Inorganic-metalorganic hybrids based on copper(II)-monosubstituted Keggin polyanions and dinuclear copper(II)-oxalate complexes. Synthesis, X-ray structural characterization, and magnetic properties

Reaction of in situ generated copper(II)-monosubstituted Keggin polyoxometalates and copper(II)-bipyridine-oxalate complexes in the corresponding alkaline acetate buffer led to the formation of hybrid metal organic-inorganic compounds K(2)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)].14H(2)O (1), K(14)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}](2)[SiW(11)O(39)Cu(H(2)O)].55H(2)O (2), (NH(4))(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (3), and Rb(4)[{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}].10H(2)O (4). Their structures have been established by single-crystal X-ray diffraction. The main structural feature of these compounds is the presence of copper(II)-monosubstituted alpha-Keggin polyoxoanions as inorganic building blocks, on which the mu-oxalatodicopper metalorganic blocks are supported. Compound 1contains the discrete hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(H(2)O)(2)(mu-ox)}(2)](2)(-), whereas the polymeric hybrid polyanion [{SiW(11)O(39)Cu(H(2)O)}{Cu(2)(bpy)(2)(mu-ox)}(2)](n)(4)(n)(-) gives a monodimensional character to compounds 2-4. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on both the [Cu(2)(bpy)(2)(H(2)O)(4)(mu-ox)](2+) cationic complex and the metalorganic blocks have been performed in order to determine the optimized geometry and the magnetic coupling constants, respectively.     

Phase separation in manganites induced by orbital-ordering strains

Doped manganite perovskites AMnO(3) exhibit a rich variety of electronic properties, resulting from the interplay of charge (Mn(3+)/Mn(4+)), spin (Mn magnetic moment) and orbital (Mn(3+) Jahn-Teller distortion) degrees of freedom. Magnetisation measurements and ESR spectra have been used to study a series of eight AMnO(3) perovskites, in which the A cation sites are occupied by a distribution of 70% trivalent lanthanide and 30% divalent Ca, Sr or Ba ions. These all have a mean A cation radius of 1.20 Angstrom but different values of the cation size variance sigma(2). A change from orbital disorder to order (cooperative Jahn-Teller distortions) was previously found in the insulating regime at sigma(2) = approximately 0.005 Angstrom(2). This work has shown that co-existence of the orbitally ordered and disordered phases is found in sigma(2)= 0.0016-0.0040 Angstrom(2) samples, with a difference of 40 K between their Curie temperatures. This is ascribed to competition between orbital ordering and microstructural lattice strains. At larger sigma(2) > 0.005 Angstrom(2), the orbital ordering strains are dominant and only this phase is observed. This intermediate temperature phase segregation is one of many strain-driven separation phenomena in manganites.     

Pentacoordinate nickel(II) complexes double bridged by phosphate ester or phosphinate ligands: spectroscopic, structural, kinetic, and magnetic studies

The bis(phosphatediester)-bridged complexes [[Ni([12]aneN(3))(mu-O(2)P(OR)(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; R=Me (1), Bu (2), Ph (3), Ph-4-NO(2) (4); [12]aneN(3)=Me(4)[12]aneN(3), 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene; R=Me (5), Bu (6), Ph (7), Ph-4-NO(2) (8)] were prepared by hydrolysis of the phosphate triester with the hydroxo complex [[Ni([12]aneN(3))(mu-OH)](2)](PF(6))(2) or by acid-base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid-base reaction was also used to synthesise the phosphinate-bridged complexes [[Ni([12]aneN(3))(mu-O(2)PR(2))](2)](PF(6))(2) [[12]aneN(3)=Me(3)[12]aneN(3), R=Me (9), Ph (10); [12]aneN(3)=Me(4)[12]aneN(3), R=Me (11), Ph (12)]. The molecular structures of complexes 2, 3 and 12 were established by single crystal X-ray diffraction studies. The eight-membered rings defined by the nickel atoms and the bridging ligands show distorted twist-boat, chair and boat-boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least-squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=-0.11 cm(-1), D=-9.5 cm(-1) and g=2.20 for 2; J=-0.97 cm(-1), D=-9.3 cm(-1) and g=2.21 for 3; and J=-0.14 cm(-1), D=-11.9 cm(-1) and g=2.195 for 12. The magnetic-exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the O-P-O bridges. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [[Ni(Me(3)[12]aneN(3))(mu-OH)](2)](PF(6))(2) was studied by UV-visible spectroscopy. The proposed mechanism for TNP-promoted hydrolysis can be described as one-substrate/two-product, and can be fitted to a Michaelis-Menten equation.     

A novel organic-inorganic hybrid based on a dinuclear copper complex supported on a keggin polyoxometalate

The autoassembly process of copper-oxalate dimers and Keggin type polyoxometalates leads to the first example of a new family of organic-inorganic hybrids, K(14)[(Cu(2)(bpy)(2)(mu-ox))(SiW(11)O(39)Cu(H(2)O))](2)[SiW(11)O(39)Cu(H(2)O)]. approximately 55H(2)O. This compound crystallizes in the monoclinic space group C2/m, a = 37.932(6) A, b = 21.303(3) A, c = 12.546(2) A, beta = 106.16(1) degrees, Z = 2. The crystal structure reveals the presence of a polymeric hybrid built up of alternating dimer and polyoxometalate entities.     

Structural analysis, spectroscopic, and magnetic properties of the 1D triple-bridged compounds [M(dca)2(bpa)] (M = Mn, Fe, Co, Zn; dca = dicyanamide; bpa = 1,2-bis(4-pyridyl)ethane) and the 3D [Ni(dca)(bpa)2]dca·6H2O

The family of compounds [Mn(dca)(2)(bpa)] (1), [Fe(dca)(2)(bpa)] (2), [Co(dca)(2)(bpa)] (3), [Zn(dca)(2)(bpa)] (4), and [Ni(dca)(bpa)(2)]dca·6H(2)O (5), with dca = dicyanamide and bpa = 1,2-bis(4-pyridyl)ethane, has been synthesized. These compounds have been characterized by single crystal (1, 2, 4, and 5) and powder X-ray diffraction (3), by Fourier transform infrared (FTIR), UV-vis, and electron paramagnetic resonance (EPR) spectroscopies, and by magnetic measurements. Compound 1 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.757(6), b = 9.692(3), and c = 13.073(4) ?, and β = 123.02(2)°; Compound 2 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.588(5), b = 9.661(3), c = 12.970(5) ?, and β = 123.16(3)°; Compound 4 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.519(2), b = 9.643(2), c = 12.943(2) ?, and β = 123.15(1)°; Compound 5 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 18.504(4), b = 19.802(3), and c = 8.6570(18) ?, and β = 99.74(2)°. The compounds 1-4 are isostructural and show a one dimensional (1D) disposition, with the metal(II) ions bridged by double μ(1,5) dca ligands and unusually by a third bridge consisting of the bpa ligand, which adopts a very low torsion angle to accommodate in the structure. This kind of structure is unusual, even considering the voluminous bpa bridge. The compound 5 shows a 3D structure with layers of Ni-bpa joined by single dca bridges. Magnetic susceptibility measurements show antiferromagnetic couplings, increasing for 1-3. Compound 5 shows very slight antiferromagnetic interactions.     

Antioxidant activity of methimazole-copper(II) bioactive species and spectroscopic investigations on the mechanism of its interaction with Bovine Serum Albumin

Free radical-mediated oxidative stress has been implicated in numerous autoimmune disorders including Graves’ disease. Hyperthyroidism results in a marked increase in intracellular antioxidant enzymes including superoxide dismutase. The later activity is significantly increased in untreated Graves’ patients while treatment with methimazole results in normalization of the free radical and antioxidant activity indices. In this context, and considering the findings mentioned above, the aim of the present study was to evaluate unknown biological activities of methimazole and its methimazole-copper(II) complex investigating their superoxide scavenger power. Under the applied experimental conditions, methimazole did not show superoxide dismutase (SOD) activity while the copper complexes exhibited a strong superoxide radical scavenging capacity. Bearing in mind that the capacity of drugs to bind and/or interact with albumin is essential for their pharmacokinetic and pharmacodynamic properties, a complete investigation of the binding ability of both compounds by using Fourier transform infrared (FT-IR), Raman and Fluorescence spectroscopies, and UV-Vis spectrophotometry was included. Besides, in order to probe the copper ligand environment the EPR spectra of such compounds were analyzed.     

Magnetic and structural characterization of silver-iron oxide nanoparticles obtained by the microemulsion technique

In the present paper we report the magnetic characterization of silver-iron oxide nanocomposite obtained by the chemical microemulsion method. TEM images and X-ray diffractograms show that the nanocomposite consists of Ag nanoparticles of ～ 7 nm surrounded by a quasiamorphous matrix. The ZFC–FC curves and Mössbauer spectra obtained at different temperatures show a typical evolution of a system composed of weakly interacting nanoparticles with a blocking temperature (T_b) of ～50 K. The analysis of the magnetic data reveals that the matrix is formed by γ-Fe₂O₃ phase with a structural range order of ～2 nm.     

New Perspectives for Old Clusters: Anderson–Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d–4 f Species

A series of nine [Sb₇W₃₆O₁₃₃Ln₃M₂(OAc)(H₂O)₈]^17? heterometallic anions ( Ln₃M₂ ; Ln=La–Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs‐type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW₉O₃₃} capping unit formed by a planar {MW₆O₂₄} fragment to which three {WO₂} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ?‐Keggin cluster. It is shown, for the first time, that classical Anderson–Evans {MW₆O₂₄} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk‐shaped species is also revealed. The Ln₃M₂ anions possess chirality owing to a {Sb₄O₄} cluster being encapsulated in left‐ or right‐handed orientations. Their ability to self‐associate in blackberry‐type vesicles in solution has been assessed for the Ce₃Co₂ derivative.