Solvothermal reactions of 3-(3-methylpyridin-4-yl)benzoic acid (Hmpba) with Mn(NO3)2or Co(NO3)2yielded isostructural porous coordination polymers, [Mn(mpba)2]·guest (MCF-56, 1·g) and [Co(mpba)2]·guest (MCF-57, 2·g), respectively. X-ray diffraction revealed that 1·gand 2·gpossess similar one-dimensional ultramicroporous channels, and guest-free [Mn(mpba)2] (1′) and [Co(mpba)2] (2′) possess significantly and slightly contracted channels, respectively. Single-component C3H6/C3H8adsorption isotherms and computational simulations showed the typical nonporous-to-porous structural transformations for 1′, in which C3H6exhibits a significantly lower threshold pressure, and the typical small-pore-to-large-pore structural transformations for 2′, in which C3H6exhibits a slightly lower threshold pressure. Mixture column breakthrough experiments showed that the C3H6/C3H8separation performances of 2′are obviously better than those of 1′, because the latter cannot adsorb C3H6below the threshold pressure for pore opening, and the pore opened by C3H6can adsorb C3H8.