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Articolo in rivista, 2023, ENG, 10.1039/d3qi00931a

Neutral cobalt(II)-bis(benzimidazole)pyridine field-induced single-ion magnets for surface deposition

Jana Juráková, Ondrej F. Fellner, Sören Schlittenhardt, ?árka Vavre?ková, Ivan Neme, Radovan Herchel, Erik ?i?már, Vinicius Tadeu Santana, Milan Orlita, Denis Gentili, Giampiero Ruani, Massimiliano Cavallini, Petr Neugebauer, Mario Ruben, Ivan ?alitro?

- Central European Institute of Technology, Brno University of Technology, Purky?ova 123, 61200 Brno Czech Republic - Department of Inorganic Chemistry, Faculty of Science, Palacký University, 17. listopadu 12, 771 46 Olomouc, Czech Republic - Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany). - Institute of Physics, Faculty of Science, P.J. ?afárik University Park Angelinum 9, 04154 Ko?ice, Slovakia - LNCMI-EMFL, CNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, Univ. Toulouse 3, INSA-T, Grenoble and Toulouse, France - Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Via P. Gobetti 101, 40129 Bologna, Italy - Department of Inorganic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava. Bratislava SK-81237, Slovakia.

Two novel hexacoordinated Co(II)-based single-ion magnets were prepared and characterised. Both neutral complexes feature metal-centred coordination with one terminal and one bidentate nitrate anions along with tridentate derivatives of a 2,6-bis(1H-benzimidazole-2-yl)pyridine ligand containing either n-octyl (complex 1) or n-dodecyl (complex 2) chains. The presence of long aliphatic chains ensures their solubility in low polarity and volatile solvents frequently used for lithography patterning. This enabled the preparation of microstructural layers and patterns on technologically relevant substrates by easy-to-handle and low-cost wet lithographic techniques. On the other hand, attempts at surface deposition via sublimation were not successful due to thermal instability. The electronic structure of complexes typically features an orbitally non-degenerate ground state well-separated from the lowest excited state, which allows one to analyse magnetic anisotropy by the spin Hamiltonian approach. Zero-field splitting parameters obtained from CASSCF-NEVPT2 calculations and from the analysis of magnetic data suggest that both compounds display positive axial D parameters within a range of 17-25 cm(-1). Combined results from high-field electron paramagnetic resonance (X-band and HF-EPR) and Fourier-transform infrared magnetic spectroscopy (FIRMS) simulated with the spin Hamiltonian provided the axial and rhombic zerofield splitting terms D = +23.7 cm(-1) for complex 1 and D = +24.2 cm(-1) for complex 2, together with pronounced rhombicity in the range of E/D approximate to 0.15-0.19 for both compounds. Dynamic magnetic investigations have revealed the field-induced slow relaxation of magnetisation, with maximal relaxation times (tau) of 7.6 ms for 1 and 0.8 ms for 2. This relaxation is governed via a combination of several relaxation mechanisms, among which the quantum tunnelling was efficiently suppressed by the applied static magnetic field. The effective barriers of spin reversal U-eff = 77(4) K for 1 and U-eff = 70(2) K for 2 are consistent with the expected values calculated using the ZFS parameters.

Inorganic chemistry frontiers Online 10 (18), pp. 5406–5419