Synthesis of chiral boron imidazolate frameworks with second-order nonlinear optics

The synthesis of crystalline homochiral MOF materials is very important for their potential application in enantioselective processes and asymmetric catalysis. In this paper, four novel zinc based chiral boron imidazolate frameworks (BIFs), Zn-2[BH(2-eim)(3)](BA)(2)(OH) (BIF-132-BA, 2-eim = 2-ethylimidazolate, BA = benzoate), Zn [HBH(2-ipim)(3)](OHBA)(Ac) (BIF-133-OHBA, 2-ipim = 2-isopropylimidazolate, OHBA = o-hydroxybenzoate, Ac = acetate), Zn[HBH(2-ipim)(3)](PHBA)(Ac) (BIF-133-PHBA, PHBA = p-hydroxybenzoate), and Zn[HBH(2ipim)(3)](DHBA)(Ac) (BIF-133-DHBA, DHBA = 2,4-dihydroxybenzoate) were prepared via solvothermal synthesis. Single-crystal X-ray diffraction demonstrated that the existence of hydrogen bonds between adjacent chains results in two different structure features of BIF-131: a chiral ladder-like 1D chain (BIF-133-OHBA) and two supramolecular 2D layers (BIF-133-PHBA and BIF-133-DHBA). Then, the optical activities of as-synthesied crystals were preliminarily studied by circular dichroism (CD) spectroscopy. In addition, because they crystallized in noncentrosymmetric space groups, the powder second-harmonic generation (SHG) measurements were carried out and the SHG response of BIF-133-PHBA was almost comparable to potassium dihydrogen phosphate (KDP).