The incorporation of tetravalent cations (Zr 4+ and Sn 4+ ) inside sheets of layered double hydroxide (LDH) was reported by Velu et al. As no local structural information was provided so far, the question here is whether the LDH structure may accommodate such a presence. From three different systems presenting the cation compositions MgAlSn, MgAlZr, and CoAlSn, we provide (by means of X-ray absorption and Mo ¨ssbauer spectroscopies) clear evidence that the tetravalent cations are segregated from the LDH structure and form amorphous M IV oxide-like particles. Variation of the cell parameters, a and c, is then explained by a substitution of Al cations by the divalent cations, M II . It is also shown that despite the fact that the process of reconstruction occurs for MgAlM (M ) Zr and Sn), the tetravalent cations do not participate in this structural recovery.
A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N′)-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N′)-tri-gold(I) (2), tris(μ2-3-methyl-5-phenylpyrazolato-N,N′)-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato-N,N′)-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm−1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.
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.