Highly Anisotropic Orbitally Dependent Superexchange in Cyano‐Bridged Clusters Containing Mn(III) and Mn(II) Ions

• Published in: Chemphyschem Vol. 7; no. 4; pp. 871 - 879
• Main Authors: Palii, Andrew, Ostrovsky, Sergey M., Klokishner, Sophia I., Tsukerblat, Boris. S., Dunbar, Kim R.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 10.04.2006; Wiley
• Subjects: Atomic and molecular clusters; Atomic and molecular physics; cluster compounds; Condensed matter: electronic structure, electrical, magnetic, and optical properties; cyano‐bridged manganese clusters; Electronic and magnetic properties of clusters; Exact sciences and technology; Exchange and superexchange interactions; exchange interactions; magnetic properties; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Physics; Studies of special atoms, molecules and their ions; clusters; Energy levels; Ground states; Quantum numbers; Theoretical study; Electron transfer; Crystal field; Cyano complex; Mu complex; cluster compounds; Hamiltonians; Superexchange interactions; Manganese complexes; Polynuclear complex; Spin-orbit interactions; Kinetics; Charge transfer; Exchange interactions; cyano-bridged manganese clusters; Manganese; Magnetic properties
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200500549

10.1002/cphc.200500549.absWe study the orbitally dependent magnetic exchange in cyanide‐based clusters as a source of the barrier for reversal magnetization. We consider the Mn(III)–CN–Mn(II) dimer and linear Mn(II)–NC–Mn(III)–CN–Mn(II) trimer containing octahedrally coordinated Mn(III) and Mn(II) ions with special emphasis on the magnetic manifestations of the orbital degeneracy of the Mn(III) ion. The kinetic exchange mechanism involves the electron transfer from the single occupied t2 orbitals of the Mn(II) ion [${{}^6A_{\,1} \left( {t_2^3 e^2 } \right)}$ ground state] to the singly occupied t2 orbitals of the Mn(III) ion [${{}^3T_{\,1} \left( {t_2^4 } \right)}$ ground state] resulting in the charge‐transfer ${{}^5T_2 \left( {t_2^2 e^2 } \right)_{Mn(III)} }$${ - {}^2T_2 \left( {t_2^5 } \right)_{Mn(II)} }$ state of the pair. The deduced effective exchange Hamiltonian that takes into account orbital degeneracy leads to an essentially non‐Heisenberg energy pattern. The energy levels are shown to be dependent on both spin and orbital quantum numbers, thus providing direct information about the magnetic anisotropy of the system. Along with the magnetic exchange, the model includes an axial component of the crystal field and spin–orbit coupling operating within the ground ${{}^3T_1 \left( {t_2^4 } \right)}$ cubic term of the Mn(III) ion. We have shown that under certain conditions both named interactions lead to the occurrence of the barrier for the reversal of magnetization, which significantly increases when passing from the dimer to the trimer. This provides a possible way for raising the magnetic barrier in the family of cyano‐bridged manganese clusters. Magnetic metal clusters: Cyano‐bridged manganese‐containing dimers and trimers (see picture) are analyzed theoretically. The energy levels are shown to be dependent on both spin and orbital quantum numbers, thus providing direct information of the magnetic anisotropy of the system. Under certain conditions an appreciable barrier for the reversal of magnetization is created which significantly increases when passing from the dimer to the trimer.