Synthesis, High-Resolution Infrared Spectroscopy, and Vibrational Structure of Cubane, C8H8

Shape Symmetrization and IR-Spectral Enhancement of Aluminum Clusters via Doping with a Carbon Core

Composite nanosystems are a class of objects with interesting and potentially useful properties. Here we study mixed-composition species representing interfaces at the molecular level between such technologically relevant materials as carbon and aluminum. Specifically, core-shell C₈@Al_n (n = 16, 18) species and their isomers with the core and relaxed-shell attached outside are investigated at a DFT level in terms of structures and stabilities, charge distributions and polarities, and IR spectra and electron affinities. Among the interesting findings is the possibility of bringing the aluminum cluster into a more symmetric shape (thus making a convenient building block) via insertion of a suitable molecular-carbon skeleton. Another notable feature is the system-selective dependence of polarity on spin multiplicity, suggesting possible molecular-electronic applications. The IR spectra of the composite species are much brighter compared to those of the separated components and are highly focused for the core-shell isomers. A related aspect of interest is the apparent reflections of the system structural details in the IR spectra features (line intensities and separations) via related vibrations, facilitating an experimental analysis of the structure and detection of the species formation and transformation as well as potentially enabling the means of achieving desirable optical characteristics via a geometric design.

Cubane and cubanoid: Structural, optoelectronic and thermodynamic properties from DFT and TD-DFT method

In this paper, we report structural, electronic and optical properties of cubane (C₈H₈) and cubanoids (cubane-like molecules) using Density Functional Theory (DFT). The cubanoids are cubanes for which Carbon atoms have been substituted by Nitrogen (N), Phosphorus (P), Boron (B), Silicon (Si), Arsenic (As), Antimony (Sb) or Bismuth (Bi) atoms. These molecules presented exceptional stability with several different symmetry point groups, being the majority T_d. All calculated vibrational frequencies are positive for any studied molecules indicating that all these structures are in a stable state. The HOMO-LUMO gaps and DOS were calculated converged towards to values between 1.87 eV and 5.61 eV, actually showing promising electronic properties (Just for comparison, the cubane energy gap is 7.50 eV). The optical absorptions were also calculated for the cubanoid structure using the Time-Dependent Density Functional Theory (TD-DFT). Their dependence on the wavelength is analyzed, where five of theses structures absorb on the visible region. Finally, the extrapolation of thermodynamic properties indicates that these cubanoid could be potentially synthesized spontaneously, where four structures, the synthesis would occur for temperatures below 400 K, while for Si₄Bi₄H₄ structure, the synthesis would occur at room temperature.