Paramagnetic properties of the halide-bound derivatives of oxidised tyrosinase investigated by 1H NMR spectroscopy

The (1)H NMR relaxation characteristics of the histidines in the oxidised type-3 copper site of tyrosinase (Ty(met)) from the bacterium Streptomyces antibioticus in the halide-bound forms (Ty(met)X with X = F(-), Cl(-), Br(-)) have been determined and analysed. The (1)H NMR spectra of the Ty(met)X species display remarkably sharp, well-resolved, paramagnetically shifted (1)H signals, which originate from the protons of the six His residues coordinated to the two Cu(II) ions in the type-3 centre. From the temperature-dependence of the (1)H paramagnetic shifts the following values for the exchange-coupling parameter -2J were determined: 260 (Ty(met)F), 200 (Ty(met)Cl) and 162 cm(-1) (Ty(met)Br). The (1)H T(1) relaxation is dipolar in origin and correlates with the Cu--H distances. Electronic relaxation times tau(S) derived from the (1)H T(1) data amount to about 10(-11) s and follow the order Ty(met)F>Ty(met)Cl>Ty(met)Br. They are two orders of magnitude shorter than the tau(S) values reported for mononuclear copper systems, in accordance with the sharpness of the (1)H signals. The results corroborate the Cu(2) bridging mode of the halide ions. On the basis of the measured hyperfine interaction constants for the ligand histidine nuclei, it is concluded that 70-80 % of the spin density in the excited triplet state resides on the two copper ions and the bridging atoms.     

Syntheses, crystal structures, and properties of six new lanthanide(III) transition metal tellurium(IV) oxyhalides with three types of structures

Solid-state reactions of lanthanide(III) oxide (and lanthanide(III) oxyhalide), transition metal halide (and transition metal oxide), and TeO(2) at high temperature lead to six new lanthanide transition metal tellurium(IV) oxyhalides with three different types of structures, namely, DyCuTe(2)O(6)Cl, ErCuTe(2)O(6)Cl, ErCuTe(2)O(6)Br, Sm(2)Mn(Te(5)O(13))Cl(2), Dy(2)Cu(Te(5)O(13))Br(2), and Nd(4)Cu(TeO(3))(5)Cl(3). Compounds DyCuTe(2)O(6)Cl, ErCuTe(2)O(6)Cl, and ErCuTe(2)O(6)Br are isostructural. The lanthanide(III) ion is eight-coordinated by eight oxygen atoms, and the copper(II) ion is five-coordinated by four oxygens and a halide anion in a distorted square pyramidal geometry. The interconnection of Ln(III) and Cu(II) ions by bridging tellurite anions results in a three-dimensional (3D) network with tunnels along the a-axis; the halide anion and the lone-pair electrons of the tellurium(IV) ions are oriented toward the cavities of the tunnels. Compounds Sm(2)Mn(Te(5)O(13))Cl(2) and Dy(2)Cu(Te(5)O(13))Br(2) are isostructural. The lanthanide(III) ions are eight-coordinated by eight oxygens, and the divalent transition metal ion is octahedrally coordinated by six oxygens. Two types of polymeric tellurium(IV) oxide anions are formed: Te(3)O(8)(4)(-) and Te(4)O(10)(4)(-). The interconnection of the lanthanide(III) and divalent transition metal ions by the above two types of polymeric tellurium(IV) oxide anions leads to a 3D network with long, narrow-shaped tunnels along the b-axis. The halide anions remain isolated and are located at the above tunnels. Nd(4)Cu(TeO(3))(5)Cl(3) features a different structure. All five of the Nd(III) ions are eight-coordinated (NdO(8) for Nd(1), Nd(2), Nd(4), and Nd(5) and NdO(7)Cl for Nd(3)), and the copper(I) ion is tetrahedrally coordinated by four chloride anions. The interconnection of Nd(III) ions by bridging tellurite anions resulted in a 3D network with large tunnels along the b-axis. The CuCl(4) tetrahedra are interconnected into a 1D two-unit repeating (zweier) chain via corner-sharing. These 1D copper(I) chloride chains are inserted into the tunnels of the neodymium(III) tellurite via Nd-Cl-Cu bridges. Luminescent studies show that ErCuTe(2)O(6)Cl and Nd(4)Cu(TeO(3))(5)Cl(3) exhibit strong luminescence in the near-IR region. Magnetic measurements indicate the antiferromagnetic interactions between magnetic centers in these compounds.     

Solution behavior and structural properties of Cu(I) complexes featuring m-terphenyl isocyanides

The synthesis of the m-terphenyl isocyanide ligand CNAr (Mes2) (Mes = 2,4,6-Me 3C 6H 2) is described. Isocyanide CNAr (Mes2) readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNAr (Mes2) and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (mu-X) 2[Cu(THF)(CNAr (Mes2))] 2. Addition of CNAr (Mes2) to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNAr (Mes2)) 2 in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNAr (Mes2)) 2 to exist as a three-coordinate monomer in the solid state. As determined by solution (1)H NMR and FTIR spectroscopic studies, monomer ClCu(CNAr (Mes2)) 2 resists tight binding of a third CNAr (Mes2) unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNAr (Mes2) to cuprous iodide readily affords the tris-isocyanide species, ICu(CNAr (Mes2)) 3, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNAr (Mes2)) 3]OTf (OTf = O 3SCF 3), which is generated upon treatment of (C 6H 6)[Cu(OTf)] 2 with 6 equiv of CNAr (Mes2) in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [CuI] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNAr (Mes2)) 3]OTf itself serves as a good Lewis acid and is found to weakly bind C 6H 6 in an eta (1)- C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the eta (1)- C Cu-C 6H 6 interaction.     

Copper(I) coordination polymers [{Cu(mu-X)}2{RP(mu-NtBu)}2]n (R = OC6H4OMe-o; X = Cl, Br, and I) and their reversible conversion into mononuclear complexes [CuX{(RP(mu-NtBu)2}2]: synthesis and structural characterization

The reactions of cyclodiphosphazane cis-[tBuNP(OC6H4OMe-o)]2 (1) with 2 equiv of CuX in acetonitrile afforded one-dimensional Cu(I) coordination polymers [Cu2X2{tBuNP(OC6H4OMe-o)}2]n (2, X = Cl; 3, X = Br; 4, X = I). The crystal structures of 2 and 4 reveal a zigzag arrangement of [P(mu-N)(2)P] and [Cu(mu-X)(2)Cu] units in an alternating manner to form one-dimensional Cu(I) coordination polymers. The reaction between 1 and CuX in a 2:1 ratio afforded mononuclear tricoordinated copper(I) complexes of the type [CuX{(tBuNP(OC6H4OMe-o))2}2] (5, X = Cl; 6, X = Br; 7, X = I). The single-crystal structures were established for the mononuclear copper(I) complexes 5 and 6. When the reactant ratios are 1:1, the formation of a mixture of polymeric and mononuclear products was observed. The Cu(I) polymers (2-4) were converted into the mononuclear complexes (5-7) by reacting with 3 equiv of 1 in dimethyl sulfoxide. Similarly, the mononuclear complexes (5-7) were converted into the corresponding polymeric complexes (2-4) by reacting with 3 equiv of copper(I) halide under mild reaction conditions.     

Copper(II) carboxylate dimers prepared from ligands designed to form a robust π···π stacking synthon: supramolecular structures and molecular properties

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido)propanoate, (L(C2)(-)), (1,8-naphthalimido)ethanoate, (L(C1)(-)), and (1,8-naphthalimido)benzoate, (L(C4)(-)) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu(2)(L(C2))(4)(MeOH)(2)] (1), [Cu(2)(L(C1))(4)(MeOH)(2)]·2(CH(2)Cl(2)) (2), [Cu(2)(L(C4))(4)(EtOH)(2)]·2(CH(2)Cl(2)) (3) complexes. When the reaction of L(C1)(-) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) was carried out at -20 °C in the presence of pyridine, [Cu(2)(L(C1))(4)(py)(4)]·2(CH(2)Cl(2)) (4) was produced. At the core of complexes 1-3 lies the square Cu(2)(O(2)CR)(4) "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites. Complex 4 contains a different type of dimeric core generated by two κ(1)-bridging carboxylate ligands. Additionally, two terminal carboxylates and four trans situated pyridine molecules complete the coordination environment of the five-coordinate copper(II) centers. In all four compounds, robust π···π stacking interactions of the naphthalimide rings organize the dimeric units into two-dimensional sheets. These two-dimensional networks are organized into a three-dimensional architecture by two different noncovalent interactions: strong π···π stacking of the naphthalimide rings (also the pyridine rings for 4) in 1, 3, and 4, and intermolecular hydrogen bonding of the coordinated methanol or ethanol molecules in 1-3. Magnetic measurements show that the copper ions in the paddlewheel complexes 1-3 are strongly antiferromagnetically coupled with -J values ranging from 255 to 325 cm(-1), whereas the copper ions in 4 are only weakly antiferromagnetically coupled. Typical values of the zero-field splitting parameter D were found from EPR studies of 1-3and the related known complexes [Cu(2)(L(C2))(4)(py)(2)]·2(CH(2)Cl(2))·(CH(3)OH), [Cu(2)(L(C3))(4)(py)(2)]·2(CH(2)Cl(2)) and [Cu(2)(L(C3))(4)(bipy)]·(CH(3)OH)(2)·(CH(2)Cl(2))(3.37) (L(C3)(-) = (1,8-naphthalimido)butanoate)), while its abnormal magnitude in [Cu(2)(L(C2))(4)(bipy)] was qualitatively rationalized by structural analysis and DFT calculations.     

Synthesis, structure, and electrochemical properties of copper(I) complexes with S/N homoscorpionate and heteroscorpionate ligands

Dinuclear Cu(I) complexes with bifunctionalized homoscorpionate ligands, hydrotris(thioxotriazolyl)borato [Li(Tr(Me,o)(-)(Py)) (1) and Li(Tr(Mes,Me)) (2)], and the heteroscorpionate ligand hydro[bis(thioxotriazolyl)-3-(2-pyridyl)pyrazolyl]borato [K(Br(Mes)pz(o)(-)(Py))] (3) were synthesized and crystallographically characterized. The complexes [Cu(Tr(Mes,Me))](2) (4) and [Cu(Tr(Me,o)(-)(Py))](2) (5) exhibit a similar coordination geometry where every metal is surrounded by three thioxo groups in a trigonal arrangement. The presence of a [B-H...Cu] three-center-two-electron interaction in both compounds causes the overall coordination to become tetrahedrally distorted (S(3)H coordination for each metal). The complex [Cu(Br(Mes)pz(o)(-)(Py))](2) (6) presents a trigonal geometry in which the metals interact with two thioxo groups and a bridging pyrazolyl nitrogen atom. A weak contact with a pyridine nitrogen atom completes the coordination of the metals (S(2)N,N' coordination for each metal). [Cu(Tr(Mes,Me))](2), [Cu(Tr(Me,o)(-)(Py))](2), and [Cu(Br(Mes)pz(o)(-)(Py))](2) exhibit fluxional behavior in solution as evidenced by variable-temperature NMR spectroscopy, and for 5 and 6 two species in equilibrium [in the ratio 2/1 for 5 (CDCl(3)) and 3/2 for 6 (CD(2)Cl(2))] are distinguishable in the (1)H NMR spectra at 270 K. 2D-NOESY spectra recorded at 270 K assisted in the attribution of solution molecular geometries for each isomer of 5 and 6. The free energy of activation (DeltaG()(Tc)) was determined for both equilibria from the evaluation of the coalescence temperature. DFT calculations were performed to describe plausible molecular geometry for the minor isomer of 5 and 6 and to propose a possible mechanism of interconversion between major and minor isomers. Cyclic voltammograms were recorded in CH(2)Cl(2) (3 and 6) or CH(2)Cl(2)/CH(3)CN (1/1, v/v) (2, 4, and 5) solutions using 0.1 M TBAHFP or TBAOTf as supporting electrolytes. [Cu(Tr(Mes,Me))](2), [Cu(Tr(Me,o)(-)(Py))](2), and [Cu(Br(Mes)pz(o)(-)(Py))](2) exhibit a quasi-reversible Cu(I)/Cu(II) redox behavior with E(pa) = +719 mV and E(pc) = +538 mV for 4, E(pa) = +636 mV and E(pc) = -316 mV for 5, and E(pa) = +418 mV and E(pc) = -319 mV for 6.     

Synthesis, characterization, and DFT studies of thione and selone Cu(I) complexes with variable coordination geometries

Coordination of Cu(I) halides with N,N'-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu(4)(μ-dmise)(4)(μ-X)(2)X(2) copper complexes with average Cu-Se bond lengths of 2.42 ? and a Cu(2)(μ-X)(2) core (X = I (1) or Br (6)) that's in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)(2)X (3a, 3b, 4, and 7) or Cu(dmise)(2)X (2, 5, and 8) with average Cu-S and Cu-Se bond lengths of 2.23 ? and 2.34 ?, respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular π-π interactions, and short contact interactions between X-H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV.     

Three-coordinate [Cu(II)X(3)](-) (X=Cl, Br), trapped in a molecular crystal

Mixtures of [Ph(3)PNPPh(3)](+)Cl(-) with CuBr(2) (or CuBr(2)+CuCl(2)) in ethanol/dichloromethane yield crystals containing three-coordinate copper(II) with mixed chloride and bromide ligands, namely [Ph(3)PNPPh(3)](+)[CuCl(0.9)Br(2.1)](-) (1) and [Ph(3)PNPPh(3)](+)[CuCl(2.4)Br(0.6)](-) (2). The trigonal-planar coordination of copper(II) is angularly distorted but unambiguous, as there is no other halide ligand within 6.7 A of the copper atom. Density functional theory (DFT) calculations on planar [CuClBr(2)](-) show that the energy surface for angle bending is very soft. Crystallisation in the presence of CH(3)CN yields [Ph(3)PNPPh(3)](+)[CuCl(0.7)Br(2.3)(NCCH(3))](-) (3), in which there is additional secondary coordination by NCCH(3) (Cu-N 2.44 A). DFT calculations of the potential energy surface for this secondary coordination show that it is remarkably flat (<3 kcal mol(-1) for a variation of Cu-N by 0.8 A). The crystal packing in 1, 2 and 3, which involves multiple phenyl embraces between [Ph(3)PNPPh(3)](+) ions and numerous C-H...Cl and C-H...Br motifs, is associated with intermolecular energies that are larger than the variations in intramolecular energies. For reference, the crystal structures of [Ph(3)PNPPh(3)(+)](2)[Cu(2)Cl(6)](2-) (4) and [Ph(3)PNPPh(3)(+)](2)[Cu(2)Br(6)](2-) (5) are described. We conclude 1) that three-coordinate copper(II) with monatomic halide ligands, although uncommon, can be regarded as normal, 2) that steric control by ligands is not necessary to enforce three-coordination, 3) that a hydrophobic aryl environment stabilises [Cu(Cl/Br)(3)](-), and 4) that the energy change in the transition from three- to four-coordinate copper(II) is very small (ca 5 kcal mol(-1)).     

Structure of Dicopper Complexes of N,N,N',N'-Tetrakis[(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane with Coordinated Thiocyanate Counterions

The structures of five dicopper complexes of binucleating ligand HL-H (N,N,N',N'-tetrakis[(2-benzimidazolyl)methyl]-2-hydroxy-1,3-diaminopropane) with thiocyanate and some other counterions were investigated by the X-ray diffraction method. In Cu(2)(HL-H)(NCS)(2)Cl(2).6H(2)O.CH(3)OH, 1 (a = 12.524(5) ?, b = 14.429(4) ?, c = 16.343(3) ?, alpha = 109.01(2) degrees, beta = 92.62(2) degrees, gamma = 115.27(3) degrees, Z = 2, triclinic, P&onemacr;), one chloride is not coordinated. Distorted square pyramidal (SP) geometry is found for both CuN(3)ClN and CuN(3)ON coordination sites in which the N(3) tripodal coordination sites come from the two symmetric halves of HL-H and the other nitrogen atoms come from thiocyanate ions. In Cu(2)(HL-H)(NCS)(2)(ClO(4))(2).6H(2)O.2EtOH, 2 (a = 10.955(2) ?, b = 15.366(5) ?, c = 18.465(9) ?, alpha = 65.57(4) degrees, beta = 89.73(3) degrees, gamma = 79.81(2) degrees, Z = 2, triclinic, P&onemacr;), the coordination environments for the two copper ions are both CuN(3)ON. However, their geometries are different: one is distorted SP and the other is distorted trigonal bipyramid (TBP). In Cu(2)(HL-H)(NCS)(2)(ClO(4))(2)Cl.H(3)O.3.5H(2)O, 3 (a = 11.986(6) ?, b = 12.778(5) ?, c = 17.81(1) ?, alpha = 82.41(4) degrees, beta = 75.44(5) degrees, gamma = 78.46(4) degrees, Z = 2, triclinic, P&onemacr;), the chloride ion does not coordinate to copper ion, but it is hydrogen bonded to the hydroxy hydrogen. The coordination environments for the two copper ions are both CuN(3)ON with distorted SP geometries. In Cu(2)(HL-H)(NCS)Cl(3).6H(2)O, 4 (a = 12.026(5) ?, b = 14.369(6) ?, c = 16.430(6) ?, alpha = 111.64(3) degrees, beta = 90.51(4) degrees, gamma = 113.90(3) degrees, Z = 2, triclinic, P&onemacr;), one chloride does not coordinate. The coordination environments for the two copper ions are CuN(3)ON in severely distorted TBP geometry and CuN(3)Cl(2) in SP geometry. In Cu(2)(HL-H)(NCS)(3)OH.2H(2)O.3CH(3)OH.Et(2)O, 5 (a = 18.322(5) ?, b = 15.543(6) ?, c = 19.428(7) ?, beta = 102.78(3) degrees, Z = 4, monoclinic, P2(1)/c), the hydroxide ion does not coordinate. The coordination environments for the two copper ions are CuN(3)N(2) with a geometry inbetween SP and TBP but slightly closer to SP and CuN(3)ON in distorted SP geometry. The distances between the copper ions are in the range 4.45-7.99 ?, indicating negligible interaction between the copper ions. The hydroxy groups of HL-H in 1-5all coordinate to copper ions either in a terminal mode (in complexes 1, 4, and 5, denoted as OHR(t)) or in a bridging mode (in complexes 2 and 3, denoted as OHR(b)). These hydroxy groups do not lose their protons in all cases. All thiocyanate anions coordinate to copper ions through nitrogen atoms. All copper ions in 1-5 are pentacoordinated. The fact that the CuN(3) geometries of the tripodal coordination sites in HL-H do not allow the formation of a square planar complex, may be the driving force for the formation of pentacoordinated complexes. From the structurally known dicopper complexes of the HL-H type ligands, the relative coordinating abilities of ligands to CuN(3) are OHR(t) > NCS(-) > Cl(-)(t) > OHR(b) approximately Cl(-)(b), where the letters b and t in parentheses denote bridging and terminal coordination modes respectively.     

Cu(H4C3N2S)Cl2](n), an unprecedented diazole-bridged one-dimensional copper halide: synthesis,structure, and magnetic properties

The simultaneous desulfurization of 2-mercapto-5-methyl-1,3,4-thiadiazole with CuCl(2) x 2H(2)O via mutual diffusion in solvents results in the isolation of air-stable dark-green crystals of [Cu(H(4)C(3)N(2)S)Cl(2)](n) (approximately 65% yield). The structure is characterized by a unique one-dimensional copper chain bridged by diazine N-N single bonds rather than halogens, in sharp contrast with the halide bridging mode in conventional copper halide coordination polymers. Each Cu(II) ion shows a square planar coordination geometry featuring a strong Jahn-Teller distortion, as also supported by EPR data. The phase follows a Curie-Weiss paramagnetic behavior over 6-300 K. However, the intrachain antiferromagnetic interaction is evident (-2J = 21.1 cm(-1)). Such magnetic coupling is related to the interplay between the Cu(II)-d(x2-y2) and diazine N-N p-orbitals.     

Mononuclear-dinuclear equilibrium of grafted copper complexes confined in the nanochannels of MCM-41 silica

Following the structural concept of copper-containing proteins in which dinuclear copper centers are connected by hydroxide bridging ligands, a bidentate copper(II) complex has been incorporated into nano-confined MCM-41 silica by a multistep sequential grafting technique. Characterization by a combination of EPR spectroscopy, X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, IR spectroscopy , and solid-state (13)C and (29)Si cross-polarization magic-angle spinning (CP-MAS) NMR suggests that dinuclear Cu complexes are bridged by hydroxide and other counterions (chloride or perchlorate ions), similar to the situation for EPR-undetectable [Cu(II)···Cu(II)] dimer analogues in biological systems. More importantly, a dynamic mononuclear-dinuclear equilibrium between different coordination modes of copper is observed, which strongly depends on the nature of the counterions (Cl(-) or ClO(4)(-)) in the copper precursor and the pore size of the silica matrix (the so-called confinement effect). A proton-transfer mechanism within the hydrogen-bonding network is suggested to explain the dynamic nature of the dinuclear copper complex supported on the MCM-41 silica.     

A complete series of copper(II) halide complexes (X = F, Cl, Br, I) with a novel Cu(II)-C(sp3) bond

A complete series of copper(ii) halide complexes [CuX(tptm)](X = F (), Cl (), Br (), I (); tptm = tris(2-pyridylthio)methyl) with a novel Cu(II)-C(sp(3)) bond has been prepared by the reactions of [Cu(tptm)(CH(3)CN)]PF(6)(.PF(6)) with corresponding halide sources of KF or n-Bu(4)NX (X = Cl, Br, I), and the trigonal bipyramidal structures have been confirmed by X-ray crystallography and/or EPR spectroscopy. The iodide complex easily liberates the iodide anion in acetonitrile forming the acetonitrile complex as a result. The EPR spectra of the complexes showed several superhyperfine structures that strongly indicated the presence of spin density on the halide ligands through the Cu-X bond. The results of DFT calculations essentially matched with the X-ray crystallographic and the EPR spectroscopic results. Cyclic voltammetry revealed a quasi-reversible reduction wave for Cu(II)/Cu(I) indicating a trigonal pyramidal coordination for Cu(I) states. A coincidence of the redox potential for all [CuX(tptm)](0/+) processes indicates that the main oxidation site in each complex is the tptm ligand.     

The coordination chemistry of selenophosphite ligands. Synthesis and characterization of heterometallic tetranuclear clusters [M{CpFe(CO)(2)P(Se)(OR)(2)}(3)](PF(6)) (M = Cu, Ag; R = (n)Pr, (i)Pr) and [Cu(mu-X) {CpFe(CO)(2)P(Se)(O(i)Pr)(2)}](2) (X = Cl, Br)

A neutral selenium donor ligand, [CpFe(CO)(2)P(Se)(OR)(2)] is used for the construction of Cu(I) and Ag(I) complexes with a well-defined coordination environment. Four clusters [M{CpFe(CO)(2)P(Se)(OR)(2)}(3)](PF(6)), (where M = Cu, R = (n)Pr, ; R = (i)Pr, and M = Ag, R = (n)Pr, ; R = (i)Pr, ) are isolated from the reaction of [M(CH(3)CN)(4)(PF(6))] (where M = Cu or Ag) and [CpFe(CO)(2)P(Se)(OR)(2)] in a molar ratio of 1 : 3 in acetonitrile at 0 degrees C. The reaction of [CpFe(CO)(2)P(Se)(O(i)Pr)(2)] with cuprous halides in acetone produce two mixed-metal, Cu(I)(2)Fe(II)(2) clusters, [Cu(mu-X) {CpFe(CO)(2)P(Se)(O(i)Pr)(2)}](2) (X = Cl, ; Br, ). All six clusters have been fully characterized spectroscopically ((1)H, (13)C, (31)P, and (77)Se NMR, IR), and by elemental analyses. X-Ray crystal structures of and consist of discrete cationic clusters in which three iron-selenophosphito fragments are linked to the central copper or silver atom via selenium atoms. Both clusters and crystallize in the noncentrosymmetric, hexagonal space group P6[combining macron]2c. The coordination geometry around the copper or silver atom is perfect trigonal-planar with Cu-Se and Ag-Se distances, 2.3505(7) and 2.5581(7) A, respectively. X-Ray crystallography also reveals that each copper center in neutral heterometallic clusters and is trigonally coordinated to two halide ions and a selenium atom from the selenophosphito-iron moiety. The structures can also be delineated as a dimeric unit which is generated by an inversion center and has a Cu(2)X(2) parallelogram core. The dihedral angle between the Cu(2)X(2) plane and the plane composed of Cp ring is found to be 24.62 and 84.58 degrees for compound and , respectively. Hence the faces of two opposite Cp rings are oriented almost perpendicular to the Cu(2)X(2) plane in , but are close to be parallel in . This is the first report of the coordination chemistry of the anionic selenophosphito moiety [(RO)(2)PSe](-), the conjugated base of a secondary phosphine selenide, which acts as a bridging ligand with P-coordination on iron and Se-coordination to copper or silver.     

Anion influence on the structure and magnetic properties of a series of multidimensional pyrimidine-2-carboxylato-bridged copper(II) complexes

Seven new polynuclear copper(II) complexes of formula [Cu(mu-pymca)2] (1) (pymca(-) = pyrimidine-2-carboxylato), [Cu(mu-pymca)Br] (2), [Cu(mu-pymca)Cl] (3), [Cu(mu-pymca)(SCN)(H2O)] x 4 H2O (4), [Cu(mu-pymca)N3] (5), [Cu2(mu1,5-dca)2(pymca)2] (6) (dca = dicyanamide), and K{[mu-Au(CN)2]2[(Cu(NH3)2)2(mu-pymca)]}[Au(CN)2]2 (7) have been synthesized by reactions of K-pymca with copper(II) ions in the presence of different counteranions. Compound 1 is a linear neutral chain with a carboxylato bridging ligand in a syn-anti coordination mode, whereas complexes 2 and 3 consist of cationic linear chains with cis and trans bis(chelating) pymca bridging ligands. Complex 4 adopts a helical pymca-bridged chain structure. In complex 5, zigzag pymca-bridged chains are connected by double end-on azide bridging ligands to afford a unique honeycomb layer structure. Complex 6 is a centrosymmetric dinuclear system with double mu 1,5-dicyanamide bridging ligands and pymca end-cap ligands. Complex 7 is made of pymca-bridged dinuclear [Cu(NH3)2(mu-pymca)Cu(NH3)2](3+) units connected by [Au(CN)2](-) anions to four other dinuclear units, giving rise to cationic (4,4) rectangular nets, which are linked by aurophilic interactions to afford a singular 3D network. Variable-temperature magnetic susceptibility measurements show that complex 1 exhibits a very weak antiferromagnetic coupling through the syn-anti (equatorial-axial) carboxylate bridge (J = -0.57 cm(-1)), whereas complexes 2-4 and 7 exhibit weak to strong antiferromagnetic couplings through the bis(chelating) pymca bridging ligand J = -17.5-276.1 cm(-1)). Quantum Monte Carlo methods have been used to analyze the experimental magnetic data for 5, leading to an antiferromagnetic coupling (J = -34 cm(-1)) through the pymca ligand and to a ferromagnetic coupling (J = 71 cm(-1)) through the azide bridging ligands. Complex 6 exhibits a very weak antiferromagnetic coupling through the dicyanamide bridging ligands (J = -5.1 cm(-1)). The magnitudes of the magnetic couplings in complexes 2-5 have been explained on the basis of the overlapping between magnetic orbitals and DFT theoretical calculations.     

A novel bis tridentate bipyridine carboxamide ligand and its complexation to copper(II): synthesis, structure, and magnetism

A new bis tridentate ligand 2,2'-bipyridine-3,3'-[2-pyridinecarboxamide] H(2)L(1) which can bind transition metal ions has been synthesized via the condensation of 3,3'-diamino-2,2'-bipyridine together with 2-pyridine carbonyl chloride. Two copper(II) coordination compounds have been prepared and characterized: [Cu(2)(L(1))(hfac)(2)].3CH(3)CN.H(2)O (1) and [Cu(2)(L(1))Cl(2)].CH(3)CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic space group P1, with the unit cell parameters a = 12.7185(6) A, b = 17.3792(9) A, c = 19.4696(8) A, alpha = 110.827(2) degrees, beta = 99.890(3) degrees, gamma = 97.966(3) degrees, V = 3868.3(3) A3, Z = 4, R = 0.0321 and R(w) = 0.0826. Complex 2 crystallizes in the monoclinic space group P2(1)/n with the unit cell parameters a = 12.8622(12) A, b = 9.6100(10) A, c = 19.897(2) A, beta = 102.027(3) degrees, V = 2405.3(4) A(3), Z = 4, R = 0.0409 and R(w) = 0.1005. In both complexes the ligand is in the dianionic form and coordinates the divalent Cu(II) ions via one amido and two pyridine nitrogen donor atoms. In 1, the coordination geometry around both Cu(II) ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In 2 both Cu(II )ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu-Cl chloride ion to afford a mu-Cl-bridged dimerized [Cu(2)(L(1))Cl(2)](2) complex. The magnetic susceptibility data for 1 (2 -270 K), reveal the occurrence of weak antiferromagnetic interactions between the Cu(II) ions. In contrast, variable-temperature magnetic susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak antiferromagnetic exchange (J = -10.1 K) between the copper ions in each dinuclear copper complex and a stronger ferromagnetic exchange interaction (J = 32.9 K) between the Cu(II) ions of the Cu(mu-Cl)(2)Cu dimeric bridging units.     

Oxidative double dehalogenation of tetrachlorocatechol by a bio-inspired CuII complex: formation of chloranilic acid

Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1.     

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).     

Halide and Hydroxide Linearly Bridged Bimetallic Copper(II) Complexes: Trends in Strong Antiferromagnetic Superexchange Interactions

Centrosymmetric [Cu(2)(μ-X)(μ-L(m)*)(2)](ClO(4))(3) (X = F(-), Cl(-), Br(-), OH(-), L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene)], the first example of a series of bimetallic copper(II) complexes linked by a linearly bridging mononuclear anion, have been prepared and structurally characterized. Very strong antiferromagnetic exchange coupling between the copper(II) ions increases along the series F(-) < Cl(-) < OH(-) < Br(-), where -J = 340, 720, 808, and 945 cm(-1). DFT calculations explain this trend by an increase in the energy along this series of the antibonding antisymmetric combination of the p orbital of the bridging anion interacting with the copper(II) d(z(2)) orbital.     

Octanuclear and nonanuclear supramolecular copper(II) complexes with linear "tritopic" ligands: structural and magnetic studies

The structures and magnetic properties of self-assembled copper(II) clusters and grids with the "tritopic" ligands 2poap (a), Cl2poap (b), m2poap (c), Cl2pomp (d), and 2pomp (e) are described [ligands derived by reaction of 4-R-2,6-pyridinedicarboxylic hydrazide (R = H, Cl, MeO) with 2-pyridinemethylimidate (a-c, respectively) or 2-acetylpyridine (d, R = Cl; e, R = H)]. Cl2poap and Cl2pomp self-assemble with Cu(NO(3))(2) to form octanuclear "pinwheel" cluster complexes [Cu(8)(Cl2poap-2H)(4)(NO(3))(8)].20H(2)O (1) and [Cu(8)(Cl2pomp-2H)(4)(NO(3))(8)].15H(2)O (2), built on a square [2 x 2] grid with four pendant copper arms, using "mild" reaction conditions. Similar reactions of Cl2pomp and 2pomp with Cu(ClO(4))(2) produce pinwheel clusters [Cu(8)(Cl2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8).7H(2)O (3) and [Cu(8)(2pomp-2H)(4)(H(2)O)(8)](ClO(4))(8) (4), respectively. Heating a solution of 1 in MeOH/H(2)O produces a [3 x 3] nonanuclear square grid complex, [Cu(9)(Cl2poap-H)(3)(Cl2poap-2H)(3)](NO(3))(9).18H(2)O (5), which is also produced by direct reaction of the ligand and metal salt under similar conditions. Reaction of m2poap with Cu(NO(3))(2) produces only the [3 x 3] grid [Cu(9)(m2poap-H)(2)(m2poap-2H)(4)](NO(3))(8).17H(2)O (6) under similar conditions. Mixing the tritopic ligand 2poap with pyridine-2,6-dicarboxylic acid (picd) in the presence of Cu(NO(3))(2) produces a remarkable mixed ligand, nonanuclear grid complex [Cu(9)(2poap-H)(4)(picd-H)(3)(picd-2H)](NO(3))(9).9H(2)O (7), in which aromatic pi-stacking interactions are important in stabilizing the structure. Complexes 1-3 and 5-7 involve single oxygen atom (alkoxide) bridging connections between adjacent copper centers, while complex 4 has an unprecedented mixed micro-(N-N) and micro-O metal ion connectivity. Compound 1 (C(76)H(92)N(44)Cu(8)O(50)Cl(4)) crystallizes in the tetragonal system, space group I, with a = 21.645(1) A, c = 12.950(1) A, and Z = 2. Compound 2 (C(84)H(88)N(36)O(44)Cl(4)Cu(8)) crystallizes in the tetragonal system, space group I, with a = 21.2562(8) A, c = 12.7583(9) A, and Z = 2. Compound 4 (C(84)H(120)N(28)O(66)Cl(8)Cu(8)) crystallizes in the tetragonal system, space group I4(1)/a, with a = 20.7790(4) A, c = 32.561(1) A, and Z = 4. Compound 7(C(104)H(104)N(46)O(56)Cu(9)) crystallizes in the triclinic system, space group P, with a = 15.473(1) A, b = 19.869(2) A, c = 23.083(2) A, alpha = 88.890(2) degrees, beta = 81.511(2) degrees, gamma = 68.607(1) degrees, and Z = 2. All complexes exhibit dominant intramolecular ferromagnetic exchange coupling, resulting from an orthogonal bridging arrangement within each polynuclear structure.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.