Synthesis and Characterization of the Platinum-Substituted Keggin Anion α‑H₂SiPt­W₁₁O₄₀^4–

Acidification of an aqueous solution of K₈SiW₁₁O₃₉ and K₂Pt­(OH)₆ to pH 4 followed by addition of excess tetramethylammonium (TMA) chloride yielded a solid mixture of TMA salts of H₂SiPt­W₁₁O₄₀^4– (<b>1</b>) and SiW₁₂O₄₀^4– (<b>2</b>). The former was separated from the latter by extraction into an aqueous solution and converted into tetra-<i>n</i>-butylammonium (TBA) and potassium salts <b>TBA-1</b> and <b>K-1</b>. The α-H₂SiPtW₁₁O₄₀^4– was identified as a monosubstituted Keggin anion using elemental analysis, IR spectroscopy, X-ray crystallography, electrospray ionization mass spectrometry, ¹⁹⁵Pt NMR spectroscopy, ¹⁸³W NMR spectroscopy, and ¹⁸³W–¹⁸³W 2D INADEQUATE NMR spectroscopy. Both <b>TBA-1</b> and <b>K-1</b> readily cocrystallized with their unsubstituted Keggin anion salts, <b>TBA-2</b> and <b>K-2</b>, respectively, providing an explanation for the historical difficulty of isolating certain platinum-substituted heteropolyanions in pure form

A Combined Experimental-Computational Study on the Effect of Topology on Carbon Dioxide Adsorption in Zeolitic Imidazolate Frameworks

We report CO₂ adsorption data for four zeolitic imidazolate frameworks (ZIFs) to 55 bar, namely ZIF-7, ZIF-11, ZIF-93, and ZIF-94. Modification of synthetic conditions allows access to different topologies with the same metal ion and organic link: ZIF-7 (ZIF-94) having <b>sod</b> topology and ZIF-11 (ZIF-93) having the <b>rho</b> topology. The varying topology, with fixed metal ion and imidazolate functionality, makes these systems ideal for studying the effect of topology on gas adsorption in ZIFs. The experiments show that the topologies with the smaller pores (ZIF-7 and 94) have larger adsorptions than their counterparts (ZIF-11 and 93, respectively) at low pressures (<1 bar); however, the reverse is true at higher pressures where the larger-pore structures have significantly higher adsorption. Molecular modeling and heat of adsorption measurements indicate that while the binding potential wells for the smaller-pore structures are deeper than those of the larger-pore structures, they are relatively narrow and cannot accommodate multiple CO₂ occupancy, in contrast to the much broader potential wells seen in the larger pore structures