Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15)

The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.     

Reversible guest exchange and ferrimagnetism (T(C) = 60.5 K) in a porous cobalt(II)-hydroxide layer structure pillared with trans-1,4-cyclohexanedicarboxylate

The synthesis, characterization, and reversible guest-exchange chemistry of a new porous magnetic material that orders ferrimagnetically at 60.5 K are described. The material, Co(5)(OH)(8)(chdc).4H(2)O (chdc = trans-1,4-cyclohexanedicarboxylate), contains tetrahedral-octahedral-tetrahedral Co(II)-hydroxide layers of composition Co((oct))(3)Co((tet))(2)(OH)(8) that are linked together by bis(unidentate) chdc pillars. Noncoordinated water molecules occupy 1-D channels situated between the chdc pillars. The material remains monocrystalline during dehydration from Co(5)(OH)(8)(chdc).4H(2)O (CDCC.4H(2)O) to Co(5)(OH)(8)(chdc) (CDCC) via an intermediate Co(5)(OH)(8)(chdc).2H(2)O (CDCC.2H(2)O) upon heating or evacuation. In-situ single crystal and powder X-ray diffraction analyses indicate that the interlayer spacing decreases in two steps, each corresponding to the loss of two water molecules per formula unit as determined by thermogravimetry. The single crystal structure of the fully dehydrated material, CDCC, has no void volume due to a tilting of the pillars and 9% decrease of the interlayer spacing with water removal. Exposure of CDCC to air causes rapid rehydration of this material to CDCC.4H(2)O, as determined by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetry, and vibrational spectroscopy. Both the hydrated and dehydrated forms order magnetically below 60.5 K. The susceptibility data are consistent with ferrimagnetic behavior, and the value of the saturation magnetization at 2 K (ca. 2 micro(B)) is explained by a model of two sublattices, one comprising three octahedral cobalt atoms and another comprising two tetrahedral cobalt atoms. There is an enhanced 2-D correlation within the layer at temperatures just above the Curie temperature, as seen by nonlinearity in the ac susceptibility data and remanence in the isothermal magnetization. The crossover from 2-D to 3-D ordering occurs at T(C). The large anisotropy in the magnetization data on a single crystal suggests either a 2-D Ising or an XY magnet while the critical exponent of 0.25 is in favor of the latter. Both magnetization data in a small field in the ac and dc mode and isothermal magnetization data provide evidence of a further change in behavior at 23 K, which may originate from a reorientation of the moments within the layer. Variation of the pillar and of the guest-exchange chemistry, including the exchange of magnetic guests such as O(2), offers the possibility of tailoring the magnetic properties of this material.     

Orthogonal spin arrangement in quasi-two-dimensional La2Co2O3Se2

The crystal, electronic, and magnetic structures of the cobalt oxyselenide La(2)Co(2)O(3)Se(2) were investigated through powder neutron diffraction measurements and band structure calculations. This oxyselenide crystallizes in a tetragonal layered structure with space group I4/mmm. The Co ion is sixfold-coordinated by two oxide ions and four selenide ions, and the face-sharing CoO(2)Se(4) octahedra form Co(2)OSe(2) layers. The band structure calculations revealed that the Co ion is in the divalent high-spin state. Rietveld analysis of the neutron diffraction profiles below 200 K demonstrated that the Co moments have a noncollinear antiferromagnetic structure with the propagation vector k = (?, ?, 0). The ordered magnetic moment was determined to be 3.5 μ(B) at 10 K, and the directions of the nearest-neighbor Co moments are orthogonal each other in the c plane.     

Highly porous Co(II)-salicylate metal-organic framework: synthesis, characterization and magnetic properties

A new porous Co(II)-salicylate metal-organic framework material has been synthesized hydrothermally through the reaction of Co(II) chloride with sodium salicylate under mild alkaline pH conditions. To get an idea about the structural aspect of the material from the powder X-ray diffraction (PXRD) pattern, MAUD program has been successfully utilized and the assigned peaks match very well with a new tetragonal phase (space group, P4mm) having the unit cell parameters: a = b = 12.957 (0.042) ?; c = 12.738 (0.019) ?; α = β = γ = 90°, V = 2138.73 ?(3). N(2) adsorption/desorption analyses suggested the material is highly porous in nature having high BET surface area and pore dimensions of 2.0-3.0 nm, which is within the range of small mesopores. Thermogravimetric analysis (TGA) revealed that the H(2)O molecules may be removed from the framework without collapsing the structure and the material is stable up to ca. 573 K. The material is characterized thoroughly by using different characterization tools such as TEM, SEM, UV-visible reflectance spectroscopy, FT IR spectroscopy and photoluminescence spectroscopy. X-Ray photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the cobalt atom and presence of other elements within the framework. The material shows interesting magnetic properties, where the magnetic moments monotonically increase with the decrease in temperature down to 9 K. Below 9 K there is a steep increase in magnetization on further lowering the temperature, thereby suggesting the onset of a long range ferromagnetic transition with ferromagnetic Curie temperature, T(C) = 8.5 K. Furthermore, the M-H curve at 2 K shows a clear hysteresis loop with a coercive field 150 Oe and remnant magnetization 0.8 μ(B)/f.u.     

Nuclear and magnetic structures and magnetic properties of the layered cobalt hydroxysulfate Co5(OH)6(SO4)2(H2O)4 and its deuterated analogue, Co5(OD)6(SO4)2(D2O)4

The structures (nuclear and magnetic), magnetic properties (2-300 K, 1-10(4) bar), and heat capacity of the layered ferromagnet Co5(OH)6(SO4)2(H2O)4 are reported. The crystal structure consists of brucite-like M(II)-OH layers of edge-sharing octahedra, but having two different Co sites, which are pillared by ...O3SO-Co(H2O)4-OSO3.... The absorption spectrum confirms the presence of divalent Co, and by comparison of the two isotopic materials, the assignment of the vibrational spectra is proposed. The magnetic properties are those of a ferromagnet with a Curie temperature of 14 K. Temperature and field dependence magnetization data taken on an aligned sample suggest an easy-plane magnet. The Curie temperature increases linearly with pressure at a rate of +0.12 K/kbar, suggesting small progressive and uniform modifications of the Co-Co exchange interactions. Rietveld refinement of the neutron powder diffraction data and consideration of a group analysis reveal the direction of the moments of the Co within the layer to be along the b-axis, with a maximum moment of 3.33 micro(B) per cobalt. Those of the pillars remain random. Estimation of the entropy from the heat capacity data accounts for the presence of four ordered moments of Co with spin 1/2 at the long-range ordering temperature, while the moment of the pillaring Co contributes only at lower temperature due to the increase of the internal field as the temperature is lowered. The purely 2D-magnetic ordering in an easy-plane magnet, evidenced by neutron diffraction and heat capacity, challenges the existing theories and is a rare example of a single-layer magnet.     

Enhancement of the Curie temperature by isomerization of diarylethene (DAE) for an organic-inorganic hybrid system: Co4(OH)7(DAE)0.5.3H2O

Intercalation of an organic photochromic molecule into layered magnetic systems may provide multifunctional properties such as photomagnetism. To build up a photosensitive multifunctional magnet, an organic-inorganic hybrid system coupled with a photochromic diarylethene anion, 2,2'-dimethyl-3,3'-(perfluorocyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (DAE), and cobalt LDHs (layered double hydroxides), Co4(OH)7(DAE)0.5.3H2O, was synthesized by the anion exchange reaction between Co2(OH)3(CH3COO).H2O and DAE. In the dark and under UV-irradiated (313 nm) conditions, Co4(OH)7(DAE)0.5.3H2O with open and closed forms of DAE were obtained, respectively. The magnetic susceptibility measurements elucidated ferromagnetic intra- and interlayer interactions and Curie temperatures of TC = 9 and 20 K for cobalt LDHs with the open and closed forms of DAE, respectively. The enhancement of the Curie temperature from 9 to 20 K by substitution of the open form of DAE with the closed form of DAE as an intercalated molecule is attributed to the delocalization of the pi-electrons in the closed form of DAE, which enhances the interlayer magnetic interaction. The enhancement of the interlayer magnetic interaction induced by the delocalization of pi-electrons in intercalated molecules is strongly supported by the fact that the Curie temperature (26.0 K) of cobalt LDHs with (E,E)-2,4-hexadienedioate having a conjugated pi-electron system is enormously higher than that (7.0 K) of the cobalt LDHs with hexanedioate. By UV irradiation at 313 nm, Co4(OH)7(DAE)0.5.3H2O shows the photoisomerization of DAE from the open form to the closed one in the solid state, which leads to the enhancement of Curie temperature.     

Synthesis and Characterization of Cobalt-Carbon Core-Shell Microspheres in Supercritical Carbon Dioxide System

The synthesis of cobalt-carbon core-shell microspheres in supercritical carbon dioxide system was investigated. Cobalt-carbon core-shell microspheres with diameter of about 1 μm were prepared at 350 oC for 12 h in a closed vessel containing an appropriate amount of bis(cyclopentadienyl)cobalt powder and dry ice. Characterization by a variety of techniques, including X-ray powder diffraction, X-ray photoelectron spectroscopy, Transmission electron microscope, Fourier transform infrared spectrum and Raman spectroscopy analysis reveals that each cobalt-carbon core-shell microsphere is made up of an amorphous cobalt core with diameter less than 1 μm and an amorphous carbon shell with thickness of about 200 nm. The possible growth mechanism of cobalt-carbon core-shell microspheres is discussed, based on the pyrolysis of bis(cyclopentadienyl)cobalt in supercritical carbon dioxide and the deposition of carbon or carbon clusters with odd electrons on the surface of magnetic cobalt cores due to magnetic attraction. Magnetic measurements show 141.41 emu/g of saturation magnetization of a typical sample, which is lower than the 168 emu/g of the corresponding metal cobalt bulk material. This is attributed to the considerable mass of the carbon shell and amorphous nature of the magnetic core. Control of magnetism in the cobalt-carbon core-shell microspheres was achieved by annealing treatments.     

Crystal and magnetic structure of the double perovskite Sr2CoUO6: a neutron diffraction study

Sr2CoUO6 double perovskite has been prepared as a polycrystalline powder by solid-state reaction, in air. This material has been studied by X-ray, neutron powder diffraction (NPD) and magnetic measurements. At room temperature, the crystal structure is monoclinic, space group P2(1)/n, Z= 2, with a= 5.7916(2), b= 5.8034(2), c= 8.1790(3) A, beta= 90.1455(6)degrees. The perovskite lattice consists of a completely ordered array of CoO6 and UO6 octahedra, which exhibit an average tilting angle phi= 11.4 degrees. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below TN = 10 K. The low-temperature magnetic structure was determined by NPD, selected among the possible magnetic solutions compatible with the P2(1)/n space group, according with the group theory representation. The propagation vector is k= 0. A canted antiferromagnetic structure is observed below TN = 10 K, which remains stable down to 3 K, with an ordered magnetic moment of 2.44(7)mu(B) for Co2+ cations. The magnetic moment calculated from the Curie-Weiss law at high temperatures (5.22 mu(B)/f.u.) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co2+((4)T(1g) ground state) in a quasi-regular octahedral environment. Magnetic and structural features are consistent with an electronic configuration Co2+[3d(7)]-U6+[Rn].     

Local atomic and electronic structure of quantum dots based on Mn- and Co-doped ZnS

Solid solutions of zinc sulfide with manganese and cobalt are synthesized. Based on the analysis of X-ray diffraction profiles the conclusion is drawn about the formation of a hexagonal wurtzite type structure in the synthesized quantum dot (QD) solutions. The average crystallite sizes are 8 nm and 22 nm for the samples with manganese and cobalt respectively. Results of IR and optical spectroscopy are consistent with the powder X-ray diffraction and X-ray fluorescence data. The question about particle aggregation in isopropanol and DMF solutions is considered. The QD structures based on ZnS particles doped with Mn and Co transition metal atoms are modeled. The possibility to apply X-ray absorption near edge structure (XANES) spectroscopy to verify the atomic structure parameters around the positions of doping transition metal atoms in QDs of the ZnS family is shown. Partial densities of ZnS:Mn and ZnS:Co electronic states are calculated.     

Magnetism and Photocatalytic Degradation of Organic Dyes Based on a New Metal Formate Framework

A new MOF of [Co(HCOO)₂] · 0.33DMF (I) was prepared and characterized by IR, powder X-ray diffraction, and single-crystal X-ray diffraction (CIF file CCDC no. 1571166). Complex I exhibits a diamond framework based on Co-centered CoCo₄ tetrahedral nodes, in which all metal ions have octahedral coordination geometry and all HCOO groups link the metal ions in syn-syn/anti modes. The magnetic property shows a main antiferromagnetic interaction and the ferromagnetic phase transition below 2 K. Furthermore, the photocatalytic properties of I for degradation of the methyl violet and Rhodamine B have been explored.     

稀土复合硫化物Ln6MSi2S14(M=Co、Ni)的合成

用气固相反应合成出一系列Ln₆MSi₂S₁₄(Ln=La·Dy,M=Co、Ni)化合物,给出了X射线粉末衍射数据和晶胞参数。     

Designing binuclear transition metal complexes: a new example of the versatility of N,N'-bis(2-aminobenzyl)-4,13-diaza-18-crown-6

N,N'-Bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L) is a versatile receptor able to adapt to the coordinative preferences of different metal cation guests. With first-row transition metal ions, L tends to form binuclear complexes but, depending on the nature of the particular metal ion, the structure of the binuclear complex may be very different. Herein we report a study of the structure and magnetic properties of the corresponding nickel(II) and cobalt(II) complexes. The X-ray crystal structure of the nickel complex (1), with formula [Ni2(L)(CH3CN)4](ClO4)4.CH3CN, shows that this compound presents a symmetric coordination environment with L adopting an anti arrangement. Each Ni(II) ion is six-coordinate in a distorted octahedral environment, and both metal ions are quite far from each other. On the other hand, the X-ray crystal structure of the cobalt complex (2), with formula [Co(L)(mu-OH)Co(CH3CN)](ClO4)3, reveals a rather different structure. Coordination number asymmetry is found: one of the Co(II) is five-coordinate in a distorted trigonal-bipyramidal coordination environment, while the second Co(II) ion is six-coordinate in a distorted octahedral arrangement. Now L adopts a syn arrangement and a hydroxide group acts as a bridge between both cobalt ions. This hydroxo-bridged Co(II) binuclear complex shows structural features that mimic the active site of methionine aminopeptidases. The magnetic properties of 1 and 2 have been investigated in the temperature range 2.0-300 K. Whereas 1 displays a Curie law except for temperatures below 50 K where zero-field splitting of the S= 1 ground state is observed, antiferromagnetic exchange in the singular asymmetric binuclear Co(II) complex 2 has been observed. This magnetic behaviour has been fitted considering first-order spin-orbit coupling in the assumed axially distorted octahedral site and totally quenched orbital contribution in the five-coordinate site in which zero-field splitting of the S= 3/2 ground state is operative.     

Rational design of 1-D metal-organic frameworks based on the novel pyrimidine-4,6-dicarboxylate ligand. New insights into pyrimidine through magnetic interaction

Single crystal X-ray analysis of compounds H2pmdc.2H2O (1), KHpmdc (2), and K2pmdc (3) shows that the pyrimidine-4,6-dicarboxylate (pmdc) dianion presents an almost planar geometry which confers a potential capability to act as a bis-bidentate bridging ligand, and therefore, to construct 1-D metal complexes. Based on this assumption, we have designed the first six transition metal complexes based on this ligand of formula {[M(micro-pmdc)(H2O)2].H2O}n [M(II) = Fe (4), Co (5), Ni (6), Zn (7), Cu (8)] and {[Cu(micro-pmdc)(dpa)].4H2O}n (9) (dpa = 2,2'-dipyridylamine). The crystal structure of all of these complexes has been determined by single crystal X-ray measurements, except for compound whose X-ray powder diffraction pattern reveals that it is isostructural to compounds 4-7. The bis-chelating pmdc ligand bridges sequentially octahedrally coordinated M(II) centres leading to polymeric chains. The hexacoordination of the metal centres is completed by two water molecules in compounds 4-8 and by the two endocyclic-N atoms of a terminal dpa ligand in compound . Cryomagnetic susceptibility measurements show the occurrence of antiferromagnetic intrachain interactions for compounds and (J = -2.5 (4), -5.2 (6), -32.7 (8), and -0.9 (9) cm(-1)). Model calculations and analyses of the available experimental data have been used to examine the influence of several factors on the nature and magnitude of the magnetic coupling constants in pyrimidine bridged complexes, showing that metal deviation from the pyrimidine mean plane could lead to ferromagnetic behaviour.     

X-ray single-crystal structure and magnetic properties of Fe[CH(3)PO(3))] x H(2)O: a layered weak ferromagnet

The crystal and molecular structure of the layered weak-ferromagnet Fe[CH(3)PO(3)] x H(2)O has been solved by X-ray single-crystal diffraction techniques. Crystal data for Fe[CH(3)PO(3)] x H(2)O are the following: orthorhombic space group Pna2(1); a =17.538(2), b = 4.814(1), c = 5.719(1) A. The structure is lamellar, and it consists of alternating organic and inorganic layers along the a direction of the unit cell. The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from oxygen of the water molecule. Each phosphonate group coordinates four metal ions, through chelation and bridging, making in this way a cross-linked Fe-O network. The resultant layers are then separated by bilayers of the methyl groups, with van der Waals contacts between them. The compound is air stable, and it dehydrates under inert atmosphere at temperatures above 120 degrees C. The oxidation state of the metal ion is +2, and the electronic configuration is d(6)( )()high spin (S = 2), as determined from dc magnetic susceptibility measurements from 150 K to ambient temperature. Below 100 K, the magnetic moment of Fe[CH(3)PO(3)] x H(2)O rises rapidly to a maximum at T(max) approximately equal to 24 K, and then it decreases again. The onset of peak at T = 25 K is associated with the 3D antiferromagnetic long-range ordering, T(N). The observed critical temperature, T(N), is like all the other previously reported Fe(II) phosphonates, and it appears to be nearly independent of the interlayer spacing in this family of hybrid organic-inorganic layered compounds. Below T(N), the compound behaves as a "weak ferromagnet", and represents the third kind of magnetic materials with a spontaneous magnetization below a finite critical temperature, ferromagnets and ferrimagnets being the other two types.     

Spin-glass behavior in LaFe(x)Co(2-x)P2 solid solutions: interplay between magnetic properties and crystal and electronic structures

To explore the evolution of magnetic properties from ferromagnetic LaCo(2)P(2) to paramagnetic LaFe(2)P(2) (both of ThCr(2)Si(2) structure type) a series of mixed composition LaFe(x)Co(2-x)P(2) (x ≤ 0.5) has been comprehensively investigated by means of single-crystal and powder X-ray and neutron diffraction, magnetization and heat capacity measurements, M?ssbauer spectroscopy, and electronic band structure calculations. The Curie temperature decreases from 132 K in LaCo(2)P(2) to 91 K in LaFe(0.05)Co(1.95)P(2). The ferromagnetic ordering is suppressed at higher Fe content. LaFe(0.1)Co(1.9)P(2) and LaFe(0.2)Co(1.8)P(2) demonstrate spin-glass-like behavior, which was also confirmed by the absence of characteristic features of long-range magnetic ordering, namely, a λ-type anomaly in the heat capacity, a hyperfine splitting in the M?ssbauer spectrum, and magnetic reflections in the neutron diffraction pattern. Finally, both LaFe(0.3)Co(1.7)P(2) and LaFe(0.5)Co(1.5)P(2) exhibit paramagnetic behavior down to 1.8 K. The unit cell parameters of the mixed compounds do not follow the Vegard behavior as the increase in the Fe content results in the decrease of average M-M distances (M = Fe, Co). Quantum-chemical calculations and crystal orbital Hamiltonian population analysis reveal that upon aliovalent (nonisoelectronic) substitution of Fe for Co the antibonding character of M-M interactions is reduced while the Fermi level is shifted below the DOS peak in the 3d metal subband. As the result, at higher Fe content the Stoner criterion is not satisfied and no magnetic ordering is observed.     

Valence instabilities, phase transitions, and abrupt lattice expansion at 5 K in the YbGaGe system

The powder synchrotron X-ray diffraction technique was used to study the thermal expansion behavior of the mixed valence layered compound, YbGa1.05Ge0.95 in the temperature range 3-1123 K. A surprising abrupt isosymmetric phase transition, accompanied by a dramatic volume increase (negative thermal expansion), was found at 5 K induced by a sudden Yb valence transition from +(2 + epsilon) toward +2. At high temperatures, the material undergoes a transformation to a highly disordered structure until it eventually collapses at 1123 K to a structure with isovalent Yb ions and flat Ga/Ge planes (AlB2 type).     

Technetium tetrachloride revisited: a precursor to lower-valent binary technetium chlorides

Technetium tetrachloride has been prepared from the reaction of technetium metal with excess chlorine in sealed Pyrex ampules at elevated temperatures. The product was characterized by single-crystal and powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and alternating-current magnetic susceptibility. Solid TcCl(4) behaves as a simple paramagnet from room temperature down to 50 K with μ(eff) = 3.76 μ(B). Below 25 K, TcCl(4) exhibits an antiferromagnetic transition with a Néel temperature (T(N)) of ～24 K. The thermal behavior of TcCl(4) was investigated under vacuum at 450 °C; the compound decomposes stepwise to α-TcCl(3) and TcCl(2).     

Chiral molecular magnets: synthesis, structure, and magnetic behavior of the series [M(L-tart)] (M = Mn(II), Fe(II), Co(II), Ni(II); L-tart = (2R,3R)-(+)-tartrate)

A new series of layered magnets with the formula [M(L-tartrate)] (M = Mn(II), Co(II), Fe(II), Ni(II); L-tartrate = (2R,3R)-(+)-tartrate) has been prepared. All of these compounds are isostructural and crystallize in the chiral orthorhombic space group I222, as found by X-ray structure analysis. Their structure consists of a three-dimensional polymeric network in which each metal shows distorted octahedral coordination bound to four L-tartrate ligands, two of which chelate through an alcohol and a carboxylate group and the other two bind terminally through a monodentate carboxylate group. The chirality of the ligand imposes a Delta conformation on all metal centers. Magnetically, the paramagnetic metal centers form pseudotetragonal layers in which each metal is surrounded by four other metals, with syn,anti carboxylate bridges. These salts show intralayer antiferromagnetic or ferromagnetic interactions, depending on the electronic configuration of the metal, and weak interlayer antiferromagnetic interaction. In all cases the magnetic properties are strongly affected by the anisotropy of the system, and the presence of magnetic canting has been found. The Mn derivative behaves as a weak ferromagnet with a critical temperature of 3.3 K. The Ni derivative shows very unusual magnetic behavior in that it exhibits antiferromagnetic ordering below 6 K, the onset of spontaneous magnetization arising from spin reorientation into a canted phase below 4.5 K, and a field-induced ferromagnetic state above 0.3 T at 2 K, behavior typical of metamagnets. The Fe and Co derivatives show antiferromagnetic interactions between spin carriers, but do not order above 2 K.     

Synthesis,structural studies and bio-activity of some metal(II) complexes with glyoxal salicylaldehyde acyldihydrazones

Complexes of the type [M(gssdh)]Cl and [M(gspdh)]Cl, where M?=?Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), Hgssdh?=?glyoxal salicylaldehyde succinic acid dihydrazone and Hgspdh?=?glyoxal salicylaldehyde phthalic acid dihydrazone, have been synthesized and characterized by elemental analyses, molar conductance, magnetic moments, electronic, ESR and IR spectra and X-ray powder diffraction studies. The metal complexes are insoluble in common organic solvents and are 1?:?1 electrolytes. The magnetic moment values and electronic spectra indicate a spin–free octahedral geometry for all Co(II), Ni(II) and Cu(II) complexes. ESR spectral parameters of Cu(II) complexes suggest an elongated tetragonally–distorted octahedral stereochemistry around copper. Both ligands are monobasic hexadentate ligands coordinating through three >C=O, two >C=N– and a deprotonated phenolate group to the metal. X-ray powder diffraction parameters for three of the complexes correspond to an orthorhombic crystal lattice. The complexes show appreciable activity against various fungi and bacteria.     

Ordering double perovskite hydroxides by kinetically controlled aqueous hydrolysis

The precipitation of crystals with stoichiometric and ordered arrangements of distinct metal cations often requires carefully designed molecular precursors and/or sufficient activation energy in addition to the necessary mass transport. Here, we study the formation of ordered double perovskite hydroxides, MnSn(OH)(6) and CoSn(OH)(6), of the generic chemical formula, BB'(OH)(6) (no A site), using kinetic control of aqueous hydrolysis from simple metal salt solutions. We find that the precipitation yields ordered compounds only when the B ion is Mn(II) or Co(II), and not when it is any other divalent transition metal ion, or Zn(II). The key step in forming the compounds is the prevention of rapid and uncontrolled hydrolysis of Sn(IV), and this is achieved by a fluoride counteranion. The two compounds, MnSn(OH)(6) and CoSn(OH)(6), are studied by high-resolution synchrotron X-ray diffraction and from the temperature dependence of magnetic behavior. From maximum entropy image restoration of the electron density and from Rietveld analysis, the degree of octahedral distortion and tilting and the small extent of anti-site disorder are determined. From the nonoverlapping electron density, we infer strongly ionic character of bonding. As the first magnetic study of such materials, we report simple paramagnetic behavior with no long-range magnetic order down to 2 K for the Mn(II) compound, while the cobalt compound presents uncompensated antiferromagnetic interactions, attributed to the single-ion anisotropy of octahedral Co(II).