Formation of rutile-type Ta(IV)O2 by shock reduction and cation-deficient Ta0.8O2 by subsequent oxidation

Ta₂O₅ is reduced to Ta(IV)O₂ with the rutile structure by shock-loading to 50–60 GPa. Tetragonal unit cell parameters at room conditions are measured to be a = 4.7518(5)Å, c = 3.0878(4) Å, $\text{c}\text{a}\text{= 0.6498(1)}$, and V = 69.72(1) ų. The chemical composition is thermogravimetrically determined to be Ta_0.97±0.04O₂ by heating shock-reduced products in an oxygen gas flow to 1200°C. In the oxidation process a cation-deficient rutile-type compound Ta_0.8O₂ is found to be metastably formed.     

An infinite zigzag chain of alternating Cl-Pd-Pd-Cl and Mo-Mo units

Treatment of Pd(2)Cl(2)(CNC(6)H(3)Me(2)-2,6)(4) (1) with Mo(2)(O(2)CCF(3))(4) (2) in dichloromethane afforded an infinite zigzag chain [[Pd(2)Cl(2)(CNC(6)H(3)Me(2)-2,6)(4)][Mo(2)(O(2)CCF(3))(4)]](n) (3), where two metal-metal bonded dinuclear Pd-Pd and Mo-Mo units were bridged by chloro atoms. The Mo-Mo distance (2.1312(3) A) of 3 is significantly elongated compared to that of 2 (2.090(4) A) and lies in the range of that of the quadruple Mo-Mo bonded complexes. Such elongation might be attributed to the axial donation of the chloro atoms of the Pd-Pd unit to the Mo-Mo moiety.     

Fixed point theorems for a class of nonlinear mappings related to maximal monotone operators in Banach spaces

In this paper, the class of nonspreading mappings in Banach spaces is introduced. This class contains the recently introduced class of firmly nonexpansive type mappings in Banach spaces and the class of firmly nonexpansive mappings in Hilbert spaces. Among other things, we obtain a fixed point theorem for a single nonspreading mapping in Banach spaces. Using this result, we also obtain a common fixed point theorem for a commutative family of nonspreading mappings in Banach spaces. Received: 10 August 2007     

Novel synthesis of 2,3-diarylbuta-1,3-dienes from 1,4-dimethoxybutyne-2

It was found that 2,3-diarylbuta-1,3-dienes were readily obtained in good to excellent yields through the S_N-2′ type substitution of 1,4-dimethoxybutyne-2 with aryl Grignard reagents in the presence of a copper(I) salt.     

Reductive dimerization of dialkyl acetylenedicarboxylate catalyzed by [Rh(binap)(MeOH)2]ClO4 in methanol

Cationic Rh(I) complex [Rh(binap)(MeOH)₂]ClO₄ catalyzes reductive dimerization of dialkyl acetylenedicarboxylates 1 to give 1,2,3,4-tetrakis(alkoxycarbonyl)-1,3-butadienes 2 in methanol selectively.     

A photo-reagent system of benzimidazoline and Ru(bpy)3Cl2 to promote hexenyl radical cyclization and Dowd–Beckwith ring-expansion of α-halomethyl-substituted benzocyclic 1-alkanones

A combination of 2-aryl substituted 1,3-dimethyl-benzimidazolines (DMBIHs) and tris(2,2′-bipyridine)ruthenium(II) chloride, Ru(bpy)₃Cl₂ was used to promote photoinduced electron-transfer (PET) reactions of α-halomethyl-substituted benzocyclic 1-alkanones. This photo-reagent system stimulates free radical forming, cleavage of both carbon–bromine and carbon–chlorine bonds that are not activated by carbonyl groups. The resulting free radicals undergo 5-exo hexenyl cyclization as well as sequential cyclization and ring-expansion (Dowd–Beckwith) reactions to form radicals that abstract hydrogen atoms from the radical cation of DMBIH to yield the observed products. The results of a study of the effects of substituents located on the 2-aryl ring of DMBIH suggest that steric and hydrogen-bonding interactions influence the nature of the reaction pathways followed by the radical intermediates. PET reactions using an iridium complex and DMBIH were also investigated.     

Efficient Emission of Ultraviolet Light by Solid State Organic Fluorophores: Synthesis and Characterization of 1,4-Dialkeny-2,5-dioxybenzenes

The design and development of organic luminophores that exhibit efficient ultraviolet (UV) fluorescence in the solid state remains underexplored. Here, we report that 1,4-dialkenyl-2,5-dialkoxybenzenes and 1,4-dialkenyl-2,5-disiloxybenzenes act as such UV-emissive fluorophores. The dialkenyldioxybenzenes were readily prepared in three steps from 2,5-dimethoxy-1,4-diacetylbenzene or 2,5-dimethoxy-1,4-diformylbenzene via two to four steps from 1,4-bis(diethoxyphosphonylmethyl)-2,5-dimethoxybenzene. The dialkenyldioxybenzenes emit UV light in solution (λ_em=350–387 nm) and in the solid state (λ_em=328–388 nm). In addition, the quantum yields in the solid state were generally higher than those in solution. In particular, the adamantylidene-substituted benzenes fluoresced in the UV region with high quantum yields (Φ=0.37–0.55) in the solid state. Thin films of poly(methyl methacrylate) doped with the adamantylidene-substituted benzenes also exhibited UV emission with good efficiency (Φ=0.27–0.45). Density functional theory calculations revealed that the optical excitation of the dialkenyldimethoxybenzenes involves intramolecular charge-transfer from the ether oxygen atoms to the twisted alkenyl-benzene-alkenyl moiety, whereas the dialkenylbis(triphenylsiloxy)benzenes were optically excited through intramolecular charge-transfer from the oxygen atoms and twisted π-system to the phenyl-Si moieties of each triphenylsilyl group.     

Spherical nonspreadingness of resolvents of convex functions in geodesic spaces

In this paper, we propose the concepts of a spherically nonspreading mapping and a firmly spherically nonspreading mapping in a complete geodesic space with curvature bounded above by one and we prove that the resolvent of a proper lower semicontinuous convex function in that space is both well defined and firmly spherically nonspreading. We further discuss the existence and approximation of fixed points of such mappings and apply our results to convex optimization in geodesic spaces.     

Corannulene‐Fused Anion‐Responsive π‐Conjugated Molecules that Form Self‐Assemblies with Unique Electronic Properties

The fusion of bowl‐shaped π‐conjugated corannulene units to anion‐responsive π‐conjugated dipyrrolyldiketone‐boron complexes resulted in new molecular materials with a unique self‐assembly capability. The bowl‐fused receptor with aliphatic tails could form both supramolecular gels and mesophases through π‐stacking interactions and also exhibited anion‐responsive characteristics. The presence of the π‐bowl unit not only afforded enhanced self‐assembly capability both in solution and in the mesophases, as evidenced by gelation experiments and phase‐transition profiles, but also enhanced intrinsic charge‐carrier mobility.     

Ion‐Pair‐Based Assemblies Comprising Pyrrole–Pyrazole Hybrids

Modified 3,5‐dipyrrolylpyrazole (DPP) derivatives in their protonated form produce planar [2+2]‐type complexes with trifluoroacetate (TFA) ions. These complexes serve as constituent components of ion‐pair‐based assemblies. An essential strategy for the construction of dimension‐controlled organized structures based on these [2+2]‐type complexes is the introduction of aryl rings bearing long alkyl chains, which enables the formation of 2D patterns at interfaces, supramolecular gels, and mesophases.