Redox-Controlled Exchange Bias in a Supramolecular Chain of Fe4 Single-Molecule Magnets
Andrea Nava1,2, Luca Rigamonti1, Ennio Zangrando3
1Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia & INSTM RU of Modena and Reggio Emilia via G. Campi 183, 41125 Modena (Italy) http://www.corniagroup.unimore.it.
Abstract:
Tetrairon(III) single-molecule magnets [Fe4(pPy)2(dpm)6] (1) (H3pPy=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol, Hdpm=dipivaloylmethane) have been deliberately organized into supramolecular chains by reaction with Ru(II)Ru(II) or Ru(II)Ru(III) paddlewheel complexes. The products [Fe4(pPy)2(dpm)6][Ru2(OAc)4](BF4)x with x=0 (2 a) or x=1 (2 b) differ in the electron count on the paramagnetic diruthenium bridges and display hysteresis loops of substantially different shape. Owing to their large easy-plane anisotropy, the s=1 diruthenium(II,II) units in 2 a act as effective s(eff)=0 spins and lead to negligible intrachain communication. By contrast, the mixed-valent bridges (s=3/2, s(eff)=1/2) in 2 b introduce a significant exchange bias, with concomitant enhancement of the remnant magnetization. Our results suggest the possibility to use electron transfer to tune intermolecular communication in redox-responsive arrays of SMMs.
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