Space-group ambiguity in Tb₂(porphyrin)₃

Abstract

A triple-decker Tb2(Porphyrin)3 sandwich complex refines in both I4/m and I-4. In I4/m, the molecule has 4/m point symmetry, the refinement is stable, and the outer porphyrins are ordered, but significant disorder is modeled in the center porphyrin. Alternatively, in I-4, with molecular point symmetry -4, no disorder model is required, but heavy restraints/constraints are needed for the portion of the molecule that has 4/m point symmetry. This talk aims to stimulate discussion from the different schools of thought about which is the preferred space group choice for modeling the structure.