Two-Channel Conductivity and Carrier Crossover in CoxNi1-x(pc)I, Alloys of the Molecular Conductors (Phthalocyaninato)nickel Iodide and (Phthalocyaninato)cobalt Iodide

Article abstract of DOI:10.1021/ja00199a021

Alloys of the isostructural porphyrinic molecular conductors (phthalocyaninato)cobalt iodide, Co(pc)I, and (phthalocyaninato)nickel iodide, Ni(pc)I, of composition Co_xNi_1-x(pc)I, x = 0.02, 0.10, 0.15, 0.20, 0.33, 0.50, 0.75, 0.90, and 0.95, have been prepared and shown to be homogeneous solid solutions by EPR and energy-dispersive X-ray microprobe analysis.The high (?_RT ca. 500 Ω^-1 cm^-1) metallic conductivity of Ni(pc)I (x = 0) is associated with holes (positive thermopower) created by partial oxidation from the valence ?-band of the pc macrocycle,whereas the lower (?_RT ca. 50 Ω^-1 cm^-1) nonmetallic conductivity of Co(pc)I (x = 1) is associated with electron carriers (negative thermopower) in the partially oxidized d_z² band of the metal-ion spine.For x a maximum appears in the conductivity between 170 and 260 K.This change is attributed to paramagnetic scattering by the Co(2+) local moments.With further increase in x the conductivity continues to change smoothly toward the nonmetallic behavior of Co(pc)I.Surprisingly, the thermopower does not smoothly tend toward the large negative values for Co(pc)I but becomes increasingly positive as x is increased from 0.2 to 0.75 and begins to decrease only by x ca. 0.90.These resultsare interpreted to mean that alloys with 0.2