Hexagonal ordering of racemic Ni(ii) complexes in the interlayer space of a clay mineral

Racemic nickel complexes spontaneously form a double-molecular layer with a hexagonal arrangement in the interlayer space of a clay mineral.

Microporous Organically Pillared Layered Silicates (MOPS): A Versatile Class of Functional Porous Materials

The design of microporous hybrid materials, tailored for diverse applications, is a key to address our modern society's imperative of sustainable technologies. Prerequisites are flexible customization of host-guest interactions by incorporating various types of functionality and by adjusting the pore structure. On that score, metal-organic frameworks (MOFs) have been the reference in the past decades. More recently, a new class of microporous hybrid materials emerged, microporous organically pillared layered silicates (MOPS). MOPS are synthesized by simple ion exchange of organic or metal complex cations in synthetic layered silicates. MOFs and MOPSs share the features of "component modularity" and "functional porosity". While both, MOFs and MOPS maintain the intrinsic characteristics of their building blocks, new distinctive properties arise from their assemblage. MOPS are unique since allowing for simultaneous and continuous tuning of micropores in the sub-Ångström range. Consequently, with MOPS the adsorbent recognition may be optimized without the need to explore different framework topologies. Similar to the third generation of MOFs (also termed soft porous crystals), MOPS are structurally ordered, permanently microporous solids that may also show a reversible structural flexibility above a distinct threshold pressure of certain adsorbents. This structural dynamism of MOPS can be utilized by meticulously adjusting the charge density of the silicate layers to the polarizability of the adsorbent leading to different gate opening mechanisms. The potential of MOPS is far from being fully explored. This Concept article highlights the main features of MOPS and illustrates promising directions for further research.

Determination of the charge of Al13 Keggin oligocations intercalated into synthetic hectorite

Applying a nematic liquid crystalline phase of a synthetic Na-hectorite with layer separations >100 nm, the reaction time for pillaring with Al13 Keggin oligocation could be reduced to seconds ensuring that cation exchange is controlled by thermodynamics. With this material at hand we are able to resolve the long-standing dispute regarding the charge of intercalated Keggin oligocations. Micropore sizes as determined by physisorption isotherms, adsorption isotherms obtained via elemental analysis, and results of 27Al solid-state NMR and pyridine probe IR spectroscopy favor a charge of +7 for the Al13 pillars intercalated into hectorite unaltered.

Purely Physisorption-Based CO-Selective Gate-Opening in Microporous Organically Pillared Layered Silicates

Separation of gas molecules with similar physical and chemical properties is challenging but nevertheless highly relevant for chemical processing. By introducing the elliptically shaped molecule, 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane, into the interlayer space of a layered silicate, a two-dimensional microporous network with narrow pore size distribution is generated (MOPS-5). The regular arrangement of the pillar molecules in MOPS-5 was confirmed by the occurrence of a 10 band related to a long-range pseudo-hexagonal superstructure of pillar molecules in the interlayer space. Whereas with MOPS-5 for CO₂ adsorption, gate-opening occurs at constant volume by freezing pillar rotation, for CO the interlayer space is expanded at gate-opening and a classical interdigitated layer type of gate-opening is observed. The selective nature of the gate-opening might be used for separation of CO and N₂ by pressure swing adsorption.

Solid state vibrational circular dichroism towards molecular recognition: chiral metal complexes intercalated in a clay mineral

The solid state VCD method revealed chirality effects on the intermolecular interaction between Δ- or Λ-[Ru(phen)₃]²⁺ and R or S-BINOL intercalated in a montmorillonite clay.

Stereoselective interactions as manifested by vibrational circular dichroism spectra: the interplay between chiral metal complexes co-adsorbed in a montmorillonite clay

Solid state VCD is applied for intercalated metal complexes.