Density Functional Theory Studies of Catalytic Sites in Metal- Organic Frameworks

Theoretical methods have become indispensable tools in many fields of chemistry and materials research. Metal-organic frameworks (MOFs) are porous materials; they have been intensively developed due to their diverse properties suitable for a wide range of applications. Theoretical approaches have thus been frequently employed toward the design and characterization of MOFs. We focus here in particular on theoretical studies of single-site catalytic reactions that occur inside the cavities of MOFs. The density functional method (DFT) has been the main approach used for such studies. We briefly review the uses of DFT to examine the catalytic reactions in MOFs. We note that DFT methods are versatile and can be made to work for different purposes such as, e.g., force-field development for molecular simulations. We shall, however, cover this field only very succinctly to put it into context with our main topic

Electronic circular dichroism spectrum of uridine studied by the SAC-CI method

Abstract Symmetry-adapted cluster-configuration interaction (SAC-CI) method was applied to calculate electronic CD spectrum of a nucleoside, uridine. Based on the theoretical CD and absorption spectra, the observed peaks in the experimental spectra were assigned. The excited states of uracil, the base part of uridine, were also calculated for comparison. The origin of CD rotational strength for the lowlying p-p * and n-p * excited states was analyzed. Rotational strength of the p-p * transition depends on the magnitude of the electric and magnetic transition dipole moments, while that of the n-p * originates from the angle between the two transition moments

Covalently linked organic networks

In this review, we intend to give an overview of the synthesis of well-defined covalently bound organic network materials such as covalent organic frameworks, conjugated microporous frameworks, and other "ideal polymer networks" and discuss the different approaches in their synthesis and their potential applications. In addition we will describe the common computational approaches and highlight recent achievements in the computational study of their structure and properties. For further information, the interested reader is referred to several excellent and more detailed reviews dealing with the synthesis (Dawson et al., 2012; Ding andWang, 2013; Feng et al., 2012) and computational aspects (Han et al., 2009; Colón and Snurr, 2014) of the materials presented here

Exploration of glassy state in Prussian blue analogues

Prussian blue analogues (PBAs) are archetypes of microporous coordination polymers/metal–organic frameworks whose versatile composition allows for diverse functionalities. However, developments in PBAs have centred solely on their crystalline state, and the glassy state of PBAs has not been explored. Here we describe the preparation of the glassy state of PBAs via a mechanically induced crystal-to-glass transformation and explore their properties. The preservation of short-range metal–ligand–metal connectivity is confirmed, enabling the framework-based functionality and semiconductivity in the glass. The transformation also generates unconventional CN(−) vacancies, followed by the reduction of metal sites. This leads to significant porosity enhancement in recrystallised PBA, enabled by further accessibility of isolated micropores. Finally, mechanical stability under stress for successful vitrification is correlated to defect contents and interstitial water. Our results demonstrate how mechanochemistry provides opportunities to explore glassy states of molecular framework materials in which the stable liquid state is absent

Characterisation of redox states of metal-organic frameworks by growth on modified thin-film electrodes

The application of metal-organic framework (MOF) materials in electrochemical and electrochromic devices remain rare. One of the main reasons for this is the inability to readily access their detailed electrochemistry. The inherent insolubility of these materials does not allow interrogation by traditional solution-based electrochemical or spectroscopic methods. In this study, we report a straightforward alternative approach to the spectroelectrochemical study of MOFs. We have used two systems as exemplars in this study, MFM-186 and MFM-180. The method involves chemical modification of a working electrode to attach MOF materials without using corrosive reagents such as inorganic acids or bases which otherwise could limit their application in device development. MFM-186 demonstrates the formation of a stable radical species [MFM-186]●+ on electrochemical oxidation, and this has been characterised by electrochemical, spectroelectrochemical and EPR spectroscopic techniques coupled to DFT analysis

A new method to position and functionalize metal-organic framework crystals

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications

Geometry analysis and systematic synthesis of highly porous isoreticular frameworks with a unique topology

Porous coordination polymers are well known for their easily tailored framework structures and corresponding properties. Although systematic modulations of pore sizes of binary prototypes have gained great success, simultaneous adjustment of both pore size and shape of ternary prototypes remains unexplored, owing to the difficulty in controlling the self-assembly of multiple molecular building blocks. Here we show that simple geometry analysis can be used to estimate the influence of the linker lengths and length ratios on the synthesis/construction difficulties and framework stabilities of a highly symmetric, ternary prototype composed of a typical trinuclear metal cluster and two types of bridging carboxylate ligands. As predicted, systematic syntheses with 5×5 ligand combinations produced 13 highly porous isoreticular frameworks, which show not only systematic adjustment of pore volumes (0.49–2.04 cm3 g−1) and sizes (7.8–13.0 Å; 5.2–12.0 Å; 7.4–17.4 Å), but also anisotropic modulation of the pore shapes