Two new mixed-valent triple perovskites, Ba(3)MRu(2)O(9) (M = Li, Na), were grown from reactive hydroxide fluxes. They crystallize in the hexagonal space group P6(3)/mmc, where Ru(V) and Ru(VI) are disordered on only one crystallographic site. Upon cooling, single crystals of Ba(3)NaRu(2)O(9) undergo a complex symmetry-breaking structural transition at ca. 225 K from room-temperature hexagonal symmetry to a low-temperature orthorhombic symmetry, space group Cmcm. Accompanying this structural transition is a rather abrupt decrease in the magnetic susceptibility at 210 K followed by a steady decrease in the susceptibility with decreasing temperature. Interestingly, the lithium analogue does not display any structural transition down to 100 K. The structural transition in Ba(3)NaRu(2)O(9) generates three crystallographically unique Ru sites in the low-temperature structure as compared to only one distinct site in the room-temperature structure. On the basis of an analysis of the Ru-Ru distances in the face-sharing bi-octahedra, the structural transition also appears to involve charge ordering of Ru(V) and Ru(VI), causing all Ru(V) to occupy one set of bi-octahedra and all Ru(VI) to occupy another set.
The synthesis of novel conjugated polymers by acyclic diyne metathesis (ADIMET) is reported.
These polymers are hybrids between poly(p-phenylenevinylene) and poly(p-phenyleneneethynylene) (PPE).
They contain phenylene, ethynylene, and vinylene groups (⋮PhPh, PPVE). Simple in situ catalysts
formed from Mo(CO)6 and 4-chlorophenol were used to metathesize the dipropynyl(tetraalkyl)stilbene
monomers. The monomers are made by a combination of Horner reactions and Heck-type couplings. The
PPVEs form in high yields and are structurally defined. They show degrees of polymerization (P
n
) of 30−220
repeating units (i.e. 60−450 benzene rings), demonstrating that the presence of the double bonds does not
interfere with alkyne metathesis. The PPVEs were structurally characterized by XRD and electron microscopy.
They show fibrillar and network-type morphologies, which should make them interesting for applications in
molecular electronics. Solid samples of PPVEs display powder XRD patterns almost identical to those of the
PPEs. PPVEs thus assume similar doubly lamellar structures as the PPEs. The aggregation behavior of PPVEs
was studied. In addition, ADIMET to a poly(2,7-fluorenyleneethynylene) carrying unsaturated side chains is
reported. In this case the presence of unsaturation does neither interfer with efficient alkyne metathesis.
Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = 1 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.