Exploring Supramolecular Self-Assembly of Tetraarylporphyrins by Halogen Interactions. 3. Tin(L)2(A2B2-Porphyrin) Arrays Supported by Concerted Halogen and Hydrogen Bonding

Abstract

This work reports on a designed construction of new porphyrin-based supramolecular architectures assembled with the aid of halogen bonds and a combination of halogen and hydrogen bonding interactions. The tinIV(L)2-tetraarylporphyrin building unit (L = axial ligand) was used to this end, wherein suitable donor and acceptor functions for such bonds have been introduced in a complementary manner on the axial ligands and the porphyrin periphery. We reveal in this context eight structures involving differently substituted metalloporphyrin entities: 5,10,15,20-tetra(4′-iodophenyl)porphyrin (A4-P), 5,10,15,20-tetra(4′-pyridyl)porphyrin (B4-P), 5-(4′-pyridyl)-10,15,20-tris(4′-iodophenyl)porphyrin (A3B-P), and 5,15-bis(4′-pyridyl)-10,20-bis(4′-iodophenyl)porphyrin (A2B2-P), and various axial ligands attached to the tin center and bearing molecular recognition capacity. The latter include 3-hydroxypyridine (L1), hydroxyl (L2), 1-hydroxybenzotriazole (L3), 5-bromopyridine-3-carboxylic acid (L4), 5-bromoisophthalic acid (L5), 5-hydroxyisophthalic acid (L6), and 2,5-thiophenedicarboxylic acid (L7). The various porphyrin-Sn(L)2 combinations that could be obtained in a single-crystal form were structurally analyzed by single-crystal X-ray diffraction, and their intermolecular interaction patterns were rationalized by computational methods. The versatile (A2B2-P) system deserved the most attention, and the crystal structure of this free-base porphyrin was determined as well. The occurrence of supramolecular halogen interactions between neighboring porphyrin moieties, as structure directing agents, was successfully manifested in our systems. Other findings of particular interest are that the assembly of [Sn(3-hydroxypyridine)2(A4-P)] (compound 1) displays a short intermolecular I···O halogen interaction at 2.949 Å, facilitated by a self-activation process through concomitant involvement of the iodine substituents in I···I contacts. Compound 2 [{Zn(A4-P)}2Sn(OH)2(B4-P)] illustrates the first porphyrinic trimer assembly driven by halogen bonding interactions. Then, compounds 6 [Sn(5-bromoiso-phthalate)2(A2B2-P)·(PhNO2)], 7 [Sn(5-bromo-isophthalate)2(A2B2-P)·(DMF)], 8 [Sn(5-hydroxyisophthalate)2(A2B2-P)], and 9 [Sn(2,5-thiophene-dicarboxylate)2(A2B2-P)·(PhNO2)3] reveal strong halogen interactions alongside tight hydrogen bonding contacts. In 9 the relatively rare I···S halogen bonding has been detected in porphyrin assemblies for the first time.