Potassium phthalocyanine, KPc: One-dimensional molecular stacks bridged by K⁺ ions

We report the synthesis of potassium phthalocyanine (KPc) and its structural characterization by synchrotron X-ray powder diffraction. We find that while KPc adopts the β-polymorphic structural type (monoclinic space group P2₁/a) common for many MPc solids, its structure is characterized by unique features. The K⁺ ions, which are statistically disordered over two symmetry-equivalent positions, reside in the intrastack spacing of the rodlike molecular assemblies and strongly bond equidistantly to selected N atoms of the two neighboring Pc rings along the chain direction with an unusual 5-fold coordination. The K⁺-stuffed slipped stacks of Pc units display much greater intrastack and slippage distances than those of other β-MPc polymorphs. They may be thought as comprising disordered dimeric (Pc)₂^2- units; this leads to electron pairing and is consistent with the observed nonmagnetic response of the system.