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.

We present an exposition of the various theoretical models currently in use for describing the dynamics of molecular dissociation at surfaces. We begin by outlining the representations of the nuclear and electronic dynamics and how these define the potential energy surfaces for the interactions. Strategies for solving the nuclear motion follow with particular emphasis being paid to a quantum description on the electronic ground state which is in line with experiments employing hyperthemal molecular beams. These can be performed in either a time-dependent or timeindependent fashion and both approaches are considered. Following this, the methods that have been developed for treating the dissipative motion as the molecule nears the surface are presented. This is divided into energy loss to the electronic subsystem and to the substrate atomic vibrations. The final part of the review shows how the results of theoretical simulations have been usefully applied to rationalize data obtained from molecular beam scattering experiments.

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

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 guests in their pores via the shape and functionality of the 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. In 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 interacting with the protein. These structural changes are realised through the mechanisms of conformational selection (where a higher energy minimum characteristic of the protein is stabilised 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 characterised 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 modify the pore geometry and internal surface chemistry and thus the function of open-framework materials. Flexible MOF structures 9,10 can be rearranged in the presence of guests through mechanical mechanisms such as the repositioning of a rigid linker about an inorganic unit 11-13 or the relative displacement of two rigid networks, 14 opening a range of routes to control function 15 that are not accessible to rigid frameworks with their single structural minimum (Figure 1). Similar phenomena have been observed in the host-guest chemistry of interlocked cage molecules. 16-18 Alternatively, rotations about bonds involving sp 3 carbons 19-25 allow MOF to access different structures. For example, low energy conformational changes of dipeptide Gly-X linkers produce open and closed forms of Zn(Gly-X)2 frameworks. 26,27 The greater chemical diversity and more complex conformational space of higher order oligopeptides offer MOF with multiple open structures (Figure 1). This could allow interaction with molecules in the pores to select a specific structure for a defined function from the resulting energy landscape. That structure would be accessed through the single bond rotation pathway used by proteins (Figure 1). The tripeptide glycine-glycine-L-histidine (GGH) affords a three-dimensional chiral MOF Zn...

The influence of rotational state on the dissociation probability of H2 on Cu(111) has been investigated with 3- and 4-dimensional close-coupling wave packet calculations. Recent experimental results have shown that the energetic threshold for dissociative adsorption increases and then decreases as the J state is continuously increased. This trend can be faithfully reproduced by modeling the H2 as a planar (cartwheel) rotor scattering from a flat surface. The agreement disappears when the model is extended to a 3-dimensional rotor. Further, the degenerate mJ states have a spread of dissociation probabilities which results in a broad smearing of the dissociation threshold. This effect, which is absent from experiment, increases with Ji. These shortcomings can be partially corrected by corrugating the potential in the azimuthal coordinate in accord with recent ab initio results. The dynamical calculations also exhibit strong rotational inelasticity for the scattered fraction, during dissociation. Since this system has a late barrier for dissociation, we show that the rotational inelasticity should be enhanced by initial vibrational state. Our 4-dimensional modeling is unable simultaneously to match the relative positions of dissociation and vibrational excitation thresholds. We speculate that these processes occur on different surface sites.

No abstract

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 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.