Issue 4, 2021

Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behaviour

Abstract

A binary reversible switch between low-temperature multi-step spin crossover (SCO), through the evolution of the population γHS(T) with high-spin (HS)-low-spin (LS) sequence: HS1LS0 (state 1) ↔ HS2/3LS1/3 (state 2) ↔ HS1/2LS1/2 (state 3) ↔ HS1/3LS2/3 (state 4) ↔ HS0LS1 (state 5), and complete one step hysteretic spin transition featuring 20 K wide thermal hysteresis centred at 290 K occurs in the three-dimensional (3D) Hofmann-type porous coordination polymer {FeII(3,8phen)[Au(CN)2]2xPhNO2 (3,8phen = 3,8-phenanthroline, PhNO2 = nitrobenzene), made up of two identical interpenetrated pcu-type frameworks. The included PhNO2 guest (x = 1, 1·PhNO2) acts as a molecular wedge between the interpenetrated 3D frameworks via PhNO2-3,8phen intermolecular recognition and is the source of the strong elastic frustration responsible for the multi-step regime. Detailed X-ray single crystal analysis reflects competition between spatial periodicities of structurally inequivalent HS and LS SCO centres featuring: (i) symmetry breaking (state 3) with ⋯HS–LS⋯ ordering with γHS = 1/2; and (ii) occurrence of spatial modulation of the structure providing evidence for stabilization of local or aperiodic ordered mixed spin states for states 2 and 4 (with γHS ≈ 2/3) and 4 (with γHS ≈ 1/3), respectively. Below c.a. 20 K, structural and magnetic analyses show the photogeneration of a metastable HS*, state 6. The room-temperature single-step hysteretic regime appears with release of the guest (x = 0, 1) and the elastic frustration, and reversibly switches back to the original four-step behaviour upon guest re-adsorption. Both uncommon relevant SCO events meeting in the same material represent a rare opportunity to compare them in the frame of antiferro- and ferro-elastic transitions.

Graphical abstract: Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behaviour

Supplementary files

Article information

Article type
Edge Article
Submitted
11 8 2020
Accepted
22 11 2020
First published
23 11 2020
This article is Open Access

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

Chem. Sci., 2021,12, 1317-1326

Guest induced reversible on–off switching of elastic frustration in a 3D spin crossover coordination polymer with room temperature hysteretic behaviour

L. Piñeiro-López, F. Valverde-Muñoz, E. Trzop, M. C. Muñoz, M. Seredyuk, J. Castells-Gil, I. da Silva, C. Martí-Gastaldo, E. Collet and J. A. Real, Chem. Sci., 2021, 12, 1317 DOI: 10.1039/D0SC04420B

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