Quantum Chemical Investigations on Heavy Ligand Atom Induced Large Magnetic Anisotropy in Mn(II) Complexes.*

In Single Molecule Magnets (SMM) metal ions are considered pivotal towards achieving
large magnetic anisotropy barriers. A metal ion with strong spin-orbit coupling constant and low
coordination number results in the retention of unquenched metal-orbital angular
momentum, produces large magnetic anisotropy ^(1-2). In this context, the influence of ligands with
heavy elements, showing large spin-orbit coupling, on magnetic anisotropy barriers was
investigated using a series of Mn(II)-based complexes, in which the metal ion did not have any
orbital contribution. The mixing of metal and ligand orbitals was achieved by explicitly correlating
the metal and ligand valence electrons with Complete Active Space Self-Consistent Field
(CASSCF) calculations. The CASSCF wave functions were further used for evaluating spin-orbit
coupling and zero-field splitting parameters for these complexes. For Mn(II) complexes with heavy
ligand atoms, such as Br and I, several interesting inter-state mixings occur via the spin–orbit
operator, which results in large magnetic anisotropy in these Mn(II) complexes⁽³⁾ .


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