Structure P6-IV. The third polymorph P6-IV with triclinic symmetry (Table , fourth entry) crystallizes as brown plates containing two crystallographically independent molecules forming layers (Fig. ). The nanorings are slipped with respect to each other (Fig. ). The butadiyne linkers adopt wavy geometries, although the twisting is observed to a smaller extent than in P6-II and P6-III and the clink distances do not exceed 0.49 Å. The RMSD of porphyrin planes is 0.070-0.165 Å and the Zn ions are significantly displaced from the porphyrin plane by 0.30-0.40 Å. The rings are arranged in a porphyrinbutadiyne stacking manner (Fig. ).