The dynamic stereochemistry of the allylic ligand in a μ-allylic complex of platinum(II)

¹H NMR studies of an equilibrium mixture of 1,1,1,5,5,5-hexafluoropentane-2,4-dionato-π-allylplatinum(II) [IA] and bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)bis(μ-allyl)diplatinum(II) [IB] show that the μ-allylic ligands of (IB) exhibit temperature dependent tautomeric behaviour, giving rise to a site-exchange between protons on these ligands.     

Energy transfer in perylene-doped polyvinyl carbazole

Time resolved spectroscopy and fluorescence decay time measurements have been made on thin films of amorphous polyvinyl carbazole (PVK). The value obtained for the excimer fluorescence decay time in the undoped sample is less than that reported previously and a wavelength dependent double exponential decay is observed, which has been seen before only at low temperatures. The observed quenching of the excimer fluorescence decay times in the doped samples is evidence of direct energy transfer from excimers to perylene which is inconsistent with the model of energy transfer by exciton diffusion proposed to explain intensity quenching data. Several models for energy transfer in PVK are discussed and it is shown that the only model which predicts the observed time resolved spectroscopy results requires a long range resonant interaction strength much greater than that obtained theoretically. Several possible reasons for this are discussed.     

Time resolved spectroscopy of anthracene and tetracene doped fluorene crystals

Time resolved fluorescence spectroscopy measurements were used to investigate energy transfer in anthracene and tetracene doped fluorene crystals. The results for energy transfer from the host to anthracene molecules are consistent with both the recently proposed generalized random walk model for energy transfer and the combined exciton diffusion—long range resonance theory. The results for impurity sensitized energy transfer between anthracene and tetracene molecules in fluorene are in agreement with the predictions of long range resonance interaction. Comparisons are made with results of similar investigations of other systems.     

Structural influences on the lanthanide-actinide selectivity of some aminocarboxylates

Data for the resolution of americium from europium and terbium using 2,2′-diaminodiethylether-N,N,N′,N′-tetraacetate and 1,5-diaminopentane-N,N,N′,N′-tetraacetate are reported along with values of the formation constants of the La-Lu and Y chelates of the latter. It is shown that the minimum single-stage separation factor for Am³⁺ from Ln³⁺ cations, using 2,2′-diaminodiethylether-N,N,N′,-N′-tetraacetate with Dowex 50 resin, exceeds 1.7 for all Am-Ln pairs, and runs as high as 350 in the case of Am³⁺, La³⁺. The minimum of 1.7 occurs at Eu³⁺ in the lanthanon sequence. A novel separation of Am³⁺, Cm³⁺ and heavier actinons from each other and from all the lanthanons and yttrium appears to be feasible.     

Nickel-catalyzed cross-couplings of organosilicon reagents with unactivated secondary alkyl bromides

A metal-catalyzed cross-coupling of organosilicon compounds with alkyl halides has been developed. Noteworthy attributes of the method are its scope (secondary electrophiles), its high functional-group compatibility, and the air stability of the catalyst components.     

Templated synthesis of the novel layered silver-antimony sulfides [H3NCH2CH2NH2][Ag2SbS3 and [H3NCH2CH2NH2]2[Ag5Sb3S8

Two new silver-antimony sulfides, [C(2)H(9)N(2)][Ag(2)SbS(3)] (1) and [C(2)H(9)N(2)](2)[Ag(5)Sb(3)S(8)] (2), have been prepared solvothermally in the presence of ethylenediamine and characterized by single-crystal X-ray diffraction, thermogravimetry, and elemental analysis. Compound 1 crystallizes in the space group Pn (a = 6.1781(1) A, b =11.9491(3) A, c = 6.9239(2) A, beta =111.164(1) degrees ) and 2 in the space group Pm (a = 6.2215(2) A, b = 15.7707(7) A, c = 11.6478(5) A, beta = 92.645(2) degrees ). The structure of 1 consists of chains of fused five-membered Ag(2)SbS(2) rings linked to form layers, between which the template molecules reside. Compound 2 contains honeycomb-like sheets of fused silver-antimony-sulfide six-membered rings linked to form double layers. The idealized structure can be considered to be an ordered defect derivative of that of lithium bismuthide, Li(3)Bi, and represents a new solid-state structure type.     

The Balian-Low theorem and regularity of Gabor systems

For any positive real numbers A, B, and d satisfying the conditions , d>2, we construct a Gabor orthonormal basis for L²(ℝ), such that the generating function g∈L²(ℝ) satisfies the condition:∫_ℝ|g(x)|²(1+|x| ^A )/log ^d (2+|x|)dx < ∞ and .