Chiral metal–organic framework [Zn2(D-Cam)2(4,4′-bpy)]n@SiO2 core–shell composite for HPLC separation

Chiral metal–organic frameworks, an emerging type of chiral porous materials, possess many outstanding characteristics such as high surface area, tunable pore sizes, and good chemical stability. Herein, we prepared a chiral [Zn2(D-Cam)2(4,4′-bpy)]n@SiO2 core–shell composite on the SiO2-NH2 microspheres by an in-situ growth method. The prepared [Zn2(D-Cam)2(4,4′-bpy)]n@SiO2-packed column exhibited high-resolution separation of racemic compounds and positional isomers at a low column backpressure (9–12 bar). Twelve pairs of enantiomers including alcohols, amines, epoxides, ketones, and esters were well resolved with sharp peak shapes on the [Zn2(D-Cam)2(4,4́-bpy)]n@SiO2 chromatographic column. Compared the separation performance of [Zn2(D-Cam)2(4,4́-bpy)]n@SiO2 and two chromatographic columns (commercial Chiralpak AD-H column and as-prepared SiO2-NH2 column), the [Zn2(D-Cam)2(4,4′-bpy)]n-packed column and the commercial Chiralpak AD-H column have a good complementarity in chiral separation, and it offered better separation performance compared to the SiO2-NH2 column in the term of separating positional isomers. The effects of column temperature and analyte mass on the HPLC separation were investigated. Additionally, the [Zn2(D-Cam)2(4,4́-bpy)]n@SiO2 packed column has good repeatability and stability for HPLC separation of enantiomers and positional isomers. The relatvive standard deviations (RSDs) for repeated separations of 2,2,2-trifluoro-1-(9-anthryl)ethanol and o, m, p-bromoaniline were less than 0.8 % and 1.2 % for the retention time and peak area, respectively. After a month of continuous use, the RSDs for the retention time and peak area of them were in the range of 1.1–1.3 % and 1.5–1.8 % (inter-day and intra-day, n = 5), respectively. This work also indicates that the chiral MOFs@SiO2 composites are promising for HPLC separation.