Density functional theory and ab initio study of electronic and electrochemistry properties of the tetranuclear sandwich complex [FeIII4(H2O)2(PW9O34)2]6-.

Quantum chemistry calculations have been performed to unravel the electronic and electrochemical properties of a FeIII-sandwich polyoxometalate. Using a combination of methods, it is shown that in these clusters the first reduction occurs in the so-called external Fe, which is bonded to a water ligand. Calculations also show that the electron reductions are coupled with protonation processes, in full agreement with existing experimental results.

Highly Reduced Polyoxometalates: Ab Initio and DFT Study of [PMo8V4O40(VO)4](5)(.).

DFT and post Hartree-Fock calculations were carried out to characterize the electronic structure of the 10-electron-reduced [PMo8V4O40(VO)4](5)(-) polyoxometalate. This molecule may be viewed as a mixed-metal PMo8V4O40 Keggin structure capped with four VO units, in which the eight vanadiums form a ring. In mixed V/Mo clusters it is accepted that the first reductions occur at the V(5+) ions. The BP86 calculations on this modified Keggin anion reveal that the ground state is a septet with the six unpaired electrons delocalized over the eight V centers. The B3LYP calculations and especially the CASSCF technique modify the tendency of the BP86 method, thus reproducing the expected 8/2 distribution. The unpaired electrons residing in the eight vanadiums are antiferromagnetically coupled.

A DFT study of the electronic spectrum of the alpha-keggin anion [Co(II)W(12)O(40)](6-).

Multiplet splittings for several excited configurations of [Co(II)W(12)O(40)](6-) were calculated using DFT methods. In agreement with the experimental interpretation of the spectrum the calculations found that the first strong band corresponds to Co d-d transitions, but it is worth noting that superposed to these transitions there are charge transfer transitions from cobalt to tungsten. The calculations also showed the importance of Jahn-Teller distortions in the excited states. With the exception of the consequences derived from a smaller splitting of d cobalt orbitals the d-d spectrum of [CoCl(4)](2-) is similar to that of the more complex Keggin anion. Finally, the energy of the bielectronic transition (4)A(2) --> (4)T(1)(P) was estimated via an approximate procedure based on ligand field theory.