ABSTRACT:We report the synthesis and full characterization of the entire haloferrocene (FcX) and 1,1'-dihaloferrocene (fcX 2 ) series (X = I, Br, Cl, F; Fc = ferrocenyl, fc = ferrocene-1,1'-diyl). Finalization of this simple, yet intriguing set of compounds has been delayed by synthetic challenges associated with the incorporation of fluorine substituents. Successful preparation of fluoroferrocene (FcF) and 1,1'-difluoroferrocene (fcF 2 ) were ultimately achieved using reactions between the appropriate lithiated ferrocene species and N-fluorobenzenesulfonimide (NFSI). The crude reaction products, in addition to those resulting from analogous preparations of chloroferrocene (FcCl) and 1,1'-dichloroferrocene (fcCl 2 ), were utilized as model systems to probe the limits of a previously reported 'oxidative purification' methodology. From this investigation and careful solution voltammetry studies, we find that the fluorinated derivatives exhibit the lowest redox potentials of each of the FcX and fcX 2 series. This counter-intuitive result is discussed with reference to the spectroscopic, structural and first principles calculations of these and related materials.

We have experimentally Investigated the hydrate decomposition conditions in three different H2S-containing mixtures in the temperature region 0-30 °C. The three mixtures investigated were 4% H2S, 7% propane, 89% methane; 12% H2S, 7% propane, 81% methane; and 32% H2S, 7% propane, 61% methane. Hydrate decomposition pressures and temperatures were obtained for each of these mixtures by observation of the pressure-temperature hysteresis curves associated with formation and decomposition of the hydrate crystals. A repeatable decomposition point was observed in every case, and this was Identified as the hydrate point. The results for the 4% H2S mixture were used to adjust parameters in a computer model based on the Parrish and Prausnitz statistical thermodynamics method, coupled with the BWRS equation of state. After the parameter adjustment, the computer model correlated the behavior of the 12% H2S and the 32% H2S mixtures within 2 °C.

Recent interest in functionalised graphene has been motivated by the prospect of creating a two-dimensional semiconductor with a tuneable band gap. Various approaches to band gap engineering have been made over the last decade, one of which is chemical functionalisation. In this work, a predictive physical model of the self-assembly of halogenated carbene layers on graphene is suggested. Self-assembly of the adsorbed layer is found to be governed by a combination of the curvature of the graphene sheet, local distortions, as introduced by molecular adsorption, and short-range intermolecular repulsion. The thermodynamics of bidental covalent molecular adsorption and the resultant electronic structure are computed using density functional theory. It is predicted that a direct band gap is opened that is tuneable by varying coverages and is dependent on the ripple amplitude. This provides a mechanism for the controlled engineering of graphene's electronic structure and thus its use in semiconductor technologies.

Structural analysis of beam‐sensitive materials by transmission electron microscopy (TEM) represents a significant challenge, as high‐resolution TEM (HRTEM) requires high electron doses that limit its applicability to stable inorganic materials. Beam‐sensitive materials, e.g., organic crystals, must be imaged under low dose conditions, leading to problematic contrast interpretation and loss of fine structural details. Here, HRTEM imaging of organic crystalline materials with near‐atomic resolution of up to 1.6 Å is described, which enables real‐space studies of crystal structures, as well as observation of co‐existing polymorphs, crystal defects, and atoms. This is made possible by a low‐dose focal‐series reconstruction methodology, which provides HRTEM images where contrast reflects true object structure and can be performed on contemporary cryo‐EM instruments available to many research institutions. Copper phthalocyanine (CuPc), a perchlorinated analogue of CuPc, and indigo crystalline films are imaged. In the case of indigo crystals, co‐existing polymorphs and individual atoms (carbonyl oxygen) can be observed. In the case of CuPc, several polymorphs are observed, including a new one, for which the crystal structure is found based on direct in‐focus imaging, accomplishing real‐space crystal structure elucidation. Such direct analysis can be transformative for structure studies of organic materials.

Halides and pseudohalides of boron subphthalocyanine (BsubPc) are promising candidates for efficient yet stable organic photovoltaics. Here, the electronic structure of such molecules, obtained using density functional theory, is considered. Based on the calculations, it is found that the tetrameric boron bond is stabilized by an inductive effect at the axial substituent and by conjugative effects across the ring system. It is further found that stability is dictated mostly by the axial moiety, such that Br-BsubPc is the most fitting precursor structure for further synthesis steps, whereas F-BsubPc is the most suitable candidate for long-term device performance. H-BsubPc is examined as a new BsubPc derivative, and found to be too volatile for long term device performance. Finally, it is shown that peripheral substitution dictates the position of frontier orbitals, thereby allowing for essentially separate optimization of material properties and material stability.

An isotropic compression of graphene is shown to induce a structural deformation on the basis of Density Functional Perturbation Theory. Static instabilities, indicated by imaginary frequency phonon modes, are induced in the high symmetry Γ-K (zigzag) and Γ-M (armchair) directions by an isotropic compressive strain of the graphene sheet. The wavelength of the unstable modes (ripples) is directly related to the magnitude of the strain and remarkably insensitive to the direction of propagation in the 2D lattice. These calculations further suggest that the formation energy of the ripple is isotropic for lower strains and becomes anisotropic for larger strains. This is a result of graphene's elastic property, which is dependent on direction and strain. Within the quasi-harmonic approximation this is combined with the observation that molecular adsorption energies depend strongly on curvature to suggest a strategy for generating ordered overlayers in order to tune the functional properties of graphene.

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Halides and pseudohalides of boron subphthalocyanine (BsubPc) are promising candidates for efficient yet stable organic photovoltaics. Here, we consider the electronic structure of such molecules using density functional theory (DFT). Based on the calculations, we find that the tetrameric boron bond is stabilized by an inductive effect at the axial substituent and by conjugative effects across the ring system. We further find that stability is dictated mostly by the axial moiety, whereas peripheral substitution dictates the position of frontier orbitals, thereby allowing for separate optimization of these two important properties.