The practical use of metal–organic frameworks (MOFs) in applications ranging from adsorption separations to controlled storage and release hinges on their stability in humid or aqueous environments. ...The sensitivity of certain MOFs under humid conditions is well-known, but systematic studies of water adsorption properties of MOFs are lacking. This information is critical for developing design criteria for directing future synthesis efforts. The goal of this work is to understand the influence of the extent of Zn–O bond shielding on the relative stabilities of MOFs belonging to same family of isostructural, noncatenated pillared MOFs Zn(L)(DABCO)0.5, where L is the functionalized BDC (1,4-benzenedicarboxylic acid) linker. The different extent of Zn–O bond shielding is provided by incorporating a broad range of functional groups on the BDC ligand. The resulting MOFs have varying surface areas, pore sizes, and pore volumes. Stability is assessed through water vapor adsorption isotherms combined with powder X-ray diffraction (PXRD) experiments and surface area analyses. Our study demonstrates that integration of polar functional groups (e.g., nitro, bromo, chloro, hydroxy, etc.) on the dicarboxylate linker renders these MOFs water unstable compared to the parent MOF as these polar functional groups have a negative shielding effect; i.e., they facilitate hydrolysis of the Zn–O bond. On the other hand, placing nonpolar groups (e.g., methyl) on the BDC ligand results in structurally robust MOFs because the Zn–O bond is effectively shielded from attack by water molecules. Therefore, the anthracene- and tetramethyl-BDC MOFs do not lose crystallinity or surface area after water exposure, in spite of the large amount of water adsorption due to capillary condensation at ∼20% relative humidity (RH). This has been observed rarely in the MOF literature. The results of this work show that by ligand functionalization it is possible to adjust the water stability of a pillared MOF in both the positive and negative directions and, thus, provide an important step toward understanding the water adsorption behavior of MOFs.
Magnetic lanthanide–transition-metal hybrid materials have enjoyed increasing attraction because they not only provide examples for studying magnetic coupling involving lanthanide ions but also ...exhibit novel magnetic behavior which render them candidates for future devices for information storage and quantum computation. Herein, we review the structures and magnetic properties of lanthanide–transition-metal hybrid materials that are categorized based on the structural features and organic ligands used. The review pays special attention to the examples which show magnetic slow relaxation since these render them to be potentially applied as devices for information storage.
The rational design of metal–organic frameworks (MOFs) with structural stability in the presence of humid conditions is critical to the commercialization of this class of materials. However, the ...systematic water stability studies required to develop design criteria for the construction of water-stable MOFs are still scarce. In this work, we show that by varying the functional groups on the 1,4-benzenedicarboxylic acid (BDC) linker of DMOF Zn(BDC)(DABCO)0.5, we can systematically tune the kinetic water stability of this isostructural, pillared family of MOFs. To illustrate this concept, we have performed water adsorption studies on four novel, methyl-functionalized DMOF variations along with a number of already reported functionalized analogues containing polar (fluorine) and nonpolar (methyl) functional groups on the BDC ligand. These results are distinctly different from previous reports where the apparent water stability is improved through the inclusion of functional groups such as −CH3, −C2H5, and −CF3 which only serve to prevent significant amounts of water from adsorbing into the pores. In this study, we present the first demonstration of tuning the inherent kinetic stability of MOF structures in the presence of large amounts of adsorbed water. Notably, we demonstrate that while the parent DMOF structure is unstable, the DMOF variation containing the tetramethyl BDC ligand remains fully stable after adsorbing large amounts of water vapor during cyclic water adsorption cycles. These trends cannot be rationalized in terms of hydrophobicity alone; experimental water isotherms show that MOFs containing the same number of methyl groups per unit cell will have different kinetic stabilities and that the precise placements of the methyl groups on the BDC ligand are therefore critically important in determining their stability in the presence of water. We present the water adsorption isotherms, PXRD (powder X-ray diffraction) patterns, and BET surface areas before and after water exposure to illustrate these trends. Furthermore, we shed light on the important distinction between kinetic and thermodynamic stability in MOFs. Molecular simulations are also used to provide insight into the structural characteristics governing these trends in kinetic water stability.
Network structures based on Star‐of‐David catenanes with multiple superior functionalities have been so far elusive, although numerous topologically interesting networks are synthesized. Here, a ...metal–organic framework featuring fused Star‐of‐David catenanes is reported. Two triangular metallacycles with opposite handedness are triply intertwined forming a Star‐of‐David catenane. Each catenane fuses with its six neighbors to generate a porous twofold intercatenated gyroid framework. The compound possesses exceptional stability and exhibits multiple functionalities including highly selective CO2 capture, high proton conductivity, and coexistence of slow magnetic relaxation and long‐range ordering.
A metal–organic framework, which represents the rare networks composed of Star‐of‐David catenanes, is designed. The structural complexity of the unique framework highlights different facets of the same compound. Remarkably, the material shows highly selective CO2 capture for a molecular‐sieving effect, superionic proton conductivity, and coexistence of slow magnetic relaxation and long‐range ordering.
Acquiring adsorbents capable of effective radioiodine capture is important for nuclear waste treatment; however, it remains a challenge to develop porous materials with high and reversible iodine ...capture. Herein, we report a porous self-assembly constructed by a cup-shaped Pd
complex through intermolecular
···
interactions. This self-assembly features a cubic structure with channels along all three Cartesian coordinates, which enables it to efficiently capture iodine with an adsorption capacity of 0.60 g g
for dissolved iodine and 1.81 g g
for iodine vapor. Furthermore, the iodine adsorbed within the channels can be readily released upon immersing the bound solid in CH
Cl
, which allows the recycling of the adsorbent. This work develops a new porous molecular material promising for practical iodine adsorption.
Porous supramolecular assemblies constructed by noncovalent interactions are promising for adsorptive purification of methane because of their easy regeneration. However, the poor stability arising ...from the weak noncovalent interactions has obstructed their practical applications. Here, we report a robust and easily regenerated polyhedron‐based cationic framework assembled from a metal–organic square. This material exhibits a very low affinity for CH4 and N2, but captures other competing gases (e.g. C2H6, C3H8, and CO2) with a moderate affinity. These results underpin highly selective separation of a range of gas mixtures that are relevant to natural gas and industrial off‐gas. Dynamic breakthrough studies demonstrate its practical separation for C2H6/CH4, C3H8/CH4, CO2/N2, and CO2/CH4. Particularly, the separation time is ≈11 min g−1 for the C2H6/CH4 (15/85 v/v) mixture and ≈49 min g−1 for the C3H8/CH4 (15/85 v/v) mixture (under a flow of 2.0 mL min−1), respectively, enabling its capability for CH4 purification from light alkanes.
From a metal–organic square, a robust and renewable polyhedron‐based framework material is assembled with potential for CH4 purification from natural gas and CO2 capture from industrial off‐gas.
Ester hydrates, as the intermediates of the esterification between acid and alcohol, are very short-lived and challenging to be trapped. Therefore, the crystal structures of ester hydrates have ...rarely been characterized. Herein, we present that the mono-deprotonated ester hydrates CH
OSO
(OH)
, serving as the template for the self-assembly of a π-stacked boat-shaped macrocycle (CH
OSO
(OH)
)
(CH
OSO
)
@{ClLCo
}·Cl
·13CH
OH·9H
O (
) (L = tris(2-benzimidazolylmethyl) amine), can be trapped in the host by multiple NH···O hydrogen bonds. In the solution of CoCl
, L, and H
SO
in MeOH, HSO
reacts with MeOH, producing CH
OSO
via the ester hydrate intermediate of CH
OSO
(OH)
. Both the product and the intermediate serve as the template directing the self-assembly of the π-stacked macrocycle, in which the short-lived ester hydrate is firmly trapped and stabilized, as revealed by single-crystal analysis.
Single-crystal-to-single-crystal metalation of organic ligands represents a novel method to prepare metal-organic complexes, but remains challenging. Herein, a hierarchical self-assembly {(H
L
)·(N(C
...H
)
)
·(ClO
)
·(H
O)
} (
) (L = tris(2-benzimidazolylmethyl) amine) consisting of
-stacked cubes which are assembled from eight partially protonated L ligands is obtained. By soaking the crystals of compound
in the aqueous solution of Co(SCN)
, the ligands coordinate with Co
ions stoichiometrically and ClO
exchange with SCN
via single-crystal-to-single-crystal transformation, leading to {(CoSCNL
)
·(NC
H
)
·(SCN)
·(H
O)
} (
).
Luminescence stability is a critical consideration for applying phosphors in practical devices. In this work, we report two categories of double
p-tert
-butylthiacalix4arene (H
4
TC4A) capped ...clusters that exhibit characteristic lanthanide luminescence. Specifically, {Ln
4
(μ
4
-OH)(TC4A)
2
(DMF)
6
(CH
3
OH)
3
(HCOO)Cl
2
}·
x
CH
3
OH (Ln = Eu (
1
), Tb (
2
);
x
= 0-1) with square-planar Ln
4
(μ
4
-OH) cluster cores and {Ln
9
(μ
5
-OH)
2
(μ
3
-OH)
8
(OCH
3
) (TC4A)
2
(H
2
O)
24
Cl
9
}·
x
DMF (Ln = Gd (
3
), Tb (
4
), Dy (
5
);
x
= 2-6) with hourglass-like Ln
9
(μ
5
-OH)
2
(μ
3
-OH)
8
cluster cores are synthesized and characterized. By comparing
2
and
4
, we find that several critical luminescence properties (such as quantum efficiency and luminescence stabilities) depend directly on the cluster core structure. With the square-planar Ln
4
(μ
4
-OH) cluster cores,
2
demonstrates high quantum yield (∼65%) and excellent luminescence stability against moisture, high temperature, and UV-radiation. A white light-emitting diode (LED) with ultrahigh color quality is successfully fabricated by mixing
2
with commercial phosphors. These results imply that high quality phosphors might be achieved by exploiting the double thiacalix4arene-capping strategy, with an emphasis on the cluster core structure.
{Ln
4
} cores outperform {Ln
9
} cores in achieving stable photoluminescence from double thiacalix4arene-capped lanthanide-oxo clusters.
