Self-Selection in the Self-Assembly of Isomeric Supramolecular Squares from Unsymmetrical Bis(4-pyridyl)acetylene Ligands

A new approach wherein steric interactions between substituents of unsymmetrical bis(4-pyridyl)acetylene ligands dictate the self-selection of single isomers of [4+4] self-assembled squares is presented. Each [4+4] self-assembly is characterized by multinuclear 31P and 1H NMR spectroscopies and Electrospray Ionization mass spectrometry (ESI-MS). NMR spectroscopic studies are used to provide a means of evaluating the efficiency of bulky substituents at proximal or remote positions relative to the Pt-N bonding motif to direct self-selection. Molecular modeling using the MMFF force field is utilized to determine the relative energy of different isomers of each assembly, and modeling results reasonably explain the trend in self-selectivity with varying pyridyl substitution.