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An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Multiferroic materials are those which possess both ferroelectric and ferromagnetic properties. Clearly, there is a contradiction here since ferromagnetism requires d-electrons while ferroelectricity generally occurs only in the absence of d-electrons. Several multiferroics demonstrating magnetoelectric coupling effects have, however, been discovered in the past few years, but they generally make use of alternative mechanisms in attaining these properties. Several new ideas and concepts have emerged in the past two years, typical of them being magnetic ferroelectricity induced by frustrated magnetism, lone pair effect, charge-ordering and local non-centrosymmetry. Charge-order driven magnetic ferroelectricity is interesting in that it would be expected to occur in a large number of rare earth manganites, Ln1−xAxMnO3 (A = alkaline earth), well known for colossal magnetoresistance, electronic phase separation and other properties. In this article, we discuss novel routes to multiferroics, giving specific examples of materials along with their characteristics.
Electron diffraction studies have been performed on a number of samples within the series BiMnO3+x (for the range –0.11 < x < 0.16). Samples with a large value of x (either positive or negative) crystallize as a monoclinic perovskite supercell structure not dissimilar from the stoichiometric ideal. However, the variation of oxygen composition manifests itself as disorder in either the cation or anion sub-lattices, leading to a reduction in symmetry (to C2, P21 or P2). In addition, three new structures have been identified at compositions closer to the perovskite ideal. One structure is similar to a mixed cation phase reported by Hughes et al, while another is an n = 2 Ruddlesden-Popper phase; importantly both of these phases are acentric and so could support multiferroic properties. The third is as yet not fully characterised but seems to crystallise into a different monoclinic structure than the stoichiometric ideal phase.
Infrared studies of synthetic alamethicin fragments and model peptides containing alpha-aminoisobutyric acid (Aib) have been carried out in solution. Tripeptides and larger fragments exhibit a strong tendency to form beta turns, stabilized by 4 leads to 1 10-atom hydrogen bonds. Dipeptides show less well-defined structures, though C5 and C7 conformations are detectable. Conformational restrictions imposed by Aib residues result in these peptides populating a limited range of states. Integrated intensities of the hydrogen-bonded N-H stretching band can be used to quantitate the number of intramolecular hydrogen bonds. Predictions made from infrared data are in excellent agreement with nuclear magnetic resonance and X-ray diffraction studies. Assignments of the urethane and tertiary amide carbonyl groups in the free state have been made in model peptides. Shifts to lower frequency on hydrogen bonding are observed for the carbonyl groups. The 1--6 segment of alamethicin is shown to adopt a 3(10) helical structure stabilized by four intramolecular hydrogen bonds. The fragments Boc-Leu-Aib-Pro-Val-Aib-OMe (12--16) and Boc-Gly-Leu-Aig-Pro-Val-Aib-OMe (11--16) possess structures involving 4 leads to 1 and 5 leads to 1 hydrogen bonds. Supporting evidence for these structures is obtained from proton nuclear magnetic resonance studies.
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No abstract is provided for this article.
Triangular Au and disk-shaped Au−Cu alloy nanocrystals have been generated in thin SiO2 film matrixes, by sol−gel spin-coating followed by annealing at 800 °C in 10%H2−90%Ar. Transmission electron microscope images confirm the shapes of the embedded nanocrystals. X-ray diffraction patterns reveal that the Au and Au−Cu nanocrystals have a (111) orientation. The disk-shaped alloy nanocrystals exhibit surface plasmon absorption at wavelengths intermediate between those of Au and Cu.
Trisulfide molybdenum complexes have been employed to produce nanotubes by simple heating in a stream of hydrogen. Bamboo-like stacking (see Figure) was observed, suggesting that the stimulus for the growth of MoS2 nanotubes is similar to that of their carbon equivalents. The wide experience gained with trisulfide complexes directs this technique towards the preparation of other layered sulfide nanotubes, although other precursors are also shown to be successful.
In our effort to explore the use of the sulfite ion to design hybrid and open-framework materials, we have been able to prepare, under hydrothermal conditions, zero-dimensional [Zn(C12H8N2)(SO3)].2H2O, I (a = 7.5737(5) A, b = 10.3969(6) A, c = 10.3986(6) A, alpha = 64.172(1) degrees , beta = 69.395(1) degrees , gamma = 79.333(1) degrees , Z = 2, and space group P), one-dimensional [Zn2(C12H8N2)(SO3)2(H2O)], II (a = 8.0247(3) A, b = 9.4962(3) A, c = 10.2740(2) A, alpha = 81.070(1) degrees , beta = 80.438(1) degrees , gamma = 75.66(5) degrees , Z = 2, and space group P), two-dimensional [Zn2(C10H8N2)(SO3)2].H2O, III (a = 16.6062(1) A, b = 4.7935(1) A, c = 19.2721(5) A, beta = 100.674(2) degrees , Z = 4, and space group C2/c), and three-dimensional [Zn4(C6H12N2)(SO3)4(H2O)4], IV (a = 11.0793(3) A, c = 8.8246(3) A, Z = 2, and space group P42nm), of which the last three are coordination polymers. A hybrid open-framework sulfite-sulfate of the composition [C2H10N2][Nd(SO3)(SO4)(H2O)]2, V (a = 9.0880(3) A, b = 6.9429(2) A, c = 13.0805(5) A, beta = 91.551(2) degrees , Z = 2, and space group P21/c), with a layered structure containing metal-oxygen-metal bonds has also been described.
A molecular dynamics study of liquid N,N-dimethyl formamide has been carried out. Orientational correlation functions suggest a stacked antiparallel ordering at short distances (< 5Å) and a perpendicular + configuration at intermediate distances. The proposed ordering is in agreement with the recent 13C NMR results of Konrat and Sterk and suggests a stronger association of CH3(t) with O than of CH3(c) with O. Both the translational and the rotational motions are anisotropic. The diffusion constants for rotation along the different directions are different, in agreement with the NMR results.
The depolarized and polarized components of internal Raman bands of succinonitrile, t -butyl chloride and t -butyl bromide in their plastic crystalline and liquid phases have been analyzed to obtain rotational and vibrational correlation functions. The rotational correlation times are continuous through the plastic-liquid transition and show an Arrhenius behaviour, from which activation energies for rotation have been calculated. Vibrational correlation times are nearly constant in the range of temperature investigated, except for a small change near the plastic-liquid phase transition temperature.
FMR measurements have been carried out on several members of the Ln1−x SrxCoO3 (Ln = Rare earth) system. The results show that g eff in these systems is around 1.25 independent of x as well as the rare earth ion. It is suggested that this unusual value of g eff is due to the localized intermediate-spin Co3+ ions (t 5 2g e 1 g) located at the top of the π∗ band.
Although the growth of nanocrystals has been investigated by several workers, investigations of the growth of 1-D nanostructures have been limited. We have investigated the growth kinetics of both uncapped and poly(vinyl pyrollidone) (PVP)-capped ZnO nanorods carefully by a combined use of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) which provide direct information on size and shape and compensate for the deficiency of each other. Values of average length and diameter of the ZnO nanorods obtained by TEM and SAXS are comparable. In the presence of the capping agent, the length of the nanorods grows faster while the diameter becomes narrower. The length distribution shows periodic changes in the width in the case of the uncapped nanorods, a feature absent in the case of the capped nanorods. In the absence of the capping agent, we observe the presence of small nanocrystals next to the nanorods after a lapse of time. The occurrence of small nanocrystals as well as the periodic focusing and defocusing of the width of the length distribution lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence of the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening, while the PVP-capped nanorods show a time dependence which is best described by a combination of diffusion and surface reaction with a L3 + L2 type behavior. Collapse of all distribution curves obtained at different times of the reaction into a single universal Gaussian in the case of the PVP-capped nanorods also shows that the growth mechanism is more complex than Ostwald ripening.
Theoretically calculated lone-pair splittings in H2O2, H2S2, N2H4, P2H4, glyoxal and dithioglyoxal have been compared with experimental values. Potential functions for rotation and the effect of geometry relaxation on rotomer energies have also been examined.
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