New BDH-TTP/[M<sup>III</sup>(C<sub>5</sub>O<sub>5</sub>)<sub>3</sub>]<sup>3–</sup> (M
= Fe, Ga) Isostructural Molecular Metals
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Abstract
Two new isostructural molecular metals(BDH-TTP)<sub>6</sub>[M<sup>III</sup>(C<sub>5</sub>O<sub>5</sub>)<sub>3</sub>]·CH<sub>2</sub>Cl<sub>2</sub> (BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene,
where M = Fe (<b>1</b>) and Ga (<b>2</b>))have
been prepared and fully characterized. Compound <b>1</b> is
a molecular conductor showing paramagnetic behavior, which is due
to the presence of isolated [Fe(C<sub>5</sub>O<sub>5</sub>)<sub>3</sub>]<sup>3–</sup> complexes with high-spin <i>S</i> = <sup>5</sup>/<sub>2</sub> Fe(III) metal ions. The conductivity
originates from the BDH-TTP organic donors arranged in a κ-type
molecular packing. At 4 kbar, compound <b>1</b> behaves as a
metal down to ∼100 K, showing high conductivity (∼10
S cm<sup>–1</sup>) at room temperature. When applying a pressure
higher than 7 kbar, the metal–insulator (M-I) transition is
suppressed and the compound retains the metallic state down to low
temperatures (2 K). For <b>1</b>, ESR signals have been interpreted
as being caused by the fine structure splitting of the high-spin (<i>S</i> = <sup>5</sup>/<sub>2</sub>) state of Fe(III) in the distorted
octahedral crystal field from the ligands. At 4 kbar, the isostructural
compound <b>2</b> behaves as a metal down to ∼100 K,
although it is noteworthy that the M-I transition is not suppressed,
even at pressures of 15 kbar. For <b>2</b>, only the signal
assigned to delocalized π-electrons has been observed in the
ESR measurements
