Magnetization Slow Dynamics in Mononuclear Co(II) Field-Induced Single-Molecule Magnet
Nikoleta Malinová, Jana Juráková, Barbora Brachňaková, Jana Dubnická Midlíková, Erik Čižmár, Vinícius T. Santana, Radovan Herchel, M. Orlita, Ivan Mohelský, Ján Moncóľ, Petr Neugebauer, Ivan Šalitroš
Abstract
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 .