Self-Assembly of Water-Soluble Platinum(II)-Based Metallacalixarenes and Tuning Their Conformational Interconversion via Synergistic Effects between Solvents and Anions

The aqueous self-assembly of the flexible ligand L bis(1H-benz[d]imidazole-1-yl)methane and cis-coordinated Pt^II precursors [(en)Pt²⁺, (tmeda)Pt²⁺, en=ethylenediamine, tmeda=N,N,N′,N′-tetramethylethylenediamine)] led to the formation of the metallacalixarenes with full alternative conformations (e.g., two novel water-soluble metallacalixarenes [M₂L₂]⁴⁺ and [M₃L₃]⁶⁺ with D₂ and D₃ symmetry, respectively). Their molecular structures were determined by single crystal X-ray analyses in solid state. The two metallacalixarenes present different cavity sizes and the [M₃L₃]⁶⁺ cavity encapsulates one NO₃ ⁻. NOESY NMR revealed that the conformational interconversion between 1,3-alternate conformer in methanol and cone conformer in DMSO was tuned via the synergistic effect between solvent and anion. Guest encapsulation is also discussed.