Computational Study of Metal–Dinitrogen Keggin-Type Polyoxometalate Complexes [PW₁₁O₃₉M^IIN₂)]^5– (M = Ru, Os, Re, Ir): Bonding Nature and Dinitrogen Splitting

Abstract

Molecular geometry, electronic structure, and metal-dinitrogen bonding nature of a series of metal-dinitrogen derivatives of Keggin-type polyoxometalates (POMs) [PW11O39M(II)N2)](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 N2 adsorption with considerable adsorption energy. The electronic structure analysis shows that Os(II) and Re(II) centers in their metal-dinitrogen POM complexes possess π(2)xzπ(2)yzπ(2)xy and π(2)xzπ(2)yzπ(1)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 (ΔG(⧧)) for a transition state with a zigzag conformation is 16.05 kcal mol(-1) 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.

Reduction of NO to N2O Catalyzed by a Mn-Substituted Keggin-Type Polyoxometalate: A Density Functional Theory Study

“…The transition metal center is stabilized by four O b atoms coming from the surface oxygen of Keggin-type POM ligand (see Figure b). Due to the very large distance between metal and O a atoms, the M–O a interaction can be viewed as a weakened bonding interaction, which provides a unsaturated metal atom in the pseudo-octahedral coordinated sphere. ,, Thus, the transition metal center has an additional ability to bind to a NO molecule.…”

Epoxidation of propylene by hydrogen peroxide catalyzed by the silanol‐functionalized polyoxometalates‐supported ferrate: Electronic structure, bonding feature, and reaction mechanism

“…of POMs was validated in our previous work. [ 66 ] The LANL2DZ pseudopotential was used for metal atoms. The 6‐31G(d) basis set was used for the main‐group atoms.…”

Reduction of N2 to NH3 catalyzed by a Keggin-type polyoxometalate-supported dual-atom catalyst

“…These findings supported that a dimeric Keggin-type POM derivative of rhenium could represent the intermediate that undergoes N–N bond scission with a moderate barrier. 57 In another case, we further investigate the possible reaction mechanism of a series of mono-transition-metal-substituted Keggin-type POM–dinitrogen complexes [PW 11 O 39 M(N 2 )] n− (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, Re, Os, Ir, Pt, Au, and Hg) for the NRR, in which the mono-lacunary Keggin-type POM ligand with five oxygen donor atoms serves as a strong electron donor to the metal center for the activation of the N 2 molecule. Our DFT results also indicated that Mo II –, Tc II –, W II –, Re II –, Ru II –, and Os II –POM complexes are significant for the binding and activation of an inert N 2 molecule.…”