Selective Crystallization of Four Bis(phthalocyaninato)neodymium(III) Polymorphs

Four polymorphs of bis(phthalocyaninato)neodymium(III) were reproducibly and selectively crystallized by the slow evaporation of saturated solutions. The obtained phase depended on the initial oxidation state of the NdPc₂ molecule and the choice of solvent. Single-crystal X-ray diffraction studies were used to correct previous mis-identifications and provide missing coordinates for the γ-phase as well as a detailed comparison of molecular structure and crystal packing in all NdPc₂ polymorphs. The primary feature in all phases is columnar stacking based on parallel π π interactions, with a variety of slip angles within those stacks as well as secondary interactions between them. Chemical redox and acid-base titrations, performed on re-dissolved crystals demonstrate that NdPc₂⁺ and NdPc₂^- are easily obtained through weak oxidizing and reducing agents, respectively. Additionally, we show that the protonated form of the NdPc₂^- complex has a nearly identical UV-Vis spectra to that of neutral NdPc₂, explaining some of the confusion over chemical composition in previously published literature.