Consecutive single-crystal-to-single-crystal isomerization of novel octamolybdate anions within a microporous hybrid framework with robust water sorption properties
The 3D hybrid framework [{Cu(cyclam)}3(kMo8O27)]· 14H2O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-singlecrystal transformations upon heating to afford two
different anhydrous phases (2 a and 3a). These transitions modify the framework dimensionality and enable
the isomerization of k-octamolybdate (k-Mo8) anions
into λ (2 a) and μ (3 a) forms through metal migration.
Hydration of 3 a involves condensation of one water
molecule to the cluster to afford the γ-Mo8 isomer in 4,
which dehydrates back into 3a through the 6a intermediate. In contrast, 2a reversibly hydrates to form 5,
exhibiting the same Mo8 cluster as that of 1. It is
remarkable that three of the Mo8 clusters (k, λ and μ)
are new and that up to three different microporous
phases can be isolated from 1 (2 a, 3a, and 6a). Water
vapor sorption analyses show high recyclability and the
highest uptake values for POM-based systems. The
isotherms display an abrupt step at low humidity level
desirable for humidity control devices or water harvesting in drylands.Funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, grants IT1722-22 and KK-2022/00045). E.R.B. thanks EJ/GV for her doctoral fellowship (PRE_2018_1_0143)
