CO2-actuated spin transition tuning in an interdigitated Hofmann-type coordination polymer†
Abstract
The increased anthropogenic emission level of CO2 urges the development of CO2-responsive materials, but is it possible to regulate the inherent electronic properties through weak physisorption of a ubiquitous gas such as CO2? Herein, we intended to answer this imperative question by the first case of CO2-actuated variable spin-state stabilisation in an interdigitated Hofmann-type coordination polymer [FeIIPd(CN)4L2] (1, L = methyl isonicotinate), showing a wide shift in transition temperature (Teq) from 178 K at PCO2 = 0 kPa to 229 K at PCO2 = 100 kPa. Interestingly, the emergence of a stepped behaviour in the heating process below PCO2 = 10 kPa and overlapping magnetic susceptibility values above PCO2 = 10 kPa elucidate the selective LS state stabilisation solely correlated with the extent of CO2 accommodation. Based on the magnetic response and phase transition diagrams obtained under respective PCO2, a plausible scenario of the spin-state switching can be interpreted as (1ls + ) → (1hs + ) → 1hs at PCO2 ≤ 10 kPa, → 1hs at 100 kPa < PCO2 ≥ 32 kPa and → → 1hs at 100 kPa, where 1 and 1′ represent CO2-free and CO2-encapsulated states, respectively. The cooperative CO2 sorption with SCO based on the varied CO2 pressure corroborates a novel case for developing CO2-responsive magnetic materials henceforth.
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