Mikhail Meilikhov

Shape-Memory Nanopores Induced in Coordination Frameworks by Crystal Downsizing

Size Affects Shape Porous molecular framework materials can adopt a different phase when guest molecules absorb and uniformly distort the framework. Usually the framework returns to its original shape when the guests desorb. Sakata et al. (p. 193) noted that because surface stress drives this process, it might be avoided in smaller crystals. Indeed, a flexible porous coordination polymer, [Cu2(dicarboxylate)2(amine)]n, could retain the structure induced by guest molecules such as methanol if crystallites were made sufficiently small (submicrometer scale) and did so to a greater degree as the crystallite dimensions decreased. A porous material retains its framework shape after guest molecules desorb if its crystallites are sufficiently small. Flexible porous coordination polymers change their structure in response to molecular incorporation but recover their original configuration after the guest has been removed. We demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu2(dicarboxylate)2(amine)]n regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks. In addition to the two structures that contribute to the sorption process (that is, a nonporous closed phase and a guest-included open phase), we isolated an unusual, metastable open dried phase when downsizing the crystals to the mesoscale, and the closed phase was recovered by thermal treatment. Crystal downsizing suppressed the structural mobility and stabilized the open dried phase. The successful isolation of two interconvertible empty phases, the closed phase and the open dried phase, provided switchable sorption properties with or without gate-opening behavior.

Integration of porous coordination polymers and gold nanorods into core-shell mesoscopic composites toward light-induced molecular release.

Besides conventional approaches for regulating in-coming molecules for gas storage, separation, or molecular sensing, the control of molecular release from the pores is a prerequisite for extending the range of their application, such as drug delivery. Herein, we report the fabrication of a new porous coordination polymer (PCP)-based composite consisting of a gold nanorod (GNR) used as an optical switch and PCP crystals for controlled molecular release using light irradiation as an external trigger. The delicate core-shell structures of this new platform, composed of an individual GNR core and an aluminum-based PCP shell, were achieved by the selective deposition of an aluminum precursor onto the surface of GNR followed by the replication of the precursor into aluminum-based PCPs. The mesoscopic structure was characterized by electron microscopy, energy dispersive X-ray elemental mapping, and sorption experiments. Combination at the nanoscale of the high storage capacity of PCPs with the photothermal properties of GNRs resulted in the implementation of unique motion-induced molecular release, triggered by the highly efficient conversion of optical energy into heat that occurs when the GNRs are irradiated into their plasmon band. Temporal control of the molecular release was demonstrated with anthracene as a guest molecule and fluorescent probe by means of fluorescence spectroscopy.

Liquid-Phase Epitaxy of Multicomponent Layer-Based Porous Coordination Polymer Thin Films of [M(L)(P)0.5] Type: Importance of Deposition Sequence on the Oriented Growth

The progressive liquid-phase layer-by-layer (LbL) growth of anisotropic multicomponent layer-based porous coordination polymers (PCPs) of the general formula [M(L)(P)(0.5)] (M: Cu(2+), Zn(2+); L: dicarboxylate linker; P: dinitrogen pillar ligand) was investigated by using either pyridyl- or carboxyl-terminated self-assembled monolayers (SAMs) on gold substrates as templates. It was found that the deposition of smooth, highly crystalline, and oriented multilayer films of these PCPs depends on the conditions at the early growth cycles. In the case of a two-step process with an equimolar mixture of L and P, growth along the [001] direction is strongly preferred. However, employing a three-step scheme with full separation of all components allows deposition along the [100] direction on carboxyl-terminated SAMs. Interestingly, the growth of additional layers on top of previously grown oriented seeding layers proved to be insensitive to the particular growth scheme and full retention of the initial orientation, either along the [001] or [100] direction, was observed. This homo- and heteroepitaxial LbL growth allows full control over the orientation and the layer sequence, including introduction of functionalized linkers and pillars.

Binary Janus Porous Coordination Polymer Coatings for Sensor Devices with Tunable Analyte Affinity

Janus MOF: thin films consisting of non-centrosymmetric heterostructured metal-organic frameworks (MOFs) were fabricated directly on quartz-crystal microbalance (QCM) sensor devices. Depending on the spatial configuration of two frameworks, the thin MOF films could tune the affinity for analytes, thus giving high selectivity to the QCM sensors.

Stepwise deposition of metal organic frameworks on flexible synthetic polymer surfaces

Thin films of [Cu(3)(btc)(2)](n) (btc = 1,3,5-benzenetricarboxylate) metal organic framework were deposited in a stepwise manner on surfaces of flexible organic polymers. The thickness of films can be precisely controlled. The deposition of the first cycles was monitored by UV-vis spectroscopy. The porosity was proven by the adsorption of pyrazine, which was monitored by FT-IR and thermogravimetric analysis. The deposition of MOF thin films on flexible polymer surfaces might be a new path for the fabrication of functional materials for different applications, such as protection layers for working clothes and gas separation materials in the textile industry.

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.

The adsorbate structure of ferrocene inside [Al(OH)(bdc)]x (MIL-53): a powder X-ray diffraction study

Ferrocene is strongly adsorbed by the highly porous metal-organic framework compound [Al(OH)(bdc)l], (MIL-53; bdc = 1,4-benzenedicarboxylate). The structure of the crystalline phase {[Fe(eta5-C5H5)2][Al(OH)(bdc)]2}x, was determined by X-ray powder diffraction and Rietveld methods. The ferrocene molecules are arranged in a 1D chain-like fashion and their cyclopentadienyl rings are oriented almost parallel to the O3Al faces of the {AlO6}) octahedra without pi-stacking to the bdc.

Multiple phase-transitions upon selective CO2 adsorption in an alkyl ether functionalized metal–organic framework—an in situ X-ray diffraction study

The flexible alkyl ether functionalized metal–organic framework [Zn2(BME-bdc)2(dabco)]n (BME-bdc = 2,5-bis(2-methoxyethoxy)-1,4-benzenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) shows remarkable structural changes upon selective adsorption of CO2 as determined by in situ X-ray diffraction at 195 K. Upon accommodation of carbon dioxide [Zn2(BME-bdc)2(dabco)]n transfers from a narrow pore form to an open pore form, which exhibits a much higher unit cell volume. Due to the slow adsorption kinetics an unexpected metastable intermediate form could be identified.

Targeted functionalisation of a hierarchically-structured porous coordination polymer crystal enhances its entire function

Spatiospecific functionalisation of a shell crystal was performed in a core-shell crystal of a porous coordination polymer (PCP) via post-synthetic modification (PSM). The shell crystal allowed the core crystal to selectively accumulate N,N-dimethylaniline (DMA) and afford the intense exciplex fluorescence.

Step-by-step growth of highly oriented and continuous seeding layers of [Cu2(ndc)2(dabco)] on bare oxide and nitride substrates

The step-by-step growth of highly oriented and continuous thin films of [Cu2(ndc)2(dabco)] (1) at 50 °C was studied and compared with growth directly from solvothermal mother solution at 120 °C. The substrates were bare unmodified SiO2, Al2O3 grown by atomic layer deposition (ALD), Ta2O5 and Si3N4. The deposited layers of 1 were characterized via in-plane and out-of-plane X-ray powder diffraction (PXRD) and Scanning Electron Microscopy (SEM). The stepwise film formation process was studied by the variation of the reaction conditions and washing procedures indicating an island growth mode and the importance of storage effects. The highly oriented layers obtained by the step-by-step method were used as seeds for the deposition of thicker films of 500–700 nm with the same orientation directly from solvothermal mother solution.