyl-4-ethylacetato-1,4,7-triazacyclononane with cupric chloride in aqueous solution. The X-ray crystal structures of the complexes reveal that the ligands generate distorted square pyramidal or square planar coordination environments about the Cu(II) centre, but in three complexes (1b, 3 and 4) weak interactions to an oxygen atom from a perchlorate anion and, in the case of 4, also to an amide nitrogen leading to tetragonally elongated octahedral Cu(II) geometries. In 4, the formyl group is found to reduce the coordinating ability of the macrocyclic nitrogen to which it is attached, as evidenced by the weak CuN interaction. The formation of five-membered chelate rings on coordination of the ligands further contributes to the distortion from the ideal geometries. The crystal lattices contain a number of novel supramolecular features. 1a contains a negatively charged sodium perchlorate chain of composition [Na2(ClO4)3]x(x-), with a complex series of Na-O-Na bridges flanked by [CuL1]+ units, while 3 contains highly complex hydrogen bonded sheets approximately 20 A thick that stack through van der Waals interactions. One-dimensional chains comprised of copper complexes are found in 2 and 4, and are held together by hydrogen bonds in 2 and acetate bridges between the copper cations in 4. The solution EPR spectra indicate that the copper(II) centres exist in isolated distorted square pyramidal (possibly square planar for 4) environments, while in the solid state there is evidence for the existence of weak exchange and dipole-dipole coupling for some complexes.     

Syntheses,structures, and spectroscopic properties of copper(II) and cobalt(III) complexes containing 1,4,7-tribenzyl-1,4,7-triazacyclononane ligand

Three new complexes [CuL(N₃)₂] (1), [CuL(SCN)₂] (2), and [CoL(SCN)₃] (3) (L?=?1,4,7-tribenzyl-1,4,7-triazacyclononane) have been synthesized and structurally characterized. Complex 1 crystallizes in monoclinic space group P2(1)/n with unit cell parameters a?=?14.105(7), b?=?8.999(5), c?=?21.603(11)?Å, β?=?100.470(7)°. While 2 crystallizes in triclinic space group P-1 with unit cell parameters a?=?9.6380(16), b?=?10.6993(18), c?=?15.798(3)?Å, α?=?106.636(3), γ?=?116.478(3)°. Complex 3 crystallizes in trigonal space group P–3c1 with unit cell parameters a?=?14.744(3), b?=?14.744(3), c?=?16.098(4)?Å, γ?=?120°. Elemental analysis, IR, UV-vis spectra of complexes 1–3 and ESR spectra of complexes 1–2 were also determined.     

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.     

Copper(II) and nickel(II) complexes of the pendant arm ligand benzimidazole-2-yl-methyl-functionalized 1,4,7-triazacyclononane

Two novel complexes [ML]·(ClO₄)₂·EtOH·xH₂O M = Cu^II, x = 3; M = Ni^II, x = 2; L = 1-R-4,7-bis(benzimidazole-2-yl-methyl)-1,4,7-triazacyclononane, [R = 1-(benzimidazole-2-yl-methyl)benzimidazole-2-yl-methy], were prepared by a one-pot method using the 1,4,7-triazacyclononane ligand (tacn) and 2-chloromethylbenzimidazole as starting materials. The ES-MS and u.v. spectra of the complexes indicate that they are very stable thermodynamically and kinetically in aqueous solution. The crystal structure of the Cu^II complex shows that the Cu^II centre is octahedrally coordinated by six nitrogen atoms of three benzimidazoles and tacn.     

Binuclear copper(II) complexes of xylyl-bridged bis(1,4,7-triazacyclononane) ligands

Copper(II) complexes of three bis(tacn) ligands, [Cu(2)(T(2)-o-X)Cl(4)] (1), [Cu(2)(T(2)-m-X)(H(2)O)(4)](ClO(4))(4).H(2)O.NaClO(4) (2), and [Cu(2)(T(2)-p-X)Cl(4)] (3), were prepared by reacting a Cu(II) salt and L.6HCl (2:1 ratio) in neutral aqueous solution [T(2)-o-X = 1,2-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene; T(2)-m-X = 1,3-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene; T(2)-p-X = 1,4-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene]. Crystals of [Cu(2)(T(2)-m-X)(NPP)(mu-OH)](ClO(4)).H(2)O (4) formed at pH = 7.4 in a solution containing 2 and disodium 4-nitrophenyl phosphate (Na(2)NPP). The binuclear complexes [Cu(2)(T(2)-o-XAc(2))(H(2)O)(2)](ClO(4))(2).4H(2)O (5) and [Cu(2)(T(2)-m-XAc(2))(H(2)O)(2)](ClO(4))(2).4H(2)O (6) were obtained on addition of Cu(ClO(4))(2).6H(2)O to aqueous solutions of the bis(tetradentate) ligands T(2)-o-XAc(2) (1,2-bis((4-(carboxymethyl)-1,4,7-triazacyclonon-1-yl)methyl)benzene and T(2)-m-XAc(2) (1,3-bis((4-(carboxymethyl)-1,4,7-triazacyclonon-1-yl)methyl)benzene), respectively. In the binuclear complex, 3, three N donors from one macrocycle and two chlorides occupy the distorted square pyramidal Cu(II) coordination sphere. The complex features a long Cu...Cu separation (11.81 A) and intermolecular interactions that give rise to weak intermolecular antiferromagnetic coupling between Cu(II) centers. Complex 4 contains binuclear cations with a single hydroxo and p-nitrophenyl phosphate bridging two Cu(II) centers (Cu...Cu = 3.565(2) A). Magnetic susceptibility studies indicated the presence of strong antiferromagnetic interactions between the metal centers (J = -275 cm(-1)). Measurements of the rate of BNPP (bis(p-nitrophenyl) phosphate) hydrolysis by a number of these metal complexes revealed the greatest rate of cleavage for [Cu(2)(T(2)-o-X)(OH(2))(4)](4+) (k = 5 x 10(-6) s(-1) at pH = 7.4 and T = 50 degrees C). Notably, the mononuclear [Cu(Me(3)tacn)(OH(2))(2)](2+) complex induces a much faster rate of cleavage (k = 6 x 10(-5) s(-1) under the same conditions).     

Polynuclear complexes of the pendent-arm ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane

The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H(2)L)](ClO(4)) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co(III)(2)Co(II) (2a) and Mn(II)(2)Mn(III) (4) complexes, whereas nickel(II) produces a tetranuclear [Ni(4)(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S(t) = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S(t) = 7.0 for 4. The large ground-state spin value of S(t) = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO(2) uptake from air in methanolic solutions containing a base in the case of complex 4.     

Syntheses,structures and hydrolytic properties of copper(II) complexes of asymmetrically N-functionalised 1,4,7-triazacyclononane ligands

A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle have been prepared from the common precursor 1,4,7-triazatricyclo[5.2.1.0^4,10]decane: 1-ethyl-4-isopropyl-1,4,7-triazacyclononane (L1), 1-isopropyl-4-propyl-1,4,7-triazacyclononane (L2), 1-(3-aminopropyl)-4-benzyl-7-isopropyl-1,4,7-triazacyclononane (L3), 1-benzyl-4-isopropyl-1,4,7-triazacyclononane (L4) and 1,4-bis(3-aminopropyl)-7-isopropyl-1,4,7-triazacyclononane (L5). The corresponding monomeric copper(II) complexes were synthesised and were found to be of composition: [Cu(L1)Cl₂] · 1/2 H₂O (C1), [Cu(L4)Cl₂] · 4H₂O (C2), [Cu(L3)(MeCN)](ClO₄)₂ (C3), [Cu(L5)](ClO₄)₂ · MeCN · NaClO₄ (C4) and [Cu(L2)Cl₂] · 1/2 H₂O (C5). The X-ray crystal structures of each complex revealed a distorted square-pyramidal copper(II) geometry, with the nitrogen donors on the ligands occupying 3 (C1 and C2), 4 (C3) or 5 (C4) coordination sites on the Cu(II) centre. The metal complexes were tested for the ability to hydrolytically cleave phosphate esters at near physiological conditions, using the model phosphodiester, bis(p-nitrophenyl)phosphate (BNPP). The observed rate constants for BNPP cleavage followed the order k_C1 ≈ k_C2 > k_C5 ? k_C3 > k_C4, confirming that tacn-type Cu(II) complexes efficiently accelerate phosphate ester hydrolysis by being able to bind phosphate esters and also form the nucleophile necessary to carry out intramolecular cleavage. Complexes C1 and C2, featuring asymmetrically disubstituted ligands, exhibited rate constants of the same order of magnitude as those reported for the Cu(II) complexes of symmetrically tri-N-alkylated tacn ligands (k ∼ 1.5 × 10⁻⁵ s⁻¹).     

Phosphodiester cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands bearing single alkyl guanidine pendants

Three new metal-coordinating ligands, L(1)·4HCl [1-(2-guanidinoethyl)-1,4,7-triazacyclononane tetrahydrochloride], L(2)·4HCl [1-(3-guanidinopropyl)-1,4,7-triazacyclononane tetrahydrochloride], and L(3)·4HCl [1-(4-guanidinobutyl)-1,4,7-triazacyclononane tetrahydrochloride], have been prepared via the selective N-functionalization of 1,4,7-triazacyclononane (tacn) with ethylguanidine, propylguanidine, and butylguanidine pendants, respectively. Reaction of L(1)·4HCl with Cu(ClO(4))(2)·6H(2)O in basic aqueous solution led to the crystallization of a monohydroxo-bridged binuclear copper(II) complex, [Cu(2)L(1)(2)(μ-OH)](ClO(4))(3)·H(2)O (C1), while for L(2) and L(3), mononuclear complexes of composition [Cu(L(2)H)Cl(2)]Cl·(MeOH)(0.5)·(H(2)O)(0.5) (C2) and [Cu(L(3)H)Cl(2)]Cl·(DMF)(0.5)·(H(2)O)(0.5) (C3) were crystallized from methanol and DMF solutions, respectively. X-ray crystallography revealed that in addition to a tacn ring from L(1) ligand, each copper(II) center in C1 is coordinated to a neutral guanidine pendant. In contrast, the guanidinium pendants in C2 and C3 are protonated and extend away from the Cu(II)-tacn units. Complex C1 features a single μ-hydroxo bridge between the two copper(II) centers, which mediates strong antiferromagnetic coupling between the metal centers. Complexes C2 and C3 cleave two model phosphodiesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate (HPNPP), more rapidly than C1, which displays similar reactivity to [Cu(tacn)(OH(2))(2)](2+). All three complexes cleave supercoiled plasmid DNA (pBR 322) at significantly faster rates than the corresponding bis(alkylguanidine) complexes and [Cu(tacn)(OH(2))(2)](2+). The high DNA cleavage rate for C1 {k(obs) = 1.30 (±0.01) × 10(-4) s(-1) vs 1.23 (±0.37) × 10(-5) s(-1) for [Cu(tacn)(OH(2))(2)](2+) and 1.58 (±0.05) × 10(-5) s(-1) for the corresponding bis(ethylguanidine) analogue} indicates that the coordinated guanidine group in C1 may be displaced to allow for substrate binding/activation. Comparison of the phosphate ester cleavage properties of complexes C1-C3 with those of related complexes suggests some degree of cooperativity between the Cu(II) centers and the guanidinium groups.     

Synthesis,characterization, structure and magnetic properties of azido-bridged nickel(II) and copper(II) complexes with a pyridylpyrazole-based ligand

A new pyridylpyrazole-containing tetradentate ligand, namely N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine (L), and two of its binuclear azido-bridged complexes, [Ni₂(L)₂(N₃)₂](ClO₄)₂·2EtOH (1) and [Cu₂(L)₂(N₃)₂](ClO₄)₂ (2), have been synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of both complexes are reported. Each metal atom in the complexes has a MN₆ coordination environment with distorted octahedral geometry. Variable-temperature magnetic susceptibility measurements for complex (1) show typical antiferromagnetic behavior with J value −84.5 ± 1.3 cm⁻¹, whereas complex (2) has no magnetic interactions.     

Cobalt(II), nickel(II) and copper(II) complexes of a Schiff base ligand: synthesis,structural characterization and luminescence properties

A Schiff base ligand (HL), 2,4-dimethoxy-N-(5-chloro-2-hydroxybenzylidene)-benzenamine, derived from 5-chloro-2-hydroxybenzaldehyde and 2,4-dimethoxyaniline, and its metal complexes [Co(L)₂]·CH₃OH (1), [Ni(L)₂] (2), [Cu(L)₂] (3) have been synthesized. The compounds were characterized by analytical and spectroscopic methods. In addition, the structures of the Schiff base HL and its Co(II) complex were determined by single-crystal X-ray analysis. The Co(II) center is six-coordinate, being coordinated to two imine nitrogen, two phenolate oxygen and two methoxy oxygen atoms of two crystallographically independent Schiff base ligands. Luminescence properties of HL and its complexes were investigated both in solution and in the solid state.     

Two copper(II) complexes with 4-benzoylpyridine ligand: synthesis, crystal structure and luminescent properties

Two new copper(II) complexes Cu(NCS)2(4-Bzpy)2 (1) and Cu(NO3)2(4-Bzpy)4 (2) (4-Bzpy=4-benzoylpyridine) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Cu(II) atom has a square planar environment for 1 and an distorted octahedral environment for 2, respectively. In solid state there are C-H?π interactions and C-H?S hydrogen bonds between adjacent molecules in complex 1. The molecule of complex 2 is further connected by multiform π-π interactions, C-H?π interactions and C-H?O hydrogen bonds to form a three-dimensional supramolecular structure. The luminescent properties of the complexes 1 and 2 were both investigated in H2O solution and in solid state at room temperature, respectively.     

Lanthanide complexes of new nonadentate imino-phosphonate ligands derived from 1,4,7-triazacyclononane: synthesis, structural characterisation and NMR studies

The polyamino ligand 1,4,7-tris(2-aminoethyl)-1,4,7-triazacyclononane (1) has been used to synthesise two new ligands by Schiff-base condensation with methyl sodium acetyl phosphonate to give ligand L and methyl sodium 4-methoxybenzoyl phosphonate to give ligand L1 in the presence of lanthanide ion as templating agent to form the complexes [Ln(L)] and [Ln(L1)](Ln = Y, La, Gd, Yb). Both ligands L and L1 have nine donor atoms comprising three amine and three imine N-donors and three phosphonate O-donors and form Ln(III) complexes in which the three pendant arms of the ligands wrap around the nine-coordinate Ln(III) centres. Complexes with Y(III), La(III), Gd(III) and Yb(III) have been synthesised and the complexes [Y(L)], [Gd(L)] and [Gd(L1)] have been structurally characterised. In all the complexes the coordination polyhedron about the lanthanide centre is slightly distorted tricapped trigonal prismatic with the two triangular faces of the prism formed by the macrocyclic N-donors and the phosphonate O-donors. Interestingly, given the three chiral phosphorus centres present in [Ln(L)] and [Ln(L1)] complexes, the three crystal structures reported show the presence of only one diastereomer of the four possible. 1H, 13C and 31P NMR spectroscopic studies on diamagnetic [Y(L)] and [La(L)] and on paramagnetic [Yb(L)] complexes indicate the presence in solution of all the four different diastereomers in varying proportions. The stability of complexes [Y(L)] and [Y(L1)] in D2O in both neutral and acidic media, and the relaxivity of the Gd(III) complexes, have also been investigated.     

Coordination chemistry of a new tetranucleating 26-membered polyaza macropolycyclic ligand and a novel phenolate/phthalazine-bridged copper(II) and zinc(II) complexes

The novel phenol and phthalazine-based symmetric compartmental 26-membered polyaza macropolycyclic ligand LH₂, was synthesised, incorporating 2,6-diformyl-p-cresol and 1,4-dihydrazinophthalazine via 1:1 condensation. Its coordination behaviour with Cu^II and Zn^II ions was investigated. The tetranuclear complexes [M₄μ(Cl₂)(L)Cl₄]·2H₂O exhibited aremarkably high stability, suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions were also involved in binding the metal ion. Incorporation of the bridging units into the macrocyclic cavity influenced electronic communications between the metal ions.     

Two new copper(II) complexes containing the benzene-1,3,5-tricarboxylic acid anion and 1,4,7-triazacyclononane

Two new copper(II) complexes, [Cu(tacn)(H₂BTC)₂]·2H₂O (1) and [Cu(tacn)(H₂BTC)(H₂O)](H₂BTC)·5H₂O (2), where H₂BTC^– = the benzene-1,3,5-tricarboxylic acid anion and tacn =1,4,7-triazacyclononane, have been synthesized and their structures determined. Copper(II) ions of both (1) and (2) are five-coordinate with three nitrogen atoms of tacn and two oxygen atoms of either H₂BTC^– or H₂O. Hydrogen bonds in these two complexes result in them being differently packed in the crystal cell.     

Coordination chemistry of amine bis(phenolate) cobalt(II), nickel(II), and copper(II) complexes

Cobalt(II), nickel(II), and copper(II) (1, 2, and 3) complexes of the dianionic form of the bis(phenolate) ligand N,N-bis(3,4-dimethyl-2-hydroxybenzyl)-N',N'-dimethylethylenediamine (H2L) have been synthesized by electrochemical oxidation of the appropriate metal in an acetonitrile solution of the ligand. When copper is used as the anode, the addition of 1,10-phenanthroline to the electrolytic phase gave rise to a different compound [CuL]2.2CH3CN (4). The compounds [CoL]2.2CH3CN (1), [Ni2L2(H2O)].H2O (2), [CuL]2.3H2O (3), and [CuL]2.2CH3CN (4) were characterized by microanalysis, IR, electronic spectroscopy, FAB mass spectrometry, magnetic measurements and by single-crystal X-ray diffraction. The crystal structures show that the complexes have a dinuclear structure. In compounds 1, 3, and 4, two metal ions are coordinated by the two amine nitrogens and the two phenol oxygen atoms of a deprotonated pendant phenol ligand, with one phenolic oxygen atom from ligand acting as a bridge. In compounds 1 and 3, each metal center has a geometry that is closest to trigonal bipyramidal. Magnetic susceptibility data for both compounds show an antiferromagnetic coupling with 2J = -15 cm(-1) for the cobalt(II) complex and a strong antiferromagnetic coupling with 2J = -654 cm(-1) for the copper(II) complex. However, in 4 the geometry around the metal is closer to square pyramidal and the compound shows a lower antiferromagnetic coupling (2J = -90 cm(-1)) than in 3. The nickel atoms in the dimeric compound 2 are hexacoordinate. The NiN2O4 chromophore has a highly distorted octahedral geometry. In this structure, a dianionic ligand binds to one nickel through the two amine nitrogen atoms and the two oxygen atoms and to an adjacent nickel via one of these oxygen atoms. The nickel atoms are linked through a triple oxygen bridge involving two phenolic oxygens, each from a different ligand, and an oxygen atom from a water molecule. The two nickel ions in 2 are ferromagnetically coupled with 2J = 19.8 cm(-1).     

Synthesis, X-ray crystal structures, magnetism, and phosphate ester cleavage properties of copper(II) complexes of N-substituted derivatives of 1,4,7-triazacyclononane

Two new N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle, 1-benzyl-4,7-dimethyl-1,4,7-triazacyclononane (L2) and 1,4,7-tris(3-cyanobenzyl)-1,4,7-triazacyclononane (L3), have been prepared and, together with 1,4-dimethyl-1,4,7-triazacyclononane (L1), have been used to synthesize the corresponding hydroxo-bridged binuclear copper (II) complexes, [Cu2(mu-OH)2L2](ClO4)2.xH2O (1 L = L1, x = 0; 2 L = L2, x = 1; 3 L = L3, x = 2). The X-ray crystal structures of all three complexes reveal the presence of [Cu2(mu-OH)2]2+ cores capped by pairs of facially coordinating tacn ligands so that the Cu(II) centers reside in distorted square pyramidal coordination environments. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -36.4 cm(-1)) between the Cu(II) centers in 1, while the centers in 2 and 3 have been shown to interact ferromagnetically (J = 11.2 and 49.3 cm(-1), respectively). The variation in the strength and sign of these interactions has been rationalized in terms of the differing geometries of the [Cu2(mu-OH)2]2+ cores. The ability of the Cu(II) complexes to cleave phosphate ester bonds has been probed using the model phosphate ester bis(4-nitrophenyl)phosphate (BNPP) at pH 7.4 and a temperature of 50 degrees C. The measured rate constant for 3 (3 x 10(-4) s(-1)) is significantly greater than those previously reported for the Cu(II) complexes of the fully alkylated tacn ligands, Me3tacn and iPr3tacn, which until now have been rated as the most effective tacn-based phosphate ester cleavage agents.     

The crystal structure of a novel copper(II) complex with asymmetric ligand derived from l-histidine

The crystal structure of a novel copper(II) complex with a potentially hexadentate Schiff base ligand derived from l-histidine has been solved by a single-crystal X-ray diffraction method at pH 7.4. The copper(II) ion is coordinated asymmetrically by a tetradentate ligand with the amino and imidazole imido nitrogen atoms on one side versus imino nitrogen and carboxylate oxygen atoms on the other side in a distorted square-planar geometry. The formation of an infinite chain through carboxylate coordination is observed. The novel ligand is obtained by the reaction between the l-histidine molecules coordinated to copper(II) and 4-hydroxy-4-methylpentan-2-one formed by aldol condensation of acetone. This complex provides insights into a possible structural arrangement between copper(II) and l-histidine which is physiologically important and abundantly present in biological systems.     

Crystal structure and biological activities of water-soluble nickel(II) and copper(II) complexes of a Schiff-base derived from paeonol

Water-soluble Ni(II) and Cu(II) complexes of a flexible Schiff-base ligand have been synthesized, and the Ni(II) complex was characterized by X-ray crystallography. The interactions of the two complexes with calf thymus DNA were investigated by spectroscopic and viscosity measurements in water. The results suggest that the two complexes bind to DNA within the groove. Antioxidant experiments against OH^• and O₂^−• show that these two complexes have excellent ability to scavenge O₂^−•, and the Cu(II) complex exhibits better activity than the Ni(II) complex.