Redox-Controlled Exchange Bias in a Supramolecular Chain of Fe<inf>4</inf> Single-Molecule Magnets

Tetrairon(III) single-molecule magnets [Fe4(pPy)2-(dpm)6](1)(H3pPy = 2-(hydroxymethyl)-2-(pyridin-4-yl)pro-pane-1,3-diol, Hdpm = dipivaloylmethane) have been deliber-ately organized into supramolecular chains by reaction withRuIIRuIIor RuIIRuIIIpaddlewheel complexes.The products[Fe4(pPy)2(dpm)6][Ru2(OAc)4](BF4)xwith x = 0(2a)orx= 1(2b)differ in the electron count on the paramagneticdiruthenium bridges and display hysteresis loops of substan-tially different shape.Owing to their large easy-plane aniso-tropy, the s = 1diruthenium(II,II) units in 2a act as effectiveseff= 0spins and lead to negligible intrachain communication.By contrast, the mixed-valent bridges (s = 3/2, seff= 1/2) in 2bintroduce asignificant exchange bias,with concomitantenhancement of the remnant magnetization. Our resultssuggest the possibility to use electron transfer to tune inter-molecular communication in redox-responsive arrays ofSMMs.