Exploration of glassy state in Prussian blue analogues

Abstract

Prussian blue analogues (PBAs) are archetypes of microporous coordination polymers/metal–organic frameworks whose versatile composition allows for diverse functionalities. However, developments in PBAs have centred solely on their crystalline state, and the glassy state of PBAs has not been explored. Here we describe the preparation of the glassy state of PBAs via a mechanically induced crystal-to-glass transformation and explore their properties. The preservation of short-range metal–ligand–metal connectivity is confirmed, enabling the framework-based functionality and semiconductivity in the glass. The transformation also generates unconventional CN− vacancies, followed by the reduction of metal sites. This leads to significant porosity enhancement in recrystallised PBA, enabled by further accessibility of isolated micropores. Finally, mechanical stability under stress for successful vitrification is correlated to defect contents and interstitial water. Our results demonstrate how mechanochemistry provides opportunities to explore glassy states of molecular framework materials in which the stable liquid state is absent.

Eutectic CsHSO4-Coordination Polymer Glasses with Superprotonic Conductivity

“…Broad diffuse scattering patterns indicate an absence of long-range atomic ordering in amorphous glass, with x up to 0.5. 31 This is consistent with the limit to which the [CsHSO 4 ] x [ZnPIm] 1−x -g remains transparent. Broad diffraction peaks matching well with Cs 3 (HSO 4 ) 2 (H 2 PO 4 ), a solid acid also with superprotonic conductivity, appear at x > 0.5.…”

“…The PXRD patterns reveal the miscibility limits of CsHSO 4 fractions in which a homogeneous phase is preserved (Figure S9). Broad diffuse scattering patterns indicate an absence of long-range atomic ordering in amorphous glass, with x up to 0.5 . This is consistent with the limit to which the [CsHSO 4 ] x [ZnPIm] 1– x -g remains transparent.…”

“…Broad diffraction peaks matching well with Cs 3 (HSO 4 ) 2 (H 2 PO 4 ), a solid acid also with superprotonic conductivity, appear at x > 0.5. 32 The formation of Cs 3 (HSO 4 ) 2 (H 2 PO 4 ) suggests that the formation of mixed glasses could potentially lead to the exchange of acid oxyanion groups between ZnPIm and CsHSO 4 (further discussed by 31 P and 1 H solid-state NMR). No peak was observed under small-angle X-ray scattering (SAXS) measurement (Figure S10), and the amorphous nature is retained after 24 h under dry conditions (Figure S11).…”

“…We utilized magic-angle spinning (MAS) solid-state NMR (20 kHz) to understand the local environment of binary glass. 31 P MAS NMR of ZnPIm-g (Figure 6A) exhibits two distinct peaks, where peak I (−2. tively.…”

“…Softer nature in glassy states allows the preparation of highly transparent monoliths with a controllable thickness ranging from 1 mm to 2.5 μm, where viscosity below 10 3 Pa•s can be achieved at 65 °C. We clarify the structural transformation and enhanced proton dynamics for preserving superprotonic conductivity through variabletemperature characterizations, 31 P, and 1 H solid-state NMR.…”