Bettina Jee

Structural Complexity in Metal–Organic Frameworks: Simultaneous Modification of Open Metal Sites and Hierarchical Porosity by Systematic Doping with Defective Linkers

A series of defect-engineered metal-organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework.

Reduction of a Metal–Organic Framework by an Organometallic Complex: Magnetic Properties and Structure of the Inclusion Compound [(η5‐C5H5)2Co]0.5@MIL‐47(V)

Probing and fine tuning the physical and chemical properties of metal–organic frameworks (MOFs) by post-synthetic functionalization of the organic linkers is a challenging topic. For example, redox-inactive MIL-53(Al) can be made redox-active by functionalization of the bridging OH groups of the AlO6-type secondary building units (SBUs) of the framework with 1,1’-ferrocenediyldimethylsilane. The host–guest chemistry of MOFs (including crystalline porous coordination polymers, PCPs), which exhibit a redox-active framework and in particular involving charge-transfer between the framework and the adsorbed molecules, is an underdeveloped, but very promising area of research. The few existing reports include the framework oxidation of a nickel(II)-based MOF with I2, silver(I), and gold(III) salts. [4] Furthermore, the partial reduction of MOFs with lithium, which also involves the aromatic linkers, was discussed to increase the hydrogen uptake. Herein, we present the first case of a stoichiometric reduction of the inorganic backbone of a neutral framework in the course of gas-phase loading with an organometallic reducing agent (OMR), and the elucidation of the novel adsorbate structure of the type [OMR]@[MOF ]. The adsorption of the volatile OMR cobaltocene, [(h-C5H5)2Co], in channels of [VO(bdc)] (MIL-47(V); bdc = 1,4-benzenedicarboxylic acid; MIL = materials of the Institute Lavoisier) leads selectively to the inclusion compound of the formula [(h-C5H5)2Co]0.5@MIL-47(V) (1; Figure 1). The MIL-47(V) network is the isostructural analogue of the well-investigated, redox-inactive phase MIL-53(Al). The preparation of 1 was carried out according to previously published procedures for solvent-free loading of MOFs with organometallic compounds. The elemental analysis of 1 reveals a V/Co ratio of exactly 2:1. The FT-IR spectrum of 1 has a strong vibrational band at 860 cm , which is attributed to the formation of cobaltocenium species (Figure 2). Figure 1. Structure of 1 in the [010] projection. The cobaltocenium occupancy is 50%; that is, only every second position shown is occupied. C black, O red, Co purple; {VO6} fragments are displayed as green octahedra.

H, D and HD adsorption upon the metal-organic framework [CuZn(btc)] studied by pulsed ENDOR and HYSCORE spectroscopy

The adsorption of hydrogen has become interesting in terms of gas separation as well as safe and reversible storage of hydrogen as an energy carrier. In this regard, metal-organic framework compounds are potential candidates. The metal-organic framework [CuZn(btc)] as a partially Zn-substituted analogue of the well known compound HKUST-1 is well suited for studying adsorption geometries at cupric ions by electron paramagnetic resonance (EPR) methods due to the formation of few mixed Cu/Zn paddle wheel units with isolated S = 1/2 electron spins. The adsorption of hydrogen (H2) as well as the deuterium (D2) and HD molecules were investigated by continuous wave EPR and pulsed ENDOR and HYSCORE spectroscopy. The principal values of the proton and deuterium hyperfine coupling tensors and were determined by spectral simulations as well as of the deuterium nuclear quadrupole tensor for adsorbed HD and D2. The results show a side-on coordination of HD and D2 with identical Cu–H and Cu–D distances rCuX = 2.8 Å with the tensors and aligned parallel to the C4 symmetry axis of the paddle wheel unit. A thermodynamic non-equilibrium state with J = 1, mJ = ±1 is indicated by the experimental data with and averaged by rotation around C4.