Guo Ling-Yu, Jagodič Marko, Zeng Su-Yuan, Wang Zhi, Shi Zhi-Qiang, Wang Xing-Po, Tung Chen-Ho, Sun Di
Key Lab of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P. R. China.
Dalton Trans. 2016 May 28;45(20):8404-11. doi: 10.1039/c6dt00793g. Epub 2016 Apr 25.
Modified classical trivacant Wells-Dawson α-P2W15O56 and the assembly of related sandwiched transition metal clusters are of interest, but surprisingly few reports of these materials exist because of the sensitivity of α-P2W15O56 to the assembly environment. Herein, we describe the pH-controlled assembly of two novel Dawson-sandwiched clusters, (H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) and (H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2), involving the in situ transformation of α-P2W15O56. Both clusters were characterized by X-ray single-crystal diffraction, FT-IR spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and elemental analyses. X-ray crystallography showed that both heteropolytungstates become divacant α-P2W16O57 and symmetrically encapsulate two edge-shared CoO6 octahedra in the interior in 1, while only one divacant α-P2W16O57 is observed in 2, which combined with another trivacant α-P2W15O56 to asymmetrically clamp three edge-shared CoO6 octahedra. The α-P2W16O57 heteropolytungstate should be generated in situ from α-P2W15O56via self-decomposition equilibria in solution. Their electrochemical behaviors reveal characteristic multi-electron redox processes related to W(VI) centers. The electrocatalytic reduction performances toward nitrite, hydrogen peroxide, chlorate, bromate and iodate were fully measured and discussed; among these species, both clusters exhibit the best electrocatalytic activity towards the reduction of bromate. Magnetic measurements indicate weak ferromagnetic exchange interactions between Co atoms sandwiched by vacant polyoxometalates.
改性经典的三缺位韦尔斯-道森型α-P2W15O56以及相关夹心过渡金属簇的组装备受关注，但令人惊讶的是，由于α-P2W15O56对组装环境敏感，关于这些材料的报道很少。在此，我们描述了两种新型道森夹心簇合物(H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-四甲基-4,4'-联吡唑)和(H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2)的pH控制组装，这涉及α-P2W15O56的原位转化。两种簇合物均通过X射线单晶衍射、傅里叶变换红外光谱、紫外可见光谱、热重分析、粉末X射线衍射和元素分析进行了表征。X射线晶体学表明，两种杂多钨酸盐均变成二缺位的α-P2W16O57，并在1中对称地在内部封装两个边缘共享的CoO6八面体，而在2中仅观察到一个二缺位的α-P2W16O57，它与另一个三缺位的α-P2W15O56结合以不对称地夹住三个边缘共享的CoO6八面体。α-P2W16O57杂多钨酸盐应该是通过溶液中的自分解平衡由α-P2W15O56原位生成的。它们的电化学行为揭示了与W(VI)中心相关的特征性多电子氧化还原过程。对亚硝酸盐、过氧化氢、氯酸盐、溴酸盐和碘酸盐的电催化还原性能进行了全面测量和讨论；在这些物种中，两种簇合物对溴酸盐的还原均表现出最佳的电催化活性。磁性测量表明，被空位多金属氧酸盐夹住的Co原子之间存在弱铁磁交换相互作用。
