High-resolution X-ray diffraction, DIFFaX, NMR and first principles study of disorder in the Li2MnO3-Li[Ni1/2Mn1/2]O2 solid solution

X-ray diffraction patterns of Li[Li_(1−2x)/3Ni_xMn_2/3−x/3]O₂ show reflections between 20° and 35°, 2θ (CuKα) due to Li₂MnO₃-like ordering of the transition metal (Ni, Mn and Li) layers. The ordering is rarely perfect, resulting in characteristic broadening and changes in the intensities of these reflections. ⁶Li MAS NMR studies of Li₂MnO₃ show that the [Li_1/3Mn_2/3] layers are well ordered, the disorder arising from the stacking of the layers in the c-direction. DIFFaX was used to model the Li₂MnO₃ XRD data and extract the stacking fault frequency. The results show that even well-ordered cation layers may show only weak or no superstructure reflections, if there is no or little ordering in the c-direction.     

Layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1, 2, and 3) as insertion hosts for Li ion batteries

The layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1-3) consist of alternating perovskite-type Sr2MnO2 layers and copper sulfide layers. The copper ions can be replaced electrochemically and reversibly by Li. The lithiated materials were studied by Li MAS NMR, and Li resonances were observed with shifts that could be rationalized based on the number of sulfide layers. The materials were cycled versus Li and showed enhanced capacity retention in comparison to pure Cu2S; the good electrochemical performance was ascribed to the presence of the layered framework structure and rapid Li+ and Cu+ conductivity in the sulfide layers.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.