Magnetic Properties and Electronic Structure of the = 2 Complex [Mn{(OPPh)N}] Showing Field-Induced Slow Magnetization Relaxation.

The high-spin = 2 Mn(III) complex [Mn{(OPPh)N}] () exhibits field-induced slow relaxation of magnetization ( , , 12869). Magnetic susceptibility and dual-mode X-band electron paramagnetic resonance (EPR) studies revealed a negative value of the zero-field-splitting (zfs) parameter . In order to explore the magnetic and electronic properties of in detail, a combination of experimental and computational studies is presented herein. Alternating-current magnetometry on magnetically diluted samples (/) of in the diamagnetic gallium analogue, [Ga{(OPPh)N}], indicates that the slow relaxation behavior of is due to the intrinsic properties of the individual molecules of . Investigation of the single-crystal magnetization of both and / by a micro-SQUID device reveals hysteresis loops below 1 K. Closed hysteresis loops at a zero direct-current magnetic field are observed and attributed to fast quantum tunneling of magnetization. High-frequency and -field EPR (HFEPR) spectroscopic studies reveal that, apart from the second-order zfs terms ( and ), fourth-order terms () are required in order to appropriately describe the magnetic properties of . These studies provide accurate spin-Hamiltonian (sH) parameters of , i.e., zfs parameters || = 3.917(5) cm, || = 0.018(4) cm, = = 0, and = (3.6 ± 1.7) × 10 cm and = [1.994(5), 1.996(4), 1.985(4)], and confirm the negative sign of . Parallel-mode X-band EPR studies on / and CHCl solutions of probe the electronic-nuclear hyperfine interactions in the solid state and solution. The electronic structure of is investigated by quantum-chemical calculations by employing recently developed computational protocols that are grounded on ab initio wave function theory. From computational analysis, the contributions of spin-spin and spin-orbit coupling to the magnitude of are obtained. The calculations provide also computed values of the fourth-order zfs terms , as well as those of the and hyperfine interaction tensor components. In all cases, a very good agreement between the computed and experimentally determined sH parameters is observed. The magnetization relaxation properties of are rationalized on the basis of the composition of the ground-state wave functions in the absence or presence of an external magnetic field.