Crystal Engineering of a Chiral Crystalline Sponge That Enables Absolute Structure Determination and Enantiomeric Separation

Anew chiral metal-organic material provides a blueprintfor the design of families of chiral crystalline sponges that enableenantiomeric selectivity, and the determination of the crystal structuresof liquid enantiomers. Chiral metal-organicmaterials (CMOMs), can offer molecularbinding sites that mimic the enantioselectivity exhibited by biomoleculesand are amenable to systematic fine-tuning of structure and properties.Herein, we report that the reaction of Ni(NO3)(2), S-indoline-2-carboxylic acid (S-IDECH), and 4,4 '-bipyridine (bipy) afforded a homochiralcationic diamondoid, dia, network, [Ni(S-IDEC)(bipy)(H2O)][NO3], CMOM-5. Composed of rod building blocks (RBBs) cross-linked by bipy linkers,the activated form of CMOM-5 adapted its pore structureto bind four guest molecules, 1-phenyl-1-butanol (1P1B), 4-phenyl-2-butanol(4P2B), 1-(4-methoxyphenyl)ethanol (MPE), and methyl mandelate (MM),making it an example of a chiral crystalline sponge (CCS). Chiralresolution experiments revealed enantiomeric excess, ee, values of 36.2-93.5%. The structural adaptability of CMOM-5 enabled eight enantiomer@CMOM-5 crystalstructures to be determined. The five ordered crystal structures revealedthat host-guest hydrogen-bonding interactions are behind theobserved enantioselectivity, three of which represent the first crystalstructures determined of the ambient liquids R-4P2B,S-4P2B, and R-MPE.