Columnar Organization of Head-to-Tail Self-Assembled Pt4 Rings

Abstract

Coordination of Pt²⁺ to a family of tunable Schiff base proligands directs the 12-component self-assembly of disk-shaped Pt₄ rings in a head-to-tail fashion. Aggregation of these S₄ symmetric Pt₄ macrocycles into columnar architectures was investigated by dynamic and static light scattering, NMR spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Data from these experiments support the formation of columnar architectures for all of the structures studied except when bulky tris(4-tert-butylphenyl)methyl substituents were present. In this case, aggregation was limited to dimers in CHCl₃ (K_dim = 3200 ± 200 L mol⁻¹ at 25 °C) and a thermodynamic analysis revealed that dimerization is an entropy driven process. Columnar architectures of Pt₄ rings with branched 2-hexyldecyl substituents organize into lyotropic mesophases in nonpolar organic solvents. These new self-assembled supramolecules are promising candidates to access nanotubes with multiple linear arrays of Pt²⁺ ions.