A new 3D zinc-based metal-organic framework {[Zn7L2(DMF)3(H2O)(OH)2]·5DMF}n (1) (H6L = 5,5',5″-(methylsilanetriyl) triisophthalic acid) was constructed with an organosilicon-based linker, where H6L is a tetrahedral structure furnished with rich -COO- chelating sites for Zn(II) immobilization. Compound 1 exhibited two types of irregular one-dimensional channels and a three-dimensional skeleton with large specific surface area, making it a promising catalytic platform. Moreover, by incorporation of the second metal ion into the inorganic node of framework 1, isomorphic bimetallic MOF ZnMg-1 was successfully synthesized. ZnMg-1 demonstrated enhanced catalytic activity compared to 1 under identical conditions. Contrast experiments and theoretical calculations indicate that bimetallic active sites play a facilitating role in the chemical fixation of epoxides and CO2. It indicated that efficient chemical fixation of CO2 to cyclic carbonates was obtained over isomorphic MOF catalysts 1 and ZnMg-1.