Complex formation of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) acetates with 3,3′,4,4′,5,5′-hexamethyldipyrrolylmethene

The reactions of complex formation of Cu(II), Co(II), Zn(II), Ni(II), and Cd(II) acetates with 3,3′,4,4′5,5′-hexamethyl-2,2′-dipyrrolylmethene (HL) in DMF were studied by the electronic spectroscopy and calorimetric titration methods at 298.15 K. The main products of the above reactions are [ML₂] chelates. In the case of Cu and Ni salts, the process occurs through the spectrally recorded stage of formation of the heteroligand [ML(AcO)] complexes. The reaction with Cd acetate terminates at the stage of the heteroligand complex formation due to the large radius and decreasing electron affinity of the Cd²⁺ ion. The effect of the metal nature appears in the increasing thermodynamic stability of single-type complexes in the series [ML₂]: Ni(II) < Zn(II) < Co(II) < Cu(II) and [ML(AcO)]: Cd(II) < Ni(II) < Cu(II).     

Nitric oxide reactivity of copper(II) complexes of bidentate amine ligands: effect of substitution on ligand nitrosation

Three copper(ii) complexes with bidentate ligands L(1), L(2) and L(3) [L(1), N,N(/)-dimethylethylenediamine; L(2), N,N(/)-diethylethylenediamine and L(3), N,N(/)-diisobutylethylenediamine], respectively, were synthesized as their perchlorate salts. The single crystal structures for all the complexes were determined. The nitric oxide reactivity of the complexes was studied in acetonitrile solvent. The formation of thermally unstable [Cu(II)-NO] intermediate on reaction of the complexes with nitric oxide in acetonitrile solution was observed prior to the reduction of copper(II) centres to copper(I). The reduction was found to result with a simultaneous mono- and di-nitrosation at the secondary amine sites of the ligand. All the nitrosation products were isolated and characterized. The ratio of the yield of mono- and di-nitrosation product was found to be dependent on the N-substitution present in the ligand framework.     

Synergistic effect of Ni(II) and Co(II) ions on the sulfite induced autoxidation of Cu(II)/tetraglycine complex

The synergistic effect of Ni(II) and Co(II) on the sulfite induced autoxidation of Cu(II)/tetraglycine was investigated spectrophotometrically at 25.0 degrees C, pH = 9.0, 1 x 10(-5) mol dm(-3) < or = [S(IV)] < or = 8 x 10(-5) mol dm(-3), [Cu(II)]= 1 x 10(-3) mol dm(-3), 1 x 10(-6) mol dm(-3) < or = [Ni(II)] or [Co(II)] < or = 1 x 10(-4) mol dm(-3), [O2] approximately 2.5 x 10(-4) mol dm(-3), and 0.1 mol dm(-3) ionic strength. In the absence of added nickel(II) or cobalt(II), the kinetic traces of Cu(III)G4 formation show a large induction period (about 3 h). The addition of trace amounts of Ni(II) or Co(II) increases the reaction rate significantly and the induction period drastically decreases (less than 0.5 s). The effectiveness of Cu(III)G4 formation becomes much higher. The metal ion in the trivalent oxidation state rapidly oxidizes SO3(2-) to SO3*-, which reacts with oxygen to produce SO5*-. The strongly generated oxidants oxidize Cu(II)G4 to Cu(III).     

Coordination "oligomers" in self-assembly reactions of some "tritopic" picolinic dihydrazone ligands-mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear examples

"Tritopic" picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 x 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(II), Cu(II), and Zn(II) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(II), Co(II), Ni(II), and Cu(II), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 x 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(II), Co(II), Ni(II), and Cu(II) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(II)/Co(III) systems when starting with Co(II) salts, and reduction of Fe(III) to Fe(II) when starting with Fe(III). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features.     

New fluorescent rhodamine hydrazone chemosensor for Cu(II) with high selectivity and sensitivity

[reaction: see text] A new fluorescent probe, salicylaldehyde rhodamine B hydrazone (1), was synthesized and displayed selective Cu(II)-amplified absorbance and fluorescence emission above 500 nm in neutral buffered media. Upon the addition of Cu(II), the spirolactam ring of 1 was opened and a 1:1 metal-ligand complex was formed. The detection of Cu(II) by 1 at a lower micromolar level was successful even in buffered water.     

Copper(II) mediated anion dependent formation of Schiff base complexes

A tetranuclear mixed ligand copper(II) complex of a pyrazole containing Schiff base and a hydroxyhexahydropyrimidylpyrazole and copper(II) and nickel(II) complexes of the Schiff base having N-donor atoms have been investigated. A 2 equiv amount of 5-methyl-3-formylpyrazole (MPA) and 2 equiv of 1,3-diamino-2-propanol (1,3-DAP) on reaction with 1 equiv of copper(II) nitrate produce an unusual tetranuclear mixed ligand complex [Cu4(L1)2(L2)2(NO3)2] (1), where H2L1 = 1,3-bis(5-methyl-3-formylpyrazolylmethinimino)propane-2-ol and HL2 = 5-methyl-3-(5-hydroxyhexahydro-2-pyrimidyl)pyrazole. In contrast, a similar reaction with nickel(II) nitrate leads to the formation of a hygroscopic intractable material. On the other hand, the reaction involving 2 equiv of MPA and 1 equiv each of 1,3-DAP and various copper(II) salts gives rise to two types of products, viz. [Cu(T3-porphyrinogen)(H2O)]X2 (X = ClO4, NO3, BF4 (2)) (T3-porphyrinogen = 1,6,11,16-tetraza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen) and [Cu(H2L1)X]X x H2O (X = Cl (3), Br (4)). The same reaction carried out with nickel(II) salts also produces two types of compounds [Ni(H2L1)(H2O)2]X2 [X = ClO4 (5), NO3 (6), BF4 (7)] and [Ni(H2L1)X2] x H2O [X = Cl (8), Br (9)]. Among the above species 1, 3, and 5 are crystallographically characterized. In 1, all four copper atoms are in distorted square pyramidal geometry with N4O chromophore around two terminal copper atoms and N5 chromophore around two inner copper atoms. In 3, the copper atom is also in distorted square pyramidal geometry with N4Cl chromophore. The nickel atom in 5 is in a distorted octahedral geometry with N4O2 chromophore, where the metal atom is slightly pulled toward one of the axial coordinated water molecules. Variable-temperature (300 to 2 K) magnetic susceptibility measurements have been carried out for complex 1. The separations between the metal centers, viz., Cu(1)...Cu(2), Cu(2)...Cu(2)A, and Cu(2)A...Cu(1)A are 3.858, 3.89, and 3.858 A, respectively. The overall magnetic behavior is consistent with strong antiferromagnetic interactions between the spin centers. The exchange coupling constants between Cu(1)...Cu(2) and Cu(2)...Cu(2A) centers have turned out to be -305.3 and -400.7 cm(-1), respectively, resulting in a S = 1/2 ground state. The complexes are further characterized by UV-vis, IR, electron paramagnetic resonance, and electrochemical studies.     

Identification of a copper(I) intermediate in the conversion of 1-aminocyclopropane carboxylic acid (ACC) into ethylene by Cu(II)-ACC complexes and hydrogen peroxide

Several Cu(II) complexes with ACC (=1-aminocyclopropane carboxylic acid) or AIB (=aminoisobutyric acid) were prepared using 2,2'-bipyridine, 1,10-phenanthroline, and 2-picolylamine ligands: [Cu(2,2'-bipyridine)(ACC)(H2O)](ClO4) (1a), [Cu(1,10-phenanthroline)(ACC)](ClO4) (2a), [Cu(2-picolylamine)(ACC)](ClO4) (3a), and [Cu(2,2'-bipyridine)(AIB)(H2O)](ClO4) (1b). All of the complexes were characterized by X-ray diffraction analysis. The Cu(II)-ACC complexes are able to convert the bound ACC moiety into ethylene in the presence of hydrogen peroxide, in an "ACC-oxidase-like" activity. A few equivalents of base are necessary to deprotonate H2O2 for optimum activity. The presence of dioxygen lowers the yield of ACC conversion into ethylene by the copper(II) complexes. During the course of the reaction of Cu(II)-ACC complexes with H2O2, brown species (EPR silent and lambda max approximately 435 nm) were detected and characterized as being the Cu(I)-ACC complexes that are obtained upon reduction of the corresponding Cu(II) complexes by the deprotonated form of hydrogen peroxide. The geometry of the Cu(I) species was optimized by DFT calculations that reveal a change from square-planar to tetrahedral geometry upon reduction of the copper ion, in accordance with the observed nonreversibility of the redox process. In situ prepared Cu(I)-ACC complexes were also reacted with hydrogen peroxide, and a high level of ethylene formation was obtained. We propose Cu(I)-OOH as a possible active species for the conversion of ACC into ethylene, the structure of which was examined by DFT calculation.     

Structural characterization and formation kinetics of sitting-atop (SAT) complexes of some porphyrins with copper(II) ion in aqueous acetonitrile relevant to porphyrin metalation mechanism. Structures of aquacopper(II) and cu(II)-SAT complexes as determined by XAFS spectroscopy

The formation of the sitting-atop (SAT) complexes of 5,10,15,20-tetraphenylporphyrin (H(2)tpp), 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin (H(2)t(4-Clp)p), 5,10,15,20-tetramesitylporphyrin (H(2)tmp), and 2,3,7,8,12,13,17,18-octaethylporphyrin (H(2)oep) with the Cu(II) ion was spectrophotometrically confirmed in aqueous acetonitrile (AN), and the formation rates were determined as a function of the water concentration (C(W)). The decrease in the conditional first-order rate constants with the increasing C(W) was reproduced by taking into consideration the contribution of [Cu(H(2)O)(an)(5)](2+) in addition to [Cu(an)(6)](2+) to form the Cu(II)-SAT complexes. The second-order rate constants for the reaction of [Cu(an)(6)](2+) and [Cu(H(2)O)(an)(5)](2+) at 298 K were respectively determined as follows: (4.1 +/- 0.2) x 10(5) and (3.6 +/- 0.2) x 10(4) M(-1) s(-1) for H(2)tpp, (1.15 +/- 0.06) x 10(5) M(-1) s(-1) and negligible for H(2)t(4-Clp)p, and (4.8 +/- 0.3) x 10(3) and (1.3 +/- 0.3) x 10(2) M(-1) s(-1) for H(2)tmp. Since the reaction of H(2)oep was too fast to observe the reaction trace due to the dead time of 2 ms for the present stopped-flow technique, the rate constant was estimated to be greater than 1.5 x 10(6) M(-1) s(-1). According to the structure of the Cu(II)-SAT complexes determined by the fluorescent XAFS measurements, two pyrrolenine nitrogens of the meso-substituted porphyrins (H(2)tpp and H(2)tmp) bind to the Cu(II) ion with a Cu-N(pyr) distance of ca. 2.04 A, while those of the beta-pyrrole-substituted porphyrin (H(2)oep) coordinate with the corresponding bond distance of 1.97 A. The shorter distance of H(2)oep is ascribed to the flexibility of the porphyrin ring, and the much greater rate for the formation of the Cu(II)-SAT complex of H(2)oep than those for the meso-substituted porphyrins is interpreted as due to a small energetic loss at the porphyrin deformation step during the formation of the Cu(II)-SAT complex. The overall formation constants, beta(n), of [Cu(H(2)O)(n)()(an)(6)(-)(n)](2+) for the water addition in aqueous AN were spectrophotometrically determined at 298 K as follows: log(beta(1)/M(-1)) = 1.19 +/- 0.18, log(beta(2)/M(-2)) = 1.86 +/- 0.35, and log(beta(3)/M(-3)) = 2.12 +/- 0.57. The structure parameters around the Cu(II) ion in [Cu(H(2)O)(n)(an)(6-n)](2+) were determined using XAFS spectroscopy.     

Coordination compounds of hydrazine derivatives with transition metals. Part 27. Coordination chemistry of 4-amino-3-alkyl-5-thio-1,2,4-triazolines and 4-amino-5-oxo-3-thioxo-6-alkyl-2,3,4,5-tetrahydro-1,2,4-triazines

Summary Mono-, bis- and tris-ligand nickel(II) and cobalt(II) complexes with 4 amino-3-alkyl-5-thio-1,2,4-triazolines (HRL) (R=H, Me, or Et) and 4-amino-5-oxo-3-thioxo-6-methyl-2,3,4,5-tetrahydro-1,2,4-triazine (HL') have been prepared and characterized. In these complexes both HRL and HL' are in the neutral thione form. Nickel(II) and cobalt(II) complexes with mononegative thiolate ligands have been also isolated.The reaction of HL' with copper(II) salts in a molar ration of 11 results in the formation of [Cu(HL')X] (X=Cl or Br) and Cu(L')X (X=NO₃ or CH₃COO). However, in the presence of a large excess of HL' the reaction proceeds with partial reduction of Cu^II and both [Cu(HL')X₂] and [Cu(HL')₂]X have been isolated and characterized. The mechanism of copper(II) reduction by HL' is discussed.     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

Colorimetric recognition of Cu(II) by (2-dimethylaminoethyl)amino appended anthracene-9,10-diones in aqueous solutions: deprotonation of aryl amine NH responsible for colour changes

Chromogenic receptors 2 and 3 undergo distinct colour changes from magenta to blue on gradual addition of Cu(II) and can be used as colorimetric probes for spectrophotometric and visual analysis of Cu(II) in the presence of biological metal ions Na(I), K(I), Mg(II), Ca(II), Fe(II), Zn(II) etc. in aqueous solution (methanol-water 1 : 1 v/v). On addition of Cu(II), both 2 and 3 exhibit a bathochromic shift of Delta lambda(max) = 114 nm for 2 and Delta lambda(max)= 150 and 265 nm for receptor 3. The protonation constants and formation constants of Cu(II) complexes of receptors 2 and 3 (at pH 7) and the effect of pH on formation of these complexes has been determined by the combination of UV-vis-pH titrations of receptors 2 and 3 and their Cu(II) complexes. These results and the emergence of only one peak at 610 nm for 2 and two distinct absorption peaks at 715 and 800 nm for 3 on addition of Cu(II) unambiguously point to mono- and di-deprotonation for 2 and 3, respectively.     

Covalent linkage of the type-2 and type-3 structural mimics to model the active site structure of multicopper oxidases: synthesis and magneto- structural properties of two angular trinuclear copper(II) complexes

Two new angular trinuclear copper(II) complexes of formulation [Cu(3)(HL)LL'](ClO(4)), where L' is imidazole (Him, 1) or 1-methylimidazole (1-MeIm, 2) and H(3)L is a Schiff base obtained from the condensation of salicylaldehyde and 1,3-diaminopropan-2-ol (2:1 mole ratio), are prepared from a reaction of [Cu(2)L(mu-Br)] and [Cu(HL)] in the presence of L' and isolated as perchlorate salts. The crystal structures of 1 and 2 consist of a trinuclear copper(II) unit formed by the covalent linkage of monomeric type-2 mimic and dimeric type-3 mimic precursor complexes to give an angular arrangement of the metal atoms in the core which is a model for the active site structure of blue multicopper oxidases. In 1 and 2, the coordination geometry of two terminal copper atoms is distorted square-planar. The central copper has a distorted square-pyramidal (4 + 1) geometry. The mean Cu...Cu distance is approximately 3.3 A. The complex has a diphenoxo-bridged dicopper(II) unit with the phenoxo oxygen atoms showing a planar geometry. In addition, the complex has an endogenous alkoxo-bridged dicopper(II) unit showing a pyramidal geometry for the oxygen atom. The 1:1 electrolytic complexes show a d-d band at 607 nm. Cyclic voltammetry of the complexes in MeCN containing 0.1 M TBAP using a glassy carbon working electrode displays a Cu(3)(II)/Cu(2)(II)Cu(I) couple near -1.0 V (vs SCE). The variable temperature magnetic susceptibility measurements in the range 300-18 K show antiferromagnetic coupling in the complexes giving magnetic moments of approximately 3.0 mu(B) at 300 K and approximately 2.1 mu(B) at 18 K for the tricopper(II) unit. The experimental susceptibility data are theoretically fitted using a model with Heisenberg spin-(1)/(2) Hamiltonian for a trimer of spin-(1)/(2) copper(II) ions having two exchange parameters involving the alkoxo-bridged dicopper(II) (J1) and the diphenoxo-bridged dicopper(II) (J2) units, giving J1 and J2 values of -82.7, -73 cm(-1) for 1 and -98.3, -46.1 cm(-1) for 2, respectively. The structural features indicate a higher magnitude of anitiferromagnetic coupling in the alkoxo-bridged unit based on the greater value of the Cu-O-Cu angle in comparison to the diphenoxo-bridged unit. The core structures of 1 and 2 compare well with the first generation model complexes for the active site structure of multicopper oxidases in the oxidized form. The crystal structure of 1 exhibits a lamellar structure with a gap of approximately 7 A containing water molecules in the interlamellar space. Complex 2 forms a hexanuclear species due to intermolecular hydrogen bonding interactions involving two trimeric units. The crystal packing diagram of 2 displays formation of a three-dimensional framework with cavities containing the perchlorate anions.     

Selective determination of cobalt using polyurethane foam and 2-(2-benzothiazolylazo)-2-p-cresol as a spectrophotometric reagent

The present work describes a selective, rapid and economical method for the determination of cobalt using the 2-(2-benzothiazolylazo)-p-cresol (BTAC) as a spectrophotometric reagent associated with a solid extraction on polyurethane foam. The BTAC reacts with Co(II) in the presence of Triton-X100 surfactant forming a green complex with maximum absorption at 615 nm. The reaction is used for cobalt determination within a pH range of 6.50-7.50, with an apparent molar absorptivity of 1.62 x 10(4) L mol(-1) cm(-1). Beer's Law is obeyed for a concentration of at least 1.60 microg ml(-1). A selective procedure is proposed for cobalt determination in the presence of Fe(II), Hg(II), Zn(II) and Cu(II) up to milligram levels using masking agents. Polyurethane foam is used for the preconcentration and separation of cobalt from thiocyanate media and this procedure is applied to its determination in nickel salts and steel alloys.     

Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))3](1-), L(-)=dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the nuCC+nuCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g=2.0005 and g=2.0923, and for Cu(II) with g=2.008 and g=2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease.     

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(I,II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(4)mim][OAc], and copper(II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl)phosphonium acetate, [P(8 8 8 12)][OAc], were synthesised in a facile one-pot reaction from solutions of copper(II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using (13)C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)(2) in 1-ethyl-3-methylimidazolium acetate, [C(2)mim][OAc], crystals were obtained that revealed the structure of [C(2)mim][Cu(3)(OAc)(5)(OH)(2)(H(2)O)]·H(2)O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry.     

Metal-assisted red light-induced DNA cleavage by ternary L-methionine copper(II) complexes of planar heterocyclic bases

Ternary copper(II) complexes [Cu(l-met)B(Solv)](ClO4) (1-4), where B is a N,N-donor heterocyclic base like 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 3) and dipyrido[3,2-a:2'],3'-c]phenazene (dppz, 4), are prepared and their DNA binding and photo-induced DNA cleavage activity studied (L-Hmet =L-methionine). Complex 2, structurally characterized by X-ray crystallography, shows a square pyramidal (4 + 1) coordination geometry in which the N,O-donor L-methionine and N,N-donor heterocyclic base bind at the basal plane and a solvent molecule is coordinated at the axial site. The complexes display a d-d band at approximately 600 nm in DMF and exhibit a cyclic voltammetric response due to the Cu(II)/Cu(I) couple near -0.1 V in DMF-Tris-HCl buffer. The complexes display significant binding propensity to the calf thymus DNA in the order: 4(dppz) > 3(dpq) > 2(phen> 1(bpy). Control cleavage experiments using pUC19 supercoiled DNA and distamycin suggest major groove binding for the dppz and minor groove binding for the other complexes. Complexes 2-4 show efficient DNA cleavage activity on UV (365 nm) or red light (632.8 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The DNA cleavage activity of the dpq complex is found to be significantly more than its dppz and phen analogues.     

Dicopper(I) complexes of unsymmetrical binucleating ligands and their dioxygen reactivities

The design, synthesis, and characterization of binuclear copper(I) complexes and investigations of their dioxygen reactivities are of interest in understanding fundamental aspects of copper/O2 reactivity and in modeling copper enzyme active-site chemistry. In the latter regard, unsymmetrical binuclear systems are of interest. Here, we describe the chemistry of new unsymmetrical binuclear copper complexes, starting with the binucleating ligand UN2-H, possessing a m-xylyl moiety linking a bis[2-(2-pyridyl)ethyl]amine (PY2) tridentate chelator and a 2-[2-(methylamino)ethyl]pyridine bidentate group. Dicopper(I) complexes of UN2-H, [Cu2(UN2-H)]2+ (1), as PF6- and ClO4- salts, are synthesized. These react with O2 (Cu:O2 = 2:1, manometry) resulting in the hydroxylation of the xylyl moiety, producing the phenoxohydroxodicopper(II) complex [Cu2(UN2-O-)(OH-)(CH3CN)]2+ (2). Compound 2(PF6)2 is characterized by X-ray crystallography, which reveals features similar to those of a structure described previously (Karlin, K. D.; et al. J. Am. Chem. Soc. 1984, 106, 2121-2128) for a symmetrical binucleating analogue having two tridentate PY2 moieties; here a CH3CN ligand replaces one pyridylethyl arm. Isotope labeling from a reaction of 1 using 18O2 shows that the ligand UN2-OH, extracted from 2, possesses an 18O-labeled phenol oxygen atom. Thus, the transformation 1 + O2-->2 represents a monooxygenase model system. [CuI2(UN2-OH)(CH3CN)]2+ (3), a new binuclear dicopper(I) complex with an unsymmetrical coordination environment is generated either by reduction of 2 with diphenylhydrazine or in reactions of cuprous salts with UN2-OH. Complex 3 reacts with O2 at -80 degrees C, producing the (mu-1,1-hydroperoxo)dicopper(II) complex [CuII2(UN2-O-)(OOH-)]2+ (4) (lambda max 390 nm (epsilon 4200 M-1 cm-1), formulated on the basis of the stoichiometry of O2 uptake by 3 (Cu:O2 = 2:1, manometry), its reaction with PPh3 giving O=PPh3 (85%), and comparison to previously studied close analogues. Discussions include the relevance and comparison to other copper bioinorganic chemistry.     

Ratiometric and selective fluorescent sensor for CuII based on internal charge transfer (ICT)

A Cu(II)-sensing, ratiometric, and selective fluorescent sensor 1, N-butyl-4,5-di[(pyridin-2-ylmethyl)amino]-1,8-naphthalimide, was designed and synthesized on the basis of the mechanism of internal charge transfer (ICT). In aqueous ethanol solutions of 1, the presence of Cu(II) induces the formation of a 1:1 metal-ligand complex, which exhibits a strong, increasing fluorescent emission centered at 475 nm at the expense of the fluorescent emission of 1 centered at 525 nm. [structure: see text]     

Multinuclear copper complexes of pyridylmethylamide ligands

Copper complexes of a family of pyridylmethylamide ligands HL(Ph), HL(Me3) and HL(Ph3) were synthesized and characterized [HL(Ph) = 2-phenyl-N-(2-pyridylmethyl)acetamide; HL(Me3) = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HL(Ph3) = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide]. The reaction of copper(II) salts with the HL family and triethylamine in methanol yields copper(II) complexes [Cu4(L(Ph))4(OH)2](ClO4)2 (1), [Cu2(HL(Me3))2(OMe)2(MeOH)2](OTf)2 (2) and [Cu2(HL(Ph3))2(OMe)2(MeOH)2](OTf)2 (3). The complexes have different nuclearity owing to varying steric properties of the ligands used. Complex 1 self-assembles in the presence of excess base to form a tetranuclear complex. Complexes 2 and 3 are binuclear and are bridged by a pair of methoxide ligands. Steric encumbrance of the ligands in 2 and 3 prevent cluster formation.     

Study of the degradation of polyurethanes. III. Mechanism of the photodegradation of polyurethane

The effect of triplet sensitizers, benzophenone and anthraquinone and metal acetylacetonates [Co(II, III), Cu, Sn, and Ni] on the photodegradation of polyurethane was examined. Ultravioletvisible (UV-V) absorption spectra, gel formation, and luminescence emission of the polymer before and after irradiation were measured. Changes in UV-V absorption of the polymer and the formation of an insoluble fraction in the polymer were accelerated in the presence of the triplet sensitizers, and (Co(II, III)), Cu, and Sn acetylacetonates. Unirradiated polyurethane was excited by irradiation at 290 and 346 nm, and emitted light at 310 and 420 nm. After 1/2 hr irradiation emission of luminescence was observed at 430 nm, excitation at 290 and 346 nm; after 2hr irradiation at 530 nm, excitation at 420 nm was observed. The results suggest that photodegradation of the polyurethane proceeds via excited triplet states forming excimer between the polymers at the initial stage and exciplexes between the polymer and degradation products or intermediates after a certain irradiation.