Vacancy-ordered　perovskites　and　derivatives　represent　an　important　subclass　of　hybrid　metal　halides　with　promise　in　applications　including　light　emitting　devices　and　photovoltaics.　Understanding　the　vacancy-property　relationship　is　crucial　for　designing　related　task-specific　materials,　yet　research　in　this　field　remains　sporadic.　For　the　first　time,　we　use　the　Connolly　surface　to　quantitatively　calculate　the　volume　of　vacancy　(V,　=vacancy)　in　vacancy-ordered　double　perovskite　derivatives　(VDPDs).　A　relationship　between　void　fraction　and　the　structure,　photoluminescent　properties　and　humidity　stability　was　established　based　on　zero-dimensional　(0-D)　[N(alkyl)4]2SbCl5′-type　VDPDs.　Compared　with　the　more　commonly　studied　A2M(IV)X6-type　double　perovskite　(A=cation,　M=metal　ion,　X=halide),　[N(alkyl)4]2SbCl5′　features　double　vacancy　sites.　Our　results　demonstrate　an　inverse　relationship　between　the　photoluminescent　quantum　yield　and　V　in　0-D　VDPDs.　Additionally,　structural　transformation　from　A2SbCl5　to　A3Sb2Cl9　was　first　reported,　during　which　the　novel　‘gate-opening’　gas　adsorption　phenomenon　was　observed　in　VDPDs　for　the　first　time,　as　evidenced　by　‘S’-shaped　sorption　isotherms　for　water　vapor,　indicating　a　cation-controlled　water-vapor　response　behavior.　A　mixed-cation　strategy　was　developed　to　modulate　the　humidity　stability　of　VDPDs.　Characterized　by　controllable　water-responsive　behavior　and　unique　‘on-off-on’　luminescent　switching,　A2M(III)X5′-type　materials　show　great　promise　for　multi-level　information　anti-counterfeiting　applications.　©　2024　Wiley-VCH　GmbH.