Cosolvent Caused Homochiral Recognition of Carboxylic Acids Based on 3,5-Biaryl-2,3-Dihydro-5H-Thiazolo[3,2-a]Pyrimidines in the Crystals of Mg+2 and Ca+2 Complexes

Abstract

Complexes based on two structurally related carboxylic acids and 3,5-biaryl-2,3-dihydro-5H-thiazolo[3,2-a]pyrimidines are prepared, their crystal structure is studied. Though not isostructural, the complexes are fundamentally formed in the same way. The metal cation (magnesium or calcium) is coordinated by solvent molecules at six positions. Most of the positions are occupied by the major solvent molecules, while their smaller part is occupied by the cosolvent molecules (water in the magnesium complex and ethylene glycol in the calcium complex). Solvent molecules form the first coordination sphere of the magnesium cation, thus forming the “cationic core”. The fact that the first coordination sphere of the metal contains “defective” sites occupied by cosolvent molecules is a factor determining the subsequent asymmetric growth of the complex. Namely, the second coordination sphere formed from carboxylic acid anions via primary O–H⋯O hydrogen bonds contains two ligands of the same configuration on the opposite side from the cosolvent molecule.