Predictable adjustment of spin crossover temperature in solutions of iron(iii) complexes functionalized with alkyl-urea tails

Abstract

A new series of amphiphilic alkylurea functionalised iron(III) sal₂trien complexes were prepared by substitution of phenolic ligand site with OC_nH_2n–NHC(O)NHC_mH_2m+1 tails (n = 5, 9, m = 4, 12, 14, 16). These complexes display remarkably tunable spin-crossover (SCO) behaviour in solution. By imposing very slight structural modifications in the number of methylene recognition sites in a position remote from the functional unit, i.e. the SCO active iron(III) centre, the transition temperature T_1/2 is modulated in a predictable manner. Additionally, a correlation between the concentration of the SCO-active amphiphile and its T_1/2 allows for precise fine-tuning of the spin-transition properties and for quantifying the efficiency of self-assembly.