Electrically Conducting Materials Based On μ-Tetrathiooxalato-Bridged Bimetallic Ni(II) Anionic Complexes

A series of μ-tto- (tto = C2S42- = tetrathiooxalato) bridged bimetallic Ni(II) complexes with the general formula (Y)2{tto[Ni(L)]2} (where Y = Bu4N+, L = dsit = C3Se2S32- = 2-thioxo-1,3-dithiole-4,5-diselenolato (2) and dmise = C3SeS42- = 2-selenoxo-1,3-dithiole-4,5-dithiolato (3); and where Y = Me4N+ (4) and Et4N+ (5), L = dmit = C3S52- = 2-thioxo-1,3-dithiole-4,5-dithiolato) have been synthesized. The single-crystal X-ray structures of 2, 3, 4 and 5 have been determined: 2, (Bu4N)2{tto[Ni(dsit)]2}, monoclinic, space group P21/c, a = 9.8893(1) Å, b = 15.3544(1) Å, c = 17.8825(2) Å, β = 90.561(1)°, Z = 2; 3, (Bu4N)2{tto[Ni(dmise)]2}, orthorhombic, space group P212121, a = 9.8286(2) Å, b = 16.1741(3) Å, c = 34.3022(1) Å, Z = 4; 4, (Me4N)2{tto[Ni(dmit)]2}, monoclinic, space group C2/m, a = 13.8043(4) Å, b = 10.1081(1) Å, c = 12.0483(3) Å, β = 115.239(1)°, Z = 2; 5, (Et4N)2{tto[Ni(dmit)]2}, monoclinic, space group P21/n, a = 11.8313(1) Å, b = 11.0172(2) Å, c = 15.3014(1) Å, β = 110.951(1)°, Z = 2. All of the complexes presented are extensively conjugated and chalcogen-rich with (Bu4N)2{tto[Ni(dsit)]2} (2), (Bu4N)2{tto[Ni(dmise)]2} (3), and (Me4N)2{tto[Ni(dmit)]2} (4) also being planar as precursors to electrically conducting materials. The angle of the tto−Ni−L portion of the complexes varies with the choice of ligand and with the counterion. Cyclic voltammetry results of 2 and 3 each show a first low-potential reversible redox couple followed by a second nonreversible redox couple. The structural and electronic properties of 2−5 are compared to those of the recently communicated analogous complex, (Bu4N)2{tto[Ni(dmit)]2} (1). Electrocrystallization, interdiffusion, and chemical oxidation experiments with 1 have yielded black insoluble materials with high pressed powder conductivities of up to 0.5 S/cm.