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

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 (HL ), 1,3-Bis (3-pyridyl)-1,3-propanedione (HL ), 1-(4-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL ), and 1,3-Bis (4-pyridyl)-1,3-propanedione (HL ), to tune the magnetic relaxation behaviors of cyano-bridged {Dy Mo } systems. By reacting with DyCl  ⋅ 6H O and K Mo(CN)  ⋅ 2H O, four cyano-bridged complexes, namely {[Dy[Mo (CN) ](HL ) (H O) ]} ⋅ 6H O (1), {[Dy[Mo (CN) ](HL )(H O) (CH OH)]}  ⋅ 2CH OH ⋅ 3H O (2), {[Dy[Mo (CN) ](HL )(H O) (CH OH)] ⋅ H O} (3), and {[Dy[Mo (CN) ](HL ) (H O) ]} ⋅ 2H O⋅CH OH (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 Dy ions in all complexes have eight-coordinated configurations with the coordination spheres DyO N for 1 and 4, DyO N for 2, and DyO N 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 Dy centers.