CO 2 -actuated spin transition tuning in an interdigitated Hofmann-type coordination polymer.

The increased anthropogenic emission level of CO ₂ urges the development of CO ₂ -responsive materials, but is it possible to regulate the inherent electronic properties through weak physisorption of a ubiquitous gas such as CO ₂ ? Herein, we intended to answer this imperative question by the first case of CO ₂ -actuated variable spin-state stabilisation in an interdigitated Hofmann-type coordination polymer [Fe ^II Pd(CN) ₄ L ₂ ] (1, L = methyl isonicotinate), showing a wide shift in transition temperature ( T _eq ) from 178 K at P _{CO 2} = 0 kPa to 229 K at P _{CO 2} = 100 kPa. Interestingly, the emergence of a stepped behaviour in the heating process below P _{CO 2} = 10 kPa and overlapping magnetic susceptibility values above P _{CO 2} = 10 kPa elucidate the selective LS state stabilisation solely correlated with the extent of CO ₂ accommodation. Based on the magnetic response and phase transition diagrams obtained under respective P _{CO 2} , a plausible scenario of the spin-state switching can be interpreted as (1 _ls + ) → (1 _hs + ) → 1 _hs at P _{CO 2} ≤ 10 kPa, → 1 _hs at 100 kPa < P _{CO 2} ≥ 32 kPa and → → 1 _hs at 100 kPa, where 1 and 1' represent CO ₂ -free and CO ₂ -encapsulated states, respectively. The cooperative CO ₂ sorption with SCO based on the varied CO ₂ pressure corroborates a novel case for developing CO ₂ -responsive magnetic materials henceforth.
Competing Interests: There are no conflicts to declare.
(This journal is © The Royal Society of Chemistry.)