A new approach to the synthesis of heteronuclear propeller-like single molecule magnets

Abstract

Propeller-like [Fe₄(L)₂(dk)₆] complexes, in which Hdk is a β-diketone and H₃L is a tripodal alcohol, R–C(CH₂OH)₃, exhibit tunable magnetic anisotropy barriers and retain their magnetic memory effect when chemically anchored on metal surfaces. Heteronuclear analogues of these M₄ complexes have been sought to afford a library of compounds with different total spin (S) values, but synthetic efforts described so far gave solid solutions containing M₄ in addition to the desired M₃M′ species. We now present a novel synthetic route to M₃M′ complexes featuring a central chromium(III) ion. The three-step preparation goes through coordination of Cr^III by two equivalents of tripodal alkoxide (R = Et and Ph), followed by reaction of this complex “core” with the peripheral +III metal ions. Products have been characterised by chemical analyses together with ¹H-NMR, FTIR, W-band EPR, DC/AC magnetic susceptibility measurements and single crystal X-ray diffractometry. Due to the chemical inertness of Cr^III, this route yields 100% pure Fe₃Cr complexes without metal scrambling; what is more, it is suitable for designing novel heteronuclear single molecule magnets (SMMs) with a variety of d- and f-metals and R groups.