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

Analysis of x-ray diffraction from a single crystal of bis-benzene-1,2-dithiolato-Au(IV) [Au(bdt)(2)] at 125 K reveals a superstructure along the stacks of Au(bdt)(2) 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 Angstrom whereas a lengthening to about 3.8 Angstrom 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 Omega(-1) m(-1) rising smoothly to 0.67 Omega(-1) m(-1) at 0.55 GPa isotropic pressure.

The magnetic susceptibility chi is low compared to the spin susceptibility of a system with one free spin per molecule. An activated behavior of chi is observed, which gives rise to a monotonic increase in chi at between 275 and 420 K. Reflectivity measurements along the b axis (stacking direction) of a single crystal of Au(bdt)(2) shows a transition around 5000 cm(-1) (0.6 eV) possessing an oscillator strength approximate to 0.5 electron/molecule.

Along the c axis an absorption centered around 8000 cm(-1) is observed. The first transition (5000 cm(-1)) is attributed to an intermolecular charge-transfer process while the latter transition (8000 cm(-1)) most likely corresponds to an intramolecular excitation. The physical data presented are discussed in the context of a soft Mott insulator.