pH-controlled change of the metal coordination in a dicopper(II) complex of the ligand H-BPMP: crystal structures, magnetic properties, and catecholase activity

The dinucleating ligand 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (H-BPMP) has been used to synthesize the three dinuclear Cu(II) complexes [Cu2(BPMP)(OH)][ClO4](2).0.5C4H8O (1), [Cu2(BPMP)(H2O)2](ClO4)(3).4H2O (2), and [Cu2(H-BPMP)][(ClO4)4].2CH3CN (3). X-ray diffraction studies reveal that 1 is a mu-hydroxo, mu-phenoxo complex, 2 a diaqua, mu-phenoxo complex, and 3 a binuclear complex with Cu-Cu distances of 2.96, 4.32, and 6.92 A, respectively. Magnetization measurements reveal that 1 is moderately antiferromagnetically coupled while 2 and 3 are essentially uncoupled. The electronic spectra in acetonitrile or in water solutions give results in accordance with the solid-state structures. 1 is EPR-silent, in agreement with the antiferromagnetic coupling between the two copper atoms. The X-band spectrum of powdered 2 is consistent with a tetragonally elongated square pyramid geometry around the Cu(II) ions, in accordance with the solid-state structure, while the spectrum in frozen solution suggests a change in the coordination geometry. The EPR spectra of 3 corroborate the solid-state and UV-visible studies. The 1H NMR spectra also lead to observations in accordance with the conclusions from other spectroscopies. The electrochemical behavior of 1 and 2 in acetonitrile or in water solutions shows that the first reduction (Cu(II)Cu(II)-Cu(II)Cu(I) redox couple) is reversible and the second (formation of Cu(I)Cu(I) irreversible. In water, 1 and 2 are reversibly interconverted upon acid/base titration (pK 4.95). In basic medium a new species, 4, is reversibly formed (pK 12.0), identified as the bishydroxo complex. Only 1 exhibits catecholase activity (oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, vmax = 1.1 x 10(-6) M-1 s-1 and KM = 1.49 mM). The results indicate that the pH dependence of the catalytic abilities of the complexes is related to changes in the coordination sphere of the metal centers.     

Self assembled tetranuclear Cu4(II), Ni4(II) [2 × 2] square grids and a dicopper(II) complex of heterocycle based polytopic ligands - Magnetic studies

The ditopic ligand PyPzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) and the polytopic ligand 2-PzCAP (N'(3),N'(5)-bis[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3,5-dicarbohydrazide) were synthesized in situ by condensation of methyl imino picolinate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide and 2-acetyl pyridine with pyrazole-3,5-dicarbohydrazide respectively. The ligands PyPzOAP and PzOAP (reported earlier, Dalton Trans., 2007, 1229) self-assemble to form homoleptic [2 × 2] tetranuclear M(4) (M = Cu(II) and Ni(II)) square grids structures [Cu(4)(PyPzOAP)(4)](NO(3))(4) (1), [Cu(4)(PzOAP)(4)](ClO(4))(4) (2) and [Ni(4)(PyPzOAP)(4)](NO(3))(4)·8H(2)O·2CH(3)CN (3). While the ligand 2-PzCAP forms a dicopper(II) complex [Cu(2)(2-PzCAP)(OH)(NO(3))(H(2)O)](NO(3))·2H(2)O (4). The complex 1 is a perfect square grid (a = 4.201 ?), whereas, 2 and 3 are almost square grids. All these compounds have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. EPR studies have also been carried out for complexes 1, 2 and 4. In the Cu(4) grid (1), all the Cu(II) centers are in a distorted octahedral environment with N(4)O(2) chromophore, while, in complex 2, all four Cu(II) centers have a square pyramidal environment with N(3)O(2) chromophore. In complex 3, all four Ni(II) centers have distorted octahedral geometry with N(4)O(2) chromophore. In compound 4, the Cu(II) centers are in square pyramidal environment with N(3)O(2) chromophore. The magnetic properties of compounds 1 and 2 show the presence of intramolecular ferromagnetic exchange interaction (J = 5.88 cm(-1) for 1 and 4.78 cm(-1) for 2). The complex 3 shows weak intramolecular antiferromagnetic interaction (J = -4.02 cm(-1)). While, complex 4, shows strong antiferromagnetic behavior (J = -443 cm(-1)).     

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.     

Bi- and trinuclear copper(II) complexes of a sterically constrained phenol-based tetradentate ligand: syntheses, structures, and magnetic studies

Copper(II) complexes (1-3) of a sterically constrained phenol-based tetradentate N(2)O(2) ligand 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)piperazine (H(2)L) have been reported. The associated anions of the copper(II) ion precursors have profound influence on the stoichiometry of the products. Thus, with perchlorate ion, the product is a binuclear compound [Cu(2)L(2)] (1), while with coordinating anions viz. Cl(-) and N(3)(-), the products [Cu(3)L(2)Cl(2)(H(2)O)].1/2H(2)L (2) and [Cu(3)L(2)(N(3))(2)(CH(3)OH)].4H(2)O (3) have triangulo trinuclear composition. The syntheses, X-ray structures, and spectroscopic and magnetic properties of these complexes are described. Compound 1 has a noncentrosymmetric structure with a rectangular Cu(2)(OPh)(2) core. It appears to be a rare example of a phenolato-bridged Cu(II) dimer exhibiting ferromagnetic interactions (J = 0.93 cm(-)(1)), a behavior in agreement with the theoretical predictions but seldom observed experimentally. In compounds 2 and 3, the copper centers are triangularly disposed, and the molecules have a shape much like that of a butterfly. The terminal copper centers Cu(1) and Cu(2) in 2 and 3 have distorted square pyramidal geometry, connected to each other by a bridging chloro- (in 2) or azido ligand (in 3) in "end to end" fashion. The central copper center (Cu(3) in 2 and Cu in 3) in both the compounds has distorted square planar geometry. The separations between the metal centers, viz. Cu(1)...Cu(2), Cu(2)...Cu(3), and Cu(3)...Cu(1), are 4.826, 3.214, and 3.244 A, respectively, in 2. The corresponding distances in 3 are 5.590, 3.178, and 3.485 A, respectively. The overall magnetic behaviors in 2 and 3 are consistent with antiferromagnetic interactions between the spin centers. In 3, the exchange couplings between the terminal and central copper centers J(Cu(1))(-)(Cu) and J(Cu(2))(-)(Cu) appear to be equal (-234 cm(-)(1)), resulting in an S = (1)/(2) ground state at temperatures near or below 77 K.     

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.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Synthesis, structure, magnetism, and spectroscopic properties of heterobinuclear copper(II)-zinc(II) complexes and their copper(II)-copper(II) analogues in asymmetric ligand environments

Heterobinuclear copper(II)-zinc(II) complexes and their homobinuclear dicopper(II) counterparts (1-4) of two asymmetric ligands (H2L1 and H2L2), based on 2-aminocyclopent-1-ene-1-dithiocarboxylate, are reported. The ligands are capable of providing both donor set and coordination number asymmetry in tandem. Metal centers in these complexes are connected by a micro-alkoxo and a bridging pyrazolate moiety, as confirmed by X-ray structure analyses of 1, 3, and 4. The Cu(1) site in the dicopper complex (1) is square planar and so are the copper sites in the Cu-Zn complexes 3 and 4. The pentacoordinated Zn sites in the latter complexes have distorted TBP geometry (tau = 0.74), while the corresponding Cu site in 1 has a highly distorted square pyramidal structure (tau = 0.54). The Cu...Zn separations in 3 and 4 are 3.3782 and 3.3403 angstroms, respectively, while the Cu...Cu distance in 1 is 3.3687 angstroms. The dicopper complexes are EPR silent at 77 K, in which the copper(II) centers are coupled by strong antiferromagnetic coupling (J = ca. -290 cm(-1)) as confirmed by variable-temperature (4-300 K) magnetic measurements. These compounds (1 and 2) undergo two one-electron reductions and a single step two-electron oxidation at ca. -0.26, -1.40, and 1.0 V vs Ag/AgCl reference, respectively, as indicated by cyclic and differential pulse voltammetry done at subambient temperatures. EPR spectra of 3 and 4 display axial anisotropy at 77 K with the gperpendicular region being split into multiple lines due to N-superhyperfine coupling (AN = 15.3 x 10(-4) cm(-1)). The observed trend in the spin-Hamiltonian parameters, gparallel > gperpendicular > 2.04 and |Aperpendicular| < |Aparallel| approximately (120-150) x 10(-4) cm(-1), indicates a d(x2-y2)-based ground state with tetragonal site symmetry for the Cu(II) center in these molecules.     

Halogen exchange and scrambling between C-X and M-X' bonds in copper, nickel, and cobalt complexes of 6,6'-bis(bromo/chloromethyl)-2,2'-bipyridine. structural, electrochemical, and photochemical studies

The synthesis, reactivities, spectroscopic, electrochemical, and structural studies of copper(I), copper(II), nickel(II), and cobalt(II) complexes of 6,6'-bis(bromomethyl)-2,2'-bipyridine (bpy-Br2) and 6,6'-bis(chloromethyl)-2,2'-bipyridine (bpy-Cl2) have been reported. The copper(I) complex [CuI(bpy-Br2)2](ClO4) (1) has been obtained in two crystallographic modifications, in which the coordination geometry of the metal center has the D2d symmetry. The reaction between CuCl2.2H2O and bpy-Br2 has been followed spectrophotometrically at 45 degrees C over a period of 7 h, and a mechanism for the intramolecular halogen exchange and scrambling in the initially formed compound [CuII(bpy-Br2)Cl2] (5) has been proposed. Depending upon the reaction conditions, several halogen-exchanged products, namely [CuII(bpy-Br1.86Cl0.14)(Cl1.89Br0.11)] (2), [CuII(bpy-Br1.81Cl0.19)(Cl1.70Br0.30)(H2O)] (3), and [CuII(bpy-Br0.63Cl1.37)(Cl0.54Br1.46)] (4), have been isolated in crystalline form. The reaction between bpy-Cl2 and CuCl2.2H2O provides [CuII(bpy-Cl2)Cl2] (7) and [CuII(bpy-Cl2)Cl2(H2O)] (8), whereas CoCl2.6H2O and NiCl2.6H20 on reaction with bpy-Br2 under boiling condition produce [CoII(bpy-Br0.5Cl1.5)(ClBr)] (11) and [NiII(bpy-Br0.46Cl1.54)(Cl0.73Br1.27)(H2O)] (12), respectively. The X-ray structures determined for the 4-coordinate compounds 2, 4, and 7 show flattened tetrahedral geometry for the metal center with the D2 symmetry. Both 5-coordinate compounds 3 and 12 have square pyramidal geometry, and whereas the nickel(II) complex 12 has near-perfect geometry (tau = 0.015), considerable distortion is observed for the copper(II) complex 3 (tau = 0.25). Complexes [CuII(bpy-Cl2)Br2] (6) and [CuII(bpy-Br2)Br2] under boiling condition undergo photoreduction to produce the dimeric copper(I) complexes [{CuI(bpy-Cl1.30Br0.70)(mu-Br)}2](9) and [{CuI(bpy-Br2)(mu-Br)}2] (10), respectively. The fact that the photoreduction of [CuII(bpy-Cl2)Br2] (6) and [CuII(bpy-Br2)Br2] do not take place in absence of light has been established by spectrophotometric measurements. The crystal structures of 9 and 10 have been determined. The electrochemical behavior of all the copper complexes 1-10 has been studied in acetonitrile and dichloromethane. The E1/2 values for the CuI/CuII redox couples show strong solvent dependence and for a given system the E1/2 value is more positive in dichloromethane relative to that in acetonitrile. For the compounds [CuII(bpy-Br2-xClx)(Cl2-yBry)] (x = 0-2, y = 0-2), the E1/2 values become more positive with the increase of y value.     

Synthesis, crystal structure, spectral studies, and catechol oxidase activity of trigonal bipyramidal Cu(II) complexes derived from a tetradentate diamide bisbenzimidazole ligand

A new benzimidazole-based diamide ligand-N,N'-bis(glycine-2- benzimidazolyl)hexanediamide (GBHA)-has been synthesized and utilized to prepare Cu(II) complexes of general composition [Cu(GBHA)X]X, where X is an exogenous anionic ligand (X = Cl(-), NO(3)(-), SCN(-)). The X-ray structure of one of the complexes, [Cu(GBHA)Cl]Cl.H(2)O.CH(3)OH, has been obtained. The compound crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 26.464(3) A, b = 10.2210(8) A, c = 20.444(2) A, alpha = 90 degrees, beta = 106.554(7) degrees, gamma = 90 degrees, V= 5300.7(9) A(3), and Z = 8. To the best of our knowledge, the [Cu(GBHA)Cl]Cl.H(2)O.CH(3)OH complex is the first structurally characterized mononuclear trigonal bipyramidal copper(II) bisbenzimidazole diamide complex having coordinated amide carbonyl oxygen. The coordination geometry around the Cu(II) ion is distorted trigonal bipyramidal (tau = 0.59). Two carbonyl oxygen atoms and a chlorine atom form the equatorial plane, while the two benzimidazole imine nitrogen atoms occupy the axial positions. The geometry of the Cu(II) center in the solid state is not preserved in DMSO solution, changing to square pyramidal, as suggested by the low-temperature EPR data g( parallel) > g( perpendicular) > 2.0023. All the complexes display a quasi-reversible redox wave due to the Cu(II)/Cu(I) reduction process. E(1/2) values shift anodically from Cl(-) < NO(3)(-) < SCN(-), indicating that the bound Cl(-) ion stabilizes the Cu(II) ion while the N-bonded SCN(-) ion destabilizes the Cu(II) state in the complex. When calculated against NHE, the redox potentials turn out to be quite positive as compared to other copper(II) benzimidazole bound complexes (Nakao, Y.; Onoda, M.; Sakurai, T.; Nakahara, A.; Kinoshita, L.; Ooi, S. Inorg. Chim. Acta 1988, 151, 55. Addison, A. W.; Hendricks, H. M. J.; Reedijk, J.; Thompson, L. K. Inorg. Chem. 1981, 20 (1), 103. Sivagnanam, U.; Palaniandavar, M. J. Chem. Soc., Dalton Trans. 1994, 2277. Palaniandavar, M.; Pandiyan, T.; Laxminarayan, M.; Manohar, H. J. Chem. Soc., Dalton Trans. 1995, 457. Sakurai, T.; Oi, H.; Nakahara, A. Inorg. Chim. Acta 1984, 92, 131). It is therefore concluded that binding of amide carbonyl oxygen destabilizes the Cu(II) state. The complex [Cu(II)(GBHA)(NO(3))](NO(3)) could be successfully reduced by the addition of dihydroxybenzenes to the corresponding [Cu(I)(GBHA)](NO(3)). (1)H NMR of the reduced complex shows slightly broadened and shifted (1)H signals. The reduction of the Cu(II) complex presumably occurs with the corresponding 2e(-) oxidation of the quinol to quinone. Such a conversion is reminiscent of the functioning of a copper-containing catechol oxidase from sweet potatoes and the met form of the enzyme tyrosinase.     

Catechol oxidase activity of a series of new dinuclear copper(II) complexes with 3,5-DTBC and TCC as substrates: syntheses, X-ray crystal structures, spectroscopic characterization of the adducts and kinetic studies

A series of dinuclear copper(II) complexes has been synthesized with the aim to investigate their applicability as potential structure and function models for the active site of catechol oxidase enzyme. They have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis: [Cu 2(H 2L2 (2))(OH)(H 2O)(NO 3)](NO 3) 3.2H 2O ( 1), [Cu(HL1 (4))(H 2O)(NO 3)] 2(NO 3) 2.2H 2O ( 2), [Cu(L1 (1))(H 2O)(NO 3)] 2 ( 3), [Cu 2(L2 (3))(OH)(H 2O) 2](NO 3) 2, ( 4) and [Cu 2(L2 (1))(N 3) 3] ( 5) [L1 = 2-formyl-4-methyl-6R-iminomethyl-phenolato and L2 = 2,6-bis(R-iminomethyl)-4-methyl-phenolato; for L1 (1) and L2 (1), R = N-propylmorpholine; for L2 (2), R = N-ethylpiperazine; for L2 (3), R = N-ethylpyrrolidine, and for L1 (4), R = N-ethylmorpholine]. Dinuclear 1 and 4 possess two "end-off" compartmental ligands with exogenous mu-hydroxido and endogenous mu-phenoxido groups leading to intermetallic distances of 2.9794(15) and 2.9435(9) A, respectively; 2 and 3 are formed by two tridentate compartmental ligands where the copper centers are connected by endogenous phenoxido bridges with Cu-Cu separations of 3.0213(13) and 3.0152(15) A, respectively; 5 is built by an end-off compartmental ligand having exogenous mu-azido and endogenous mu-phenoxido groups with a Cu-Cu distance of 3.133(2) A (mean of two independent molecules). The catecholase activity of all of the complexes has been investigated in acetonitrile and methanol medium by UV-vis spectrophotometric study using 3,5-di- tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) as substrates. In acetonitrile medium, the conversion of 3,5-DTBC to 3,5-di- tert-butylbenzoquinone (3,5-DTBQ) catalyzed by 1- 5 is observed to proceed via the formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically for the first time. In methanol medium no such enzyme-substrate adduct has been detected, and the 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by 1- 5 very efficiently. The substrate TCC forms an adduct with 2- 5 without performing further oxidation to TCQ due to the high reduction potential of TCC (in comparison with 3,5-DTBC). But most interestingly, 1 is observed to be effective even in TCC oxidation, a process never reported earlier. Kinetic experiments have been performed to determine initial rate of reactions (3,5-DTBC as substrate, in methanol medium) and the activity sequence is 1 > 5 > 2 = 4 > 3. A treatment on the basis of Michaelis-Menten model has been applied for kinetic study, suggesting that all five complexes exhibit very high turnover number, especially 1, which exhibits turnover number or K cat of 3.24 x 10 (4) (h (-1)), which is approximately 3.5 times higher than the most efficient catalyst reported to date for catecholase activity in methanol medium.     

Catecholase activity of a series of dicopper(II) complexes with variable Cu-OH(phenol) moieties

The catecholase activity of a series of dicopper(II) complexes containing different numbers of phenol groups coordinated to the metal centers was studied to identify functional as well as structural models for the type III copper enzymes tyrosinase and catechol oxidase. The syntheses and characterization of complexes [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2).2H(2)O (1) and [Cu(2)(Hbtppnol)(mu-OAc)](ClO(4))(2) (2) were previously reported by us (Inorg. Chim. Acta 1998, 281, 111-115; Inorg. Chem. Commun. 1999, 2, 334-337), and complex [Cu(2)(P1-O(-))(OAc(-))](ClO(4))(2) (3) was previously reported by Karlin et al. (J. Am. Chem. Soc. 1997, 119, 2156-2162). The catalytic activity of the complexes 1-3 on the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400 nm over time in methanol saturated with O(2)/aqueous buffer pH 8 solutions at 25 degrees C. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity. A kinetic treatment of the data based on the Michaelis-Mentèn approach was applied. The [Cu(2)(H(2)bbppnol)(mu-OAc)(H(2)O)(2)]Cl(2) small middle dot2H(2)O complex showed the highest catalytic activity of the three complexes as a result of a high turnover rate (k(cat) = 28 h(-1)) combined with a moderate substrate-catalyst binding constant (K(ass) = 1.3 x 10(3) M(-1)). A mechanism for the oxidation reaction is proposed, and reactivity differences, k(cat)/K(M) of the complexes, were found to be dependent on (DeltaE)(1,2), the difference in the driving force for the reduction reactions Cu(II)(2)/Cu(II)Cu(I) and Cu(II)Cu(I)/Cu(I)(2).     

Structures and DNA-binding and cleavage properties of ternary copper(II) complexes of glycine with phenanthroline, bipyridine, and bipyridylamine

The crystal structures of the series of three complexes, [Cu(Gly)(bpy)Cl].2H2O (1) (Gly=glycine; bpy=2,2'-bipyridine), [Cu(Gly)(phen)Cl]2.7H2O (2) (phen=1,10-phenanthroline), and [Cu(Gly)(bpa)(H2O)Cl] (3) (bpa=2,2'-bipyridylamine) were determined, and the coordination modes of Cu(II) ternary complexes were compared. The central Cu(II) atoms of complexes 1 and 3 have a similar distorted octahedral coordination geometry, while the Cu(II) atom of complex 2 has a distorted square pyramidal coordination. In all complexes, the aromatic heterocyclic compounds bpy, phen, and bpa, behave as a bidentate N,N' ligand, and Gly behaves as a bidentate N,O ligand. DNA-binding properties of the complexes to calf thymus (CT) DNA were studied by using the fluorescence method. Each of the complexes showed binding propensity to CT DNA with the relative order 2>3> or =1. DNA cleavage studies indicate that each of the complexes, especially 2, can cleave plasmid supercoiled pBR322 DNA in the presence of H2O2 and ascorbic acid with cleavage efficiency in the order 2>3 approximately 1. The degradation of the conformation of CT DNA by the complexes was also reflected in the decrease in the intensities of the characteristic CD bands with the relative order 2>3 approximately 1.     

H2O2-reactivity of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine ligands with 6-phenyl substituents

The structure and H(2)O(2)-reactivity of a series of copper(II) complexes supported by tris[(pyridin-2-yl)methyl]amine (TPA) derivatives having a phenyl group at the 6-position of pyridine donor group(s) [(6-phenylpyridin-2-yl)methyl]bis[(pyridin-2-yl)methyl]amine (Ph(1)TPA), bis[(6-phenylpyridin-2-yl)methyl][(pyridin-2-yl)methyl]amine (Ph(2)TPA), and tris[(6-phenylpyridin-2-yl)methyl]amine (Ph(3)TPA) have systematically been examined to get insights into the aromatic substituent (6-Ph) effects on the coordination chemistry of TPA ligand system. The X-ray crystallographic analyses have revealed that [Cu(II)(TPA)(CH(3)CN)](ClO(4))(2) (CuTPA) and [Cu(II)(Ph(3)TPA)(CH(3)CN)](ClO(4))(2) (3) exhibit a trigonal bipyramidal structure, whereas [Cu(II)(Ph(1)TPA)(CH(3)CN)](ClO(4))(2) (1) shows a slightly distorted square pyramidal structure and [Cu(II)(Ph(2)TPA)(CH(3)CN)](ClO(4))(2) (2) has an intermediate structure between trigonal bipyramidal and square pyramidal. On the other hand, the UV-vis and ESR data have suggested that all the copper(II) complexes have a similar trigonal bipyramidal structure in solution. The redox potentials of CuTPA, 1, 2, and 3 have been determined as E(1/2) = -0.34, -0.28, -0.16, and -0.04 mV vs Ag/AgNO(3), respectively, demonstrating that introduction of each 6-Ph group causes positive shift of E(1/2) about 0.1 V. Notable difference in H(2)O(2)-reactivity has been found among the copper(II) complexes. Namely, CuTPA and 1 afforded mononuclear copper(II)-hydroperoxo complexes CuTPA-OOH and 1-OOH, respectively, whereas complex 2 provided bis(mu-oxo)dicopper(III) complex 2-oxo. On the other hand, copper(II) complex 3 was reduced to the corresponding copper(I) complex 3(red). On the basis of the H(2)O(2)-reactivity together with the X-ray structures and the redox potentials of the copper(II) complexes, the substituent effects of 6-Ph are discussed in detail.     

Binuclear copper(II) oxidation products from copper(I) complexes with tridentate ligands. Magnetostructural characterization

The bis-pyridine tridentate ligands (6-R-2-pyridylmethyl)-(2-pyridylmethyl) benzylamine (RDPMA, where R = CH(3), CF(3)), (6-R-2-pyridylmethyl)-(2-pyridylethyl) benzylamine (RPMPEA, where R = CH(3), CF(3)), and the bidentate ligand di-benzyl-(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) have been synthesized and their copper(I) complexes oxidized in a methanol solution to afford self-assembled bis-micro-methoxo-binuclear copper(II) complexes (1, 2, 4, 6) or hydroxo- binuclear copper(II) complexes (3). Oxidation of the nonsubstituted DPMA (R = H) in dichloromethane gives a chloride-bridged complex (5). The crystal structures for [Cu(MeDPMA)(MeO)](2)(ClO(4))(2) (1), [Cu(RPMPEA)(MeO)](2)(ClO(4))(2) (for 2, R= Me, and for 4, R = CF(3)), [Cu(BiBzMePMA)(MeO)](2)(ClO(4))(2) (6), [Cu(FDPMA)(OH)](2)(ClO(4))(2) (3), and [Cu(DPMA)(Cl)](2)(ClO(4))(2) (5) have been determined, and their variable-temperature magnetic susceptibility has been measured in the temperature range of 10-300 K. The copper coordination geometries are best described as square pyramidal, except for 6, which is square planar, because of the lack of one pyridine ring in the bidentate ligand. In 1-4 and 6, the basal plane is formed by two pyridine N atoms and two O atoms from the bridging methoxo or hydroxo groups, whereas in 5, the bridging Cl atoms occupy axial-equatorial sites. Magnetic susceptibility measurements show that the Cu atoms are strongly coupled antiferromagnetically in the bis-methoxo complexes 1, 2, 4, and 6, with -2J > 600 cm(-)(1), whereas for the hydroxo complex 3, -2J = 195 cm(-)(1) and the chloride-bridged complex 5 shows a weak ferromagnetic coupling, with 2J = 21 cm(-)(1) (2J is an indicator of the magnetic interaction between the Cu centers).     

Synthetic analogue approach for the functional domains of copper(II) bleomycins and its DNA cleavage activity

The dicopper(II) complex [Cu2(R'SSR)2(SO4)2] (1), where R'SSR is a Schiff base, has been prepared from the reaction of CuSO4.5H2O with the Schiff base N,N'-1,1'-dithiobis(ethylenesalicylaldimine)(H2RSSR) and structurally characterized by X-ray crystallography. The crystal structure of 1 shows two {Cu(R'SSR)}2+ units linked by two sulfate ligands each showing a eta3,mu2-binding mode. The Cu...Cu distance is 4.562(2)A with each copper having a square pyramidal (4 + 1) CuNO4 coordination geometry. The monoanionic Schiff base R'SSR has a pendant cationic amine -SCH2CH2NH3+ group which is presumably formed from the hydrolysis of one imine bond of H2RSSR. Complex 1 models the N- and C-terminus domains of bleomycins. The metal centers in 1 are essentially magnetically non-interacting giving a -2J value of 3 cm(-1) with the singlet as the ground state. Using complex 1 as a precursor, ternary copper(II) complexes [Cu(R'SSR)B(SO4)] (2-4)- are prepared, characterized and their DNA binding and cleavage properties studied (B: kanamycin A, 2; 2,2'-bipyridine, 3; 1,10-phenanthroline, 4). IR spectral data suggest a square pyramidal (4 + 1) geometry for the one-electron paramagnetic ternary complexes with the sulfate bound to copper. The complexes are non-conducting in DMF but show conductivity in aqueous medium due to dissociation of the sulfate ligand. They bind to calf thymus DNA in the minor groove giving the relative order: 4 > 2 > 1 approximately 3 (Kapp= 5.4 x 10(5) M(-1) for 4). The precursor complex 1 does not show any apparent chemical nuclease activity when treated with supercoiled (SC) DNA in the presence of 3-mercaptopropionic acid (MPA). The kanamycin A and phen adducts as such or generated under in situ reaction conditions using 1 nd the ligand display efficient chemical nuclease activity in the presence of MPA, while the bpy species shows poor cleavage activity. The ternary kanamycin A complex presents the first synthetic model for three functional domains of bleomycins.     

Mechanistic insight on the catecholase activity of dinuclear copper complexes with distant metal centers

The catecholase activity of two dinuclear Cu(II) complexes with distant metal centers is discussed together with solid state and solution studies. The crystal structure for one of them, [Cu(2)(diep)(H(2)O)(4)](ClO(4))(4)·2H(2)O, is described, showing the two copper ions are 7.457 ? apart and in a square pyramidal coordination. Both complexes display a weak antiferromagnetic coupling in the solid state that is manifest in the dimer EPR spectra obtained in frozen solution. The pH-potentiometric speciation performed in 1:1 MeOH-H(2)O allowed the assignment of hydrolyzed copper species as those catalytically active in the oxidation of 3,5-di-tert-butylcatechol (DTBC). The kinetic measurements led us to propose behavior consistent with Michaelis-Menten plus a linear dependence of the initial rate on [DTBC]. This can be associated with the presence of more than one catalytically active species, which is consistent with the evidence of several differently hydrolyzed species shown in the predominance diagrams. Product characterization studies led to establishing the formation of hydrogen peroxide during the catalytic cycle, while semiquinone and superoxide radicals were detected by EPR spectroscopy, supporting one-electron transference at each of the copper centers.     

Synthesis, magnetic behaviour, and X-ray structures of dinuclear copper complexes with multiple bridges. Efficient and selective catalysts for polymerization of 2,6-dimethylphenol

The use of a potentially tridentate mono-anionic bridging ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-2-ol (bdmpp-H), in assembling new dimeric copper complexes with interesting magnetic properties has been investigated. The reaction of copper hydroxide or copper acetate with phenyl phosphinic acid or diphenyl phosphinic acid in the presence of bdmpp-H produces the dinuclear complexes [Cu(bdmpp)(ppi)]2 (1) and [Cu(bdmpp)(dppi-H)]2(dppi)2 (2) (ppi-H = phenylphosphinic acid: dppi-H = diphenylphosphinic acid), respectively. The products have been characterized with the help of analytical, thermal, and spectroscopic (IR, UV-vis, and EPR) techniques. Single crystal X-ray diffraction studies of 1 and 2 reveal that the two bdmpp ligands hold together the dimeric copper unit in each complex through mu-O alkoxide and the pyrazolyl nitrogen ligating centers. Two phenyl phosphinate ligands additionally bridge the dicopper core in 1 to result in octahedral coordination geometry around each metal ion. The diphenyl phosphinic acid acts as a terminal ligand in 2, and thus completes a square pyramidal geometry around each copper ion. Both complexes show a very short Cu...Cu separation (3.001 and 3.065 angstroms for 1 and 2, respectively). The investigation of the magnetic properties reveals the efficiency of the double alkoxide bridge between the two paramagnetic copper ions to mediate strong antiferromagnetic interactions [J/k(B) = -620(5) K (-431(4) cm(-1)) and -685(5) K (-476(4) cm(-1)) for 1 and 2, respectively]. Compounds 1 and 2, along with a few other copper phosphate complexes, were tested as catalysts for the oxidative polymerization of 2,6-dimethylphenol; 1 and 2 were found to be efficient catalysts with an increased selectivity for the formation of the polyphenylene ether. However a related mononuclear octahedral copper complex [Cu(imz)4(dtbp)2] (dtbp-H = di-tert-butylphosphate) was found to be more efficient.     

Polyoxometalate-supported transition metal complexes and their charge complementarity: synthesis and characterization of [M(OH)6Mo6O18[Cu(Phen)(H2O)2]2][M(OH)6Mo6O18[Cu(Phen)(H2O)Cl]2].5H2O (M = Al(+, Cr3+)

Two Anderson-type heteropolyanion-supported copper phenanthroline complexes, [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2]1+ (1c) and [Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2]1- (1a) complement their charges in one of the title compounds [Al(OH)6Mo6O18[Cu(phen)(H2O)2]2][Al(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5H2O [1c][1a].5 H2O 1. Similar charge complementarity exists in the chromium analogue, [Cr(OH)6Mo6O18[Cu(phen)(H2O)2]2][Cr(OH)6Mo6O18[Cu(phen)(H2O)Cl]2].5 H2O [2c][2a].5 H2O 2. The chloride coordination to copper centers of 1a and 2a makes the charge difference. In both compounds, the geometries around copper centers are distorted square pyramidal and those around aluminum/chromium centers are distorted octahedral. Three lattice waters, from the formation of intermolecular O-H.....O hydrogen bonds, have been shown to self-assemble into an "acyclic water trimer" in the crystals of both 1 and 2. The title compounds have been synthesized in a simple one pot aqueous wet-synthesis consisting of aluminum/chromium chloride, sodium molybdate, copper nitrate, phenanthroline, and hydrochloric acid, and characterized by elemental analyses, EDAX, IR, diffuse reflectance, EPR, TGA, and single-crystal X-ray diffraction. Both compounds crystallize in the triclinic space group P. Crystal data for 1: a = 10.7618(6), b = 15.0238(8), c = 15.6648(8) angstroms, alpha = 65.4570(10), beta = 83.4420(10), gamma = 71.3230(10), V = 2182.1(2) angstroms3. Crystal data for 2: a = 10.8867(5), b = 15.2504(7), c = 15.7022(7) angstroms, alpha = 64.9850(10), beta = 83.0430(10), gamma = 71.1570(10), V = 2235.47(18) angstroms3. In the electronic reflectance spectra, compounds 1 and 2 exhibit a broad d-d band at approximately 700 nm, which is a considerable shift with respect to the value of 650-660 nm for a square-pyramidal [Cu(phen)2L] complex, indicating the coordination of [M(OH)6Mo6O18]3- POM anions (as a ligand) to the monophenanthroline copper complexes to form POM-supported copper complexes 1c, 1a, 2c, and 2a. The ESR spectrum of compound 1 shows a typical axial signal for a Cu2+ (d9) system, and that of compound 2, containing both chromium(III) and copper(II) ions, may reveal a zero-field-splitting of the central Cr3+ ion of the Anderson anion, [Cr(OH)6Mo6O18]3-, with an intense peak for the Cu2+ ion.     

铜(Ⅱ)-牛磺酸缩2-吡啶甲醛席夫碱-3,5-二羟基苯甲酸三元配合物的合成及其晶体结构

牛磺酸缩2-吡啶甲醛席夫碱,3,5-二羟基苯甲酸与醋酸铜在50%甲醇中反应合成了铜(Ⅱ)-牛磺酸缩2-吡啶甲醛席夫碱-3,5-二羟基苯甲酸三元配合物{[Cu(C8H9N2O3S)(C7H6O4).(H2O)2].2H2O(1)},其结构经IR,元素分析和X-射线单晶衍射法表征。1属三斜晶系,空间群P-1,晶胞参数a=7.066(2),b=11.891(4),c=12.859(4),α=104.034(14)°,β=96.884(13),°γ=99.053(10)°,V=1020.9(6)3,Z=2,Dc=1.633 g.cm-3,μ=1.233 mm-1,F(000)=518,R1=0.1108,wR2=0.322。1的中心铜离子与席夫碱配体的两个N原子,3,5-二羟基苯甲酸羧酸根上一个O原子以及两个水分子的O原子配位,形成一个五配位的四方锥结构。由结晶水分子,没参与配位的磺酸基氧,配位水分子间形成的氢键以及吡啶环、苯环间的π┈π相互作用,使1分子堆积成三维超分子网状结构,稳定了整个晶体结构。     

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.