A　novel　guanidine-containing　polyoxotantalate　(POTa),　H12[CN3H6]12Na2(H2O)6[Cu(en)2(H2O)]3[Ta6O19]4·32H2O　(1)　has　been　synthesized　by　adding　the　CH6N3+　as　counter　cations.　The　[Ta6O19]8−　clusters　in　compound　1　are　connected　by　sodium　ions　to　form　a　2-D　layered　structure,　which　is　further　connected　through　[Cu(en)2(H2O)]2+　to　form　a　3-D　supramolecular　framework　structure.　Moreover,　it　is　demonstrated　that　compound　1　exhibits　reversible　thermochromism　behavior,　changing　from　purple　to　dark　blue　upon　heating　and　dehydration,　which　endows　it　with　potential　application　in　the　field　of　anti-counterfeiting　functional　materials.　©　2023　Elsevier　Inc.