Formation of Three-Dimensional Electronic Networks Using Axially Ligated Metal Phthalocyanines as Stable Neutral Radicals

Abstract

Organic π-radical crystals are potential single-component molecular conductors, as they involve charge carriers. We fabricated new organic π-radical crystals using axially ligated metal phthalocyanine anions ([MIII(Pc)L2]−) as starting materials. Electrochemical oxidation of [MIII(Pc)L2]− afforded single crystals of organic π-radicals of the type MIII(Pc)Cl2·THF (M = Co or Fe, THF = tetrahydrofuran), where the π-conjugated macrocyclic phthalocyanine ligand is one-electron oxidized. The X-ray crystal structure analysis revealed that MIII(Pc)Cl2 formed three-dimensional networks with π-π overlaps. The electrical resistivities of CoIII(Pc)Cl2·THF and FeIII(Pc)Cl2·THF at room temperature along the a-axis were 6 × 102 and 6 × 103 Ω cm, respectively, and were almost isotropic, meaning that MIII(Pc)Cl2·THF had three-dimensional electronic systems.

Diamond lattice in single-component molecular crystals comprising tetrabenzoporphyrin neutral radicals

“…22 Consequently, all the absolute values of s 1 -s 4 , |s|, are 5.2 Â 10 À3 and predictably identical. |s| is remarkably larger than that for radical crystals comprising M(Pc)L 2 , 13,14 and comparable to that for a M(Pc)(CN) 2 -based partially oxidized salt, which exhibits metallic nature. 23 The large |s| values for M(tbp)L 2 despite the radical crystals arise owing to the intermolecular short contacts between the pyrrole carbon atoms, where the highest electron density of the HOMO is located, and the carbon atoms of the benzene rings in neighboring molecules (Fig.…”

“…A number of molecular crystals comprising neutral radicals of coordination complexes M III (Pc À )L 2 , where M III = trivalent metal ion, Pc 2À = phthalocyaninato ligand, and L = axial ligand, were reported during the investigation of molecular conductors. [12][13][14] The crystal structures of the M III (Pc À )L 2 radicals depend upon the crystal solvents and axial ligands, resulting in various molecular arrangements. However, the diamond lattice has not been reported for M III (Pc À )L 2 crystals.…”