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

New amphiphilic and spin-labile Mn-III complexes based on dianionic N4O2-hexadentate sal(2)trien or sal(2)bapen ligands, which contain OC6H13, OC12H25, or OC18H37 alkoxy substituents at different positions of the salicylidene unit were prepared (H(2)sal(2)trien = N, N"'-bis(salicylidene)-1,4,7,10-tetraazadecane, H(2)sal(2)bapen = 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 sal(2)trien complexes (S = 2) and gradual spin crossover for sal(2)bapen complexes from high to low spin (S = 1). The chain length strongly influences the spin crossover, as C-18-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 (C-12 or C-18) as well as a mutual syn-orientation of these molecular recognition sites were required for the Langmuir monolayers to be stable.