Crystal structures and physical properties of single-component molecular conductors consisting of nickel and gold complexes with bis(trifluoromethyl)tetrathiafulvalenedithiolate ligands

Abstract

The neutral nickel and gold complexes with bis(trifluoromethyl)tetrathiafulvalenedithiolate ligands, [M(hfdt)₂] (M = Ni, Au) were prepared in order to examine the possibility of the development of single-component molecular conductors soluble in organic solvents. However, in contrast to the previous report, the crystals did not show any solubility in the usual organic solvents. On the other hand, the crystal structure analyses showed unique two-dimensional layered structures, despite that the single-component molecular conductors usually tend to take a compact three-dimensional molecular arrangement. Each layer is separated by the terminal CF₃ groups to form the “CF₃ bilayer structure”. The shortest intermolecular F⋯F distance (3.018 Å for [Ni(hfdt)₂] and 2.862 Å for [Au(hfdt)₂]) is significantly longer than the van der Waals F⋯F distance (2.70 Å) and the distribution of the frontier electrons is almost zero around the CF₃ bilayer region. This is due to the strong F⋯F segregation effect, which will provide a useful way to control the molecular aggregation in the single-component molecular conductors. Extended-Hückel tight-binding band structure calculations and the ab initio local density approximation (LDA) band structure calculations were made for [Ni(hfdt)₂], which explains the semiconducting and non-magnetic properties of the system. Extended-Hückel tight-binding band structure calculations were also made for [Au(hfdt)₂]. The calculated band structure is consistent with the semiconducting and almost non-magnetic properties of [Au(hfdt)₂].