Multicomponent Self-Assembly of PdII /PtII Interlocked Molecular Cages: Cage-to-Cage Conversion and Self-Sorting in Aqueous Medium.

Abstract

Coordination-driven self-assembly is an efficient approach for constructing complicated molecules with the aid of reversible bond formation. However, constructing topologically complicated interlocked systems and their formation studies remain challenging tasks. The formation of two water-soluble hexanuclear interlocked cages by multicomponent self-assembly of a flexible triimidazole donor (L1) and a rigid tripyridyl donor (L2) based on a triazine core in combination with 90° cis-blocked PdII and PtII acceptors is reported here. Formation of interlocked systems having a composition of M6 (L1)2 (L2)2 (M=Pd or Pt) becomes feasible through cavity-induced self-recognition of two similar units having a composition of M3 (L1)(L2). Self-sorting of two independently prepared cages of [M3 (L1)2 ] and [M6 (L2)4 ] in aqueous medium leads to the formation of interlocked systems, and their formation was monitored by time-dependent 1 H NMR spectroscopy. Self-recognition of L1 by [M6 (L2)4 ] or L2 by [M3 (L1)2 ] leads to the formation of interlocked systems, as confirmed from 1 H NMR spectroscopic titrations of L1 with cages {M6 (L2)4 } and L2 with {M3 (L1)2 }, respectively. Both the interlocked cages of Pd and Pt are highly stable, and formation of either system is equally probable as observed from the treatments of Pd3 (L1)2 with Pt6 (L2)4 or Pt3 (L1)2 with Pd6 (L2)4 , which lead to the formation of two different self-assembled homometallic interlocked cages [Pt6 (L1)2 (L2)2 +Pd6 (L1)2 (L2)2 ] instead of forming any other heterometallic assemblies. Formation of interlocked cages is dependent on the steric bulk of the diamine ligand bound to the metal acceptors. A N-alkyl-substituted blocking amine prefers the non-interlocked cage instead of the interlocked analogue.