Complexes Between 1,1′-Binaphthyl-2,2′-Dicarboxylic Acid and Pyrazoles: A Case of Manual Sorting of Conglomerate Crystals (Triage)

The crystal and molecular structure of two salts, I and III , and one molecular complex, II , formed by combining 1,1′-binaphthyl-2,2′-dicarboxylic acid (BNDA) with pyrazole ( 3 ) and 3,5-dimethylpyrazole ( 4 ) has been determined by X-ray crystallography. The most striking feature is the spontaneous resolution of the racemic BNDA host by co-crystallization with 4 , an achiral guest, to form the salt III . The absolute configuration of three manually selected crystals of III have been established by crystallographic methods. The two crystals formed by the (P)-enantiomer display a negative Cotton effect. ¹³C-CPMAS-NMR Spectroscopy has been used to compare the compounds obtained by crystallization with those prepared by mechanical grinding.