A versatile approach designing supramolecular assemblies for molecular magnetism relies on metallosupramolecular polyelectrolyte amphiphile complexes, which are self-assembled from ditopic bisterpyridine ligands, transition metal ions, and amphiphilic molecules. We report on measurements at powdered samples using energy-dispersive small angle x-ray scattering, x-ray magnetic circular dichroism, and magnetic measurements. We observe a spin crossover of the ${\mathrm{Fe}}^{2+}$ ions into a remanent state above room temperature driven and stabilized by a structural phase transition of the two dimensional amphiphilic matrix of the supramolecular complex. The temperature of spin crossover scales with the number of amphiphilic molecules attached to the polyelectrolyte backbone. The spin crossover itself can be rationalized by a transition of the ${\mathrm{Fe}}^{2+}$ ions from a $S=0$, $t_{2g}^6{e}_g^0$ low-spin state to a magnetic $S=2$, $t_{2g}^4{e}_g^2$ high-spin state and is independent from the number of amphiphiles per unit. The remanence in powdered samples might be caused by the disorder and interdigitation of amphiphilic molecules. Low temperature measurements suggest a possible antiferromagnetic coupling between ${\mathrm{Fe}}^{2+}$ ions.

• Received 11 March 2006

DOI:https://doi.org/10.1103/PhysRevB.76.064422