Interplay of Axial Ligation, Hydrogen Bonding, Self-Assembly, and Conformational Landscapes in High-Spin Ni(II) Porphyrins

The molecular structures of four bis-ligated high-spin Ni(II) complexes of the sterically crowded, nonplanar 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetranitroporphyrin (NiOETNP) are reported. The ligands are imidazole (Im), imidazole plus 2-methylimidazole (2-MeIm) in the crystal lattice, 1-methylimidazole (1-MeIm), and 2,1,3-benzoselenadiazole (BSeD). Extensive intermolecular hydrogen bonding is observed in the three imidazole-ligated structures consisting of NH···O and CH···O bonding from the imidazoles to neighboring nitro groups and of NH···N interactions to a nearby 2-MeIm. The different modes of hydrogen bonding, typical of those frequently observed in proteins, mediate the self-assembly of discrete porphyrin dimers as well as more extensive two- and three-dimensional arrays. Only the bis-BSeD complex remains monomeric. The presence or absence of the different types of hydrogen bonds controls the orientations of the axial ligands and also modulates the conformations of the porphyrin skeletons. Thi...