Real-time tracking of molecular cluster assembly and precise hierarchical reassembly into pure POM host–guest architecture

In this work, we report an <i>in operando</i> spectroscopy strategy to track the molecular cluster assembly and thereby realize a precise bottom-up hierarchical reassembly of building blocks into a pure POM host-guest architecture. Through precise flow chemical synthesis combined with <i>in operando</i> Raman characterization, we systematically tracked key building block intermediates emerging during the evolution from WO₄ ^2- precursors to the {P₂W₁₈} cluster and validated with ESI-MS and ³¹P NMR. Capitalizing on the dynamic assembly behaviour, we further realized precise hierarchical re-assembly of building blocks PW₉O₃₄ ^9- ({PW₉}): eight {PW₉} were used as secondary building units (SBUs) to form tertiary building units (TBUs, K₄₂P₈W₇₂, and {PW₉}₈), and then TBUs were further linked by alkali metals, resulting in a purely inorganic host-guest architecture {[K₆₆Na₁₄H₁₀(H₂O)₁₅₀(PW₉O₃₄)₈]·(PW₉O₃₄)₂·43H₂O} (compound 1, {PW₉}₂@{PW₉}₈) with interpenetrating three-dimensional channels containing discrete nano-sized SBUs. Unlike the irreversible and limited electrochemical reaction behaviour of SBUs, compound 1 exhibited markedly distinct electrochemical properties with multi-step multi-electron redox behaviours at 0.23 V, 0.01 V, -0.49 V and -0.87 V <i>vs.</i> NHE, respectively. These findings refine the understanding of the assembly behaviours and pave the way for designing atomically defined and functional clusters.