119 research outputs found
The Adsorption of Small Molecules on the Copper Paddle-Wheel: Influence of the Multi-Reference Ground State
We report a theoretical study of the adsorption of a set of small molecules (CH, CO, CO, O, HO, CHOH, CHOH) on the metal centers of the âcopper paddle-wheelââa key structural motif of many MOFs. A systematic comparison between DFT of different rungs, single-reference post-HF methods (MP, SOSâMP, MP, DLPNOâCCSD(T)), and multi-reference approaches (CASSCF, DCDâCAS(2), NEVPT2) is performed in order to find a methodology that correctly describes the complicated electronic structure of paddle-wheel structure together with a reasonable description of non-covalent interactions. Apart from comparison with literature data (experimental values wherever possible), benchmark calculations with DLPNOâMRâCCSD were also performed. Despite tested methods show qualitative agreement in the majority of cases, we showed and discussed reasons for quantitative differences as well as more fundamental problems of specific case
Coronenohelicenes with Dynamic Chirality
The synthesis of a new type of chiral and dynamic nonplanar aromatics containing a combination of fused peryleneâbased coronenes and helicenes is reported. Either one or two helicene moieties were fused to the bay regions of an extended perylene core. The target compounds contain either identical or two different helicene building blocks. The combination with two helicene units leads to six different isomers, including two pairs of enantiomers and two meso forms. The experimental determination of the isomerization barriers the corresponding double [5]âhelicenes revealed activation energies of E=24.81 and 25.38 kcalâmol, which is slightly above the barrier of the parent [5]âhelicene. Resolution of all possible regioâ and stereoisomers allowed for the systematic investigation of the chiroptical properties. They revealed remarkable dissymmetry factors IgI of up to 1.2Ă10, which mirror the synergy between the strong absorbing perylenes and the inherent chirality of helicenes
ÏâExtended Diaza[7]helicenes by Hybridization of Naphthalene Diimides and Hexaâperiâhexabenzocoronenes
The synthesis of an unprecedented, Ïâextended hexabenzocorene (HBC)âbased diaza[7]helicene is presented. The target compound was synthesized by an orthoâfusion of two naphthalene diimide (NDI) units to a HBCâskeleton. A combination of DielsâAlder and Schollâtype oxidation reactions involving a symmetric diâNDIâtolane precursor were crucial for the very selective formation of the helical superstructure via a hexaphenylâbenzene (HPB) derivative. The formation of the diaza[7]helicene moiety in the final Scholl oxidation is favoured, affording the symmetric Ïâextended helicene as the major product as a pair of enantiomers. The separation of the enantiomers was successfully accomplished by HPLC involving a chiral stationary phase. The absolute configuration of the enantiomers was assigned by comparison of circular dichroism spectra with quantum mechanical calculations
A Robust and CostâEfficient Scheme for Accurate Conformational Energies of Organic Molecules
GraphocrownâA Novel, Two-Dimensional Oxocarbon: A Theoretical Study
An innovative 2D-material, graphocrown, was designed and studied. Our graphocrown computations revealed a higher stability compared to previous materials studied with the same generalized CO formula. The energetic benefit of the graphocrown formation from benzenehexol was also evaluated. The structure and properties of graphocrowns with various layer arrangements were analysed and compared. In addition, the formation of potassium complexes with the new material was studied. It was found that graphocrown binds potassium better than 18-crown-6, and the intercalation of graphocrown with potassium is more favourable, compared to graphite. Finally, the band structure, as well as the mobility of the charge carriers in the graphocrown, were investigated
Carbon Origami via an Alumina-Assisted Cyclodehydrofluorination Strategy
The synthesis of pristine nonâplanar nanographenes (NGs) via a cyclodehydrofluorination strategy is reported and the creation of highly strained systems via aluminaâassisted CâF bond activation is shown. Steric hindrance could execute an alternative coupling program leading to rare octagon formation offering access to elusive nonâclassical NGs. The combination of two alternative ways of folding could lead to the formation of various 3D NG objects, resembling the Japanese art of origami. The power of the presented âorigamiâ approach is proved by the assembly of 12 challenging nanographenes that are Ïâisoelectronic to planar hexabenzocoronene but forced out of planarity
Analytical Model of CVD Growth of Graphene on Cu(111) Surface
Although the CVD synthesis of graphene on Cu(111) is an industrial process of outstanding importance, its theoretical description and modeling are hampered by its multiscale nature and the large number of elementary reactions involved. In this work, we propose an analytical model of graphene nucleation and growth on Cu(111) surfaces based on the combination of kinetic nucleation theory and the DFT simulations of elementary steps. In the framework of the proposed model, the mechanism of graphene nucleation is analyzed with particular emphasis on the roles played by the two main feeding species, C and C. Our analysis reveals unexpected patterns of graphene growth, not typical for classical nucleation theories. In addition, we show that the proposed theory allows for the reproduction of the experimentally observed characteristics of polycrystalline graphene samples in the most computationally efficient way
Theoretical Investigations of (Oxidative) Dehydrogenation of Propane to Propylene over Palladium Surfaces
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