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1. Ultrastable Carboxyl‐Functionalized Pore‐Space‐Partitioned Metal‐Organic Frameworks for Gas Separation

   https://doi.org/10.1002/adma.202408042  

   Ajayan, Pooja; Wang, Wei; Chen, Yichong; Bu, Xianhui; Feng, Pingyun (August 2024, Advanced Materials)

   Abstract Isoreticular chemistry, which enables property optimization by changing compositions without changing topology, is a powerful synthetic strategy. One of the biggest challenges facing isoreticular chemistry is to extend it to ligands with strongly coordinating substituent groups such as unbound −COOH, because competitive interactions between such groups and metal ions can derail isoreticular chemistry. It is even more challenging to have an isoreticular series of carboxyl‐functionalized MOFs capable of encompassing chemically disparate metal ions. Here, with the simultaneous introduction of carboxyl functionalization and pore space partition, a family of carboxyl‐functionalized materials is developed in diverse compositions from homometallic Cr³⁺and Ni²⁺to heterometallic Co²⁺/V³⁺, Ni²⁺/V³⁺, Co²⁺/In³⁺, Co²⁺/Ni²⁺. Cr‐MOFs remain highly crystalline in boiling water. Unprecedentedly, one Cr‐MOF can withstand the treatment cycle with 10mNaOH and 12mHCl, allowing reversible inter‐conversion between unbound −COOH acid form and −COO⁻base form. These materials exhibit excellent sorption properties such as high uptake capacity for CO₂(100.2 cm³ g⁻¹) and hydrocarbon gases (e.g., 142.1 cm³ g⁻¹for C₂H₂, 110.5 cm³ g⁻¹for C₂H₄) at 1 bar and 298K, high benzene/cyclohexane selectivity (up to ≈40), and promising separation performance for gas mixtures such as C₂H₂/CO₂and C₂H₂/C₂H₄. 

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2. Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate

   https://doi.org/10.1002/chem.202401204  

   Vanga, Mukundam; Muñoz‐Castro, Alvaro; Dias, H_V_Rasika (June 2024, Chemistry – A European Journal)

   Abstract Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a isoleptic series of coinage metal complexes. The treatment of [4‐(Ph₃B)‐2,6‐Trip₂Py]K (Trip=2,4,6‐ⁱPr₃C₆H₂) with CuBr(PPh₃), AgCl(PPh₃) or AuCl(PPh₃) (Py=pyridine) afforded the corresponding [4‐(Ph₃B)‐2,6‐Trip₂Py]M(PPh₃) (M=Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids. Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems. The X‐ray structures revealed that they are two‐coordinate metal adducts. The M−N and M−P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members. Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i. e., pyridyl borate) ligand. A comparison of structures and bonding of [4‐(Ph₃B)‐2,6‐Trip₂Py]Au(PPh₃) to pyridine andm‐terphenyl complexes, {[2,6‐Trip₂Py]Au(PPh₃)}[SbF₆] and [2,6‐Trip₂Ph]Au(PPh₃) are also provided. The Au(I) isocyanide complex, [4‐(Ph₃B)‐2,6‐Trip₂Py]Au(CNBu^t) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold‐ligand moieties as well. 

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3. Basal Plane Hydrogen Evolution Activity from Mixed Metal Nitride MXenes Measured by Scanning Electrochemical Microscopy

   https://doi.org/10.1002/adfm.202001136  

   Djire, Abdoulaye; Wang, Xiang; Xiao, Chuanxiao; Nwamba, O_Charles; Mirkin, Michael_V; Neale, Nathan_R (May 2020, Advanced Functional Materials)

   Abstract 2D early transition metal carbide and nitride MXenes have intriguing properties for electrochemical energy storage and electrocatalysis. These properties can be manipulated by modifying the basal plane chemistry. Here, mixed transition metal nitride MXenes, M‐Ti₄N₃T_x(M = V, Cr, Mo, or Mn; T_x= O and/or OH), are developed by modifying pristine exfoliated Ti₄N₃T_xMXene with V, Cr, Mo, and Mn salts using a simple solution‐based method. The resulting mixed transition metal nitride MXenes contain 6–51% metal loading (cf. Ti) that exhibit rich electrochemistry including highly tunable hydrogen evolution reaction (HER) electrocatalytic activity in a 0.5mH₂SO₄electrolyte as follows: V‐Ti₄N₃T_x> Cr‐Ti₄N₃T_x> Mo‐Ti₄N₃T_x> Mn‐Ti₄N₃T_x> pristine Ti₄N₃T_xwith overpotentials as low as 330 mV at −10 mA cm⁻²with a charge‐transfer resistance of 70 Ω. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M‐Ti₄N₃T_xas well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications. 

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4. Solvothermal Synthesis of [Cr ₇ S ₈ (en) ₈ Cl ₂ ]Cl ₃  ⋅ 2H ₂ O with Magnetically Frustrated [Cr ₇ S ₈ ] ⁵⁺ Double‐Cubes**

   https://doi.org/10.1002/chem.202103761  

   Gamage, Eranga_H; Clark, Judith_K; Yazback, Maher; Cheng, Hai‐Ping; Shatruk, Michael; Kovnir, Kirill (December 2021, Chemistry – A European Journal)

   Abstract A novel transition metal chalcohalide [Cr₇S₈(en)₈Cl₂]Cl₃ ⋅ 2H₂O, with [Cr₇S₈]⁵⁺dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant,θ=−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions betweenS=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)⁷=16384 microstates from seven Cr³⁺centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to beJ₁=−21.4 cm⁻¹andJ₂=−30.2 cm⁻¹, confirming competing AFM coupling between the shared Cr³⁺center and the peripheral Cr³⁺ions of the dicubane cluster. The best simulation of the experimental data was obtained withJ₁=−20.0 cm⁻¹andJ₂=−21.0 cm⁻¹, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr³⁺ions as compared to the AFM exchange between the central and peripheral Cr³⁺ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks. 

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5. The Cool Circumgalactic Medium of Low-redshift Star-forming Galaxies. I. Empirical Model and Mean Properties

   https://doi.org/10.3847/1538-4357/acf217  

   Faerman, Yakov; Werk, Jessica K (October 2023, The Astrophysical Journal)

   Abstract We present an analytic model for the cool,T∼ 10⁴K, circumgalactic medium (CGM), describing the gas distribution, and thermal and ionization states. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation, and allows for nonthermal pressure support, parameterized by the ratio of thermal pressures,η=P_hot,th/P_cool,th. We apply the model to the COS-Halos measurements and find that a nominal model withη= 3, gas distribution out tor≈ 0.6R_vir, andM_cool= 3 × 10⁹M_⊙, corresponding to a volume filling fraction off_V,cool≈ 1%, reproduces the Hiand low/intermediate metal ions (Cii, Ciii, Siii, Siiii, and Mgii) mean column densities. Variation of ±0.5 dex inηorM_coolencompasses ∼2/3 of the scatter between objects. Our nominal model underproduces the measured Civand Siivcolumns, and these can be reproduced with (i) a cool phase withM_cool∼ 10¹⁰M_⊙andη≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, withM∼ 1.5 × 10¹⁰M_⊙and occupying ∼1/2 of the total CGM volume. For cool gas withf_V,cool≈ 1%, we estimate an upper limit on the cloud sizes,R_cl≲ 0.5 kpc. Our results suggest that for the average galaxy CGM, the mass and nonthermal support in the cool phase are lower than previously estimated, and extreme scenarios are not necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be offset, allowing ${\dot{M}}_{\mathrm{cool}}\approx 0$over long timescales. 

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