Large Energy Barrier and Magnetization Hysteresis at 5 K for a Symmetric {Dy 2 } Complex with Spherical Tricapped Trigonal Prismatic Dy III Ions.

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH ₂ ) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy ₂ (NO ₃ ) ₄ (sacbH) ₂ (H ₂ O) ₂ (MeCN) ₂ ] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two Dy ^III ions. As a result, the {Dy ^III ₂ } compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.3(1) K for the reversal of magnetization. Fast and efficient quantum tunneling of magnetization, attributed to the strong tails of signals below ∼15 K, was suppressed through the application of a small dc field, yielding entirely visible χ _M ″ signals below 27 K. Single-crystal magnetic hysteresis studies confirmed the single-molecule magnet (SMM) behavior of 1; the hysteresis loops appear at temperatures below ∼5 K, which is one of the highest blocking temperatures in the field of 4f-SMMs to date. This joint magneto-structural and ab initio study demonstrates the ability of more common coordination numbers (i.e., 9), but with rare coordination geometries (i.e., spherical tricapped trigonal prismatic), to promote axiality that enhances the molecular anisotropy and subsequently the magnetization dynamics of the system.