Chalcogenide derivatives of imidotin cage complexes

Reaction of the secocubane [Sn3(mu2-NHtBu)2(mu2-NtBu)(mu3-NtBu)] (1) with dibutylmagnesium produces the heterobimetallic cubane [Sn3Mg(mu3-NtBu)4] (4) which forms the monochalcogenide complexes of general formula [ESn3Mg(mu3-NtBu)4] (5a, E = Se; 5b, E = Te) upon reaction with elemental chalcogens in THF. By contrast, the reaction of the anionic lithiated cubane [Sn3Li(mu3-NtBu)4]- with the appropriate quantity of selenium or tellurium leads to the sequential chalcogenation of each of the three Sn(II) centres. Pure samples of the mono- or dichalcogenides are, however, best obtained by stoichiometric redistribution reactions of [Sn3Li(mu3-NtBu)4]- and the trichalcogenides [E3Sn3Li(mu3-NtBu)4]- (E = Se, Te). These reactions are conveniently monitored by using 119Sn NMR spectroscopy. The anion [Sn3Li(mu3-NtBu)4]- also acts as an effective chalcogen-transfer reagent in reactions of selenium with the neutral cubane [{Snmu3-N(dipp)}4] (8) (dipp = 2,6-diisopropylphenyl) to give the dimer [(thf)Sn{mu-N(dipp)}2Sn(mu-Se)2Sn{mu-N(dipp)}2Sn(thf)] (9), a transformation that results in cleavage of the Sn4N4 cubane into four-membered Sn2N2 rings. The X-ray structures of 4, 5a, 5b, [Sn3Li(thf)(mu3-NtBu)4(mu3-Se)(mu2-Li)(thf)]2 (6a), [TeSn3Li(mu3-NtBu)4][Li(thf)4] (6b), [Te2Sn3Li(mu3-NtBu)4][Li([12]crown-4)2] (7b') and 9 are presented. The fluxional behaviour of cubic imidotin chalcogenides and the correlation between NMR coupling constants and tin-chalcogen bond lengths are also discussed.     

Accessing Extended Fused Isoindolinones Via Sequential Anionic Intramolecular Cyclizations

Sequential anionic intramolecular cyclizations and modelling were used for the first time to access unusual fused heterocyclic frameworks in excellent yields. 5-Exo-dig cyclizations yielded isoindolinone motifs and a subsequent 6-exo- and 7-endo-dig cyclization was directed to provide either fused isoquinoline or azepine frameworks. Regioselectivities were controlled by exploiting stereoelectronic effects via n_C−→π*_(Ph) interactions, and modelling studies provided reaction scope.     

Surface-enhanced emission from single semiconductor nanocrystals

The fluorescence behavior of single CdSe(ZnS) core-shell nanocrystal (NC) quantum dots is dramatically affected by electromagnetic interactions with a rough metal film. Observed changes include a fivefold increase in the observed fluorescence intensity of single NCs, a striking reduction in their fluorescence blinking behavior, complete conversion of the emission polarization to linear, and single NC exciton lifetimes that are >10(3) times faster. The enhanced excited state decay process for NCs coupled to rough metal substrates effectively competes with the Auger relaxation process, allowing us to observe both charged and neutral exciton emission from these NC quantum dots.     

Crystal structures, EPR and magnetic properties of 2-ClC6H4CNSSN˙ and 2,5-Cl2C6H3CNSSN˙

The β-sheet structure associated with chlorinated aromatics (d(Cl···Cl)≈ 4.0 ?) has been implemented to drive formation of π-stacked structures of dithiadiazolyl radicals. Both title compounds exhibit an increase in paramagnetism above 150 K but solid-state EPR studies indicate that the origin of the paramagnetism in these two systems is different.     

Response of multiple layered media

A recently developed method for estimating the response of multiple coupled one-dimensional dynamic systems can be adapted to deal with the response of multiple layered media. This paper discusses this adaptation. The purpose is to bring this method to bear on this important subject, on the one hand, and to expand the range of applicability of the method on the other. In the method the interactions between the one-dimensional dynamic systems are defined in terms of reflection and transmission coefficients at junctions at which the dynamic systems terminate. In that sense the formalism is cast in terms of standard procedures in the investigations of the response of multiple layered media and, therefore, the adaptation is straightforward. Once the adaptation is instituted, the procedures are extended so that the formalism can treat situations in which steady flows are present in the layers. This extension has previously received only meager analytical attention. It is argued that in certain situations of this kind, the flows may introduce significant modifications in the response. The conditions and the nature of such modifications are defined and examined.