Complexes based on ethylene- and propylene-bridged-pentadentate-Fe(III)-units allow interplay between magnetic centers and multistability investigated by Mössbauer spectroscopy

Abstract

The propylene-based ⁵3,3-L=[N,N′-Bis(1-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and ethylene-based pentadentate ligand ⁵2,2-L=[N,N′-Bis(1-hydroxy-2-benzylidene)-1,5-diamino-3-azapentane] has been prepared. Complexation with Fe(III) yields high-spin (S=5/2) complexes of [Fe^III(⁵2,2-L)Cl] and [Fe^{III 5}3,3-L)Cl]. Such precursors were combined with [M(CN) _x ]^y− (M=W(IV), Mo(IV), Ru(II), Co(III)) and heptanuclear and nonanuclear clusters of [M(CN-Fe^III(⁵2,2-L) _x ]Cl _y and [M(CN-Fe^III(⁵3,3-L) _x ]Cl _y resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 20 K in all presented ethylene compounds the iron(III) centers switch to a second high-spin state as proven by Mössbauer spectra with a yield of about 30%, i.e., multiple electronic transitions. The propylene compounds, however, perform a high-spin to low-spin transition. Mössbauer spectra taken during green light irradiation indicate changes in the population of the different electronic states, i.e. concerted inorganic reaction.