Synthesis, crystal structure and magnetic properties of a polymeric copper(II) Schiff-base complex having binuclear units covalently linked by isonicotinate ligands

The polynuclear copper(II) complex [{Cu2L(O2CC5H4N)}. C2H5OH](x) (1), where H3L is a 1∶2 Schiff base derived from 1,3-diaminopropan-2-ol and salicylaldehyde, has been prepared and structurally characterized. The structure consists of a one-dimensional zigzag chain in which the binuclear [Cu2L](+) units are covalently linked by isonicotinate ligands to give a syndiotactic arrangement of the copper ions protruding outside the chain. In the basic unit, the copper(II) centres are bridged by an alkoxo and a carboxylato ligand, giving a Cu ... Cu distance of 3.492(3) Angstrom and a Cu-O-Cu angle of 130.9(2)degrees. While one copper centre has a square-planar geometry, the other copper is square-pyramidal with the pyridine nitrogen being the axial ligand. The visible electronic spectrum of 1 shows a broad d-d band at 615 nm. The complex shows a rhombic X-band EPR spectral pattern in the polycrystalline phase at 77 K. Magnetic susceptibility measurements in the temperature range 22 to 295 K demonstrate the antiferromagnetic behaviour of 1. A theoretical fit to the magnetic data is based on a model assuming 1 as an equimolar mixture of copper atoms belonging to an antiferromagnetically coupled one-dimensional Heisenberg chain with the other copper atoms outside the chain behaving like paramagnetic centres.

Crystal structure and thermal and electrical properties of the perovskite solid solution Nd1-xSrxFeO3-delta (0 <= x <= 0.4)

The crystal structure, thermal expansion and electrical conductivity of strontium-doped neodymium ferrite (Nd1-xSrxFeO3-delta where 0less than or equal toxless than or equal to0.4) were investigated. All compositions had the GdFeO3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction. The orthorhombic distortion decreases with increasing Sr substitution. The pseudocubic lattice parameter shows a minimum at x=0.3. The thermal expansion curves for x=0.2-0.4 displayed rapid increase in slope at higher temperatures. The electrical conductivity increased with Sr content and temperature. The calculated activation energies for electrical conduction decreased with increasing x. The electrical conductivity can be described by the small polaron hopping mechanism. The charge compensation for divalent ion on the A-site is provided by the formation of Fe4+ ions on the B site and vacancies on the oxygen sublattice. The results indicate two defect domains: for low values of x, the predominant defect is Fe4+ ions, whereas for higher values of x, oxygen vacancies dominate. (C) 2002 Elsevier Science B.V. All rights reserved.

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1-xCoxO3 (0 <= x <= 0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd0.7Sr0.3Fe1-xCoxO3 for 0 less than or equal to x less than or equal to 0.8 were investigated. All compositions had the GdFeO3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe4+ ions on the B-site (in preference to Co4+ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe4+ ions by Co4+ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log sigmaT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co3+ ions. (C) 2002 Elsevier Science B.V. All rights reserved.

Structural model for the Cu-B site of dopamine beta-hydroxylase: Crystal structure of a copper(II) complex showing N3OS coordination with an axial sulfur ligation

A copper(II) complex containing a NSO-donor Schiff base and NN-donor 2,2'-bipyridine has been prepared and structurally characterized. The square pyramidal complex with an axial sulfur ligation is a structural model for the CUB site of dopamine-hydroxylase in its oxidized form. The copper(II) complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species which is proposed to have a four-coordinate structure with a N3S coordination geometry.

Synthesis, crystal structure and catalytic properties of (p-cymene)ruthenium(II) azophenol complexes: azophenyl to azophenol conversion by oxygen insertion to a ruthenium---carbon bond

Azophenol complexes of formulation [(η6-p-cymene)RuCl(Ln)] (1–6, n=1–6) were prepared by two synthetic methods involving either an oxygen insertion to the Ru---C bond in cycloruthenated precursors forming complexes 1 and 2 or from the reaction of [{(η6-p-cymene)RuCl}2(μ-Cl)2] with azophenol ligands (HL3–HL6) in the presence of sodium carbonate in CH2Cl2. The molecular structure of the 1-(phenylazo)-2-naphthol complex has been determined by X-ray crystallography. The complex has a η6-p-cymene group, a chloride and a bidentate N,O-donor azophenol ligand. The complexes have been characterized from NMR spectral data. The catalytic activity of the complexes has been studied for the conversion of acetophenone to the corresponding alcohol in the presence of KOH and isopropanol. Complexes 4 and 6 having a methoxy group attached to the ortho-position of the phenylazo moiety and 2 with a methyl group in the meta-position of the phenolic moiety show high percentage conversion (>84%).

Variable temperature x-ray crystal structure analysis of a type I langbeinite: Rb2Cd2(SO4)(3)

The structure of a type I langbeinite, Rb2Cd2(SO4)(3), displays three different phases, cubic with a = 10.378(5) Angstrom (space group P2(1)3) at room temperature, monoclinic at 120 K with a = 10.328(3), b = 10.322(3), c = 10.325(3) Angstrom, beta = 89.975(1)degrees (space group P2(1)), and orthorhombic at 85 K with a = 10.319(2), b = 10.321(2), c = 10.320(2) Angstrom (space group P2(1)2(1)2(1)), respectively. Precise single-crystal analyses of these phases indicate that Rb2Cd2(SO4)(3) distorts initially from cubic to monoclinic upon cooling followed by a significant reorientation of the SO4 tetrahedra, resulting in an orthorhombic symmetry upon further cooling. The three structures have been established unequivocally using the same crystal. There is no indication of the formation of an intermediate triclinic phase or any lattice disorder as conjectured in several earlier reports on compounds belonging to the type I langbeinite. The bond valence sum analyses of the coordination around the Rb sites indicate asymmetry in the bond strengths which could be the driving force of the ferroelectric behavior in these materials.

Novel double insertion of carbon disulfide into two Ru-H bonds of [(dppm)(2)Ru(H)(2)] (dppm = Ph2PCH2PPh2): Synthesis and crystal structure of a methanedithiolate complex

Addition of excess carbon disulfide to cis/trans-[(dPPM)(2)Ru(H)(2)] results in the methanedithiolate complex [(dppm)(2)Ru(eta(2)-S2CH2)] 4 via the intermediacy of cis-[(dppm)(2)Ru(H)(SC(S)H)] 2. The X-ray crystal structure of this species has been determined.

Stereochemistry of the marine sesquiterpene 2-thiocyanatoneopupukeanane: Crystal structure of neopupukean-2-yl 4-nitrobenzoate

Single crystal X-ray diffraction analysis of neopupukean-2-yl p-nitrobenzoate unambiguously established the stereochemistry of the thiocyanate group as endo in the marine sesquiterpene 2-thiocyanatoneopupukeanane.

Crystal structure of quenched and in-field electroluminescent phosphors

Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.

Crystal Structure, Thermal Expansion and ElectricaH Conductivity of Yo.sCao.2Fel-x Mnx03+o (0 < x < 1.0)

The crystal structure, thennal expansion and electrical conductivity of the solid solutions YOgCao.2Fel-x MnxOJ+c5 (0 ~ x ~ 1.0) were investigated. All compositions had the GdFeOrtype orthorhombic perovskite structure with trace amounts of a second phase present in case of x = 0.8 and 1.0. The lattice parameters were detennined at room tempe'rature by using X-ray powder diffraction (XRPD). The pseudocubic lattice constant decreased with increasing x. The average I inear thermal expansion coefficient (anv) in the temperature range from 673 to 973 K showed negligible change with x up to x = 0.4. The thennal expansion curve for x = I had a slope approaching zero in the temperature range from 648 to 948 K. The calculated activation energy values for electrical conduction indicate that conduction occurs primarily by the small polaron hopping mechanism. The drastic drop in electrical conductivity for a small addition of Mn (0 ~ x ~ 0.2) is caused by the preferential fonnation of Mn4t ion~ (rather than Fe4 +) which act as carrier traps. This continues till the charge compensation for the divalent ions on the A-site is complete. The results indicate that with further increase in manganese content (beyond x =0.4) in the solid solutions, there is an increase in exc :::ss oxygen and consequently, a small increase in Mn'll il>I1~, which are charge compensated by the formation of cation vancancies.

Crystal structure of a beta-prism II lectin from Remusatia vivipara

The crystal structure of a beta-prism II (BP2) fold lectin from Remusatia vivipara, a plant of traditional medicinal value, has been determined at a resolution of 2.4 A. This lectin (RVL, Remusatia vivipara lectin) is a dimer with each protomer having two distinct BP2 domains without a linker between them. It belongs to the ``monocot mannose-binding'' lectin family, which consists of proteins of high sequence and structural similarity. Though the overall tertiary structure is similar to that of lectins from snowdrop bulbs and garlic, crucial differences in the mannose-binding regions and oligomerization were observed. Unlike most of the other structurally known proteins in this family, only one of the three carbohydrate recognition sites (CRSs) per BP2 domain is found to be conserved. RVL does not recognize simple mannose moieties. RVL binds to only N-linked complex glycans like those present on the gp120 envelope glycoprotein of HIV and mannosylated blood proteins like fetuin, but not to simple mannose moieties. The molecular basis for these features and their possible functional implications to understand the different levels of carbohydrate affinities in this structural family have been investigated through structure analysis, modeling and binding studies. Apart from being the first structure of a lectin to be reported from the Araceae/Arum family, this protein also displays a novel mode of oligomerization among BP2 lectins.

Synthesis, X-ray crystal structure, DNA binding, antioxidant and cytotoxicity studies of Ni(II) and Pd(II) thiosemicarbazone complexes

New complexes, [Ni(HL)(PPh3)]Cl (1), [Pd(L)(PPh3)](2), and [Pd(L)(AsPh3)](3), were synthesized from the reactions of 4-chloro-5-methyl-salicylaldehyde thiosemicarbazone [H2L] with [NiCl2(PPh3)(2)], [PdCl2(PPh3)(2)] and [PdCl2(AsPh3)(2)]. They were characterized by IR, electronic, H-1-NMR spectral data. Further, the structures of the complexes have been determined by single crystal X-ray diffraction. While the thiosemicarbazone coordinated as binegative tridentate (ONS) in complexes 2 and 3, it is coordinated as mono negative tridentate (ONS) in 1. The interactions of the new complexes with calf thymus DNA was examined by absorption and emission spectra, and viscosity measurements. Moreover, the antioxidant properties of the new complexes have also been tested against DPPH radical in which complex 1 exhibited better activity than that of the other two complexes 2 and 3. The in vitro cytotoxicity of complexes 1-3 against A549 and HepG2 cell lines was assayed, and the new complexes exhibited higher cytotoxic activity with lower IC50 values indicating their efficiency in killing the cancer cells even at very low concentrations.

Synthesis, spectroscopic properties and biological evaluation of transition metal complexes of salicylhydrazone of anthranilhydrazide: X-ray crystal structure of copper complex

The transition metal complexes of salicylhydrazone of anthranilhydrazide (H2L) were synthesised. The structures of metal complexes were characterized by various spectroscopic [IR, NMR, UV-Vis, EPR], thermal and other physicochemical methods. The single-crystal X-ray diffraction study of [Cu(HL)Cl]center dot H2O reveal its orthorhombic system with space group P2(1)2(1)2 and Z=4. The copper center has a distorted square planar geometry with ONO and Cl as the donor atoms. The ligand and its metal chelates have been screened for their antimicrobial and anti-tubercular activities using serial dilution method. Metal complexes in general have exhibited better antibacterial and antifungal activity than the free ligand and in few cases better than the standard used. Among the bacterial strains used, the complexes are highly potent against Gram-positive strains compared to Gram-negative. Anti-tubercular activity exhibited by the Co(II) complex is comparable with the standard used. (C) 2011 Elsevier B. V. All rights reserved.