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Low-temperature synthesis routes are necessary for selectively synthesizing many metastable solid-state materials. Here, we identify a cooperative effect that starting materials have in lowering temperatures in solid-state metathesis reactions by studying the formation of yttrium manganese oxide. Previous studies have shown that YMnO3 can be synthesized by ternary metathesis with an alkali halide being produced as a secondary product. In this contribution, we show that by using alkaline earth metals instead of alkali metals, the polymorph selectivity of the reaction is changed, as orthorhombic YMnO3 forms at lower temperatures than the hexagonal polymorph. Reactions were studied using ex post facto synchrotron X-ray diffraction. These experiments reveal that reactions using alkaline earth manganese oxides as a starting material require high temperatures to progress. Reaction temperatures can be lowered from 700 to 550 °C while maintaining phase selectivity by reacting both MgMn2O4 and CaMn2O4 with YOCl in a cooperative "cometathesis"reaction. The nascent halide salts appear to improve the reaction kinetics. Since the onset temperature for YMnO3 formation falls 50 °C below the MgCl2-CaCl2 liquidus, the enhanced reactivity is consistent with the surface melting of a nasscent salt byproduct at the interfaces. Cometathesis routes have similar phase selectivity and temperature reduction in reactions that form TbMnO3, ErMnO3, and DyMnO3. Cometathesis lowers reaction temperatures while preserving the reaction selectivity of the end members, making it a valuable approach for synthesizing metastable targets.

In the synthesis of complex oxides, solid-state metathesis provides low-temperature reactions where product selectivity can be achieved through simple changes in precursor composition. The influence of precursor structure, however, is less understood in solid-state synthesis. Here we present the ternary metathesis reaction (LiMnO2 + YOCl → YMnO3 + LiCl) to target two yttrium manganese oxide products, hexagonal and orthorhombic YMnO3, when starting from three different LiMnO2 precursors. Using temperature-dependent synchrotron X-ray and neutron diffraction, we identify the relevant intermediates and temperature regimes of reactions along the pathway to YMnO3. Manganese-containing intermediates undergo a charge disproportionation into a reduced Mn(II,III) tetragonal spinel and oxidized Mn(III,IV) cubic spinel, which lead to hexagonal and orthorhombic YMnO3, respectively. Density functional theory calculations confirm that the presence of Mn(IV) caused by a small concentration of cation vacancies (∼2.2%) in YMnO3 stabilizes the orthorhombic polymorph over the hexagonal. Reactions over the course of 2 weeks yield o-YMnO3 as the majority product at temperatures below 600 °C, which supports an equilibration of cation defects over time. Controlling the composition and structure of these defect-accommodating intermediates provides new strategies for selective synthesis of complex oxides at low temperatures.

We report the CO2 capture properties of an ultramicroporous physisorbent [Ni(WO2F4)(pyrazine)2]n, WO2F4-1-Ni, which crystallizes in I4/mcm (a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO2F4 anion is acentric with polarizable W＝O bonds offering unique potential properties within a porous structure. Despite isostructural compounds being previously reported, the effect of this distorted anion on CO2 capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO2 (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmolCO2 gsorbent−1 under dry conditions and 0.685 mmolCO2 gsorbent−1 at 75%RH, the highest capacity for a physisorbent reported to date. [ABSTRACT FROM AUTHOR]

The fabrication of porous molecules, such as metal–organic polyhedra (MOPs), porous organic cages (POCs) and others, has given rise to the potential for creating "solid solutions" of molecular fillers and polymers. Such solid solutions circumvent longstanding interface issues associated with mixed matrix membranes (MMMs), and are referred to as molecularly mixed composite membranes (MMCMs) to distinguish them from traditional two‐phase MMMs. Early investigations of MMCMs highlight the advantages of solid solutions over MMMs, including dispersion of the filler, anti‐plasticization of the polymer network, and removal of deleterious interfacial issues. However, the exact microscopic structure as well as the transport modality in this new class of membrane are not well understood. Moreover, there are clear engineering challenges that need to be addressed for MMCMs to transition into the field. In this Minireview, the authors outline several scientific and technological challenges associated with the aforementioned questions and their suggestions to tackle them. [ABSTRACT FROM AUTHOR]

Industrial specifications require CO2 concentrations in natural gas below 50 ppm during liquefaction because of corrosion and CO2 freezing. Herein, we report a physisorbent (TIFSIX-3-Ni) that exhibits new benchmark CO2/CH4 selectivity and fast kinetics, thereby enabling one-step LNG processing to CO2 levels of 25 ppm. [ABSTRACT FROM AUTHOR]

Phases of a 2-fold pcu hybrid ultramicroporous material (HUM), SIFSIX-14-Cu-i, exhibiting 99%, 93%, 89%, and 70% partial interpenetration have been obtained. 1 : 99 C2H2/C2H4 gas separation studies reveal that as the proportion of interpenetrated component decreases, so does the separation performance. [ABSTRACT FROM AUTHOR]

Fine-tuning of hybrid ultramicroporous materials (HUMs) can significantly impact their gas sorption performance. This study reveals that offset interpenetration can be antagonistic with respect to C2H2 separation from C2H2/C2H4 gas mixtures. [ABSTRACT FROM AUTHOR]

The synthesis of complex oxides at low temperatures brings forward aspects of chemistry not typically considered. This study focuses on perovskite LaMnO 3 , which is of interest for its correlated electronic behavior tied to the oxidation state and thus the spin configuration of manganese. Traditional equilibrium synthesis of these materials typically requires synthesis reaction temperatures in excess of 1000 °C, followed by subsequent annealing steps at lower temperatures and different p (O 2 ) conditions to manipulate the oxygen content postsynthesis (e.g., LaMnO 3+ x ). Double-ion exchange (metathesis) reactions have recently been shown to react at much lower temperatures (500-800 °C), highlighting a fundamental knowledge gap for how solids react at lower temperatures. Here, we revisit the metathesis reaction, LiMnO 2 + LaOX, where X is a halide or mixture of halides, using in situ synchrotron X-ray diffraction. These experiments reveal low reaction onset temperatures (ca. 450-480 °C). The lowest reaction temperatures are achieved by a mixture of lanthanum oxyhalide precursors: 2 LiMnO 2 + LaOCl + LaOBr. In all cases, the resulting products are the expected alkali halide salt and defective La 1-ϵ Mn 1-ϵ O 3 , where ϵ = x /(3 + x ). We observe a systematic variation in defect concentration, consistent with a rapid stoichiometric local equilibration of the precursors and the subsequent global thermodynamic equilibration with O 2 (g), as revealed by computational thermodynamics. Together, these results reveal how the inclusion of additional elements (e.g., Li and a halide) leads to the local equilibrium, particularly at low reaction temperatures for solid-state chemistry.

We report the CO 2 capture properties of an ultramicroporous physisorbent [Ni(WO 2 F 4 )(pyrazine) 2 ] n , WO 2 F 4 -1-Ni, which crystallizes in I 4/ mcm ( a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO 2 F 4 anion is acentric with polarizable WO bonds offering unique potential properties within a porous structure. Despite isostructural compounds being previously reported, the effect of this distorted anion on CO 2 capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO 2 (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmol CO 2 g sorbent -1 under dry conditions and 0.685 mmol CO 2 g sorbent -1 at 75%RH, the highest capacity for a physisorbent reported to date.