Metal-organic frameworks (MOFs) represent a new class of hybrid organic-inorganic supramolecular materials comprised of ordered networks formed from organic electron donor linkers and metal cations. They can exhibit extremely high surface areas, as well as tunable pore size and functionality, and can act as hosts for a variety of guest molecules. Since their discovery, MOFs have enjoyed extensive exploration, with applications ranging from gas storage to drug delivery to sensing. This review covers advances in the MOF field from the past three years, focusing on applications, including gas separation, catalysis, drug delivery, optical and electronic applications, and sensing. We also summarize recent work on methods for MOF synthesis and computational modeling.

The adsorption of noble gases (Ar, Kr, Xe, and Rn) and N 2 by a diverse range of Metal−Organic Frameworks (MOFs) containing open metal sites (OMS) was systematically investigated using volumetric gas porosimetry and grand canonical Monte Carlo simulation. The ten MOFs considered are grouped into two series. The first, MOF-74-x, is based upon MOF-74/CPO-27, which has divalent metal ions Mg, Co, Ni, and Zn, and was chosen to explore the effect of metal identity within a constant topology. The second series, nbo-MOFs, consists of NOTT-100, NOTT-101, NOTT-102, NOTT-103, and PCN-14 and probes the effect of pore size while maintaining constant OMS identity and similar coordination environment. Comparisons of the nbo-MOFs with HKUST-1 are also made, since this MOF has a similar chemical structure, although the topology is different from the nbo structures. Gas uptake and Henry's constant (k H ) for nbo-MOFs increase with decreasing pore size, and as pore size decreases, the effect of gas polarizability on k H becomes more profound. This implies that tailored pore size can strongly influence k H , especially for the more polarizable gases Kr and Xe. A detailed analysis of the void space in the nbo-series reveals large cages connected by narrow pores, resulting in tortuous, zigzag diffusion pathways that likely increase the strength of the MOF−gas interaction. Data for the MOF-74-x series show that both the density of OMS and their accessibility in this topology enhance the framework interaction with the noble gases. However, because the interaction is largely due to (point charge)−(induced-dipole) interactions and the charge on the metal ion varies little, the specific identity of the metal ion is relatively unimportant. Consequently, new MOFs tailored to maximize noble gas uptake from air should target structures with both a high density of OMS and pores that are approaching the size of the gas of interest.

Photoluminescence (PL) spectroscopy was used to characterize nanoscale ZnO impurities, amine-donor charge-transfer exciplexes, and framework decomposition in samples of MOF-5 prepared by various methods. The combined results cast doubt on previous reports describing MOF-5 as a semiconductor and demonstrate that PL as a tool for characterizing MOF purity possesses advantages such as simplicity, speed, and sensitivity over currently employed powder XRD MOF characterization methods.

A systematic investigation of the effects of linker polarizability on the adsorption properties of weakly interacting gases (N 2 , Ar, Kr, and Xe) is reported. Experimental and simulated adsorption properties were measured for a complete isoreticular series of monohalogenated metal−organic frameworks (MOFs). Variations on IRMOF-2, in which one linker hydrogen is replaced with −F, −Cl, −Br, or −I, comprise the series. Both experimental and simulated results indicate that increasing linker polarizability correlates with increased gas uptake. Evidence of increased adsorbate interaction with increased linker polarizability is also observed in the Kr/N 2 , Xe/N 2 , and Xe/ Kr selectivity data and in isosteric heats of adsorption. Unexpectedly, comparison between simulated and experimental isotherms reveals that the agreement between the two improves with the size of the adsorbate, with essentially identical results for Xe. This is apparently due to the creation of regions inaccessible to any of the noble gases as a result of halogen functionalization. Simulated adsorption isotherms are also reported for radon, which is difficult to measure experimentally due to its radioactivity.

The exemplary structural versatility and permanent porosity of Metal-Organic Frameworks (MOFs) and their consequent potential for breakthroughs in diverse applications have caused these hybrid materials to become the focus of vigorous investigation. These properties also hold significance for applications beyond those traditionally envisioned for microporous materials, such as radiation detection and other luminescence-based sensing applications. In this contribution we demonstrate that luminescence induced by ionizing radiation (also known as scintillation) is common in appropriately designed MOFs and describe how this property can be harnessed to generate novel materials useful for detecting radiation. Through a diverse selection of MOFs, we explore the structural properties of MOFs that give rise to scintillation and photoluminescence in these materials. These results enable us to define a new structure-based hierarchical system for understanding luminescent properties in MOFs. Finally, we describe some performance metrics for MOF-based scintillation counters, such as luminosity and resistance to radiation damage, and discuss how these materials relate to the current state of the art in scintillation counters.