The　incorporation　of　3d-5p　heterometallic　clusters　into　polyoxotungstates　not　only　enables　the　construction　of　novel　and　intriguing　structures　but　also　enhances　the　resultant　materials　with　exceptional　properties.　Here,　we　present　an　unique　strontium-bridged　purely　inorganic　two-dimensional　layered　polyoxotungstate,　H7Sr2.5(H2O)15.5[Ni7Sb6O9(OH)6(B-α-SiW9O34)2]·25.5H2O　(1),　which　is　composed　of　a　sandwich-type　thirteen-nuclear　Ni-Sb　heterometallic　cluster　{Ni7Sb6}　and　two　{B-α-SiW9O34}　units.　Notably,　compound　1　undergoes　a　single-crystal-to-single-crystal　transformation,　accompanied　by　the　partial　substitution　of　Sr2+　ions　with　Co2+　ions,　resulting　in　a　transition　from　a　two-dimensional　to　a　three-dimensional　structure　while　maintaining　excellent　crystallinity.　This　process　provides　an　opportunity　to　elucidate　the　ions　exchange　mechanism　at　the　atomic　level.　Furthermore,　electrochemical　impedance　studies　reveal　that　1　exhibits　good　proton　conductivity,　reaching　1.40　×　10−3　S　cm−1,　under　conditions　of　85　°C　and　98　%　relative　humidity.　©　2025　Elsevier　B.V.