Regulating the distortion degree of the square antiprism coordination geometry in Dy–Na single ion magnets

Abstract

A novel [Dy^IIINa^I] complex, [DyNa(L)₂(MeOH)]·MeOH (1, H₂L = N,N′-bis(2-oxy-3-methoxybenzylidene)-1,2-phenylenediamine), and a zigzag 1D chain based on the [Dy^IIINa^I₂] subunit, [DyNa₂(L)₂(NO₃)]_n·MeOH (2), were obtained by employing a multidentate Schiff base ligand H₂L reacting with Dy(NO₃)₃·5H₂O, NaN₃ and NMe₄OH·5H₂O in MeOH or reacting with Dy(NO₃)₃·5H₂O and NaOH in methanol. Structural analyses revealed that the Dy^III in 1 and 2 is sandwiched between two L₂⁻ ligands, namely, the Dy^III ion was coordinated by four phenoxido O and four amine N atoms from two L₂⁻ ligands. SHAPE software calculations and structural analysis indicated that the coordination geometry of Dy^III in 1 and 2 is a distorted square antiprism (D_4d), but the distortion degree of Dy^III in 1 was smaller than that in 2. Additionally, in 1, one Na^I is located on one of the N₂O₂ planes, and the Na^I is coordinated by three phenoxido O and three methoxy O atoms from two L²⁻ ligands and one coordinated MeOH molecule. However, in 2, two Na^I ions are located on each of the N₂O₂ planes, in which the coordination environment of each Na^I is completed by three phenoxido O atoms, three methoxy O atoms and two O atoms from one NO₃⁻ ion. Moreover, the [Dy^IIINa^I₂] units are linked into a zigzag 1D chain by nitrate anions. ac magnetic susceptibility measurements revealed that both complexes 1 and 2 exhibit field-induced single ion magnet behavior under a 1000 Oe dc field, with values of the effective energy barrier (U_eff) of 65.33(1) K for 1 and 84.23(1) K for 2. Interestingly, the U_eff values of 1 and 2 are both higher than the corresponding value of 40.1 K for a reported complex with the coordination geometry of a bicapped triangular prism. The moderate SIM performance of 1 and 2 in the Dy(III)-based SIMs with a SAP coordination geometry could be ascribed to the compressed SAP coordination environment of Dy^III ions, dipole–dipole interactions and the deviation of the anisotropic axes from the S₈ axis.