Influence of lattice water molecules on the magnetization dynamics of binuclear dysprosium(iii) compounds: insights from magnetic and ab initio calculations

Abstract

Lattice water effects on the structures and magnetic properties of single-molecule magnets (SMMs) have attracted considerable attention. Herein, we have successfully synthesized two centrosymmetric binuclear compounds [Dy₂(2,3′-ppcad)₂(C₂H₃O₂)₄(H₂O)₂] (1) and [Dy₂(2,3′-ppcad)₂(C₂H₃O₂)₄(H₂O)₂]·6H₂O (2) (2,3′-Hppcad = N³-(2-pyrazinyl)-3-pyridinecarboxamidrazone) by elaborately varying the amount of the base (LiOH·H₂O). Through isothermal titration calorimetry (ITC), the interactions between Dy^III ions and 2,3′-Hppcad with different amounts of LiOH·H₂O were monitored in real time. Magnetic studies reveal that two compounds exhibit the typical zero-field single-molecule magnet behavior with different energy barrier (U_eff) values of 103.43 K for 1 and 386.48 K for 2, wherein the SMM performance for 2 stands out among the reported nine-coordinated Dy₂-SMMs systems with spherical capped square antiprism (C_4v) geometries. To rationalize the observed difference in the magnetic properties of 1 and 2, ab initio calculations have been performed. The introduction of lattice water molecules leads to differences in the J values observed for 1 and 2. The stronger antiferromagnetic Dy^III–Dy^III couplings in 2 were presented and the fast quantum tunneling of magnetization was further suppressed, thereby achieving a higher U_eff value. This work provides an effective strategy to enhance the SMM performance, and combines with ab initio calculations to explain how lattice water molecules can affect the magnetic interactions of Dy₂-SMMs.