Cyano-bridged homodinuclear copper(II) complexes

The synthesis and structural analysis (single crystal X-ray data) of two mononuclear ([Cu(L(1))(CN)]BF(4) and [Cu(L(3))(CN)](BF(4))) and three related, cyanide-bridged homodinuclear complexes ([{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O, [{Cu(L(2))}(2)(CN)](BF(4))(3) and [{Ni(L(3))}(2)(CN)](BF(4))(3)) with a tetradentate (L(1)) and two isomeric pentadentate bispidine ligands (L(2), L(3); bispidines are 3,7-diazabicyclo[3.3.1]nonane derivatives) are reported, together with experimental magnetic, electron paramagnetic resonance (EPR), and electronic spectroscopic data and a ligand-field-theory-based analysis. The temperature dependence of the magnetic susceptibilities and EPR transitions of the dicopper(II) complexes, together with the simulation of the EPR spectra of the mono- and dinuclear complexes leads to an anisotropic set of g- and A-values, zero-field splitting (ZFS) and magnetic exchange parameters (Cu1: g(z) = 2.055, g(x) = 2.096, g(y) = 2.260, A(z) = 8, A(x) = 8, A(y) = 195 × 10(-4) cm(-1), Cu2: g and A as for Cu(1) but rotated by the Euler angles α = -6°, β = 100°, D(exc) = -0.07 cm(-1), E(exc)/D(exc) = 0.205 for [{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O; Cu1,2: g(z) = 2.025, g(x) = 2.096, g(y) = 2.240, A(z) = 8, A(x) = 8, A(y) = 190 × 10(-4)cm(-1), D(exc) = -0.159 cm(-1), E(exc)/D(exc) = 0.080 for [{Cu(L(2))}(2)(CN)](BF(4))(3)). Thorough ligand-field-theory-based analyses, involving all micro states and all relevant interactions (Jahn-Teller and spin-orbit coupling) and DFT calculations of the magnetic exchange leads to good agreement between the experimental observations and theoretical predictions. The direction of the symmetric magnetic anisotropy tensor D(exc) in [{Cu(L(2))}(2)(CN)](BF(4))(3) is close to the Cu···Cu vector (22°), that is, nearly perpendicular to the Jahn-Teller axis of each of the two Cu(II) centers, and this reflects the crystallographically observed geometry. Antisymmetric exchange in [{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O causes a mixing between the singlet ground state and the triplet excited state, and this also reflects the observed geometry with a rotation of the two Cu(II) sites around the Cu···Cu axis.     

Multifrequency EPR and redox reactivity investigations of a bis(mu-thiolato)-dicopper(II,II) complex

From a new tripodal ligand [N2SS'H] with mixed N, S(thioether), and S(thiolate) donor set, the corresponding bis(mu-thiolato)dicopper(II) complex has been prepared and characterized. X-ray crystallographic analysis of the complex [Cu2(N2SS')2](ClO4)2.C4H10O (1) demonstrates that the two five-coordinated Cu atoms are bridged by two thiolates leading to a nearly planar Cu2S2 core with a Cu1...Cu1* distance of 3.418(8) A and a large bridging angle Cu1S1Cu1* of 94.92 degrees. X-band (10 GHz), Q-band (34 GHz), and F-Band (115 GHz) EPR spectra of 1 are consistent with a weakly coupled dicopper(II,II) center attributed to an S = 1 state. Simulations for the three frequencies are obtained with a unique set of electronic parameters. The mean values of the spin Hamiltonian parameters for 1 are D = 0.210(3) cm(-1), E = 0.0295(5) cm(-1), |E/D| = 0.140, gx = 2.030(2), gy = 2.032(2), gz = 2.128(2). The electrochemical one-electron reduction of 1 generates the mixed-valent CuIICuI species. EPR and UV-vis spectra are consistent with a type I localized mixed-valent species, while dinuclear CuA centers of native cytochrome c oxidase (CcO)1-3 or nitrous oxide reductase (N2OR)4 have a delocalized CuIICuI mixed-valent state. After reoxidation of the CuIICuI species, the initial complex 1 is regenerated through a reversible interconversion process.     

Dicopper(II) complexes of a new di-para-xylyldioxatetraazamacrocycle and cascade species with dicarboxylate anions: thermodynamics and structural properties

The new dioxatetraazamacrocycle (L1) was synthesized by a 2 + 2 condensation and characterized. Stability constants of its copper(II) complexes were determined by spectrophotometry in DMSO at 298.2 K in 0.10 mol dm(-3) KClO4. Mainly dinuclear complexes are formed and the presence of mononuclear species is dependent on the counterion (Cl- or ClO4-). The association constants of the dinuclear copper(II) complexes with dicarboxylate anions [oxalate (oxa(2-)), malonate (mal(2-)), succinate (suc(2-)), and glutarate (glu(2-))] were also determined by spectrophotometry at 298.2 K in DMSO, and it was found that values decrease with an increase of the alkyl chain between the carboxylate groups. X-Band EPR spectra of the dicopper(II) complexes and of their cascade species in frozen DMSO exhibit dipole-dipole coupling, and their simulation, together with their UV-vis spectra, showed that the copper centres of the complexes in solution had square pyramidal geometries though with different distortions. From the experimental data, it was also possible to predict the Cu...Cu distances, the minimum being found at 6.4 angstroms for the Cu2L1Cl4 complex and then successively this distance slightly increases when the chloride anions are replaced by dicarboxylate anions, from 6.6 angstroms for oxa(2-) to 7.8 angstroms for glu(2-). The crystal structures of the dinuclear copper cascade species with oxa(-2) and suc(2-) were determined and showed one anion bridging both copper centres and Cu...Cu distances of 5.485(7) angstroms and 6.442(8) angstroms, respectively.     

Pyrazolate-based copper(II) and nickel(II) [2 x 2] grid complexes: protonation-dependent self-assembly, structures and properties

The pyrazole-based diamide ligand N,N'-bis(2-pyridylmethyl)pyrazole-3,5-dicarboxamide (H(3)L) has been structurally characterised and successfully employed in the preparation of [2 x 2] grid-type complexes. Thus, the reaction of H(3)L with Cu(ClO(4))2.6H(2)O or Ni(ClO(4))2.6H(2)O in the presence of added base (NaOH) affords the tetranuclear complexes [M(4)(HL(4))].8H(2)O (1: M = Cu, 2: M = Ni). Employment of a mixture of the two metal salts under otherwise identical reaction conditions leads to the formation of the mixed-metal species [Cu(x)Ni(4-x)(HL)(4)].8H(2)O (x相似文献   

Structurally distinct active sites in the copper(II)-substituted aminopeptidases from Aeromonas proteolytica and Escherichia coli

The aminopeptidase from Aeromonas proteolytica (AAP) was titrated with copper, which bound sequentially at two distinct sites. Both the mono- and disubstituted forms of AAP exhibited catalytic hyperactivity relative to the native dizinc enzyme. Monosubstituted AAP exhibited an axial Cu(II) EPR spectrum with slight pH dependence: at pH 6.0 g(parallel) = 2.249, g( perpendicular ) = 2.055, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1), whereas at pH 9.65 g(parallel) = 2.245, g( perpendicular ) = 2.056, and A(parallel)((63/65)Cu) = 1.77 x 10(-)(2) cm(-)(1). These data indicate oxygen and nitrogen ligation of Cu. AAP further substituted with copper exhibited a complex signal with features around g approximately 2 and 4. The features at g approximately 4 were relatively weak in the B(0) perpendicular B(1) (perpendicular) mode EPR spectrum but were intense in the B(0) parallel B(1) (parallel) mode spectrum. The g approximately 2 region of the perpendicular mode spectrum exhibited two components, one corresponding to mononuclear Cu(II) with g(parallel) = 2.218, g( perpendicular ) = 2.023, and A(parallel)((63/65)Cu) = 1.55 x 10(-)(2) cm(-)(1) and likely due to adventitious binding of Cu(II) to a site distant from the active site. Excellent simulations were obtained for the second component of the spectrum assuming that two Cu(II) ions experience dipolar coupling corresponding to an inter-copper distance of 5 A with the two Cu(II) g(z)() directions parallel to each other and at an angle of approximately 17 degrees to the inter-copper vector (H = betaB.g(CuA).S(CuA) + betaB.g(CuB).S(CuB) + [S.A.I](CuA) + [S.A.I](CuB) + [S(CuA).J.S(CuB)]; g(parallel(CuA,CuB)) = 2.218, g( perpendicular )((CuA,CuB)) = 2.060; A(parallel(CuA,CuB))((63/65)Cu) = 1.59 x 10(-)(2) cm(-)(1), J(isotropic) = 50 cm(-)(1), r(Cu)(-)(Cu) = 4.93 A, and chi = 17 degrees ). The exchange coupling between the two copper ions was found to be ferromagnetic as the signals exhibited Curie law temperature dependence. The Cu-Cu distance of approximately 5 A indicated by EPR was significantly higher than the inter-zinc distance of 3.5 A in the native enzyme, and the dicopper species therefore represents a novel dinuclear site capable of catalysis of hydrolysis. In contrast to AAP, the related methionyl aminopeptidase from Escherichia coli (EcMetAP) was found to bind only one Cu(II) ion despite possessing a dinuclear binding site motif. A further difference was the marked pH dependence of the signal in EcMetAP, suggestive of a change in ligation. The structural motifs of these two Cu(II)-substituted aminopeptidases provide important insight into the observed catalytic activity.     

Thermodynamics of ligand exchange reactions between bis(dithiocarbamato)copper(II) and copper(II) salts. An EPR study

EPR spectroscopy was chosen to investigate the ligand exchange reactions between copper(II) bis(dithiocarbamate), Cu(dtc)2, and copper(II) salts which proceeds with the formation of mixed-ligand complexes of the type Cu(dtc)X, where X = Cl, NO3, ClO4. Large concentrations of 1:1 mixed-ligand complexes of this type are obtained as indicated by the EPR spectra of acetone, CHCl3/EtOH, CHCl3/i-PrOH, CCl4/EtOH and CCl4/i-PrOH, solutions of Cu(dtc)2 and the appropriate copper(II) salt CuCl2, Cu(NO3)2 or Cu(ClO4)2. Double integration of Cu(dtc)2 EPR signals obtained at temperatures between 240 and 310 K affords the calculation of the equilibrium constant (K) of the reaction: Cu(dtc)2 + CuX2 <==> 2 Cu(dtc)X in all solvents as a function of T. From the values of K the stability constant beta of the mixed-ligand complexes has been derived. The error associated with the calculated stability constant is +/- 10%. Thermodynamic parameters (deltaH0, deltaG0 and deltaS0) are determined from the temperature dependence of K as measured by EPR spectroscopy.     

Magnetic properties and crystal structure of a one-dimensional phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II)

A new crystalline polymorphic phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2(1)/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu...Cu distance of 2.6494(8) angstroms. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S...S-Cu(II) interdimer interactions [S...S separation: 3.975(2) angstroms]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm(-1), consistent with a ferromagnetic Cu...Cu exchange interaction at low temperature.     

Self-assembly of high-nuclearity metal clusters: programmed expansion of a metallasiloxane cage to an octacopper(II) cluster

The novel octanuclear copper(II) cluster [Cu6[(PhSiO2)6]2[NCCu(Me6tren)]2(MeOH)4]2+ (1) has been isolated as a perchlorate salt by reacting the hexacopper(II) metallasiloxane cage [Cu6[(PhSiO2)6]2(nBuOH)x] (x = 4, 6) with [Cu(Me6tren)CN]ClO4 in a methanol/chloroform mixture (Me6tren = tris(2-(dimethylamino)ethyl) amine). Crystal data for 1(ClO4)2 x MeOH: monoclinic, space group P2(1)/n (no. 14), a = 16.8490(3) angstroms, b = 22.2966(4) angstroms, c = 17.2508(3) angstroms, beta = 94.7658(5) degrees, V = 6458.3(2) angstroms3, Z = 2. The structure comprises a highly distorted hexagonal Cu6 array linked to two [Cu(Me6tren)] units via cyanide bridges. Magnetic measurements reveal that the addition of the copper cyanide complexes dramatically affects the magnetism of the Cu6 unit, whose ground spin state changes from S = 3 to S = 0.     

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.     

Copper(II) hexaaza macrocyclic binuclear complexes obtained from the reaction of their copper(I) derivates and molecular dioxygen

Density functional theory (DFT) calculations have been carried out for a series of Cu(I) complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c-8c) generated by their interaction with molecular O2. For complexes 1c-7c, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(mu-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu(II) complexes 4e, 5e, and 8e have been obtained by O2 oxidation of their corresponding Cu(I) complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types of Cu(II)2 structures: (a) For 4e, the Cu(II) centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cu(II) centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cu(II) centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c-8c toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior: (a) strong antiferromagnetic (AF) coupling with J = -482.0 cm(-1) (g = 2.30; rho = 0.032; R = 5.6 x 10(-3)) for 4e; (b) AF coupling with J = -286.3 cm(-1) (g = 2.07; rho = 0.064; R = 2.6 x 10(-3)) for 5e; (c) an uncoupled Cu(II)2 complex for 8e.     

Synthesis and spectroscopic studies on copper(II) binuclear complexes of 1-phenylamidino-O-alkylurea (alkyl = n-propyl, n- and iso-butyl) with 1,3-diaminopropane or ethylenediamine

Copper(II) binuclear complexes [Cu(II)(1-phenylamidino-O-n-propylurea)tn]2 (H2O)2(Cl2)2 (1), [Cu(II)(1-phenylamidino-O-n-butylurea)tn]2(H2O)2(Cl2)2(2), [Cu(II)(1-phenylamidino-O-i-butylurea)tn]2(H2O)2(Cl2)2(3), and [Cu(II)(1-phenyamidino-O-i-butylurea)en]2(H2O)2(Cl2)2 (4) have been reported. The binuclear complexes 3 and 4 crystallize in a monoclinic structure with unit cell dimensions a = 15.252(17) A, b = 14.682(10) A, c = 13.606(13) A, and beta = 111.2(1) degrees and a = 15.278(35) A, b = 14.665(21) A, c = 13.603(27) A, and beta = 111.1(1) degrees , respectively. The EPR spectra of all the solid complexes at room temperature consisted of fine-structure transitions (DeltaM(s) = 1) with zero-field splitting (ZFS) of 0.0500 cm(-1) and a half-field signal (DeltaM(s) = 2) at ca. 1600 G, suggesting the formation of binuclear complexes (S = 1). From the observed ZFS, we estimated the average Cu-Cu distance. From the temperature dependence of the EPR signal intensity, we evaluated the isotropic exchange interaction constant J. It appears that the exchange interaction between the two interacting spins of the binuclear complexes is ferromagnetic in nature. The formation of ferromagnetically coupled copper binuclear complexes was further confirmed from the high magnetic-moment values at room temperature. When the EPR spectra were recorded in the temperature range 300-400 K, it was observed that the triplet-state EPR signal completely and irreversibly disappeared at ca. 380 K with the appearance of a new signal attributable to the mononuclear complex (S = 1/2). Thermal studies of these complexes in this temperature range suggested the loss of two water molecules, which might be responsible for binding two mononuclear species. EPR, IR, and thermal studies indicate a long-range ferromagnetic exchange mediated through hydrogen bonding between copper(II) ions (S = 1/2).     

Binuclear copper(II) complexes with N4O3 coordinating heptadentate ligand: synthesis, structure, magnetic properties, density-functional theory study, and catecholase activity

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1).     

ESR, zero-field splitting, and magnetic exchange of exchange-coupled copper(II)-copper(II) pairs in copper(II) tetraphenylporphyrin N-oxide

The crystal structures of the dimer form of copper(II) tetraphenylporphyrin N-oxide, [Cu(tpp-N-O)]2 (3-dimer), and zinc(II) tetraphenylporphyrin N-oxide, [Zn(tpp-N-O)]2 (4-dimer), were established. The geometry at the copper ion in 3-dimer is essentially square-pyramidal with one oxygen bridge [O(1A)] occupying the apical site, giving a much larger Cu-O bond distance compared to those at the basal plane. The respective Cu...Cu distance and Cu-O-Cu angle in the core of 3-dimer are 3.987(4) A and 148.1(3) degrees. The Zn(1) atom in 4-dimer has a distorted square-pyramidal [4 + 1] coordination geometry that gives a tau-value of 0.19. The respective Zn...Zn distance and Zn-O-Zn angle in the dimeric unit of 4-dimer are 4.025(3) A and 148.1(2) degrees. The 3-dimer displays axial X-band electron paramagnetic resonance spectral features (Es = 0) in the powder state at 4 K, giving g parallel = 2.51 (A(parallel,s) = (9.6 +/- 0.2) x 10-3 cm(-1)) and g(perpendicular) = 2.11 and in the same powder state at 293 K giving Ds = 0.0731 cm(-1) (as derived from DeltaMs = 1 lines) or 0.0743 cm(-1) (as derived from the DeltaMs = 2 lines). In addition, 3-dimer displays a DeltaMs = 2 transition at g = 4.17 indicating the presence of spin-exchange coupling. The anisotropic exchange interaction (Ds(ex)= 0.132 cm(-1)) gives the main contribution to Ds in 3-dimer. The theoretical fit of the susceptibility and effective magnetic moment data of 3-dimer in the temperature range of 5-300 K gives 2J = 68 cm(-1), g = 2.01, p = 0.06, and a temperature-independent paramagnetism of 10(-6) cm3 mol(-1). This magnetic susceptibility data indicates that the copper(II) ions in 3-dimer are coupled in a ferromagnetic manner with the ground-spin triplet stabilized by 68 cm(-1) with regard to the singlet.     

Mono-, di- and trinuclear 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes: syntheses, crystal structures and magnetic properties

Three new copper(ii) complexes of formula [Cu(tppz)(NCO)(2)].0.4H(2)O (1), [Cu(2)(tppz)Br(4)](2) and [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)].7H(2)O (3)[tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; C(5)O(5)(2-) = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione] have been synthesised and structurally characterized by X-ray diffraction methods. The structure of complex is made up of neutral [Cu(tppz)(NCO)(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper distance of 3.9244(4) angstroms. The structure of complex 1 consists of neutral tppz-bridged [Cu(2)(tppz)Br(4)] dinuclear units, the copper-copper separation across tppz being 6.6198(1) angstroms. The dinuclear units are further connected through weak, double out-of-plane Cu-Br...Cu bridges [Br(1)...Cu(1a) 4.0028(17) angstroms] creating tetranuclear entities, the copper-copper separation through this interaction being 4.3299(21) angstroms. The structure of complex 3 is built of neutral [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)] trinuclear units and uncoordinated water molecules. Tppz and one of the croconate groups act as bridging ligands, the former exhibiting the bis-terdentate coordination mode and the latter adopting an unusual asymmetrical bis-bidentate bridging mode through three adjacent oxygen atoms. The other two croconate groups exhibit the bidentate coordination mode. The intramolecular copper-copper separations are 6.5417(9)(across tppz) and 4.3234(9) angstroms (through bis-bidentate croconato). The magnetic properties of 2 and 3 have been investigated in the temperature range 1.9-300 K. The magnetic behaviour of complex 2 is that of an antiferromagnetically coupled copper(II) dimer (J = -40.9 cm(-1), the Hamiltonian being H = -JS(A).S(B)). In the case of compound , the chi(M) T vs. T plot is typical of an overall antiferromagnetic coupling with a low-lying spin doublet being fully populated at T < 10 K. The values of the intramolecular antiferromagnetic interactions in 3 are -19.9 (across tppz) and -32.9 cm(-1)(through bridging croconato). Density functional type calculations were performed on model dinuclear fragments of 3 in order to analyze the efficiency of the exchange pathways involved and also to substantiate the coupling parameters.     

EPR of Cu(II)-doped seven-coordinate inclusion compounds, M(stpy)3(NO3)2 x 1/2stpy (M = Cd(II) and Zn(II), stpy = trans-4-styrylpyridine): low symmetry effects in admixture of ground states

Single crystal EPR of Cu(II)-doped low symmetry pentagonal bipyramidal Werner-type clathrate inclusion complexes of Cd(stpy)3(NO3)2 x 1/2stpy(1) and Zn(stpy)3(NO3)2 x 1/2stpy(2) (stpy = trans-4-styrylpyridine) is reported. The spin Hamiltonian parameters are found to be orthorhombic with g33 = 2.298, g22 = 2.108, g11 = 2.066, A33 = 107.3, A22 = 54.4 and A11 = 23.1 x 10(-4) cm(-1) for 1 and g33 = 2.292, g22 = 2.111, g11 = 2.067, A33 = 107.5, A22 = 54.7 and A11 = 22.9 x 10(-4) cm(-1) for 2. Angular variation studies for both 1 and 2 suggest that the Cu(II) ions are substitutionally incorporated in the host lattices. The magnitude of Cu(II) hyperfine coupling constant (A33) in both 1 and 2 are found to be low, in comparison to those of the pure Cu(II) complex, indicative of low symmetry for the substitutional sites in accordance with the crystal data. Such large reductions in Cu(II) hyperfine coupling are explicable in terms of a mixed d(x2 - y2)/dz2 ground state and delocalization of unpaired spin density onto the ligands.     

Covalent linkage of the type-2 and type-3 structural mimics to model the active site structure of multicopper oxidases: synthesis and magneto- structural properties of two angular trinuclear copper(II) complexes

Two new angular trinuclear copper(II) complexes of formulation [Cu(3)(HL)LL'](ClO(4)), where L' is imidazole (Him, 1) or 1-methylimidazole (1-MeIm, 2) and H(3)L is a Schiff base obtained from the condensation of salicylaldehyde and 1,3-diaminopropan-2-ol (2:1 mole ratio), are prepared from a reaction of [Cu(2)L(mu-Br)] and [Cu(HL)] in the presence of L' and isolated as perchlorate salts. The crystal structures of 1 and 2 consist of a trinuclear copper(II) unit formed by the covalent linkage of monomeric type-2 mimic and dimeric type-3 mimic precursor complexes to give an angular arrangement of the metal atoms in the core which is a model for the active site structure of blue multicopper oxidases. In 1 and 2, the coordination geometry of two terminal copper atoms is distorted square-planar. The central copper has a distorted square-pyramidal (4 + 1) geometry. The mean Cu...Cu distance is approximately 3.3 A. The complex has a diphenoxo-bridged dicopper(II) unit with the phenoxo oxygen atoms showing a planar geometry. In addition, the complex has an endogenous alkoxo-bridged dicopper(II) unit showing a pyramidal geometry for the oxygen atom. The 1:1 electrolytic complexes show a d-d band at 607 nm. Cyclic voltammetry of the complexes in MeCN containing 0.1 M TBAP using a glassy carbon working electrode displays a Cu(3)(II)/Cu(2)(II)Cu(I) couple near -1.0 V (vs SCE). The variable temperature magnetic susceptibility measurements in the range 300-18 K show antiferromagnetic coupling in the complexes giving magnetic moments of approximately 3.0 mu(B) at 300 K and approximately 2.1 mu(B) at 18 K for the tricopper(II) unit. The experimental susceptibility data are theoretically fitted using a model with Heisenberg spin-(1)/(2) Hamiltonian for a trimer of spin-(1)/(2) copper(II) ions having two exchange parameters involving the alkoxo-bridged dicopper(II) (J1) and the diphenoxo-bridged dicopper(II) (J2) units, giving J1 and J2 values of -82.7, -73 cm(-1) for 1 and -98.3, -46.1 cm(-1) for 2, respectively. The structural features indicate a higher magnitude of anitiferromagnetic coupling in the alkoxo-bridged unit based on the greater value of the Cu-O-Cu angle in comparison to the diphenoxo-bridged unit. The core structures of 1 and 2 compare well with the first generation model complexes for the active site structure of multicopper oxidases in the oxidized form. The crystal structure of 1 exhibits a lamellar structure with a gap of approximately 7 A containing water molecules in the interlamellar space. Complex 2 forms a hexanuclear species due to intermolecular hydrogen bonding interactions involving two trimeric units. The crystal packing diagram of 2 displays formation of a three-dimensional framework with cavities containing the perchlorate anions.     

Synthesis, X-ray crystal structures, magnetism, and phosphate ester cleavage properties of copper(II) complexes of N-substituted derivatives of 1,4,7-triazacyclononane

Two new N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle, 1-benzyl-4,7-dimethyl-1,4,7-triazacyclononane (L2) and 1,4,7-tris(3-cyanobenzyl)-1,4,7-triazacyclononane (L3), have been prepared and, together with 1,4-dimethyl-1,4,7-triazacyclononane (L1), have been used to synthesize the corresponding hydroxo-bridged binuclear copper (II) complexes, [Cu2(mu-OH)2L2](ClO4)2.xH2O (1 L = L1, x = 0; 2 L = L2, x = 1; 3 L = L3, x = 2). The X-ray crystal structures of all three complexes reveal the presence of [Cu2(mu-OH)2]2+ cores capped by pairs of facially coordinating tacn ligands so that the Cu(II) centers reside in distorted square pyramidal coordination environments. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -36.4 cm(-1)) between the Cu(II) centers in 1, while the centers in 2 and 3 have been shown to interact ferromagnetically (J = 11.2 and 49.3 cm(-1), respectively). The variation in the strength and sign of these interactions has been rationalized in terms of the differing geometries of the [Cu2(mu-OH)2]2+ cores. The ability of the Cu(II) complexes to cleave phosphate ester bonds has been probed using the model phosphate ester bis(4-nitrophenyl)phosphate (BNPP) at pH 7.4 and a temperature of 50 degrees C. The measured rate constant for 3 (3 x 10(-4) s(-1)) is significantly greater than those previously reported for the Cu(II) complexes of the fully alkylated tacn ligands, Me3tacn and iPr3tacn, which until now have been rated as the most effective tacn-based phosphate ester cleavage agents.     

Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "roof-shaped" Cu2X2 dimers with hydroxide, methoxide, and azide bridges

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.     

Functional superoxide dismutase mimics. Structural characterization and magnetic exchange interactions of copper(II)-N-substituted sulfonamide dimer complexes

Dinuclear copper(II) complexes with N-substituted sulfonamide ligands as superoxide dismutase (SOD) mimics have been investigated. The new N-(thiazol-2-yl)toluenesulfonamide (Htz-tol) and N-(thiazol-2-yl)naphthalenesulfonamide (Htz-naf) ligands have been prepared and structurally characterized. The complexes derived from these ligands, [Cu(2)(tz-tol)(4)] (1) and [Cu(2)(tz-naf)(4)] (2), have been synthesized, and their crystal structure, magnetic properties, and EPR spectra were studied in detail. In both compounds the metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the coppers in the dinuclear entity of 1 and 2 is distorted square planar with two N-thiazole and two N-sulfonamido atoms. Magnetic susceptibility data show a strong antiferromagnetic coupling, with -2J = 121.3 cm(-1) for compound 1 and -2J = 104.3 cm(-1) for compound 2. The EPR spectra of the polycrystalline samples of compounds 1 and 2 have been measured at the X- and Q-band frequencies at different temperatures. Above 20 K the spectra are characteristic of S = 1 species with zero-field splitting parameter D = 0.230 cm(-1) for compound 1 and 0.229 cm(-1) for compound 2. The EPR parameters are discussed in terms of the known binuclear structures. The complexes exhibit high SOD activity, as shown by the low IC(50) values obtained with the xanthine/xanthine oxidase/NBT assay: 0.13 microM for compound 1; 0.17 microM for compound 2.     

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.