Synthesis, Crystal Structures and Magnetic Properties of Composites Incorporating an Fe(II) Spin Crossover Complex and Polyoxometalates

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 (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 χ m T 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.

Spin-Crossover Complexes

“…Imoto and co-workers [19] demonstrate the metal dilution effect on SCO cooperativity for the cyano-bridged Fe(II) SCO network and reveal that the decrease in cooperativity by increasing Co(II) concentration may lead to more gradual SCO transitions and lower transition temperatures. For the development of novel multifunctional SCO hybrid compounds, Kuramochi and co-workers [20] develop Fe(II) SCO hybrid molecular systems with a polyoxometalate (POM) anion, which is known as a multi-functional unit. They clarify the crystal structures and magnetic properties of the SCO-POM hybrids and find that the hydrogen bonding interactions between the Fe(II) cation and POM anion strongly influenced the spin state of the Fe(II) cation.…”

Redox and guest tunable spin-crossover properties in a polymeric polyoxometalate

“…[26][27][28][29] To our knowledge, there are very few reports of POMs showing SCO behavior. 30,31 In a previous work, we explored this topic through the incorporation of 1-bpp into a Mn III Anderson POM. 32 We rst prepared the 1-bpp bifunctionalized Anderson POM and subsequently, by reaction with Fe 2+ , the amorphous polymeric compound (C 16 H 36 N)[Fe(MnMo 6 O 24 (C 16 H 15 N 6 O) 2 )]-$(H 2 O) 4 .…”

Iron(III) Azadiphenolate Compounds in a New Family of Spin Crossover Iron(II)–Iron(III) Mixed-Valent Complexes

“…Unknown at the outset was the effect that ionic interactions or intermolecular interactions might have on the spin crossover properties of the individual sites, not to mention the effects that two SCO sites might have on each other. There is, however, precedence for the isolation of crystalline hybrid double salts in which the cation is a SCO site while the anion has a separate function such as electron transfer; e.g., [Fe(qsal) 2 ][Ni(dmit) 2 ] [10][11][12] (qsal = (N-8-quinolyl)-5-X-salicylaldiminate and dmit = 2-thioxo-1,3-dithiole-4,5-dithio-lato), [15] (dppOH = 2,6-di(pyrazol-1-yl)-4-(hydroxymethyl)pyridine). We also recently described one of the ways that the double SCO salt reaction design can lead, surprisingly, to other products, often with very interesting properties, viz.…”