Toward Atomic-Scale Inorganic Double Helices via Carbon Nanotube Matrices - Induction of Chirality to Carbon Nanotubes

SnIP, an atomic-scale inorganic double helix compound is composed of a hexagonal rod packing of double helices in the bulk phase. A racemic mixture of P- and M-SnIP double helices is energetically most favored and present in the solid. In order to evaluate if enantiomer-pure SnIP might be able to realize three different stacking models of seven chiral double helices, an enantiomer-pure, a 2:1, and a racemic 1:1 ratio were investigated according to their energies of formation. While a top-down approach did not lead to single isolated double helices, the development of a bottom-up approach might be beneficial. Motivated by templating strategies in confined geometries we performed first principles density functional theory (DFT) calculations using carbon nanotubes (CNTs) featuring different electronic properties and suitable sizes as matrices to accommodate chiral SnIP double helices. With the aid of DFT, we determined the ideal diameter, stability, and electronic properties of different SnIP@CNT systems. Appropriate molecular starting materials and a feasible formation mechanism are identified based on chemical considerations. An interaction between the CNTs and the SnIP units is evident, causing structure and property modifications of the hybrids. The intercalation of SnIP into a suitable CNT leads to a gain in total energy compared to the isolated systems. Based on our findings, a straightforward way to introduce chirality in suitable CNTs via SnIP@CNT hybrids is feasible.