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 [Fe^IIPd(CN)₄L₂] (1, L = methyl isonicotinate), showing a wide shift in transition temperature (T_eq) from 178 K at P_CO2 = 0 kPa to 229 K at P_CO2 = 100 kPa. Interestingly, the emergence of a stepped behaviour in the heating process below P_CO2 = 10 kPa and overlapping magnetic susceptibility values above P_CO2 = 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 P_CO2, a plausible scenario of the spin-state switching can be interpreted as (1_ls + ) → (1_hs + ) → 1_hs at P_CO2 ≤ 10 kPa, → 1_hs at 100 kPa < P_CO2 ≥ 32 kPa and → → 1_hs 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.