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

Abstract

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.

Preserving the spin transition properties of iron-triazole coordination polymers within silica-based nanocomposites

“…[31][32][33][34] These two features could also be associated within a unique molecular component, using lipophilic sulfonate counter-anions to drive the formation of supramolecular gels. 35 Alternatively, a series of triazole ligands bearing large lipophilic a Sorbonne Universités, UPMC Univ Paris 06, Collège de France, UMR CNRS 7574, substituents were used to form one-dimensional coordination polymers that could further assemble in a gel phase. 10,13 These works have evidenced the importance of the dimensional structure (two-or three-) in the cooperativity effect associated with the spin transition, where the temperature dependence of the high spin molar fraction strongly depends on intermolecular interactions.…”

Solution and solid state properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands

“…This included the discovery of several new examples of SCO compounds [3,[9][10][11], the explanation of different types of SCO profiles [4,12] and the modification of SCO compounds to increase cooperativity and to direct their application into materials science [13]. Scientists have developed SCO networks [14][15][16], frameworks [17][18][19], gels [20][21][22], liquid crystals [23][24][25], nanoparticles and nanocrystals [26][27][28][29], nanowires [30], thin films [31][32][33] and have also applied patterning techniques to fabricate SCO devices [34]. Among complexes displaying SCO, [Fe(salEen) 2 ] + derivatives (salEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate) are known to undergo thermal SCO sensitive to unit cell contents and supramolecular packing in the crystal [35].…”

Towards Langmuir–Blodgett films of magnetically interesting materials: solution equilibria in amphiphilic iron(ii) complexes of a triazole-containing ligand

“…These systems have either been polymeric systems of the form {[Fe(4R-trz) 3 ]X 2 } n , where 4R-trz is a 1,2,4-triazole moiety with a hydrophobic substituent at N 4 of the triazole ring, 6 or discrete complexes of the form [FeL 2 (NCS) 2 ], where L represents 50 either phenanthroline or 2,2'-bipyridine groups that have been modified to contain long alkyl chains. 7 ,8 Recently, Aida et al 9 reported the preparation of gels of the form [Fe(4R-trz) 3 ](C n SO 3 ) 2 , where C n SO 3 represents the sulfonate derivative of an alkyl chain containing n carbon 55 atoms. These systems incorporate hydrophobicity both in the ligand, and in the non-coordinating counterion used (when n is large).…”