A DyIII2 Dimer in a Radical Straitjacket: The Importance of Dipolar Interactions in Dysprosium Single Molecule Magnets

We present three air-stable radical-containing compounds [MIII2(phsq)4(NO3)2(MeOH)2]∙2MeOH (M = Dy (1), Y (2), Gd (3); Hphsq = 9,10-phenanthrenesemiquinone) in which strong intramolecular inter-radical interactions force two lan-thanide ions into close proximity and isolate them from the lattice. Magnetic measurements on (1) showed it to be an SMM with maxima in the ac susceptibility up to 18 K (1000 Hz). Modeling the magnetic data using three different analytical approaches reveals the absence of zero-field quantum tunneling of magnetization (ZFQTM) as a relaxation pathway. This is a result of significant internal magnetic fields identified by ab initio calculations that appear to quench the ZFQTM. This can be verified from the measurements performed on a Y-doped sample (1a) in which one of the DyIII ions is largely replaced by diamagnetic YIII and switches ZFQTM back on.