Structural robustness of crystalline sulfonated calix[4]arene complexes incorporating organic and metal cations

Six different sulfonated calix[4]arene-based compounds incorporating diverse metal ions (Na + , Y 3+ , Gd 3+ ), organic guests (EMIM + , PPh 4 + ), and solvents were synthesized and structurally characterized. Single-crystal X-ray analysis showed that the calixarene scaffold consistently adopts the typical cone conformation, stabilized by multiple weak intramolecular interactions. Subtle variations in metal cation coordination (e.g., mono- versus hetero-metallic assemblies) drive minor shifts in the coordination geometry, leading to previously unreported polymorphic forms and coordination motifs. In metal-only frameworks, sodium ions bridge sulfonate groups to form tightly packed bilayers devoid of guest inclusion, while heterometallic Y Na networks enhance structural stability through complementary coordination and supramolecular forces. The introduction of bulky PPh 4 + cations expands the unit cell sixfold involving C-H···π interactions without disrupting primary metal-ligand coordination interactions. In contrast, complex with both EMIM + and PPh 4 + exhibit mixed host-guest behaviour where EMIM + is included in the calixarene cavity, while PPh 4 + molecules fill the interstices/voids between the bilayers. A new PPh 4 + inclusion polymorph displays unique mixed phenyl embraces and significantly increased hydration relative to known structures. Collectively, these findings reveal how minimal compositional adjustments govern crystal packing and host-guest inclusion, providing valuable insights for the design of customised calixarene-based materials. Six sulfonated calix[4]arene compounds with diverse metal ions (Na + , Y 3+ , Gd 3+ ) and organic guests (EMIM + , PPh 4 + ) were synthesized and structurally characterized, revealing that the calixarene scaffold consistently adopts a cone conformation with subtle coordination variations driving new polymorphic forms. The compounds range from sodium-bridged bilayers without guest inclusion to heterometallic Y Na networks and mixed systems where EMIM + occupies the calixarene cavity while PPh 4 + fills interstices, including a new PPh 4 + inclusion polymorph with unique phenyl embraces. • New polymorphs and coordination motifs in sulfonated calix[4]arene assemblies • Sodium and lanthanide cations reveal structural persistence and subtle variability • Large organic cations alter lattice symmetry and regulate host–guest interactions