Post-Synthetic Modification Unlocks a 2D-to-3D Switch in MOF Breathing Response: A Single-Crystal-Diffraction Mapping Study

Post‐synthetic modification (PSM) of the interpenetrated diamondoid metal–organic framework (Me₂NH₂)[In(BDC‐NH₂)₂] (BDC‐NH₂=aminobenzenedicarboxylate) SHF‐61 proceeds quantitatively in a single‐crystal‐to‐single‐crystal manner to yield the acetamide derivative (Me₂NH₂)[In(BDC‐NHC(O)Me)₂] SHF‐62. Continuous breathing behaviour during activation/desolvation is retained upon PSM, but pore closing now leads to ring‐flipping to avert steric clash of amide methyl groups of the modified ligands. This triggers a reduction in the amplitude of the breathing deformation in the two dimensions associated with pore diameter, but a large increase in the third dimension associated with pore length. The MOF is thereby converted from predominantly 2D breathing (in SHF‐61) to a distinctly 3D breathing motion (in SHF‐62) indicating a decoupling of the pore‐width and pore‐length breathing motions. These breathing motions have been mapped by a series of single‐crystal diffraction studies.

Amino Acid Residues Determine the Response of Flexible Metal-Organic Frameworks to Guests

Flexible metal-organic frameworks (MOFs) undergo structural transformations in response to physical and chemical stimuli. This is hard to control because of feedback between guest uptake and host structure change. We report a family of flexible MOFs based on derivatized amino acid linkers. Their porosity consists of a one-dimensional channel connected to three peripheral pockets. This network structure amplifies small local changes in linker conformation, which are strongly coupled to the guest packing in and the shape of the peripheral pockets, to afford large changes in the global pore geometry that can, for example, segment the pore into four isolated components. The synergy among pore volume, guest packing, and linker conformation that characterizes this family of structures can be determined by the amino acid side chain, because it is repositioned by linker torsion. The resulting control optimizes noncovalent interactions to differentiate the uptake and structure response of host-guest pairs with similar chemistries.

Hydrogen bonding vs. halogen bonding: the solvent decides

Control of intermolecular interactions is integral to harnessing self-assembly in nature. Here we demonstrate that control of the competition between hydrogen bonds and halogen bonds, the two most highly studied directional intermolecular interactions, can be exerted by choice of solvent (polarity) to direct the self-assembly of co-crystals. Competitive co-crystal formation has been investigated for three pairs of hydrogen bond and halogen bond donors, which can compete for a common acceptor group. These competitions have been examined in seven different solvents. Product formation has been determined and phase purity has been examined by analysis of powder X-ray diffraction patterns. Formation of hydrogen-bonded co-crystals is favoured from less polar solvents and halogen-bonded co-crystals from more polar solvents. The solvent polarity at which the crystal formation switches from hydrogen-bond to halogen-bond dominance depends on the relative strengths of the interactions, but is not a function of the solution-phase interactions alone. The results clearly establish that an appreciation of solvent effects is critical to obtain control of the intermolecular interactions.

Crystallographic studies of gas sorption in metal-organic frameworks

Metal-organic frameworks (MOFs) are a class of porous crystalline materials of modular design. One of the primary applications of these materials is in the adsorption and separation of gases, with potential benefits to the energy, transport and medical sectors. In situ crystallography of MOFs under gas atmospheres has enabled the behaviour of the frameworks under gas loading to be investigated and has established the precise location of adsorbed gas molecules in a significant number of MOFs. This article reviews progress in such crystallographic studies, which has taken place over the past decade, but has its origins in earlier studies of zeolites, clathrates etc. The review considers studies by single-crystal or powder diffraction using either X-rays or neutrons. Features of MOFs that strongly affect gas sorption behaviour are discussed in the context of in situ crystallographic studies, specifically framework flexibility, and the presence of (organic) functional groups and unsaturated (open) metal sites within pores that can form specific interactions with gas molecules.

Evaluation of a large-scale frozen blood program

The characteristics of previously frozen red blood cells, prepared in a large-scale frozen blood program using the Red Cross method were evaluated. The use of the method as originally described resulted in approximately 91 per cent freeze-thaw-wash recovery of red blood cells. When the glycerolization step was modified by adding the partially glycerolized erythrocytes into 300 ml of 6.2M glycerol, freeze-thaw-wash recoveries were decreased. However, gradient addition of glycerol to the red blood cells without the use of stylet, resulted in acceptable in vitro recoveries. Thawing frozen units in waterbath, to which no antiseptic was added, could introduce bacteria into units of previously frozen red blood cells. Therefore, it seems advisable to use dry heat thawing procedures. Previously frozen red blood cells prepared in the large scale maintained normal levels of ATP and 2,3 DPG. Therapeutic transfusions had acceptable 24-hour survival in vivo.