Dinuclear CuII Complexes Research Articles

Dinuclear Copper(II) Complexes of Macrocyclic Polyamines: Synthesis, Characterization, and DNA Cleavage

Two macrocyclic polyamine ligands and their dinuclear copper(II) (CuII) complexes were synthesized and characterized. In the complexes, two 1,4,7,10-tetraazacyclododecane (cyclen) moieties were bridged by a dipeptide spacer, and CuII as metal ion was coordinated to the ligands to form the novel complexes. These complexes were characterized by UV/VIS, IR, EPR, and ESI-MS analyses. The catalyzed DNA cleavage and DNA binding properties of these complexes were studied under physiological conditions. The effects of complex concentrations, cleavage time, and temperature on the DNA cleavage reactions were systematically investigated. The results strongly suggested that the plasmid DNA (pUC 19) can be cleaved by the dinuclear CuII complexes. At pH 7.0 and 37 degrees, incubating DNA with the complexes for 24 h, all Form I was selectively converted into Form II. At 55 degrees, pH 7.0, the time was shortened to less than 30 min. According to the mechanism experiment, these complexes cleave plasmid pUC19 DNA by oxidative mechanism. The synergistic effect of the CuII ions is important to improve the DNA cleavage.

μ-10,22-Dichloro-3,6-bis(2-furylmethyl)-3,6,14,18-tetraazatricyclo[18.3.1.18,12]pentacosa-1(23),8,10,12(25),13,18,20(24),21-octaene-24,25-diolato-κ8N3,N6,O24,O25:N14,N18,O24:O25]bis[chloridocopper(II)] acetonitrile solvate

The title compound, [Cu2(C31H30Cl2N4O4)Cl2]·CH3CN, was synthesized by cyclo­condensation between N,N′-bis­(2-fur­yl)-N,N′-bis­(3-formyl-5-chloro­salicylaldehyde)ethyl­enediamine and 1,3-diamino­propane in the presence of CuII ions. It is an unsymmetrical dinuclear CuII complex. The coordination geometry for each CuII atom can be discribed as distorted square-pyramidal. The two Cu atoms are bridged by two phenolate O atoms with a Cu⋯Cu distance of 3.0274 (9) Å.

Two Dinuclear CuII - Tetrazolate Complexes: Syntheses, Structures, and Magnetic Properties

Two μ2-tetrazolyl bridged dinuclear CuII complexes, [Cu(L1)(N3)(phen)]2 1 (HL1 = 5-phenyltetrazole, phen = 1,10-phenanthroline) and [Cu(L2)2(NH3)2]2 2 (HL2 = 5-(2-methylphenyl)-1H-tetrazole), were synthesized and characterized by X-ray single crystal diffraction and IR spectroscopy. The two complexes are dinuclear CuII entities, in which the CuII centres are linked by tetrazolate bridging ligands. However, the CuII ions of the two complexes show different coordination geometries, square pyramidal for complex 1 and trigonal-bipyramidal for complex 2, which may lead to different magnetic properties. In complex 1, a weak ferromagnetic coupling was found to exist between CuII ions, but in complex 2, weak antiferromagnetic coupling was found to be present. A van Vleck equation for the CuII dimer was written using the Ĥ = –2J[Ŝ1Ŝ2] Hamiltonian, and it was used to fit the experimental data with fitting parameters J = 0.26 cm–1 and g = 2.17 for complex 1, J = –2.34 cm–1 and g = 2.17 for complex 2, respectively.

Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies

AbstractThe synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16‐pentaaza[17]metacyclophane (L1) and 2,6,9,12,16‐pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the para L2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri‐ or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri‐ to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono‐ and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped‐flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu–L1‐AMP, Cu–L2‐AMP, and Cu–L3‐AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6‐dimethylpyridine as a spacer, is also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

μ-2,8-Dimethyl-1,4,5,6,7,10,11,12-octahydrodiimidazo[4,5-h;4′,5′-c][1,6]diazecine-5,11-diacetato]bis[diaquanitratocopper(II)] trihydrate

The title compound, [Cu2(C16H20N6O4)(NO3)2(H2O)4]·3H2O, crystallizes with two dinuclear CuII complex mol­ecules, each lying on an inversion center, and six solvent water mol­ecules per unit cell. The central 1,6-diazecine ring adopts the common chair conformation invariably found in the family of complexes bearing such ligands. The CuII atoms have an octa­hedral geometry, with a very strong tetra­gonal distortion due to the Jahn–Teller effect. Axial sites are occupied by a nitrate ion and a water mol­ecule. The Cu⋯Cu separations [7.3580 (9) and 7.3341 (9) Å] are compatible with a potential catecholase activity. Neighboring mol­ecules in the crystal structure are connected via O—H⋯O hydrogen bonds formed by water mol­ecules and carboxyl­ate O atoms. N—H⋯O hydrogen bonds are also present.

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.

Equilibrium and Kinetic Properties of CuII Cyclophane Complexes: The Effect of Changes in the Macrocyclic Cavity Caused by Changes in the Substitution at the Aromatic Ring

AbstractThe o‐B232, m‐B232 and p‐B232 cyclophanes result from attaching the terminal amine groups of 1,4,8,11‐tetraazaundecane (232) to the benzylic carbons of the corresponding o‐, m‐ or p‐xylanes. The cavity size of these cyclophanes changes moderately as a consequence of the substitution at the aromatic ring. The effects caused by these changes on the equilibrium constants for protonation and CuII complex formation of the cyclophanes are analyzed and compared with those of the noncyclic 232 polyamine. All three cyclophanes form mononuclear complexes, but only o‐B232 is able to coordinate to CuII through the four amine groups simultaneously, whereas m‐B232 and p‐B232 can only use three nitrogen donors. The larger cavity and higher flexibility of the latter two cyclophanes allow them to form stable dinuclear CuII complexes. The kinetics of the acid‐promoted dissociation of CuII from its mono‐ and dinuclear complexes has also been studied and the results indicate the existence of large differences in the kinetic properties for the complexes with these three closely related ligands. Whereas the mononuclear m‐B232 and p‐B232 complexes decompose with very similar kinetic behaviour to that of the Cu(232)2+ complex, the lability of the Cu–N bonds is largely reduced in the Cu(o‐B232)2+ complex, and this leads to slower decomposition and even to a different rate law for this complex. The dinuclear complexes are not formed with o‐B232, and very different decomposition kinetics is observed for the complexes formed by m‐B232 and p‐B232. In the case of m‐B232, the two metal ions are situated very close to each other, which causes a rapid release of one of them upon reaction with acid. In contrast, the larger size of p‐B232 allows it to accommodate two metal ions without important electrostatic or steric interactions so that they are released with statistically controlled kinetics.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Manganese(III,IV) and Manganese(III) Oxide Clusters Trapped by Copper(II) Complexes

Reactions of quinquedentate Schiff base ligands with Mn and Cu ions afforded icosa- and hexadecanuclear mixed-metal clusters in which dinuclear CuII complexes trapped oxo-bridged [MnIII8MnIV4O12] and [MnIII6O6] cores, respectively. Maximum entropy method analysis for synchrotron X-ray diffraction data was used to determine the oxidation states of the Mn ions.

Oxalato‐Bridged Dinuclear Copper(II) Complexes of N‐Alkylated Derivatives of 1,4,7‐Triazacyclononane: Synthesis, X‐ray Crystal Structures and Magnetic Properties

AbstractThe synthesis, X‐ray crystal structure and magnetic properties of two oxalato‐bridged dinuclear CuII complexes, [L‐Cu(μ‐ox)Cu‐L](ClO4)2, where ox = oxalate and L = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane (Me3tacn) or 1‐benzyl‐4,7‐dimethyl‐1,4,7‐triazacyclononane (BzMe2tacn) are reported, as well as the X‐ray crystal structure of the mononuclear complex, [Cu(Me3tacn)(OH2)2](ClO4)2, which features an extended H‐bonding network between the ligand and the perchlorate counterions. The crystal structures of the dinuclear complexes both feature a centrosymmetric complex cation in which the two copper centres exist in a distorted square‐pyramidal geometry, with each end capped by a facially coordinated “tacn” unit, and are bridged by an oxalate anion. Variable‐temperature magnetic susceptibility measurements revealed strong antiferromagnetic interactions between the CuII centres, with 2J values of ca. –300 cm–1, even though the Cu···Cu separation is very long, viz. 5.18 Å (BzMe2tacn) and 5.47 Å (Me3tacn). The separation for the Me3tacn complex is the longest separation reported for this type of CuII complex. No pattern could be detected between the J values and structural features for 21 oxalato‐bridged complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis, Structures and Catecholase Activity of a New Series of Dicopper(II) Complexes of Reduced Schiff Base Ligands

AbstractA series of dinuclear CuII complexes of reduced Schiff bases from substituted salicylaldehydes and amino acids have been synthesized and characterized. They are: [Cu2(RScp11)2(H2O)2] {H2RScp11 = 1‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclopentane‐1‐carboxylic acid; R = H (1), Cl (2), CH3 (3), OH (4)}, [Cu2(RSch11)2(H2O)x] {H2RSch11 = 1‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclohexane‐1‐carboxylic acid; R = H and x = 1 (5), R = Cl and x = 2 (6), R = CH3 and x = 2 (7)}, [Cu2(RSch12)2(H2O)2] {H2RSch12 = 2‐[(2‐hydroxy‐5‐R‐benzyl)amino]cyclohexane‐1‐carboxylic acid; R = H (8), CH3 (10) and [Cu2(ClSch12)2]·2H2O (9)}, [Cu2(Diala5)2(H2O)2]·H2O [H3Diala5 = N‐(2,5‐dihydroxybenzyl)‐L‐alanine] (11), [Cu2(Diala4)2(H2O)2]·H2O [H3Diala4 = N‐(2,4‐dihydroxybenzyl)‐L‐alanine] (12), and [Cu2(Diala3)2(H2O)2]·H2O [H3Diala3 = N‐(2,3‐dihydroxybenzyl)‐L‐alanine] (13). They were isolated and characterized by chemical and spectroscopic methods. Single crystal X‐ray crystallographic studies have revealed that [Cu2(Scp11)2(MeOH)2] (1a), [Cu2(ClScp11)2(DMF)(H2O)]·MeCN (2a), [Cu2(MeScp11)2(MeOH)2]·2 MeOH (3a), [Cu2(ClSch11)2(MeOH)2]·2 MeOH (6a), [Cu2(ClSch12)2]·2 MeOH (9a), and [Cu2(Diala4)2(DMSO)2]·2 DMSO·2 acetone (12a) have 1D hydrogen‐bonded polymeric structures while 4 has a 3D hydrogen‐bonded network structure. Complex 8 displays a 2D coordination polymeric network structure. The complexes 1–13 have been investigated as functional models for the catechol oxidase by employing 3,5‐di‐tert‐butylcatechol as a model substrate. Electron‐withdrawing substituents reduced the activity while electron‐donating substituents enhanced the activity. Variable‐temperature magnetic studies conducted on compound 8 suggest the presence of strong inter‐dimer antiferromagnetic coupling. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Mono-, Di-, and Oligonuclear Complexes of CuIIIons andp-Hydroquinone Ligands: Syntheses, Electrochemical Properties, and Magnetic Behavior

Four highly soluble square-planar Cu(II) and Ni(II) complexes of siloxy-salens (2SiCu, 2SiNi) and hydroxy-salens (2Cu, 2Ni) have been synthesized. An X-ray crystal structure analysis was performed on 2SiCu, 2SiNi, and 2Ni. The compounds have been investigated by cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, and EPR spectroscopy. According to these results, the monooxidized species [2SiCu]+ and [2SiNi]+ are to be classified as Robin-Day class II and III systems, respectively. Magnetic measurements on the dinuclear (PMDTA)Cu(II) complex 1Cu2 x (PF6)2 with deprotonated 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)-benzene (1) linker revealed antiferromagnetic coupling between the two Cu(II) ions thereby resulting in an isolated dimer compound. Coordination polymers [1Cu]n(H2O)(2n) of Cu(II) ions and bridging p-hydroquinone linkers were obtained from CuSO4 x 5 H2O and 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)benzene. X-ray crystallography revealed linear chains running along the crystallographic a-direction and stacked along the b-axis. Within these chains, the Cu(II) ions are coordinated by two pyrazolyl nitrogen atoms and two p-hydroquinone oxygen atoms in a square-planar fashion.

Hydroquinone-bridged dinuclear CuII complexes and single-crystalline CuII coordination polymers

Cationic dinuclear Cu(II) complexes 3 and 4 have been prepared using the novel hydroquinone-based imine chelators 2,5-((i)Pr(2)NCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (1) and 2,5-(pyCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (2), respectively (py = 2-pyridyl). X-Ray quality crystals of both complexes were grown from their DMF solutions. The sterically more encumbered compound crystallizes in the form of discrete dinuclear entities with Cu(II) centres in a distorted square-planar ligand environment (one coordination site is occupied by a DMF molecule). The pyridyl derivative 4 features dinuclear hydroquinone-bridged subunits similar to 3. However, the Cu(II) ions are now six-coordinate with two DMF molecules at an axial and an equatorial position of a Jahn-Teller-distorted octahedron. Moreover, the dinuclear subunits are no longer isolated but linked with each other via bridging hydroquinone oxygen atoms which occupy the second apical position of each octahedron. The structure suggests that the magnetic properties of the resulting coordination polymer of 4 could be described by a model valid for dimerized spin chains. As a result of this analysis the antiferromagnetic coupling constants J(1)/k(B) = 9.9 K (intradimer) and J(2)/k(B) = 0.9 K (interdimer) are obtained. Both in 3 and in 4, the hydroquinone --> semiquinone transition of the central bridging unit (E degrees ' = + 0.57 V, 3; E degrees ' = + 0.51 V, 4; DMF; vs. SCE) displays features of chemical reversibility. In the case of , reduction of Cu(II) centres requires a peak potential of E(p) = - 0.42 V.

Tetrakis(μ-phenylacetato-κ2O:O′)bis[(N,N-dimethylformamide-κO)copper(II)

In the crystal structure of the title complex, [Cu2(C8H7O2)4(C3H7NO)2], two independent dinuclear CuII complex mol­ecules, bridged by phenyl­acetate anions, are located on inversion centres. The Cu⋯Cu separations of 2.6414 (8) and 2.6261 (8) Å suggest no bonding between the Cu atoms. The CuII ions exist in a square-pyramidal coordination environment, defined by one N,N-dimethyl­formamide and four phenyl­acetate O atoms.

Tetra-μ-phenoxyacetato-bis[(acetonitrile)copper(II)](Cu—Cu)

The title centrosymmetric compound, [Cu2(C8H7O3)4(C2H3N)2], is a carboxyl­ate-bridged dinuclear CuII complex with four phenoxy­acetate and two acetonitrile mol­ecules as ligands. Each of the four phenoxy­acetate anions straddles the pair of Cu atoms, the Cu—Cu distance being 2.6618 (10) Å. A weak C—H⋯π inter­action connects the dinuclear CuII units into a one-dimensional chain.

Spectroscopy and Redox Behaviour of Dicopper(II) and Dinickel(II) Complexes of Bis(cyclen) and Bis(cyclam) Ligands

AbstractThe dinuclear CuII and NiII complexes of meta‐xylyl and pyridyl biscyclen and biscyclam have been prepared and characterised in solution by means of UV/Visible spectra, electrochemical and EPR studies. X‐ray structures of copper biscyclen complexes have been obtained. The comparison of all the data shows that the potentially coordinating N(py) pyridyl atom promotes the interaction between the two metal centers, whether it is spontaneously coordinated (biscyclen complexes) or not (biscyclam ones). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Cyanide and imidazolate bridged macrocyclic dinuclear CuII complexes: Synthesis, structure and magnetic properties

Reaction of [Cu 2L](ClO 4) 4 with CH 3CN in acetonitrile, and Him in DMF gave cyanide and imidazolate bridged macrocyclic dinuclear copper (II) complexes with the formula [Cu 2L(CN)](ClO 4) 3 ( 1) and [Cu 2L(im)](ClO 4) 2 · 0.7Br · 0.3Cl, ( 2), respectively (L = N[(CH 2) 2NHCH 2(C 6H 4- p)CH 2NH(CH 2) 2] 3N). In 2, each Cu(II) atom is coordinated with four macrocyclic nitrogen atoms and one imidazolate N atom, forming a slightly distorted square pyramidal geometry. Magnetic susceptibility measurements of 1 and 2 show that the two Cu(II) atoms of the binuclear unit are antiferromagnetically coupled with g = 2.148, J = −86.09 cm −1 for 1, and g = 2.047, J = −38.20 cm −1 for 2. The correlation between the structures and the J values is discussed.

Binucleating Aza‐Sulfonate and Aza‐Sulfinate Macrocycles — Synthesis and Coordination Chemistry

AbstractThe preparation and ligating properties of S‐oxygenated derivatives of a macrobinucleating hexaazadithiophenolate macrocycle H2L1 of the Robson type towards nickel(II) and zinc(II) ions are reported. Nickel complexes of the hexaazadiphenylsulfonate ligand (L2)2− [(L2)NiII2(μ‐L)]+ (L = m‐Cl‐OBz− (3), Cl− (4) and OAc− (6)] are readily obtained in high yields by oxidation of the respective [(L1)NiII2(μ‐L)]+ parent complexes [L = m‐Cl‐OBz− (2), Cl− (1), OAc− (5)] with meta‐chloroperoxybenzoic acid or hydrogen peroxide. Decomposition of the sulfonate complexes gives the free macrocycle H2L2 which, upon treatment with Zn(OAc)2·2H2O, produces the diamagnetic zinc complex [(L2)ZnII2(OAc)]+ (8). A dinuclear CuII complex of the hexaazadisulfinate derivative (L3′)2−, [(L3)CuII2]2+ (9), is formed rather unexpectedly by air oxidation of (L1)2− in the presence of CuI. The crystal‐structure determinations of the perchlorate or tetraphenylborate salts of 2, 3, and 4 show that the new ligands support the formation of binuclear complexes with bowl‐shaped, calixarene‐like binding cavities. NMR spectroscopic studies of 8 show that the complexes retain their solid‐state structures in solution. A crystal‐structure determination of 9 reveals two five‐coordinate CuII ions bridged by the two sulfinate functions of (L3)2−. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Dinuclear copper(II) complexes with ferromagnetic and antiferromagnetic interactions mediated by a bridging oxalato group: structures and magnetic properties of [Cu2L4(μ-C2O4)](PF6)2(H2O)2 and [Cu2L2(μ-C2O4)(NO3)2((CH3)2NCOH)2] (L = di-2-pyridylamine)

Two dinuclear CuII complexes of formula [Cu2(dpyam)4(μ-C2O4)](PF6)2(H2O)2(1) and [Cu2(dpyam)2(μ-C2O4)(NO3)2(DMF)2] (2) (dpyam=di-2-pyridylamine) have been synthesized and their spectroscopic and magnetic properties characterized. Complex (1) crystallizes in the non-centrosymmetric monoclinic space group Pc, while (2) crystallizes in the non-centrosymmetric triclinic space group P1. Compound (1) involves the compressed octahedral CuII environment, whereas (2) exhibits an elongated octahedral CuII geometry. Both complexes contain six-coordinate metal centers bridged by planar bis-didentate oxalate group. The geometry, spectroscopic properties and the effective magnetic moment of (1) are very close to those of the recently published [Cu2(dpyam)4 (μ-C2O4)](ClO4)2(H2O)3 and [Cu2(dpyam)4(μ-C2O4)](BF4)2(H2O)3. Thus (1) is expected to exhibit a very weak ferromagnetic interaction between the CuII centers which is confirmed by EPR spectrum. Those of (2) are comparable to those of the recently published [Cu2(dpyam)2(μ-C2O4)(NO3)2(DMSO)2]. Therefore a strong antiferomagnetic interaction is expected. The effective magnetic moment at room temperature of (1) was measured to be 2.55 BM/dimer, which agrees with the spin only value of CuII, 2.45BM calculated for two uncoupled spin=1/2 centers. In (2) the room temperature effective magnetic moment of 2.16 BM/dimer indicates the partial spin paring by antiferromagnetic coupling. This is confirmed by the e.p.r. spectrum and is explained as a result of the magnetic interaction between the coplanar \({\rm d}_{x^2-y^2}\) orbitals on the two copper atoms.

Carboxy Ester Hydrolysis Promoted by a Dicopper(II) Macrocyclic Polyamine Complex with Hydroxypropyl Pendant Groups

AbstractA dinuclear CuII complex containing a hexaaza macrocyclic ligand bearing two 2‐hydroxypropyl pendants, 3,6,9,16,19,22‐hexaaza‐6,19‐bis(2‐hydroxypropyl)tricyclo[22.2.2.211,14]triaconta‐1,11,13,24,27,29‐hexaene (L), was synthesized. The title complex [Cu2(H−2L)Cl2]·6.5H2O was isolated as a blue crystal, orthorhombic, space group Fddd, with a = 16.4581(12), b = 32.248(2), c = 35.830(2) Å, V = 19017(2) Å3, Z = 16, R1 = 0.0690, and wR2 = 0.1546 [I > 2σ(I)]. The protonation constants of Cu2L were determined by potentiometric titration, and it was found that the alcoholic hydroxypropyl group of the complex Cu2L exhibits low pKa values of pKa1 = 7.31, pKa2 = 7.83 at 25 °C. The hydrolysis kinetics of 4‐nitrophenyl acetate (NA) promoted by the title complex have also been studied. The pH‐rate profile for Cu2L gave a sigmoidal curve and showed a second‐order rate constant of 0.39 ± 0.02 M−1 s−1 in 10% CH3CN/H2O(v/v), which is greater than that of the dinuclear CuII complex formed by a hexaaza macrocycle without pendants. The reason for the higher catalytic activity of the title complex is discussed. We found that the volume of nucleophile RO− can effect the hydrolysis of the carboxy ester, the nucleophilicity of RO− and the Lewis acidity of the metal macrocycle also affect the carboxy ester hydrolysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis, characterization and properties of ternary copper(ii) complexes containing reduced Schiff base N-(2-hydroxybenzyl)-α-amino acids and 1,10-phenanthrolineElectronic supplementary information (ESI) available: ESI-MS and UV titration data. See http://www.rsc.org/suppdata/dt/b2/b211496h/

Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)-α-amino acid, where α-amino acid = glycine (H2sgly), L-alanine (H2sala) and L-valine (H2sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear CuII complexes [Cu(L)(phen)]·xH2O (L = sgly (1), sala (2), sval (3)) have been prepared from Cu(OAc)2·H2O, H2L, phen, LiOH in the ratio 1 ∶ 1 ∶ 1 ∶ 2 in H2O–MeOH. The monodeprotonated CuII complexes [Cu(HL)(phen)](ClO4)·xH2O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO4)2·6H2O, H2L, phen, LiOH in the ratio 1 ∶ 1 ∶ 1 ∶ 1 in H2O–MeOH. The dinuclear CuII complexes [Cu2(L)(phen)3](ClO4)2·xH2O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1–3 when Cu(ClO4)2·6H2O was used in the place of Cu(OAc)2·H2O. The electronic spectral titration experiments indicate that the neutral mononuclear compounds could be converted to protonated 4–6 but not vice versa. The protonated phenolic oxygen is involved in medium to weak interaction with CuII–OH distances, 2.446(3) Å in 4, and 2.73(4) and 2.79(4) Å in 5. Compound 4 is a mononuclear cation while 5 is a helical coordination polymer in the solid state with the carboxylate group in anti–anti bridging mode. The structures of 1, 4, 5 and 7 have been determined by X-ray crystallography. Variable temperature magnetic measurements of the helical polymer 5 showed very weak ferromagnetic coupling with μeff per Cu remaining constant at 1.80 BM between 300 and 30 K, then a rapid increase to 2.07 BM at 4 K. Fitting to a Heisenberg S = ½ chain model gave a J value of 1.2 cm−1.