Jonathan P. Rourke

Graphene Oxide: Structural Analysis and Application as a Highly Transparent Support for Electron Microscopy

We report on the structural analysis of graphene oxide (GO) by transmission electron microscopy (TEM). Electron diffraction shows that on average the underlying carbon lattice maintains the order and lattice-spacings of graphene; a structure that is clearly resolved in 80 kV aberration-corrected atomic resolution TEM images. These results also reveal that single GO sheets are highly electron transparent and stable in the electron beam, and hence ideal support films for the study of nanoparticles and macromolecules by TEM. We demonstrate this through the structural analysis of physiological ferritin, an iron-storage protein.

The Real Graphene Oxide Revealed: Stripping the Oxidative Debris from the Graphene-like Sheets†

It′ll come out in the wash! Graphene oxide has been shown to be a stable complex of oxidative debris (red ellipses in the picture) strongly adhered to functionalized graphene-like sheets. Under basic conditions the oxidative debris is stripped from the graphene-like sheets, and the resulting graphene oxide is conducting and cannot easily be resuspended in water.

A delicate balance between sp2 and sp3 C-H bond activation: a Pt(II) complex with a dual agostic interaction.

2-tert-Butyl-6-(4-fluorophenyl)pyridine reacts with K(2)PtCl(4) via the activation of an sp(2) C-H bond to give a cyclometalated complex that contains a bifurcated agostic interaction. Rearrangement of this complex results in the activation of an sp(3) C-H bond, and reaction eventually leads to a doubly cyclometalated complex where both sp(2) and sp(3) C-H bonds have been activated. Deuterium exchange studies show that a delicate balance exists between the two cyclometalations.

Physical Vapor Deposition of Metal Nanoparticles on Chemically Modified Graphene: Observations on Metal–Graphene Interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to ∼1.5 nm for Au) and coverage (up to 5 × 10(4) μm(-2) for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metal-graphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.

Sulfur‐Functionalized Graphene Oxide by Epoxide Ring‐Opening

The treatment of graphene oxide (GO) with potassium thioacetate followed by an aqueous work-up yields a new material via the ring-opening of the epoxide groups. The new material is a thiol-functionalized GO (GO-SH) which is able to undergo further functionalization. Reaction with butyl bromide gives another new material, GO-SBu, which shows significantly enhanced thermal stability compared to both GO and GO-SH. The thiol-functionalized GO material showed a high affinity for gold, as demonstrated by the selective deposition of a high density of gold nanoparticles.

Imaging the structure, symmetry, and surface-inhibited rotation of polyoxometalate ions on graphene oxide

Atomic-resolution imaging of discrete [γ-SiW10O36]8- lacunary Keggin ions dispersed onto monolayer graphene oxide (GO) films by low voltage aberration corrected transmission electron microscopy is described. Under low electron beam dose, individual anions remain stationary for long enough that a variety of projections can be observed and structural information extracted with ca. ± 0.03 nm precision. Unambiguous assignment of the orientation of individual ions with respect to the point symmetry elements can be determined. The C2v symmetry [γ-SiW10O36]8- ion was imaged along its 2-fold C2 axis or orthogonally with respect to one of two nonequivalent mirror planes (i.e., σv). Continued electron beam exposure of a second ion imaged orthogonal to σv causes it to translate and/or rotate in an inhibited fashion so that the ion can be viewed in different relative orientations. The inhibited surface motion of the anion, which is in response to H-bonding-type interactions, reveals an important new property for GO in that it demonstrably behaves as a chemically modified (i.e., rather than chemically neutral) surface in electron microscopy. This behavior indicates that GO has more in common with substrates used in imaging techniques such as atomic force microscopy and scanning tunneling microscopy, and this clearly sets it apart from other support films used in transmission electron microscopy.

A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF3)] studied with NMR and time-resolved IR spectroscopy

The organometallic alkane complexes Re(Cp)(CO)(PF3)(alkane) and Re(Cp)(CO)2(alkane) have been detected after the photolysis of Re(Cp)(CO)2(PF3) in alkane solvent. NMR and time-resolved IR experiments reveal that the species produced by the interaction of n-pentane with [Re(Cp)(CO)(PF3)] are an equilibrium mixture of Re(Cp)(CO)(PF3)(pentane) and Re(Cp)(CO)(PF3)(pentyl)H. The interaction of cyclopentane with [Re(Cp)(CO)(PF3)] most likely results in a similar equilibrium between cyclopentyl hydride and cyclopentane complexes. An increasing proportion of alkane complex is observed on going from n-pentane to cyclopentane to cyclohexane, where only a small amount, if any, of the cyclohexyl hydride form is present. In general, when [Re(Cp)(CO)(PF3)] reacts with alkanes, the products display a higher degree of oxidative cleavage in comparison with [Re(Cp)(CO)2], which favors alkane complexation without activation. Species with the formula Re(Cp)(CO)(PF3)(alkane) have higher thermal stability and lower reactivity toward CO than the analogous Re(Cp)(CO)2(alkane) complexes.

Chiral cyclopalladated liquid crystals from amino acids

Abstract The cyclopalladation of mesogenic Schiff bases and subsequent reaction with natural l -amino acids yields a novel series of metallomesogens. The transition temperatures of the complexes are uniformly higher that those of the free ligands, with smectic A phases being exhibited. Download full-size image

On the structure and topography of free-standing chemically modified graphene

The mechanical, electrical and chemical properties of chemically modified graphene (CMG) are intrinsically linked to its structure. Here, we report on our study of the topographic structure of free-standing CMG using atomic force microscopy (AFM) and electron diffraction. We find that, unlike graphene, suspended sheets of CMG are corrugated and distorted on nanometre length scales. AFM reveals not only long-range (100 nm) distortions induced by the support, as previously observed for graphene, but also short-range corrugations with length scales down to the resolution limit of 10 nm. These corrugations are static not dynamic, and are significantly diminished on CMG supported on atomically smooth substrates. Evidence for even shorter-range distortions, down to a few nanometres or less, is found by electron diffraction of suspended CMG. Comparison of the experimental data with simulations reveals that the mean atomic displacement from the nominal lattice position is of order 10% of the carbon–carbon bond length. Taken together, these results suggest a complex structure for CMG where heterogeneous functionalization creates local strain and distortion.

Platinum(II) N-heterocyclic carbene complexes: coordination and cyclometallation.

Four different NHC ligands have been coordinated to Pt(II) centres; for the first time cyclometallation of the NHC ligand was observed, but only when the platinum centre had a DMSO and two methyl co-ligands. Cyclometallation resulted in the exclusive formation of five-membered rings, and the absence of any double cyclometallation reactions with appropriate ligands rules out the possibility of an oxidative addition type mechanism for the cyclometallation reaction.