Slow Magnetic Relaxation in Two New 1D/0D Dy^III Complexes with a Sterically Hindered Carboxylate Ligand

Two carboxylate-bridged Dy^III complexes, [Dy₂(piv)₅(μ₃-OH)­(H₂O)]_<i>n</i> (<b>1</b>) and [Dy₂(piv)₆(phen)₂] (<b>2</b>) (pivH = pivalic acid; phen = 1,10-phenanthroline), have been synthesized and structurally characterized. Complex <b>1</b> takes a one-dimensional (1D) chain structure based on [Dy₄(μ₃-OH)₂(piv)₈(H₂O)₂]²⁺ units, while complex <b>2</b> is a dinuclear structure bridged by <i>syn</i>,<i>syn</i>-carboxylates. Magnetic investigation indicates weak ferromagnetic interaction between adjacent Dy^III ions of the Dy₄ unit in <b>1</b> and weak intramolecular antiferromagnetic interaction between Dy^III ions and/or depopulation of the Dy^III excited-state Stark sublevels in <b>2</b>. Alternating-current susceptibility measurements revealed frequency- and temperature-dependent out-of-phase signals under a zero direct-current field in <b>1</b>, with typical slow magnetic relaxation behavior with an anisotropic barrier <i>U</i> ≈ 4.5 K, while <b>2</b> exhibits field-induced single-molecule-magnet behavior with Δ<i>E</i>/<i>k</i>_B = 28.43 K under a 2 kOe external field