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The prediction of new compounds via crystal structure prediction may transform how the materials chemistry community discovers new compounds. In the prediction of inorganic crystal structures there are three distinct classes of prediction: performing crystal structure prediction via heuristic algorithms, using a range of established crystal structure prediction codes, an emerging community using generative machine learning models to predict crystal structures directly and the use of mathematical optimisation to solve crystal structures exactly. In this work, we demonstrate the combination of heuristic and generative machine learning, the use of a generative machine learning model to produce the starting population of crystal structures for a heuristic algorithm and discuss the benefits, demonstrating the method on eight known compounds with reported crystal structures and three hypothetical compounds. We show that the integration of machine learning structure generation with heuristic structure prediction results in both faster compute times per structure and lower energies. This work provides to the community a set of eleven compounds with varying chemistry and complexity that can be used as a benchmark for new crystal structure prediction methods as they emerge.

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal-organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognize and order multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

We describe the hydroxyl and mixed hydroxyl-water structures formed on a stepped copper surface following the reaction of adsorbed O with water at a low temperature and compare them to the structures found previously on plane copper surfaces. Thermal desorption profiles, STM, and low-energy electron diffraction show that water reacts with O at temperatures below 130 K on Cu(511). Two well-defined phases appear as the OH/H 2 O layer is heated to desorb excess water, a 1OH:1H 2 O phase and a pure OH phase. The 1OH:1H 2 O structure consists of 1D chains binding across two adjacent copper steps, with a double period along the step. Electronic structure calculations show that the structure has a zigzag chain of water along the terrace, stabilized by hydrogen bonds to OH groups adsorbed in the step bridge sites. This structure binds OH in its favored site and is similar to the structure observed on other open faces of Cu and Ni, suggesting that this structural arrangement may be common on other surfaces that have steps or rows of close packed metal atoms. The hydroxyl/water chains decompose at 210 K to leave OH adsorbed in the Cu step bridge site, with some forming H-bonded trimers that bridge between two Cu steps. Heating the surface causes hydroxyl to disproportionate near 300 K, desorbing water to leave chemisorbed O., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The crystal structures of known materials contain the information about the interatomic interactions that produced these stable compounds. Similar to the use of reported protein structures to extract effective interactions between amino acids, that has been a useful tool in protein structure prediction, we demonstrate how to use this statistical paradigm to learn the effective inter-atomic interactions in crystalline inorganic solids. By analyzing the reported crystallographic data for inorganic materials, we have constructed statistically derived proxy potentials (SPPs) that can be used to assess how realistic or unusual a computer-generated structure is compared to the reported experimental structures. The SPPs can be directly used for structure optimization to improve this similarity metric, that we refer to as the SPP score. We apply such optimization step to markedly improve the quality of the input crystal structures for DFT calculations and demonstrate that the SPPs accelerate geometry optimization for three systems relevant to battery materials. As this approach is chemistry-agnostic and can be used at scale, we produced a database of all possible pair potentials in a tabulated form ready to use., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Computational exploration of the compositional spaces of materials can provide guidance for synthetic research and thus accelerate the discovery of novel materials. Most approaches employ high-throughput sampling and focus on reducing the time for energy evaluation for individual compositions, often at the cost of accuracy. Here, we present an alternative approach focusing on effective sampling of the compositional space. The learning algorithm PhaseBO optimizes the stoichiometry of the potential target material while improving the probability of and accelerating its discovery without compromising the accuracy of energy evaluation., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

Crystalline materials enable essential technologies, and their properties are determined by their structures. Crystal structure prediction can thus play a central part in the design of new functional materials 1,2 . Researchers have developed efficient heuristics to identify structural minima on the potential energy surface 3-5 . Although these methods can often access all configurations in principle, there is no guarantee that the lowest energy structure has been found. Here we show that the structure of a crystalline material can be predicted with energy guarantees by an algorithm that finds all the unknown atomic positions within a unit cell by combining combinatorial and continuous optimization. We encode the combinatorial task of finding the lowest energy periodic allocation of all atoms on a lattice as a mathematical optimization problem of integer programming 6,7 , enabling guaranteed identification of the global optimum using well-developed algorithms. A single subsequent local minimization of the resulting atom allocations then reaches the correct structures of key inorganic materials directly, proving their energetic optimality under clear assumptions. This formulation of crystal structure prediction establishes a connection to the theory of algorithms and provides the absolute energetic status of observed or predicted materials. It provides the ground truth for heuristic or data-driven structure prediction methods and is uniquely suitable for quantum annealers 8-10 , opening a path to overcome the combinatorial explosion of atomic configurations., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The choice of metal and linker together define the structure and therefore the guest accessibility of a metal-organic framework (MOF), but the large number of possible metal-linker combinations makes the selection of components for synthesis challenging. We predict the guest accessibility of a MOF with 80.5 % certainty based solely on the identity of these two components as chosen by the experimentalist, by decomposing reported experimental three-dimensional MOF structures in the Cambridge Structural Database into metal and linker and then learning the connection between the components' chemistry and the MOF porosity. Pore dimensions of the guest-accessible space are classified into four ranges with three sequential models. Both the dataset and the predictive models are available to download and offer simple guidance in prioritization of the choice of the components for exploratory MOF synthesis for separation and catalysis based on guest accessibility considerations., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

We report the aperiodic titanate Ba 10 Y 6 Ti 4 O 27 with a room-temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low-thermal-conductivity oxides is metastable and located within a quaternary phase field that has been previously explored. Its isolation thus requires a precisely defined synthetic protocol. The necessary narrowing of the search space for experimental investigation was achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that would favour synthetically accessible new compositions, and assessment of their properties with machine-learning models., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nickel is an active catalyst for hydrogenation and re-forming reactions, with the reactions showing a strong dependence on the surface exposed. Here, we describe the mixed hydroxyl-water phases formed during water dissociation on Ni(110) using scanning tunneling microscopy and low-current low-energy electron diffraction. Water dissociation starts between 150 and 180 K as the H-bond structure evolves from linear one-dimensional (1D) chains of intact water into a two-dimensional (2D) network containing short rows of face-sharing hexagonal rings. As further water desorbs, the hexagonal rows adopt a local (2 × 3) arrangement, forming small, disordered domains separated by strain relief features. Decomposition of this phase occurs near 220 K to form linear 1D structures consisting of flat, zigzag water chains, with each water stabilized by donating one H to hydroxyl to form a branched chain structure. The OH-H 2 O chains repel each other, with the saturation layer ordering into a (2 0, 1 4) structure that decomposes to OH near 245 K as further water desorbs. The structure of the mixed OH/H 2 O phases is discussed and contrasted with those found on the related Cu(110) surface, with the differences attributed to strain in the 2D H-bond network caused by the short Ni lattice spacing and strong bond to OH/H 2 O., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Flexible metal-organic frameworks (MOFs) undergo structural transformations in response to physical and chemical stimuli. This is hard to control because of feedback between guest uptake and host structure change. We report a family of flexible MOFs based on derivatized amino acid linkers. Their porosity consists of a one-dimensional channel connected to three peripheral pockets. This network structure amplifies small local changes in linker conformation, which are strongly coupled to the guest packing in and the shape of the peripheral pockets, to afford large changes in the global pore geometry that can, for example, segment the pore into four isolated components. The synergy among pore volume, guest packing, and linker conformation that characterizes this family of structures can be determined by the amino acid side chain, because it is repositioned by linker torsion. The resulting control optimizes noncovalent interactions to differentiate the uptake and structure response of host-guest pairs with similar chemistries.

We present a new method of evolving crystal structures for crystal structure prediction. The method of chemically directed structure evolution uses chemical models to quantify the environment of atoms and vacancy sites in a crystal structure, with that information used to inform how to modify the structure to make a move on the potential energy surface. We have developed a method of chemically directed swapping, where we swap atoms in the least favourable chemical environments. This method has been implemented in the crystal structure prediction code ChemDASH (Chemically Directed Atom Swap Hopping), which explores the potential energy surface using a basin-hopping approach, and evaluates chemical environments using either the bond valence sum or electrostatic site potential. ChemDASH has a variety of methods of initialising structures, optimising structures, and swapping atoms. This gives ChemDASH the flexibility to be applied to a wide range of systems. We used ChemDASH to examine the effectiveness of the directed swapping method. Directed swapping finds the ground states of TiO2 and SrTiO3 faster than random (non-directed) swapping, but is less effective than random swapping for Y2Ti2O7.

Hydration layers play a key role in many technical and biological systems, but our understanding of these structures remains very limited. Here, we investigate the molecular processes driving hydration of a chiral metal-organic surface, bitartrate on Cu(110), which consists of hydrogen-bonded bitartrate rows separated by exposed Cu. Initially water decorates the metal channels, hydrogen bonding to the exposed O ligands that bind bitartrate to Cu, but does not wet the bitartrate rows. At higher temperature, water inserts into the structure, breaks the existing intermolecular hydrogen bonds, and changes the adsorption site and footprint. Calculations show this process is driven by the creation of stable adsorption sites between the carboxylate ligands, to allow hydration of O-Cu ligands within the interior of the structure. This work suggests that hydration of polar metal-adsorbate ligands will be a dominant factor in many systems during surface hydration or self-assembly from solution.

Materials that bind strongly to water structure the contact layer, modifying its chemical and physical properties in a manner that depends on the symmetry and reactivity of the surface. Although detailed models have been developed for several inert surfaces, much less is known about reactive surfaces, particularly those with a symmetry different from that of ice. Here we investigate water adsorption on a rectangular surface, Ni(110), an active re-forming catalyst that interacts strongly with water. Instead of forming a network of H-bonded cyclic rings, water forms flat 1D water chains, leaving half the Ni atoms exposed. Second layer water also follows the surface symmetry, forming chains of alternating pentamer and heptamer rings in preference to an extended 2D structure. This behavior is different from that found on other surfaces studied previously and is driven by the short lattice spacing of the solid and the strength of the Ni-water bond.

A new porous and flexible metal-organic framework (MOF) has been synthesized from the flexible asymmetric linker N -(4-carboxyphenyl)succinamate (CSA) and heptanuclear zinc oxo-clusters of formula [Zn 7 O 2 (carboxylate) 10 DMF 2 ] involving two coordinated terminal DMF ligands. The structural response of this MOF to the removal or exchange of its guest molecules has been probed using a combination of experimental and computational approaches. The topology of the material, involving double linker connections in the a and b directions and single linker connections along the c axis, is shown to be key in the material's anisotropic response. The a and b directions remain locked during guest removal, whereas the c axis linker undergoes large changes significantly reducing the material's void space. The changes to the c axis linker involve a combination of a hinge motion on the linker's rigid side and conformational rearrangements on its flexible end, which were probed in detail during this process despite the presence of crystallographic disorder along this axis, which prevented accurate characterization by experimental methods alone. Although inactive during guest removal, the flexible ends of the a and b axis linkers are observed to play a prominent role during DMF to DMSO solvent exchange, facilitating the exchange reaction arising in the cluster., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Metal-organic frameworks (MOFs) are crystalline synthetic porous materials formed by binding organic linkers to metal nodes: they can be either rigid 1,2 or flexible 3 . Zeolites and rigid MOFs have widespread applications in sorption, separation and catalysis that arise from their ability to control the arrangement and chemistry of guest molecules in their pores via the shape and functionality of their internal surface, defined by their chemistry and structure 4,5 . Their structures correspond to an energy landscape with a single, albeit highly functional, energy minimum. By contrast, proteins function by navigating between multiple metastable structures using bond rotations of the polypeptide 6,7 , where each structure lies in one of the minima of a conformational energy landscape and can be selected according to the chemistry of the molecules that interact with the protein. These structural changes are realized through the mechanisms of conformational selection (where a higher-energy minimum characteristic of the protein is stabilized by small-molecule binding) and induced fit (where a small molecule imposes a structure on the protein that is not a minimum in the absence of that molecule) 8 . Here we show that rotation about covalent bonds in a peptide linker can change a flexible MOF to afford nine distinct crystal structures, revealing a conformational energy landscape that is characterized by multiple structural minima. The uptake of small-molecule guests by the MOF can be chemically triggered by inducing peptide conformational change. This change transforms the material from a minimum on the landscape that is inactive for guest sorption to an active one. Chemical control of the conformation of a flexible organic linker offers a route to modifying the pore geometry and internal surface chemistry and thus the function of open-framework materials.

Heterogeneous ice nucleation is a key process in many environmental and technical fields and is of particular importance in modeling atmospheric behavior and the Earth's climate. Despite an improved understanding of how water binds at solid surfaces, no clear picture has emerged to describe how 3D ice grows from the first water layer, nor what makes a particular surface efficient at nucleating bulk ice. This study reports how water at a corrugated, hydrophilic/hydrophobic surface restructures from a complex 2D network, optimized to match the solid surface, to grow into a continuous ice film. Unlike the water networks formed on plane surfaces, the corrugated Cu(511) surface stabilizes a buckled hexagonal wetting layer containing both hydrogen acceptor and donor sites. First layer water is able to relax into an "icelike" arrangement as further water is deposited, creating an array of donor and acceptor sites with the correct spacing and corrugation to stabilize second layer ice and allow continued commensurate multilayer ice growth. Comparison to previous studies of flat surfaces indicates nanoscale corrugation strongly favors ice nucleation, implying surface corrugation will be an important aspect of the surface morphology on other natural or engineered surfaces.

Computationally led materials discovery requires efficient methods to generate either exact or approximate crystal structures that span the composition range of a chosen phase space. Here we present a new tool, the Flexible Unit Structure Engine (FUSE), for the generation of approximate 'probe structures' to predict regions of composition space where compounds can be experimentally realised. We then test FUSE by applying it to 42 compositions in the Y3+-Sr2+-Ti4+-O2- phase field. FUSE correctly identifies all of the target compounds in the regions of stability and identifies the exact crystal structure for 8 out of the 10 compositions.

It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO 2 , was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li + for Zn 2+ as a stable, potentially p-type, doping mechanism in SrZnO 2 . Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn 1- x Li x O 2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO 2 and SrZn 1- x Li x O 2 were experimentally verified. The band gap of SrZnO 2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient of 353(4) μV K -1 for SrZn 1- x Li x O 2 , where x = 0.021, confirmed that the compound is a p-type conductor, which is consistent with the p O 2 dependence of the electrical conductivity observed in all SrZn 1- x Li x O 2 samples. The conductivity of SrZn 1- x Li x O 2 is up to 15 times greater than that of undoped SrZnO 2 (for x = 0.028 σ = 2.53 μS cm -1 at 600 °C and 1 atm of O 2 ).

Hexaferrites are an important class of magnetic oxides with applications in data storage and electronics. Their crystal structures are highly modular, consisting of Fe- or Ba-rich close-packed blocks that can be stacked in different sequences to form a multitude of unique structures, producing large anisotropic unit cells with lattice parameters typically >100 Å along the stacking axis. This has limited atomic-resolution structure solutions to relatively simple examples such as Ba 2 Zn 2 Fe 12 O 22 , whilst longer stacking sequences have been modelled only in terms of block sequences, with no refinement of individual atomic coordinates or occupancies. This paper describes the growth of a series of complex hexaferrite crystals, their atomic-level structure solution by high-resolution synchrotron X-ray diffraction, electron diffraction and imaging methods, and their physical characterization by magnetometry. The structures include a new hexaferrite stacking sequence, with the longest lattice parameter of any hexaferrite with a fully determined structure.

Highly corrugated, stepped surfaces present regular 1D arrays of binding sites, creating a complex, heterogeneous environment to water. Rather than decorating the hydrophilic step sites to form 1D chains, water on stepped Cu(511) forms an extended 2D network that binds strongly to the steps but bridges across the intervening hydrophobic Cu(100) terraces. The hydrogen-bonded network contains pentamer, hexamer, and octomer water rings that leave a third of the stable Cu step sites unoccupied in order to bind water H down close to the step dipole and complete three hydrogen bonds per molecule.

The discovery of new materials is hampered by the lack of efficient approaches to the exploration of both the large number of possible elemental compositions for such materials, and of the candidate structures at each composition. For example, the discovery of inorganic extended solid structures has relied on knowledge of crystal chemistry coupled with time-consuming materials synthesis with systematically varied elemental ratios. Computational methods have been developed to guide synthesis by predicting structures at specific compositions and predicting compositions for known crystal structures, with notable successes. However, the challenge of finding qualitatively new, experimentally realizable compounds, with crystal structures where the unit cell and the atom positions within it differ from known structures, remains for compositionally complex systems. Many valuable properties arise from substitution into known crystal structures, but materials discovery using this approach alone risks both missing best-in-class performance and attempting design with incomplete knowledge. Here we report the experimental discovery of two structure types by computational identification of the region of a complex inorganic phase field that contains them. This is achieved by computing probe structures that capture the chemical and structural diversity of the system and whose energies can be ranked against combinations of currently known materials. Subsequent experimental exploration of the lowest-energy regions of the computed phase diagram affords two materials with previously unreported crystal structures featuring unusual structural motifs. This approach will accelerate the systematic discovery of new materials in complex compositional spaces by efficiently guiding synthesis and enhancing the predictive power of the computational tools through expansion of the knowledge base underpinning them.

Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces.

Adsorption of thymine on a defined Cu(110) surface was studied using reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and scanning tunnelling microscopy (STM). In addition, density functional theory (DFT) calculations were undertaken in order to further understand the energetics of adsorption and self-assembly. The combination of RAIRS, TPD, and DFT results indicates that an upright, three-point-bonded adsorption configuration is adopted by the deprotonated thymine at room temperature. DFT calculations show that the upright configuration adopted by individual molecules arises as a direct result of strong O-Cu and N-Cu bonds between the molecule and the surface. STM data reveal that this upright thymine motif self-assembles into 1D chains, which are surprisingly oriented along the open-packed [001] direction of the metal surface and orthogonal to the alignment of the functional groups that are normally implicated in H-bonding interactions. DFT modelling of this system reveals that the molecular organisation is actually driven by dispersion interactions, which cause a slight tilt of the molecule and provide the major driving force for assembly into dimers and 1D chains. The relative orientations and distances of neighbouring molecules are amenable for π-π stacking, suggesting that this is an important contributor in the self-assembly process.

Ice formation is a complex cooperative process that is almost invariably catalysed by the presence of an interface on which ice crystals nucleate. As yet there is no clear picture of what factors make a surface particularly good at nucleating ice, but the importance of having a template with a suitable lattice parameter has often been proposed. Here we report the contrasting wetting behaviour of a series of pseudomorphic surfaces, designed to form an ordered template that matches the arrangement of water in a bulk ice Ih(0001) bilayer. The close-packed M(111) surfaces (M = Pt, Pd, Rh, Cu and Ni) form a (√3 × √3) R30° Sn substitutional alloy surface, with Sn atoms occupying sites that match the symmetry of an ice bilayer. The lattice constant of the alloy changes from 4% smaller to 7% greater than the lateral spacing of ice across the series. We show that only the PtSn surface, with a lattice parameter some 7% greater than that of a bulk ice layer, forms a stable water layer, all the other surfaces being non-wetting and instead forming multilayer ice clusters. This observation is consistent with the idea that the repeat spacing of the surface should ideally match the O-O spacing in ice, rather than the bulk ice lattice parameter, in order to form a continuous commensurate water monolayer. We discuss the role of the lattice parameter in stabilising the first layer of water and the factors that lead to formation of a simple commensurate structure rather than an incommensurate or large unit cell water network. We argue that lattice match is not a good criteria for a material to give low energy nucleation sites for bulk ice, and that considerations such as binding energy and mobility of the surface layer are more relevant.

The Extended Module Materials Assembly computational method for structure solution and prediction has been implemented for close-packed lattices. Exploring the family of B-site deficient materials in hexagonal perovskite barium cobalt niobates, it is found that the EMMA procedure returns the experimental structures as the most stable for the known compositions of Ba3CoNb2O9, Ba5Nb4O15 and Ba8CoNb6O24. The unknown compositions Ba11Co2Nb8O33 and Ba13CoNb10O39, having longer stacking sequences, are predicted to form as intergrowths of Ba3CoNb2O9 and Ba5Nb4O15, and are found to have similar stability to pure Ba3CoNb2O9 and Ba5Nb4O15, indicating that it is likely they can be synthesised.

Porous materials are attractive for separation and catalysis-these applications rely on selective interactions between host materials and guests. In metal-organic frameworks (MOFs), these interactions can be controlled through a flexible structural response to the presence of guests. Here we report a MOF that consists of glycyl-serine dipeptides coordinated to metal centres, and has a structure that evolves from a solvated porous state to a desolvated non-porous state as a result of ordered cooperative, displacive and conformational changes of the peptide. This behaviour is driven by hydrogen bonding that involves the side-chain hydroxyl groups of the serine. A similar cooperative closure (reminiscent of the folding of proteins) is also displayed with multipeptide solid solutions. For these, the combination of different sequences of amino acids controls the framework's response to the presence of guests in a nonlinear way. This functional control can be compared to the effect of single-point mutations in proteins, in which exchange of single amino acids can radically alter structure and function.

The peptide-based porous 3D framework, ZnCar, has been synthesized from Zn(2+) and the natural dipeptide carnosine (β-alanyl-L-histidine). Unlike previous extended peptide networks, the imidazole side chain of the histidine residue is deprotonated to afford Zn-imidazolate chains, with bonding similar to the zeolitic imidazolate framework (ZIF) family of porous materials. ZnCar exhibits permanent microporosity with a surface area of 448 m(2)  g(-1) , and its pores are 1D channels with 5 Å openings and a characteristic chiral shape. This compound is chemically stable in organic solvents and water. Single-crystal X-ray diffraction (XRD) showed that the ZnCar framework adapts to MeOH and H2 O guests because of the torsional flexibility of the main His-β-Ala chain, while retaining the rigidity conferred by the Zn-imidazolate chains. The conformation adopted by carnosine is driven by the H bonds formed both to other dipeptides and to the guests, permitting the observed structural transformations., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

The design of complex inorganic materials is a challenge because of the diversity of their potential structures. We present a method for the computational identification of materials containing multiple atom types in multiple geometries by ranking candidate structures assembled from extended modules containing chemically realistic atomic environments. Many existing functional materials can be described in this way, and their properties are often determined by the chemistry and electronic structure of their constituent modules. To demonstrate the approach, we isolated the oxide Y(2.24)Ba(2.28)Ca(3.48)Fe(7.44)Cu(0.56)O21, with a largest unit cell dimension of over 60 angstroms and 148 atoms in the unit cell, by using a combination of this method and experimental work and show that it has the properties necessary to function as a solid oxide fuel-cell cathode.

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden-Popper structure La(2)Sr(2)Mn(3)O(10) in epitaxial thin film form by sequentially layering La(1-x)Sr(x)MnO(3) and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr(2+) predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature T(g) ≈ 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

Repeating boundaries: the buried interfaces in artificial heterostructures produced by sequential deposition of nanosized units are critical to their properties. With density functional theory it was shown that in Y(2)O(3):ZrO(2) (YSZ) and SrTiO(3) (STO) heterostructures reconstruction of the interfaces between the component units is required to access the most favorable structure., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Water adsorbs and desorbs intact on Pd(111), forming a hydrogen-bonded wetting layer whose structure we examine by low energy electron diffraction (LEED) and He atom scattering (HAS). LEED shows that water forms commensurate (√3 × √3)R30° clusters that aggregate into a partially ordered, approximately (7 × 7) superstructure as the layer completes. HAS indicates that the water layer remains disordered on a local (approximately 10 Å) scale. Based on workfunction measurements and density functional theory simulations we propose that water forms small, flat domains of a commensurate (√3 × √3)R30° water network, separated by disordered domain boundaries containing largely H-down water. This arrangement allows the water layer to adapt its density and relieve the lateral strain associated with adsorbing water in the optimum flat atop adsorption site. We discuss different possibilities for the structure of these domain walls and compare this strain relief mechanism to the highly ordered, large unit cell structures formed on surfaces such as Pt(111)., (© 2012 IOP Publishing Ltd)

Unexpected local chiral switching events are shown to occur within strongly chemisorbed homochiral domains, in which a pair of surface-bonded molecules dynamically switches their chiral configuration for a short period of time., (This journal is © The Royal Society of Chemistry 2011)

Recent studies show that structures based on the traditional "icelike" water bilayer are not stable on flat transition metal surfaces and, instead, more complex wetting layers are formed. Here we show that an ordered bilayer can be formed on a SnPt(111) alloy template and determine the structure of the water layer by low energy electron diffraction. Close agreement is found between experiment and the structure calculated by density functional theory. Corrugation of the alloy surface allows only alternate water molecules to chemisorb, stabilizing the H-down water bilayer by reducing the metal-hydrogen repulsion compared to a flat surface.

Porous materials find widespread application in storage, separation, and catalytic technologies. We report a crystalline porous solid with adaptable porosity, in which a simple dipeptide linker is arranged in a regular array by coordination to metal centers. Experiments reinforced by molecular dynamics simulations showed that low-energy torsions and displacements of the peptides enabled the available pore volume to evolve smoothly from zero as the guest loading increased. The observed cooperative feedback in sorption isotherms resembled the response of proteins undergoing conformational selection, suggesting an energy landscape similar to that required for protein folding. The flexible peptide linker was shown to play the pivotal role in changing the pore conformation.

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

In close quarters: When confined in a metal-organic framework, magnesium borohydride reacts with arenes by a hydroboration pathway (see scheme), in contrast to its reactivity under analogous homogeneous solution-phase conditions. Framework-imposed organization of the reactive groups is required, which is achieved by a combination of the metal coordination and two hydrogen bonds.

The growth of an intact water monolayer on Ru(0001) has been investigated by comparing the ordering of O and Ru, determined by low-energy electron diffraction (LEED), with that of the top layer of O and H, as probed by He atom scattering (HAS). Although LEED shows that water forms an extended commensurate (square root 3 x square root 3) R30 degrees structure as the coverage approaches 0.67 monolayer, the HAS distributions are insensitive to the exact water coverage and show a very low specular reflectivity, indicating a disordered water layer. The angular profile from a D2O monolayer shows a broad diffuse peak in the angular scattering distribution at a momentum exchange similar to the position of the second-order (1/3, 1/3) peaks, but the maxima show little variation with scattering azimuth. H2O shows a slightly higher He reflectivity and more clearly resolved angular structure, with broad, faint peaks appearing close to the first-order diffraction positions. The origin of this disorder is discussed based on density functional calculations for the monolayer which find that water forms chains of flat and H-down molecules within a hexagonal hydrogen-bonding network, rather than the ice bilayer usually assumed. This arrangement leads to long-range order in the O location, but disorder in the O height and the proton orientation. We discuss how this combination of lateral order in the adsorption site, but disorder in the water orientation, is reflected in the sharp square root 3 LEED pattern but diffuse, broad peaks in He scattering.

Reaction of L-cysteine with M(NO3)2 x xH2O (M = Cd, Zn) generates M(L-cysteinate), which feature one-dimensional substructures that can be viewed as fragments of bulk structures of CdS (rock salt high pressure phase) and ZnS (wurtzite) because of the bridging modes accessible to the sulfur atom of L-cysteine. The MS substructures are arranged in a regular and periodic fashion within the crystal via the carboxylate function of L-cysteine. Considering the structural similarities with bulk materials, the optical properties of M(L-cysteinate) were studied and indicate blue shifts of the band gap of 2.59 eV (M = Cd, compared to CdS rock salt) and 1.37 eV (M = Zn, compared to ZnS wurtzite) with respect to the bulk MS structures, due to the low dimensionality of the metal-sulfur arrangement. The chelating nature of the cysteine ligand imposes an unusual mer arrangement of three binding S moieties at Cd with a correspondingly high Cd coordination number in a chalcogenide-based material. Density of states calculations show strong electronic structure similarities with the bulk phases and rationalize the band gap changes.

Superconductivity emerges for the A15 polymorph of the fulleride Cs3C60 upon compression to a pressure of approximately 4 kbar. Using density functional theory we study the bonding in the A15 phase as a function of unit cell volume comparing it to that in the fcc polymorph. We find that, despite its smaller packing density, the bcc-derived A15 phase has both a substantially wider bandwidth for the partially occupied t1u band and a higher density of states at the Fermi level. This result can be traced to the striking differences in the nature of the interanion Tc--the two sphere packings (body centered versus face centered) observed experimentally produce two electronically distinct classes of fulleride superconductors.

We describe the effect of growth temperature and OHH(2)O composition on the wetting behavior of Pt(111). Changes to the desorption rate of ice films were measured and correlated to the film morphology using low energy electron diffraction and thermal desorption of chloroform to measure the area of multilayer ice and monolayer OHH(2)O exposed. Thin ice films roughen, forming bare (radical39 x radical39)R16 degrees water monolayer and ice clusters. The size of the clusters depends on growth temperature and determines their kinetic stability, with the desorption rate decreasing when larger clusters are formed by growth at high temperature. Continuous films of more than approximately 50 layers thick stabilize an ordered incommensurate ice film that does not dewet. OH coadsorption pins the first layer into registry with Pt, forming an ordered hexagonal (OH+H(2)O) structure with all the H atoms involved in hydrogen bonding. Although this layer has a similar honeycomb OH(x) skeleton to ice Ih, it is unable to reconstruct to match the bulk ice lattice parameter and does not form a stable wetting layer. Water aggregates to expose bare monolayer (OH+H(2)O), forming bulk ice crystallites whose size depend on preparation temperature. Increasing the proportion of water in the first layer provides free OH groups which stabilize the multilayer. The factors influencing multilayer wetting are discussed using density functional theory calculations to compare water adsorption on top of (OH+H(2)O) and on simple models for commensurate water structures. We show that both the (OH+H(2)O) structure and "H-down" water layers are poor proton acceptors, bonding to the first layer being enhanced by the presence of free OH groups. Formation of an ordered ice multilayer requires a water-metal interaction sufficient to wet the surface, but not so strong as to prevent the first layer relaxing to stabilize the interface between the metal and bulk ice.

The introduction of mixed valency into extended main-group solids is discussed using the example of hole-doped LiBC, where a combination of experimental measurements and density functional theory calculations is used to understand the observed electronic properties in terms of deviation from the expected rigid-band electronic structure behaviour.

The authors have investigated the structure and energetics of the first hydration layer on NaCl(100) by means of density functional calculations. They have analyzed in detail the role of the hydrogen bond between the adsorbed molecules for the determination of the most favorable structures. They have shown that, using the water dimers as basic building blocks, very stable structures can be constructed. They discuss here two important examples: (i) a model with (1x1) periodicity at 2 ML coverage, and (ii) icelike bilayers with a c(4x2) unit cell at 1.5 ML. Both structures present high adsorption energies per water molecule of approximately 570 meV, in comparison to the 350 meV adsorption energy obtained for the previously studied (1x1) structures composed of weakly interacting monomers. Based on these findings, they propose an interpretation for the experimental observations of Toennies et al. [J. Chem. Phys. 120, 11347 (2004)], who found a transition of the periodicity of the first hydration layer on NaCl(100) from (1x1) to c(4x2) upon electron irradiation. According to the model, the transition would be driven by the partial desorption of (1x1) bilayer structures corresponding to a local coverage of 2 ML and the further rearrangement of the remaining water molecules to form a quasihexagonal structure with c(4x2) periodicity at coverage close to 1.5 ML.

At low coverage and temperature the water-surface interaction determines the adsorption geometry of the water molecule on the NaCl(100) surface. However, at room temperature the molecules are also able to move on the surface and form islands where the water molecules are held together by hydrogen bonds. As a step toward the description of such complex phenomenology, in this work we have used density functional theory calculations to study the most favorable adsorption geometry of an isolated water molecule and the energy barriers associated with different hopping mechanisms between equivalent adsorption configurations on this surface. We propose different hopping processes that can be classified as translations, if the molecule moves from one adsorption site to the adjacent one, or reorientations, if the molecule only changes its orientation on the surface and remains in the same adsorption site. The straightforward parallel translation of the water molecule along the surface exhibits the highest barrier. All other processes, either translations or reorientations, involve the rotation of the water molecule around certain axes and present much smaller barriers (at least 50% smaller). To obtain a net movement of the molecule along the surface it is always necessary to combine one of these translational and reorientational processes. Such combinations provide favorable and plausible pathways for the diffusion of the water molecule on the NaCl(100) substrate.

The synthetic search for materials related to the 39 K superconductor MgB2 has been difficult. The most promising theoretical suggestion, hole doping of LiBC, does not lead to a new superconductor. We show here that a combination of density functional theory (DFT) calculations, materials synthesis, and structural characterization reveals the origin of the puzzling absence of superconductivity in Li1/2BC as a subtle change in the electronic structure driven by structural response to the introduction of holes. This indicates that the unique aspects of the electronic structure of MgB2 will be demanding to replicate in other systems.

The role of the hydride anion in controlling the electronic properties of the transition metal oxide hydride LaSrCoO(3)H(0.7) is investigated theoretically by full potential DFT band structure calculation and experimentally by determination of the Neel temperature for three-dimensional magnetic ordering. The mechanism by which hydrogen is introduced into the solid is addressed by in situ X-ray diffraction studies of the formation of the oxide hydride, which reveal both a relationship between the microscopic growth of the observed oxide hydride order and the anisotropic broadening of the diffraction profile, and the existence of a range of intermediate compositions.