Volume 2 Issue 5, May 2010

We should do less staged science and more science on stage, suggests Michelle Francl.

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.

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 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.

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.

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.

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.

Single-molecule magnets are clusters of metal ions linked together by organic bridges, with properties typically arising from exchange coupling of unpaired metal electrons. In mixed-valence systems, another magnetic mechanism involving itinerant electrons can also occur and induce a high-spin ground state. Now, such electron delocalization has been observed through an imidazolate bridge — a common linker in metal-organic architectures — which may enable the construction of higher spin clusters or three-dimensional magnets.

N-heterocyclic carbenes have been shown to be versatile ligands for metal catalysts and even catalysts in their own right. Here, bulky N-heterocyclic carbenes are shown to stabilize paramagnetic and electron-poor species sufficiently for their crystallographic characterization.

Interfaces between organic molecules and metal surfaces have a key role in determining the performance of many emerging technologies. Now an intensive experimental study — supported by calculations — of tetracyano-p-quinodimethane molecules on a copper surface, reveals structural rearrangement of both the organic molecules and the surface atoms after charge transfer across the interface.

Chiral thiols and organosulfur compounds are important in many areas of chemistry but there are relatively few methods available for their efficient enantioselective synthesis. Here, a kinetic resolution of chiral thiols is reported along with a demonstration that a concomitant desymmetrization of the acylating agent is beneficial for the selectivity of both processes.

Although the triiodide/iodide redox couple works efficiently in dye-sensitized solar cells it restricts functionality by absorbing visible light. Now, a disulfide/thiolate redox couple that has negligible absorption in the visible spectral range is presented, which in conjunction with a sensitized heterojunction, displays an efficiency of 6.4% under standard illumination test conditions.

Helium is a reluctant participant when it comes to chemical reactions and bonding and it is one of only two stable elements for which there are currently no known crystalline derivatives. Now, based on a computational investigation, compounds containing helium atoms that form charge-shift, rather than covalent bonds have been proposed.

Viruses are ideal templates for engineering multifunctional materials. They can exhibit multiple copies of surface ligands and encapsulate inorganic and organic materials. Here, viruses are assembled into well-defined micrometre-sized objects by the addition of dendritic linkers. The linkers are designed to decompose on irradiation, which results in the release of the original virus particles.

Although enzymes are known to use diiron centres to cleave carbon–hydrogen bonds, preparing synthetic compounds that can break these strong, stable bonds has remained notoriously difficult. Now, converting a low-spin ‘diamond core’ iron–oxo biomimetic complex into its high-spin ‘open core’ counterpart has enhanced its C–H bond cleavage ability by over a million times.

Macrocyles capable of hosting other molecules inside their hollow interiors have been used extensively to make threaded complexes and interlocked molecules. Now, a relatively large and flexible tetracationic macrocycle has been shown to bind anionic guests to form pseudorotaxanes that form extended structures in solution and the solid state.

Porous coordination polymers — PCPs, also known as metal–organic framework materials — have been widely investigated for their useful properties, but controlling their size and shape in a nanocrystalline form is difficult. Now, a rapid method of preparing porous crystalline nanosized PCPs that uses a microemulsion system under ultrasonic irradiation has been reported.

Identifying the best catalyst for a particular reaction traditionally involves testing a wide variety of metal and ligand combinations in standard reactions. Here, the best catalyst is found by using mass spectrometry to identify the least stable — and thus most reactive — intermediate in a dynamic mixture of complexes.

Uranium is best known, and feared, for its involvement in nuclear energy. Marisa J. Monreal and Paula L. Diaconescu take a look at how its unique combination of properties is now increasingly attracting the attention of chemists.