Spin-Crossover Physical Gels: A Quick Thermoreversible Response Assisted by Dynamic Self-Organization

Iron(II) triazolate coordination polymers with lipophilic sulfonate counterions with alkyl chains of different lengths have been synthesized. In hydrocarbon solvents, these polymers formed a physical gel and showed a thermoreversible spin transition upon the sol–gel phase transition. The formation of a hydrogen‐bonding network between the triazolate moieties and sulfonate ions, bridged by water molecules, was found to play an important role in the spin‐crossover event. The spin‐transition temperature was tuned over a wide range by adding a small amount of 1‐octanol, a scavenger for hydrogen‐bonding interactions. This additive was essential for the iron(II) species to adopt a low‐spin state. Compared with nongelling references in aromatic solvents, the spin‐crossover physical gels are characterized by their quick thermal response, which is due to a rapid restoration of the hydrogen‐bonding network, possibly because of a dynamic structural ordering through an enhanced lipophilic interaction of the self‐assembling components in hydrocarbon solvents. Always back for more: Upon sol–gel phase transition, iron(II) triazolate coordination polymers H‐bonded with lipophilic sulfonate counterions undergo a thermoreversible spin transition that can be repeated many times without deterioration. These gels have a rapid thermal response, and the spin‐transition temperature can be tuned over a wide range by the addition of a H‐bond scavenger.