Regulating\nthe Structures of Self-Assembled Mechanically\nInterlocked Moleculecular\nConstructs via Dianion Precursor Substituent Effects

Substituent effects play critical\nroles in both modulating reaction\nchemistry and supramolecular self-assembly processes. Using substituted\nterephthalate dianions (p-phthalic acid dianions; PTADAs), the effect of varying the type, number, and position\nof the substituents was explored in terms of their ability to regulate\nthe inherent anion complexation features of a tetracationic macrocycle,\ncyclo[2]­(2,6-di­(1H-imidazol-1-yl)­pyridine)­[2]­(1,4-dimethylenebenzene)\n(referred to as the Texas-sized molecular box; 14+), in the form of its tetrakis-PF6– salt in DMSO. Several of the tested substituents, including 2-OH,\n2,5-di­(OH), 2,5-di­(NH2), 2,5-di­(Me), 2,5-di­(Cl), 2,5-di­(Br),\nand 2,5-di­(I), were found to promote pseudorotaxane formation in contrast\nto what was seen for the parent PTADA system. Other derivatives\nof PTADA, including those with 2,3-di­(OH), 2,6-di­(OH),\n2,5-di­(OMe), 2,3,5,6-tetra­(Cl), and 2,3,5,6-tetra­(F) substituents,\nled only to so-called outside binding, where the anion interacts with 14+ on the outside of the macrocyclic cavity. The\ndiffering binding modes produced by the choice of PTADA derivative were found to regulate further supramolecular self-assembly\nwhen the reaction components included additional metal cations (M).\nDepending on the specific choice of PTADA derivatives\nand metal cations (M = Co2+, Ni2+, Zn2+, Cd2+, Gd3+, Nd3+, Eu3+, Sm3+, Tb3+), constructs involving one-dimensional\npolyrotaxanes, outside-type rotaxanated supramolecular organic frameworks\n(RSOFs), or two-dimensional metal–organic rotaxane frameworks\n(MORFs) could be stabilized. The presence and nature of the substituent\nwere found to dictate which specific higher order self-assembled structure\nwas obtained using a given cation. In the specific case of the 2,5-di­(OH),\n2,5-di­(Cl), and 2,5-di­(Br) PTADA derivatives and Eu3+, so-called MORFs with distinct fluorescence emission properties\ncould be produced. The present work serves to illustrate how small\nchanges in guest substitution patterns may be used to control structure\nwell beyond the first interaction sphere.