Tuning intramolecular dipole interactions in dinuclear single-molecule magnetic complexes of Er(III) with monosubstituted cyclooctatetraenide ligands

Manipulating magnetic couplings in molecular magnets is of great importance in improving the magnetic properties of such materials. It has been proved that by adjusting the strength of magnetic couplings and the arrangement of the intermolecular magnetic dipoles, magnetic blocking can be significantly enhanced. Herein manipulating the intramolecular dipole interactions by ligand modification was attempted with the use of three closely related dinuclear Er(III) complexes of a common chemical formula of [(COTR)Er(mu-Cl) (THF)]2 (COTR is monosubstituted cyclooctatetraenide dianions with R = diphenylmethylsilyl (Ph2MeS) for 1, triethylsilyl (TES) for 2, and triisopropylsilyl (TIPS) for 3). Each of these complexes features a centrosymmetric dinuclear core unit with their component Er(III) ions doubly bridged by two chloro ligands and further coordinated with a capping substituted COTR ligand and a coordinated THF molecule. Magnetic studies reveal that the complexes display similar ferromagnetic couplings with comparable single-molecule magnetic behaviors. The ferromagnetic couplings dominated by the intramolecular dipole interactions are found to be 0.7614, 0.7380, and 0.5635 cm-1 for 1, 2, and 3, respectively. The angles (B) between the magnetic easy axes and the intramolecular Er-Er lines are 24.88(2)degrees, 25.23(1)degrees, and 31.85(5)degrees, leading to transversal dipole fields of 0.0114, 0.0113, and 0.0125 T for 1, 2, and 3, respectively. Although the different ligand substitution generates a sizable difference of about 7 degrees in the B angle, the resulting difference in the dipole interactions is not sufficiently strong to cause any significant differences in their magnetic properties. Further change in the B angles to the "side-by-side" (B = 90 degrees) or "head-to-tail" (B = 0 degrees) arrangement of the magnetic easy axes, achievable by rational molecular design, is expected to lead to molecular magnetic materials with much enhanced properties. (c) 2024 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.