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Geometry optimization Directory `calc_structure_optimization_ReaxFF`: calculation files of the structure optimization of all studied structures, done with ReaxFF. Directory `calc_structure_optimization_DFT`: validation calculation files of the ReaxFF-optimized structures using DFT optimization. Electronic structure calculations Directory `calc_electronic_properties_DFT`: calculation files of electronic structure calculations on the DFT level. Directory `calc_electronic_properties_DFTB`: calculation files of electronic structure calculations on the DFTB level Results Directory `structures_rigidly_twisted`: structure files in cif format of the rigidly twisted (flat) systems, labeled by their twist angle. Directory `structures_fully_optimized`: structure files in cif format of the fully ReaxFF-optimized systems, labeled by their twist angle. Directory `movies`: visualization of the change of the interlayer distance landscape and the strain fields with the twist angle. Additionally, the script `plot_interlayer_distance.py` is included, which was used to create the individual frames of the movie showing the interlayer distance.

The synthesis of homogeneous covalent organic framework (COF) thin films on the desired substrate with decent crystallinity, porosity, and uniform thickness has great potential for optoelectronic applications. We have used a solution- processable sphere transmutation process to synthesize 300±20 nm uniform COF thin films on a 2×2 cm2 TiO2-coated FTO surface. This process controls the nucleation of COF crystallites and molecular morphology that helps the nanospheres to arrange periodically to form homogeneous COF thin films. We have synthesized four COF thin films (TpDPP, TpEtBt, TpTab, and TpTta) with different functional backbones. In a close agreement between the experiment and density functional theory, the TpEtBr COF film showed the lowest optical bandgap (2.26 eV) and highest excited-state lifetime (8.52 ns) among all four COF films. Hence, the TpEtBr COF film can participate in efficient charge generation and separation. We constructed optoelectronic devices having a glass/FTO/TiO2/COF-film/Au architecture, which serves as a model system to study the optoelectronic charge transport properties of COF thin films under dark and illuminated conditions. The visible light with a calibrated intensity of 100 mW cm-2 was used for the excitation of COF thin films. All the COF thin films exhibit significant photocurrent after illumination with visible light in comparison to the dark. Hence, all the COF films behave as good photoactive substrates with minimal pin hole defects. The fabricated out-of-plane photodetector device based on the TpEtBr COF thin film exhibits high photocurrent density (2.65 ± 0.24 mA cm-2 at 0.5 V) and hole mobility (8.15±0.64 ×10-3 cm2 V-1 S- 1) compared to other as-synthesized films, indicating the best photoactive characteristics.

"ReaxFF_structure_optimization.zip": contains the inputs and outputs for all structure optimizations for ML, BL, and tBL systems using the Reax force field, performed using LAMMPS. " bilayer_verification_ReaxFF_with_DFT.zip": contains the inputs and outputs for verifying the results of the Reax force field by running DFT geometry optimization and total energy calculations in FHI-aims for the high-symmetry bilayer stackings. "QATK_band_structures_and_eff_mass.zip": contains the inputs and outputs of all calculations done via QuantumATK (QATK), including calculations for ML, BL, and tBL systems on DFT and DFTB level of theory. "TB_fit.zip": contains the Python scripts and input data (DFTB band structure) used to fit the TB Hamiltonians as described in the Methods section and shown in the Supplementary Material. "effective_masses_from_bands.zip": contains the extraction of the effective hole masses from the bands calculated at the DFTB level of theory in QATK.

Radionuclide migration is one of the key problems for the long-term safety of nuclear waste repositories. One possible mechanism to retard or prevent the migration of radionuclides from the repository to the biosphere is the adsorption onto mineral surfaces of the surrounding host rock. Clay rock formations such as the Opalinus Clay are being considered for potential sites for nuclear waste repositories, partly due to the strong sorption potential of clay minerals. Phyllosilicates, such as clay minerals or mica, have shown a high affinity for adsorption of various radionuclides in several experimental studies. However, mineral surfaces in natural environments are often subjected to reactions (e.g., dissolution) that may alter the surface nanotopography and, consequently, affect the overall adsorption process. Recently, it has been reported that the nanotopography of calcite surfaces leads to heterogonous sorption of europium due to differences in the atomic configuration of the adsorption sites [1]. In this study, we investigate the influence of surface site coordination on the adsorption energy barrier and the resulting overall distribution of radionuclide adsorption on the mineral surface. We utilize numerical methods to study the adsorption of Eu(OH)3 on a muscovite (001) surface with different nanotopographic structures. Density Functional Theory (DFT) calculations are performed to obtain the adsorption energy barriers of several surface sites present on muscovite. For each site, the adsorption energy is calculated based on a series of geometry optimizations with increasing Eu–site distance. The values of the site-specific adsorption energy barriers are then implemented in a Kinetic Monte Carlo (KMC) model based on a previous study [2]. In the KMC model, larger surface structures, such as steps or etch pits, are placed on the muscovite surface and a dissolution simulation is performed to create a realistic nanotopography. Based on the adsorption energy barriers obtained with DFT, Eu(OH)3 is adsorbed on the generated muscovite surface in a second KMC model step. The KMC model is then used to predict the distribution of adsorbed Eu(OH)3 and the temporal evolution of the adsorption. Using this combined numerical approach, we show the effect of surface site coordination on radionuclide adsorption reactions and the resulting adsorption heterogeneity on mineral surfaces at large scales.

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

A key problem for the long-term safety of nuclear waste repositories is radionuclide migration in the geosphere. The adsorption of radionuclides onto mineral surfaces of the surrounding host rock can provide an important mechanism to retard or prevent migration from the repository to the biosphere. Due to the strong sorption potential of clay minerals, clay rock formations such as the Opalinus Clay are being considered as potential sites for nuclear waste repositories. Phyllosilicates, such as clay minerals or mica, have shown a high affinity for the adsorption of various radionuclides in several experimental studies. In natural environments, mineral surfaces are exposed to reactions (e.g., dissolution) over long periods. These processes can lead to an alteration of the surface nanotopography, thereby affecting the adsorption efficiency. In a recent study, the authors report that the nanotopography of calcite surfaces leads to heterogonous sorption of europium due to differences in the atomic configuration of the adsorption sites [1]. In this study, we investigate the influence of muscovite surface site coordination on the adsorption energy barrier and the resulting overall distribution of radionuclide adsorption on the mineral surface. Numerical methods are applied to study the adsorption of Eu(OH)3 on a muscovite (001) surface with different nanotopographic structures. Density Functional Theory (DFT) calculations are performed for eleven surface sites present on muscovite to obtain the adsorption energy barriers. The adsorption energy barrier is calculated based on a series of geometry optimizations with increasing Eu–site distance. All site-specific adsorption energy barriers are then implemented in a Kinetic Monte Carlo (KMC) model developed based on a previous study [2]. Here, larger muscovite surface portions can be simulated with structures such as dissolution etch pits for a more realistic nanotopography. Eu(OH)3 is then adsorbed on the generated muscovite surface considering the adsorption energy barriers obtained from DFT calculations. The distribution of adsorbed Eu(OH)3 and the temporal evolution of the process can be simulated with KMC and linked to the surface structures. This combined numerical approach allows us to show the effects of surface site coordination on radionuclide adsorption reactions and the resulting adsorption heterogeneity on mineral surfaces at larger scales. References: [1] T. Yuan, S. Schymura, T. Bollermann, K. Molodtsov, P. Chekhonin, M. Schmidt, T. Stumpf, C. Fischer, Environ. Sci. Technol. 2021, 55, 15797–15809. [2] J. Schabernack, I. Kurganskaya, C. Fischer, A. Luttge, Minerals 2021, 11, 468.

In cove-edged zigzag graphene nanoribbons (ZGNR-C), one terminal CH group per length unit is removed on each zigzag edge, forming a regular pattern of coves which controls their electronic structure. Based on three structural parameters that unambiguously characterize the atomistic structure of ZGNR-C, we present a scheme that classifies their electronic state, i.e., if they are metallic, topological insulators or trivial semiconductors, for all possible widths N, unit lengths a and cove position offsets at both edges b, thus showing the direct structure-electronic structure relation. We further present an empirical formula to estimate the band gap of the semiconducting ribbons from N,a, and b. Finally, we identify all geometrically possible ribbon terminations and provide rules to construct ZGNR-C with well-defined electronic structure.

By performing a swarm-intelligent global structure search combined with first-principles calculations, a stable twodimensional (2D) AlB3 heterostructure with directed, covalent Al-B bonds forms due to a nearly perfect lattice match between 2D borophene and the Al(111) surface. The AlB3 heterosheet with the P6mm space group is composed of a planar Al(111) layer and a corrugated borophene layer, where the in-plane coordinates of Al covalently link with the corrugated B atoms. The resulting structure shows a similar interlayer interaction energy to that of the Al(111) surface layer to the bulk and high mechanical and thermal stability, possesses multiple Dirac points in the Brillouin zone with a remarkably high Fermi velocity of 1.09 × 106 m s-1, which is comparable to that of graphene. Detailed analysis of the electronic structure employing the electron localisation function and topological analysis of the electron density confirm the covalent Al-B bond with high electron localisation between the Al and B centres and with only little interatomic charge transfer. The combination of borophene with metal monolayers in 2D heterostructures opens the door to a rich chemistry with potentially unprecedented properties.

The β-emitting 99Tc isotope is a high-yield fission product in 235U and 239Pu nuclear reactors, raising special concern in nuclear waste management due to its long half-life and the high mobility of pertechnetate (TcO4−). In the conditions of deep nuclear waste repositories, retention of Tc is achieved via biotic and abiotic reduction of TcO4− to compounds like amorphous TcO2·xH2O precipitates. It is generally accepted that these precipitates have linear (Tc(μ O)2(H2O)2)n chains, with trans H2O. Although corresponding Tc Tc and Tc O distances have been obtained from Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, this structure is largely based on analogy with other compounds. Here, we combine Density-Functional Theory with EXAFS measurements of fresh and aged samples to show that, instead, TcO2·xH2O forms zigzag chains that undergo a slow aging process whereby they combine to form longer chains and, later, a tridimensional structure that might lead to a new TcO2 polymorph.

The repository contains the inputs and outputs of tight-binding (TB) calculations of ZGNR-C based on PythTB. For each analysed structure one subdirectory is created, labelled as "N-ZGNR-C_a_b_inv_cellα_termination". This corresponds to a N-ZGNR-C(a,b) with inversion center at the unit cell boundary S or L ("inv"), unit cell angle α ("cellα": 60°, 90°, or 120°) and a given unit cell termination (armchair, zigzag or bearded). Each directory contains the atomic structure in xsf and cif format, the PythTB input file, the output as a json file, and the calculated band structure as image file. The json file contains the band structure information (path and eigenvalues), the raw Zak phase in units of π without modulo 2, and the final ℤ2 invariant.

Dataset of outputs produced by DFT and KMC simulation described in the associated paper. KMC data: Adsorption distribution (Ad_mov_01.pdb to Ad_mov_10.pdb) Surface nanotopography (surface_1.pdb) Statistic files for dissolution and adsorption (Ad_num.txt, Ad_Sites_Stat.txt, sites_stat_1.txt, diss_num.txt) Input files (testmusc9_KMC_Mica_1_6.inp, EuAdsorption_2_0.inp) Excel files for adsorption evaluation (Adsorption_Results_File), input energy calculation (EnergyParameterCalc) and site sorting (Site-INDL-Sorting) DFT data: Excel file adsorption energy barriers (Adsorption_Energy_Barrier) Site adsorption energies (.cvs files) Site adsorption trajectories (.xyz files) Excel file for the estimation of the desorption factor

Single iron atom and nitrogen-codoped carbon (Fe–N–C) electrocatalysts, which have great potential to catalyze the kinetically sluggish oxygen reduction reaction (ORR), have been recognized as the most promising alternatives to the precious metal platinum. Unfortunately, the ORR properties of the existing Fe–N–C catalysts are significantly hampered by the inferior accessibility and intrinsic activity of FeN4 moieties. Here, we constructed densely exposed surface FeN4 moieties on a hierarchically porous carbon (sur-FeN4-HPC) by Fe ion anchoring and a subsequent pyrolysis strategy using the nitrogen- doped hierarchically porous carbon (NHPC) as the scaffold. The high surface area of the NHPC with abundant surface Fe anchoring sites enabled the successful fabrication of densely accessible FeN4 active moieties (34.7 􏰁x 10^19 sites g^-􏰂1) on sur-FeN4-HPC. First-principles calculations further suggested that the edge effect could regulate the electronic structure of the single Fe site, hence promoting the intrinsic ORR activity of the FeN4 moiety. As a result, the sur-FeN4-HPC electrocatalyst exhibited excellent ORR activity in acidic media with a high half-wave potential of 0.83 V (vs. the reversible hydrogen electrode). We further examined sur-FeN4-HPC as a cathode catalyst in proton exchange membrane fuel cells (PEMFCs). The membrane electrode assembly delivered a high current density of 24.2 mA cm􏰂2 at 0.9 ViR-free (internal resistance-compensated voltage) under 1.0 bar O2 and a maximum peak power den- sity of 0.412 W cm􏰂2 under 1.0 bar air. Importantly, the catalyst demonstrated promising durability during 30000 voltage cycles under harsh H2 and air conditions. The PEMFC performance of sur-FeN4-HPC outperforms those of the previously reported Fe–N–C electrocatalysts. The engineering of highly acces- sible and dense surface FeN4 sites on sur-FeN4-HPC offers a fruitful pathway for designing high- performance electrocatalysts for different electrochemical processes.

For some years now, research on adsorptive separation of hydrogen isotopes such as deuterium (D) and tritium (T) has been evolving with a view toward nuclear fusion. Experimental and theoretical investigations show that H2 strongly binds to undercoordinated Cu+ sites and more strongly when one H2O ligand is added to Cu+.[1] To understand the vibrational behavior that drives the hydrogen isotopologue selectivity of Cu+(H2O)(H2)2 formation, harmonic and anharmonic vibrational spectra have been computed and compared to infrared photodissociation (IRPD) spectroscopy results from the gas phase. Our calculations show that geometries and harmonic frequencies at the MP2/def2-TZVPP level match CCSD(T)/aug-cc-pVTZ ones very closely. Scaling the harmonic frequencies by a factor of 0.95 [2] improves the agreement with the available experimental data, but fails to produce the combination bands. By contrast, anharmonic VPT2 calculations at the MP2/def2-TZVPP level not only predict these bands but they also reproduce the experimental frequencies very well. In addition to that, we found a similar structure for Cu+(H2O)(H2)2 as a previous study[1]: a planar arrangement with C2v symmetry (Figure 1) but with a significantly shorter Cu+–H2 bond length (1.62 Å vs 1.71 Å). Finally, the obtained results show that CCSD(T) calculations are not required and VPT2 frequencies at the MP2/def2-TZVPP level are identified as a particularly good compromise for future modeling of the vibrational properties driving isotopologue-selective H2 adsorption at undercoordinated Cu+ sites. Reference [1] Paul R. Kemper et al., J. Am. Chem. Soc., 120:51,13494-13502 (1998) [2] N. Heine et al., J. Phys. Chem. Lett., 6(12):2298-2304 (2015)

Technetium is the lightest element without a stable isotope. The β‑emitting ⁹⁹Tc is especially relevant for nuclear waste management due to its long half-life (ca. 2.1×10⁵ years) and relatively high formation yield (≥6%) in ²³⁵U and ²³⁹Pu nuclear reactors. In this context, redox reactions at mineral/water interfaces are crucial for the safety of nuclear waste repositories. In the absence of complexing agents, Tc exists in water as Tc(VII) and Tc(IV). The former predominates in non-reducing conditions as TcO₄⁻(aq), which is highly mobile in the environment due to its solubility and weak interaction with adsorbents. Studies show that Fe(II) minerals can reduce Tc(VII) to Tc(IV), which is then immobilized by adsorption onto or incorporation into the oxidized Fe mineral and by precipitation as TcO₂·xH₂O. However, even in the simpler case (precipitation) the structure of TcO₂·xH₂O remains controversial. Lukens et al. [1] demonstrated that, despite being amorphous, TcO₂·xH₂O has a well-defined local structure. Based on EXAFS measurements, they proposed that TcO₂·xH₂O forms linear chains of equally spaced edge-sharing TcO₄(H₂O)₂ octahedra, with terminal H₂O ligands at the apical positions. Vichot et al. [2] obtained similar results but, despite having extracted only one Tc‑Tc distance from the EXAFS, proposed that Tc atoms would be separated by shorter and longer alternating distances as in the monoclinic TcO₂ crystal. More recently, Yalçintaş et al. [3] showed that both models can be fitted equally well to the EXAFS and, thus, the TcO₂·xH₂O structure remained unsolved. In this work, we use density functional theory (DFT) to investigate the polymeric TcO₂·xH₂O structure. Our calculations reveal that, in contrast to previous models, a zigzag configuration with the terminal H₂O groups at neighboring positions of the octahedra is more likely. The zigzag configuration is energetically more favored and results in a better agreement with the EXAFS measurement. [1] Lukens et al. (2002), Environ. Sci. Technol. 36, 1124-1129. [2] Vichot et al. (2002), Radiochim. Acta 90, 575-579. [3] Yalçintaş et al. (2016), Dalton Trans. 45, 17874-17885.

Key questions for the study of chemical bonding in actinide compounds are the degree of covalency that can be realized in the bonds to different donor atoms and the relative participation of 5f and 6d orbitals. A manifold of theoretical approaches is available to address these questions, but hitherto no comprehensive assessments are available. Here, we present an in-depth analysis of the metal–ligand bond in a series of actinide metal–organic compounds of the [M(salen)₂] type (M = Ce, Th, Pa, U, Np, Pu) with the Schiff base N,N′-bis(salicylidene)ethylenediamine (salen). All compounds except the Pa complex (only included in the calculations) have been synthesized and characterized experimentally. The experimental data are then used as a basis to quantify the covalency of bonds to both N- and O-donor atoms using simple electron-density differences and the quantum theory of atoms in molecules (QTAIM) with interacting quantum atoms. In addition, the orbital origin of any covalent contributions was studied via natural population analysis (NPA). The results clearly show that the bond to the hard, charged O-donor atoms of salen is consistently not only stronger but also more covalent than bonds to the softer N-donor atoms. On the other hand, in a comparison of the metals, Th shows the most ionic bond character even compared to its 4f analogue Ce. A maximum of the covalency is found for Pa or Np by their absolute and relative covalent bond energies, respectively. This trend also correlates with a significant f- and d-orbital occupation for Pa and Np. These results underline that only a comprehensive computational approach is capable of fully characterizing the covalency in actinide complexes.

The electronic properties of π -conjugated two-dimensional (2D) polymers near the Fermi level are determined by structural topology and chemical composition. Thus tight-binding (TB) calculations of the corresponding fundamental network can be used to explore the parameter space to find configurations with intriguing properties before designing the atomistic 2D polymer network. The vertex-transitive fes lattice, which is also called a square-octagon, 4-8, or 4.82 lattice, is rich in interesting topological features including Dirac points and flat bands. Herein, we study its electronic and topological properties within the TB framework using representative parameters for chemical systems. Secondly, we demonstrate that the rational implementation of band structure features obtained from TB calculations in 2D polymers is feasible with a family of 2D polymers possessing fes structure. A one-to-one band structure correspondence between the fundamental network and 2D polymers is found. Moreover, changing the relative length of linkers connecting the triangulene units in the 2D polymers reflects tuning of hopping parameters in the TB model. These perturbations allow sizable local band gaps to open at various positions in the Brillouin zone. From analysis of the Berry curvature flux, none of the polymers exhibits a large topologically nontrivial band gap. However, we find a particular configuration of semimetallic characteristics with separate electron and hole pockets, which possess very low effective masses both for electrons (as small as m∗e = 0.05) and for holes (as small as m∗h = 0.01).

Based on first principles calculations, we report the design of three two-dimensional (2D) binary honeycomb-kagome polymers composed of B- and N-centered heterotriangulenes in the same plane with a periodically alternate arrangement as in hexagonal boron nitride. The 2D binary polymers with donor-acceptor characteristics, are semiconductors with a direct band gap of 1.98-2.28 eV. The enhanced in-plane electron conjugation contributes to high charge carrier mobilities for both electrons and holes, about 6.70 and 0.24 × 103 cm2 V-1 s-1, respectively, for the 2D binary polymer with carbonyl bridges (2D CTPAB). With appropriate band edge alignments to match the water redox potentials and pronounced light adsorption for the ultraviolet and visible range of spectra, 2D CTPAB is predicted to be an effective individual photocatalyst to promote overall water splitting.

We study the isotopologue-selective binding of dihydrogen at the undercoordinated boron site of undeca-X-closo-dodecaborates B₁₂X₁₁⁻ (X = H, F, Cl, Br, I, CN) using ab initio quantum chemistry. With a Gibbs free energy of H₂ attachment reaching up to 80 kJ∙mol⁻¹ (ΔG at 300 K for X = CN), these sites are even more attractive than most undercoordinated metal centers studied so far. We thus believe that they can serve as an edge case close to the upper limit of isotopologue-selective H₂ adsorption sites. Differences of the zero-point energy of attachment average 5.0 kJ∙mol⁻¹ between D₂ and H₂ and 2.7 kJ mol⁻¹ between HD and H₂, resulting in hypothetical isotopologue selectivities as high as 2.0 and 1.5, respectively, even at 300 K. Interestingly, even though attachment energies vary substantially according to the chemical nature of X, isotopologue selectivities remain very similar. We find that the H–H activation is so strong that it likely results in the instantaneous heterolytic dissociation of H₂ in all cases (except, possibly, for X = H), highlighting the extremely electrophilic nature of B₁₂X₁₁⁻ despite its negative charge. Unfortunately, this high reactivity also makes B₁₂X₁₁⁻ unsuitable for practical application in the field of dihydrogen isotopologue separation. Thus, this example stresses the two-edged nature of strong H₂ affinity, yielding a higher isotopologue selectivity on the one hand but risking dissociation on the other, and helps define a window of adsorption energies into which a material for selective adsorption near room temperature should ideally fall.

Efficient photoelectrocatalytic (PEC) water splitting could be the solution for environmental and energy problems on planet Earth. Here, we explore 2D palladium thiophosphate Pd3(PS4)2, which is a promising photocatalyst absorbing light in the visible range. We obtain a few-layer Pd3(PS4)2 through lithium-assisted exfoliation from the bulk phase and characterize it employing Raman spectroscopy, XPS, AFM, and STM combined with DFT calculations. The measured band gap for as-obtained few-layer Pd3(PS4)2 is 2.57 eV (indirect) and its band edges span the electrochemical potentials of the hydrogen and oxygen evolution reactions. The performance in the water-splitting reaction is studied under acidic, neutral, and alkaline conditions under violet irradiation at 420 nm. 2D palladium phosphochalcogenides semiconductor with bifunctional electrocatalytic and photoelectrocatalytic properties. Our results show competitive performance compared with industrial Pt/C catalysts for solar-driven water splitting under acidic and alkaline conditions.

This dataset contains output files of DFT and DLPNO calculations of the investigated species. At the DFT level of theory full geometry optimizations and frequency analysis where done. At DLPNO level of theory single point calculations were done.

We systematically explore the stability and properties of [B₁₂X₁₁NG]⁻ adducts resulting from the binding of noble gas atoms to anionic [B₁₂X₁₁]⁻ clusters in the gas phase of mass spectrometers. [B₁₂X₁₁]⁻ can be obtained by stripping one X⁻ off the icosahedral closo-dodecaborate dianion [B₁₂X₁₂]²⁻. We study the binding of the noble gas atoms He, Ne, Ar, Kr and Xe to [B₁₂X₁₁]⁻ with substituents X = F, Cl, Br, I, CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B₁₂(CN)₁₁Xe]⁻. The predicted B–NG equilibrium distance in the complexes with Ar, Kr and Xe is only 0.10 to 0.25 Å longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B₁₂ cage is observed.

First-principles calculations predicted electronic topological properties for 2D honeycomb–kagome polymers, which have been now confirmed experimentally thanks to improvements in on-surface synthesis.

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ~1.5 µm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate an efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN ) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ~60 µm 2 and tunable thickness from 6 to 16 nm. The molecular‐level structures are clearly resolved by high‐resolution transmission electron microscopy (HR‐TEM) and selected‐area electron diffraction (SAED) which are supported by density functional theory (DFT) calculation. Due to the high crystallinity, facile thin‐film processability, high mechanical stability as well as the incorporation of electroactive porphyrin monomers, a hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning‐erasing‐forgetting memory process. Pulsed voltage input induces the polarization of the film that is critical to emulate the potentiation of the neuronal membrane. This work paves the way to develop highly crystalline 2D COF thin film as an easy‐to‐fabricate active component applicable for CMOS‐compatible neuromorphic computing.

While the isotope-dependent hydrogen permeability of graphene membranes at ambient condition has been demonstrated, the underlying mechanism has been controversially discussed during the past five years. The reported room temperature H+-over-D+ selectivity is 10, much higher than in any competing method. Yet, it has not been understood how protons can penetrate through graphene membranes – proposed hypotheses include atomic defects and local hydrogenation. However, neither could explain both the high permeability and high selectivity of the atomically thin membranes. Here, we confirm that ideal graphene is quasi-impermeable to protons, yet the most common defect in sp2 carbons, the topological Stone-Wales defect, has a calculated penetration barrier below 1 eV and H+-over-D+ selectivity of 7 at room temperature and, thus, explains all experimental results on graphene membrane that are available to date. We challenge the competing explanation, local hydrogenation, which also reduces the penetration barrier, but shows significantly lower isotope selectivity

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 mm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN ) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ≈60 mm2 and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning-erasing-forgetting memory process.

Visible-light-driven hydrogen (H2) production from water is a promising strategy to convert and store solar energy as chemical energy. Covalent organic frameworks (COFs) are front runners among different classes of organic photocatalysts. The photocatalytic activity of COFs depends on numerous factors such as the electronic band gap, crystallinity, surface area, exciton migration, stability of transient species, charge separation and transport, etc. However, it is challenging to fine tune all of these factors simultaneously to enhance the photocatalytic activity. Hence, in this report, an effort has been made to understand the interplay of these factors and identify the key factors for efficient photocatalytic H2 production through a structure−property−activity relationship. Careful molecular engineering allowed us to optimize all of the above plausible factors impacting the overall catalytic activities of a series of isoreticular COFs. The present study determines three prime factors: light absorption, charge carrier generation, and its transport, which influence the photocatalytic H2 production of COFs to a much greater extent than the other factors.

There are around 200 two-dimensional (2D) networks with different topologies. The structural topology of a 2D network defines its electronic structure. Including the electronic topological properties, it gives rise to Dirac cones, topological flat bands and topological insulators. In this Tutorial Review, we show how electronic properties of 2D networks can be calculated by means of a tight-binding approach, and how these properties change when 2nd-neighbour interactions and spin-orbit coupling are included. We explain how to determine whether or not the resulting electronic features have topological signatures by calculation of Chern numbers, Z2 invariants, and by the nanoribbon approach. This tutorial gives suggestions how such topological properties could be realized in explicit atomistic chemical 2D systems made of molecular frameworks, in particular in 2D polymers, where the edges and vertices of a given 2D net are substituted by properly selected molecular building blocks and stitched together in such a way that long-range π-conjugations is retained.

Recent experiments have demonstrated transport and separation of hydrogen isotopes in layered materials, such as hexagonal boron nitride and molybdenum disulphide. Here, based on first-principles calculations combined with well-tempered metadynamics simulations, we report the chemical interactions and mobility of protons (H+) and protium (H atoms) in the interstitial space of these layered materials. We show that both H+ and H can be transported between the layers of h-BN and MoS2 with low free energy barriers, while they are immobilized in graphite, in accordance with the experimental observations. In h-BN and MoS2, the transport mechanism involves a hopping process between the adjacent layers, which is assisted by the low- energy phonon shear modes. Defects present in MoS2 suppress the transport and act as traps for H species.

Switchable pillared layer metal–organic frameworks M₂(2,6-ndc)₂(dabco) (DUT-8(M), M = Ni, Co, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]octane, DUT – Dresden University of Technology) were synthesised in two different crystallite size regimes to produce particles up to 300 μm and smaller particles around 0.1 μm, respectively. The textural properties and adsorption-induced switchability of the materials, obtained from both syntheses, were studied by physisorption of N2 at 77 K, CO2 at 195 K and n-butane at 273 K, revealing pronounced differences in adsorption behavior for Ni and Co analogues. While the smaller nano-sized particles (50–200 nm) are rigid and show no gating transitions confirming the importance of crystallite size, the large particles show pronounced switchability with characteristic differences for the two metals resulting in distinct recognition effects for various gases and vapours. Adsorption of various vapours demonstrates consistently a higher energetic barrier for the “gate opening” of DUT-8(Co) in contrast to DUT-8(Ni), as the “gate opening” pressure for Co based material is shifted to a higher value for adsorption of dichloromethane at 298 K. Evaluation of crystallographic data, obtained from single crystal and powder X-ray diffraction analysis, showed distinct geometric differences in the paddle wheel units of the respective MOFs. These differences are further disclosed by solid-state UV-vis, FT-IR and Raman spectroscopy. Magnetic properties of DUT-8(Co) and DUT-8(Ni) were investigated, indicating a high-spin state for both materials at room temperature. Density functional theory (DFT) simulations confirmed distinct energetic differences for Ni and Co analogues with a higher energetic penalty for the structural “gate opening” transformation for DUT-8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs.

New 2D materials open access to a whole new world of compounds and properties. Graphene monolayer is such a material, since it has special electron transport features due to its honeycomb topology. Apart from the honeycomb net, there are many more topologies, which promise a manifold of new properties, e.g. the kagomé or the Lieb lattice. As recently shown in the case of the kagomé net, 2D polymers (covalent organic frameworks) can be designed in a way, that their geometric and electronic structures match the desired topology.[1] Other nets, e.g. the Lieb lattice, can at the moment only be realized as optical lattices or via adsorption of molecules on a surface.[2] In this project, we want to work out the relation between topology and electronic properties. For this purpose, we employ a tight-binding model. In Fig. 1, exemplary results for the aforementioned kagomé and Lieb lattices are shown. Based on these findings, we want to propose new 2D polymers with the desired structures and new properties using density- functional theory. [1] Y. Jing, T. Heine, J. Am. Chem. Soc. 141, 2, 743 (2019) [2] S. Mukherjee et al., Phys. Rev. Lett. 114, 245504 (2015); S. Taie et al., Sci. Adv. 1, e1500854 (2015); M. R. Slot et al., Nat. Phys. 13, 672 (2017)

In organic photovoltaics, porphyrins (PPs) are among the most promising compounds owing to their large absorption cross section, wide spectral range, and stability. Nevertheless, a precise adjustment of absorption band positions to reach a full coverage of the so-called green gap has not been achieved yet. We demonstrate that a tuning of the PP Q- and the Soret bands can be done using a computational approach where substitution patterns are optimized in silico. The Most promising candidate structures were then synthesized. The experimental UV/Vis data for the solvated compounds were in excellent agreement with the theoretical predictions. By attaching further functionalities, which allow using the PP chromophores as linkers for the assembly of metal-organic frameworks (MOFs), we were additionally able to exploit packing effects resulting in pronounced red shifts, which allowed to further optimizing the photophysical properties of PP assemblies. Finally, we use a layer-by-layer method to assemble the PP linkers into surface-mounted MOFs (SURMOFs), thus obtaining high optical quality, homogeneous and crystalline multilayer films. Experimental results are in full accord with the calculations, demonstrating a huge potential of computational screening methods in the tailoring of MOF and SURMOF photophysical properties.

Sulfur-containing deposits form on a monolithic V2O5-WO3/TiO2 (VWT) catalyst during SCR-DeNOx with NH3 at 473 and 523 K and pressures up to 500 kPa in the presence of SO2 with sulfate contents of 1.7 to 13.0 wt.-%. Using TGA and DRIFTS, these deposits are determined to be mainly NH4HSO4 for SCR temperatures > 523 K. At lower temperatures, (NH4)2SO4 is formed. The thermal stability of NH4HSO4 supported on different transition metal oxides including V2O5, WO3, TiO2, MoO3 and Al2O3 varies with decomposition temperatures from 620 to 820 K. Using DFT calculations, it is show that the thermal stability of supported NH4HSO4 is mainly determined by hydrogen bonding of the HSO4- anions with the metal oxide surface. Increasing electronegativity of the metal atoms of the support oxide leads to weakening of the S-O bonds in the HSO4- anions and to lower decomposition temperatures of the supported NH4HSO4.