Studying manganese carbonyl photochemistry in a permanently porous metal-organic framework

Mn(diimine)(CO)3X (X = halide) complexes are critical components of chromophores, photo- and electrocatalysts, and photoactive CO-releasing molecules (photoCORMs). While these entities have been incorporated into metal-organic frameworks (MOFs), a detailed understanding of the photochemical and chemical processes that occur in a permanently porous support is lacking. Here we site-isolate and study the photochemistry of a Mn(diimine)(CO)3Br moiety anchored within a permanently porous MOF support, allowing for not only the photo-liberation of CO from the metal but also its escape from the MOF crystals. In addition, the high crystallinity and structural flexibility of the MOF allows crystallographic snapshots of the photolysis products to be obtained. We report these photo-crystallographic studies in the presence of coordinating solvents, THF and acetonitrile, showing the changing coordination environment of the Mn species as CO loss proceeds. Using time resolved experiments, we report complementary spectroscopic studies of the photolysis chemistry and characterize the final photolysis product as a possible Mn(ii) entity. These studies inform the chemistry that occurs in MOF-based photoCORMs and where these moieties are employed as catalysts.

Engineering Metal-Organic Frameworks for Selective Separation of Hexane Isomers Using 3-Dimensional Linkers

Metal-organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo[1.1.1]pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.

MicroED characterization of a robust cationic σ-alkane complex stabilized by the [B(3,5-(SF5)2C6H3)4]- anion, via on-grid solid/gas single-crystal to single-crystal reactivity

Microcrystalline (∼1 μm) [Rh(Cy₂PCH₂CH₂PCy₂)(norbornadiene)][S-BAr^F₄], [S-BAr^F₄] = [B(3,5-(SF₅)₂C₆H₃)₄]⁻, reacts with H₂ in a single-crystal to single-crystal transformation to form the σ-alkane complex [Rh(Cy₂PCH₂CH₂PCy₂)(norbornane)][S-BAr^F₄], for which the structure was determined by microcrystal Electron Diffraction (microED), to 0.95 Å resolution, via an on-grid hydrogenation, and a complementary single-crystal X-ray diffraction study on larger, but challenging to isolate, crystals. Comparison with the [BAr^F₄]⁻ analogue [Ar^F = 3,5-(CF₃)₂(C₆H₃)] shows that the [S-BAr^F₄]⁻ anion makes the σ-alkane complex robust towards decomposition both thermally and when suspended in pentane. Subsequent reactivity with dissolved ethene in a pentane slurry, forms [Rh(Cy₂PCH₂CH₂PCy₂)(ethene)₂][S-BAr^F₄], and the catalytic dimerisation/isomerisation of ethene to 2-butenes. The increased stability of [S-BAr^F₄]⁻ salts is identified as being due to increased non-covalent interactions in the lattice, resulting in a solid-state molecular organometallic material with desirable stability characteristics.

The thermally and chemically robust σ-alkane complex [Rh(Cy₂PCH₂CH₂PCy₂)(norborane)][B(3,5-(SF₅)₂C₆H₃)₄] is characterized by micro-electron diffraction using on-grid single-crystal to single-crystal reactivity.

Templated synthesis of zirconium(IV)-based metal-organic layers (MOLs) with accessible chelating sites

Metal-organic layers (MOLs) are of great interest in heterogeneous catalysis, particularly materials that can accommodate extraneous metal centres. Here, we demonstrate a two-step preorganisation/delamination synthetic strategy using CuI as a template to prepare Zr-based MOLs with accessible 'syn' bis-pyrazolyl chelating sites (named UAM-2·ns) that are poised for quantitative post-synthetic metalation with late transition metals.