Metal–organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal–organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal–organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal–organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal–organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal–organic magnet research that laid the foundation for structurally characterized metal–organic framework magnets. Sections 3 and 4 then outline the literature of metal–organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal–organic framework magnets while maintaining structural integrity and additional function.

The potential utility of paramagnetic transition metal complexes as chemical shift 19F magnetic resonance (MR) thermometers is demonstrated.

Electrochemical and photoelectrochemical water splitting offers a scalable approach to producing hydrogen from renewable sources for sustainable energy storage. Depending on the applications, oxygen evolution catalysts (OECs) may perform water splitting under a variety of conditions. However, low stability and/or activity present challenges to the design of OECs, prompting the design of self-healing OECs composed of earth-abundant first-row transition metal oxides. The concept of self-healing catalysis offers a new tool to be employed in the design of stable and functionally active OECs under operating conditions ranging from acidic to basic solutions and from a variety of water sources.

We report a Co-based magnetic resonance (MR) probe that enables the ratiometric quantitation and imaging of pH through chemical exchange saturation transfer (CEST). This approach is illustrated in a series of air- and water-stable Co complexes featuring CEST-active tetra(carboxamide) and/or hydroxyl-substituted bisphosphonate ligands. For the complex bearing both ligands, variable-pH CEST and NMR analyses reveal highly shifted carboxamide and hydroxyl peaks with intensities that increase and decrease with increasing pH, respectively. The ratios of CEST peak intensities at 104 and 64 ppm are correlated with solution pH in the physiological range 6.5-7.6 to construct a linear calibration curve of log(CEST/CEST) versus pH, which exhibits a remarkably high pH sensitivity of 0.99(7) pH unit at 37 °C. In contrast, the analogous Co complex with a CEST-inactive bisphosphonate ligand exhibits no such pH response, confirming that the pH sensitivity stems from the integration of amide and hydroxyl CEST effects that show base- and acid-catalyzed proton exchange, respectively. Importantly, the pH calibration curve is independent of the probe concentration and is identical in aqueous buffer and fetal bovine serum. Furthermore, phantom images reveal analogous linear pH behavior. The Co probe is stable toward millimolar concentrations of HPO/HPO, CO, SO, CHCOO, and Ca ions, and more than 50% of melanoma cells remain viable in the presence of millimolar concentrations of the complex. The stability of the probe in physiological environments suggests that it may be suitable for in vivo studies. Together, these results highlight the ability of dinuclear transition metal PARACEST probes to provide a concentration-independent measure of pH, and they provide a potential design strategy toward the development of MR probes for ratiometric pH imaging.

Hydrogen evolution from a weak acid, acetic acid, occurs at extremely high rates for iron tetraphenylporphyrin in the presence tertiary amine as a cocatalyst. Kinetic analysis of H2 evolution for a range of amines with varying coordinative and acid–base properties reveals a dramatic rate enhancement derived from enhanced proton activity of a heteroconjugated adduct between acetic acid and the amine. Additionally, nonbulky tertiary amines (quinuclidine and diazabicyclooctane) result in a further increase in activity resulting from a trans effect for a TPPFe­(II)–H hydride intermediate. These findings reveal the design principle of a cocatalyst for creating more efficient molecular systems for hydrogen evolution electrocatalysis.