Fine-Tuning Ligand Fields with Schiff-Base Ligands in Dy2 Compounds

Three dinuclear coordination compounds, [Ln(2)(Hhms)(2)(NO3)(4)]center dot MeCN [Ln = Dy (1) and Er (2)] and [Dy-2(Hhms)(2)(NO3)(2)(H2O)(3)]center dot(NO3)(2)center dot MeCN center dot(H2O)(2) (3), have been isolated bearing the asymmetric Schiff-base ligand 1-(2hydroxy-3-methoxybenzylidene) semicarbazide (H(2)hms). The potentially tetradentate ONOO-donor ligand shows considerable metal-ion-selective phenoxo bridging in 1-3. Compounds 1 and 2 display a hula-hoop-like coordination geometry, whereas this geometry is broken by an additional mu(2)-OH2 bridge in compound 3. The structural discrepancies induced by the different bridging modes in 1 and 3 affect the magnetism. Compound 1 exhibits slow relaxation of the magnetization, which suggests single-molecule magnet (SMM) behavior, whereas no out-ofphase alternating-current signal was observed for 3. Meanwhile, compared with a previously reported Dy-2 compound, compound 1 has the same coordination sphere but exhibits different magnetic properties, which has been attributed to differences in the ligand backbone. Fine-tuning of the ligand field is dominated by mu-O bridges and by the extent of conjugation in the backbone of the ligand, which affects the SMM/non-SMM behavior.