Abstract
Analysis of x-ray diffraction from a single crystal of bis-benzene-1,2-dithiolato-Au(IV) [Au] at 125 K reveals a superstructure along the stacks of Au 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 rising smoothly to 0.67 at 0.55 GPa isotropic pressure. The magnetic susceptibility is low compared to the spin susceptibility of a system with one free spin per molecule. An activated behavior of is observed, which gives rise to a monotonic increase in at between 275 and 420 K. Reflectivity measurements along the axis (stacking direction) of a single crystal of Au shows a transition around 5000 (0.6 eV) possessing an oscillator strength ≈0.5 electron/molecule. Along the axis an absorption centered around 8000 is observed. The first transition (5000 ) is attributed to an intermolecular charge-transfer process while the latter transition (8000 ) most likely corresponds to an intramolecular excitation. The physical data presented are discussed in the context of a soft Mott insulator.
- Received 18 May 1995
DOI:https://doi.org/10.1103/PhysRevB.53.1773
©1996 American Physical Society