Syntheses, Molecular Structures, and Spectroscopy of Gold(III) Dithiolate Complexes

Two Au(III) dithiolate complexes, [Au(dbbpy)(tdt)]PF6 and Au(η2-C,N-ppy)(tdt), (dbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine; tdt = 3,4-toluenedithiolate; ppy = C-deprotonated 2-phenylpyridine), have been prepared and
structurally characterized by X-ray crystallography. The complexes have low-energy absorption bands that exhibit
mild solvatochromism (λmax = 444 nm (ε, 2310 M-1 cm-1) in CH2Cl2 and 406 nm (ε, 3170 M-1 cm-1) in DMSO)
and are tentatively assigned to a charge-transfer-to-diimine transition. This transition occurs at higher energy
than the analogous charge-transfer transition in related Pt(II) complexes (e.g., Pt(dbbpy)(tdt), λmax = 563 nm (ε,
7200 M-1 cm-1). Whereas neither Au(III) complex is emissive, their respective dichloride precursors, [Au(dbbpy)Cl2]PF6 and Au(η2-C,N-ppy)Cl2, luminesce in low-temperature glass matrixes from an excited state that
is tentatively assigned as intraligand π−π*. The neutral complex, Au(η2-C,N-ppy)(tdt), is more easily oxidized
(Eox = 0.925 V vs 1.589 V (vs NHE)) and less easily reduced (Ered = −1.339 V vs −0.255 V (vs NHE)) than
the cationic complex, [Au(dbbpy)(tdt)]PF6. Both dithiolate complexes exhibit approximately square planar
coordination. Yellow crystals of [Au(dbbpy)(tdt)]PF6 (C25H30AuF6N2PS2) are triclinic, space group P1̄ (No. 2),
with a = 7.1977(2) Å, b = 11.7292(1) Å, c = 17.5820(5) Å, α = 104.537(2)°, β = 96.592(2)°, γ = 102.455(2)°,
V = 1380.41(6) Å3, Z = 2, and final R = 0.050 (Rw = 0.1062) for 3446 unique reflections. Orange crystals of
Au(η2-C,N-ppy)(tdt) (C18H14AuNS2) are monoclinic, space group P21/c (No. 14), with a = 8.852(1) Å, b =
11.726(2) Å, c = 15.499(5) Å, β = 101.34(2)°, V = 1577.5(6) Å3, Z = 4, and final R = 0.0438 (Rw = 0.0759)
for 3685 unique reflections. A structural trans effect in Au(η2-C,N-ppy)(tdt) results in a significantly longer
Au−S distance (ca. 0.1 Å) trans to the Au−C bond than that trans to the Au−N bond. In the solid state, the
[Au(dbbpy)(tdt)]+ cations are arranged in stacks with alternating intermolecular Au···Au separations of 3.60 and
3.75 Å while the Au(η2-C,N-ppy)(tdt) molecules form stacks with an intermolecular Au···Au separation of 3.81
Å.