High-valent Ru V -oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co 3 O 4 ] subcluster via the singlestep assembly reaction of Co II (OAc) 2 (H 2 O) 4 (OAc = acetate), perruthenate (RuO 4 − ), and pyridine (py) yielded an unprecedented Ru(O)Co 3 (μ 3 -O) 4 (OAc) 4 (py) 3 cubane featuring an isolable, yet reactive, Ru Voxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru V (S = 1/2)Co III 3 (S = 0)O 4 ] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the Ru V -oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py) 3 (OAc) 4 Co 3 (μ 3 -O) 4 Ru]-O-[RuCo 3 (μ 3 -O) 4 (OAc) 4 (py) 3 ]. Redox activity of the Ru Voxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co 3 O 4 ] unit in supporting the Ru V -oxo moiety via a strong π-electron donation.

Most C 4 hydrocarbons are obtained as byproducts of ethylene production or oil refining, and complex and energyintensive separation schemes are required for their isolation. Substantial industrial and academic effort has been expended to develop more cost-effective adsorbent-or membrane-based approaches to purify commodity chemicals such as 1,3-butadiene, isobutene, and 1-butene, but the very similar physical properties of these C 4 hydrocarbons makes this a challenging task. Here, we examine the adsorption behavior of 1-butene, cis-2-butene and trans-2-butene in the metal-organic frameworks M 2 (dobdc) (M = Mn, Fe, Co, Ni; dobdc 4− = 2,5-dioxidobenzene-1,4-dicarboxylate) and M 2 (m-dobdc) (m-dobdc 4− = 4,6-dioxidobenzene-1,3dicarboxylate), which all contain a high density of coordinatively-unsaturated M 2+ sites. We find that both Co 2 (m-dobdc) and Ni 2 (m-dobdc) are able to separate 1-butene from the 2-butene isomers, a critical industrial process that relies largely on energetically demanding cryogenic distillation. The origin of 1-butene selectivity is traced to the high charge density retained by the M 2+ metal centers exposed within the M 2 (m-dobdc) structures, which results in a reversal of the cis-2-butene selectivity typically observed at framework open metal sites. Selectivity for 1-butene adsorption under multicomponent conditions is demonstrated for Ni 2 (mdobdc) in both the gaseous and liquid phases via breakthrough and batch adsorption experiments.

Developing O 2 -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 x Fe 2 (bdp) 3 (A = Na + , K + ; bdp 2− = 1,4benzenedipyrazolate; 0 < x ≤ 2), which feature coordinatively saturated iron centers, are capable of strong and selective adsorption of O 2 over N 2 at ambient (25 °C) or even elevated (200 °C) temperature. A combination of gas adsorption analysis, singlecrystal X-ray diffraction, magnetic susceptibility measurements, and a range of spectroscopic methods, including 23 Na solid-state NMR, Mossbauer, and X-ray photoelectron spectroscopies, are employed as probes of O 2 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 O 2 uptake behavior similar to that of A x Fe 2 (bdp) 3 in an expanded-pore framework analogue and thereby gain additional insight into the O 2 adsorption mechanism. The chemical reduction of a robust metal−organic framework to render it capable of binding O 2 through such an outer-sphere electron transfer mechanism represents a promising and underexplored strategy for the design of next-generation O 2 adsorbents.