Narrow Results

Abundant asymmetric unit of the [FeBr₄]₂[py.H]₃Br magnetic molecule in the acetonitrile solvent was characterized via Debye function analysis (DFA) of the X-ray powder diffraction pattern from dilute solution. A diluted solution of the material in acetonitrile solvent has been prepared to reduce, as far as possible, the interaction between the molecular units. The X-ray diffraction from the sample was measured and Debye function simulations of three out of ten chemically plausible molecular units were observed to suitably comply with the experimental results. These three configurations were further optimized with first-principles method in the framework of density functional theory (DFT) and the most stable structure according to the calculated total energy is presented.

The recently suggested modified microscopic theory of liquids has been used successfully to explain the collective dynamics of liquid Al near its melting point. Considering the frequency-dependent self-diffusion coefficient occurring in the intermediate self-correlation function, which is inextricably linked with the collective dynamics of the system, the observed variation in dynamical structure factor of Al can be quantitatively reproduced for wave vector range 0.42 Å^-1 to 1.38 Å^-1 taking into account single relaxation time.

While the As-rich 2 × 4 reconstruction of GaAs(001) is well explained by the so-called β₂ structure, the atomic structure of the Ga-rich 4 × 2 phase has been discussed for a long time. In this review, the most important structural models for the GaAs(001) (4 × 2)/c(8 × 2) surface are compared from different theoretical and experimental points of view. The selected reconstructions include the recently proposed ζ model, a new mixed dimer model, and the well-known β, β₂, Cerdà and Skala models. The different structures are compared on the basis of total energy calculations, simulations of STM experimental images and interpretation of X-ray diffraction data. Only the ζ model satisfies all criteria, and provides therefore a satisfactory explanation of the atomic structure of GaAs(001)-(4 × 2).

X-ray scattering techniques were used to study the effects of heating on whole eye lens and α-crystallin gels. The temperature range used was from 20 to 70°C. The position of single X-ray reflection seen in whole lens was unchanged in the temperature range 20 to 45°C, with a continuous spacing of 152 Å. However, at 50°C the spacing increased from 152 Å to 165 Å. An interpretation of these results is that in eye lens, α-crystallin is protecting other lens proteins from super-aggregation up to 50°C. In α-crystallin gels a moderate increase in both the spacing and intensity of the reflection was observed from 20 to 45°C, followed by a dramatic increase from 45 to 70°C. Over the whole temperature range the spacing changed from 138 Å at 70°C to 195 Å at 70°. After eleven hours of cooling, this effect was found to be irreversible.

Many living organisms grow crystalline inorganic components (usually to add mechanical strength, but also for sensing and other applications). These organisms exert a high degree of control not just over the crystal orientation but also over the structure and composition of the crystals. They do this in wet environments, without the use of ultrahigh vacuum. There have been efforts to mimic this process in the laboratory by growing minerals under floating (Langmuir) monolayers, which serve as ordered organic templates. We have studied such processes using grazing-incidence X-ray diffraction to determine the structure of both organic and inorganic films during deposition. These studies illustrate that some of the same phenomena familiar to surface scientists working in UHV occur also in "real world" environments.

New inorganic-organic hybrid open-framework materials of the phosphate - oxalate family, [Fe₂(H₂O₂- (HPO₄)₂(C₂O₄)]·H₂O) (I), [Fe₂(H₂O₂- (HPO₄)₂(C₂O₄)]·2H₂O(II), [C₃N₂H₁₂]- [Fe₂(HPO₄)₂(C₂O₄)_1.5]₂(III), and [C₃N₂OH₁₂][Fe₂(HPO₄)₂(C₂O₄)_1.5]₂(IV) have been synthesized hydrothermally in the presence of structure-directing amines. The amine molecules are incorporated inIII and IV, whereas I and II are devoid of them. The oxalate units act as a bridge between the layers in all the compounds. The layers in I and II are entirely inorganic, being formed by FeO₆ and PO₄ units, whereas in III and IV oxalate units constitute the inorganic layers and act as the bridge between these layers. Such a dual role of the oxalate unit is unique and noteworthy. The formation of two types of inorganic layers in I and II consisting of four-, six-, and eight-membered rings, indicates the interconversions between the various rings in the phosphate - oxalates to be facile. All the phosphate - oxalates show antiferromagnetic ordering at low temperatures.