Modifying VNU-18 (a MOF with a partial cone-sql layer pillared by the chains of pillars decorated with OH-) by substitution of OH- with Cl-, a new isoreticular structure, [Cu6(L)5·(Cl-)2·H2O·4DMF]·4DMF·6(H2O) (SNNU-Bai67, SNNU-Bai = Shaanxi Normal University Bai's group), has been successfully synthesized. Furthermore, we deeply investigated the selective C2 hydrocarbon separation properties of SNNU-Bai67 and VNU-18 by single-component gas adsorption experiments, breakthrough experiments and simulation studies. They exhibit highly selective adsorption for C2 hydrocarbons over CH4 compared to many reported MOFs for the separation of C2 hydrocarbons from CH4, due to the suitable pore sizes of the partial corn sql-layer built from the isophthalic acid analogy and Cu-paddlewheel units. Interestingly, with the counterion of OH- in VNU-18 tuned by Cl- in SNNU-Bai67, the adsorption uptake values of C2 hydrocarbons were apparently improved by 15.0% for C2H2, 20.4% for C2H4 and 25.3% for C2H6, respectively, while the IAST selectivities of C2 hydrocarbons/CH4 were still nearly the same, which may be because the synergistic effect of interactions of HC2/1OCOO, HC2/1N/CPy, HPyCC2, ππ or HC2CC2 between the gas molecules and the framework is enhanced by the weaker polarity of Cl- decorating the framework.