Dobariya, PriyankaPriyankaDobariyaThakur, VinayVinayThakurA., AmruthaAmruthaA.Marvaniya, KaranKaranMarvaniyaMaurya, AshishAshishMauryaPachfule, PradipPradipPachfuleKumar, PrashantPrashantKumarRanganathan, RaghavanRaghavanRanganathanKushwaha, ShilpiShilpiKushwahaPatel, KetanKetanPatel2026-01-222026-01-222026-01-0110.1021/jacs.5c176442-s2.0-105028970058https://repository.iitgn.ac.in/handle/IITG2025/33968Achieving angstrom-level control over porosity is a long-standing challenge in translating molecular design into selective membranes. We present the supramolecular assembly of crown-type [P8W48O184]40– polyoxometalate (POM) by alkylammonium functionalization using [CnH2n+1]4N+, where n = 4 (Q4P8), 7 (Q7P8), and 10 (Q10P8), into continuous POM thin films (POMbranes) featuring periodically aligned ∼1 nm intrinsic pores (Ip) of P8 (visualized with electron microscopy). Alkyl chain length modulations direct supramolecular packing and tune the extrinsic porosity (Ep) in POMbranes across large lateral dimensions (∼50 cm2) while preserving IP. Q7P8 and Q10P8 POMbranes with restricted Ep enforce precise sieving via Ip, whereas Q4P8 permits dual-path transport through Ip and Ep, as confirmed by cross-flow separations and molecular dynamics simulations. Q7P8 and Q10P8 POMbranes deliver single-digit pore selectivity (Isoporosity) and ∼10× higher separation efficiency for narrow molecular weight differences (100–200 Da) than state-of-the-art benchmark membranes, establishing a scalable strategy to embed crystalline nanopores for selective separation.en-USArticle1520-5126WOS:001661493500001WOS:001661493500001WOS:001661493500001