We herein show that the μ₂-OH bridging groups in the double M₁₂O₈(OH)₁₄ clusters of hcp UiO-66 could act as a preferential CO₂ sorption site, compared to fcu UiO-66. As such, hcp-UiO-66-0.015 shows a high binay CO₂ sorption capacity of 0.31 mmol g^-1 and CO₂/N₂ (15/85) mixture selectivity of 87 at 298 K and 1 bar, which holds great potential for post-combustion CO₂ capture.