A rare ferromagnetically coupled asymmetric doubly azido bridged copper(II) dimer with an N,N, O donor Schiff base

A new end-to-end (EE) doubly azido bridged dinuclear complex [Cu₂L₂(μ_1,3-N₃)₂] (1) [where L = (E)-4-(2-(dimethylamino)ethylimino)-1,1,1-trifluoropentan-2-one)] has been synthesized and characterized by elemental and spectroscopic techniques. Single crystal X-ray diffraction analysis reveals that the dimeric complex possesses a center of inversion. Each copper atom in 1 is in a distorted square pyramidal geometry with a CuN₄O chromophore as revealed from the τ value, 0.19. The four basal positions are occupied by two imine N and one keto O atom of the Schiff base and one N atom from the azide anion. Another N atom from a coordinated azide occupies the apical position. Temperature dependent magnetic susceptibility of 1 was fitted using the Bleaney–Bowers expression which led to the parameters J = 13.6 cm⁻¹ and R = 3.4 × 10⁻⁵. It indicates a ferromagnetic interaction through the double azido bridges connecting the individual copper Schiff base units.     

Structural and kinetic study of reversible CO2 fixation by dicopper macrocyclic complexes. From intramolecular binding to self-assembly of molecular boxes

A study of the reversible CO2 fixation by a series of macrocyclic dicopper complexes is described. The dicopper macrocyclic complexes [Cu2(OH)2(Me2p)](CF3SO3)2, 1(CF3SO3)2, and [Cu2(mu-OH)2(Me2m)](CF3SO3)2, 2(CF3SO3)2, (Scheme 1) containing terminally bound and bridging hydroxide ligands, respectively, promote reversible inter- and intramolecular CO2 fixation that results in the formation of the carbonate complexes [{Cu2(Me2p)}2(mu-CO3)2](CF3SO3)4, 4(CF3SO3)4, and [Cu2(mu-CO3)(Me2m)](CF3SO3)2, 5(CF3SO3)2. Under a N2 atmosphere the complexes evolve CO2 and revert to the starting hydroxo complexes 1(CF3SO3)2 and 2(CF3SO3)2, a reaction the rate of which linearly depends on [H2O]. In the presence of water, attempts to crystallize 5(CF3SO3)2 afford [{Cu2(Me2m)(H2O)}2(mu-CO3)2](CF3SO3)4, 6(CF3SO3)4, which appears to rapidly convert to 5(CF3SO3)2 in acetonitrile solution. [Cu2(OH)2(H3m)]2+, 7, which contains a larger macrocyclic ligand, irreversibly reacts with atmospheric CO2 to generate cagelike [{Cu2(H3m)}2(mu-CO3)2](ClO4)4, 8(ClO4)4. However, addition of 1 equiv of HClO4 per Cu generates [Cu2(H3m)(CH3CN)4]4+ (3), and subsequent addition of Et3N under air reassembles 8. The carbonate complexes 4(CF3SO3)4, 5(CF3SO3)2, 6(CF3SO3)4, and 8(ClO4)4 have been characterized in the solid state by X-ray crystallography. This analysis reveals that 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 consist of self-assembled molecular boxes containing two macrocyclic dicopper complexes, bridged by CO32- ligands. The bridging mode of the carbonate ligand is anti-anti-mu-eta1:eta1 in 4(CF3SO3)4, anti-anti-mu-eta2:eta1 in 6(CF3SO3)4 and anti-anti-mu-eta2:eta2 in 5(CF3SO3)2 and 8(ClO4)4. Magnetic susceptibility measurements on 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 indicate that the carbonate ligands mediate antiferromagnetic coupling between each pair of bridged CuII ions (J = -23.1, -108.3, and -163.4 cm-1, respectively, H = -JS1S2). Detailed kinetic analyses of the reaction between carbon dioxide and the macrocyclic complexes 1(CF3SO3)2 and 2(CF3SO3)2 suggest that it is actually hydrogen carbonate formed in aqueous solution on dissolving CO2 that is responsible for the observed formation of the different carbonate complexes controlled by the binding mode of the hydroxy ligands. This study shows that CO2 fixation can be used as an on/off switch for the reversible self-assembly of supramolecular structures based on macrocyclic dicopper complexes.     

First examples of two ferromagnetic end-to-end cyanate bridged 1D linear coordination polymers of nickel(ii) containing an unsymmetrical diamine

Two new end-to-end (EE) cyanate bridged 1D coordination polymers of Ni(II) are isolated which contain linear (180°) Ni-N-C and Ni-O-C angles in Ni-NCO-Ni bridges and show ferromagnetic (F) coupling in agreement with the reported theoretical model for linear EE bridges.     

Coordination polymers assembled from angular dipyridyl ligands and CuII, CdII, CoII salts: crystal structures and properties

Six new metal-organic coordination networks based on linking unit 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (L(1)) or 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L(3)) and inorganic Cu(II), Cd(II), and Co(II) salts have been prepared and structurally characterized by single-crystal X-ray analysis. Using L(1) to react with three different Cu(II) salts, Cu(OAc)(2).H(2)O, Cu(NO(3))(2).3H(2)O, and CuSO(4).5H(2)O, respectively, two different one-dimensional (1-D) coordination polymers, [[Cu(2)L(1)(mu-OAc)(4)](CHCl(3))(2)](n) (1) [triclinic, space group P1, a = 7.416(3) A, b = 8.207(3) A, c = 14.137(5) A, alpha = 100.333(7) degrees, beta = 105.013(6) degrees, gamma = 94.547(6) degrees, Z = 1] and [[CuL(1)(NO(3))(2)](CHCl(3))(0.5)](n) (2) [monoclinic, space group C2/c, a = 28.070(8) A, b = 9.289(3) A, c = 15.235(4) A, beta = 113.537(5) degrees, Z = 8], and a chiral 3-D open framework, [[CuL(1)(H(2)O)(SO(4))](H(2)O)(2)](n) (3) [orthorhombic, space group P2(1)2(1)2(1), a = 5.509(2) A, b = 10.545(4) A, c = 29.399(11) A, Z = 4], were obtained. Reaction of L(1) and Cd(ClO(4))(2).6H(2)O or Co(ClO(4))(2).6H(2)O, in the presence of NH(4)SCN, yielded another 3-D open framework, [[CdL(1)(NCS)(2)](CH(3)OH)(1.5)](n) (4) [monoclinic, space group C2/c, a = 28.408(10) A, b = 9.997(5) A, c = 7.358(4) A, beta = 99.013(8) degrees, Z = 4], or a 2-D network, [[Co(L(1)())(2)(NCS)(2)](H(2)O)(2.5)](n) (5) [orthorhombic, space group Pnna, a = 22.210(5) A, b = 12.899(3) A, c = 20.232(4) A, Z = 4]. When L(1) was replaced by L(3) to react with Co(ClO(4))(2).6H(2)O and NH(4)SCN, another 2-D coordination polymer, [Co(L(3))(2)(NCS)(2)](n) (6) [monoclinic, space group P2(1)/c, a = 8.120(3) A, b = 9.829(4) A, c = 17.453(6) A, beta = 103.307(6) degrees, Z = 2], was constructed. These results indicate that the nature of the ligands, metal centers, or counteranions plays the critical role in construction of these novel coordination polymers. The interesting porous natures of two 3-D open frameworks 3 and 4 were investigated by TGA and XPRD techniques, and the magnetic properties of the Cu(II) and Co(II) complexes were studied by variable-temperature magnetic susceptibility and magnetization measurements.     

Olefin‐Dependent Discrimination between Two Nonheme HO?FeVO Tautomeric Species in Catalytic H2O2 Epoxidations

Wet oxygenase models : Unprecedented high levels of water incorporation into products (up to 75 %) is observed in epoxidation reactions with H₂O₂ by a bioinspired nonheme iron catalyst. A surprising substrate‐dependent incorporation of water is observed, and is proposed to arise from fast equilibrium between two high‐valent HO? Fe^V?O isomeric species exhibiting different reactivity.

     

Novel magnetization processes in ferrimagnetic multilayers with random anisotropy

We carried out a numerical study of magnetization processes in ferrimagnetic multilayers in the presence of pinning forces acting on one of the magnetic components. The multilayers consist of an alternation of two ferromagnetic materials (M and T) which are assumed antiferromagnetically coupled through the interfaces (as in Fe/Tb multilayers for instance). A random anisotropy field acts on the magnetization of material T. The reversal of the magnetization of the multilayers when the applied field is swept from positive saturation to negative saturation is characterized by a competition between coherent rotation and nucleation-propagation mechanisms. In this competition the rotational hysteresis induced by the random anisotropy on the magnetization of material T plays a crucial role. Very original features have been observed in the magnetization processes of these systems such as crossed hysteresis loops with a negative remanent magnetization. An overview of these magnetization processes below and above the compensation temperature is given in this paper.     

Thermal studies on the anation and decomposition of trans-fluoroaquobis(ethylenediamine) and trans-fluoroaquoabis(propylenediamine) dithionate

The anation and decomposition reaction of trans[CrF(H₂O)(aa′)₂]S₂O₆ [aa′ = ethylenediamine (en); 1,3-diaminepropane (tmd)] have been studied by means of ATD, TG and DSC techniques. The first and only perfectly defined step is the anation reaction forming the species cis[CrF(S₂O₆)(aa′)₂]. By means of DSC techniques, the enthalpies of reaction and the activation energies of both reactions have been estimated. The electronic spectra of the resultant products suggest cis configuration. A second step, preceding total decomposition of the complex, involves cis[CrF(S₂O₆)(aa′)₂] → cis[CrF(SO₄)(aa′)₂] + SO₂ which is contaminated by decomposition reactions.     

Spectrophotometric determination of cysteine and/or carbocysteine in a mixture of amino acids, shampoo, and pharmaceutical products using p-benzoquinone

A simple, sensitive, and selective method has been developed for determination of cysteine (Cys) or carbocysteine (carboCys) in pharmaceutical products, shampoos and a mixture of amino acids. The results showed the reaction between p-benzoquinone (PBQ) and Cys occurs through the sulfhydryl group. Previous derivatization or extraction is not necessary before the assay is carried out. The method is based on the fact that the product of reaction between PBQ and Cys absorbs at 352 and 500 nm or PBQ and carboCys absorbs at 500 nm. Beer's law is followed in the range 0-40 mug/ml for Cys and 0-150 mug/ml for carboCys. The product of reaction PBQ-Cys is stable for 2 h with absorption bands at 352 and 500 nm. In the presence of amino acids, PBQ is highly selective to Cys. Several substances such as amino acids, urea, salts, and dipeptide did not interfere with the proposed method. A recovery of about 100% is observed for both Cys and carboCys, when the method is applied to determine Cys in a mixture of amino acids resembling blood plasma, shampoo, and pill food as well as carboCys in pharmaceutical products.