Radical or Not Radical: Compared Structures of Metal (M = Ni, Au) Bis-Dithiolene Complexes with a Thiazole Backbone

A complete series of dianionic, monoanionic,
and neutral dithiolene complexes formulated as [Ni­(Et-thiazdt)2]n, with n =
−2, −1, 0, and Et-thiazdt: N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate,
is prepared using an optimized procedure described earlier for the
N–Me derivatives. Electrochemical and spectroscopic properties
confirm the electron-rich character of the Et-thiazdt dithiolate ligand.
The three complexes are structurally characterized by single-crystal
X-ray diffraction. The paramagnetic anionic complex [Ni­(Et-thiazdt)2]−1, as Ph4P+ salt,
exhibits side-by-side lateral interactions leading to a Heisenberg
spin chain behavior. The solid-state structure of the neutral, diamagnetic
[Ni­(Et-thiazdt)2]0 complex shows a face-to-face
organization with a large longitudinal shift, at variance with the
structure of its radical and neutral gold dithiolene analogue described
earlier and formulated as [Au­(Et-thiazdt)2]•. Comparison of the two structures, and those of the other few structurally
characterized pairs of Ni/Au dithiolene complexes, demonstrates the
important role played by overlap interactions between gold dithiolene
radical species. Despite its closed-shell character, the neutral nickel
complex [Ni­(Et-thiazdt)2]0 exhibits a semiconducting
behavior with a room-temperature conductivity σRT ≈ 0.014 S cm–1.