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Abstract
[Fe(dppOH)2]2+ (dppOH = 2,6-di(pyrazol-1-yl)-4-(hydroxymethyl)pyridine) is known to show spin crossover (SCO) behavior and light-induced excited spin state transitions (LIESST). Here, we show that the SCO properties of the [Fe(dppOH)2]2+ complex can be altered by a crystal engineering approach employing counter anion exchange with polyoxometalate (POM) anions. Using this strategy, two new composite materials (TBA)[Fe(dppOH)2][PMo12O40] (1) and [Fe(dppOH)2]3[PMo12O40]2 (2) (TBA = tetra-n-butylammonium) have been isolated and studied by single crystal X-ray diffraction and magnetic susceptibility measurements. 1 was found to be in a high spin state at 300 K and showed no spin crossover behavior due to a dense packing structure induced by hydrogen bonding between the hydroxyl group of the dppOH ligands and the POM anions. Conversely, 2 contains two crystallographically unique Fe centers, where one is in the low spin state whilst the other is locked in a high spin state in a manner analogous to 1. As a result, 2 was found to show partial spin crossover behavior around 230 K with a decrease in the χmT value of 1.9 emu·mol−1·K. This simple approach could therefore provide a useful method to aid in the design of next generation spin crossover materials.
Highlights
Spin crossover (SCO) materials have been studied extensively due to their ability to reversibly switch spin states in response to external stimuli, allowing their potential application in molecular electronic devices [1,2]
[Fe(dpp)2 ]2+ complexes show light-induced excited spin state transitions (LIESST) [8,10], where the spin state can be controllably switched in response to visible light
[Fe(dppOH)2 ](HClO4 )2 show spin crossover behavior with T1/2 = 271 K and 284 K, respectively [10], whilst the Fe(II) ion in 1 is ”locked” in the high-spin state and shows no spin crossover behavior. It whilst the Fe(II) ion in 1 is ”locked” in the high-spin state and shows no spin crossover behavior. It follows that the high spin state of Fe(II) is stabilized in the crystal structure of 1, and we follows that the high spin state of Fe(II) is stabilized in the crystal structure of 1, and we have considered the following explanations
Summary
Spin crossover (SCO) materials have been studied extensively due to their ability to reversibly switch spin states in response to external stimuli, allowing their potential application in molecular electronic devices [1,2]. [Fe(dpp)2 ]2+ complexes show light-induced excited spin state transitions (LIESST) [8,10], where the spin state can be controllably switched in response to visible light. POMs are of interest due to their appealing properties, including reversible, multi-electron redox behavior, electrocatalytic activity [17], photo-oxidizing properties [18,19] and Inorganics 2017, 5, 48; doi:10.3390/inorganics5030048 www.mdpi.com/journal/inorganics proton conductivity [20,21], and show great promise for advanced applications. POMs can act as efficient efficient spacers spacers to to magnetically magnetically isolate isolate paramagnetic paramagnetic species: species: for for example, example, Miyasaka, Miyasaka, Hayashi
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