A useful parameter describing magnetic coupling interactions has been inspected in transition metal dimers, in which two transition metal ions are bridged by extended bis-bidentate ligands. This parameter is the square of overlap integral between the spatial parts of magnetic orbitals in the broken symmetry state. The oxalato-bridged Cu (II) dimers, in which the Cu (II) atom is either in tetrahedral or square pyramid coordination environment, have been calculated with the density functional theory coupling the broken symmetry approach.

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.

The long disputed mechanism for the F2 addition to ethene is elucidated by density functional theory calculations. With hybrid functionals and a large basis set, DFT provides an excellent description for the dissociation of ground state F2, and a reasonable account for the F2

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.

The influence of the structural parameters of Cu2CO2 core on magnetic coupling is studied in model alkoxo-bridged Cu (II) dimers using the density functional method and the broken symmetry approach. The effect of the hinge distortion of the bridge and the out-of-plane displacement of alkoxo group is also analyzed. A small Cu