Despite　tremendous　efforts,　precise　control　in　the　synthesis　of　porous　materials　with　pre-designed　pore　properties　for　desired　applications　remains　challenging.　Newly　emerged　porous　metal-organic　materials,　such　as　metal-organic　polyhedra　and　metal-organic　frameworks,　are　amenable　to　design　and　property　tuning,　enabling　precise　control　of　functionality　by　accurate　design　of　structures　at　the　molecular　level.　Here　we　propose　and　validate,　both　experimentally　and　computationally,　a　precisely　designed　cavity,　termed　a　＇single-molecule　trap＇,　with　the　desired　size　and　properties　suitable　for　trapping　target　CO2　molecules.　Such　a　single-molecule　trap　can　strengthen　CO2-host　interactions　without　evoking　chemical　bonding,　thus　showing　potential　for　CO2　capture.　Molecular　single-molecule　traps　in　the　form　of　metal-organic　polyhedra　are　designed,　synthesised　and　tested　for　selective　adsorption　of　CO2　over　N-2　and　CH4,　demonstrating　the　trapping　effect.　Building　these　pre-designed　single-molecule　traps　into　extended　frameworks　yields　metal-organic　frameworks　with　efficient　mass　transfer,　whereas　the　CO2　selective　adsorption　nature　of　single-molecule　traps　is　preserved.