Homochiral layered indium phosphonates: solvent modulation of morphology and chiral discrimination adsorption

Abstract

Assembling chiral coordination polymers into nano/microflower structures may improve their performance in applications such as chiral recognition and separation. In this study, we chose a chiral metal phosphonate system, i.e., In(NO₃)₃/R-, S-pempH₂ [pempH₂ = (1-phenylethylamino)methylphosphonic acid], and carried out systematic work on the self-assembly of this system in different alcohol/H₂O mixed solvents under solvothermal conditions. Enantiomeric compounds R-, S-[In₂(pempH)₂(μ₂-OH)₂(H₂O)₂](NO₃)₂ (R-, S-1) were obtained showing dense layered structures, but their morphologies varied with alcohol solvent. We obtained crystals of R-, S-1C in triethylene glycol (TEG)/H₂O mixed solvent and spiral microflowers of R-, S-1MF in isopropanol (IPA)/H₂O mixed solvent. Adsorption isotherms using enantiopure R-2-butanol and S-2-butanol as probe molecules revealed that compounds R-1MF and S-1MF had higher adsorption capacity compared to the crystalline sample and displayed enantioselective adsorption behaviour.