Crystal structures of metalloporphyrin complexes. Effects of Fe(III)-halide bond lengths and intermolecular interactions on crystal packing

The structures of four Fe(III) complexes dedicated to the memory of Prof. A. B. P. Lever (Barry), which involve porphyrin halides Fe(TPP)X (where TPP²⁻ =meso-tetraphenylporphyrinate; X=F, Fe–F; Cl, Fe–Cl; Br, Fe–Br; I, Fe–I), at 100(2) K, as well as Fe–F at 143(2) K, have been determined through single-crystal X-ray diffraction. In solution, all four compounds exhibit C_4v symmetry; however, they form different crystal structures mainly due to variations in Fe–X bond lengths and intermolecular interactions. Crystals of Fe–F and Fe–Cl belong to the tetragonal I4/m (No. 87) and I4 (No. 79) space groups, respectively, maintaining the C₄ axis through the Fe–X bonds. Both Fe–Br and Fe–I adopt the monoclinic P2₁/n (No. 14) space group with unique features. The shortest Fe–Fe distances are 9.6782Å in Fe–F (I4/m), 9.7086Å in Fe–Cl (I4), and 8.943Å and 9.019Å in Fe–Br and Fe–I, respectively. Hirshfeld surface analyses were performed to examine intermolecular interactions within the crystal structures of Fe–X. Hirshfeld volumes and surfaces for Fe–Br and Fe–I are smaller than those for Fe–F and Fe–Cl, suggesting that the longer Fe–Br and Fe–I bonds influence the transition to the monoclinic crystal system with denser packing.