Mechanochemical
methods have been successful in providing rapid
access to a number of inorganic–organic functional materials
under mild conditions. Recently, we demonstrated a novel mechanochemical
strategy for metal–organic framework (MOF) preparation based
on predesigned oxo-centered secondary building units. Herein, we develop
this method for the facile preparation of the isoreticular MOF (IRMOF)
family members based on a combination of an oxozinc amidate cluster,
[Zn4(μ4-O)(NHOCPh)6], and selected
ditopic aminoterephthalate and 4,4′-biphenyldicarboxylate as
well as tritopic 1,3,5-benzenetribenzoate ligands. The resulting IRMOF-3,
IRMOF-10, and MOF-177 crystalline materials were characterized using
powder X-ray diffraction, IR spectroscopy, scanning electron microscopy
(SEM), and thermogravimetric analysis. We found that the character
of the organic linker strongly affects the nature of the resulting
MOF crystallites after activation processes. The SEM images demonstrate
that IRMOF-3 formed microcrystallites in the range of 400–500
nm, while the two other materials exhibited microstructures of amorphous
phases. The porosity of each sample was estimated by N2 sorption measurements at 77 K. These results provide an efficient
and general method for the mechanosynthesis of Zn-based MOF materials
using a predesigned oxozinc cluster.
Metal-oxo clusters can serve as directional and rigid building units of coordination and noncovalent supramolecular assemblies. Therefore, an in-depth understanding of their multi-faceted chemistry is vital for the development of self-assembled solid-state structures of desired properties. Here we present a comprehensive comparative structural analysis of isostructural benzoate, benzamidate, and new benzamidinate zinc-oxo clusters incorporating the [O,O]-, [O,NH]- and [NH,NH]-anchoring donor centers, respectively. We demonstrated that the NH groups in the proximal secondary coordination sphere are prone to the formation of intermolecular hydrogen bonds, which affects the packing of clusters in the crystal structure. Coordination sphere engineering can lead to the rational design of new catalytic sites and novel molecular building units of supramolecular assemblies.
Despite decades of extensive studies on the reactivity of magnesium alkyls towards O2, the isolation and structural characterization of discrete products of these reactions still remains a challenge. Although the formation of the most frequently encountered magnesium alkoxides through unstable alkylperoxide intermediates has commonly been accepted, the latter species have been elusive for over 100 years. Probing the oxygenation of a seemingly simple well‐defined neo‐pentylmagnesium complex stabilized by a β‐diketiminate ligand, (dippBDI)MgCH2CMe3, we report on the isolation and structure characterization of both a dimeric magnesium alkoxide [(dippBDI)Mg(μ‐OCH2CMe3)]2 and the first example of monomeric magnesium alkylperoxide [(dippBDI)Mg(thf)OOCH2CMe3] (dippBDI=[(ArNCMe)2CH]− and Ar=C6H3iPr2‐2,6). The formation of monomeric magnesium alkylperoxide demonstrates a crucial role of an additional Lewis base for stabilizing the most elusive oxygenation products likely due to increasing of the electron density on the metal centre. Moreover, the 1H NMR studies at −80 °C revealed that the dissociation of a coordinated Lewis base from the solvated complex (dippBDI)Mg(L)CH2CMe3 (where L=thf or 4‐methylpyridine) is likely not required prior to the effective attack of an O2 molecule on the metal centre and the four‐coordinate alkylmagnesium complex reacts smoothly with O2 under these conditions. The results can be expected to aid future engineering of various organomagnesium/O2‐based reaction systems.
Colloidal nanoplatelets (NPLs) and nanosheets with controlled thickness have recently emerged as an exciting new class of quantum-sized nanomaterials with substantially distinct optical properties compared to 0D quantum dots. Zn-based NPLs are an attractive heavy-metal-free alternative to the so far most widespread cadmium chalcogenide colloidal 2D semiconductor nanostructures, but their synthesis remains challenging to achieve. The authors describe herein, to the best of their knowledge, the first synthesis of highly stable ZnO NPLs with the atomically precise thickness, which for the smallest NPLs is 3.2 nm (corresponding to 12 ZnO layers). Furthermore, by means of dynamic nuclear polarization-enhanced solid-state 15 N NMR, the original role of the benzamidine ligands in stabilizing the surface of these nanomaterials is revealed, which can bind to both the polar and non-polar ZnO facets, acting either as X-or L-type ligands, respectively. This bimodal stabilization allows obtaining hexagonal NPLs for which the surface energy of the facets is modulated by the presence of the ligands. Thus, in-depth study of the interactions at the organic-inorganic interfaces provides a deeper understanding of the ligand-surface interface and should facilitate the future chemistry of stable-by-design nano-objects.
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