Induction of Chirality in Boron Imidazolate Frameworks: The Structure-Directing Effects of Substituents.

ABSTRACT

By enhancing steric hindrance of substituents on the imidazole ring, the fan-shaped molecule of a tridentate boron imidazolate ligand (KBH(2-ipim)3, 2-ipim = 2-isopropylimidazolate) with racemic chirality was obtained. Then, seven novel boron imidazolate frameworks (BIFs) were prepared by mixing KBH(2-ipim)3 ligands with various derivatives of benzene carboxylic acid under solvothermal conditions. All of these seven materials contain a ladder-like zinc-boron-imidazolate chain as a basic building block, and the ligand BH(2-ipim)3- exists in the same handedness in one chain. The structural variations are associated with the position of substituents of the auxiliary ligand. Of particular interest is the spontaneous resolution of BH(2-ipim)3- ligands into two independent enantiomorphous homochiral structures, BIF-131-S and BIF-131-R, which contain both a chiral chain and an absolute helix embedded in the nets.