Chemical tuning of high-spin complexes based on 3- and 4-hydroxy-pentadentate-Fe (III) complex-units investigated by Moessbauer spectroscopy

The pentadentate ligands 3-OH-5L [N,N'-Bis(1,3-dihydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and 4-OH-5L = [N,N'-Bis(1,4-dihydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] has been prepared by a Schiff base condensation between 1,7-diamino-4-azaheptane and the dihydroxybenzaldehyde. Complexation with Fe(III) yields high-spin (S 5/2) complexes of [FeIII(3-OH-5L)Cl] and [FeIII(4-OH-5L)Cl]. These 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-FeIII(3-OH-5L)}x]Cly and [M{(CN-FeIII(4-OH-5L)}x]Cly resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 10 K some of the iron(III) centers switch to a second high-spin state as proven by Moessbauer spectra, i.e. multiple electronic transitions. Parts of the compounds perform a high-spin to high-spin transition.