Due to phase separation in the silicate melt, the synthesis of fluorosmectites
([Na0.5]inter[Mg2.5Li0.5]oct[Si4]tetO10F2) from the melt without mechanical mixing yields an
inhomogeneous material. Because of the solid solution capability of the 2:1 layer silicate
structure, the nonuniformity in chemical and mineral composition inevitably will lead to
fluorosmectites that adopt a range of charge densities. This will be detrimental to many
possible applications due to the large influence of layer charge on the properties of clay
minerals. The problem can be circumvented by rotating the crucible during synthesis in a
horizontal mounting, which will continuously force mixing of the melt mechanically. The
product obtained is homogeneous at all length scales as judged by chemical analysis and its
uniform intracrystalline reactivity. Noteworthy is its tendency to form regularly interstratified intercalates of monolayers and bilayers upon alkylammonium exchange and of rectorite
type phases upon partial K+ exchange. We expect that the two dissimilar types of galleries,
which are stacked in a regularly alternating pattern, can be selectively addressedleading
to interesting intercalation materials.
191 X-ray structure analysis of the [22]coproporphyrin I1 Zb space group P2,/n. a = 828.1(5), b = 2619.5(6), c = 1028.7(6) pm, fl = 100.30(2)'. Z = 2, four-circle diffractometer CAD4 (Enraf-Nonius) (Cu,,, L = 154.178 pm, graphite monochromator), 3561 measured reflections. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlichtechnische Information mbH. W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-54603, the names of the authors, and the journal citation. (lo] H. Konig, C. Eickmeier, M. Moller, U. Rodewald, B. Franck.
2.2.2]Paracyclophane forms the adducts CZ4HZ4 . AsC13 (l), remains uncoordinated. Chlorine-bridging between antimony C24H24 . (SbC13)2 . C6H6 (2) and CZ4H2, . (BiCl& . C6H6 (3). atoms leads to tetrameric units (SbCI3), in the lattice. -In For solutions in polar solvents NMR spectra indicate extensive the bismuth compound 3 each benzene ring of the hydrocardissociation and/or fluxionality. In the crystals adduct 1 fea-bon is engaged in centroid ($)x complexation, with the BiC13 tures a weak addition of the AsC13 molecule to one open side units crosslinked by chlorine bridges. The average of the of a paracyclophane molecule with long intermolecular con-Biring distances (3.08,2.98, and 2.99 A) is shorter than for the tacts approaching C,, symmetry. -Crystalline 2 shows SbCls Sb-ring distances in 2 (3.047 and 3.050 A), indicating stronger coordination to two of the benzene rings of the hydrocarbon bonding. The crystal benzene is not coordinating. in a quasi-centered q6 mode, while one of the benzene rings
An electrothermal vaporization-inductively coupled plasma-mass spectrometric (ETV-ICP-MS) method based on selective volatilization of cesium with KSCN as modifier has been developed for determination of radiocesium, i.e. 135Cs and 137Cs, in the presence of isobaric barium. A 10,000 times excess of barium, which was volatilized at a temperature of 1,100 degrees C, resulted only in a 1% signal increase in the signal of mass 135 amu. The recommended concentration of KSCN is 0.3 mM, and pretreatment and volatilization temperatures are 400 degrees C and 1,100 degrees C, respectively. A ramp time of 1 s is recommeded for the volatilization step. The achieved limit of detection for 135Cs is 0.2 pg/mL (10 microBq/mL) and 4 fg (0.2 microBq) absolute for a sample volume of 20 microL. This means a limit of detection for 137Cs of 0.2 pg/mL (0.6 Bq/mL) and of 4 fg (0.01 Bq) absolute. Signal variations of 135Cs and 137Cs, respectively, in spiked samples with various matrices were investigated.
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