Structural, electrical, magnetic, and optical properties of bis-benzene-1,2-dithiolato-Au(IV) crystals

Abstract

Analysis of x-ray diffraction from a single crystal of bis-benzene-1,2-dithiolato-Au(IV) [Au(Formula presented)] at 125 K reveals a superstructure along the stacks of Au(Formula presented) molecules corresponding to a dimerization of the molecules along the stack. Within a dimer, intermolecular sulfur-sulfur contacts are shortened from 3.7 to 3.6 Å whereas a lengthening to about 3.8 Å is found between dimers. Electrical resistivity measured by a four-probe method between 230 and 450 K uncovers an activated resistivity with a characteristic energy of 0.30 eV. The room-temperature conductivity at zero applied pressure is 0.11 (Formula presented) rising smoothly to 0.67 (Formula presented) at 0.55 GPa isotropic pressure. The magnetic susceptibility (Formula presented) is low compared to the spin susceptibility of a system with one free spin per molecule. An activated behavior of (Formula presented) is observed, which gives rise to a monotonic increase in (Formula presented) at between 275 and 420 K. Reflectivity measurements along the (Formula presented) axis (stacking direction) of a single crystal of Au(Formula presented) shows a transition around 5000 (Formula presented) (0.6 eV) possessing an oscillator strength ≈0.5 electron/molecule. Along the (Formula presented) axis an absorption centered around 8000 (Formula presented) is observed. The first transition (5000 (Formula presented)) is attributed to an intermolecular charge-transfer process while the latter transition (8000 (Formula presented)) most likely corresponds to an intramolecular excitation. The physical data presented are discussed in the context of a soft Mott insulator. © 1996 The American Physical Society.