Regulating Magnetic Relaxations of Cyano-Bridged {DyIIIMoV} Systems by Tuning the N-Sites in β-Diketone Ligands

Abstract

Cyano-bridged 4d–4f molecular nanomagnets have re-called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β-diketone ligands bearing different substitution N-sites were designed and synthesized, namely 1-(2-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL1), 1,3-Bis (3-pyridyl)-1,3-propanedione (HL2), 1-(4-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL3), and 1,3-Bis (4-pyridyl)-1,3-propanedione (HL4), to tune the magnetic relaxation behaviors of cyano-bridged {DyIIIMoV} systems. By reacting with DyCl3 ⋅ 6H2O and K4Mo(CN)8 ⋅ 2H2O, four cyano-bridged complexes, namely {[Dy[MoV(CN)8](HL1)2(H2O)3]} ⋅ 6H2O (1), {[Dy[MoV(CN)8](HL2)(H2O)3(CH3OH)]}2 ⋅ 2CH3OH ⋅ 3H2O (2), {[Dy[MoV(CN)8](HL3)(H2O)2(CH3OH)] ⋅ H2O}n (3), and {[Dy[MoV(CN)8](HL4)2(H2O)3]} ⋅ 2H2O⋅CH3OH (4) were obtained. Structural analyses revealed that 1 and 4 are binuclear complexes, 2 has a tetragonal structure, and 3 exhibits a stair-like polymer chain structure. The DyIII ions in all complexes have eight-coordinated configurations with the coordination spheres DyO7N1 for 1 and 4, DyO6N2 for 2, and DyO5N3 for 3. Magnetic measurements indicate that 1 is a zero-field single-molecule magnet (SMM) and complexes 2–4 are field-induced SMMs, with complex 4 featuring a two-step relaxation process. The magnetic characterizations and ab initio calculations revealed that changing the N-sites in the β-diketone ligands can effectively alter the structures and magnetic properties of cyano-bridged 4d–4f nanomagnets by adjusting the coordination environments of the DyIII centers.