Dimeric CuII Research Articles

Crystal structures, electron spin resonance, and thermogravimetric analysis of three mixed-valence copper cyanide polymers.

The crystal structures of three mixed-valence copper cyanide alkanolamine polymers are presented, together with thermogravimetric analysis (TGA) and electron spin resonance (ESR) data. In all three structures, a CuII moiety on a crystallographic center of symmetry is coordinated by two alkanolamines and links two CuICN chains via cyanide bridging groups to form diperiodic sheets. The sheets are linked together by cuprophilic CuI-CuI interactions to form a three-dimensional network. In poly[bis(μ-3-aminopropanolato)tetra-μ-cyanido-dicopper(I)dicopper(II)], [Cu4(CN)4(C3H8NO)2]n, 1, propanolamine bases have lost their hydroxyl H atoms and coordinate as chelates to two CuII atoms to form a dimeric CuII moiety bridged by the O atoms of the bases with CuII atoms in square-planar coordination. The ESR spectrum is very broad, indicating exchange between the two CuII centers. In poly[bis(2-aminopropanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(C3H9NO)2]n, 2, and poly[bis(2-aminoethanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(CH7NO)2]n, 3, a single CuII atom links the CuICN chains together via CN bridges. The chelating alkanolamines are not ionized, and the OH groups form rather long bonds in the axial positions of the octahedrally coordinated CuII atoms. The coordination geometries of CuII in 2 and 3 are almost identical, except that the Cu-O distances are longer in 2 than in 3, which may explain their somewhat different ESR spectra. Thermal decomposition in 2 and 3, but not in 1, begins with the loss of HCN(g), and this can be correlated with the presence of OH protons on the ligands in 2 and 3, which are not present in 1.

A redox model for NO oxidation, NH3 oxidation and high temperature standard SCR over Cu-SSZ-13

A kinetic model is developed to predict the influence of temperature and hydrothermal aging on the redox of active Cu sites under standard SCR, NO oxidation and NH3 oxidation conditions over a practically relevant fully-formulated Cu-SSZ-13 catalyst. NO2/N2 production during NO/NH3 titration of CuII sites is utilized to identify rate parameters associated with NO-only RHC (reduction half cycle) and NH3-only RHC respectively. Integral N2 formation during subsequent NO + NH3 titration is consistent with the production of one NO2 per two CuII sites reduced during NO-only RHC and one N2 per six CuII sites reduced during NH3-only RHC. Decreased reduction of CuII sites by NO/NH3 upon hydrothermal aging, along with the production of one NO2 per two CuII sites during NO-only RHC, is accordant with the involvement of proximal ZCuOH and oxygen-bridged dimeric CuII sites. Oxidation of partially solvated and framework coordinated ZCu (CuI) sites occurs in presence of O2, does not produce N2 and can lead to the consumption of Brønsted acid sites. A global OHC kinetic model is developed to predict transient and integral N2 formation during exposure of CuI sites to a mixture of NO and O2. The resulting redox kinetic model quantitatively predicts NO and NH3 consumption during isothermal transient response Cu redox (TRCR) protocols, along with temperature and age dependent steady-state standard SCR and oxidation conditions. The redox model presented in this work synthesizes recent kinetic, spectroscopic and computational findings to provide a foundational description of active site redox during standard SCR, NO oxidation and NH3 oxidation over Cu-SSZ-13.

In Situ Reactivity of Electrochemically Generated Nitro Radical Anion on Tinidazole and Its Monomeric and Dimeric CuII Complexes on Model Biological Targets with Relative Manifestation of Preventing Bacterial Biofilm Formation.

Formation of nitro radical anion (−NO2•–) and other reduction products of 5-nitroimidazoles, although important for antimicrobial activity, makes the drugs neurotoxic. Hence, an appropriate generation and their role in the free radical pathway needs proper realization. This was attempted by studying the action of tinidazole and its CuII complexes on model targets (nucleic acid bases and calf thymus DNA). Results obtained were correlated with studies on biological species where prevention of biofilm formation on Staphylococcus aureus and Pseudomonas aeruginosa was followed. Tinidazole and its CuII complexes subjected to electrochemical reduction in aqueous solution, under de-aerated conditions, interact with model nucleic acid bases and calf thymus DNA. These model targets were followed to realize what happens when such compounds undergo enzymatic reduction within cells of microorganisms that they eventually kill. Studies reveal that CuII complexes were better in modifying nucleic acid bases and calf thymus DNA than tinidazole; damage caused to nucleic acid bases was correlated with that caused to DNA, indicating that compounds affect DNA rich in thymine and adenine. Minimum bactericidal concentrations on sessile S. aureus and P. aeruginosa for the monomeric CuII complex were 12.5 and 20.25 μM respectively, while those for the dimeric complex were 40.0 and 45.0 μM, respectively. Biofilm formation by P. aeruginosa and S. aureus and viability count of sessile cells were also determined. CuII complexes of tinidazole brought about substantial reduction in carbohydrate and protein content in S. aureus and P. aeruginosa. Downregulation of quorum sensing signaling mechanism viz. reduced production of pyocyanin and elastase during biofilm formation was also detected. CuII complexes showed much higher tendency to prevent biofilm formation than tinidazole, almost comparable to amoxicillin, an established drug in this regard.

Anionic Bisoxazoline Ligands Enable Copper-Catalyzed Asymmetric Radical Azidation of Acrylamides.

Asymmetric radical azidation for the synthesis of chiral alkylazides remains a tremendous challenge in organic synthesis. We report here an unprecedented highly enantioselective radical azidation of acrylamides catalyzed by 1 mol % of a copper catalyst. The substrates were converted to the corresponding alkylazides in high yield with good-to-excellent enantioselectivity. Notably, employing an anionic cyano-bisoxazoline (CN-Box) ligand is crucial to generate a monomeric CuII azide species, rather than a dimeric CuII azide intermediate, for this highly enantioselective radical azidation.

Anionic Bisoxazoline Ligands Enable Copper‐Catalyzed Asymmetric Radical Azidation of Acrylamides

AbstractAsymmetric radical azidation for the synthesis of chiral alkylazides remains a tremendous challenge in organic synthesis. We report here an unprecedented highly enantioselective radical azidation of acrylamides catalyzed by 1 mol % of a copper catalyst. The substrates were converted to the corresponding alkylazides in high yield with good‐to‐excellent enantioselectivity. Notably, employing an anionic cyano‐bisoxazoline (CN‐Box) ligand is crucial to generate a monomeric CuII azide species, rather than a dimeric CuII azide intermediate, for this highly enantioselective radical azidation.

Identifying Cu-oxo species in Cu-zeolites by XAS: A theoretical survey by DFT-assisted XANES simulation and EXAFS wavelet transform

Abstract Cu-exchanged zeolites are attracting increasing attention as platforms for high-impact selective redox chemistry, including NH3-mediated selective catalytic reduction of harmful nitrogen oxides (NH3-SCR) and selective oxidation of methane to methanol (MTM). X-ray absorption spectroscopy (XAS) today represents a well-established and widespread technique for the characterization of these systems, but open challenges remain to accurately determine nuclearity and chemical identity of Cu-oxo species stabilized under high-temperature oxidative conditions. To systematically assess limitations and potential of XAS in this context, here we consistently explored by DFT a set of monomeric and dimeric CuII species incorporated in the chabazite (CHA) and mordenite (MOR) frameworks, envisaged as key players for both NH3-SCR and MTM. We present a combined DFT-assisted analysis based on both full-potential XANES simulation and Wavelet Transform Analysis (WTA) applied to computed EXAFS signals. The resulting theoretical insights set the bases for an easier and more robust interpretation of the XAS data collected on Cu-zeolite systems. In particular, we evidenced possible fingerprint features in the XANES region, together with the difficulties in discriminating among monomeric and dimeric CuII moieties solely based on their XANES signatures. We then show the potential of Wavelet Transform Analysis as a new tool in the identification and visualization of EXAFS atomic contributions, to possibly enhance the EXAFS sensitivity to the nuclearity of Cu-oxo species in Cu-zeolites.

Joining of trinuclear (CuL)2M (M = MnII and CdII) nodes by 1,3- and 1,4-benzenedicarboxylate linkers: positional isomeric effect on co-crystallization

Among the four one-dimensional coordination polymers obtained by joining (CuL)2M (M = MnII and CdII) nodes with 1,3- and 1,4-benzenedicarboxylate linkers, the chains derived from 1,3-benzenedicarboxylate are co-crystallized with dimeric CuII units.

Effects of the substituents of pyrazole/thiazine ligands on the magnetic properties of chloro-bridged Cu(ii) complexes

The structures and magnetic properties of monomeric and chloro-bridged dimeric CuII complexes can be modulated by steric hindrance.

Synthesis, structure, and magnetic properties of two dimer paddle-wheel CuII toluate complexes with nitronyl nitroxide radicals

Two new paddle-wheel dimeric copper complexes, [Cu2(4-MePhCOO)4(NITmPy)2] (1) and [Cu2(3-MePhCOO)4(NITmPy)2] (2) (NITmPy = 2-(3-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro1H-imidazolyl-1-oxyl-3-oxide), were synthesized by reaction of copper toluate and NITmPy. Single crystal X-ray analyses revealed that both complexes are symmetrical dimers. Cu with four deprotonated methyl-benzoate bridging ligands form a paddle-wheel core and pyridyl nitrogen of radical ligands at the apical position. Based on the Cu–Cu axis of 1 and 2, we exploited the steric constraints of the methyl groups and induced the paddle-wheel. Two magnetic exchange pathways with strong antiferromagnetic interaction between dimeric CuII ions and weak antiferromagnetic interaction between NITmPy ligands exist in the complexes. IR and powder X-ray diffraction of the complexes were also studied.

Spin transport and magnetic properties of a copper(II) coordination organometallic molecule

We study the effects of the characteristics of electrodes and electrode-molecule contacts on the spin-polarized transport properties of a dimeric CuII magnetic single-molecule [Cu2(L1)(hfac)2]·3CH3CN·H2O by density-functional theory (DFT) combined with the Keldysh nonequilibrium Green's-function (NEGF) formalism. It is found that the I–V curve shows negative differential resistance behavior due to the shifting of electrode band structure and the asymmetric coupling between the molecule and the electrodes under bias. In addition, the device presents integrated spintronic functionalities such as switch, spin valve and spin filter, associated with perfect negative magnetoresistance.

An organic–inorganic hybrid 1-D double-chain copper–yttrium heterometallic silicotungstate [Cu(dap)2(H2O)]2{Cu(dap)2[α-H2SiW11O39Y(H2O)2]2}·10H2O

An organic–inorganic hybrid 1-D double-chain CuII–YIII heterometallic silicotungstate [Cu(dap)2(H2O)]2 {Cu(dap)2[α-H2SiW11O39Y(H2O)2]2}·10H2O (1) has been synthesized by reaction of Na10[A-α-SiW9O34]·18H2O, CuCl2·2H2O, YCl3 and dap (dap = 1,2-diaminopropane) under hydrothermal conditions and characterized by elemental analyses, IR spectrum, UV spectrum and single-crystal X-ray diffraction. 1 exhibits a novel 1-D double-chain structure constructed from dimeric CuII–YIII heterometallic silicotungstate units. To our knowledge, 1 is the first organic–inorganic hybrid 1-D double-chain CuII–YIII heterometallic polyoxometalate. Thermogravimetry-differential thermal analysis of 1 has been measured from 25 to 750 °C and the thermogravimetric curve indicates two steps of weight loss.

Synthesis, Structure, Magnetic Properties and Aqueous Optical Citrate Detection of Chiral Dinuclear CuII Complexes

AbstractTwo chiral dimeric CuII Schiff base complexes, Na2[Cu(S‐lys)2·(H2O)2]·(ClO4)2 (1) and [Cu(S‐ornH)2·(H2O)2]·(ClO4)2 (2) have been prepared by an easy one‐pot method in which the L‐lysine and L‐ornithine‐based Schiff base ligands are generated in situ. These complexes have been characterized by various spectroscopic techniques and single‐crystal X‐ray diffraction. The molecular structures show that both complexes are indeed dimeric with CuII centers that are phenolate‐bridged. Variable‐temperature magnetic analysis revealed that a strong antiferromagnetic coupling interaction was mediated through the phenolate bridge between the two CuII centers. Since these compounds were highly soluble in water, we explored carboxylate sensing capability through colorimetric indicator displacement assays (IDAs). By using pyrocatechol violet (PV) as a displaceable colorimetric indicator, citrate ion selectivity was demonstrated in 100 % water solution in the physiological pH range.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Bis{μ-(E)-5-methoxy-2-[1-(3-oxidopropylideneamino)ethyl]phenolato}copper(II)

The title dimeric CuII complex, [Cu2(C12H15NO3)2], is centrosymmetric. Two CuII atoms related by an inversion center are bridged by two O atoms of propanolamine. The CuII atom assumes a distorted square-planar geometry.

The cyclic dimer bis(μ2-4-sulfonatobenzoato)bis[(di-2-pyridylamine)copper(II)] trihydrate

The title complex, [Cu2(C7H4O5S)2(C10H9N3)2]·3H2O, comprises the centrosymmetric cyclic dimeric CuII complex and uncoordinated water mol­ecules. The CuII atom displays a distorted square-pyramidal geometry. Within the cyclic dimer, the Cu⋯Cu separation is 9.5362 (12) Å.

Dinuclear Complexes of MII Thiocyanate (M = Ni and Cu) Containing a Tridentate Schiff‐Base Ligand: Synthesis, Structural Diversity and Magnetic Properties

AbstractA dinuclear NiII complex, [Ni2(L)2(H2O)(NCS)2]·3H2O (1) in which the metal atoms are bridged by one water molecule and two μ2‐phenolate ions, and a thiocyanato‐bridged dimeric CuII complex, [Cu(L)NCS]2 (2) [L = tridentate Schiff‐base ligand, N‐(3‐aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3‐diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single‐crystal X‐ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C2 symmetry in which each NiII atom is in a distorted octahedral environment. The Ni–O distance and the Ni–O–Ni angle, through the bridged water molecule, are 2.240(11) Å and 82.5(5)°, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di‐μ1,3‐NCS ions; each CuII ion is in a square‐pyramidal environment with τ = 0.25. Variable‐temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm–1, whereas complex 2 exhibits weak antiferromagnetic coupling between the CuII centers with J = –1.7 cm–1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Structural diversity in copper(II) complexes of bis(thiosemicarbazone) and bis(semicarbazone) ligands

Two symmetrical bis(carbazone) ligands, H4L1 and H4L2, were prepared by condensation of 4,6-diacetylresorcinol with thiosemicarbazide and semicarbazide, respectively. Their structures were elucidated by elemental analyses and IR, electronic and 1H NMR spectroscopy. Both ligands are tetrabasic and contain two sets of SNO (H4L1) or ONO (H4L2) coordinating sites. Binuclear, trinuclear and dimeric CuII complexes and also adducts with organic bases were prepared. Reactions of H4L1 with several CuII salts, including Cl−, AcO−, , and , in addition to CuI as CuI, afforded different binuclear complexes depending on the salt and the working conditions, except for CuCl2, where a trinuclear complex with a unique mode of bonding was obtained. These complexes reflect the strong coordinating power of Cl−, and AcO− compared to . The mode of bonding and the basicity of the H4L1 ligand are also influenced by the counteranion, the pH of the reaction medium, the working conditions and the oxidation state of copper. The reactivity of the binuclear CuII complexes of both H4L1 and H4L2 towards 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bpy), N,N,N′,N′-tetramethylethylenediamine (Tmen) and 8-hydroxyquinoline (Oxine; Ox) were investigated. Adducts with organic bases were obtained in the mole ratio 2 : 1 : 1 for H4L1 and 2 : 1 : 2 for H4L2 [CuII : ligand : base (base = Phen, Bpy or Ox)], which reflects the difference in size of S and O. With Tmen, dimeric complexes were obtained containing no Tmen molecules instead of the expected adducts for both H4L1 and H4L2. Evidently the presence of Tmen in the reaction mixture enhances the dimerization process. Characterization and structure elucidation of the complexes was achieved by elemental and thermal analyses, electronic, IR, mass and ESR spectroscopy, as well as conductance and magnetic susceptibility measurements. Finally, the antifungal and antibacterial activities of H4L1 and its metal complexes were investigated.

The effect of small ions on transition metal complex configurations. Synthesis, crystal structures and properties of two new copper(II) complexes containing a tripodal ligand

The monomeric CuII complex, [Cu(TLA)C2O4].2O (1), and dimeric CuII complex, [Cu2(TLA)2(C4O4)](ClO4)2(1), where TLA=[tris(6-methyl-2-pyridyl)methyl]amine, have been synthesized and characterized. Both complexes have been obtained as single crystals and their structures were determined by X-ray diffraction analysis. The configuration of (1) is pseudo-octahedral owing to the fact that one of the Cu-Npyridyl bonds is much longer than the others. Two molecules of (1) link via hydrogen bonding to the oxalic oxygen in the unit cell. The copper complex (2) dimer is obtained, using the squarate ion as a bridging ligand, from a monomer copper complex, [Cu(TLA)N3].4ClO4(3). By comparison of the configurations of (1), (2) with that of (3), the copper center is coordinated with TLA first, and then with secondary ligands, such as the azido group, squaric acid, or oxalate ion. The configurations of the transition metal complexes are affected by the smaller ions, as is further discussed below. The variable temperature magnetic susceptibilities of (2) have been studied, and the exchange integral is J=−2.5474 cm-, g=2.061, indicating the existence of a weaker anti-ferromagnetic interaction between the two copper ions in compound (2). The spectral behavior of the title complexes in solution has been studied by u.v.–vis. and i.r. techniques, and the results are discussed.