Two Types of Hexanuclear Partial Tetracubane [NiLn] (Ln = Dy, Tb, Ho) Complexes of Thioether-Based Schiff Base Ligands: Synthesis, Structure, and Comparison of Magnetic Properties.

New Schiff base ligand HL containing NOS donor atoms has been explored for its ability to provide complexes of selected 3d and 4f metal ions. Room temperature reaction of HL with NiCl·6HO and Ln(NO)·5HO in the presence of EtN in MeCN-MeOH (2:1) medium resulted in [NiLn(L)(μ-Cl)(μ-OH)(HO)]Cl·2HO (where Ln = Dy (), Tb (), and Ho () and HL = 2-((2-(2-(2-hydroxy-3-methoxybenzylideneamino)ethylthio)ethylimino)methyl)-6-methoxyphenol). Use of Ni(SCN)·4HO during synthesis provided SCN ions for bridging and terminal coordination in [NiLn(L)(μ-NCS)(μ-OH)(NCS)(HO)]·MeOH·HO (where Ln = Dy (), = 2, = 4; Tb () and Ho (), = 0, = 14.1). All six complexes possess a hexanuclear defective tetracubane topology having exchangeable bridging groups. The study of direct current magnetic susceptibility measurements revealed that the Ni(II) ions are engaged in ferromagnetic interaction with the Dy, Tb, and Ho ions and have significant magnetic anisotropy in all six complexes. Alternating current susceptibility measurements confirmed that both of the two types of compounds qualify as zero-field single-molecule magnets (SMMs), and the effective barrier for the reversal of the magnetic moment was found to be in the range = 23-31 K for - and -, respectively. Detailed insight into the electronic structure and magnetic properties was calculated using DFT- and CASSCF-based analyses. The found isotropic exchange parameter () values are = -4.7 cm for and = +29.2 cm for and clearly indicate that the μ-NCS-bridge is a better candidate than μ-Cl for ferromagnetic exchange interactions. Out of the six complexes, only complex displays Tb centered emission peaks at 451 and 480 nm.