Search

Chiral metal-organic materials, CMOMs, are of interest as they can offer selective binding sites for chiral guests. Such binding sites can enable CMOMs to serve as chiral crystalline sponges (CCSs) to determine molecular structure and/or purify enantiomers. We recently reported on the chiral recognition properties of a homochiral cationic diamondoid, dia, network {[Ni( S -IDEC)(bipy)(H 2 O)][NO 3 ]} n ( S -IDEC = S -indoline-2-carboxylicate, bipy = 4,4'-bipyridine), CMOM-5[NO 3 ] . The modularity of CMOM-5[NO 3 ] means there are five feasible approaches to fine-tune structures and properties via substitution of one or more of the following components: metal cation (Ni 2+ ); bridging ligand ( S -IDEC); linker (bipy); extra-framework anion (NO 3 - ); and terminal ligand (H 2 O). Herein, we report the effect of anion substitution on the CCS properties of CMOM-5[NO 3 ] by preparing and characterizing {[Ni( S -IDEC)(bipy)(H 2 O)][BF 4 ]} n , CMOM-5[BF 4 ] . The chiral channels in CMOM-5[BF 4 ] enabled it to function as a CCS for determination of the absolute crystal structures of both enantiomers of three chiral compounds: 1-phenyl-1-butanol (1P1B); methyl mandelate (MM); ethyl mandelate (EM). Chiral resolution experiments revealed CMOM-5[BF 4 ] to be highly selective toward the S -isomers of MM and EM with enantiomeric excess, ee, values of 82.6 and 78.4%, respectively. The ee measured for S -EM surpasses the 64.3% exhibited by [DyNaL(H 2 O) 4 ] 6H 2 O and far exceeds that of CMOM-5[NO 3 ] (6.0%). Structural studies of the binding sites in CMOM-5[BF 4 ] provide insight into their high enantioselectivity., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Chiral metal-organic materials (CMOMs), can offer molecular binding sites that mimic the enantioselectivity exhibited by biomolecules and are amenable to systematic fine-tuning of structure and properties. Herein, we report that the reaction of Ni(NO 3 ) 2 , S -indoline-2-carboxylic acid ( S -IDECH), and 4,4'-bipyridine (bipy) afforded a homochiral cationic diamondoid, dia , network, [Ni( S -IDEC)(bipy)(H 2 O)][NO 3 ], CMOM-5 . Composed of rod building blocks (RBBs) cross-linked by bipy linkers, the activated form of CMOM-5 adapted its pore structure to 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). Chiral resolution experiments revealed enantiomeric excess, ee , values of 36.2-93.5%. The structural adaptability of CMOM-5 enabled eight enantiomer@ CMOM-5 crystal structures to be determined. The five ordered crystal structures revealed that host-guest hydrogen-bonding interactions are behind the observed enantioselectivity, three of which represent the first crystal structures determined of the ambient liquids R -4P2B, S-4P2B, and R -MPE., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Although crystal engineering strategies are generally well explored in the context of multicomponent crystals (cocrystals) formed by neutral coformers (molecular cocrystals), cocrystals comprised of one or more salts (ionic cocrystals, ICCs) are understudied. We herein address the design, preparation, and structural characterization of ICCs formed by phenolic moieties, a common group in natural products and drug molecules. Organic and inorganic bases were reacted with the following phenolic coformers: phenol, resorcinol, phloroglucinol, 4-methoxyphenol, and 4-isopropylphenol. Nine ICCs were crystallized, each of them sustained by the phenol-phenolate supramolecular heterosynthon (PhOH···PhO - ). Such ICCs are of potential utility, and there are numerous examples of phenolic compounds that are biologically active, some of which suffer from low aqueous solubility. The propensity to form ICCs sustained by the PhOH···PhO - supramolecular heterosynthon was evaluated through a combination of Cambridge Structural Database (CSD) mining, structural characterization of nine novel ICCs, and calculation of interaction energies. Our analysis of these 9 ICCs and the 41 relevant entries archived in the CSD revealed that phenol groups can reliably form ICCs through charge-assisted PhOH···PhO - interactions. This conclusion is supported by hydrogen-bond strength calculations derived from CrystalExplorer that reveal the PhOH···PhO - interaction to be around 3 times stronger than the phenol-phenol hydrogen bond. The PhOH···PhO - supramolecular heterosynthon could therefore enable crystal engineering studies of a large number of phenolic pharmaceutical and nutraceutical compounds with their conjugate bases., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)