Dicopper Species Research Articles

High Superoxide Dismutase Activity of a Novel, Intramolecularly Imidazolato-Bridged Asymmetric Dicopper(II) Species. Design, Synthesis, Structure, and Magnetism of Copper(II) Complexes with a Mixed Pyrazole-Imidazole Donor Set.

A new dinucleating ligand, 1,5-bis(1-pyrazolyl)-3-[bis(2-imidazolyl)methyl] azapentane (Hbpzbiap), containing pyrazoles and imidazoles has been designed and synthesized. The synthesis and characterization of the copper complexes with the ligand Hbpzbiap and its dehydronated form are described. This study is aimed at modeling the active site of copper-zinc superoxide dismutase (SOD). Single crystals of the imidazolato-bridged complex [Cu(2)(bpzbiap)Cl(3)] (1) and non-imidazolato-bridged complex [Cu(2)(Hbpzbiap)Cl(4)] (2) were obtained and their structures determined by X-ray diffraction. Both structures show two copper centers in two different coordination environments: a distorted square pyramid and a distorted tetrahedron. The Cu-nitrogen bond lengths range from 1.919(4) to 2.039(3) Å and are as expected. The copper-copper distances from 5.566(1) to 6.104(1) Å being only slightly shorter than that found in bovine erythrocyte SOD. Temperature-dependent magnetic susceptibility study of 1 shows antiferromagnetic behavior with -2J = 96 cm(-)(1). From pH-dependent electron paramagnetic resonance and electronic spectra, [Cu(2)(bpzbiap)Cl(3)] has been demonstrated to be stable over a quite wide pH range including the physiological pH values. A low concentration of this complex (1) catalyzes the dismutation of superoxide at biological pH. Voltammetric studies indicate a quasi-reversible redox behavior in aqueous solution at pH 7. These results clearly indicate that complex 1 is a good model for superoxide dismutase.

Two different types of folding of isomeric macrocycles induced by metal ion co-ordination

The crystal structure of the dicopper(I) complex of a novel 30-membered macrocyclic Schiff-base type ligand with two dithiadiimine co-ordination sites, linked by two meta-substituted benzene rings, has revealed an achiral folding of the macrocycle (‘squeezed ring’), with two tetrahedral co-ordination sites and π-stacked benzene rings. The dicopper(I) compound of the isomeric 32-membered macrocycle with π-stacked para-substituted benzene rings has a chiral double helical (‘twisted ring’) conformation. The co-ordination geometries of the two copper(I) chromophores of both structures are very similar, and this emerges also from the solid-state UV/VIS spectra [metal-to-ligand charge-transfer transitions at 375 and 355 nm for the dicopper(I) species with the 30- and 32-membered macrocycle, respectively]. Proton NMR experiments and UV/VIS spectroscopy indicate that the folded structures are preserved in solution and that the metal-free compounds both have an open cyclic structure.

Synthesis, structure, and redox properties of dicopper(II,II) complexes of N-(2-hydroxyphenyl)salicylamide and homologues. Facile oxidation to dicopper-(II,III) and -(III,III) species; crystal structure of bis(tetrabutylphosphonium) bis{[(2-oxidobenzoyl)(2′-oxidophenyl)amido(3–)-NO2,µ-O2′]cuprate(II)}

Binuclear copper (II) complexes of N-(2- hydroxyphenyl)salicylamide (H3L1) and its homologues with a substituent on the ‘2-hydroxyphenyl’ moiety (5-Me, H3L2; 5-Cl, H3L3; 5-NO2, H3L4) have been obtained as tetrabutylphosphonium salts [PBu4]2[CU2L2]. The structure of [ PBu4]2[Cu2L12] was solved by single-crystal X-ray crystallography, which demonstrated that two copper ions are bridged by the phenolic oxygen of the ‘aminophenol’ moiety with a Cu ⋯ Cu separation of 3.035(2)A. Each copper ion adopts an essentially planar configuration, and the Cu–O and Cu–N bond distances involving the salicylamide moiety are relatively short [1.838(6) and 1.915(6)A respectively]. Cryomagnetic investigations (80–300 K) revealed a significant antiferromagnetic spin exchange though the bridging oxygen, the 2J value (energy separation between the spin singlet and triplet states) being –393.4 to –448.8 cm–1. The cyclic voltammogram of each complex showed two oxidation waves attributable to Cu2II,III–Cu2II,III and Cu2II,III–Cu2III,III processes at significantly low potentials. The dicopper(II,III) species of the L2 complex was generated by electrochemical and chemical (with Br2) oxidation and identified by e.s.r. investigations. The mixed-valence complex in dichloromethane showed an e.s.r. signal with a four-line hyperfine structure (Aav. = 79 ×10–4cm–1) at g= 2.10 at room temperature, indicating that the unpaired electron is localized on one of the copper ions on the e.s.r. time-scale. The mixed-valence complexes each showed an intense absorption in the visible region which is tentatively assigned to the intervalence transitions.

The syntheses and X-ray structure analyses of the heteronuclear monoanions [Os10C(CO)24Cu(NCMe)]? and [Os10C(CO)24Au(PPh3)]? as Their [PPh3Me]+ Salts

The high nuclearity mixed-metal cluster monoanions [Os10C(CO)24Cu(NCMe)]–(1) and [Os10C(CO)24Au(PPh3)]–(2) have been obtained by reaction of the carbido-dianion [Os10C(CO)24]2–(3) with one equivalent of [Cu(NCMe)4][BF4] or Au(PPh3)Cl, respectively, in CH2Cl2. Addition of excess [Cu(NCMe)4][BF4] to either (1) or (3) gives the di-copper species [Os10C(CO)24{Cu(NCMe)}2](4). X-Ray analysis of the [PPh3Me]+ salts of (1) and (2) show that the Cu and Au ligands have added to capping tetrahedra of the dianion (3) in µ3- and µ-bridging positions, respectively. Crystals of [PPh3Me][Os10C(CO)24Cu(NCMe)] are triclinic, space group P, with a= 16.452(3), b= 13.881(3), c= 13.290(3)Å, α= 82.1 2(3), β= 93.23(3), γ= 96.40(3)°, Z= 2; refinement of atomic parameters using 4 325 absorption corrected data converged at R 0.0492. The salt [PPh3Me][Os10C(CO)24Au(PPh3)] also crystallises in the triclinic space group P, with a= 17.296(4), b= 15.403(3), c= 15.191(3)Å, α= 107.31(3), β= 98.28(3), γ= 88.99(3)°, Z= 2; refinement of atomic co-ordinates using 5 314 absorption corrected data gave R 0.0551.

Synthesis, structure and properties of the isomeric dinuclear complexes [(DENC) 2CuX 2] 2 (DENC = N,N-diethylnicotinamide; X = Cl or Br) and the kinetics of their reactions with DENC in methylene chloride

Tetrahalo - tetrakis - (N,N-diethylnicotinamide)dicopper(II) species [(DENC) 2CuX 2] 2 (X = Cl or Br) differ in that while the chloro complex is bridged by two DENC molecules in the solid but two chloro groups in solution, the bromo complex is always bromo-bridged. These conclusions result from an X-ray structural determination of (DENC)Cl 2Cu(DENC,DENC)CuCl 2(DENC) and from spectroscopic comparisons. The kinetics of conversion of the respective dimers to monomeric (DENC) 3CuX 2 species have been measured in methylene chloride solution.

Acyclic and macrocyclic schiff base complexes of lanthanides and actinides

Acyclic and macrocyclic schiff base complexes of lanthanides and actinides