A novel strategy for post-synthesis amine borane functionalization of MOFs under gas-solid phase transformation, utilizing gaseous diborane, is reported. The covalently confined amine borane derivative decorated on the framework backbone is stable when preserved at low temperature, but spontaneously liberates soft chemical hydrogen at room temperature, leading to the development of an unusual borenium type species (-NH=BH2+ ) ion-paired with a hydroborate anion. Furthermore, the unsaturated amino borane (-NH=BH2 ) and the μ-iminodiborane (-μ-NHB2 H5 ) were detected as final products. A combination of DFT based molecular dynamics simulations and solid state NMR spectroscopy, utilizing isotopically enriched materials, were undertaken to unequivocally elucidate the mechanistic pathways for H2 liberation.

Two-dimensional networks inspired by graphene are of prime importance in nanoscience. We present a computational study of an infinite molecular sheet confined on a water surface to assess its properties and formation mechanism. Terpyridine-based ligand molecules are interlinked by Zn ions to form an extended 2D metal-organic framework. We show that the network is stable on the water surface, and that the substrate affects the dynamic properties of the sheet, exhibiting a confining effect and flattening the sheet by 30%. We use metadynamics to characterize the process of network formation and breaking and determine an intra-network binding energy of 143 kJ mol−1. Based on this mechanistic insight we propose that the 2D network strength can be tuned by varying the rigidity of the ligand through its chemical structure.

Although large efforts have been dedicated to studying two-dimensional materials for catalysis, a rationalization of the associated trends in their intrinsic activity has so far been elusive. In the present work we employ density functional theory to examine a variety of two-dimensional materials, including, carbon based materials, hexagonal boron nitride (h-BN), transition metal dichalcogenides (e.g. MoS2, MoSe2) and layered oxides, to give an overview of the trends in adsorption energies. By examining key reaction intermediates relevant to the oxygen reduction, and oxygen evolution reactions we find that binding energies largely follow the linear scaling relationships observed for pure metals. This observation is very important as it suggests that the same simplifying assumptions made to correlate descriptors with reaction rates in transition metal catalysts are also valid for the studied two-dimensional materials. By means of these scaling relations, for each reaction we also identify several promising candidates that are predicted to exhibit a comparable activity to the state-of-the-art catalysts.

Suitable corrosion inhibitors are of prime importance in order to prevent degradation of surfaces by oxidizing chemicals. In this work we studied ten symmetrical thiourea derivatives on aluminum and their efficacy in preventing oxidation by hydrochloric acid computationally and experimentally. We carried out DFT calculations of the inhibitors in both tautomer forms adsorbed on an aluminum-terminated alpha-alumina surface, focusing on the structure and energetics of adsorption as well as electronic properties. Chemisorption is dominated by electron transfer from the inhibitor S atom toward the surface as well as into the first few layers of the solid. We find that the aggregated amount of transferred charge is an important parameter of the system that correlates with the inhibition efficiency as determined with potentiodynamic measurements. The measurements indicate that the thiourea derivatives are cathodic-type inhibitors, which hinder the reduction of protons and thus indirectly the surface oxidation. This is rationalized with the formation of a positively charged layer on the surface that may repel protons. Our results may serve to further improve corrosion inhibitors on this technologically important surface.

Surfaces that efficiently catalyse the oxygen reduction reaction (ORR) are highly desirable for applications in energy utilization. Here, we computationally investigate the ORR on hexagonal boron nitride (h-BN) supported on Ni, Cu, and Co. We find a significant influence of the metal on the reaction energetics. In particular, h-BN/Cu is predicted to catalyse the ORR with a low overpotential, while on the other substrates the reaction is impeded by the formation of too stable surface hydroxyl species. Our results highlight trends in the reactivity of these heterostructures and may guide further rational design of O2-activating catalysts based on supported h-BN.

Two-dimensional molecular sheets are of prime interest in nanoscience and technology. A promising class of such materials is 2D metal–organic frameworks (MOFs), assembled by cross-linking precursors with metal ions. It was recently demonstrated that such MOFs can be synthesized from monomers confined at an air–water interface. In order to elucidate this process at the atomic scale, we study a large flat tris-terpyridine-derived molecule (TTPB) on a water surface using ab initio molecular dynamics. We investigate the properties of the molecule and examine its reaction with Zn ions from the liquid phase. The fluid substrate significantly stabilizes the adsorbate while maintaining sufficient conformational flexibility to allow dynamic rearrangement and chemical reactions. The successful uptake and binding of ions is the first step toward linking TTPB molecules to dimers and large 2D MOFs.

Chemisches Institut, Universitat Zurich, W Switzerland. E-mail: hberke@chem.uzh.ch; 6802 Institut für Anorganische Chemie und Struk Düsseldorf, Germany Department of Chemistry, University of Division, Lawrence Berkeley National L Institute at Berkeley, Berkeley, California 947 King Fahd University of Petroleum and Min † Electronic supplementary information synthesis of 2,6-H2azd), Fig. S1–S3 (mo incorporated different primary H2 bind isotherm and TGA spectra). CCDC crystallographic data in CIF or o 10.1039/c4ta04393f Cite this: J. Mater. Chem. A, 2014, 2, 18823

To improve the binding energy of hydrogen, incorporation of internally polarized organic units into metal–organic frameworks (MOFs) should be a promising strategy. In this study, two novel MOFs composed of internally polarized 2,6-azulenedicarboxylate (2,6-azd), termed MOF-649 [Zn2(2,6-azd)2(dabco), where dabco = 1,4-diazabicyclo[2.2.2]octane] and MOF-650 [Zn4O(2,6-azd)3], have been synthesized, and their crystal structures were determined by single-crystal X-ray diffraction analyses. Both materials displayed permanent microporosity, and the Brunauer–Emmett–Teller (BET) surface areas of MOF-649 and MOF-650 are estimated to be 910 and 2630 m2 g−1, respectively. The H2 adsorption measurements showed that MOF-650 adsorbs 14.8 mg g−1 of hydrogen at 77 K and 1 bar. The polarization effect of the azulene unit in the framework is supported by high initial isosteric heat of adsorption of 6.8 kJ mol−1 for MOF-650. A detailed computational analysis using density functional theory was carried out in order to investigate the structure and electronic properties of MOF-650 and subsequently to understand its site-specific interactions with hydrogen.

We validate a computational setup based on density functional theory to investigate hexagonal boron nitride (h-BN) monolayers grown on different transition metals exposing hexagonal surfaces. An extended assessment of our approach for the characterization of the geometrical and electronic structure of such systems is performed. Due to the lattice mismatch with the substrate, the monolayers can form Moiré-type superstructures with very long periodicities on the surface. Thus, proper models of these interfaces require very large simulation cells (more than 1,000 atoms) and an accurate description of interactions that are modulated with the specific registry of h-BN on the metal. We demonstrate that efficient and accurate calculations can be performed in such large systems using Gaussian basis sets and dispersion corrections to the (semi-)local density functionals. Four different metallic substrates, Rh(111), Ru(0001), Cu(111), and Ni(111), are explicitly considered, and the results are compared with previous experimental and computational studies.

Hexagonal boron nitride (h-BN) adsorbed on metal surfaces shows great promise for applications in nanoscience. Depending on the nature of the substrate, effects such as an extended corrugation of the monolayer can be observed and utilized, e.g. for the patterning of adsorbed molecules. Here we present an in-depth computational study of the structural and electronic properties of a 6 nm Moiré pattern formed by a rotated layer of h-BN on a Cu(111) surface. In contrast to related systems, the h-BN layer undergoes only minute structural changes upon adsorption. Nevertheless, the projected density of states at various atoms in the cell and the electrostatic potential above the surface are periodically modulated, leading to the experimentally observed electronic corrugation. We rationalize this observation with the variation in adsorption registry resulting in periodic changes of the lateral, rather than vertical, h-BN–Cu distances.

Suitable templates to steer the formation of nanostructure arrays on surfaces are indispensable in nanoscience. Recently, atomically thin sp(2)-bonded layers such as graphene or boron nitride (BN) grown on metal supports have attracted considerable interest due to their potential geometric corrugation guiding the positioning of atoms, metallic clusters or molecules. Here, we demonstrate three specific functions of a geometrically smooth, but electronically corrugated, sp(2)/metal interface, namely, BN/Cu(111), qualifying it as a unique nanoscale template. As functional adsorbates we employed free-base porphine (2H-P), a prototype tetrapyrrole compound, and tetracyanoquinodimethane (TCNQ), a well-known electron acceptor. (i) The electronic moirons of the BN/Cu(111) interface trap both 2H-P and TCNQ, steering self-organized growth of arrays with extended molecular assemblies. (ii) We report an effective decoupling of the trapped molecules from the underlying metal support by the BN, which allows for a direct visualization of frontier orbitals by scanning tunneling microscopy (STM). (iii) The lateral molecular positioning in the superstructured surface determines the energetic level alignment; i.e., the energy of the frontier orbitals, and the electronic gap are tunable.

Hexagonal boron nitride (h-BN) adsorbed on metal surfaces shows great promise for applications in nanoscience. Depending on the nature of the substrate, effects such as an extended corrugation of the monolayer can be observed and utilized, e.g. for the patterning of adsorbed molecules. Here we present an in-depth computational study of the structural and electronic properties of a 6 nm Moiré pattern formed by a rotated layer of h-BN on a Cu(111) surface. In contrast to related systems, the h-BN layer undergoes only minute structural changes upon adsorption. Nevertheless, the projected density of states at various atoms in the cell and the electrostatic potential above the surface are periodically modulated, leading to the experimentally observed electronic corrugation. We rationalize this observation with the variation in adsorption registry resulting in periodic changes of the lateral, rather than vertical, h-BN-Cu distances.

The size- and structure-dependence of the magnetic moment in Pd-n clusters (n = 13, 19, 38) was studied with density functional theory. We compare the Becke-Perdew gradient-corrected exchange-correlation functional with the parameterized meta-generalized gradient approximation functional by Zhao and Truhlar (M06-L). Although the former functional shows the expected quenching of the clusters' magnetic moment with increasing nuclearity, the latter one predicts a strongly increasing magnetic moment. In a series of fixed-spin calculations with the two functionals at different geometries, we observe a strong dependence of the magnetic moment on the cluster structure, where the untypically long metal-metal bonds predicted by the M06-L functional are a dominant influence on the stability of the high-spin cluster configurations. Furthermore, we observe differing behavior of the two functionals with respect to the magnetic moment as particular bonds in the cluster are strained, indicating that, in addition to the structural contribution, the description of exchange-correlation energy in the M06-L functional may intrinsically favor high magnetic moments in these Pd clusters. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 112: 113-120, 2012

Ultrathin films of boron nitride (BN) have recently attracted considerable interest given their successful incorporation in graphene nanodevices and their use as spacer layers to electronically decouple and order functional adsorbates. Here, we introduce a BN monolayer grown by chemical vapor deposition of borazine on a single crystal Cu support, representing a model system for an electronically patterned but topographically smooth substrate. Scanning tunneling microscopy and spectroscopy experiments evidence a weak bonding of the single BN sheet to Cu, preserving the insulating character of bulk hexagonal boron nitride, combined with a periodic lateral variation of the local work function and the surface potential. Complementary density functional theory calculations reveal a varying registry of the BN relative to the Cu lattice as origin of this electronic Moiré-like superstructure.

The performance of eight generalized gradient approximation exchange-correlation (xc) functionals is assessed by a series of scalar relativistic all-electron calculations on octahedral palladium model clusters Pd(n) with n = 13, 19, 38, 55, 79, 147 and the analogous clusters Au(n) (for n up through 79). For these model systems, we determined the cohesive energies and average bond lengths of the optimized octahedral structures. We extrapolate these values to the bulk limits and compare with the corresponding experimental values. While the well-established functionals BP, PBE, and PW91 are the most accurate at predicting energies, the more recent forms PBEsol, VMTsol, and VT{84}sol significantly improve the accuracy of geometries. The observed trends are largely similar for both Pd and Au. In the same spirit, we also studied the scalability of the ionization potentials and electron affinities of the Pd clusters, and extrapolated those quantities to estimates of the work function. Overall, the xc functionals can be classified into four distinct groups according to the accuracy of the computed parameters. These results allow a judicious selection of xc approximations for treating transition metal clusters.