Buffered Coordination Modulation as a Means of Controlling Crystal Morphology and Molecular Diffusion in an Anisotropic Metal-Organic Framework.

Significant advances have been made in the synthesis of chemically selective environments within metal-organic frameworks, yet materials development and industrial implementation have been hindered by the inability to predictively control crystallite size and shape. One common strategy to control crystal growth is the inclusion of coordination modulators, which are molecular species designed to compete with the linker for metal coordination during synthesis. However, these modulators can simultaneously alter the pH of the reaction solution, an effect that can also significantly influence crystal morphology.

Negative cooperativity upon hydrogen bond-stabilized O adsorption in a redox-active metal-organic framework.

The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal-organic framework Co(OH)(bbta) (Hbbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) leads to strong and reversible adsorption of O. In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O adsorption.

Water Enables Efficient CO Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework.

Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO emissions. However, the separation of CO from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO.

Enantioselective Recognition of Ammonium Carbamates in a Chiral Metal-Organic Framework.

Chiral metal-organic frameworks have attracted interest for enantioselective separations and catalysis because of their high crystallinity and pores with tunable shapes, sizes, and chemical environments. Chiral frameworks of the type M(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) seem particularly promising for potential applications because of their excellent stability, high internal surface areas, and strongly polarizing open metal coordination sites within the channels, but to date these materials have been isolated only in racemic form. Here, we demonstrate that when appended with the chiral diamine trans-1,2-diaminocyclohexane (dach), Mg(dobpdc) adsorbs carbon dioxide cooperatively to form ammonium carbamate chains, and the thermodynamics of CO capture are strongly influenced by enantioselective interactions within the chiral pores of the framework.

Calcium Coordination Solids for pH-Triggered Release of Olsalazine.

Calcium coordination solids were synthesized and evaluated for delivery of olsalazine (H olz), an anti-inflammatory compound used for treatment of ulcerative colitis. The materials include one-dimensional Ca(H olz)⋅4 H O chains, two-dimensional Ca(H olz)⋅2 H O sheets, and a three-dimensional metal-organic framework Ca(H olz)⋅2DMF (DMF=N,N-dimethylformamide). The framework undergoes structural changes in response to solvent, forming a dense Ca(H olz) phase when exposed to aqueous HCl.

Highly effective ammonia removal in a series of Brønsted acidic porous polymers: investigation of chemical and structural variations.

Although a widely used and important industrial gas, ammonia (NH) is also highly toxic and presents a substantial health and environmental hazard. The development of new materials for the effective capture and removal of ammonia is thus of significant interest. The capture of ammonia at ppm-level concentrations relies on strong interactions between the adsorbent and the gas, as demonstrated in a number of zeolites and metal-organic frameworks with Lewis acidic open metal sites.

A Microporous Amic Acid Polymer for Enhanced Ammonia Capture.

Amic acids, consisting of carboxylic acids and amides, are often utilized as intermediates that can further undergo a dehydration-cyclization step to yield polymeric cyclic imides. Compared with imide-based materials, the presence of Brønsted acidic groups and multiple hydrogen-bond donors and acceptors in materials incorporating amic acids opens up the possibility for a variety of host-guest interactions. Here we report a facile and catalyst-free synthesis of a Brønsted acidic porous poly(amic acid) (PAA) and present its NH uptake properties using gas adsorption and breakthrough measurements.

Olsalazine-Based Metal-Organic Frameworks as Biocompatible Platforms for H2 Adsorption and Drug Delivery.

The drug olsalazine (H4olz) was employed as a ligand to synthesize a new series of mesoporous metal-organic frameworks that are expanded analogues of the well-known M2(dobdc) materials (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate; M-MOF-74). The M2(olz) frameworks (M = Mg, Fe, Co, Ni, and Zn) exhibit high surface areas with large hexagonal pore apertures that are approximately 27 Å in diameter. Variable temperature H2 adsorption isotherms revealed strong adsorption at the open metal sites, and in situ infrared spectroscopy experiments on Mg2(olz) and Ni2(olz) were used to determine site-specific H2 binding enthalpies.