Experimental and theoretical evidences of the effect of the electronic structure and flexibility of the counteranion on the magnetization relaxation in [Dy(L)2(H2O)5]3+ (L = phosphine oxide derivative) pentagonal bipyramidal SIMs
We report here a new DyIII-SIM [Dy(OPCy3)2(H2O)5](CF3SO3)3·2OPCy3 (OPCy3 = triclohexylphosphine oxide) with pentagonal bipyramidal geometry, which exhibits a blocking temperature TB = 8.5 K and an anisotropy barrier Ueff = 562 K. Ab initio calculations show that this complex exhibits the largest Ucalc = 732 K among the DyIII-SIMs complexes containing the [Dy(L)2(H2O)5]3+ (L = phosphine oxide derivative) cationic unit, which is essentially due to the electronic effects of the triflate anion that increase the charge difference between the oxygen atoms of the ligands L coordinated in axial positions and those belonging to the equatorial water molecules. This charge difference enhancement, which is also reflected in a larger difference between the corresponding Dy-O distances (), appears to be the driving force to push up the Ucalc value. The comparative smaller experimental Ueff value observed for this compound has been justified by the flexibility of the structural network due to the size of the triflate counteranions. The absence of a clear correlation between TB and Ueff (or Ucalc) suggests the involvement of Raman and QTM mechanism in the magnetization relaxation process.