Luminescent Metal-Organic Framework Sensor: Exceptional Cd2+ Turn-On Detection and First In Situ Visualization of Cd2+ Ion Diffusion into a Crystal.

With regard to fluorescence quenching commonly observed during metal-ion detection, "turn-on" chemical sensing has been rarely reported, but could be extremely important because it facilitates the selective recognition of target objects of interest against a dark background. A metal-organic framework (MOF) chemosensor has been prepared that serves as an efficient platform for the selective detection of Cu2+ and Cd2+ ions over other metal ions. In particular, this framework shows the highest fluorescence enhancement (≈60-fold relative to Cd-free MOF) for the hazardous metal ion Cd2+ among luminescent MOFs and displays excellent reusability in repeated cycles. The direct diffusion of Cd2+ into the crystal pores has also been visualized for the first time.

Superprotonic conductivity of a UiO-66 framework functionalized with sulfonic acid groups by facile postsynthetic oxidation.

Facile postsynthetic oxidation of the thiol-laced UiO-66-type framework UiO-66(SH)2 enabled the generation of UiO-66(SO3 H)2 with sulfonic acid groups covalently linked to the backbone of the system. The oxidized material exhibited a superprotonic conductivity of 8.4×10(-2)  S cm(-1) at 80 °C and 90 % relative humidity, and long-term stability of the conductivity was observed. This level of conductivity exceeds that of any proton-conducting MOF reported to date and is equivalent to the conductivity of the most effective known electrolyte, Nafion.

pH-dependent proton conducting behavior in a metal-organic framework material.

A porous metal-organic framework (MOF), [Ni2(dobdc)(H2O)2]⋅6 H2O (Ni2(dobdc) or Ni-MOF-74; dobdc(4-)=2,5-dioxido-1,4-benzenedicarboxylate) with hexagonal channels was synthesized using a microwave-assisted solvothermal reaction. Soaking Ni2(dobdc) in sulfuric acid solutions at different pH values afforded new proton-conducting frameworks, H(+)@Ni2(dobdc). At pH 1.8, the acidified MOF shows proton conductivity of 2.2×10(-2) S cm(-1) at 80 °C and 95% relative humidity (RH), approaching the highest values reported for MOFs. Proton conduction occurs via the Grotthuss mechanism with a significantly low activation energy as compared to other proton-conducting MOFs. Protonated water clusters within the pores of H(+)@Ni2(dobdc) play an important role in the conduction process.

Dehydration-triggered magnetic phase conversion in the porous Cu(II)Mn(III) metal-organic framework.

Dehydration of the three-dimensional Cu(II)-Mn(III) coordination network undergoes a dramatic magnetic phase transformation from a paramagnetic state to a long-range magnetic ordered phase with glassy behavior. The gas adsorption behavior and re-entrant spin glass character are uniquely apparent in the dehydrated sample.

Selective CO2 adsorption and proton conductivity in the two-dimensional Zn(II) framework with protruded water molecules and flexible ether linkers.

A two-dimensional (2D) Zn(II) metal-organic framework with flexible aryl ether linkers and water molecules exposed to the pores was prepared. The supramolecular three-dimensional (3D) network is generated by the presence of extensive π-π contacts, which could be responsible for gas uptake. The water molecules and oxygen atoms from the flexible linkers create a polar environment within the integrated framework, leading to simultaneous selective CO2 adsorption and proton conductivity in the two-dimensional Zn(II) framework.

Reversible structural transformation and selective gas adsorption in a unique aqua-bridged Mn(II) metal-organic framework.

An aqua-bridged Mn metal-organic framework was prepared, and a dramatic structural transformation occurs upon solvent exchange-resolvation and desolvation-resolvation processes. The desolvated phase, formed by removing the aqua bridges, exhibits selective CO(2) uptake over N(2), H(2), and CH(4). Further, antiferromagnetic couplings are also found between Mn spins in the secondary building units.

Charge effect of foreign metal ions and the crystal growth process in hybridized metal-organic frameworks.

A paddle-wheel-type Cu metal-organic framework CuHTPO involving hydrogen bonds in the network is utilized to obtain composite systems with different metal ions of Zn(2+) and Tb(3+). The framework stability and crystal transformation are affected by the charges of foreign cations.