This　work　reports　the　interesting　and　unique　cation-exchange　behaviors　of　the　first　indium-bridged　purely　inorganic　3D　framework　based　on　high-nuclearity　polyoxoniobates　as　building　units.　Each　nanoscale　polyoxoniobate　features　a　fascinating　near-icosahedral　core–shell　structure　with　six　pairs　of　unique　inorganic　＇molecular　tweezers＇　that　have　changeable　openings　for　binding　different　metal　cations　via　ion-exchanges　and　exhibit　unusual　selective　metal-uptake　behaviors.　Further,　the　material　has　high　chemical　stability　so　that　can　undergo　single-crystal-to-single-crystal　metal-exchange　processes　to　produce　a　dozen　new　crystals　with　high　crystallinity.　Based　on　these　crystals　and　time-dependent　metal-exchange　experiments,　we　can　visually　reveal　the　detailed　metal-exchange　interactions　and　mechanisms　of　the　material　at　the　atomic　precision　level.　This　work　demonstrates　a　rare　systematic　and　atomic-level　study　on　the　ion-exchange　properties　of　nanoclusters,　which　is　of　significance　for　the　exploration　of　cluster-based　ion-exchange　materials　that　are　still　to　be　developed.　©　2022　Wiley-VCH　GmbH.