COK‐16: A Cation‐Exchanging Metal–Organic Framework Hybrid

Abstract

X‐ray spectroscopy: Substoichiometric encapsulation of polyoxometalate ions into a metal–organic framework results in a fully functional cation exchanger with accessible porosity. Cu2+ cations compensating the charge of [PW12O40]3− in the as‐synthesized material can be exchanged with cations such as Na+ and Eu3+. When exchanged with Eu3+, the material appears bright red under UV irradiation (see figure).

Enhanced Self‐Assembly of Metal Oxides and Metal‐Organic Frameworks from Precursors with Magnetohydrodynamically Induced Long‐Lived Collective Spin States

“…Together with the appearance of a half‐field transition (DQ effect) in the powder EPR spectrum a significant, positive influence of the magnetic field on the formation of the EPR silent spin coupled copper dimers is evident. As expected, both phases (MHD and HD only) contain a spectral component due to the presence of mononuclear, extraframework Cu +2 compensating the charge of the HPA units enclosed in the pores . The broad, isotropic signal resulting from the inter‐dimer interaction between the AF coupled [Cu‐Cu] 4+ dimers, indicates increased diamagnetism of the phase crystallized in presence of the magnetic field.…”

“…Metal Organic Framework COK‐16 : In case of polyoxometalate encapsulated metal organic framework COK‐16, magneto hydrodynamic (MHD) synthesis results in the appearance of a double quantum excitation in the electron paramagnetic resonance (EPR) spectrum ( Figure ) without changing the framework structure, according to X‐ray Diffraction (XRD) (Figure S3). These double quantum excitations (DQ) are typically observed when magnetic dipole/dipole coupling between Cu 2+ sites or Cu 2+ pairs gain importance, relative to the direct exchange or super‐exchange coupling in the pairs.…”

Eu@COK-16, a host sensitized, hybrid luminescent metal–organic framework

“…Using a highly Cu 2+ selective di-iminoacetate resin, these extra Cu 2+ ions can selectively be exchanged for Na + while the MOF structure remains intact. 8 The high affinity of polyoxometalate anions for trivalent rare earth ions 12,13 allows exchanging COK-16 directly with the RE 3+ ions. In case of europium, this yields the Eu 3+ exchanged COK-16 as the first example of a new class of hybrid luminescent materials, where the luminescent ions reside in the pore system of a framework which acts as an antenna.…”

“…Only one Eu position was consistent with identical distances of 3.7 Å between the rare earth and four tungsten ions of the Keggin ion, which showed an occupation factor of roughly 75% of the available cavities of type L2 in the HKUST-1 topology. 8,17 The occupation of the Eu 3+ freely converged to 1 Eu 3+ ion per Keggin ion. In addition to the 4 O atoms from [PW12O40] 3at a distance of 2.5 Å, the coordination of Eu is completed with 4 water molecules at a distance of 2.3 Å, identified by inspection of the observed electron density map.…”

The development of MOFs-based nanomaterials in heterogeneous organocatalysis

“…Owing to the characteristics of well-organized configuration, high specific surface area, and tailorable porosity, MOFs are considered to be an ideal sacrificial templates to synthesize the heteroatoms-doped carbon-based nanocatalysts. To date, an enormous of researches have concentrated on the preparation of MOFsderived hetero-atoms doped metal-carbon composites, and plentiful of MOFs have been employed for this target, such as ZIF-8 [100], ZIF-67 [101], Cu(BTC) 3 [102], and MOF-5 [103].…”