Synthesis and self-assembly of spin-labile and redox-active manganese(III) complexes

New amphiphilic and spin-labile MnIII complexes based on dianionic N4O2-hexadentate sal2trien or sal2bapen ligands, which contain OC6H13, OC12H25, or OC18H37 alkoxy substituents at different positions of the salicylidene unit were prepared (H2sal2trien = N,N′′′-bis(salicylidene)-1,4,7,10-tetraazadecane, H2sal2bapen = N,N′′′-bis(salicylidene)-1,5,8,12-tetraazadodecane). According to electrochemical measurements, these complexes undergo two (quasi)reversible redox processes. Temperature-dependent magnetic measurements revealed a high-spin configuration for all sal2trien complexes (S = 2) and gradual spin crossover for sal2bapen complexes from high to low spin (S = 1). The chain length strongly influences the spin crossover, as C18-functionalization stabilizes the low spin state at much higher temperatures than shorter alkyl chains. Moreover, long alkyl chains allow for spontaneous self-assembly of the molecules, which was investigated in single crystals and in Langmuir-films at the air–water interface. Long alkyl chains (C12 or C18) as well as a mutual syn-orientation of these molecular recognition sites were required for the Langmuir monolayers to be stable.