title: Non-Porous Iron(II)-Based Sensor: Crystallographic Insights into a Cycle of Colorful Guest-Induced Topotactic Transformations.
abstract: Materials capable of sensing volatile guests at room temperature by an easily monitored set of outputs are of great appeal for development as chemical sensors of small volatile organics and toxic gases. Herein the dinuclear iron(II) complex, [FeII2(L)2(CH3CN)4](BF4)4⋅2 CH3CN (1) [L=4-(4-methylphenyl)-3-(3-pyridazinyl)-5-pyridyl-4H-1,2,4-triazole], is shown to undergo reversible single-crystal-to-single-crystal (SCSC) transformations upon exposure to vapors of different guests: 1 (MeCN)⇌2 (EtOH)→3 (H2O)⇌1 (MeCN). Whilst 1 and 2 remain dimetallic, SCSC to 3 involves conversion to a 1D polymeric chain (due to a change in L bridging mode), which, remarkably, can undergo SCSC de-polymerization, reforming dimetallic 1. Additionally, SC-XRD studies of two ordered transient forms, 1TF3 and 2TF3, confirm that guest exchange occurs by diffusion of the new guests into the non-porous lattices as the old guests leave. These reversible SCSC events also induce color and magnetic responses. Indeed dark red 1 is spin crossover active (T1/2↓ 356 K; T1/2↑ 369 K), whilst orange 2 and yellow 3 remain high spin.
authors.affiliation: Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand.
authors.forename: Santiago
authors.initials: S
authors.lastname: Rodríguez-Jiménez
authors.affiliation: Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand.
authors.forename: Humphrey L C
authors.initials: HL
authors.lastname: Feltham
authors.affiliation: Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin, 9054, New Zealand.
authors.forename: Sally
authors.identifier: 0000-0002-5878-8238
authors.initials: S
authors.lastname: Brooker
keywords: chemical sensor; crystal engineering; reversible guest exchange; single-crystal-to-single-crystal transformation; spin crossover