Synthesis and Biomedical Applications of Highly Porous Metal-Organic Frameworks

In this review, aspects of the synthesis, framework topologies, and biomedical applications of highly porous metal-organic frameworks are discussed. The term "highly porous metal-organic frameworks" (HPMOFs) is used to denote MOFs with a surface area larger than 4000 m² g^-1. Such compounds are suitable for the encapsulation of a variety of large guest molecules, ranging from organic dyes to drugs and proteins, and hence they can address major contemporary challenges in the environmental and biomedical field. Numerous synthetic approaches towards HPMOFs have been developed and discussed herein. Attempts are made to categorise the most successful synthetic strategies; however, these are often not independent from each other, and a combination of different parameters is required to be thoroughly considered for the synthesis of stable HPMOFs. The majority of the HPMOFs in this review are of special interest not only because of their high porosity and fascinating structures, but also due to their capability to encapsulate and deliver drugs, proteins, enzymes, genes, or cells; hence, they are excellent candidates in biomedical applications that involve drug delivery, enzyme immobilisation, gene targeting, etc. The encapsulation strategies are described, and the MOFs are categorised according to the type of biomolecule they are able to encapsulate. The research field of HPMOFs has witnessed tremendous development recently. Their intriguing features and potential applications attract researchers' interest and promise an auspicious future for this class of highly porous materials.

Chiral Motifs in Highly Interpenetrated Metal-Organic Frameworks Formed from Achiral Tetrahedral Ligands

Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane-shaped cages in a single network, making these crystals new entries in the collection of diamondoid-type metal-organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks' degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10-, 16-, and 32-fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å.

Visualization and Quantification of Geometric Diversity in Metal-Organic Frameworks

With ever-growing numbers of metal-organic framework (MOF) materials being reported, new computational approaches are required for a quantitative understanding of structure-property correlations in MOFs. Here, we show how structural coarse-graining and embedding ("unsupervised learning") schemes can together give new insights into the geometric diversity of MOF structures. Based on a curated data set of 1262 reported experimental structures, we automatically generate coarse-grained and rescaled representations which we couple to a kernel-based similarity metric and to widely used embedding schemes. This approach allows us to visualize the breadth of geometric diversity within individual topologies and to quantify the distributions of local and global similarities across the structural space of MOFs. The methodology is implemented in an openly available Python package and is expected to be useful in future high-throughput studies.

Four new MOFs based on an imidazole-containing ligand and multicarboxylates: syntheses, structures and sorption properties

Four new coordination complexes based on M(ii)-L layer structures with different 3D frameworks and topologies have been successfully tuned by auxiliary dicarboxylates.

Functional group effects on structure and topology of cadmium(ii) frameworks with mixed organic ligands

Cadmium(ii) complexes were obtained by tuning functional groups of benzenedicarboxylate and reaction conditions, their ferroelectric and photoluminescence properties were studied.

A highly stable face-extended diamondoid cluster–organic framework incorporating infinite inorganic guests

A highly stable face-extended cluster–organic framework with infinite inorganic guests is hydrothermally made, in which the tetrahedral O-centred Cu₄O cluster is firstly found as the face-extended building unit to further make a diamondoid cluster–organic framework.

An acentric 3-D metal–organic framework with threefold interpenetrated diamondoid network: second-harmonic-generation response, potential ferroelectric property and photoluminescence

An solvothermally synthesized acentric 3-D Cd(ii) metal–organic framework was found to exhibit a unique threefold-interpenetration diamondoid architecture, second-harmonic-generation efficiency, potential ferroelectric property and photoluminescence.

A huge diamondoid metal–organic framework with a neo-mode of tenfold interpenetration

A huge diamondoid framework with edge distances of the adamantane cages of up to 25.95 Å, is reported. This MOF displays a tenfold interpenetration, which is constructed from bulky and elongated aromatic-rigid dicarboxylate scaffolds, exhibits a self-catenated net with a point symbol of {(6².8⁴)(6⁴.8.10)₂}.

Microporous metal–organic layer built from pentanuclear tetrahedral units: gas sorption and magnetism

A porous layer built by connecting orthorhombic cages with accessible metal centers shows high selectivity for CO₂ over CH₄.

Bilayer architecture based on hexanuclear heterometal cluster units

An unprecedented bilayer architecture based on “head-to-head” hexanuclear heterometal clusters and linked by parallel [Cu^IL₂] motifs has been hydrothermally made.