Imaging the Structure, Symmetry, and Surface-Inhibited Rotation of Polyoxometalate Ions on Graphene Oxide

Abstract

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.

Carbon Nanotubes as Electrically Active Nanoreactors for Multi-Step Inorganic Synthesis: Sequential Transformations of Molecules to Nanoclusters and Nanoclusters to Nanoribbons

“…However, the tumbling motion of the nanoclusters can be beneficial for understanding their 3D structures in HRTEM analysis, as a rotating nanocluster allows direct visualisation of all of its principal projections by time-series imaging of the same cluster within the nanotube (Fig 2b-f) without any need to tilt the specimen. Extensive AC-HRTEM image acquisition combined with structural modelling and HRTEM image simulations (Supporting Information file) strongly indicate a highly symmetrical octahedral arrangement of metal atoms with eight  3 -I bridging I-atoms capping each face of the octahedron, and a further six  1 -I atoms coordinated to each metal (Fig 2h-k), yielding a shape topologically similar to polyoxometalate (POM) clusters [31,32] and an overall stoichiometry M6I14 agreeing well with the EDX elemental analysis. The new set of low-frequency Raman bands in the 50 130 cm -1 range emerging as a result of polyiodide and metal complex reaction in SWNT is consistent with the anionic form of the clusters [W6I14] 2- (Fig 2l) and [Mo6I14] 2- (Fig 3k), whereas the G-band is significantly blue-shifted for both clusters with respect to empty nanotubes (Fig 2m and 2j), suggesting that the electrons abstracted from SWNT by iodine in the first step of the inorganic synthesis have been passed onto the metal iodide nanocluster such that the host-nanotube remains positively charged, and the overall structure being described as n·[M6I14] 2-@SWNT 2n+ (Fig 1c).…”

Covalently Binding Atomically Designed Au9 Clusters to Chemically Modified Graphene

“…Thei nhibited rotation is caused by interaction with the electron beam and is indicative of as et of metastable orientations.P rior work has observed similar electron beam induced molecular motion on graphene oxide, [32] on carbon nanotubes, [33,34] and for molecules attached to carbon nanohorns,where it was shown that lower acceleration voltages in the TEM resulted in higher frequency of molecular motion as aresult of alarger scattering cross-section. [35,36] An accelerat- Figure 2.…”

Aberration corrected imaging of a carbon nanotube encapsulated Lindqvist Ion and correlation with Density Functional Theory

“…Fig. 1(b) shows a wider field of view image of two parallel DWNTs, one empty, one containing a discrete [W 6 O 19 ] 2-anion. Comparison of a detail of the same structure anion as imaged using the 300 kV HR-TEM (C s = 0.6 mm) in Fig.…”

“…In the present context, they provide molecular-scale heavy atom motifs with observable symmetry than can be imaged by conventional high resolution transmission electron microscopy (HRTEM) when mounted in single or double walled carbon nanotubes (i.e. SWNTs or DWNTs) or graphene oxide [5,6] 2-ion in DWNTs [5] ( Fig. 1(a)) by HR-TEM and have imaged the W 2 -W 2 atom column separations in the equatorial plane of the anion.…”