Intermetallic interactions in face-to-face homo- and heterodinuclear bismacrocyclic complexes of copper(II) and nickel(II)

New face-to-face heterodinuclear complexes containing copper(II) and nickel(II) in identical tetraazamacrocyclic environments have been synthesized and characterized using ESI mass-spectrometry, X-ray diffraction, spectroscopic methods, and elemental analysis. These new bismacrocyclic systems were compared with the respective mono- and bismacrocyclic and [2]catenane homonuclear complexes. Interactions between the metal centers were monitored by magnetic and electrochemical measurements. Magnetic data indicate that all copper compounds studied behave as weakly interacting magnets. In the case of copper [2]catenane, the extent of magnetic interactions decreased when a benzocrown moiety was introduced between the macrocyclic units. On the basis of electrochemical data, the interactions between the metal centers were found to be substantially larger for the nickel complexes than for the corresponding copper ones. Interlocking of a benzocrown ether to form [2]catenane led to a nonequivalence of the metal centers and to the increase of donor abilities of the catenane compared to the respective bismacrocyclic complex. This is reflected by the shift of the first formal potential to less positive values. Intermetallic interactions for the heteronuclear nickel/copper complexes were found intermediary compared to the homonuclear ones. They were strengthened by shortening the spacer between the two tetraazamacrocyclic subunits which is a convenient way of fine-tuning the interactions. The increase of intermetallic interactions led to the increased stability of the intermediate mixed-valence states indicated by the higher values of comproportionation constants.     

Syntheses,structures, and properties of imidazolate-bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) dinuclear complexes of a single macrocyclic ligand with two hydroxyethyl pendants

The imidazolate-bridged homodinuclear Cu(II)-Cu(II) complex, [(CuimCu)L]ClO(4).0.5H(2)O (1), and heterodinuclear Cu(II)-Zn(II) complex, [(CuimZnL(-)(2H))(CuimZnL(-)(H))](ClO(4))(3) (2), of a single macrocyclic ligand with two hydroxyethyl pendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,2(11,14)]triaconta-1,11,13,24,27,29-hexaene), have been synthesized as possible models for copper-zinc superoxide dismutase (Cu(2),Zn(2)-SOD). Their crystal structures analyzed by X-ray diffraction methods have shown that the structures of the two complexes are markedly different. Complex 1 crystallizes in the orthorhombic system, containing an imidazolate-bridged dicopper(II) [Cu-im-Cu](3+) core, in which the two copper(II) ions are pentacoordinated by virtue of an N4O environment with a Cu.Cu distance of 5.999(2) A, adopting the geometry of distorted trigonal bipyramid and tetragonal pyramid, respectively. Complex 2 crystallizes in the triclinic system, containing two similar Cu-im-Zn cores in the asymmetric unit, in which both the Cu(II) and Zn(II) ions are pentacoordinated in a distorted trigonal bipyramid geometry, with the Cu.Zn distance of 5.950(1)/5.939(1) A, respectively. Interestingly, the macrocyclic ligand with two arms possesses a chairlike (anti) conformation in complex 1, but a boatlike (syn) conformation in complex 2. Magnetic measurements and ESR spectroscopy of complex 1 have revealed the presence of an antiferromagnetic exchange interaction between the two Cu(II) ions. The ESR spectrum of the Cu(II)-Zn(II) heterodinuclear complex 2 displayed a typical signal for mononuclear trigonal bipyramidal Cu(II) complexes. From pH-dependent ESR and electronic spectroscopic studies, the imidazolate bridges in the two complexes have been found to be stable over broad pH ranges. The cyclic voltammograms of the two complexes have been investigated. Both of the two complexes can catalyze the dismutation of superoxide and show rather high activity.     

Novel copper(II) homobinuclear macrocyclic complexes: cyclic voltammetry, biological properties and spectral studies

A series of five new copper(II) macrocyclic complexes have been synthesized by template condensation. The bonding and stereochemistry of the complexes have been characterized by elemental analysis, molar conductance, magnetic susceptibility, IR, UV-visible, EPR spectral studies and electrochemical properties. g-Values are calculated for all of the complexes in polycrystalline form as well as in DMSO solution. The magnetic and spectral data indicate square planar geometry for all the complexes. Cyclic voltammograms for all the complexes are similar and involve two quasi-reversible redox processes. Cu(II)Cu(II)<=>Cu(II)Cu(I)<=>Cu(I)Cu(I). Their biological properties have also been studied. The macrocyclic complexes show more anti-bacterial than controlled one. The anti-bacterial activities of the compounds were tested against Streptococcus fecalis and Escherichia coli with different concentrations.     

Thiohydrazone copper(II) complexes. The relationship between redox properties and superoxide dismutase mimetic activity

The redox behaviour of copper(II) complexes with the open chain ligand, benzilbisthiosemicarbazone, and the macrocyclic one [3,4,10,11-tetraphenyl-1,2,5,8,9,12,13-octaazacyclotetradeca-7,14- dithione- 2,4,9,11-tetraene] has been explored by cyclic voltammetry. The half-wave potential values for the copper(II)/copper(I) redox couple and the spectral data obtained on dimethylsulfoxide (DMSO) solution agree with the superoxide dismutase (SOD)-mimetic activity of the complexes. The macrocyclic complexes show more positive reduction potential and more activity than the open chain derivatives. From our results it follows that the structure and conformation of ligand has influence on the redox potential of central atom in coordination compound. The changes in the coordination sphere are connected with the change of biological function of compounds represented by SOD-mimic activity. In addition, the L1H6 derivatives show quasireversible waves associated to Cu(II)/Cu(III) process.     

Copper(II) Complexes of the Hexaaza Macrocyclic Ligand 3,6,9,16,19,22-Hexaaza-27,28-dioxatricyclo[22.2.1.1(11,14)]octacosa-1(26),11,13,24-tetraene and Their Interaction with Oxalate, Malonate, and Pyrophosphate Anions

The hexaaza macrocyclic ligand 3,6,9,16,19,22-hexaaza-27,28-dioxatricyclo[22.2.1.1(11,14)]octacosa-1(26),11,13,24-tetraene (BFBD), forms both mono- and dinuclear complexes, as well as several protonated and hydroxo chelates, with Cu(II) ions. These cationic species can bind inorganic and organic anions through coordination and hydrogen bonding. Stability constants of the mono- and dinuclear Cu(II) complexes of BFBD and their interaction with oxalate, malonate, and pyrophosphate anions have been measured potentiometrically. The nature of the bonding between the hosts and the guests is discussed. The crystal structures of two new dinuclear Cu(II) complexes, determined by X-ray crystallography, are also reported. [BFBDCu(2)(Cl)(3)]ClO(4).0.5H(2)O crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.267(2) ?, b = 12.155(6) ?, c = 18.461 0 ?, beta = 90.86(2) degrees, and Z = 4. Each Cu(II) ion is coordinated by three nitrogen atoms from the diethylenetriamine unit of the macrocyclic ligand and two chloride anions, forming a square pyramidal geometry. [BFBDCu(2)(Ox)](BF(4))(1.8)Cl(0.2) crystallizes in the triclinic system, space group P1, with a = 6.772(1) ?, b = 10.646(2) ?, c = 11.517(2) ?, alpha = 64.74(3) degrees, beta = 79.79(3) degrees, gamma = 81.94(3) degrees, and Z = 1. The environment of each copper is intermediate between square pyramidal and trigonal pyramidal. The oxalate anion bridges in a bis-bidentate fashion between two Cu(II) ions.     

Dicopper(II) complexes of a new pyrazolate-containing Schiff-base macrocycle and related acyclic ligand

Dicopper(II) complexes of two new 3,5-disubstituted-pyrazole-based ligands, bis(quadridentate) macrocyclic ligand (L1)(2-) and bis(terdentate) acyclic ligand (L2)(-), were synthesised by Schiff base condensation of 3,5-diformylpyrazole and either one equivalent of 1,3-diaminopropane or two equivalents of 2-(2-aminoethyl)pyridine in the presence of one or two equivalents of copper(II) ions, respectively. Copper(II) acetate monohydrate was employed in the synthesis of [Cu(2)(L1)(OAc)(2)], [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] and [Cu(II)(2)(L1)(NCS)(2)]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu(2)(L2)(NCS)(2)(DMF)]BF(4), was prepared using copper(II) tetrafluoroborate hexahydrate, along with two equivalents of NaOH and six of NaSCN. All four of these dimetallic complexes have been characterised by single crystal X-ray diffraction: the two macrocyclic complexes are the first such Schiff base complexes to be so characterised. A feature common to all four of the structures is bridging of the two copper(II) centres by the pyrazolate moiety/moieties. The structure determinations show that the coordination mode of the acetate groups in both [Cu(2)(L1)(OAc)(2)].2MeOH.H(2)O and [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] is unidentate as had been tentatively predicted by analysis of the infrared spectra (DeltaOCO of 199 and 208 cm(-1), respectively). The magnetochemical studies of the macrocyclic complexes, over the temperature range 4-300 K, revealed strong antiferromagnetic coupling with J = -169 and -213 cm(-1) for [Cu(2)(L1)(OAc)(2)].2H(2)O and [Cu(II)(2)(L1)(NCS)(2)].DMF respectively. The J values have been discussed in relation to a published correlation involving the CuN(pyrazolate)N(pyrazolate) angles.     

Magnetic, electronic and electrochemical studies of mono and binuclear Cu(II) complexes using novel macrocyclic ligands

A series of new mono and binuclear copper (II) complexes [Cul]X(2)and [Cu(2)lX(2)] where 1 = L(1), L(2) and L(3) are the macrocyclic ligands. In mononuclear complexes the geometry of Cu(II) ion is distorted squareplanar and in binuclear complexes the geometry of Cu(II) is tetragonal. The synthesized complexes were characterized by spectroscopic (IR,UV-vis and ESR) techniques. Electrochemical studies of the complexes reveals that all the mononuclear Cu(II) complexes show a single quasireversible one-electron transfer reduction wave (E(pc) = -0.76 to -0.84V) and the binuclear complexes show two quasireversible one electron transfer reduction waves (E(pc)(1) = -0.86 to -1.01V, E(pc)(2) = -1.11 to -1.43V) in cathodic region. The ESR spectra of mononuclear complexes show four lines with nuclear hyperfine splittings with the observed g(11) values in the ranges 2.20-2.28, g( perpendicular) = 2.01-2.06 and A(11) = 125-273. The binuclear complexes show a broad ESR spectra with g = 2.10-2.11. The room temperature magnetic moment values for the mononuclear complexes are in the range [mu(eff) = 1.70-1.72BM] and for the binuclear complexes the range is [mu(eff) = 1.46-1.59BM].     

Tetraimine macrocyclic transition metal complexes as building blocks for molecular devices

The synthetic strategy initiated by Busch and further developed in recent years resulted in an impressive variety of new azamacrocyclic ligand superstructures. In this contribution, we have reviewed papers containing general synthetic strategies, structural and electronic properties and results of electrochemical studies for a long series of neutral and charged macrocyclic tetraimine complexes of transition metals leading to a new type of homo- and heteronuclear[2]catenanes as examples of switchable molecular machines. The whole series consists of neutral and charged mono-, bis- and trismacrocycles and appropriate reference neutral molecules and many of their derivatives. The bismacrocyclic moieties are constructed from simpler tetraazamacrocyclic fragments. When two of them are linked through polymethylene chains, they form face-to-face biscyclidenes—rectangular box-like moieties. They can host some small guest molecules (water, π-electron-donating compounds) and are stabilized by hydrogen bonds with solvent molecules or a shell of neighboring counterions. Neutral thiol derivatives are used as recognition sites of monolayers self-assembled on electrode surfaces to be employed in devices based on donor–acceptor interactions.Our catenanes consist of bismacrocyclic transition metal complexes linked by aliphatic chains and interlocked with a substituted crown ether. We have proved that under external stimuli – electrochemical pulses – the heteronuclear catenane exhibits controlled intramolecular relocation of the crown ether between two positions. The relocation is possible due to π?π interactions between the aromatic fragments of the crown ether and the transition metal (Ni, Cu) coordinating macrocyclic rings.Our model tetraimine complexes of transition metals can also be used to solve the problem of controlling directional relative movement of molecular fragments present in complex supramolecules. On the way to this aim we have synthesized trismacrocyclic derivatives which are now appropriately modified to serve as components of complex catenanes.     

A new dinuclear heme-copper complex derived from functionalized protoporphyrin IX

A new biomimetic model for the heterodinuclear heme/copper center of respiratory oxidases is described. It is derived from iron(III) protoporphyrin IX by covalent attachment of a Gly-L-His-OMe residue to one propionic acid substituent and an amino-bis(benzimidazole) residue to the other propionic acid substituent of the porphyrin ring, yielding the Fe(III) complex 1, and subsequent addition of a copper(II) or copper(I) ion, according to needs. The fully oxidized Fe(III)/Cu(II) complex, 2, binds azide more strongly than 1, and likely contains azide bound as a bridging ligand between Fe(III) and Cu(II). The two metal centers also cooperate in the reaction with hydrogen peroxide, as the peroxide adducts obtained at low temperature for 1 and 2 display different optical features. Support to this interpretation comes from the investigation of the peroxidase activity of the complexes, where the activation of hydrogen peroxide has been studied through the phenol coupling reaction of p-cresol. Here the presence of Cu(II) improves the catalytic performance of complex 2 with respect to 1 at acidic pH, where the positive charge of the Cu(II) ion is useful to promote O-O bond cleavage of the iron-bound hydroperoxide, but it depresses the activity at basic pH because it can stabilize an intramolecular hydroxo bridge between Fe(III) and Cu(II). The reactivity to dioxygen of the reduced complexes has been studied at low temperature starting from the carbonyl adducts of the Fe(II) complex, 3, and Fe(II)/Cu(I) complex, 4. Also in this case the adducts derived from the Fe(II) and Fe(II)/Cu(I) complexes, that we formulate as Fe(III)-superoxo and Fe(III)/Cu(II)-peroxo exhibit slightly different spectral properties, showing that the copper center participates in a weak interaction with the dioxygen moiety.     

Identification of Cu(II)/Cu(III) couples in binuclear copper(II) complexes

A new series of binuclear copper(II) complexes were synthesised and studied by magnetic, spectral, ESR and cyclic voltammetry methods. The μ_eff values per copper atom correspond to the values observed for mononuclear copper(II) complexes. ESR spectral data in solution indicate weak interactions resulting from the electron delocalisation through the ligand system. Two nearly reversible red-ox couples are identified at $\text{+}\text{?}$0.50 V and $\text{+}\text{?}$0.75 V vs SCE. They correspond to Cu(II)αCu(III) red-ox processes, successively occurring at the two copper sites in the binuclear complexes.     

Novel [2]catenane structures introducing communication between transition metal centers via pi...pi interactions

[2]Catenane systems containing copper(II) and nickel(II) as metal centers have been self-assembled using tetraazamacrocyclic complexes and benzo-24-crown-8 as building blocks. A variety of methods, including X-ray crystallography, ESI mass spectrometry, (13)C and (1)H NMR, and electrochemistry, were applied to characterize these new face-to-face bismacrocyclic systems. Weak pi...pi interactions introduced by interlocking transition metal complexes with benzocrown moieties were shown to increase the communication (cooperativity) of metal centers. Introduction of the benzocrown increases the stability of the mixed valence state of the macrocyclic complex, which is reflected in high values of conproportionation constants. Moreover, this effect was found to be stronger than that obtained by shortening the length of the spacer between the two tetraazamacrocyclic subunits in the parent bismacrocycles. The extent of communication is larger for the nickel catenane than for the copper one.     

Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.     

Synthesis of lateral macrobicyclic compartmental ligands: structural,magnetic, electrochemical,and catalytic studies of mono- and binuclear copper(II) complexes

A series of putative mono- and binuclear copper(II) complexes, of general formulas [CuL](ClO(4)) and [Cu(2)L](ClO(4))(2), respectively, have been synthesized from lateral macrocyclic ligands that have different compartments, originated from their corresponding precursor compounds (PC-1, 3,4:9,10-dibenzo-1,12-[N,N'-bis[(3-formyl-2-hydroxy-5-methyl)benzyl]diaza]-5,8-dioxacyclotetradecane; and PC-2, 3,4:9,10-dibenzo-1,12-[N,N'-bis[(3-formyl-2-hydroxy-5-methyl)benzyl]diaza]-5,8-dioxacyclopentadecane). The precursor compound PC-1 crystallized in the triclinic system with space group P(-)1. The mononuclear copper(II) complex [CuL(1a)](ClO(4)) is crystallized in the monoclinic system with space group P2(1)/c. The binuclear copper(II) complex [Cu(2)L(2c)](ClO(4))(2) is crystallized in the triclinic system with space group P(-)1; the two Cu ions have two different geometries. Electrochemical studies evidenced that one quasi-reversible reduction wave (E(pc) = -0.78 to -0.87 V) for mononuclear complexes and two quasi-reversible one-electron-transfer reduction waves (E(1)(pc) = -0.83 to -0.92 V, E(2)(pc) = -1.07 to -1.38 V) for binuclear complexes are obtained in the cathodic region. Room-temperature magnetic-moment studies convey the presence of antiferromagnetic coupling in binuclear complexes [mu(eff) = (1.45-1.55)mu(B)], which is also suggested from the broad ESR spectra with g = 2.10-2.11, whereas mononuclear complexes show hyperfine splitting in ESR spectra and they have magnetic-moment values that are similar to the spin-only value [mu(eff) = (1.69-1.72)mu(B)]. Variable-temperature magnetic susceptibility study of the complex shows that the observed -2J value for the binuclear complex [Cu(2)L(1b)](ClO(4))(2) is 214 cm(-1). The observed initial rate-constant values of catechol oxidation, using complexes as catalysts, range from 4.89 x 10(-3) to 5.32 x 10(-2) min(-1) and the values are found to be higher for binuclear complexes than for the corresponding mononuclear complexes.     

Synthesis,structural studies and bio-activity of some metal(II) complexes with glyoxal salicylaldehyde acyldihydrazones

Complexes of the type [M(gssdh)]Cl and [M(gspdh)]Cl, where M?=?Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), Hgssdh?=?glyoxal salicylaldehyde succinic acid dihydrazone and Hgspdh?=?glyoxal salicylaldehyde phthalic acid dihydrazone, have been synthesized and characterized by elemental analyses, molar conductance, magnetic moments, electronic, ESR and IR spectra and X-ray powder diffraction studies. The metal complexes are insoluble in common organic solvents and are 1?:?1 electrolytes. The magnetic moment values and electronic spectra indicate a spin–free octahedral geometry for all Co(II), Ni(II) and Cu(II) complexes. ESR spectral parameters of Cu(II) complexes suggest an elongated tetragonally–distorted octahedral stereochemistry around copper. Both ligands are monobasic hexadentate ligands coordinating through three >C=O, two >C=N– and a deprotonated phenolate group to the metal. X-ray powder diffraction parameters for three of the complexes correspond to an orthorhombic crystal lattice. The complexes show appreciable activity against various fungi and bacteria.     

Kinetic and equilibrium studies on the polyazamacrocycle neotetren: metal-complex formation and DNA interaction

The macrocyclic polyamine 2,5,8,11,14-pentaaza[15]-[15](2,9)[1,10]phenanthrolinophane (neotetren) is studied in its ability to coordinate Cu(ii) even at very low pH values and to interact, as a metal complex, with DNA. The kinetics and equilibria for 1 : 1 and 2 : 1 metal-ligand complexes formation are studied by the stopped-flow method and UV spectrophotometry. Differently protonated complexes are formed, with rate constants much lower than that of water exchange at copper(II) and other Cu(II)/amine systems, this behaviour being ascribed to ring effects and intra-molecular hydrogen bonds. Concerning the DNA/copper(II)-neotetren complexes interaction, analysis of data suggests an intercalative mode of binding. The kinetic results for both DNA/CuL and DNA/Cu(2)L systems agree with the sequence D + S <-->D,S <-->DS where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D,S) which is converted into an intercalated complex (DS). A very slow process is also detected and ascribed to a conformational change in the polynucleotide secondary structure where the metal centre plays a crucial role. Chromatographic experiments demonstrate that both the investigated Cu(II)/L complexes are able to cleave DNA, but only in the presence of hydrogen peroxide.     

Exceptional affinity of nanostructured organic-inorganic hybrid materials towards dioxygen: confinement effect of copper complexes

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.     

Benzo[h]quinoline based Macrocyclic Copper(II), Cobalt(II) Complexes: Synthesis,Characterization and Light induced DNA Cleavage Studies

A new ligand dibenzo[h]quinolineno[1,3,7,9] tetraazacyclododecine-7,15 (14H, 16H)-dibenzene (L) and its Co(II)/Cu(II) metal complexes of type [MLX₂] (Where (M = Co(II) (5), Cu(II) (6) and X = Cl) were synthesized and are well characterized by FT-IR, ¹H-NMR, FAB mass elemental analysis, and electronic spectral data. The role of the cobalt/copper metals in photo-induced DNA cleavage reactions was explored by designing complex molecules having macrocyclic structure. Finally, we have shown that photocleavage of plasmid DNA is more efficiently enhanced when this macrocyclic ligand is irradiated in the presence of copper(II) than that of cobalt metal.     

Steric and hydrogen-bonding effects on the stability of copper complexes with small molecules

A series of the copper(II) complexes with tripodal tetradentate tris(pyridyl 2-methyl)amine-based ligands possessing the hydrogen-bonding 6-aminopyridine units (tapa, three amino groups; bapa, two amino groups; mapa, one amino group) have been synthesized, and their copper(II) complexes with a small molecule such as dioxygen and azide have been studied spectroscopically and structurally. The reaction of their Cu(II) complexes with NaN(3) have given the mononuclear copper complexes with azide in an end-on mode, [Cu(tapa)(N(3))]ClO(4) (1a), [Cu(bapa)(N(3))]ClO(4) (2a), [Cu(mapa)(N(3))]ClO(4) (3a), and [Cu(tpa)(N(3))]ClO(4) (4a) (tpa, no amino group). The crystal structures have revealed that the coordination geometries around the metal centers are almost a trigonal-bipyramidal rather than a square-planar except for 1a with an intermediate between them. The UV-vis and ESR spectral data indicate that the increase of NH(2) groups of ligands causes the structural change from trigonal-bipyramidal to square-pyramidal geometry, which is regulated by a combination of steric repulsion and hydrogen bond. The steric repulsion of amino groups with the azide nitrogen gives rise to elongation of the Cu-N(py) bonds, which leads to the positive shift of the redox potentials of the complexes. The hydrogen bonds between the coordinated azide and amino nitrogens (2.84-3.05 A) contribute clearly to the fixation of azide. The Cu(I) complexes with bapa and mapa ligands have been obtained as a precipitate, although that with tapa was not isolated. The reactions of the Cu(I) complexes with dioxygen in MeOH at -75 degrees C have given the trans-micro-1,2 peroxo dinuclear Cu(II) complexes formulated as [((tapa)Cu)(2)(O(2))](2+) (1c), [((bapa)Cu)(2)(O(2))](2+) (2c), and [((mapa)Cu)(2)(O(2))](2+) (3c), whose characterizations were confirmed by UV-vis, ESR, and resonance Raman spectroscopies. UV-vis spectra of 1c, 2c, and 3c exhibited intense bands assignable to pi(O(2)(2)(-))-to-d(Cu) charge transfer (CT) transitions at lambda(max)/nm (epsilon/M(-1)cm(-1)) = 449 (4620), 474 (6860), and 500 (9680), respectively. The series of the peroxo adducts generated was ESR silent. The resonance Raman spectra exhibited the enhanced features assignable to two stretching vibrations nu((16)O-(16)O/(18)O-(18)O)/cm(-1) and nu(Cu-(16)O/Cu-(18)O)/cm(-1) at 853/807 (1c), 858/812 (2c), 847/800 (3c), and at 547/522 (2c), 544/518 (3c), respectively. The thermal stability of the peroxo-copper species has increased with increase in the number of the hydrogen-bonding interactions between the peroxide and amino groups.     

Pentacoordinated Cu(II)/Zn(II) complexes bearing macrocyclic skeleton: synthesis, spectroscopic and molecular structure optimization studies

2,6-Diacetylpyridine and 1,2-diaminoethane in the presence of copper(II) and zinc(II) chlorides containing a few drops of acetic acid were condensed into compositions [CuLH2]2.2HCl.H2O (1), [Cu2LPyz]2.2HCl.4CH3COCH3 (2) [CuZnLPyz]2.2HCl.2CH3COCH3.10H2O (3) and [ZnL'Cl]3.3HCl.3H2O (4) substantiated by elemental analyses, IR, UV-vis, 1H NMR and FAB mass spectral data. Demetallation of a Ni(II) complex (isolated as above) afforded macrocyclic skeleton LH4, whereas L' symbolizes a skeleton of the ligand containing only ethylenediamine and 2,6-diacetylpyridine. Molecular structure optimization using MM2 force field calculations for the complexes revealed distorted square pyramidal geometry around Cu(II) centers in complexes 1 and 2 and tetrahedral geometry around Cu(II) and Zn(II) centers with different degrees of distortion in complex 3 whereas three Zn(II) atoms (each in distorted square pyramidal geometry) attached via Cl bridges form a cyclic structure in complex 4. In complexes 1 and 2,Cu-Cu = 2.63-2.66 angstroms indicated the possibility of coupling between the two Cu(II) centers which has been supported by lower magnetic moment as well as ESR spectra showing half-field signal.     

Physical parameters and electron-transfer kinetics of the copper(II/I) complex with the macrocyclic sexadentate ligand [18]aneS6

The electron-transfer kinetics of the complex formed by copper(II/I) with the sexadentate macrocyclic ligand 1,4,7,10,13,16-hexathiacyclooctadecane ([18]aneS6) have been measured in acetonitrile with a series of three oxidizing agents and three reducing agents. These studies have been supplemented by determinations of the redox potential and the stability constants of the Cu(I)- and Cu(II)([18]aneS6) complexes in both acetonitrile and aqueous solution. The Marcus cross relationship has been applied to the cross-reaction rate constants for the six reactions studied to resolve the electron self-exchange rate constant for the Cu(II/I)([18]aneS6) complex. An average value of k11 = 3 x 10(3) M(-1) s(-1) was obtained at 25 degrees C, mu = 0.10 M in acetonitrile. This value is approximately 2 orders of magnitude smaller than the values reported previously for the corresponding Cu(II/I) complexes with the quadridentate and quinquedentate homoleptic homologues having all ethylene bridges, namely, 1,4,7,10-tetrathiacyclododecane ([12]aneS4) and 1,4,7,10,13-pentathiacyclopentadecane ([15]aneS5). This significant difference in reactivity is attributed to the greater rearrangement in the geometry of the inner-coordination sphere that accompanies electron transfer in the Cu(II/I)([18]aneS6) system, wherein two Cu-S bonds are ruptured upon reduction. In contrast to other Cu(II/I) complexes with macrocyclic polythiaethers that have self-exchange rate constants within the same range, no evidence for conformationally gated electron transfer was observed, even in the case of the most rapid oxidation reaction studied.