The effect of the second coordination sphere on the magnetism of [Ln(NO₃)₃(H₂O)₃]·(18-crown-6) (Ln = Dy and Er)

The objective of this work was the exploration of the effect of the second coordination sphere on the magnetic properties of [Ln(NO₃)₃(H₂O)₃]·(18C6) (Ln = Dy (1) and Er (2)) compounds comprising co-crystallized 18-crown-6 ethers. Both compounds were identified as field-induced single molecule magnets (SMMs) with estimated magnetization reversal barriers <i>U</i> _eff = 66-71 K for 1 and <i>U</i> _eff = 21-24 K for 2. Theoretical calculations with the B3LYP functional revealed substantial change and redistribution of the electrostatic potential upon accounting for the second coordination sphere represented by two 18C6 molecules, which resulted in the change of the crystal-field around metal atoms. As a result, the multireference CASSCF calculations exposed significant impact of the second coordination sphere on the energy splitting of the respective ⁶ <i>H</i> _15/2 (Dy^III) and ⁴ <i>I</i> _15/2 (Er^III) ground states, the magnetization reversal barrier and the magnetic anisotropy parameters. Moreover, the calculated magnetization reversal barriers, <i>U</i> _calc. = 57 K for 1 and <i>U</i> _calc. = 16 K for 2, are in good agreement with the experimental values accentuating the importance of the second coordination sphere on the magnetic properties of SMMs.