Dinuclear and trinuclear cyano-bridged {DyIIIMIV} (M = W, Mo) single-ion magnets supported by pentadentate Schiff-base ligands

Abstract

The modular construction method provides a feasible way to construct pre-designed cyano-bridged {Ln^IIIM^IV/V} systems with more attractive structures and adjustable interactions between 4d/5d and 4f ions. In this work, the pentadentate Schiff-base ligands H₂Lⁿ (H₂L¹: 2,6-diacetylpyridine bis(nicotinoylhydrazone); H₂L²: 2,6-diacetylpyridine bis(isonicotinoylhydrazone)) with multiple coordination sites were designed to coordinate with Dy^III ions firstly, and then combined with K₄M(CN)₈·2H₂O (M = W, Mo) by a liquid–liquid diffusion method to successfully synthesize two trinuclear structures {Dy[M^IV(CN)₈]_0.5(HL¹)(H₂O)₃}₂·8H₂O (1: M = W; 2: M = Mo), and two dinuclear structures {[Dy[M^IV(CN)₈](H₃L²)(H₂O)₃]}·sol (3: M = W, sol = 11.5H₂O; 4: M = Mo, sol = 2CH₃OH·9.5H₂O). Interestingly, deprotonation occurs in ligand H₂L¹ during the formation of complexes 1 and 2, while deprotonation/protonation processes both occur in ligand H₂L² during the synthesis of complexes 3 and 4. Magnetic analyses reveal that complexes 1–4 are all field-induced single-ion magnets (SIMs). The energy barriers (U_eff/k_B) of complexes 1 and 2 are 92.83 K and 101.08 K, respectively, which are nearly three-fold higher than those of complexes 3 (30.19 K) and 4 (32.77 K). Ab initio calculations were performed on these series of {Ln^IIIM^IV} heteronuclear complexes to provide more insights into the magnetic relaxation properties. This work provides another example of improving the SMM behaviors of cyano-bridged {Ln^IIIM^IV} systems by deprotonation/protonation at different sites in the ligands.