RESUMEN
Soluble and transparent wholly aromatic polyamides (PAs) were synthesized from an unsymmetrical diamine monomer having trifluoromethyl (CF3) groups, 4-(4'-aminophenoxy)-3,5-bis(trifluoromethyl)aniline. The monomer was polymerized with several dicarboxylic acid monomers via the Yamazaki-Higashi polycondensation method. All of the synthesized polyamides have an amorphous morphology, and they are soluble in many polar organic solvents at room temperature. Flexible and transparent films of the polyamides were prepared by solution casting and these polymer films show good optical transparencies with cut-off wavelengths of 337-367 nm and transparencies of 88%-90% at 550 nm. In addition, all the polymers were thermally stable over 400 °C and exhibited glass transition temperatures (Tg) higher than 300 °C. Unsymmetrically inserted trifluoromethyl groups on polyamides improves the solubility as well as the transparency of the polymers while maintaining good thermal properties. They also showed low refractive indices around 1.5333~1.5833 at 633 nm owing to the existence of low polarizable trifluoromethyl groups.
RESUMEN
A cobalt-silyl moiety reveals metal-ligand cooperative group transfer to generate isocyanate from the reaction of alkyl azide and CO. This reaction involves the reversible insertion of a nitrene group into a Co-Si bond. Photolysis leads to ligand substitution of a Co(CO)2 species, allowing the successful catalytic conversion of AdN3 to AdNCO under CO(g).
RESUMEN
A novel lithium-rich transition metal selenite, Li13Mn(SeO3)8, that is composed of a Jahn-Teller distortive cation, Mn3+, in the high spin d4 state, and a second-order Jahn-Teller (SOJT) distortive lone pair cation, Se4+, has been synthesized via hydrothermal and high temperature solid state reactions. The selenite is classified as a molecular compound consisting of MnO6 octahedra, SeO3 trigonal pyramids, and Li+ cations. Considering the Li-O interactions, the structure of Li13Mn(SeO3)8 may be described as a pseudo-three-dimensional framework as well. The title compound is thermally stable up to 500 °C and starts decomposing above the temperature attributable to the volatilization of SeO2. While the MnO6 octahedra in Li13Mn(SeO3)8 exhibit six identical Mn-O bond distances at room temperature due to the dynamic Jahn-Teller effect, a clear elongation of two Mn-O bonds along a specific direction is observed at 100 K. A series of isostructural selenites with different transition metals, i.e., Li13M(SeO3)8 (M = Sc, Cr, and Fe), have been also successfully obtained in phase pure forms using similar synthetic methods. Magnetic properties, spectroscopic characterizations, and local dipole moments calculations for all the synthesized selenites are presented.
