Structural and transport properties of neutral radical crystals of CoIII(tmp)(CN)2 (tmp = 5,10,15,20-tetramethylporphyrinato) and the CN-bridged polymer [CoIII(tmp)(CN)]n

Abstract

An axially ligated Co(tmp) (tmp = 5,10,15,20-tetramethylporphyrinato) anion, [Co^III(tmp)(CN)₂]⁻, has been prepared and subjected to electrochemical oxidation to obtain the open shell tmp π-ligand. With acetone as the solvent, solvent-free neutral radical crystals of Co^III(tmp)(CN)₂ are obtained, whereas solvent-inclusive crystals of Co^III(tmp)(CN)₂·2CH₃CN are obtained with CH₃CN as the solvent. In both crystals, the open shell tmp ring deforms into a ruffled form, which makes the π–π interactions in the crystal weak. Thus, the electrical conductivity is low, and the crystals behave as semiconductors with a room temperature resistivity of 10⁶ Ω cm and an activation energy of about 0.3 eV. When the solvent is acetone, non-oxidized crystals of the CN-bridged polymer {[Co^III(tmp)(CN)](acetone)}_n are obtained as a byproduct. The closed shell tmp ring deforms into a ruffled form, and there π–π interactions in the crystal are negligible. The room temperature resistivity is rather high at about 10⁸ Ω cm.