Magnetization Slow Dynamics in Mononuclear Co(II) Field-Induced Single-Molecule Magnet

The novel tridentate ligand L (2,6-bis(1-( n -decyl)-1 H -benzimidazol-2-yl)pyridine) was used for the synthesis of mononuclear Co(II) complex 1 with the general formula [Co(L)Br 2 ]. A single-crystal X-ray structural investigation confirmed the expected molecular structure, and noncovalent contacts were inspected by a Hirschfeld surface analysis. The electronic structure of square-pyramidal complex 1 contains an orbitally degenerate ground state which predetermines the use of the Griffith–Figgis Hamiltonian for the analysis of magnetic properties. CASSCF-NEVPT2 calculations and far-infrared magnetic spectroscopy show excellent agreement with the Griffith–Figgis Hamiltonian parameters obtained from the magnetic investigation. The high and negative value of the axial crystal field parameter Δ ax and the calculated g -tensor components suggest the axial magnetic anisotropy of 1 . The low-temperature X-band EPR spectra were analyzed within a simplified effective spin-1/2 Hamiltonian to determine effective g -tensor components of the ground Kramers doublet, which agree with the electronic structure predicted within the CASSCF-NEVPT2 theory. An AC magnetic investigation revealed field-supported single-channel slow relaxation of magnetization with maximum relaxation time τ ≈ 28 ms at low temperatures. The comprehensive analysis of the field and temperature evolution of τ indicates that direct, Raman, and Orbach processes are all involved in slow relaxation of magnetization in 1 .