Role of the Orbitally Degenerate Mn(III) Ions in the Single-Molecule Magnet Behavior of the Cyanide Cluster {[MnII(tmphen)2]3[MnIII(CN)6]2} (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline)

• Published in: Journal of the American Chemical Society Vol. 126; no. 51; pp. 16860 - 16867
• Main Authors: Palii, Andrei V, Ostrovsky, Sergei M, Klokishner, Sophia I, Tsukerblat, Boris S, Berlinguette, Curtis P, Dunbar, Kim R, Galán-Mascarós, José Ramón
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 29.12.2004
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Exchange and superexchange interactions; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Physics; Hamiltonian theory; Temperature dependence; Nitrogen heterocycle; Manganese Complexes; Organic ligand; Theoretical study; Cyano complex; Transition elements Complexes; Magnetic anisotropy; Polynuclear complex; Spin-orbit interactions; Exchange interactions; Magnetic properties
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja046771a

We report a new theoretical model that accounts for the unusual magnetic properties of the cyanide cluster {[MnII(tmphen)2]3[MnIII(CN)6]2} (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The model takes into account (1) the spin−orbit interaction, (2) the trigonal component of the crystal field acting on the ground-state cubic 3 T 1( ) terms of the apical Mn(III) ions, and (3) the isotropic contribution to the exchange interaction between Mn(III) and Mn(II) ions. The ground state of the cluster was shown to be the state with the total angular momentum projection |M J | = 15/2; the energies of the low-lying levels obtained from this treatment increase with decreasing |M J | values, a situation that leads to a barrier for the reversal of magnetization (U eff ≈ 30 cm-1). The new model explains the recently discovered single-molecule magnet behavior of the {[MnII(tmphen)2]3[MnIII(CN)6]2} in contrast to the traditional approach that takes into account only the ground-state spin (S) and a negative zero-field splitting parameter (D S < 0).