Structural analysis of and selective CO2 adsorption in mixed-ligand hydroxamate-based metal-organic frameworks

Alkoxy-Functionalized Hydroxamate/Zinc Metal-Organic Frameworks and the Effects of Substituents and Acid Addition on Their Structures

Single crystals of alkoxy-functionalized hydroxamate/zinc metal-organic frameworks (MOFs) were obtained by fixating the hydroxamate moiety via intramolecular hydrogen bonding. The resulting MOF structures depend on the steric demand of the alkoxy groups, whereby the incorporation of bulky isopropyl groups affords porous hydroxamate/zinc MOFs. The topological structures of the isopropyl-substituted MOFs could be controlled by adding acid.

Zn-Based Metal-Organic Frameworks Using Triptycene Hexacarboxylate Ligands: Synthesis, Structure, and Gas-Sorption Properties

A series of metal-organic frameworks (MOFs) based on zinc ions and two triptycene ligands of different size have been synthesized under solvothermal conditions. Structural analyses revealed that they are isostructural 3D-network MOFs. The high porosity and thermal stability of these MOFs can be attributed to the highly rigid triptycene-based ligands. Their BET specific surface areas depend on the size of the triptycene ligands. In contrast to these surface-area data, the H2 and CO2 adsorption of these MOFs is larger for MOFs with small pores. Consequently, we introduced functional groups to the bridge-head position of the triptycene ligands and investigated their effect on the gas-sorption properties. The results unveiled the role of the functional groups in the specific CO2 binding via an induced interaction between adsorbates and the functional groups. Excellent H2 and CO2 properties in these MOFs were achieved in the absence of open metal sites.

Metal-hydrogen-pi-bonded organic frameworks

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.

Hydroxamate based transition metal-organic coordination polymers with semiconductive properties

In addtion to carboxylate and N-donor linkers, hydroxamates are a kind of new emerging ligand to form coordination polymers. However, owing to the difficulty in controlling reversible formation of strong...

Assembly, photocatalytic and fluorescence properties of three new coordination complexes of zinc(II) and nickel(II) with two kinds of flexible bis(pyridyl)-bis(amide) ligands

Three new coordination complexes [Zn(btec)0.5(L1)0.5(H2O)] n (1), [Ni(H2btec)(L1)(H2O)2] n (2), and {[Ni(btec)0.5(L2)(H2O)3]·2H2O} n (3) [H4btec = 1,2,4,5-benzenetetracarboxylic acid), L1 = N,N′-bis(3-pyridyl)adipamide, L2 = N,N′-bis(3-pyridyl)octanediamide] have been obtained under hydrothermal conditions. Single-crystal X-ray diffraction analysis has revealed that complex 1 has a layer structure based on [Zn(btec)0.5] n ribbons and the μ 2-bridging ligands L 1 . Complex 2 possesses a layered framework constructed by [Ni(H2btec)] n linear chains and [Ni(L1)] n wave-like chains. Complex 3 forms layers based on [Ni(L2)] n helical chains and μ 2-bridging L2 ligands, representing an interesting 4-fold interpenetrating 2D braided framework. The three different 2D frameworks exhibit 3,4-connected {4.62}2{42.62.82} topology for 1, 4-connected {44.62} topology for 2 and 3-connected {63} topology for 3. Their adjacent layers are further linked by hydrogen bonding interactions to generate 3D supramolecular structures. The differences in the nature of both the metal ions and the organic ligands lead to various coordination modes in the final structures. The photocatalytic activities and the fluorescence properties of complexes 1–3 were investigated.