Synthesis and magnetic properties of nickel ferrite nano-octahedra

High yield of nickel ferrite nano-octahedra with size distribution from 40 to 90 nm were synthesized through a simple hydrothermal method. The formation of faceted octahedra enclosed by {111} planes implies the much faster growth rate along 〈100〉 over 〈111〉 for face-centered cubic phase during hydrothermal process. Magnetic measurements indicated that the sample is soft-magnetic materials with much lower coercivity and much higher saturation magnetization compared to the nickel ferrite nano-crystals with similar size distribution but irregular shapes reported earlier.     

Controlled synthesis of monodisperse silver nanocubes in water

Monodisperse silver nanocubes with edge length of 55 +/- 5 nm were, for the first time, synthesized in water on the basis of HTAB-modified silver mirror reaction at 120 degrees C (HTAB, n-hexadecyltrimethylammonium bromide). The individual nanocube was crystallographically well defined with a single crystal bonded by six {200} facets. The nanocubes were soluble to form stable aqueous solutions and had a strong tendency to assemble into two-dimensional arrays with regular checked pattern on substrate.     

Synthesis of monodisperse,magnetic latex particles with polystyrene core

A novel method for producing monodisperse, submicron-sized magnetic latex particles is described. The method provides coating of polymer particles with surface-modified magnetic particles during soap-free polymerization. Experiments were performed with styrene monomer, potassium persulfate initiator, Fe ₃O ₄ magnetic particles, and silane-coupling reagents of methacryloxypropyltrimethoxysilane (MPTMS) and methacryloxypropyldimethoxysilane (MPDMS). The morphology of the magnetic particles depended on the silane-coupling reagents. Use of the tri-functional coupling reagent MPTMS produced particles having a disk-like or concave-like shape, whereas use of the di-functional coupling reagent MPDMS produced spherical particles that had a coefficient of variation of 4.4%, which was much smaller than the standard criteria of monodispersity, 10%.     

Synthesis,characterization, and optical properties of monodisperse chiral oligofluorenes

The first series of monodisperse chiral oligofluorenes was synthesized and characterized. Chain length was found to play an important role in solid morphology. Whereas dimer through tetramer are amorphous, pentamer through hexadecamer all show cholesteric mesomorphism with varying degrees of morphological stability against crystallization. Pristine spin-cast films, approximately 90 nm in thickness, are amorphous but exhibit pronounced circular dichroism and highly efficient circularly polarized fluorescence, suggesting the presence of chiral assemblies that remain to be experimentally characterized. A nonamer with two sets of the 2S-methylbutyl group replaced by the 3S,7-dimethyloctyl group was prepared and shown to be capable of forming a monodomain, glassy cholesteric film with thermal treatment. The cholesteric film is responsible for an order-of-magnitude increase in circular dichroism and a handedness reversal in circularly polarized fluorescence as compared to the amorphous pristine film. Molecular dynamics simulation furnished new insight into the molecular origin of the observed chiral optical properties in neat films.     

Synthesis and electronic properties of monodisperse oligophenothiazines

Starting from N-hexylphenothiazine, a versatile construction kit of brominated and borylated phenothiazines can be easily prepared by a sequence of bromination, bromo-lithium exchange/borylation, and Suzuki coupling. Subsequent Suzuki arylation of the building blocks gives soluble, monodisperse, and structurally well defined oligophenothiazines in good yields. The molecular weights at the peak maximum (Mp), obtained by GPC (gel permeation chromatography), and the actual molecular weights of the oligomer series, obtained by mass spectrometry, show excellent correlation. A QM/MM conformational analysis for the complete series reveals that the obvious butterfly-shaped phenothiazine structure multiplies and significantly reduces the hydrodynamic volume of the oligomers. The electronic properties (absorption and emission spectroscopy and cyclic voltammetry) give reasonable correlations with the chain length. With regard to the emission maxima, the effective conjugation length is already reached with the hexamer. Oligophenothiazines are highly fluorescent, with high fluorescence quantum yields, and are simultaneously highly electroactive, with low oxidation potentials.     

Synthesis and properties of monodisperse polydimethylsiloxane networks

α,ω-Divinyl-terminated polydimethylsiloxane polymers with low polydispersivity were synthesized via anionic polymerization of hexamethylcyclotrisiloxane (D₃). Five “monodisperse” polymers with different molecular weights were hydrosilylated with tetrakisdimethylsiloxysilane in the presence of platinum catalysts and inhibitors to form crosslinked networks. Control studies to determine the effect of platinum, silicon hydride, and heat were performed to verify that no redistribution occurred during hydrosilylation. The properties of these cured samples were characterized chemically by degradation with trifluoromethanesulfonic acid in the presence of hexamethyldisiloxane, infrared spectroscopy, and nuclear magnetic spectroscopy. Mechanical properties were studied by measurements of Shore A hardness, dynamic shear modulus, and tensile modulus. The relationship between the molecular weight of the vinyl polymer and the final properties of the cured networks was measured. © 1993 John Wiley & Sons, Inc.     

Synthesis, structure, and magnetic properties of amine-templated open-framework nickel(II) sulfates

Two organically templated nickel sulfates of the compositions [C(4)N(2)H(12)][Ni(3)F(2)(SO(4))(3)(H(2)O)(2)] (I) and [C(4)N(2)H(12)][Ni(2)F(4)(SO(4))H(2)O] (II) with open architectures have been synthesized under hydro/solvothermal conditions in the presence of piperazine. I has a layered structure formed by sinusoidal chains comprising hexameric units, whereas II has a three-dimensional structure with 10-membered channels. The layered Ni(II) sulfate, I, is ferrimagnetic, exhibiting hysteresis at low temperatures. The three-dimensional Ni(II) sulfate, II, is essentially paramagnetic. We have also obtained layered compounds isostructural with I containing other amines.     

Synthesis and magnetic properties of one-dimensional zinc nickel oxide solid solution

A novel facile method has been demonstrated for large-scale synthesis of zinc-oxide-based one-dimensional solid solution with a series percentage of nickel dopant. The obtained Zn1-xNixO nanorods were characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and energy dispersed X-ray spectroscopy. The result shows that the obtained Zn1-xNixO nanorods are single crystalline with the Ni2+ dopants occupying tetrahedral Zn2+ cation sites of wurtzite ZnO. Moreover, the Zn1-xNixO nanorods exhibit robust high-Curie-temperature (TC) ferromagnetism at 300 K.     

Synthesis and magnetic properties of dithiooxamide-bridged nickel(II) complexes

Two novel nickel(II) dinuclear complexes [Ni2(cyclam)2- (DTA)](ClO4)2 (1) and [Ni2(TAA)2(DTA)] (ClO4)2 (2) (TAA=N(CH2CH2NH2)3 , cyclam = 1,4,8,11-tetraazacyclotetradecane, DTA=dithiooxamide) have been prepared and studied by elemental analyses, i.r. and electronic spectra and magnetic measurements. The magnetic susceptibility temperature dependence was measured over the 77–300K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2) giving the exchange integral J=–23.09cm–1 for (1) and J= –26.0cm–1 for (2).     

Synthesis,characterization, luminescence and magnetic properties of composite of polyaniline with nickel bisacetylacetonate complex

The present study involves the synthesis of polyaniline (PANI) and its composite with nickel bis(acetylacetonate) complex (Ni(acac)₂) via chemical oxidative polymerization method. PANI-Ni(acac)₂ composite was characterized by energy dispersive X-rays (EDX), fourier transformer infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Luminescence study was performed by UV–visible and fluorescence techniques. Relative fluorescence quantum yield of composite is a few orders of magnitude higher than pure PANI. The high fluorescence quantum yield of composite is probably due to greater chances of exciton formation and subsequent radiative decay to the ground state. Differential scanning calorimetric analysis (DSC) revealed higher thermal stability of composite than pure PANI, thereby allowing its use in devices which run at higher temperatures. On increasing the applied magnetic field, magnetic moment increases in both Ni(acac)₂ complex and PANI-Ni(acac)₂ composite, unlike to that in pure PANI. Thus, the present study holds promise for thermal purposes, luminescence properties and magnetic applications of the polyaniline composite.     

Highly selective synthesis of catalytically active monodisperse rhodium nanocubes

Monodisperse sub-10 nm Rh nanocubes were synthesized with high selectivity (>85%) by a seedless polyol method. The {100} faces of the Rh NCs were effectively stabilized by chemically adsorbed Br- ions from trimethyl(tetradecyl)ammonium bromide (TTAB). This simple one-step polyol route can be readily applied to the preparation of Pt and Pd nanocubes. Moreover, the organic molecules of PVP and TTAB that encapsulated the Rh nanocubes did not prevent catalytic activity for pyrrole hydrogenation and CO oxidation.     

Synthesis,crystal structure and magnetic properties of N -benzesulfonyl-L-glutamic acid-bridged binuclear nickel(II) complex

N-benzesulfonyl-L-glutamic acid-bridged binuclear nickel(II) complex, [Ni₂(Bs-Glu)₂(bipy)₂ (H₂O)₂]?·?3H₂O (Bs-Glu?=?N-benzesulfonyl-L-glutamic acid dianion, bipy?=?2,2′-bipyridine), has been synthesized and characterized structurally and magnetically. It crystallizes in the triclinic space group P 1. The α-carboxyl group coordinates to Ni(II) in a monodentate mode, while the γ-carboxyl group coordinates in a chelating mode. In the temperature range 2–300?K, magnetic measurements show that the exchange interaction of the two Ni(II) ions is antiferromagnetic, and the values for J, g are ?2.47?cm^?1 and 2.18, respectively.     

Synthesis and magnetic properties of nickel(II) complexes with the nitronyl nitroxides

Four novel complexes of nickel(II), Ni(tfac)2(NITPa)2 (1), Ni(tfac)2(NITPhNO2)2 (2), Ni(pfpr)2(NITPa)2 (3) and Ni(pfpr)2(NITPhNO2)2 (4), [tfac=trifluoro- acetato, NITPa=2-(3,4-methylenedioxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxy-3-oxid, NITPhNO2= 2-(3-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxid, pfpr=pentafluoropropionato], have been prepared and characterized by elemental analysis, i.r., and electronic spectra, and molar conductances. The temperature dependence of the magnetic susceptibility for complexes (1) and (3) was measured (4–300K). The observed data were successfully simulated giving the exchange integral J=–1.48cm–1 for (1) and J=–1.25cm–1 for (3). These results indicate a weak antiferromagnetic spin exchange interaction between nickel(II) ion and the radicals.     

Synthesis, magnetic properties, and STM spectroscopy of an unprecedented octanuclear chloro-bridged nickel(II) double cubane

Reaction of nickel(II) chloride hexahydrate with N-n-butyldiethanolamine H(2)L (3) in the presence of LiH in anhydrous THF leads to the formation of the unique octanuclear chloro-bridged nickel(II) double cubane [({Ni(II)(4)(μ(3)-OH)Cl(3)(HL)(3)}μ(2)-Cl)(2)] (4) in 57% yield. According to single crystal X-ray structure analysis, complex 4·4CH(2)Cl(2) possesses a [({Ni(4)(μ(3)-OH)(μ(3)-O)(3)(OH)(3)(N)(3)(Cl)(3)}μ(2)-Cl)(2)] core and crystallizes in the monoclinic space group P2(1)/c with a = 18.292(2), b = 19.8972(5), c = 23.295(2) ?, β = 98.408(6)°, V = 8387.3(8) ?(3), and four molecules in the unit cell. The analysis of the SQUID magnetic susceptibility data identified 4 as a weakly coupled dimer (J(1) = 14.5 K, J(2) = -0.6 K) with a ground state of S = 0, resulting from two S = 4 states of each {Ni(4)} subunits. Although complex 4 does not show an ac out-of-phase signal in a zero dc field at temperatures of 1.8 K and higher, low-temperature magnetization measurements revealed that complex 4 is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies. The eye-catching feature of complex 4 is the presence of two different blocking temperatures (0.9 K around zero field and 1.3 K at higher fields). The origin of this highly unusual behavior can be assigned to the dimer-nature of the interaction between the two S = 4 units. Furthermore STM and current imaging tunnelling spectroscopy (CITS) were performed on aggregates of 4 drop-coated on highly oriented pyrolytic graphite (HOPG) surfaces. CITS measurements show a strong contrast in the area of the nickel centers and a HOMO-LUMO gap of approximately 0.8 V.     

Synthesis, crystal structures, and magnetic properties of a new nickel(II) complex with nitronyl nitroxide

A new nickel(II) complex [Ni(NIT-1′-MeBzIm)₂(H₂O)₂] · ClO₄ · H₂O (NIT-1′-MeBzIm = 2-{2′-[(l′-methyl)benzimidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been prepared and structurally characterized by single-crystal X-ray diffraction. Complex I crystallizes in monoclinic, space group C2/c, Z = 4. Crystal data: C₃₀H₄₆N₈O₁₆ClNi, Mr = 869.06, a = 13.958(3), b = 15.904(4), c = 18.514(5) Å, β = 101.047(3)°. The X-ray analysis reveals that Ni²⁺ ion resides in a distorted octahedron center, the complex was linked by intermolecular hydrogen bonds, resulting in a 2D network configuration. Magnetic investigation indicates the existence of interamolecular interactions is antiferromagnetic with J = ?40.76 cm^?1.     

Synthesis and properties of mixed-substituted nickel triazolephthalocyaninates

Homo- and mixed-substituted nickel triazolephthalocyaninates were synthesized by the reactions of nickel complexes of substituted 3,5-bis(3-iminoisoindolin-1-ylideneamino)-1,2,4-triazoles with 4-phenoxyphthalonitrile and 4-phenylthiophthalonitrile. The structures of these compounds were established by UV-Vis and IR spectroscopy, mass spectrometry, and elemental analysis, and their physicochemical properties were studied.     

Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.