Charge transport in two zinc metal-organic frameworks (MOFs) has been investigated using periodic semiempirical molecular orbital calculations with the AM1* Hamiltonian. Restricted Hartree-Fock calculations underestimate the band gap (Koopmans theorem), which however becomes more realistic when the wavefunction is allowed to become unrestricted. Charge-transport simulations using propagation of the electron- or hole-density in imaginary time allow charge-transport paths to be determined, although the calculated mobilities must still be improved. In general, the techniques discussed appear to be useful for investigating electroactive MOFs.
The effectiveness of molecular-based light harvesting relies on transport of optical excitations, excitons, to charg-transfer sites. Measuring exciton migration has, however, been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. In organic semiconductors, common bulk methods employ a series of films terminated at quenching substrates, altering the spatioenergetic landscape for migration. Here we instead define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native n…
Charge migration is a ubiquitous phenomenon with profound implications throughout many areas of chemistry, physics, biology and materials science. The long-term vision of designing functional materials with tailored molecular scale properties has triggered an increasing quest to identify prototypical systems where truly molecular conduction pathways play a fundamental role. Such pathways can be formed due to the molecular organization of various organic materials and are widely used to discuss electronic properties at the nanometer scale. Here, we present a computational methodology to study c…
Kinetics of singlet fission in organic semiconductors, in which the excited singlet state (S_1) spontaneously splits into a pair of triplet (T) excitons, is known to be strongly influenced by back geminate annihilation of TT-pairs. We show that this influence can be properly described only by taking into account the diffusive exciton migration. The migration effect is treated in the model of two kinetically coupled states: the intermediate state of interacting TT-pairs and the state of migrating excitons. Within this model the singlet fission (including magnetic field effects) is studied as ap…
Organic-inorganic hybrid perovskites (OIHPs) exhibiting exceptional photovoltaic and optoelectronic properties are of fundamental and practical interest, owing to their tunability and low manufacturing cost. For practical applications, however, challenges such as material instability and the photocurrent hysteresis occurring in perovskite solar cells under light exposure need to be understood and addressed. While extensive investigations have suggested that ion migration is a plausible origin of these detrimental effects, detailed understanding of the ion migration pathways remains elusive. He…
Density functional theory and ab initio molecular dynamics simulations are applied to investigate the migration of Mn(II) ions to above-surface sites on spinel Li(x)Mn(2)O(4) (001) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on graphite anode solid electrolyte interphase (SEI) passivating films after Mn(II) ions diffuse through the separator. The dissolution mechanism proves complex, the much-quoted Hunter disproportionation of Mn(III) to form Mn(II) is far from sufficient. Key steps that facilitate Mn(II) loss include concerted liqu…
Metal halide perovskites possess many physical properties amenable to optoelectronic applications, whereas the realization of these potentials has been hampered by their environmental and electronic instabilities. The morphological and molecular low dimensional perovskites and perovskite related materials have shown much promise in enhancing the chemical stability due to their unique molecular structures. Here we report on robust and reproducible four-terminal (4T) electrical measurements in a one-dimensional (1D) organic metal halide hybrid, (R)-α-methylbenzylammonium lead triiodide ((R-α-MBA…
We report a bistable organic memory made of a single organic layer embedded between two electrodes, we compare to the organic/metal nanoparticle/organic tri-layers device [L.P. Ma, J. Liu, and Y. Yang, Appl. Phys. Lett. 80, 2997 (2002)]. We demonstrate that the two devices exhibit similar temperature-dependent behaviors, a thermally-activated behavior in their low conductive state (off-state) and a slightly "metallic" behavior in their high conductive state (on-state). This feature emphasizes a similar origin for the memory effect. Owing to their similar behavior, the one layer memory is advan…
The physics of organic semiconductors is dominated by the effects of energetic disorder. We show that image forces reduce the electrostatic component of the total energetic disorder near an interface with a metal electrode. Typically, the variance of energetic disorder is dramatically reduced at the first few layers of organic semiconductor molecules adjacent to the metal electrode. Implications for charge injection into organic semiconductors are discussed.
In this work, we present an investigation of the Ag-PPP (polyparaphenylene) interface using ballistic electron emission microscopy. Our work is the first successful application of the BEEM technique to metal-organic interfaces. We observe nanometer scale injection inhomogeneities. They have an electronic origin, since we find corresponding Schottky barrier variations. We also determine the transmission function of Ag-PPP interface and find that it agrees qualitatively with the theoretical calculations for a metal-phenyl ring interface. We conclude that charge transport across inhomogeneous bar…
We have shown, both experimentally and theoretically, that the metal-induced gap states (MIGS) can exist in epitaxially grown organic insulator/metal interfaces. The experiment is done for alkane/Cu(001) with an element-selective near edge x-ray absorption fine structure (NEXAFS), which exhibits a pre-peak indicative of MIGS. An {\it ab initio} electronic structure calculation supports the existence of the MIGS. When the Cu substrate is replaced with Ni, an interface magnetism (spin-polarized organic crystal at the interface) is predicted to be possible with a carrier doping.
The amplitude of the roughness-induced energetic disorder at the metal/organic interface is calculated. It was found that for moderately rough electrodes, the correction to the electrostatic image potential at the charge location is small. For this reason, roughness-induced energetic disorder cannot noticeably affect charge carrier injection, contrary to the recent reports.
The binding energy of an electron in a material is a fundamental characteristic, which determines a wealth of important chemical and physical properties. For metal-organic frameworks this quantity is hitherto unknown. We present a general approach for determining the vacuum level of porous metal-organic frameworks and apply it to obtain the first ionisation energy for six prototype materials including zeolitic, covalent and ionic frameworks. This approach for valence band alignment can explain observations relating to the electrochemical, optical and electrical properties of porous frameworks.
Based on the assumption that the contact barrier height determines the current flow in organic semiconductor-based electronic devices, charge injection at metal-organic (MO) interfaces has been extensively investigated, while space-charge conduction in organic bulk is generally overlooked. Recent theoretical modeling and simulation have pointed out that such a simplification is questionable due to the hopping nature of charge injection and hopping-related space-charge conduction. Here we show experimentally that charge transport in metal-organic diodes is complex interplay between injection-li…
Based on first principles calculations, we predict and characterize the flexibility of two aluminium-based Metal-Organic Frameworks (MOFs), CAU-13 and NOTT-300. Both materials have a wine rack topology similar to that of MIL-53(Al), the archetypal breathing MOF, yet their flexibility has not been demonstrated so far.
The barrier formation for metal/organic semiconductor interfaces is analyzed within the Induced Density of Interface States (IDIS) model. Using weak chemisorption theory, we calculate the induced density of states in the organic energy gap and show that it is high enough to control the barrier formation. We calculate the Charge Neutrality Levels of several organic molecules (PTCDA, PTCBI and CBP) and the interface Fermi level for their contact with a Au(111) surface. We find an excellent agreement with the experimental evidence and conclude that the barrier formation is due to the charge trans…
A computational approach for predictive simulations of the nanoscale morphology in the early steps of the formation of the interface between metals and organic molecular semiconductors is presented. Despite the relevance of the metal-molecule junction for the development of electronic applications, structural details at the interface are often difficult to assess. Our approach, based on the integration of density functional theory with methods for the simulation of growth dynamics, allows to unravel the structural details of the formation of gold aggregates onto molecular materials. Simulation…
We investigate the bias-induced insulator-metal transition in organic electronics devices, on the basis of the Su-Schrieffer-Heeger model combined with the non-equilibrium Green's function formalism. The insulator-metal transition is explained with the energy levels crossover that eliminates the Peierls phase and delocalizes the electron states near the threshold voltage. This may account for the experimental observations on the devices that exhibit intrinsic bistable conductance switching with large on-off ratio.
Since the discovery of the TTF-TCNQ charge transfer complex as the first metallic material composed of molecules, many other molecular metals were reported. It was however only recently that the first metal-free single-component organic metal was characterized by Kobayashi et al. Although the measured properties of a poorly crystalline sample clearly showed metallic behavior, the crystal structure itself could not be solved, so that the conduction mechanism in this material is still unknown. Here, we present the results of theoretical crystal structure prediction calculations for the TED molec…
An electronic band with quasi-one dimensional dispersion is found at the interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a Au(111) surface. Combined local spectroscopy and numerical calculations show that the band results from a complex mixing of metal and molecular states. The molecular layer folds the underlying metal states and mixes with them selectively, through the TTF component, giving rise to anisotropic hybrid bands. Our results suggest that, by tuning the components of such molecular layers, the dimensionality and dispersion of organic-metal interface states…
Ferromagnetic metal-organic semiconductor (FM-OSC) hybrid interfaces have shown to play an important role for spin injection in organic spintronics. Here, 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) is introduced as an interfacial layer in Co-OSCs heterojunction with an aim to tune the spin injection. The Co/TNAP interface is investigated by use of X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS), near edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD). Hybrid interface states (HIS) are observed at Co/TNAP interface resulting from ch…
Metal-organic frameworks (MOFs) are constructed from a combination of inorganic and organic units to produce materials which display high porosity, among other unique and exciting properties. MOFs have shown promise in many wide-ranging applications, such as catalysis and gas separations. In this review, we highlight MOF research conducted by Germany-based research groups. Specifically, we feature approaches for the synthesis of new MOFs, high-throughput MOF production, advanced characterization methods and examples of advanced functions and properties.
A simple method for the fabrication of metal nanoparticles is introduced. Heating metal-organic crystals in vacuum results in the formation of well defined metal particles embedded in a carbon matrix. The method is demonstrated for iron-phthalocyanine. At 500C homogeneously distributed iron nanoparticles with a reasonably narrow size distribution form by nucleation and ripening. After this initial phase the formation kinetics changes drastically. The particles move in the matrix to incorporate material. The "gluttony" phase shows astonishing similarities with the search for nutrition of living…
Transition-metal perovskite oxides constitute a series of functional material systems for electronics, catalysis and energy-conversion processes, in which oxygen migration and evolution play a key role. However, the stable metal-oxygen (M-O) bond forms large energy barrier inhibiting ion diffusion. Therefore, seeking efficient and facile approaches to accelerate oxygen kinetics has become a significant issue. Here, the interaction (interfacial charge transfer and cooperative bonding) between noble metal (Pt, Ag) and perovskites oxide (SrCoO3-delta) is employed to weaken (M-O) bond and decrease…
Three driving forces control the energy level alignment between transition-metal oxides and organic materials: the chemical interaction between the two materials, the organic electronegativity and the possible space charge layer formed in the oxide. This is illustrated in this letter by analyzing experimentally and theoretically a paradigmatic case, the TiO2(110) / TCNQ interface: due to the chemical interaction between the two materials, the organic electron affinity level is located below the Fermi energy of the n-doped TiO2. Then, one electron is transferred from the oxide to this level and…
Metal/semiconductor interfaces govern the operation of semiconductor devices through the formation of charge injection barriers that can be controlled by tuning the metal work function. However, the controlling ability is typically limited to being static. We show that a dynamic nature can be imparted to the interfaces using electrode surface modification with a structurally disordered molecular monolayer. The barrier height at the interfaces is altered significantly in a reversible way by an external electric field. As a result, a dramatic change in the carrier transport properties through th…
Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.
Using density functional theory (DFT), we investigate mechanical properties of a few 2D metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) having Dirac and flat bands. These porous materials have become a subject of great captivation because of their physical stability, distinctive structural characteristics and large surface to volume ratio. The inherent porosity of these frameworks gives rise to many fascinating and occasionally surprising phenomena, which makes them potential candidates for technological applications. For reliable usage of MOFs/COFs in functional nanodev…
The silver-p-phenylene (Ag-PPP) interface is investigated using ballistic electron emission microscopy (BEEM). Multiple injection barriers and spatial nonuniformity of carrier injection over nanometer length scales are observed. No unique injection barrier is found. Physical reasons for these features are discussed. BEEM current images and the surface topography of the silver film are uncorrelated.
The presence of open active metal sites in Metal-Organic Frameworks (MOFs) exhibit higher catalytic activity. However, rational accomplishment of MOFs in heterogeneous catalysis is limited due to coordination bonds. Recently balanced characteristic feature with combination of both the covalent bonds (structural stability) and open metal sites (single site catalysis) introduced an entirely organic alternative architecture named as Metalated Porous-Organic-Polymers (M-POPs). In this contribution, we demonstrate successful construction of two Fe-POPs (Fe-Tt-POP & Fe-Rb-POP) by ternary copolymeriz…
We report an investigation of the "missing-linker phenomenon" in the Zr-based metal-organic framework UiO-66 using atomistic forcefield and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge capping mechanism involves acetic acid or Cl-/H2O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the f…
Metal-organic frameworks (MOFs) are an important class of materials that present intriguing opportunities in the fields of sensing, gas storage, catalysis, and optoelectronics. Very recently, two-dimensional (2D) MOFs have been proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the interaction with the substrate masks the intrinsic electronic properties of the MOF. Here, we demonstrate synthesis of 2D honeyco…
Controlling the transport of thermal energy is key to most applications of metal-organic frameworks. Analyzing the evolution of the effective local temperature, the interfaces between the metal nodes and the organic linkers are identified as the primary bottlenecks for heat conduction. Consequently, changing the bonding strength at that node-linker interface and the mass of the metal atoms can be exploited to tune the thermal conductivity. This insight is generated employing molecular dynamics simulations in conjunction with advanced, ab initio parametrized force fields. The focus of the prese…
Understanding helium accumulation in plasma-facing or structural materials in a fusion reactor starts from uncovering the details of the migration of single and paired He interstitials. We have carried out a first-principles density functional theory investigation into the migration of both a single interstitial He atom and an interstitial He-pair in bcc (Fe, Mo and W) and fcc (Cu, Pd and Pt) metals. By identifying the most stable configurations of an interstitial He-pair in each metal and decomposing its motion into rotational, translational, and rotational-translational routines, we are able…
The interface between the tetrathiafulvalene / tetracyanoquinodimethane (TTFTCNQ) organic blend and the Au(111) metal surface is analyzed by Density Functional Theory calculations, including the effect of the charging energies on the molecule transport gaps. Given the strong donor and acceptor characters of the TTF and TCNQ molecules, respectively, there is a strong intermolecular interaction, with a relatively high charge transfer between the two organic materials. We find that the TCNQ LUMO peak is very close to the Fermi level; due to the interaction with the metal surface, the organic blen…
In this letter, we address magnetization switching by oxygen adsorption in porous metal-organic framework systems. To this end, we construct a simple localized spin model combined with a Langmuir-type formula for oxygen adsorption and study its finite-temperature properties using Monte Carlo simulation. We successfully explain the main features of this phenomenon, such as the discontinuous changes in magnetic states, sensitivity of the magnetic transition temperatures to oxygen pressure, and absence of singularities in adsorbed oxygen. Based on this model, we also reproduce the observed magnet…
Superconductivity is a fascinating quantum phenomenon characterized by zero electrical resistance and the Meissner effect. To date, several distinct families of superconductors (SCs) have been discovered. These include three-dimensional (3D) bulk SCs in both inorganic and organic materials as well as two-dimensional (2D) thin film SCs but only in $inorganic$ materials. Here we predict superconductivity in 2D and 3D $organic$ metal-organic frameworks by using first-principles calculations. We show that the highly conductive and recently synthesized Cu-benzenehexathial (BHT) is a Bardeen-Cooper-…
We combine infrared spectroscopy, nano-indentation measurements, and \emph{ab initio} simulations to study the evolution of structural, elastic, thermal, and electronic responses of the metal organic framework MOF-74-Zn when loaded with H$_2$, CO$_2$, CH$_4$, and H$_2$O. We find that the molecular adsorption in this MOF triggers remarkable responses in all of these properties of the host material, with specific signatures for each of the guest molecules. With this comprehensive study we are able to clarify and correlate the underlying mechanisms regulating these responses with changes of the p…
Two dimensional pi conjugated metal porphyrin covalent organic frameworks were produced in aqueous solution on an iodine-modified Au(111) surface by on site azomethine coupling of Fe(III) 5,10,15,20 tetrakis(4 aminophenyl)porphyrin (FeTAPP) with terephthal dicarboxaldehyde and investigated in detail using in-situ scanning tunneling microscopy. Mixed covalent organic porphyrin frameworks consisting of FeTAPP and metal-free TAPP (H2TAPP) were prepared through simultaneous adsorption in a mixed solution as well as partial replacement of FeTAPP by H2TAPP in an as prepared metal porphyrin framework…
The metal-organic framework (MOF) MFU-4l containing Co(II) centers and Cl- ligands has recently shown promising redox activity. Aiming for further improved MOF catalysts for oxidation processes employing molecular oxygen we present a density-functional theory (DFT) based computational screening approach to identify promising metal center and ligand combinations within the MFU-4l structural family. Using the O2 binding energy as a descriptor for the redox property, we show that relative energetic trends in this descriptor can reliably be obtained at the hybrid functional DFT level and using sma…
The minimum energy paths for the migration of interstitial Mg in wurtzite GaN are studied through density functional calculations. The study also comprises Li, Na, and Be dopants to examine the dependence on size and charge of the dopant species. In all cases considered, the impurities diffuse like ions without any tendency of localizing charge. Li, Mg, and to some extent Na, diffuse almost isotropically in GaN, with average diffusion barriers of 1.1, 2.1, and 2.5 eV, respectively. Instead Be shows a marked anisotropy with energy barriers of 0.76 and 1.88 eV for diffusion paths perpendicular a…
Metal-insulator transitions (MIT),an intriguing correlated phenomenon induced by the subtle competition of the electrons' repulsive Coulomb interaction and kinetic energy, is of great potential use for electronic applications due to the dramatic change in resistivity. Here, we demonstrate a reversible control of MIT in VO2 films via oxygen stoichiometry engineering. By facilely depositing and dissolving a water-soluble yet oxygen-active Sr3Al2O6 capping layer atop the VO2 at room temperature, oxygen ions can reversibly migrate between VO2 and Sr3Al2O6, resulting in a gradual suppression and a …
Although the magnetoelectric effects - the mutual control of electric polarization by magnetic fields and magnetism by electric fields, have been intensively studied in a large number of inorganic compounds and heterostructures, they have been rarely observed in organic materials. Here we demonstrate magnetoelectric coupling in a metal-organic framework [(CH3)2NH2]Mn(HCOO)3 which exhibits an order-disorder type of ferroelectricity below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss law at the paraelectric-ferroelectric transition temperature, suggesting an enhanceme…
Metal-organic frameworks are a novel family of chemically diverse materials, which are of interest across engineering, physics, chemistry, biology, and medicine-based disciplines. Since the development of the field in its current form more than two decades ago, priority has been placed on the synthesis of new structures. However, more recently, a clear trend has emerged in shifting the emphasis from material design to exploring the chemical and physical properties of those already known. In particular --- while such nanoporous materials were traditionally seen as rigid crystalline structures -…
The mechanism and products of the structural collapse of the metal-organic frameworks (MOFs) UiO-66, MIL-140B and MIL-140C upon ball-milling are investigated through solid state 13C NMR and pair distribution function (PDF) studies, finding amorphization to proceed by the breaking of a fraction of metal-ligand bonding in each case. The amorphous products contain inorganic-organic bonding motifs reminiscent of the crystalline phases. Whilst the inorganic Zr6O4(OH)4 clusters of UiO-66 remain intact upon structural collapse, the ZrO backbone of the MIL-140 frameworks undergoes substantial distorti…
The hydrogen adsorption sites in MOF5 were determined using neutron powder diffraction along with first-principles calculations. The metal-oxide cluster is primarily responsible for the adsorption while the organic linker plays only a secondary role. Equally important, at low temperatures and high-concentration, H2 molecules form unique interlinked high-symmetry nano-clusters with intermolecular distances as small as 3.0 Ang. and H2-uptake as high as 10-wt%. These results hold the key to optimizing MOF materials for hydrogen storage applications and also suggest that MOFs can be used as templa…
We present the frequency-dependant (dynamic) dielectric response of a group of topical polycrystalline zeolitic imidazolate-based metal-organic framework (MOF) materials in the extended infrared spectral region. Using synchrotron-based FTIR spectroscopy in specular reflectance, in conjunction with density functional theory (DFT) calculations, we have revealed detailed structure-property trends linking the THz region dielectric response to framework porosity and structural density. The work demonstrates that MOFs are promising candidate materials not only for low-\k{appa} electronics applicatio…
The rich polymorphism exhibited by inorganic/organic interfaces is a major challenge for materials design. In this work we present a method to efficiently explore the potential energy surface and predict the formation energies of polymorphs and defects. This is achieved by training a machine learning model on a list of only 100 candidate structures that are evaluated via dispersion-corrected Density Functional Theory (DFT) calculations. We demonstrate the power of this approach for tetracyanoethylene on Ag(100) and explain the anisotropic ordering that is observed experimentally.
Water absorption in the metal-organic framework (MOF) material Cu-BTC, up to a concentration of 3.5 H$_2$O per Cu ion, is studied via density functional theory at the meta-GGA+U level. The stable arrangements of water molecules show chains of hydrogen-bonded water molecules and a tendency to form closed cages at high concentration. Water clusters are stabilized primarily by a combination of water-water hydrogen bonding and Cu-water oxygen interactions. Stability is further enhanced by van der Waals interactions, electric field enhancement of water-water bonding, and hydrogen bonding of water t…
We simulate the electron transport across the Au(111)-pentacene interface using non-equilibrium Green's functions and density-functional theory (NEGF-DFT), and calculate the bias-dependent electron transmission. We find that the electrical contact resistance is dominated by the formation of a Schottky barrier at the interface, and show that the conventional semiconductor transport models across Schottky barriers need to be modified in order to describe the simulation data. We present an extension of the conventional Schottky barrier transport model, which can describe our simulation results an…
Using single-crystal transistors, we have performed a systematic experimental study of electronic transport through oxidized copper/rubrene interfaces as a function of temperature and bias. We find that the measurements can be reproduced quantitatively in terms of the thermionic emission theory for Schottky diodes, if the effect of the bias-induced barrier lowering is included. Our analysis emphasizes the role of the coupling between metal and molecules, which in our devices is weak due to the presence of an oxide layer at the surface of the copper electrodes.
X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 and (Pr,Y)0.55Ca0.45CoO3 compositions reveal that the valence of praseodymium ions is stable and essentially +3 (Pr [4f 2]) in the metallic state, but abruptly changes when carriers localize approaching the oxidation state +4 (Pr [4f 1]). This mechanism appears to be the driving force of the metal-insulator transition. The ground insulating state of Pr0.5Ca0.5CoO3 is an homogeneous Co3.5-d state stabilized by a charge transfer from Pr to Co sites: 1/2Pr3+ + Co3.5 \to 1/2Pr3+2d + Co3.5-d, with 2d \approx 0.26 e-.
The electronic properties of interfaces between two different solids can differ strikingly from those of the constituent materials. For instance, metallic conductivity, and even superconductivity, have been recently discovered at interfaces formed by insulating transition metal oxides. Here we investigate interfaces between crystals of conjugated organic molecules, which are large gap undoped semiconductors, i.e. essentially insulators. We find that highly conducting interfaces can be realized with resistivity ranging from 1 to 30 kOhm square, and that, for the best samples, the temperature de…
Outstanding functional tunability underpinning metal-organic framework (MOF) confers a versatile platform to contrive next-generation chemical sensors, optoelectronics, energy harvesters and converters. We report a rare exemplar of a porous 2D nanosheet material, constructed from an extended 3D MOF structure. We develop a rapid supramolecular self-assembly methodology at ambient conditions, to synthesize readily-exfoliatable MOF nanosheets, functionalized in situ by adopting the Guest@MOF (Host) strategy. Nanoscale confinement of light-emitting molecules (as functional guest) inside the MOF po…
Defect engineering has arisen as a promising approach to tune and optimise the adsorptive performance of metal-organic frameworks. However, the balance between enhanced adsorption and structural stability remains an open question. Here both CO2 adsorption capacity and mechanical stability are calculated for the zirconium-based UiO-66, which is subject to systematic variations of defect scenarios. Modulator-dependence, defect concentration and heterogeneity are explored in isolation. Mechanical stability is shown to be compromised at high pressures where uptake is enhanced with an increase in d…
We report the development of a forcefield capable of reproducing accurate lattice dynamics of metal-organic frameworks. Phonon spectra, thermodynamic and mechanical properties, such as free energies, heat capacities and bulk moduli, are calculated using the quasi-harmonic approximation to account for anharmonic behaviour due to thermal expansion. Comparison to density functional theory calculations of properties such as Gr$\mathrm{\ddot{u}}$neisen parameters, bulk moduli and thermal expansion supports the accuracy of the derived forcefield model. Material properties are also reported in a full…
The title paper by Boopathi and Ramasamy reports a study on the crystal growth and characterization of dibromobis (L-proline)Cd(II) (1). Many points of criticism, concerning the crystal structure of (1) and the magnetic properties of (1) dibromo bis(L-proline)Zn(II) (2) and diiodo bis(2-aminopyridine)Cd(II) (3) are reported to show that compounds 1 to 3 are not soft magnets but instead diamagnetic solids.
