<div><p>Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe₂(bdp)₃ (bdp²⁻ = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A₂Fe₂(bdp)₃∙<i>y</i>THF(A = Li⁺, Na⁺, K⁺). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na_0.5Fe₂(bdp)₃and Li₂Fe₂(bdp)₃ and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation­–π interactions. Hydrogen adsorption data indicate that these cation-framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe₂(bdp)₃. In contrast, Mg_0.85Fe₂(bdp)₃ exhibits enhanced H₂ affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H₂ interactions.</p></div>

Developing O₂-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that the chemically reduced metal–organic framework A<i>_x</i>Fe₂(BDP)₃ (A = Na⁺, K⁺; BDP²⁻ = 1,4-benzenedipyrazolate; 0 < <i>x</i> ≤ 2), which features coordinatively-saturated iron centers, is capable of strong and selective adsorption of O₂ over N₂ at ambient (25 °C) or even elevated (200 °C) temperature. Through a combination of gas adsorption measurements, single-crystal X-ray diffraction, and numerous spectroscopic probes, including ²³Na solid-state NMR and X-ray photoelectron spectroscopy, we demonstrate that selective O₂ uptake likely occurs as a result of outer-sphere electron transfer from the framework to form superoxide species, which are subsequently stabilized by intercalated alkali metal cations that reside in the one-dimensional triangular pores of the framework. The chemical reduction of a robust metal–organic framework to render it capable of binding O₂ through an outer-sphere electron transfer mechanism thus represents a promising and underexplored strategy for the design of next-generation O₂ adsorbents.

Developing O₂-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that chemically reduced metal–organic framework materials of the type A<i>_x</i>Fe₂(bdp)₃ (A = Na⁺, K⁺; bdp²⁻ = 1,4-benzenedipyrazolate; 0 < <i>x</i> ≤ 2), which feature coordinatively saturated iron centers, are capable of strong and selective adsorption of O₂ over N₂ at ambient (25 °C) or even elevated (200 °C) temperature. A combination of gas adsorption analysis, single-crystal X-ray diffraction, magnetic susceptibility measurements, and a range of spectroscopic methods, including ²³Na solid-state NMR, Mössbauer, and X-ray photoelectron spectroscopies, are employed as probes of O₂ uptake. Significantly, the results support a selective adsorption mechanism involving outer-sphere electron transfer from the framework to form superoxide species, which are subsequently stabilized by intercalated alkali metal cations that reside in the one-dimensional triangular pores of the structure. We further demonstrate similar O₂ uptake behavior to that of A<i>_x</i>Fe₂(bdp)₃ in an expanded-pore framework analogue and thereby gain additional insight into the O₂ adsorption mechanism. The chemical reduction of a robust metal–organic framework to render it capable of binding O₂ through such an outer-sphere electron transfer mechanism represents a promising and underexplored strategy for the design of next-generation O₂ adsorbents.

<p><b>The discovery of conductive and magnetic two-dimensional (2D) materials is critical for the development of next generation spintronics devices. Coordination chemistry in particular represents a highly versatile, though underutilized, route toward the synthesis of such materials with designer lattices. Here, we report the synthesis of a conductive, layered 2D metal–organic kagome lattice, Mn₃(C₆S₆), using mild solution-phase chemistry. Strong geometric<i> </i>spin frustration in this system mediates spin freezing at low temperatures, which results in glassy magnetic behavior consistent with a geometrically frustrated (topological) spin glass. Notably, the material exhibits a large exchange bias of 1625 Oe, providing the first example of exchange bias in a coordination solid or a topological spin glass. More generally, these results demonstrate the potential utility of geometrically frustrated lattices in the design of new nanoscale spintronic materials.</b></p>

Developing O₂-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that chemically reduced metal–organic framework materials of the type A<i>_x</i>Fe₂(bdp)₃ (A = Na⁺, K⁺; bdp²⁻ = 1,4-benzenedipyrazolate; 0 < <i>x</i> ≤ 2), which feature coordinatively saturated iron centers, are capable of strong and selective adsorption of O₂ over N₂ at ambient (25 °C) or even elevated (200 °C) temperature. A combination of gas adsorption analysis, single-crystal X-ray diffraction, magnetic susceptibility measurements, and a range of spectroscopic methods, including ²³Na solid-state NMR, Mössbauer, and X-ray photoelectron spectroscopies, are employed as probes of O₂ uptake. Significantly, the results support a selective adsorption mechanism involving outer-sphere electron transfer from the framework to form superoxide species, which are subsequently stabilized by intercalated alkali metal cations that reside in the one-dimensional triangular pores of the structure. We further demonstrate similar O₂ uptake behavior to that of A<i>_x</i>Fe₂(bdp)₃ in an expanded-pore framework analogue and thereby gain additional insight into the O₂ adsorption mechanism. The chemical reduction of a robust metal–organic framework to render it capable of binding O₂ through such an outer-sphere electron transfer mechanism represents a promising and underexplored strategy for the design of next-generation O₂ adsorbents.