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.

A scanning tunneling microscopy and potentiometry study of epitaxial thin films of La0.7Ca0.3MnO3

To investigate the role of grain boundaries and other growth related microstructure in manganite films, a scanning tunneling microscope is used to simultaneously probe surface topography and local potential distribution under current flow at nanometer level in films of epitaxial thin films of La0.7Ca0.3MnO3 deposited on single crystal SrTiO3 and NdGaO3 substrate by laser ablation. We have studied two types of films strained and strain relaxed. Thin (50nm) films (strained due to lattice mismatch between substrate and the film) show step growth (unit cell steps) and have very smooth surfaces. Relatively thicker films (strain relaxed, thickness 200nm) do not have these step growths and show rather smooth well connected grains. Charge transport in these films is not uniform on the nanometer level and is accompanied by potential jumps at the internal surfaces. In particular scattering from grain boundaries results in large variations in the local potential resulting in fields as high as 104-105V/cm located near the grain boundaries. We discuss the role of local strain and strain inhomogeneties in determining the current transport in these films and their resistance and magnetoresistivity. In this paper we attempt to correlate between bulk electronic properties with microscopic electronic conduction using scanning tunneling microscopy and scanning tunneling potentiometry.

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.

Magnetic order of the hexagonal rare-earth manganite Dy(0.5)Y(0.5)MnO(3)

Hexagonal Dy(0.5)Y(0.5)MnO(3), a multiferroic rare-earth manganite with geometrically frustrated antiferromagnetism, has been investigated with single-crystal neutron diffraction measurements. Below 3.4 K magnetic order is observed on both the Mn (antiferromagnetic) and Dy (ferrimagnetic) sublattices that is identical to that of undiluted hexagonal DyMnO(3) at low temperature. The Mn moments undergo a spin reorientation transition between 3.4 K and 10 K, with antiferromagnetic order of the Mn sublattice persisting up to 70 K; the antiferromagnetic order in this phase is distinct from that observed in undiluted (h) DyMnO(3), yielding a qualitatively new phase diagram not seen in other hexagonal rare-earth manganites. A magnetic field applied parallel to the crystallographic c axis will drive a transition from the antiferromagnetic phase into the low-temperature ferrimagnetic phase with little hysteresis.

Thermodynamic properties of calcium titanates: CaTiO3, Ca4Ti3O10, and Ca3Ti2O7

The chemical potentials of CaO in two-phase fields (TiO2 + CaTiO3), (CaTiO3 + Ca4Ti3O10), and (Ca4Ti3O10 + Ca3Ti2O7) of the pseudo-binary system (CaO + TiO2) have been measured in the temperature range (900 to 1250) K, relative to pure CaO as the reference state, using solid-state galvanic cells incorporating single crystal CaF2 as the solid electrolyte. The cells were operated under pure oxygen at ambient pressure. The standard Gibbs free energies of formation of calcium titanates, CaTiO3, Ca4Ti3O10, and Ca3Ti2O7, from their component binary oxides were derived from the reversible e.m.f.s. The results can be summarised by the following equations: CaO(solid) + TiO2(solid) → CaTiO3(solid), ΔG° ± 85/(J · mol−1) = −80,140 − 6.302(T/K); 4CaO(solid) + 3TiO2(solid) → Ca4Ti3O10(solid), ΔG° ± 275/(J · mol−1) = −243,473 − 25.758(T/K); 3CaO(solid) + 2TiO2(solid) → Ca3Ti2O7(solid), ΔG° ± 185/(J · mol−1) = −164,217 − 16.838(T/K). The reference state for solid TiO2 is the rutile form. The results of this study are in good agreement with thermodynamic data for CaTiO3 reported in the literature. For Ca4Ti3O10 Gibbs free energy of formation obtained in this study differs significantly from that reported by Taylor and Schmalzried at T = 873 K. For Ca3Ti2O7 experimental measurements are not available in the literature for direct comparison with the results obtained in this study. Nevertheless, the standard entropy for Ca3Ti2O7 at T = 298.15 K estimated from the results of this study using the Neumann–Koop rule is in fair agreement with the value obtained from low-temperature heat capacity measurements.

Temperature dependence of the energy gap and free carrier absorption in bulk InAs0.05Sb0.95 single crystals

Temperature dependence of the energy gap and free carrier absorption in a high-quality InAs0.05Sb0.95 single crystal was studied between 90 K and 430 K through the absorption spectra. At this alloy concentration, the room-temperature energy gap was measured to be 0.15 eV. Varshni- and the Bose–Einstein-type fit parameters were obtained from the measured temperature dependence of the energy gap, and the latter gave the zero-temperature gap to be 0.214 eV. It was found that although Weider’s empirical formula for the dependence of the energy gap on temperature and the alloy concentration agrees with the value of the gap at room temperature, it is inaccurate in describing its temperature dependence. From the free carrier absorption measurements, the phonon limited cross section of 7.35×10−16 cm2 at 15 μm was deduced at room temperature.

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.

Evaluation of DNA binding, antioxidant and cytotoxic activity of mononuclear Co(III) complexes of 2-oxo-1,2-dihydrobenzoh]quinoline-3-carbaldehyde thiosemicarbazones

Four new 2-oxo-1,2-dihydrobenzoh]quinoline-3-carbaldehyde N-substituted thiosemicarbazone ligands (H-2-LR, where R = H, Me, Et or Ph) and their corresponding new cobalt(III) complexes have been synthesized and characterized. The structures of the complexes 2 and 3 were determined by single crystal X-ray diffraction analysis. The interactions of the new complexes with DNA were investigated by absorption, emission and viscosity studies which indicated that the complexes bind to DNA via intercalation. Antioxidant studies of the new complexes showed that the significant antioxidant activity against DPPH radical. In addition, the in vitro cytotoxicity of complexes 1-4 against A549 cell line was assayed which showed higher cytotoxic activity with lower IC50 values indicating their efficiency in killing the cancer cells even at very low concentrations. (C) 2012 Elsevier Masson SAS. All rights reserved.

Quasi-static crack tip fields in rate-sensitive FCC single crystals

In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. Finite element simulations are performed within a mode I, plane strain modified boundary layer framework by prescribing the two term (K-T) elastic crack tip field as remote boundary conditions. The material is assumed to obey a rate-dependent crystal plasticity theory. The orientation of the single crystal is chosen so that the crack surface coincides with the crystallographic (010) plane and the crack front lies along 101] direction. Solutions corresponding to different stress intensity rates K., T-stress values and strain rate exponents m are obtained. The results show that the stress levels ahead of the crack tip increase with K. which is accompanied by gradual shrinking of the plastic zone size. However, the nature of the shear band patterns around the crack tip is not affected by the loading rate. Further, it is found that while positive T-stress enhances the opening and hydrostatic stress levels ahead of crack tip, they are considerably reduced with imposition of negative T-stress. Also, negative T-stress promotes formation of shear bands in the forward sector ahead of the crack tip and suppresses them behind the tip.

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-nitrobenzoic acid with methyl carbazate as ancillary ligand. Crystal structure of the copper(II) complex

Divalent metal complexes of general formula M(2-nb)(2)(mc)(2)].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH2NHCOOCH3), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II) complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG-DTA. Emission studies show that these complexes are fluorescent.

Gel Sculpture: Moldable, Load-Bearing and Self-Healing Non-Polymeric Supramolecular Gel Derived from a Simple Organic Salt

An easy access to a library of simple organic salts derived from tert-butoxycarbonyl (Boc)-protected L-amino acids and two secondary amines (dicyclohexyl- and dibenzyl amine) are synthesized following a supramolecular synthon rationale to generate a new series of low molecular weight gelators (LMWGs). Out of the 12 salts that we prepared, the nitrobenzene gel of dicyclohexylammonium Boc-glycinate (GLY.1) displayed remarkable load-bearing, moldable and self-healing properties. These remarkable properties displayed by GLY.1 and the inability to display such properties by its dibenzylammonium counterpart (GLY.2) were explained using microscopic and rheological data. Single crystal structures of eight salts displayed the presence of a 1D hydrogen-bonded network (HBN) that is believed to be important in gelation. Powder X-ray diffraction in combination with the single crystal X-ray structure of GLY.1 clearly established the presence of a 1D hydrogen-bonded network in the xerogel of the nitrobenzene gel of GLY.1. The fact that such remarkable properties arising from an easily accessible (salt formation) small molecule are due to supramolecular (non-covalent) interactions is quite intriguing and such easily synthesizable materials may be useful in stress-bearing and other applications.

A Rare Phenoxido/Acetato/Azido Bridged Trinuclear and an Unprecedented Phenoxido/Azido Bridged One-Dimensional Polynuclear Nickel(II) Complexes: Synthesis, Crystal Structure, and Magnetic Properties with Theoretical Investigations on the Exchange Mechanism

The reaction of a tridentate Schiff base ligand HL (2-(3-dimethylaminopropylimino)-methyl]-phenol) with Ni(II) acetate or perchlorate salts in the presence of azide as coligand has led to two new Ni(II) complexes of formulas Ni3L2(OAc)(2)(mu(1,1)-N-3)(2)(H2O)(2)]center dot 2H(2)O (1) and Ni2L2(mu(1,1)-N-3) (mu(1,3)-N-3)](n)(2). Single crystal X-ray structures show that complex 1 is a linear trinuclear Ni(II) compound containing a mu(2)-phenwddo, an end-on (EO) azido and a syn-syn acetato bridge between the terminal and the central Ni(II) ions. Complex 2 can be viewed as a one-dimensional (1D) chain in which the triply bridged (di-mu(2)-phenoxido and EO azido) dimeric Ni-2 units are linked to each other in a zigzag pattern by a single end-to-end (EE) azido bridge. Variable-temperature magnetic susceptibility studies indicate the presence of moderate ferromagnetic exchange coupling in complex 1 with J value of 16.51(6) cm(-1). The magnetic behavior of 2 can be fitted in an alternating ferro- and antiferromagnetic model J(FM) = +34.2(2.8) cm(-1) and J(AF) = -21.6(1.1) cm(-1)] corresponding to the triple bridged dinuclear core and EE azido bridge respectively. Density functional theory (DFT) calculations were performed to corroborate the magnetic results of 1 and 2. The contributions of the different bridges toward magnetic interactions in both compounds have also been calculated.

Synthesis, Spectral Characterization, Crystal Structure and Thermal Behavior of Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate

Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate was prepared from the ethanolic solution of 1-chloro-2,4-dinitrobenzene, tert-butyl 3-oxobutanoate and triethylamine. Acetyl group in tert-butyl 3-oxobutanoate has cleaved off during the formation of the title molecule. UV-VIS, IR, 1H NMR, 13C NMR, Proton-Proton COSY data and single crystal XRD results support the proposed structure. Flammability test, impact sensitivity test and TG/DTA studies at different heating rates on the synthesized molecule imply that it is an insensitive high energy density material.

1-D Hydrogen bonded water in Cu(II)-picolinate coordination polymer: synthesis, crystal structure, and thermogravimetric analysis

A new Cu(II)-picolinate complex was synthesized and characterized by single crystal X-ray crystallography. The complex crystallizes in the centrosymmetric triclinic space group P (1) over bar (no. 2). Picolinate in the complex extends the neutral unit into a 1-D chain through mu(2)-bridging carboxylate. The complex has a hydrogen bonding acceptor in the second coordination sphere allowing lattice water to assemble neighboring chains. Water self-assembles to form a zig-zag 1-D chain. The adjacent chains are assembled by C-H center dot center dot center dot O interactions result in the formation 2-D hydrogen bonded network. The overall hydrogen bonding between water chain and Cu-picolinate network yields a 3-D hydrogen bonded coordination network. X-ray structural analysis, FTIR and thermal analysis have been used to characterize the reported compound in the solid state.

Acoustic and optical phonon dynamics from femtosecond time-resolved optical spectroscopy of the superconducting iron pnictide Ca(Fe0.944Co0.056)(2)As-2

We report the temperature evolution of coherently excited acoustic and optical phonon dynamics in the superconducting iron pnictide single crystal Ca(Fe0.944Co0.056)(2)As-2 across the spin density wave transition at T-SDW similar to 85 K and the superconducting transition at T-SC similar to 20 K. The strain pulse propagation model applied to the generation of the acoustic phonons yields the temperature dependence of the optical constants, and longitudinal and transverse sound velocities in the temperature range from 3.1 K to 300 K. The frequency and dephasing times of the phonons show anomalous temperature dependence below T-SC indicating a coupling of these low-energy excitations with the Cooper-pair quasiparticles. A maximum in the amplitude of the acoustic modes at T similar to 170 is seen, attributed to spin fluctuations and strong spin-lattice coupling before T-SDW. Copyright (c) EPLA, 2012