New BDH-TTP/[MIII(C505)3]3- (M = Fe, Ga) Isostructural Molecular Metals.

Two new isostructural molecular metals-- (BDH- TTP)6[MIII(C505)3]-CH2C12 (BDH-TTP = 2,5-bis(1,3-dithioian-2-ylidene)-l,3,4,6-tetrathiapentalene, where M = Fe (1) and Ga (2))--have been prepared and fully characterized. Compound 1 is a molecular conductor showing paramagnetic behavior, which is due to the presence of isolated [Fe(C5O5)3]3- complexes with high-spin S = 5/2 Fe (III) metal ions. The conductivity originates from the BDH-TTP organic donors arranged in a K-type molecular packing. At 4 kbar, compound 1 behaves as a metal down to ~100 K, showing high conductivity (~10 S cm-1) 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 1, ESR signals have been interpreted as being caused by the fine structure splitting of the high-spin (S = 5/2) state of Fe(III) in the distorted octahedral crystal field from the ligands. At 4 kbar, the isostructural compound 2 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 2, only the signal assigned to delocalized π-electrons has been observed in the ESR measurements. [ABSTRACT FROM AUTHOR]