Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
J Phys Chem A. 2011 Mar 24;115(11):2291-6. doi: 10.1021/jp108344k. Epub 2011 Mar 3.
We have conducted a comparative computational investigation of the molecular structure and water adsorption properties of molybdenum oxide and sulfide clusters using density functional theory methods. We have found that while Mo₃O₆⁻ and Mo₃S₆⁻ assume very similar ring-type isomers, Mo₃O₉⁻ and Mo₃S₉⁻ clusters are very different with Mo₃O₉⁻ having a ring-type structure and Mo₃S₉⁻ having a more open, linear-type geometry. The more rigid ∠(Mo-S-Mo) bond angle is the primary geometric property responsible for producing such different lowest energy isomers. By computing molecular complexation energies, it is observed that water is found to adsorb more strongly to Mo₃O₆⁻ than to Mo₃S₆⁻, due to a stronger oxide-water hydrogen bond, although dispersion effects reduce this difference when molybdenum centers contribute to the binding. Investigating the energetics of dissociative water addition to Mo₃X₆⁻ clusters, we find that, while the oxide cluster shows kinetic site-selectivity (bridging position vs terminal position), the sulfide cluster exhibits thermodynamic site-selectivity.
我们使用密度泛函理论方法对氧化钼和硫化钼簇的分子结构和水吸附特性进行了比较计算研究。我们发现，虽然 Mo₃O₆⁻ 和 Mo₃S₆⁻ 假设非常相似的环型异构体，但 Mo₃O₉⁻ 和 Mo₃S₉⁻ 簇非常不同，Mo₃O₉⁻ 具有环型结构，而 Mo₃S₉⁻ 具有更开放的线型几何形状。更刚性的 ∠(Mo-S-Mo) 键角是产生这种不同最低能量异构体的主要几何性质。通过计算分子络合能，观察到水与 Mo₃O₆⁻ 的吸附强度大于与 Mo₃S₆⁻ 的吸附强度，这是由于氧化键与水之间的氢键更强，尽管当钼中心有助于结合时，色散效应会降低这种差异。研究了 Mo₃X₆⁻ 簇上的缔合水加成的能量学，我们发现，虽然氧化物簇表现出动力学位选择性（桥接位置与末端位置），但硫化物簇表现出热力学位选择性。
