Search

Two new infinite coordination chain compounds [Gd(CH3CO2)3(dmf)]8 (1) and {[Gd(HO(CH2)3CO2)3- (H2O)]·H2O}8 (2) have been obtained attempting to modify a prototype molecular cooler. The structures of both compounds as determined by single-crystal X-ray diffraction are reported, together with a detailed study of their magnetic and thermal properties, describing for both compounds a large magneto-caloric effect. The dominant ferromagnetic interaction present in 2 clearly favours this material at low applied magnetic fields, with respect to 1 that exhibits antiferromagnetic interactions. Magnetostructural correlations of the sign and strength of the magnetic interactions are derived for carboxylatobridged Gd(III) systems. [ABSTRACT FROM AUTHOR]

The red glaze (slip) that characterizes the Terra Sigillata potteries greatly contributed to their success during the Roman period. The colour of the slip can in fact be partially explained by the microstructure (crystalline phases, grain sizes) and the physico-chemistry (composition) of the ceramics. However, the precise process and the diffusion of this technique are still not fully known. In particular, we do not know yet how the production of sigillata took place in the south of Gaul, and the role that was played by the production under Italian influence (pre-sigillata) preceding the first local sigillata. In this work, a combination of transmission electron microscopy (TEM) and X-ray synchrotron diffraction techniques was used to study the microstructure of pre-sigillata slips from the main southern Gaul workshop (La Graufesenque), in order to compare their characteristics with those of high-quality sigillata. These first results seem to indicate that the antique potters chose clays adapted to their firing conditions and to the type of coating that they wanted to make. These productions cannot be described as an initial phase for the later sigillata production and, rather, seem to correspond to the intention of developing a specific type of pottery only inspired by the famous Italian sigillata forms. [ABSTRACT FROM AUTHOR]

The crystal structure of the mineral zdenekite NaPbCu[sub 5](AsO[sub 4])[sub 4]Cl · 5H[sub 2]O was established (Bruker SMART CCD diffractometer, synchrotron radiation, λ = 0.6843 Å, R = 0.096 for 1356 reflections). Single-crystal X-ray diffraction study demonstrated that zdenekite belongs to the monoclinic system with the unit-cell parameters a = 10.023(7) Å, b = 19.55(1) Å, c = 10.023(6) Å, β = 90.02(1)°, sp. gr. P2[sub 1]/n, Z = 4. The structure consists of polyhedral layers parallel to the (010) plane. These layers are formed by Cuφ[sub 5] polyhedra (φ = O, Cl, H[sub 2]O) and AsO[sub 4] tetrahedra. Distorted Na octahedra and Pb 7-vertex polyhedra and H[sub 2]O molecules coordinated to these metal atoms are located between the layers. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The crystal structure of strontium hilgardite, CaSr[B[sub 5]O[sub 9]]C1 H[sub 2]O, was established by the method of X-ray diffraction analysis (synchrotron radiation; diffractometer equipped with a position-sensitive detector; λ = 0.688 Å; 3191 reflections with F > 4σ(F); R = 0.045 in the anisotropic approximation). The triclinic unitcell parameters are as follows: a = 6.5732(6) Å, b = 6.4445(6) Å, c = 6.3693(6) Å, α = 60.995(2)°, β = 61.257(2)°, γ= 77.191(2)° sp. gr. P1; Z= 1. The Ca and Sr atoms were found to be disordered over two positions. The structures of strontium hilgardite and hilgardite-1A differ in the configurations of the seven-vertex Sr- and Ca(2)-polyhedra. The structure solved in this work is consistent with two series of borates studied previously. One of these groups involves pentaborates with different degrees of hydration of borate complexes, and the second group includes Sr-containing borates. [ABSTRACT FROM AUTHOR]