ABSTRACT
(39)K NMR spectra and relaxation times of polycrystalline K(3)Fe(5)F(15) have been used as a microscopic detector of the local magnetic fields at the magnetic transition at T(N) = 123 K. The NMR lineshape widens abruptly upon crossing T(N) due to the onset of internal magnetic fields, while we find no significant lineshift. The paraelectric to ferroelectric transition at T(c) = 490 K and the magnetic transition at T(N) have also been studied using X-band EPR (electron paramagnetic resonance). An increase and subsequent decrease in the EPR susceptibilities is observed on approaching T(N) from above. There is also a significant increase in the linewidth. At the same time the g-factor first decreases and then increases with decreasing temperature. The local magnetic field is different at different K sites and is much smaller than the magnetic field around the Fe sites. This seems to be consistent with the behaviour of a weak ferrimagnet. The ferrimagnetism does not seem to be due to spin canting as the lattice is disordered, but may arise from thermal blocking of superparamagnetic percolation clusters. The ferroelectric transition at T(c) shows no electronic anomaly, demonstrating that we are dealing with a classical phonon anomaly as found in conventional oxides rather than an electronic transition.
ABSTRACT
The purpose of this study was to develop an accurate and precise analytical procedure for the determination of the content of antimony in coordination compounds of metal(II) hexafluoroantimonates(V) (M(SbF(6))(2) compounds, where M=Mg, Ca, Sr or Ba) synthesized in our laboratory. The major problem was to find an appropriate reagent for reductive decomposition of SbF(6)(-) to Sb(3+) required for the determination of antimony by redox titration. Effective reduction of Sb(5+) regardless of the metal M bound to SbF(6)(-) species was achieved using metallic aluminium powder in acidic medium. Precipitated Sb(0) was quantitatively reoxidized to Sb(3+) and determined potentiometrically with KBrO(3) or KMnO(4). Other metals were determined complexometrically with disodium ethylenediaminetetraacetic acid (EDTA). Highly accurate and reproducible results were obtained in the concentration range 5-25 mg Sb with an RSD smaller than 0.6%. Antimony-fluoro-hydroxo species and fluoride did not interfere with the complexometric determinations of other metals with EDTA. The developed method enabled, for the first time, complete elemental chemical analysis of M(SbF(6))(2) compounds in the bulk form.
ABSTRACT
Xenon(IV) - carbon bonding has been realized for the first time in the product formed from the reaction of XeF(4) with C(6)F(5)BF(2) in CH(2)Cl(2) at -55 degrees C [Eq. (1)]. [C(6)F(5)XeF(2)][BF(4)] is a strong oxidative fluorinating agent. This xenon(IV) compound fluorinates (C(6)F(5))(3)P to (C(6)F(5))(3)PF(2), C(6)F(5)I to C(6)F(5)IF(2), and I(2) to IF(5). In all cases, [C(6)F(5)Xe][BF(4)] was obtained as a by-product.
