Study of the structural,electronic, and magnetic properties of the barium-rich iron(IV) oxides,Ba(2)FeO(4) and Ba(3)FeO(5)

Crystals of Ba(2)FeO(4) and Ba(3)FeO(5), grown from a "self-sealing" KOH-Ba(OH)(2) flux, have been characterized by single-crystal X-ray diffraction, M?ssbauer spectroscopy, and magnetic measurements. Ba(2)FeO(4) forms nonmerohedral twinned crystals with the monoclinic space group P2(1)/n, a = 6.034(2) A, b = 7.647(2) A, c = 10.162(3) A, beta = 92.931(6) degrees, and Z = 4. Ba(3)FeO(5) crystallizes in the orthorhombic space group Pnma, with a = 10.301(1) A, b = 8.151(1) A, c = 7.611(1) A, and Z = 4. While both compounds feature discrete FeO(4)(4-) tetrahedra, the anion found in Ba(2)FeO(4) has shorter Fe-O bonds and is significantly distorted relative to the Ba(3)FeO(5) anion. An iron valence of 4+ was confirmed by magnet susceptibility measurements and by the low-temperature isomer shifts of -0.152 and -0.142 mm/s relative to alpha-iron for Ba(2)FeO(4) and Ba(3)FeO(5), respectively.     

Determination of the antimony valence state in Eu10Mn6Sb13

The antimony-121 M?ssbauer spectra of Eu10Mn6Sb13 have been measured between 2 and 295 K. Although the Zintl formalism indicates that the nine crystallographically distinct antimony sites in Eu10Mn6Sb13 should have formal valence states of -2, -1, 0, and +1, the M?ssbauer spectral isomer shifts reveal that the valence states of the different sites are all quite similar and correspond to an average electronic configuration for antimony of 5s(1.7)5p(4.0). This configuration corresponds to an excess of negative charge on the antimony of 0.7 or an average valence of -0.7, a valence which is rather consistent with the average antimony valence of -0.61 obtained from the Zintl formalism for the nine antimony sites in Eu10Mn6Sb13. The spectra obtained between 90 and 295 K are more consistent with the absence rather than the presence of any transferred magnetic hyperfine field at the antimony. In contrast, the spectra obtained at 2 and 5 K reveal the presence of an average transferred magnetic hyperfine field of ca. 8 T, a field that arises from the ferromagnetic ordering of the near-neighbor manganese(II) ions.     

1,1,3,3,3-Pentafluoropropene secondary amine adducts new selective fluorinating agents

Addition of secondary amine SA (dimethylamine DMA, diethylamine DEA, pyrrolidine Pyr, piperidine Pip, morpholine Mor) to pentafluoropropene PFP gives rise to generation of mixtures of two products (1-dialkylamine-1,3,3,3-tetrafluoropropene and N,N-dialkyl-1,1,3,3,3-pentafluoropropylamine) in different ratios. Those reaction mixtures, however, were found to be efficient fluorinating agents replacing hydroxyl groups in alcohols into fluorine. In general, they react with alcohols yielding corresponding fluorides, equimolar amounts of appropriate 3,3,3-trifluoropropionamide and hydrogen fluoride. Aliphatic primary alcohols including octanol and benzylic alcohol yield only alkyl fluorides. The secondary and tertiary alcohols, beside the desired fluorides, give usually considerably amount of alkenes.     

Structural chemistry and magnetic properties of Nd18Li8Fe5O39 and Nd18Li8Co4O39: the interplay of cation and spin ordering

Polycrystalline samples of Nd(18)Li(8)Fe(5)O(39) and Nd(18)Li(8)Co(4)O(39) have been synthesized using a solid-state method and studied by a combination of neutron diffraction, direct and alternating current magnetometry, and, in the case of Nd(18)Li(8)Fe(5)O(39), Mossbauer spectroscopy. Both compounds adopt a cubic structure (space group Pm3n, a(0) approximately 11.9 A) based on intersecting 111 chains made up of alternating octahedral and trigonal-prismatic coordination sites. The Fe(4+) cations in Nd(18)Li(8)Fe(5)O(39) are found on only the smaller of the two distinct octahedral sites in the structure; Fe(3+) and Li(+) are disordered over the larger octahedral site and the trigonal-prismatic site. The Nd(3+) cations occupy sites between the chains. The smaller octahedral site is fully occupied by cobalt in Nd(18)Li(8)Co(4)O(39), with 25% of the larger octahedral sites being vacant; Li(+) is only found on the prismatic sites. Nd(18)Li(8)Fe(5)O(39) shows spin-glass-like behavior with a spin-freezing temperature of 5.75 K, whereas Nd(18)Li(8)Co(4)O(39) appears to order antiferromagnetically at 2.3 K. In both cases, the magnetic coupling involves the Nd(3+) sublattice.     

Synthesis and characterization of two intensely colored tris(benzoylcyanoxime)iron(II) anionic complexes

Two intensely blue-colored complexes, P(C 6H 5) 4[Fe(BCO) 3] ( 1) and Na[Fe(BCO) 3] ( 2), where BCO (-) is the benzoylcyanoxime anion, have been prepared and characterized in solution and in the solid state. The crystal structure of 1 has been determined at several temperatures (100, 155, 225, and 293 K) and consists of layers of P(C 6H 5) 4 (+) cations and [Fe(BCO) 3] (-) anions. The latter exist as a pair of fac-Delta and Lambda enantiomers in a monoclinic unit cell in the P2(1)/ n space group. Iron(II) has a trigonal-prismatic N 3O 3 coordination environment with average Fe-N and Fe-O bond distances of 1.866 and 1.956 A, respectively, bonds that are unusually short and indicate a (1)A 1g low-spin ground state for iron(II). A sample of 1 prepared with iron-57 has been studied by Mossbauer spectroscopy between 4.2 and 430 K and found to be low-spin iron(II) in studied temperature range. The stepwise formation constants for 1 in aqueous solution at 296 K and pH of 7 are log beta 1 = 0.85 +/- 0.1, log beta 2 = 3.55 +/- 0.15, and log beta 3 = 6.36 +/- 0.15. Both 1 and 2 exhibit irreversible oxidation of iron(II) at approximately 1.0 V, indicating a significant degree of the ligand-to-iron charge transfer. Thus, 1 and 2 are rare examples of highly colored iron(II) anionic complexes that do not contain aromatic heterocyclic amine ligands, such as bipyridine or phenanthroline.     

Hydrolysis–condensation reactions of diethylphosphato-ethyltriethoxysilane with tetraethoxysilane studied by 29Si-NMR: Solvent and phosphonate catalytic effect

Hydrolysis and condensation reactions of diethylphosphato-ethyltriethoxysilane (SiP) and a mixture of SiP and tetraethoxysilane (TEOS) have been studied in ethanol and N-methylacetamide (NMA) as solvent. Conditions of reaction used for both SiP and SiP/TEOS mixture were Si/solvent (ethanol or NMA)/water molar ratio equals to 1/20/5 at 30 °C and without addition of external catalyst. The reactions have been investigated by high resolution ²⁹Si nuclear magnetic resonance (NMR). The hydrolyzed and condensed species, from SiP and TEOS were identified and quantified for both solvents as a function of reaction time. The influences of the amide medium as well as the catalytic effect of the phosphonate function of SiP on TEOS hydrolysis were established.     

Ethylene-Coordinative Chain-Transfer Polymerization-Induced Self-Assembly (CCTPISA)

Block copolymers based on ethylene (E) and butadiene (B) were prepared using the ansa-bis(fluorenyl) complex {Me₂Si(C₁₃H₈)₂Nd(BH₄)₂Li(THF)}₂ in combination with (n-Bu)(n-Oct)Mg (BOMAG) as a chain-transfer agent. The diblock copolymers incorporating a soft poly(ethylene-co-butadiene) segment, called ethylene butadiene rubber (EBR), and a hard polyethylene (PE) one were obtained by simply adjusting the different feeds of monomers during the polymerization. The soluble EBR block was formed first by feeding the catalytic system dissolved in toluene at 70 °C with a mixture of ethylene and butadiene (E/B molar ratio 80 : 20). Then the feeding was stopped leading to the consumption of a large part of the residual monomers. The reactor was finally fed with ethylene to form the PE block. By varying the molar mass of the latter, it is shown that the resulting soft-b-hard block copolymers can self-assemble simultaneously to the growth of the PE block in agreement with a polymerization-induced self-assembly (PISA) mechanism. The self-assembly is discussed considering the reaction conditions, the crystallization of the PE block, and the polymerization mechanism involved.     

Synthesis of copolyamides based on PA 66 bearing lithium sulfonate groups and having unique thermal properties

Copolyamides of PA 66/6 lithium 5‐sulfoisophthalic acid (LiSIPA) containing up to 40 mol % of LiSIPA were prepared in a 1L‐pilot reactor operating at high pressures and high temperatures. Interestingly, the presence of lithium sulfonate moieties highly impacted the glass transition temperature of the polyamide. The T_g increased from 59 °C for PA 66 to 155 °C for a copolymer containing about 40 mol % of LiSIPA. 1,3‐Dihexylbenzenedicarboxamide and lithium p‐toluenesulfonate were synthesized as model compounds to investigate the interaction of lithium sulfonate moieties and amide functions. Infrared spectroscopy using ATR technology performed on mixture of both compounds showed that the carbonyl group of amide functions interacts with the lithium cation of lithium sulfonate moieties. Similar S? O and C? O adsorption bands were observed in copolyamides PA 66/6LiSIPA and in mixture of model compounds, which strongly suggest the formation in the copolyamides of physical cross‐linking points centered on lithium cations coordinated by carbonyl groups of amide functions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011