Homochiral boron imidazolate frameworks built from mixed Chiral and achiral ligands

Chiral metal-organic frameworks (MOFs) have been studied extensively because of the potential application. Based on the complexity of chiral structure, it is a great challenge to study the formation of novel chiral centers under self-assembly conditions. By mixing chiral and achiral ligands, five unusual homochiral BIFs materials were synthesized by using d-camphoric acid (D-H2cam) and KBH(mim)3 (mim = 2-methylimidazole) under solvothermal condition. The orientations of mim rings had been locked to a specific angle in these structures and freed tridentate BH(mim)3- ligands were separated into two enantiomers, S–BH(mim)3- and R–BH(mim)3-. BIF-123 and BIF-124 exhibited similar (3, 4)-connected pillared-layer chiral structures with a pair of opposite helical substructures. BIF-125, 126 and 127 exhibited a 4-connected chiral diamond structure, which incorporates the homochiral helical substructures containing only S–BH(mim)3- ligand. These homochiral BIFs showed high pore volume in gas adsorption measurements and good stability under different solvent environments. Furthermore, the obvious CD signals of BIF-126 proved the chirality of bulk samples.