The theoretical calculations on magnetic exchange of the title complex are carried out by using multiconfigurational second-order perturbation theory, CASPT2, and density functional theory combined with broken-symmetry approach, DFT-BS. The CASPT2 calculated quartet ground state, stabilized by 8.02 cm1 compared with the nearest excited doublet state, is close to 5cm 1 of the experimental measurement. The dependence of energy levels on the ratio J23/J12,13 validates occurrence of the spin frustration phenomenon. Both CASPT2 and DFT-BS calculations reproduce well experimentally coupling constants of J12, 13=9.35cm 1, J23=3.95cm 1, for CASPT2 J12, 13=6cm 1, J23=2cm 1 and for DFT-BS J12, 13=11.31cm 1, J23=4.20m 1. The methodological comparison is briefly discussed.

The calculations on magnetic exchange interaction of Cl3FeOFeCl3 2- and the related modeling compounds were performed by using the density functional theory coupling the broken symmetry approach. The calculated results show the absence of a direct Cl3Fe-FeCl3 magnetic coupling and the effect of the terminal Cl ligands on magnetic exchange interaction in [Fe-O-Fe]4+, while the protonation of

Magnetic exchange interaction for the μ-hydroxo bridged vanadium (IV) dimers is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is found that there is an exponential correlation between the V-O (hydroxo)-V angle, the V-O (hydroxo) distance and the exchange coupling constants J. Meanwhile, the calculated results reveal that the deprotonation of the bridging hydroxo ligand causes a sharp increase of the exchange coupling interaction, but the magnetic coupling constant J is insensitive to the deprotonation of the bridging aquo ligand. Moreover, simplifying each 1,2-bridging squarate ligand with two OCH2 groups almost does not influence magnetic exchange behavior between the two vanadium (IV) ions, and the principle of the shortest superex-change pathway is available for the multiplicity of the bridging ligand in the μ-hydroxo bridged vanadium (IV) di-mers.

The magnetic exchange behaviour for l-hydroxo and l-acetato double-bridged chromium (III) dimer is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is demonstrated that there is a magnetic exchange cooperative effect of the two bridging ligands in a double-bridged dimer systems with approximate equal coupling intensity. Meanwhile, the calculated results reveal that the deprotonation of the l-hydroxo ligand causes a sharp increase of the magnetic exchange interaction between the chromium centers. Replacing either the l-hydroxo bridging ligand by one water bridging ligand or the l-acetato bridging ligands by two terminal water ligands produces a relatively reasonable model to examine the contribution on the magnetic exchange interaction of another individual bridging ligand.

In order to theoretically study on the magnetic coupling interaction in the Mn-Mn dimer, quantum chemical calculations on the equilibrium Mn-Mn distance Re, total energy ET, binding energies Be and exchange interaction energies EðSÞ under dierent spin multiplets were performed at CASPT2 level of theory. It is found that the calculated Re, ET, and Be values are correlated with the spin multiplet, and with increasing the total spin S, Re increases, but ET and Be exhibit a decrease trend. The exchange interaction energies EðSÞ "deviate significantly from the Lande interval rule". This unusual magnetic phenomenon is primarily attributed to the biquadratic jðSa SbÞ2 term contribution in spin Hamiltonian for the Mn-Mn dimer.