Neutral Copper Research Articles

Efficient Atom-Transfer Radical Polymerization of Methacrylates Catalyzed by Neutral Copper Complexes

Copper homoscorpionate complexes TpxCu(I)(NCMe) efficiently catalyze the Atom Transfer Radical Polymerization (ATRP) of methacrylate (MMA) and other methacrylates at 50 °C in the absence of any reducing agents. Plots of Mn vs monomer conversion are linear with low molecular weight distributions (Mw/Mn = 1.09) being obtained. The effects induced by the Tpx ligand, the nature of the methacrylate substrate, the initiator and the temperature have been studied.

Self-assembly of neutral hexanuclear circular copper(ii) meso-helicates: topological control by sulfate ions

Bis-pyridylimine ligands with different linking elements are capable of forming unique hexanuclear circular Cu(II) meso-helicates; the self-assembly is controlled by coordination of sulfate ions to the metal centres.

Bis[bis(methoxycarbimido)aminato]copper(II) 1-methylpyrrolidin-2-one disolvate

The title compound, [Cu(C(4)H(8)N(3)O(2))(2)].2C(5)H(9)NO, consists of a neutral copper complex, in which the Cu(II) centre coordinates to two bis(methoxycarbimido)aminate ligands, solvated by two molecules of 1-methylpyrrolidin-2-one. The complex is planar and centrosymmetric, with the Cu(II) centre occupying a crystallographic inversion centre and adopting approximately square-planar geometry. N-H...O hydrogen-bonding interactions exist between the amine NH groups of the ligands and the O atoms of the 1-methylpyrrolidin-2-one molecules. The associated units pack to form sheets.

Synthesis, crystal structure, antibacterial activities, and DNA-binding studies of a new μ-oxamido-bridged binuclear copper(II) complex

A new μ-oxamido-bridged dicopper(II) complex, Cu2(heap)(NO3)2 (1), where heap is the dianion of N,N′-bis(N-hydroxyethylaminopropyl)oxamide, has been synthesized and characterized by elemental analysis, molar conductivity, IR and electronic spectral studies, and X-ray single-crystal diffraction. The complex consists of a neutral centro-symmetric binuclear copper(II) unit with an inversion center at the midpoint of the Cl−Cli bond. The copper(II) has square-pyramidal coordination geometry and the bridging heap adopts a bis-tetradentate conformation. The binuclear units are linked into a 3-D framework by N−H ··· O, O−H ··· O, and C−H ··· O hydrogen bonds. Due to weak coordination between copper(II) and nitrate, the neutral dicopper(II) units are present as binuclear cations and nitrate anions in solution. Antibacterial assays indicate that the complex shows better activity than the ligand. Interactions of the complex with herring sperm DNA (HS-DNA) have been investigated by using cyclic voltammetry, UV absorption titrations, ethidium bromide fluorescence displacement experiments, and viscometry measurements. The results suggest that the binuclear copper(II) complex interacts with HS-DNA by electrostatic interaction with intrinsic binding constant of 3.33 × 104 M−1.

Evaluation of exchange‐correlation functionals for time‐dependent density functional theory calculations on metal complexes

The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) < 3.5% and epsilon(SF) values close to unity (>0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes.

Laser-microwave spectroscopy of Cu I atoms in S, P, D, F and G Rydberg states

Energy-level positions of neutral copper atoms in S, P, D, F and G Rydberg series for principal quantum number n = 23–38 have been determined with sub-MHz accuracy by means of laser-microwave spectroscopy in the 73–321 GHz frequency range. Quantum defects of L = 0–4 levels and fine-structure splittings of P, D, F and G levels have been found from a global analysis of the measured frequencies of 79 single- and two-photon resonance transitions. Hyperfine multiplets were observable in several cases below n = 30 whose splitting frequencies are consistent with n−3 scaling from low-lying levels. An improved value of the Cu I ionization potential 62 317.46 ± 0.03 cm−1 has been obtained.

Thermodynamic and Structural Investigations on the Complexation Process of Dioxo Macrocyclic Ligands: Towards Neutral Copper Complexes at Physiological pH

AbstractTwo dioxotetraza macrocycles 9,12,16,19‐tetraazatricyclo[19.4.0.02,7]pentacosa‐1(21),2,4,6,22,24‐hexaene‐8,20‐dione(L1) and 9,13,16,20‐tetraazatricyclo[20.4.0.02,7]hexacosa‐1(22),2,4,6,23,25‐hexaene‐8,21‐dione (L2) and two bis(dioxotetraaza) macrocycles 7,10,14,17,25,28,32,35‐octaazatetracyclo[17.17.2.05,37.023,38]octatriaconta‐1,3,5(37),19,21,23(38)‐hexaene‐6,18,24,36‐tetrone (L3) and 7,11,14,18,26,30,33,37‐octaazatetracyclo[18.18.2.05,39.024,40]tetraconta‐1,3,5(39),20,22,24(40)‐hexaene‐6,19,25,38‐tetrone (L4) were prepared. Their protonation constants and the overall complexation constants of their copper(II) complexes were determined by potentiometry at 25 °C (I = 1, KNO3). In aqueous solution, the complexation sequence was elucidated for each ligand by means of UV/Vis and EPR spectroscopy. According to the ligand structure, two complexation mechanisms can be characterized. For ligand L1, a neutral complex [CuL1H–2] is readily obtained in one step at pH ≈ 5, and it is the sole species above pH 7. Its structure was confirmed by X‐ray analysis. For ligands L2 and L4, the neutral complexes [CuL2H–2] and [Cu2L4H–4] were formed by successive deprotonation of [CuL2]2+ and [Cu2L4]4+, respectively.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

RF‐Ionised Physical Vapour Deposition for Cu Thin Films: Deposition on Polymer Substrate

AbstractIonised physical vapour deposition (IPVD), performed with a magnetron and a one‐loop radio frequency (RF) coil, was used to deposit copper thin films on polymer substrates in order to cover complex shapes. This process allows improving the films conformity and their resistivity by ionising the sputtered vapour. The coil coupling was adapted in order to optimise the process. The film resistivity is influenced by the RF power and the pressure. A substrate cleaning phase, required to obtain good film adhesion, was done using the RF coil. The influence of treatment parameters (pressure, RF power, duration) was studied on the adhesion. Optical emission and absorption spectroscopy were performed to identify and quantify neutral and ionic copper species in the plasma and furthermore to study the influence of the coil on the vapour properties.

LINEAR POLARIZATION OF FLASH SPECTRUM OBSERVED FROM A TOTAL SOLAR ECLIPSE IN 2008

We measured linear polarization signals of the flash spectrum ranging from 502.5 nm to 528.5 nm after second contact of a total solar eclipse which occurred on 2008 August 1 in China. A large group of spectral lines (especially those lines produced by neutral iron, neutral copper, and as carbon molecules) are found with very high polarization degrees relative to the continuum polarization, and the linear polarization spectrum is more abundantly structured than the flash spectrum itself. According to the observational result, we conclude that coherent scattering and scattering geometry as well as other mechanisms may together play a very important role in producing the high polarization amplitudes. This will help us deepen our understanding of the physical conditions of the solar upper atmospheres and the physical processes occurring there.

Growth Mechanism and Chemical Bonding in Scandium‐Doped Copper Clusters: Experimental and Theoretical Study in Concert

Size matters! The electronic structure and size-dependent stability of neutral and cationic scandium-doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank-Kasper-shaped Cu(16)Sc(+) cluster (shown here), which could be the germ of a new crystallization process.Electronic structure and size-dependent stability of scandium-doped copper cluster cations, Cu(n)Sc(+), were investigated by using a dual-target dual-laser vaporization production scheme followed by mass spectrometric studies and also quantum chemical computations in the density functional theory framework. The neutral species also were studied by using computational methods. Enhanced abundances and dissociation energies were measured in the case of Cu(n)Sc(+) for n=4, 6, 8, 10 and 16, the last of these identified as being extraordinary stable. Neutral clusters are stable with n=5, 7, 9 and 15, which are isoelectronic with respect to the number of the valence s electrons with the stable cationic clusters; hence a simple electron count determines cluster properties to a great extent. The Cu(17)Sc cluster was found to be a superatomic molecule, containing Cu(16)Sc(+) and Cu(-) units; however, the charge separation is not as pronounced as in the case of CuLi. Cu(15)Sc was found to be a stable cluster with a large dissociation energy and a closed electronic structure; hence this can be regarded as a superatom, analogous to the noble gases. The main factors determining the growth patterns of these clusters are the central position of the scandium atom and the successive filling of the shell orbitals. For smaller clusters, the reaction paths appear to diverge yielding various products; however all paths ultimately lead to the most stable Frank-Kasper shaped Cu(16)Sc cluster, which in turn can be the germ of the crystallization process.

Synthesis, characterization, toxicity, cytogenetic and in vivo antitumor studies of 1,1-dithiolate Cu(II) complexes with di-, tri-, tetra- amines and 1,3-thiazoles. Structure–activity correlation

A series of new mixed-ligand neutral copper(II) complexes of the general type [Cu(amine)(i-MNT)] and [Cu(tz)(i-MNT)] was prepared and characterized by elemental, spectroscopic methods, μ eff, Λ μ measurements and molecular modeling studies. The acute toxicity, the cytogenetic and the in vivo antitumor activity of the new complexes, is related to their chemical and physicochemical properties. Among the Cu(II) compounds tested the complex with 2-amino-5-methyl thiazole increases significantly the life span of leukemia P388 bearing mice in vivo.

A new two-dimensional polymeric copper(II) complex bridged both by oxamidate and azide groups: synthesis, structure and DNA binding properties

A new two-dimensional polymeric copper(II) complex, [Cu2(heae)(N3)2] n , where heae stands for the dianion of N,N′-bis(N-hydroxyethylaminoethyl)oxamide, has been synthesized and characterized by elemental analysis, molar conductivity measurement, IR, electronic spectral studies and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system, P21/c space group with crystallographic data: a = 9.1588(18) Å, b = 6.6238(13) Å, c = 14.602(3) Å and Z = 2. The X-ray analysis reveals a two-dimensional copper(II) polymeric coordination network constructed by bis-tridentate chelated [Cu(trans-heae)Cu]2+ building blocks and end-on azido ligands. The environment around the copper(II) atom can be described as a square-based pyramid. The azido bridge is very asymmetric with one Cu–N bond distance short and the other long. The Cu ··· Cu separations through μ-trans-oxamidate and μ-azido bridges are 5.2996(13) Å and 4.2464(7) Å, respectively. The copper(II) complex is a polymer in the solid state, whereas in solution it exists as discrete neutral binuclear copper(II) species. Coordination mode of the azide in solution is proved by electronic spectra. The DNA-binding properties of the binuclear copper(II) species were investigated by emission spectral and electrochemical techniques, indicating the binuclear copper(II) complex binds to HS-DNA via a groove mode.

Photofragmentation Pathways and Photodeposition of Nanoparticles from a Gas Phase Copper-Containing Precursor

Pulsed laser excitation of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (Cu(TMHD)(2)) in the gas phase produced neutral gaseous copper atoms and nanoparticulate copper deposits on substrates. Copper atoms were formed by the complete dissociation of the ligands from the metal. Time of flight mass spectrometry and resonance enhanced multiphoton ionization spectroscopy were used to study the details of this reaction and led to the discovery of other gaseous fragments that were produced by incomplete fragmentation of the ligands including monoligated species and coordinated ligand fragments. Laser-assisted chemical vapor deposition resulted in monodispersed nanoparticles under 100 nm in diameter. X-ray photoelectron spectroscopy and energy dispersive analysis of X-rays were used to determine the elemental composition of the deposit. The relationships between the photofragmentation pathways and the deposited particles are discussed.

Di-μ-chlorido-bis[chlorido(1,4,6-trimethyl-6-nitro-1,4-diazepine)copper(II)

The title neutral copper complex, [Cu2Cl4(C8H17N3O2)2], shows a binuclear center with a Cu—(μ-Cl)2—Cu core, in which each copper ion is coordinated by the N,N,O donor atoms of the tridentate ligand 1,4,6-trimethyl-6-nitro-1,4-diazepine (meaaz-NO2) and three chloride exogenous ligands. Each metal ion is facially coordinated by meaaz-NO2 through N,N,O donor atoms, whereas two bridging and one terminal chloride ions occupy the other face of the highly Jahn–Teller-distorted octa­hedron. Two N atoms from tertiary amine groups of the meaaz-NO2 ligand and two exogenous Cl atoms with short Cu—N and Cu—Cl distances define the equatorial plane. The coordination around each CuII ion is completed by another Cl atom and an O atom from the NO2 group, in the axial positions. The binuclear complex exhibits a centrosymmetric structure with point symmetry .

Reversible substrate binding at copper centers in neutral copper(i) carbene complexes derived from bis(3-tert-butylimidazole-2-ylidene)methane

Deprotonation of the CH2-bridged bis-imidazolium salt [H2(BIM(tBu))]Br2 followed by reaction with CuBr afforded polymeric [(BIM(tBu))2(CuBr)2]n (3), where BIM(tBu) = bis(3-tert-butylimidazole-2-ylidene)methane. In the solid state, compound 3 is an organometallic polymer with an unusual (-L-Cu-(micro-Br)2-Cu-L-)n type of bonding. The reaction of 3 with nitrogen bases N-tert-butylimidazole or piperidine splits the polymer and afforded the corresponding mononuclear amine adducts [(BIM(tBu))2(CuBr)2(amine)] (6 and 7, respectively). Their molecular structures revealed a unique bonding pattern, which has no precedents in copper-NHC coordination chemistry. The amine binding energies in 6 or 7 of 0.7-7.7 kcal mol(-1), calculated by DFT methods, are consistent with an experimentally observed ligand exchange in solution, fast on the NMR time scale.

Neutral Nickel(II) and Copper(II) Tetraazamacrocyclic Complexes as Molecular Rods Attached to Gold Electrodes

New dithiolated derivatives of neutral Cu(II) and Ni(II) tetraazamacrocyclic complexes have been synthesized and characterized by spectroscopic and diffractional methods. These rod-shaped molecules were assembled in monocomponent and mixed monolayers on gold electrodes. In the mixed monolayers, the active molecules were embedded in a hexanethiol matrix. The dithiolated complexes are oriented perpendicularly to the electrode, and reveal faster kinetics of electron transfer than those assembled in a single-component monolayer. They appear as protrusions, which are easily addressed by using the STM method. In the presence of a suitable electron acceptor in the solution, the donor properties of the anchored Cu complex were weakened, which revealed donor-acceptor interactions with the monolayer. The peak position in the voltammogram indicates a stronger interaction of the solution-based acceptor with the reduced Cu(II) form than with the Cu(III) complex. This suggests the possibility of switching the association on or off by applying an appropriate potential.

Synthesis, Molecular Structures, and Reactivity of Mono- and Binuclear Neutral Copper(I) Carbenes

Mononuclear, neutral copper(I) carbenes [Bu(t)(2)P(NSiMe(3))(2)-kappa(2)N]Cu=CPh(2) and [Bu(t)(2)P(NSiMe(3))(2)-kappa(2)N]Cu=C(p-NO(2)C(6)H(4))(2) (4a,b) as well as the binuclear mu-carbene copper complex {[Bu(t)(2)P(NSiMe(3))(2)-kappa(2)N]Cu}(2)(mu-CPh(2)) (5) have been synthesized. The solid-state structures of 4b and 5 are reported. Carbene 4b is active in cyclopropanation of styrene. Reaction of 4b with (p-MeC(6)H(4))C=N(2) afforded [Bu(t)(2)P(NSiMe(3))(2)-kappa(2)N]Cu=C(p-MeC(6)H(4))(2), the corresponding mixed azine Ar(2)C=N-N=CAr'(2) and the carbene dimer Ar(2)C=CAr'(2), demonstrating an important pathway for carbene loss in cyclopropanation of olefins via reaction of the copper(I) carbene with nucleophilic diazo compounds. Complex 5 reacted with C(2)H(4) or styrene to give 1:1 mixtures of the terminal carbene 4a and of the corresponding copper(I) olefin complexes, proving unambiguously that binuclear complexes like 5 are not relevant for copper-catalyzed cyclopropanation of olefins with diazo compounds. The electronic structure of 4b was investigated by means of DFT calculations.

A new hybrid material constructed from octamolybdate anion and neutral dinuclear copper units

A new organic–inorganic hybrid material constructed from octamolybdate anion and neutral dinuclear copper(I) units, H4{[Cu2(ophen)2]2[Mo8O26]}[Cu2(ophen)2] · H2O (1) (Hophen =2-hydroxy-1,10-phenanthroline), has been prepared under hydrothermal condition and characterized by elemental analysis, IR, XPS, TGA and single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P 1, with a = 9.9091(8), b = 13.3981(8), c = 14.8266(10) Å, α = 84.6310(10), β = 83.0620(10)°, γ = 77.7800(10), V = 1905.0(2) Å3, Z = 1. Compound 1 contains a centrosymmetric polyoxoanion {[Cu2(ophen)2]2[Mo8O26]}4−, in which the β-[Mo8O26]4− is bisupported by two copper(I) coordination groups through the terminal oxygen atoms. The discrete molecules of 1 are extended into a 3-D supramolecular array through C–H ··· O hydrogen bonds and strong aromatic π–π stacking contacts.

Di-μ-chlorido-bis({2-[1-(2-pyridylethylimino)ethyl]pyrrolato-κ3N,N′,N′′}copper(II))

The title compound, [Cu(2)(C(13)H(14)N(3))(2)Cl(2)], is a neutral dimeric copper(II) complex. The two Cu(II) atoms are asymmetrically bridged by two chloride ions. Each Cu(II) atom is also bound to the three N atoms of a deprotonated tridentate Schiff base ligand, giving a distorted square-pyramidal N(3)Cl(2) coordination environment overall. The dinuclear complex lies across an inversion centre in the space group P1. This work demonstrates the effect of ligand flexibility and steric constraints on the structures of copper(II) complexes.

Synthesis, Structure and DNA Binding Properties of [Cu2(heae)(SCN)2] n · nH2O the First One-Dimensional Polymeric Copper(II) Complex Bridged Alternately by Oxamidate and Double End-to-End Thiocyanate Ligands

A new one-dimensional polymeric copper(II) complex, [Cu2(heae)(SCN)2] n · nH2O [H2heae is N,N′-bis(N-hydroxyethylaminoethyl)oxamide], has been synthesized and characterized by elemental analysis, molar conductivity measurement, IR and electronic spectra studies, and single-crystal X-ray diffraction. The structure of the complex exhibits a neutral one-dimensional polymeric copper(II) zigzag chain [Cu2(heae)(SCN)2] n constructed by μ-trans-heae and double μ-1,3-thiocyanate ligands. The environment about copper can be described as a square-pyramid. The neighboring second building units (SBUs), [Cu(trans-heae)Cu]2+, are unequal with Cu···Cu separations of 5.287 and 5.273 A for Cu1···Cu1i and Cu2···Cu2ii, respectively. The double thiocyanate ligands function as μ(1,3)-bridges to link these unequal SBUs thereby forming zigzag chains with a Cu1···Cu2 separation of 5.454 A. The hydrogen bonds in the crystal structure self-assemble the one-dimensional chains into a three-dimensional supramolecular structure. The interaction of the polymeric copper(II) complex with herring sperm DNA (HS-DNA) has been investigated by using absorption and emission spectra, electrochemical techniques and viscometry. The results reveal that the polymeric copper(II) complex interacts with HS-DNA via a groove binding mode with the intrinsic binding constant of 1.38 × 104 M−1. To the best of our knowledge, this is the first example about the structure and DNA-bonding studies of a one-dimensional polymeric copper(II) complex that is bridged alternately by trans-oxamidate and double-thiocyanate ligands.