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 CrIII 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 CrIII, 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.