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The engineering of intermolecular interaction is challenging but critical for magnetically switchable molecules. Here, we prepared two cyanide‐bridged [Fe4Co4] cube complexes via the alkynyl‐ and alcohol‐functionalized trispyrazoyl capping ligands. The alkynyl‐functionalized complex 1 exhibited a thermally‐induced incomplete metal‐to‐metal electron transfer (MMET) behaviour at around 220 K, while the mixed alkynyl/alcohol‐functionalized cube of 2 showed a complete and abrupt MMET behaviour at 232 K. Remarkably, both compounds showed a long‐lived photo‐induced metastable state up to 200 K. The crystallographic study demonstrated that the incomplete transition of 1 was likely due to the possible elastic frustration originating from the competition between the anion‐propagated elastic interactions and inter‐cluster alkynyl‐alkynyl & CH‐alkynyl interactions, whereas the latter are eliminated in 2 as a result of the partial substitution by the alcohol‐functionalized ligand. Additionally, the introduction of chemically distinguishable cobalt centers within the cube unit of 2 did not lead to a two‐step but a one‐step transition, possibly because of the strong ferroelastic intramolecular interaction through the cyanide bridges. [ABSTRACT FROM AUTHOR]

• Radicals could be rapidly generated in HSO 3 −/Fe2+/PDS system (O 2 atmosphere). • Iron as single-electron shuttle enables interdependent activation of two oxidation processes. • The SO 4 •− production could be maximized by tuning electron transfer inside the system. • The system could inactivate chlorine-resistant pathogens in the distribution system. The generation of reactive oxygen species generally requires initiators in various environmental remediation processes, which necessitates high dosage of activators and downstream treatment for eliminating the accumulation of deactivated catalysts. Herein, a coupled process was constructed using trace iron for simultaneously activating HSO 3 −/O 2 system and peroxydisulfate (PDS) oxidation system, where the iron ions (2 mg/L) transferred single-electron from the former system to the latter due to the moderate redox potential (Fe3+/Fe2+, +0.77 V) between the potentials of SO 3 ·−/HSO 3 − (+0.63 V) and PDS/SO 4 ·− (+2.01 V). Hence, the phenol degradation quickly occurred at a first-order kinetic constant of k 1 =0.223 min−1 due to the accelerated generation of sulfate radical (SO 4 ·−) and hydroxyl radical (·OH) in the process. The k 1 value was almost 6-fold of that in the deoxygenated condition (0.040 min−1). Density function theory reveals that the single electron shuttle spatially separates the electron-donating activation of HSO 3 − and electron-accepting activation of PDS, while avoiding the "mutual-annihilation" of HSO 3 − and S 2 O 8 2− via direct two-electron transfer. Finally, utilizing the in-situ generated electron-shuttle (dissolved iron from cast iron pipe), the HSO 3 −/PDS reagent could efficiently inactivate the chlorine-resistant pathogens and inhibits biofilm regrowth inside the distribution systems at regular intervals or infectious disease outbreak in a neighborhood. [ABSTRACT FROM AUTHOR]