Fluorescent Zr(IV) Metal-Organic Frameworks Based on an Excited-State Intramolecular Proton Transfer-Type Ligand.

We report here the preparation of a series of Zr(IV) metal-organic frameworks (MOFs) of the MIL-140 structure type incorporating a ligand exhibiting an intense excited-state intramolecular proton transfer (ESIPT) fluorescence. These solids were obtained by systematically varying the substitution rate of 4,4'-biphenyldicarboxylate by 2,2'-bipyridine-3,3'-diol-5,5'-dicarboxylate, and they were thoroughly characterized by complementary techniques, including high-resolution powder X-ray diffraction, solid-state NMR spectroscopy, nitrogen sorption experiments, and time-resolved fluorescence. We show that the incorporation of the ESIPT-type ligand induces an increase of the hydrophilicity, leading ultimately to a higher sensitivity toward hydrolysis, a phenomenon rarely observed in this structure type, which is considered as one of the most stable among the Zr carboxylate MOFs. Eventually, optimization of the amount of fluorescent ligand within the structure allowed combining a decent microposity ( SBET > 750 m2·g-1) and a high stability even in boiling water, together with a high fluorescence quantum yield (>30%).

Co(2+)@Mesoporous Silica Monoliths: Tailor-Made Nanoreactors for Confined Soft Chemistry.

Mesoporous silica monoliths with various ordered nanostructures containing transition metal M(2+) cations in variable amounts were elaborated and studied. A phase diagram depicting the different phases as a function of the M(2+) salt/tetramethyl orthosilicate (TMOS) and surfactant P123/TMOS ratios was established. Thermal treatment resulted in mesoporous monoliths containing isolated, accessible M(2+) species or condensed metal oxides, hydroxides, and salts, depending on the strength of the interactions between the metal species and the ethylene oxide units of P123. The ordered mesoporosity of the monoliths containing accessible M(2+) ions was used as a nanoreactor for the elaboration of various transition metal compounds (Prussian blue analogues, Hofmann compounds, metal-organic frameworks), and this opens the way to the elaboration of a large range of nanoparticles of multifunctional materials.

In situ site-selective transition metal K-edge XAS: a powerful probe of the transformation of mixed-valence compounds.

We present herein the first in situ site-selective XAS experiment performed on a proof-of-principle transformation of a mixed-valence compound: the calcination of the K0.1Co(II)4[Co(III)(CN)6]2.7·20H2O Prussian Blue analogue (containing Co(2+) and Co(3+) ions in two different Oh sites) into Co3O4 (containing Co(2+) ions in a Td site and Co(3+) in an Oh site). By recording the Co K-edge X-ray absorption spectra using a spectrometer aligned at the Co Kß1,3 emission line, the evolution of each species was singly monitored from 20 °C up to the oxide formation. The experimental spectrum of the Co(2+)(Td) and Co(3+) (Oh) species in Co3O4 is reported for the first time. Our results demonstrate the possibilities offered by site-selective XAS for the investigation of chemical transformations and the study of materials under working conditions whenever the chemical element of interest is present in several states and/or sites.

Towards bottom-up nanopatterning of Prussian blue analogues.

Ordered nanoperforated TiO2 monolayers fabricated through sol-gel chemistry were used to grow isolated particles of Prussian blue analogues (PBA). The elaboration of the TiO2/CoFe PBA nanocomposites involves five steps. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) all along the synthesis process. Selected physico-chemical parameters have been varied in order to determine the key steps of the synthesis process and to optimize it. This study is an important step towards the full control of the fabrication process.