The Structure of Poly-molybdate Ions and It's Relevance to the Electroplating of Molybdenum Alloy

用异常x射线散射（AXS）、EXAFS、小角x射线散射和因子分析等方法研究了Ni-Mo酸性水溶液中多钼酸盐离子的结构。在只含钼离子的溶液中，钼离子形成由七个共用边的MoO6八面体组成的多钼酸盐离子。在同时含有Mo和Ni离子的溶液中，在Ni离子周围存在另一种由6个共边MoO6组成的多钼酸盐离子。柠檬酸离子的加入使Mo-Mo对的配位数降低了一半。这表明，由于形成柠檬酸配合物，大的钼酸盐离子被分解成较小的钼酸盐离子。SAXS的测量结果也证实了这一点。由于没有柠檬酸离子的溶液中不能电沉积钼镍合金，因此我们认为，溶液中大量多钼酸离子的分解与钼镍合金诱导共沉积的机理密切相关。

Structures of poly-molybdate ions in acid Ni-Mo aqueous solutions have been investigated by the anomalous x-ray scattering (AXS), EXAFS, small angle x-ray scattering, and factor analysis methods. In a solution containing only molybdenum ions, molybdenum ions form a poly-molybdate ion consisting of seven edge-sharing MoO6 octahedra. In a solution containing both Mo and Ni ions, there exists another poly-molybdate ion consisting of 6 edge-sharing MoO6 surrounding a Ni ion. The coordination number of Mo-Mo pairs decreases by half by adding citric ions. This indicates that the large ply-molybdate ion is decomposed to smaller molybdate ions due to formation of citric complexes. This is also confirmed by the SAXS measurements. Since molybdenum-nickel alloys are not electrodeposited from the solutions without citric ions, we expect that the decomposition of large poly-molybdate ions in the solution is closely related with the mechanism of the induced codeposition of molybdenum and nickel alloy.