Syntheses of new TTF-based metal complexes for conducting and magnetic systems: Schiff base-type metal complex with partially oxidized TTF moiety

Abstract

New TTF-based ligands (TTF=tetrathiafulvalene) with Schiff base-type coordination sites have been synthesized: 4,5-bis(4-salicylideneiminophenyl)-4′,5′-ethylenedithio-TTF ( 1a), 4,5-bis(4-picolinideneiminophenyl)-4′,5′-ethylenedithio-TTF ( 1b), and 4-(2-salicylideneiminoethylthio)-5-methyl-4′,5′-ethylenedithio-TTF (Hsae-TTF). X-ray crystallography for 1a revealed that 1a has rigid structure around the coordination sites, which prevents it to form metal complexes. On the other hand, Hsae-TTF ligand has flexibility around its coordination sites due to alkyl chain spacer, and gave mononuclear complexes with Ni(II) and Cu(II) ions, [M II(saeTTF) 2] (M II=Ni(II) and Cu(II)). The metal ions in [M II(saeTTF) 2] have a square planar coordination structure with two TTF-based ligands, which was sandwiched by two neutral TTF moieties. The Cu(II) complex, [Cu II(saeTTF) 2], yielded charge transfer (CT) complexes with acceptors such as F 4TCNQ, DDQ, and iodine. CT complexes with F 4TCNQ and iodine were semiconductive, but that with DDQ was insulator. This is due to the difference of the degree of charge transfer; TTF moiety in F 4TCNQ salt was partially oxidized but that of DDQ salt was completely oxidized. The radical cation salts of [Cu II(saeTTF) 2] with PF 6 ‐ anion was also obtained in 1:1 donor and anion ratio by electrocrystallization. The donor and anion ratio indicates that the oxidation state of TTF moieties in the radical salt, [Cu II(saeTTF) 2]PF 6, was partial oxidation state.