Computational Study of Metal-Dinitrogen Keggin-Type Polyoxometalate Complexes [PW11O39MIIN2)]5- (M = Ru, Os, Re, Ir): Bonding Nature and Dinitrogen Splitting

Molecular geometry, electronic structure, and metal dinitrogen bonding nature of a series of metal-dinitrogen derivatives of Keggin-type polyoxometalates (P0Ms) [(PW11O39MN2)-N-11)](5-) (M = Ru, Os, Re, Ir) have been studied by using a density functional theory (DFT) method with the M06L functional. Among these Keggin-type POM complexes, Os- and Re-substituted POM complexes are the most active for N-2, adsorption with considerable adsorption energy. The electronic structure analysis shows that Os" and Rell centers in their metal dinitrogen POM complexes possess pi(2)(xz)pi(2)(yz)pi(2)(xy) and pi(2)(xz)pi(2)(yz)pi(2)(xy) configurations, respectively. DFT-M06L calculations show that the possible synthesis routes proposed in this work for the Ru, Os, and Re dinitrogen POM complexes are thermodynamically feasible under various solvent environments. Meanwhile, the Re dinitrogen POM complex was assessed for the direct cleavage of dinitrogen molecule. In the reaction mechanism, a dimeric Keggin-type POM derivative of rhenium could represent the intermediate which undergoes N N bond scission. The calculated free energy barrier (AO for a transition state with a zigzag conformation is 16.05 kcal moll in tetrahydrofuran, which is a moderate barrier for the cleavage of the N N bond when compared with the literature values. In conclusion, regarding the direct cleavage of the dinitrogen molecule, the findings would be very useful to guide the search for a potential N2 cleavage compound into totally inorganic POM fields