σ/σ- and π/π-Interactions Are Equally Important: Multilayered Graphanes

Abstract

The properties of single-sheet [n]graphanes, their double-layered forms (diamondoids), and their van der Waals (vdW) complexes (multilayered [n]graphanes) were studied for n = 10-97 at the dispersion-corrected density functional theory (DFT) level utilizing B97D with a 6-31G(d,p) basis set; for comparison, we also computed a series of structures at M06-2X/6-31G(d,p) as well as B3LYP-D3/6-31G(d,p) and evaluated SCS-MP2/cc-pVDZ single-point energies. The association energies for the vdW complexes reach 120 kcal mol(-1) already at 2 nm particle size ([97]graphane dimer), and graphanes adopt layered structures similar to that of graphenes. The association energies of multilayered graphanes per carbon atom are rather similar and independent of the number of layers (ca. 1.2 kcal mol(-1)). Graphanes show quantum confinement effects as the HOMO-LUMO gaps decrease from 8.2 eV for [10]graphane to 5.7 eV for [97]graphane, asymptotically approaching 5.4 eV previously obtained for bulk graphane. Similar trends were found for layered graphanes, where the differences in the electronic properties of double-sheet CH/σ vdW and double-layered CC/σ diamondoids vanish at particles sizes of 1 nm. For comparison, we studied the parent CC/π systems, i.e., the single- and double-sheet [n]graphenes (n = 10-130) for which the association energies demonstrate the same trends as in the case of [n]graphanes; in both cases the band gaps decrease with an increase in system size. The [112]graphene dimer (HOMO-LUMO gap = 0.5 eV) already approaches the 2D metallic properties of graphite.

Compressed representation of dispersion interactions and long-range electronic correlations

“…This is in agreement with other literature findings. [60][61][62] We also verified that the relative contribution of σ and π electrons was well-represented by our approximate T disp 2 (see Supporting Information for a more detailed discussion).…”

A Refined Intermolecular Interaction Potential for Methane: Spectral Analysis and Molecular Dynamics Simulations

“…Such counter-intuitive di-hydrogen bonds or s-s interactions have recently attracted much attention and stimulated many exciting discussions. [5][6][7] In Table 1 we show the basis set dependence of the calculated binding energies (i.e. the dissociation energy from the equilibrium point), bond lengths (i.e.…”

“…[1][2][3][4] The newly identified di-hydrogen bonds or s-s interactions have attracted much attention and stimulated many exciting discussions. [5][6][7] Obtaining information about the intermolecular interactions among hydrocarbons from solely experimental means has been a very challenging task mainly because the formed complexes are dominated by dispersion forces. To accurately describe dispersion interactions, modern quantum chemistry methodology has been proven to be indispensable.…”

London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte

“…[105] Im Gegensatz dazu zeigen starre Alkane wie die Polyhedrane außerordentlich hohe Schmelzpunkte und Assoziationsenergien. [98] Die Untersuchung noch grçßerer all-Sessel-Cyclohexanbasierter Alkandimere ("Graphane"; Abbildung 3) und der Vergleich mit Aryl-Aryl-(p-p)-Dimeren ergab,dass p-p-und s-s-Wechselwirkungen gleich wichtig (nicht gleich) sind, [106] wobei die p-p-Wechselwirkungen mit zunehmender Molekülgrçße energetisch schneller anwachsen. [82,107] Diese Schlussfolgerung wurde unabhängig bestätigt [107] und insofern weiterentwickelt, als dass s-s-und s-p-Wechselwirkungen als lokal betrachtet werden kçnnen, während die p-p-Stapelung inhärent nichtlokal ist und nichtadditive Effekte ermçg-licht.…”

“…B. bei dem gut polarisierbaren CS 2 .G enauso ist 1,6-Di-tert-butylcyclooctatetraen, das offensichtlich das sterisch stärker Abbildung 3. Exemplarische Abbildungen großer,r egelmäßiger s-sund p-p-Dimere vergleichbarer Grçße: [106] [121]Graphan und [130]Graphen und ihre Assoziationsenergien pro Kohlenstoffatom, die anhand der Dimerisierungsenergien von Coronen und Perhydrocoronen auf CCSD(T)-Niveau abgeschätzt wurden. [107] Schema 2.…”