Hermann Sachdev

Supramolecular Assemblies Formed on an Epitaxial Graphene Superstructure

The seminal work of Novoselov et al. has stimulated great interest in the controllable growth of epitaxial graphene monolayers. While initial research was focussed on the use of SiC wafers, the promise of transition metals as substrates has also been demonstrated and both approaches are scalable to large-area production. 12] The growth of graphene on transition metals such as Ru, Rh and Ir leads to a moir!-like superstructure, 10,12,13] similar to that observed for BN monolayers. Here we show that such a superstructure can be used to control the organization of extended supramolecular nanostructures. The formation of two-dimensional supramolecular arrays has received increasing attention over recent years primarily due to potential applications in nanostructure fabrication as well as fundamental interest in self-assembly processes. Such studies can be highly dependent on the nature of the substrate used, and the interplay between surface and adsorbed supramolecular structure is a topic of significant conjecture. Until now metallic surfaces or highly oriented pyrolytic graphite (HOPG) have typically been the surfaces of choice for such studies. Our results demonstrate that graphene is compatible with, and can strongly influence molecular selfassembly. We have studied the adsorption of perylene tetracarboxylic diimide (PTCDI) and related derivatives on a graphene monolayer grown on a Rh(111) heteroepitaxial thin film (Figure 1). In particular, we show that a near-commensur-

Quasifreestanding single-layer hexagonal boron nitride as a substrate for graphene synthesis

We demonstrate that freeing a single-atom thick layer of hexagonal boron nitride (h-BN) from tight chemical bonding to a Ni(111) thin film grown on a W(110) substrate can be achieved by intercalation of Au atoms into the interface. This process has been systematically investigated using angle-resolved photoemission spectroscopy, X-ray photoemission and absorption techniques. It has been demonstrated that the transition of the h-BN layer from the “rigid” into the “quasi-freestanding” state is accompanied by a change of its lattice constant. Using chemical vapor deposition, graphene has been successfully synthesized on the insulating, quasi-freestanding h-BN monolayer. We anticipate that the in situ synthesized weakly interacting graphene/h-BN double layered system could be further developed for technological applications and may provide perspectives for further inquiry into the unusual electronic properties of graphene.

How Does Graphene Grow? Easy Access to Well‐Ordered Graphene Films

The selective formation of large-scale graphene layers on a Rh-YSZ-Si(111) multilayer substrate by a surface-induced chemical growth mechanism is investigated using low-energy electron diffraction, X-ray photoelectron spectroscopy, X-ray photoelectron diffraction, and scanning tunneling microscopy. It is shown that well-ordered graphene layers can be grown using simple and controllable procedures. In addition, temperature-dependent experiments provide insight into the details of the growth mechanisms. A comparison of different precursors shows that a mobile dicarbon species (e.g., C(2)H(2) or C(2)) acts as a common intermediate for graphene formation. These new approaches offer scalable methods for the large-scale production of high-quality graphene layers on silicon-based multilayer substrates.

Synthesis, Reactivity and Molecular Structures of Bis(diphenylphosphanyl)methane‐Bridged Heterobimetallic Iron−Platinum Isocyanide Complexes: Breaking and Formation of Metal−Metal Bonds

When [(OC)3Fe(μ-CO)(μ-dppm)PtCl2] (1) is allowed to react with stoichiometric amounts of various isocyanides, cleavage of the metal−metal bond occurs, yielding the heterodinuclear isocyanide complexes [(OC)4Fe{μ-dppm}Pt(Cl)2(CNR)] (2a: R = 2,6-xylyl; 2b: R = o-anisyl; 2c: R = benzyl; 2d: R = cyclohexyl; 2e: R = tosylmethyl). Reduction of 2a−2e by NaBH4 in the presence of PPh3 affords the isocyanide-bridged complexes [(OC)3Fe(μ-C=N−R)(μ-dppm)Pt(PPh3)] (3a: R = 2,6-xylyl; 3b: R = o-anisyl; 3c: R = benzyl; 3d: R = cyclohexyl; 3e: R = tosylmethyl). Metathesis of 2a−2d with NaI rapidly results in the formation of [(OC)4Fe{μ-dppm}PtI2(CNR)] (4a−4d), which is slowly transformed under extrusion of CO giving [(OC)2IFe{μ-dppm}(μ-CO)PtI(CNR)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = benzyl; 6d: R = cyclohexyl), bearing an iodine ligand at the iron center. Due to this intramolecular iodide migration from Pt to Fe, an FeI d7 fragment interacts with a PtI d9 fragment through a covalent bond. Alternatively, 6a−6d are obtained by stoichiometric treatment of [(CO)3Fe(μ-I)(μ-dppm)PtI] (5) with CNR. Single-crystal X-ray diffraction studies are performed on 2d, 2e and 3c as well as on 6d. In the solid state, the two metal centers of 2e remain in close contact (3.862 A), whereas in the case of 2d they are separated by 6.573 A after cleavage of the metal−metal bond by CNR. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

New Aspects in the Coordination Chemistry of Magnesium Hydrazides

The coordination chemistry of alkaline earth metal hydrazides has been investigated, and the synthesis and crystal structures of monomeric magnesium bis[N-phenyl-N′,N′-bis(trimethylsilyl)hydrazide] (1) and dimeric magnesium bis[N,N-dimethyl-N′-(trimethylsilyl)hydrazide] (2) are presented. An unusual coordination sphere of the magnesium atom was observed in the first structurally characterized monomer magnesium hydrazide 1, a highly reactive compound with side-on coordinated hydrazide ligands forming a bent butterfly-type structure. The Mg−N distances range from 1.92 to 2.45 A and intramolecular C−H···Mg interactions in the range 2.42 to 2.63 A are observed. This structural motif is unprecedented in the coordination chemistry of magnesium hydrazides. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A New Type of Anionic Rearrangement in Metalated Benzylhydrazines

Metalation of N,N-dibenzyl-N′-(trimethylsilyl)hydrazine with organyllithium and -magnesium compounds led to the migration of the benzyl group, and the deprotonation of Si−Me groups was observed. The syntheses and crystal structures of Bzl2N−NH2, [Bzl(Li)N−N(SiMe3)Bzl]2, and [Mg[BzlN−N(SiMe2CH2)Bzl]2 are presented. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Coordination chemistry of furfurylsilylamides

The syntheses and crystal structures of three new furfurylamides are described, tetrameric lithium furfurylamide (1), dimeric magnesium furfurylamide (2), and dimeric dimethylaluminiumfurfurylamide (3). The compounds were characterized by 1H-, 13C-, 29Si- and 7Li- NMR spectroscopy and by X-ray crystallography.