Helical Coordination Polymers from Achiral Components in Crystals. Homochiral Crystallization, Homochiral Helix Winding in the Solid State, and Chirality Control by Seeding

Abstract

An achiral anthracene−pyrimidine derivative (5-(9-anthracenyl)pyrimidine, 1 ) forms adduct 1 ·Cd(NO 3 ) 2 ·H 2 O·EtOH ( 2 ) in chiral space group P 2 1 . The metal ion is hexacoordinated with two pyrimidine ligands (equatorial cis), water and ethanol (equatorial cis), and two nitrate ions (axial trans). The chirality arises from a pyrimidine−Cd 2+ helical array and is preserved not only in each crystal via homochiral interstrand water−nitrate hydrogen bonding but also in all the crystals in the same chirality as a result of single-colony homochiral crystal growth. Compound 1 also forms achiral ( Pbca ) trihydrate adduct 1 ·Cd(NO 3 ) 2 ·3H 2 O ( 3 ) having nonhelical pyrimidine−Cd 2+ zigzag chains. Achiral zigzag polymer 3 and chiral helical polymer 2 are interconvertible with each other in the solid states upon exchange of volatile ligands (ethanol and water). The helix winding associated with the conversion of adduct 3 to 2 can be made homochiral by seeding.