Cofacial Assembly of Metallomacrocycles as an Approach to Controlling Lattice Architecture in Low-Dimensional Molecular Solids. Chemical, Structural, Oxidation-State, Transport, and Optical Properties of the Coordination Polymer [Fe(phthalocyaninato)(μ-pyrazine)]_n and the Consequences of Halogen Doping

This contribution reports the first integrated chemical and physicochemical study of the consequences of iodine doping on the cofacially joined metallomacrocyclic coordination polymers [Fe(Pc)(μ-pyz)]_n (Pc = phthalocyaninato, pyz = pyrazine). Polymers {[Fe(Pc)(μ-pyz)]I_y}_n, y ≲ 3, were prepared via the reaction of either [Fe(Pc)(μ-pyz)]_n or Fe(Pc)(pyz)₂ with iodine, and stoichiometry was established by elemental analysis and TGA/DTA (the latter measurements evidence stepwise loss of I₂, which is rather weakly bound, and then pyrazine). X-ray diffractometry indicates that the I₂-doped polymer is not highly crystalline, but that the undoped polymer is readily regenerated upon iodine removal. Resonance Raman spectroscopy indicates, by the reduced nature of the iodine species, that the polymer has been oxidized, while both ⁵⁷Fe Mössbauer (which supports the {[Fe(Pc)(μ-pyz)I_y}_n structural formulation) and ESR spectroscopy argue that the oxidation is largely ligand centered. Reflectance spectroscopy indicates that any plasmalike edge in the infrared is extremely weak, in marked contrast to previously studied {[M(Pc)O]I_1.1}_n polymers, M = Si, Ge. Four-probe charge-transport measurements on polycrystalline samples reveal large increases (up to 10⁶) in electronic conductivity with increasing dopant level (σ(max) ≈ 0.1 Ω^-1 cm^-1 at 300 K); the dependence of conductivity upon dopant level suggests the importance of percolation. The conductivity is thermally activated, with the apparent activation energies decreasing with increasing dopant level. A detailed analysis of the temperature dependence yields results in agreement with fluctuation-induced carrier tunneling through parabolic potential barriers separating the conducting regions.