title: Methane activation by V3PO10(˙+) and V4O10(˙+) clusters: a comparative study.
abstract: A series of vanadium and phosphorus heteronuclear oxide cluster cations (V(x)P(y)O(z)(+)) are prepared by laser ablation and the reactions of V(3)PO(10)˙(+) and V(4)O(10)˙(+) with methane in a fast flow reactor under the same conditions are studied. A time of flight mass spectrometer is used to detect the cluster distribution before and after reactions. In addition to previously identified reaction of V(4)O(10)˙(+) + CH(4)→ V(4)O(10)H(+) + CH(3)˙, the observation of hydrogen atom pickup cluster V(3)PO(10)H(+) suggests the reaction: V(3)PO(10)˙(+) + CH(4)→ V(3)PO(10)H(+) + CH(3)˙. The rate of the reaction of V(4)O(10)˙(+) with CH(4) is approximately 2.5 times faster than that of V(3)PO(10)˙(+) with CH(4). Density functional theory (DFT) calculations predict that structure of V(3)PO(10)˙(+) is topologically similar to that of V(4)O(10)˙(+), as well as that of P(4)O(10)˙(+), which is very similar to V(4)O(10)˙(+) in terms of methane activation in previous studies. The facile methane activation by the homo- and hetero-nuclear oxide clusters can all be attributed to the presence of an oxygen-centered radical (O˙) in these clusters. Further theoretical study indicates that the O˙ radical (or spin density of the cluster) can transfer within the high symmetry V(4)O(10)˙(+) and P(4)O(10)˙(+) clusters quite easily, and CH(4) molecule further enhances the rate of intra-cluster spin density transfer. In contrast, the intra-cluster spin density transfer within low symmetry V(3)PO(10)˙(+) is thermodynamically forbidden. The experimentally observed reactivity difference is consistent with the theoretical consideration of the intra-cluster spin density transfer.
authors: Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors: Jia-Bi
authors: JB
authors: Ma
authors: Xiao-Nan
authors: XN
authors: Wu
authors: Xian-Xia
authors: XX
authors: Zhao
authors: Xun-Lei
authors: XL
authors: Ding
authors: Sheng-Gui
authors: SG
authors: He