Reviews & Analysis

Sunlight is potentially an ideal green 'reagent' for chemical synthesis, but poor absorption by organic substrates makes direct solar photochemistry generally inefficient. Here, recent progress in the use of the simple organometallic complexes to harness the power of the sun is summarized, and prospects for the future of this exciting field highlighted.

The absorption of a single photon can cause the excitation of more than one electron, but the mechanism of this 'multi-exciton generation' process is elusive. Now, calculations on pentacene show that geometrical distortions and intermediate excited states assist in producing two excited electrons from one photon.

Can two identical reactors with the same concentrations, under identical physical conditions, have reaction rates that differ by a factor of a thousand? A study now shows that, although not true in uncrowded environments, a reactant's starting point makes a large difference to reaction kinetics in identically crowded systems, such as cellular nuclei.

Ultrasound can be used to control molecular processes as delicate as rotation around a single carbon–carbon bond.

Mechanical linking of small cage structures leads to a type of metal–organic framework with an architecture topologically distinct from those constructed so far.

Controlling the movements of molecular systems through external stimuli is crucial for the construction of nanoscale mechanical machines. A spring-like compound has now been prepared — a double helicate that retains its handedness under ion-triggered extension and contraction.

Despite knowing that the active centres of many metalloprotein enzymes are iron porphyrin 'haem' complexes, chemists find them difficult to imitate. Now, the assembly of haem-like centres into a crystalline, stable, nanoporous array shows promise for biomimetic catalysis.

The composition of dynamic small-molecule libraries can be biased by the addition of a target compound — such as a protein — that binds selectively to one of the components in the mixture. The chemistry of the library must, however, be compatible with the target and it has now been shown that aniline-catalysed exchange of acylhydrazones fits the bill.

The catalytic reduction of atmospheric N₂ to NH₃ under mild conditions is one of the challenges of organometallic chemistry. An iron-based complex that binds and activates N₂ has now been developed. Its electrochemistry and coordination properties shed light on potential mechanisms by which N₂-to-NH₃ reduction might be achieved.

A new concept termed 'robust dynamics' is presented as the intellectual centerpiece to the union between metal–organic frameworks (MOFs) and mechanically interlocking molecules. Robust dynamics allows highly flexible entities, which are bound covalently to MOF backbones, to carry out repeated movements without affecting the integrity of the overall structure.

Molecular 'boxes' can hold other molecules and often serve as the moving parts in molecular switches. The latest addition to this class of compounds is a simple-to-prepare positively charged macrocycle that can encircle molecular guests of appropriate size and charge — and offers new opportunities for assembling stimuli-responsive structures.

To improve organic electronic devices, the principles underlying organic-film/metal-electrode interfaces must be understood. A comprehensive study of the organic electron acceptor TCNQ on a copper surface reveals a structural rearrangement of both the organic molecule and the metal surface atoms after charge transfer across the interface.

The iron active sites of enzymes routinely cleave strong C–H bonds, but synthetic complexes have so far been much slower and less efficient. Now, the reactivity of a biomimetic diiron complex has been dramatically enhanced by converting its oxo bridge into a terminal ligand, and its iron centre from low spin to high spin.

Single-molecule magnets are coordination clusters with magnetic properties that are typically reliant on the coupling between pairs of metal centres. Now, a cluster in which magnetism arises from delocalized electrons — built using an imidazolate bridge, a common linker in metal–organic architectures — shows promise for molecular memory devices.

Spin transitions are the most common mechanism for switching molecules between two distinct energy states, for uses as diverse as memory devices and displays. How the transition is triggered is crucial, and a pentanuclear cluster has now been reported in which the spin transition is promoted by redox transfer between different metal ions.

The synthesis or separation of chiral compounds is crucial for many areas of chemistry, with chiral solids having important roles as catalysts or separating agents. This Review covers recent progress and future avenues for developing methods of preparing chiral solids from achiral starting materials.