title: Rational electrostatic design of easy-axis magnetic anisotropy in a Zn(II) -Dy(III) -Zn(II) single-molecule magnet with a high energy barrier.
abstract: Two novel trinuclear complexes [ZnCl(μ-L)Ln(μ-L)ClZn][ZnCl3 (CH3 OH)]⋅3 CH3 OH (Ln(III) =Dy (1) and Er (2)) have been prepared from the compartmental ligand N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2 L). X-ray studies reveal that Ln(III) ions are coordinated by two [ZnCl(L)](-) units through the phenoxo and aldehyde groups, giving rise to a LnO8 coordination sphere with square-antiprism geometry and strong easy-axis anisotropy of the ground state. Ab initio CASSCF+RASSI calculations carried out on 1 confirm that the ground state is an almost pure MJ =±15/2 Kramers doublet with a marked axial anisotropy, the magnetic moment is roughly collinear with the shortest DyO distances. This orientation of the local magnetic moment of the Dy(III) ion in 1 is adopted to reduce the electronic repulsion between the oblate electron shape of the MJ =±15/2 Kramers doublet and the phenoxo-oxygen donor atoms involved in the shortest DyO bonds. CASSCF+RASSI calculations also show that the ground and first excited states of the Dy(III) ion are separated by 129 cm(-1) . As expected for this large energy gap, compound 1 exhibits, in a zero direct-current field, thermally activated slow relaxation of the magnetization with a large Ueff =140 K. The isostructural Zn-Er-Zn species does not present significant SMM behavior as expected for the prolate electron-density distribution of the Er(III) ion leading to an easy-plane anisotropy of the ground doublet state.
authors.affiliation: Departamento de Química Aplicada, Facultad de Química, UPV/EHU, Paseo Manuel de Lardizabal 3, 20018 Donostia-San Sebastián (Spain).
authors.forename: Itziar
authors.initials: I
authors.lastname: Oyarzabal
authors.forename: José
authors.initials: J
authors.lastname: Ruiz
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Seco
authors.forename: Marco
authors.initials: M
authors.lastname: Evangelisti
authors.forename: Agustín
authors.initials: A
authors.lastname: Camón
authors.forename: Eliseo
authors.initials: E
authors.lastname: Ruiz
authors.forename: Daniel
authors.initials: D
authors.lastname: Aravena
authors.forename: Enrique
authors.initials: E
authors.lastname: Colacio
keywords: ab initio calculations; dysprosium; erbium; magnetic properties; single-molecule magnet