Issue 36, 2023

Guest-induced pore breathing controls the spin state in a cyanido-bridged framework


Iron(II) spin cross-over (SCO) compounds combine a thermally driven transition from the diamagnetic low-spin (LS) state to the paramagnetic high-spin (HS) state with a distinct change in the crystal lattice volume. Inversely, if the crystal lattice volume was modulated post-synthetically, the spin state of the compound could be tunable, resulting in the inverse effect for SCO. Herein, we demonstrate such a spin-state tuning in a breathing cyanido-bridged porous coordination polymer (PCP), where the volume change resulting from guest-induced gate-opening and -closing directly affects its spin state. We report the synthesis of a three-dimensional coordination framework {[FeII(4-CNpy)4]2[WIV(CN)8]·4H2O}n (1·4H2O; 4-CNpy = 4-cyanopyridine), which demonstrates a SCO phenomenon characterized by strong elastic frustration. This leads to a 48 K wide hysteresis loop above 140 K, but below this temperature results in a very gradual and incomplete SCO transition. 1·4H2O was activated under mild conditions, producing the nonporous {[FeII(4-CNpy)4]2[WIV(CN)8]}n (1) via a single-crystal-to-single-crystal process involving a 7.3% volume decrease, which shows complete and nonhysteretic SCO at T1/2 = 93 K. The low-temperature photoswitching behavior in 1 and 1·4H2O manifested the characteristic elasticity of the frameworks; 1 can be quantitatively converted into a metastable HS state after 638 nm light irradiation, while the photoactivation of 1·4H2O is only partial. Furthermore, nonporous 1 adsorbed CO2 molecules in a gated process, leading to {[FeII(4-CNpy)4]2[WIV(CN)8]·4CO2}n (1·4CO2), which resulted in a 15% volume increase and stabilization of the HS state in the whole temperature range down to 2 K. The demonstrated post-synthetic guest-exchange employing common gases is an efficient approach for tuning the spin state in breathing SCO-PCPs.

Graphical abstract: Guest-induced pore breathing controls the spin state in a cyanido-bridged framework

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Article information

Article type
Edge Article
26 6月 2023
14 8月 2023
First published
16 8月 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2023,14, 9651-9663

Guest-induced pore breathing controls the spin state in a cyanido-bridged framework

M. Magott, K. Płonka, B. Sieklucka, K. Dziedzic-Kocurek, W. Kosaka, H. Miyasaka and D. Pinkowicz, Chem. Sci., 2023, 14, 9651 DOI: 10.1039/D3SC03255H

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