Inter-layer magnetic tuning by gas adsorption in π-stacked pillared-layer framework magnets

Abstract

Magnetism of layered magnets depends on the inter-layer through-space magnetic interactions (J_NNNI). Using guest sorption to address inter-layer pores in bulk-layered magnets is an efficient approach to magnetism control because the guest-delicate inter-layer distance (l_trans) is a variable parameter for modulating J_NNNI. Herein, we demonstrated magnetic changes induced by the adsorption of CO₂, N₂, and O₂ gases in various isostructural layered magnets with a π-stacked pillared-layer framework, , (M = Co, 1, Fe, 2, Cr, 3; Cp* = η₅-C₅Me₅; 2,3,5,6-F₄PhCO₂⁻ = 2,3,5,6-tetrafluorobenzoate; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane). Each compound had almost identical adsorption capability for the three types of gases; only CO₂ adsorption was found to have a gated profile. A breathing-like structural modulation involving the extension of l_trans occurred after the insertion of gases into the isolated pores between the [Ru₂]₂–TCNQ ferrimagnetic layers, which is more significant for CO₂ than for O₂ and N₂, due to the CO₂-gated transition. While adsorbent 1 with M = Co (S = 0) was an antiferromagnet with T_N = 75 K, 1⊃CO₂ was a ferrimagnet with T_C = 76 K, whereas 1⊃N₂ and 1⊃O₂ were antiferromagnets with T_N = 68 K. The guest-insertion effect was similarly confirmed in 2 and 3, and was characteristically dependent on the type of sandwiched spin in as M = Fe (S = 1/2) and Cr (S = 3/2), respectively. This study reveals that common gases such as CO₂, O₂, and N₂ can serve as crucial triggers for the change in magnetism as a function of variable parameter l_trans.