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

Propeller-like [Fe(L)(dk)] complexes, in which Hdk is a beta-diketone and HL is a tripodal alcohol, R-C(CHOH), exhibit tunable magnetic anisotropy barriers and retain their magnetic memory effect when chemically anchored on metal surfaces. Heteronuclear analogues of these M 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 M in addition to the desired MM' species. We now present a novel synthetic route to MM' complexes featuring a central chromium(iii) ion. The three-step preparation goes through coordination of Cr 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 H-NMR, FTIR, W-band EPR, DC/AC magnetic susceptibility measurements and single crystal X-ray diffractometry. Due to the chemical inertness of Cr, this route yields 100% pure FeCr 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.