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‐benzd]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.