Polyoxometalates　(POMs)　have　good　potential　for　applications　in　different　fields,　including　conducting　materials,　optics,　and　electrocatalysis.　Of　particular　significance　is　the　synthesis　and　development　of　addendum　POMs.　Molybdenum-oxo　clusters,　which　are　renowned　for　their　diverse　structures　and　electronic　properties,　were　utilized　to　facilitate　the　synthesis　of　innovative　materials.　Herein,　we　employed　presynthesized　{XW9　Nb3O40}　(X=　Si/Ge)　polyanions　as　secondary　building　units　and　different　molybdenum-oxo　clusters　as　linkers.　Four　new　addendum　POMs　were　constructed,　including　two　dimeric　compounds　Cs10[H2(SiW9Nb3O40)2(Mo2O4C2O4)]·19H2O　(1)　and　Cs8[H4(GeW9Nb3O40)2(Mo2O4C2O4)]·17H2O　(2),　and　two　tetrameric　compounds　Cs15(NH4)[(SiW9Nb3O40)4(Mo4O6)]·42H2O　(3)　and　Cs10K5[H(GeW9Nb3O40)4(Mo4O6)]·39H2O　(4).　Notably,　this　is　the　first　report　of　Mo/W/Nb　ternary　mixed-addendum　POMs.　In　addition,　compounds　3　and　4　facilitate　the　transfer　of　protons　through　extended　hydrogen-bonding　networks　with　conductivity　values　of　1.16　×　10-2　and　7.73　×　10-3　S·cm-1　at　85　°C　and　98%　relative　humidity,　respectively.　Furthermore,　no　discernible　decline　in　conductivity　was　noted　over　the　course　of　10　h.　©　2024　American　Chemical　Society.