Metal-organic frameworks from chiral square-pyramidal copper(II) complexes: Enantiospecific inclusion and perfectly polar alignment of guest and host molecules

The physical properties of [CuL12(H2O)] (1) and [CuL22(H2O)] (2) and preparation and crystal structures of the inclusion compounds 1·(P)-C2H4Br2, 2·(M)-C2H4Br2, 1·CH3CN and 2·CH3CN are described. HL1 and HL2 (H represents the dissociable phenolic proton) are the N,O-donor chiral reduced Schiff bases N-(2-hydroxy-5-nitrobenzyl)-(R)-α-methyl-benzylamine and N-(2-hydroxy-5-nitrobenzyl)-(S)-α-methylbenzylamine, respectively. All the compounds crystallize in the non-centrosymmetric space group C2. In the crystal lattice, the host [CuLn2(H2O)] (1 and 2) molecules connected by O−H⋯O and C−H⋯O interactions form perfectly polar two-dimensional networks. In these chiral and polar host frameworks, enantiospecific inclusion with polar ordering of the right-handed (P) and the left-handed (M) gauche form of 1,2-dibromoethane as well as polar alignment of acetonitrile molecules are observed. The host and guest molecules are linked by C−H⋯O interactions. The O-atoms of the nitro substituent on the ligands of 1 and 2 act as the acceptors in all these intermolecular O−H⋯O and C−H⋯O interactions. The structures reported in this work provide rare examples of enantiospecific trapping of the chiral rotamers of 1,2-dibromoethane as well as perfectly polar alignment of both guest and host molecules.